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== Spin Boost Pillar Article? ==
Design and Simulation of a 10 MW Photovoltaic Power Plant
My latest discussions and minor edits to [[Anti-gravity]] got me thinking we should have a new article covering ''Spin Boost Pillars''. Good idea? --{{User:Wildgoosespeeder/sig}} 18:47, 29 January 2016 (EST)
 
:If a official source or a guide can say that Spin Boost Pillars are distinct fron Spin Boost and if Spin Boost Pillars is the official name, then I don't see the problem to have this be split.--{{User:LudwigVon/sig}}  10:38, 1 February 2016 (EST)
Miss. Sonawane Kalyani D.
::If not, what about {{tem|Conjecture}}? --{{User:Wildgoosespeeder/sig}} 22:23, 1 February 2016 (EST)
ME Student, Department of Electrical Engineering
:::Conjecture is only add if there is no source found at all (in the game, official guide...). If there is a source that implied the Spin Boost Pillar (or other name) and if they appear to be distinct from Spin Boost, then it can have a page. If you want a better result if yes or no, the wiki can have a page here, make a proposal, present arguments, why you think it should have a article on Mario Wiki.--{{User:LudwigVon/sig}} 22:42, 1 February 2016 (EST)
Miss. Sonawane Vidya D.
::::I think I'll wait for my other proposal to finish ({{tem|not-unused}}). I don't think it would be a good idea to have one user create a few proposals at the same time, even though I don't think there is a rule against it. As for calling them ''Spin Boost Pillars'', [[Mario Kart 8 From the Pit]] (episode 3) may have the answer. The host Andrew says "''by colliding with things in your environment or another racer''", which may imply that it is like the case of [[Rainbow Mario]] and [[Rainbow Star]]; there needs to be an object to trigger an action or state. --{{User:Wildgoosespeeder/sig}} 01:19, 2 February 2016 (EST)
BE Student, Department of Electrical Engineering
:::::Well, we ''do'' have an article on a common named stage element, the [[Boost Pad]] and [[Ramp]], so an article for the pillars make sense. There isn't a rule against creating multiple proposals. I've done it before, just to reassure you. I don't think this even needs a proposal; you can go right ahead and create the article. {{User:Bazooka Mario/sig}} 01:46, 2 February 2016 (EST)
Department of Electrical Engineering SND COE &RC                                                                                                     
::::::The Prima official game guide does name these objects Spin Boost Pillars, and I do own the book. Possibly pointless to say the former, I hope to find this helpful for fellow contributors.[[User:296lmn20|296lmn20]] ([[User talk:296lmn20|talk]]) 15:26, 10 July 2017 (EDT)296lmn20
 
Abstract- The paper deals with the components design and the simulation of a photovoltaic power generation system using MATLAB and Simulink software. The power plant is composed of photovoltaic panels connected in series and parallel strings, a DC-DC boost converter and a three-phase inverter which connects to a 0.4 KV three-phase low voltage grid and a 20 KV medium voltage grid by means of a step-up transformer. The DC-DC boost converter uses a MPPT controller and the inverter uses a control method based on d-q theory with a PI current regulator. Some cases for which the dynamic behavior of the configured photovoltaic system presents interest are simulated. They address the solar irradiance and temperature change.
 
Keywords-      
               
                Ⅰ. INTRODUCTION
In todays, The production of electrical energy without polluting actions and on the environment and depletion of its resources is a very topical problem. The solar energy radiation, considered relative to the life on Earth, seems to be inexhaustible. The photovoltaic solar energy relies on the direct generation of electricity by means of silicon cells. Under favorable climate conditions, when shining, the sun provides a power of 1 kW/m2. The photovoltaic panels allow for direct conversion in electricity of 10-15% from the above mentioned energy. The efficiency of PV system is a permanent concern.
The irradiance energy of the sun to electrical energy can be converted through photovoltaic (PV) power generation systems. If the power generation system does not include batteries to store the DC energy, instead including a common capacitor between the DC-DC and DC-AC converters to store the energy on the side of DC-Link, then a fully non-polluting source is obtained. To get an optimization of the power supplied to the network, depending on the irradiance intensity of the sun, it is preferred to select a configuration in which the photo-voltaic power generation system uses an efficient controller such as Maximum Power Point Tracking (MPPT).
 
Ⅲ.SYSTEM DESIGN
1 DESIGN OF THE PV POWER GENERATION SYSTEM:
The design of a PV power generation system, with an installed power of 10 MW, is proposed which follows.
The electric power supplying by using a PV equipment is made according to the requirements imposed by the electric energy provider who operates at the PV site, two options being available: the low voltage connection (400 V) and the medium voltage connection (20 kV), by means of the step-up transformer (LV/MV)
The designed PV power generation system is composed of following
1) A PV array of PV panels grouped in series and/or parallel strings such as to obtain a maximum power of 10 MW;
2) A DC-DC boost converter used as a load regulator and respectively to convert the output voltage of the PV array to a suitable voltage for the inverter;
3) A three-phase DC-AC converter (i.e. inverter) to export the electrical energy to the three-phase grid;
4) A three-phase step-up transformer to adapt the 0.4 kV low voltage output of the inverter to the 20 kV voltage of the grid;
5) The PV power generation system controller, which contains the MPPT controller for the DC-DC boost converter and the inverter's controller.
DESIGN OF THE PV ARRAY
Every panel (module) used by the designed installation consists in cells of series connected polycrystalline cells. The front side of the PV module includes a highly transparent glass sheet, characterized by a significant resistance against mechanic shocks.
The frame of anodized aluminum (covered through electrolysis by a layer of protective oxide), forms the structural support of the module. All these provide an adequate protection against atmospheric agents like hail, snow, ice and storm. Each module contains by-pass diodes introduced in the connection (distribution) box. These diodes will allow the “off-lining” of the modules where the sunshine does not reach, in order to prevent their behavior as consumers for the panels getting radiation from sun and therefore avoiding their undesired heating.The technical specifications for one module are given in Table I.
Cell type Silicon Polycrystalline
Number of cells per module: 60
Open circuit voltage VOC 41.79 V
Current at maximum power point IMP 6.63 A
Short-circuit current ISC 7.13 A
Voltage at maximum power point VMP 33.9 V
Temperature coefficient of VOC -0.105 V/°C
Temperature coefficient of ISC 0.00214 A/°C
Temperature coefficient of VMP -0.101 V/°C
Temperature coefficient of IMP -0.0006634 A/°C
 
Table 1 :-Technical Specifications Of One Sanyo Hip-225hde1 Pv Module
 
The number of necessary series-connected modules per string and parallel strings is determined by the DC-DC boost converter input voltage value and the inverter power. The rated DC input voltage for the boost converter is normally chosen half the output voltage, i.e. the DC-Link voltage.
Considering that the output voltage of a string of series connected PV modules is the sum of the component modules, and also considering the minimum DC-Link voltage for the inverter, one can obtain  the number of PV modules connected in series NSER based on:
 
N_SER=V_(dc-link)/V_mp
Where:
NSER          =    Number of necessary series connected modules;
VDC-LINK  =    The DC-Link voltage at the inverter input;
VMP            =    PV module voltage at maximum power point;
Fig.1. The basic schematic of one 360 kW photovoltaic array generator
A lower voltage can be selected for the inverter input, but as the voltage decreases (keeping the output voltage constant), a higher current will flow through the DC-DC boost converter. Therefore higher rated IGBT-s are needed
The minimum DC-Link voltage for the inverter can be computed with
Vdc-link  ≥  2√2 VPHASE
Where
VPHASE = the RMS value of the phase voltage at the inverter's output
Hence, the DC link voltage must be greater than 653V.
PMP is located  at the intersection between the voltage-current characteristic curve of the PV array is shown in Fig. 2. In Fig. 2, VOL is the open-load voltage of the PV cell, ISC represents its short-circuit current value. IMP and VMP are the current and voltage corresponding to the maximum power.
Fig. 2:-. The Voltage-Current characteristic of a PV cell
Thus, in order to obtain an installed power of 10 MW, we need a number of inverters NINV and PV arrays NARRAYS given by: NINV=NARRAYS = PTOTMAX/ PINV
where;
PTOT MAX = desired installed power for the PV park. The design of the DC-DC-AC converter is done backwards: firstly the inverter and then the DC-DC boost
converter.
SIZING THE DC-AC INVERTER:
 
Inverter’s sizing is done considering the PV array's peak output power for a 2-level inverter offered by IGBT manufacturer Semikron. The specialized Semisel online application is used, having the RMS output voltage, output power, efficiency, switching frequency and overload factor as input.
For the maximum power of 360 kW and a worst-case efficiency of 85%, the RMS current through inverter is equal to 611.3 A:
I_(INV-RMS)=P_inv/〖3.V〗_PHASE
The PWM coils inductance is calculated with
Where:-
δ= the overload factor
fcom = the switching frequency of the inverter.
The overload factor 􀄯 generated by transients varies within the range [120...180]% [5]. One selected a value of 150% for δ and a switching frequency of 2.5 kHz, considering a compromise between the high cost and bulkiness of the PWM coils for a low switching frequency and the higher losses at a high switching frequency. Also, a higher switching frequency offers a lower THD for the injected current and PCC voltage. The value of the DC-link capacitor is computed to limit the DC-link voltage ripple to 5% of the DC-Link voltage. For a sinusoidal waveform, the average value of the current IAVG is 63.6% from the peak value or 0.9 from the RMS value:
The capacitor’s value CDC-LINK can now be determined with
 
4  SIZING THE DC-DC BOOST CONVERTER:
The parameters imposed for the DC-DC boost converter are centralized in Table II.
 
Rated input voltage 350 V
Minimum input voltage VMIN 300 V
Rated output voltage VDC-LINK 700 V
Rated output voltage IOUT_RMS 611 A
Switching frequency fCOM_BOOST 2 kHz
 
Table 2: Technical Specifications Of The Dc-Dc Boost Converter
 
Considering the boost converter's coil resistance of 35mΩ  and the IGBT and diode losses, the efficiency of the converter is estimated to be 90% .
The duty cycle DMAX at the minimum input voltage VMIN can be computed with
The maximum current through the IGBT can be computed with
Sizing the LBOOST coil inductance is done considering a 5% ripple current from the maximum current through the IGBT. Hence, the peak-to-peak value of current ripple is
The minimum LBOOST coil inductance is calculated with
Considering (17), the minimum inductance is computed as 0.89 mH, so a 1 mH boost inductor is chosen.
An input capacitor in necessary for the boost converter's stability. Considering the power involved, a 100 micro F input capacitor is selected [16].
 
5 THE FLOWCHART OF THE PHOTOVOLTAIC SYSTEM DESIGN:
 
Fig 3: The flowchart of the photovoltaic system design
6  SIMULATION OF ONE 360 KW PHOTOVOLTAIC ARRAY GENERATOR
 
RESULTS
By using the designing parameters of the PV park presented below and the data from datasheet, a simulation of a field with PV cells corresponding to one of the 28 inverters was done in the Simulink module which belongs to MATLAB.
The Simulink model of the PV field is built by using elements from the library SimPowerSystems. The solving method is of discrete type and uses a fix step of 1 􀈝s. The control system operates at a sampling step of 100 􀈝s, in order to reproduce as accurate as possible the digital control and respectively to be appropriate for loading in microcontrollers and in developing platforms as dSPACE is.
The Simulink model of the generating PV system includes:
- an instrument to build signals related to solar radiation and panels temperature (Signal Builder Tool), in order to test the generation system's reactions in different contexts;
- the field with PV cells;
- the DC-DC converter, along with the dedicated control system MMPT (Maximum Power Point Tracking);
- the three-phase inverter along with the dedicated control system;
- the step-up transformer for connection to the network, of 0.4/20 kV;
- the network of 20 kV toward which the generated electric power is transferred.
The model of PV field includes the configuration of the number of PV cells in series and in parallel, as well as the possibility to access different predefined models of panels from several manufacturers. The module Sanyo HIP- 225HDE1 was selected. The control system MPPT allows for a maximal energy recovering, irrespective to temperature and illumination. The voltage VPV and the current IPV are continuously measured in order to deduce the power extracted from the panel. The power is compared to its previous value. After comparison, the voltage at panel’s terminals is increased or reduced by means of the duty cycle from the input of the PWM generator.
The control of the three-phase inverter is performed such as to export the power provided by the PV field in the AC network of 0.4 kV, respectively of 20 kV and to preserve a constant voltage of 400 V at the output terminals, along with a constant voltage of 700 V across the DC bars, irrespective to the operating conditions (power of PV panels). It consists of a block for test and transformation into the d-q coordinates, a DC voltage regulator, a current regulator, a reference voltage generator and a PWM generator for 2-Level three-phase inverters.
The model of the network in which the PV generating system exports power includes a MV load, step-up transformers, models for long lines and an equivalent generator of 24 kV connected by using a step-up transformer 24/120 kV.
Fig.4: The evolution of the solar irradiance (top) and PV cell temperature (bottom) during simulation.
The inverter’s control pulses are inputs for a block used to introduce switching outages of 3 microseconds, in order to avoid the short-circuits between the IGBT-s from the same side. The chain of events was selected to last 4 seconds, as follows (Fig. 4):
- the solar radiation has an initial value of 1000 W/m2, (regular value), than falls up to 250 W/m2 , smoothly along 0.5 seconds in order to simulate the apparition of some clouds;
- in the 2nd second, the solar radiation comes back to 1000 W/m2 along a period of 0.5 seconds;
- the temperature of the PV cells is increased from 25°C up to 75°C beginning with the 3rd second, along 0.5 sec.
   
Fig 5: The waveforms at the boost converter side during simulation: the output power (top), the input voltage (middle) and the duty cycle (bottom).
The evolution of voltage and power of the PV field is depicted by Fig. 5. The panels’ power decreases from 360 kW (corresponding to maximum solar radiation) up to 80 kW at 250 W/m2. One can notice that the voltage does not decrease significantly. It means that the control algorithm MPPT operates in a correct manner by limiting the current injected into the network. Close to the end of the simulation period, the input voltage decreases up to 320 V because the PV cells increases. The duty cycle increases to 0.6 to keep the output voltage constant (Fig. 5). The waveforms at the inverter side during simulation aredepicted by Fig. 6. No large deviations from the DC-Link reference voltage or the RMS standard 400 V voltage value on the LV bus are observed.
Fig.6: The waveforms at the inverter side during simulation. From top to bottom: the reference and measured DC-Link voltage, the duty cycle, the RMS line voltage, the RMS phase current
Fig 7: The evolution of the active powers during simulation, from the PV array to the MV grid
Fig 8: Detail of the waveforms of the phase voltages (top) and currents (bottom) at the output of the inverter
The active powers in the conversion chain are depicted by Fig. 7. The efficiency of the power conversion depends greatly on the boost and coupling inductors resistances. An efficiency of 0.88 is obtained for the boost converter and an efficiency of 0.94 is obtained for the inverter. In order to estimate the harmonic distortion level for thevoltage in the 0.4 kV bars, as well as the current injected into the network, a special analysis tool was used (FFT Analysis Tool) from the user graphic interface "Power GUI". By using this instrument one can notice the efficiency of the coil used for coupling to the network with the switching frequency 2.5 kHz and small values for the harmonic distortion of voltage(2.3%) and respectively for current (0.8%). The waveforms of the phase voltages and currents at the output of the inverter are depicted in Fig. 8. In the 20 kV the total harmonic distortion is even smaller (< 1%) because of the transformer’s inductance.
 
CONCLUSION
The simulation of the designed PV park by using Simulink made possible the testing and observation of its stability and efficiency. The PV generation system behaves well in different conditions of solar radiance and temperature of PV panels, preserving its stability and succeeding in extracting the maximum power from the PV panels owing to the control algorithm MPPT.
          REFERENCES
J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. C. P. Guisado, Ma. A. M. Prats, J. I. Leon, N. Moreno-Alfonso, “PowerElectronic Systems for the Grid Integration of Renewable Energy Sources: A Survey”, IEEE Trans. on Ind. Electr., Vol. 53, Issue 4, June 2006, pp. 1002 – 1016.
M, A. Green, K. Emery, Y. Hishikawa and W. Warta , „Solar cell efficiency tables (version 37).” Progress in Photovoltaics: Research and Applications, vol. 19, pp. 84-92 (2011).
B. J. Szymanski, K. Kompa, L. Roslaniec, A. Dmowski and J. Szymanski, “Operation of photovoltaic power systems with energy storage”, 2011 7th International Conference-Workshop on Compatibility and Power Electronics (CPE), Tallinn, 2011, pp. 86-91.
N. O. Cherchali, A. Morsli, M. S. Boucherit, L. Barazane and A. Tlemçani, "Comparison of two maximum power point trackers for photovoltaic systems using robust controllers," 2014 3rd International Symposium on Environmental Friendly Energies and Applications (EFEA), St. Ouen, 2014, pp. 1-5.
 
 
 
 
 
 
s
Design and Simulation of a 10 MW Photovoltaic Power Plant
 
Miss. Sonawane Kalyani D.
ME Student, Department of Electrical Engineering
Miss. Sonawane Vidya D.
BE Student, Department of Electrical Engineering
Department of Electrical Engineering SND COE &RC                                                                                                     
 
Abstract- The paper deals with the components design and the simulation of a photovoltaic power generation system using MATLAB and Simulink software. The power plant is composed of photovoltaic panels connected in series and parallel strings, a DC-DC boost converter and a three-phase inverter which connects to a 0.4 KV three-phase low voltage grid and a 20 KV medium voltage grid by means of a step-up transformer. The DC-DC boost converter uses a MPPT controller and the inverter uses a control method based on d-q theory with a PI current regulator. Some cases for which the dynamic behavior of the configured photovoltaic system presents interest are simulated. They address the solar irradiance and temperature change.
 
Keywords-       
               
                Ⅰ. INTRODUCTION
In todays, The production of electrical energy without polluting actions and on the environment and depletion of its resources is a very topical problem. The solar energy radiation, considered relative to the life on Earth, seems to be inexhaustible. The photovoltaic solar energy relies on the direct generation of electricity by means of silicon cells. Under favorable climate conditions, when shining, the sun provides a power of 1 kW/m2. The photovoltaic panels allow for direct conversion in electricity of 10-15% from the above mentioned energy. The efficiency of PV system is a permanent concern.
The irradiance energy of the sun to electrical energy can be converted through photovoltaic (PV) power generation systems. If the power generation system does not include batteries to store the DC energy, instead including a common capacitor between the DC-DC and DC-AC converters to store the energy on the side of DC-Link, then a fully non-polluting source is obtained. To get an optimization of the power supplied to the network, depending on the irradiance intensity of the sun, it is preferred to select a configuration in which the photo-voltaic power generation system uses an efficient controller such as Maximum Power Point Tracking (MPPT).
 
Ⅲ.SYSTEM DESIGN
1 DESIGN OF THE PV POWER GENERATION SYSTEM:
The design of a PV power generation system, with an installed power of 10 MW, is proposed which follows.
The electric power supplying by using a PV equipment is made according to the requirements imposed by the electric energy provider who operates at the PV site, two options being available: the low voltage connection (400 V) and the medium voltage connection (20 kV), by means of the step-up transformer (LV/MV)
The designed PV power generation system is composed of following
1) A PV array of PV panels grouped in series and/or parallel strings such as to obtain a maximum power of 10 MW;
2) A DC-DC boost converter used as a load regulator and respectively to convert the output voltage of the PV array to a suitable voltage for the inverter;
3) A three-phase DC-AC converter (i.e. inverter) to export the electrical energy to the three-phase grid;
4) A three-phase step-up transformer to adapt the 0.4 kV low voltage output of the inverter to the 20 kV voltage of the grid;
5) The PV power generation system controller, which contains the MPPT controller for the DC-DC boost converter and the inverter's controller.
DESIGN OF THE PV ARRAY
Every panel (module) used by the designed installation consists in cells of series connected polycrystalline cells. The front side of the PV module includes a highly transparent glass sheet, characterized by a significant resistance against mechanic shocks.
The frame of anodized aluminum (covered through electrolysis by a layer of protective oxide), forms the structural support of the module. All these provide an adequate protection against atmospheric agents like hail, snow, ice and storm. Each module contains by-pass diodes introduced in the connection (distribution) box. These diodes will allow the “off-lining” of the modules where the sunshine does not reach, in order to prevent their behavior as consumers for the panels getting radiation from sun and therefore avoiding their undesired heating.The technical specifications for one module are given in Table I.
Cell type Silicon Polycrystalline
Number of cells per module: 60
Open circuit voltage VOC 41.79 V
Current at maximum power point IMP 6.63 A
Short-circuit current ISC 7.13 A
Voltage at maximum power point VMP 33.9 V
Temperature coefficient of VOC -0.105 V/°C
Temperature coefficient of ISC 0.00214 A/°C
Temperature coefficient of VMP -0.101 V/°C
Temperature coefficient of IMP -0.0006634 A/°C
 
Table 1 :-Technical Specifications Of One Sanyo Hip-225hde1 Pv Module
 
The number of necessary series-connected modules per string and parallel strings is determined by the DC-DC boost converter input voltage value and the inverter power. The rated DC input voltage for the boost converter is normally chosen half the output voltage, i.e. the DC-Link voltage.
Considering that the output voltage of a string of series connected PV modules is the sum of the component modules, and also considering the minimum DC-Link voltage for the inverter, one can obtain  the number of PV modules connected in series NSER based on:
 
N_SER=V_(dc-link)/V_mp
Where:
NSER          =    Number of necessary series connected modules;
VDC-LINK  =    The DC-Link voltage at the inverter input;
VMP            =    PV module voltage at maximum power point;
Fig.1. The basic schematic of one 360 kW photovoltaic array generator
A lower voltage can be selected for the inverter input, but as the voltage decreases (keeping the output voltage constant), a higher current will flow through the DC-DC boost converter. Therefore higher rated IGBT-s are needed
The minimum DC-Link voltage for the inverter can be computed with
Vdc-link  ≥  2√2 VPHASE
Where
VPHASE = the RMS value of the phase voltage at the inverter's output
Hence, the DC link voltage must be greater than 653V.
PMP is located  at the intersection between the voltage-current characteristic curve of the PV array is shown in Fig. 2. In Fig. 2, VOL is the open-load voltage of the PV cell, ISC represents its short-circuit current value. IMP and VMP are the current and voltage corresponding to the maximum power.
Fig. 2:-. The Voltage-Current characteristic of a PV cell
Thus, in order to obtain an installed power of 10 MW, we need a number of inverters NINV and PV arrays NARRAYS given by: NINV=NARRAYS = PTOTMAX/ PINV
where;
PTOT MAX = desired installed power for the PV park. The design of the DC-DC-AC converter is done backwards: firstly the inverter and then the DC-DC boost
converter.
SIZING THE DC-AC INVERTER:
 
Inverter’s sizing is done considering the PV array's peak output power for a 2-level inverter offered by IGBT manufacturer Semikron. The specialized Semisel online application is used, having the RMS output voltage, output power, efficiency, switching frequency and overload factor as input.
For the maximum power of 360 kW and a worst-case efficiency of 85%, the RMS current through inverter is equal to 611.3 A:
I_(INV-RMS)=P_inv/〖3.V〗_PHASE
The PWM coils inductance is calculated with
Where:-
δ= the overload factor
fcom = the switching frequency of the inverter.
The overload factor 􀄯 generated by transients varies within the range [120...180]% [5]. One selected a value of 150% for δ and a switching frequency of 2.5 kHz, considering a compromise between the high cost and bulkiness of the PWM coils for a low switching frequency and the higher losses at a high switching frequency. Also, a higher switching frequency offers a lower THD for the injected current and PCC voltage. The value of the DC-link capacitor is computed to limit the DC-link voltage ripple to 5% of the DC-Link voltage. For a sinusoidal waveform, the average value of the current IAVG is 63.6% from the peak value or 0.9 from the RMS value:
The capacitor’s value CDC-LINK can now be determined with
 
4  SIZING THE DC-DC BOOST CONVERTER:
The parameters imposed for the DC-DC boost converter are centralized in Table II.
 
Rated input voltage 350 V
Minimum input voltage VMIN 300 V
Rated output voltage VDC-LINK 700 V
Rated output voltage IOUT_RMS 611 A
Switching frequency fCOM_BOOST 2 kHz
 
Table 2: Technical Specifications Of The Dc-Dc Boost Converter
 
Considering the boost converter's coil resistance of 35mΩ  and the IGBT and diode losses, the efficiency of the converter is estimated to be 90% .
The duty cycle DMAX at the minimum input voltage VMIN can be computed with
The maximum current through the IGBT can be computed with
Sizing the LBOOST coil inductance is done considering a 5% ripple current from the maximum current through the IGBT. Hence, the peak-to-peak value of current ripple is
The minimum LBOOST coil inductance is calculated with
Considering (17), the minimum inductance is computed as 0.89 mH, so a 1 mH boost inductor is chosen.
An input capacitor in necessary for the boost converter's stability. Considering the power involved, a 100 micro F input capacitor is selected [16].
 
5 THE FLOWCHART OF THE PHOTOVOLTAIC SYSTEM DESIGN:
 
Fig 3: The flowchart of the photovoltaic system design
6  SIMULATION OF ONE 360 KW PHOTOVOLTAIC ARRAY GENERATOR
 
RESULTS
By using the designing parameters of the PV park presented below and the data from datasheet, a simulation of a field with PV cells corresponding to one of the 28 inverters was done in the Simulink module which belongs to MATLAB.
The Simulink model of the PV field is built by using elements from the library SimPowerSystems. The solving method is of discrete type and uses a fix step of 1 􀈝s. The control system operates at a sampling step of 100 􀈝s, in order to reproduce as accurate as possible the digital control and respectively to be appropriate for loading in microcontrollers and in developing platforms as dSPACE is.
The Simulink model of the generating PV system includes:
- an instrument to build signals related to solar radiation and panels temperature (Signal Builder Tool), in order to test the generation system's reactions in different contexts;
- the field with PV cells;
- the DC-DC converter, along with the dedicated control system MMPT (Maximum Power Point Tracking);
- the three-phase inverter along with the dedicated control system;
- the step-up transformer for connection to the network, of 0.4/20 kV;
- the network of 20 kV toward which the generated electric power is transferred.
The model of PV field includes the configuration of the number of PV cells in series and in parallel, as well as the possibility to access different predefined models of panels from several manufacturers. The module Sanyo HIP- 225HDE1 was selected. The control system MPPT allows for a maximal energy recovering, irrespective to temperature and illumination. The voltage VPV and the current IPV are continuously measured in order to deduce the power extracted from the panel. The power is compared to its previous value. After comparison, the voltage at panel’s terminals is increased or reduced by means of the duty cycle from the input of the PWM generator.
The control of the three-phase inverter is performed such as to export the power provided by the PV field in the AC network of 0.4 kV, respectively of 20 kV and to preserve a constant voltage of 400 V at the output terminals, along with a constant voltage of 700 V across the DC bars, irrespective to the operating conditions (power of PV panels). It consists of a block for test and transformation into the d-q coordinates, a DC voltage regulator, a current regulator, a reference voltage generator and a PWM generator for 2-Level three-phase inverters.
The model of the network in which the PV generating system exports power includes a MV load, step-up transformers, models for long lines and an equivalent generator of 24 kV connected by using a step-up transformer 24/120 kV.
Fig.4: The evolution of the solar irradiance (top) and PV cell temperature (bottom) during simulation.
The inverter’s control pulses are inputs for a block used to introduce switching outages of 3 microseconds, in order to avoid the short-circuits between the IGBT-s from the same side. The chain of events was selected to last 4 seconds, as follows (Fig. 4):
- the solar radiation has an initial value of 1000 W/m2, (regular value), than falls up to 250 W/m2 , smoothly along 0.5 seconds in order to simulate the apparition of some clouds;
- in the 2nd second, the solar radiation comes back to 1000 W/m2 along a period of 0.5 seconds;
- the temperature of the PV cells is increased from 25°C up to 75°C beginning with the 3rd second, along 0.5 sec.
Fig 5: The waveforms at the boost converter side during simulation: the output power (top), the input voltage (middle) and the duty cycle (bottom).
The evolution of voltage and power of the PV field is depicted by Fig. 5. The panels’ power decreases from 360 kW (corresponding to maximum solar radiation) up to 80 kW at 250 W/m2. One can notice that the voltage does not decrease significantly. It means that the control algorithm MPPT operates in a correct manner by limiting the current injected into the network. Close to the end of the simulation period, the input voltage decreases up to 320 V because the PV cells increases. The duty cycle increases to 0.6 to keep the output voltage constant (Fig. 5). The waveforms at the inverter side during simulation aredepicted by Fig. 6. No large deviations from the DC-Link reference voltage or the RMS standard 400 V voltage value on the LV bus are observed.
Fig.6: The waveforms at the inverter side during simulation. From top to bottom: the reference and measured DC-Link voltage, the duty cycle, the RMS line voltage, the RMS phase current
Fig 7: The evolution of the active powers during simulation, from the PV array to the MV grid
Fig 8: Detail of the waveforms of the phase voltages (top) and currents (bottom) at the output of the inverter
The active powers in the conversion chain are depicted by Fig. 7. The efficiency of the power conversion depends greatly on the boost and coupling inductors resistances. An efficiency of 0.88 is obtained for the boost converter and an efficiency of 0.94 is obtained for the inverter. In order to estimate the harmonic distortion level for thevoltage in the 0.4 kV bars, as well as the current injected into the network, a special analysis tool was used (FFT Analysis Tool) from the user graphic interface "Power GUI". By using this instrument one can notice the efficiency of the coil used for coupling to the network with the switching frequency 2.5 kHz and small values for the harmonic distortion of voltage(2.3%) and respectively for current (0.8%). The waveforms of the phase voltages and currents at the output of the inverter are depicted in Fig. 8. In the 20 kV the total harmonic distortion is even smaller (< 1%) because of the transformer’s inductance.
 
CONCLUSION
The simulation of the designed PV park by using Simulink made possible the testing and observation of its stability and efficiency. The PV generation system behaves well in different conditions of solar radiance and temperature of PV panels, preserving its stability and succeeding in extracting the maximum power from the PV panels owing to the control algorithm MPPT.
          REFERENCES
J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. C. P. Guisado, Ma. A. M. Prats, J. I. Leon, N. Moreno-Alfonso, “PowerElectronic Systems for the Grid Integration of Renewable Energy Sources: A Survey”, IEEE Trans. on Ind. Electr., Vol. 53, Issue 4, June 2006, pp. 1002 – 1016.
M, A. Green, K. Emery, Y. Hishikawa and W. Warta , „Solar cell efficiency tables (version 37).” Progress in Photovoltaics: Research and Applications, vol. 19, pp. 84-92 (2011).
B. J. Szymanski, K. Kompa, L. Roslaniec, A. Dmowski and J. Szymanski, “Operation of photovoltaic power systems with energy storage”, 2011 7th International Conference-Workshop on Compatibility and Power Electronics (CPE), Tallinn, 2011, pp. 86-91.
N. O. Cherchali, A. Morsli, M. S. Boucherit, L. Barazane and A. Tlemçani, "Comparison of two maximum power point trackers for photovoltaic systems using robust controllers," 2014 3rd International Symposium on Environmental Friendly Energies and Applications (EFEA), St. Ouen, 2014, pp. 1-5.

Revision as of 11:15, April 11, 2018

Design and Simulation of a 10 MW Photovoltaic Power Plant 

Miss. Sonawane Kalyani D.

ME Student, Department of Electrical Engineering Miss. Sonawane Vidya D. BE Student, Department of Electrical Engineering Department of Electrical Engineering SND COE &RC


Abstract- The paper deals with the components design and the simulation of a photovoltaic power generation system using MATLAB and Simulink software. The power plant is composed of photovoltaic panels connected in series and parallel strings, a DC-DC boost converter and a three-phase inverter which connects to a 0.4 KV three-phase low voltage grid and a 20 KV medium voltage grid by means of a step-up transformer. The DC-DC boost converter uses a MPPT controller and the inverter uses a control method based on d-q theory with a PI current regulator. Some cases for which the dynamic behavior of the configured photovoltaic system presents interest are simulated. They address the solar irradiance and temperature change.

Keywords- 


                Ⅰ. INTRODUCTION
In todays, The production of electrical energy without polluting actions and on the environment and depletion of its resources is a very topical problem. The solar energy radiation, considered relative to the life on Earth, seems to be inexhaustible. The photovoltaic solar energy relies on the direct generation of electricity by means of silicon cells. Under favorable climate conditions, when shining, the sun provides a power of 1 kW/m2. The photovoltaic panels allow for direct conversion in electricity of 10-15% from the above mentioned energy. The efficiency of PV system is a permanent concern.

The irradiance energy of the sun to electrical energy can be converted through photovoltaic (PV) power generation systems. If the power generation system does not include batteries to store the DC energy, instead including a common capacitor between the DC-DC and DC-AC converters to store the energy on the side of DC-Link, then a fully non-polluting source is obtained. To get an optimization of the power supplied to the network, depending on the irradiance intensity of the sun, it is preferred to select a configuration in which the photo-voltaic power generation system uses an efficient controller such as Maximum Power Point Tracking (MPPT).

Ⅲ.SYSTEM DESIGN 1 DESIGN OF THE PV POWER GENERATION SYSTEM: The design of a PV power generation system, with an installed power of 10 MW, is proposed which follows. The electric power supplying by using a PV equipment is made according to the requirements imposed by the electric energy provider who operates at the PV site, two options being available: the low voltage connection (400 V) and the medium voltage connection (20 kV), by means of the step-up transformer (LV/MV) The designed PV power generation system is composed of following 1) A PV array of PV panels grouped in series and/or parallel strings such as to obtain a maximum power of 10 MW; 2) A DC-DC boost converter used as a load regulator and respectively to convert the output voltage of the PV array to a suitable voltage for the inverter; 3) A three-phase DC-AC converter (i.e. inverter) to export the electrical energy to the three-phase grid; 4) A three-phase step-up transformer to adapt the 0.4 kV low voltage output of the inverter to the 20 kV voltage of the grid; 5) The PV power generation system controller, which contains the MPPT controller for the DC-DC boost converter and the inverter's controller. DESIGN OF THE PV ARRAY Every panel (module) used by the designed installation consists in cells of series connected polycrystalline cells. The front side of the PV module includes a highly transparent glass sheet, characterized by a significant resistance against mechanic shocks. The frame of anodized aluminum (covered through electrolysis by a layer of protective oxide), forms the structural support of the module. All these provide an adequate protection against atmospheric agents like hail, snow, ice and storm. Each module contains by-pass diodes introduced in the connection (distribution) box. These diodes will allow the “off-lining” of the modules where the sunshine does not reach, in order to prevent their behavior as consumers for the panels getting radiation from sun and therefore avoiding their undesired heating.The technical specifications for one module are given in Table I. Cell type Silicon Polycrystalline Number of cells per module: 60 Open circuit voltage VOC 41.79 V Current at maximum power point IMP 6.63 A Short-circuit current ISC 7.13 A Voltage at maximum power point VMP 33.9 V Temperature coefficient of VOC -0.105 V/°C Temperature coefficient of ISC 0.00214 A/°C Temperature coefficient of VMP -0.101 V/°C Temperature coefficient of IMP -0.0006634 A/°C

Table 1 :-Technical Specifications Of One Sanyo Hip-225hde1 Pv Module

The number of necessary series-connected modules per string and parallel strings is determined by the DC-DC boost converter input voltage value and the inverter power. The rated DC input voltage for the boost converter is normally chosen half the output voltage, i.e. the DC-Link voltage. Considering that the output voltage of a string of series connected PV modules is the sum of the component modules, and also considering the minimum DC-Link voltage for the inverter, one can obtain the number of PV modules connected in series NSER based on:

N_SER=V_(dc-link)/V_mp Where: NSER = Number of necessary series connected modules; VDC-LINK = The DC-Link voltage at the inverter input; VMP = PV module voltage at maximum power point;

Fig.1. The basic schematic of one 360 kW photovoltaic array generator A lower voltage can be selected for the inverter input, but as the voltage decreases (keeping the output voltage constant), a higher current will flow through the DC-DC boost converter. Therefore higher rated IGBT-s are needed The minimum DC-Link voltage for the inverter can be computed with Vdc-link ≥ 2√2 VPHASE Where VPHASE = the RMS value of the phase voltage at the inverter's output Hence, the DC link voltage must be greater than 653V. PMP is located at the intersection between the voltage-current characteristic curve of the PV array is shown in Fig. 2. In Fig. 2, VOL is the open-load voltage of the PV cell, ISC represents its short-circuit current value. IMP and VMP are the current and voltage corresponding to the maximum power.

Fig. 2:-. The Voltage-Current characteristic of a PV cell Thus, in order to obtain an installed power of 10 MW, we need a number of inverters NINV and PV arrays NARRAYS given by: NINV=NARRAYS = PTOTMAX/ PINV where; PTOT MAX = desired installed power for the PV park. The design of the DC-DC-AC converter is done backwards: firstly the inverter and then the DC-DC boost converter. SIZING THE DC-AC INVERTER:

Inverter’s sizing is done considering the PV array's peak output power for a 2-level inverter offered by IGBT manufacturer Semikron. The specialized Semisel online application is used, having the RMS output voltage, output power, efficiency, switching frequency and overload factor as input. For the maximum power of 360 kW and a worst-case efficiency of 85%, the RMS current through inverter is equal to 611.3 A: I_(INV-RMS)=P_inv/〖3.V〗_PHASE The PWM coils inductance is calculated with

Where:- δ= the overload factor fcom = the switching frequency of the inverter. The overload factor 􀄯 generated by transients varies within the range [120...180]% [5]. One selected a value of 150% for δ and a switching frequency of 2.5 kHz, considering a compromise between the high cost and bulkiness of the PWM coils for a low switching frequency and the higher losses at a high switching frequency. Also, a higher switching frequency offers a lower THD for the injected current and PCC voltage. The value of the DC-link capacitor is computed to limit the DC-link voltage ripple to 5% of the DC-Link voltage. For a sinusoidal waveform, the average value of the current IAVG is 63.6% from the peak value or 0.9 from the RMS value: The capacitor’s value CDC-LINK can now be determined with


4 SIZING THE DC-DC BOOST CONVERTER: The parameters imposed for the DC-DC boost converter are centralized in Table II.

Rated input voltage 350 V Minimum input voltage VMIN 300 V Rated output voltage VDC-LINK 700 V Rated output voltage IOUT_RMS 611 A Switching frequency fCOM_BOOST 2 kHz

Table 2: Technical Specifications Of The Dc-Dc Boost Converter

Considering the boost converter's coil resistance of 35mΩ and the IGBT and diode losses, the efficiency of the converter is estimated to be 90% . The duty cycle DMAX at the minimum input voltage VMIN can be computed with

The maximum current through the IGBT can be computed with

Sizing the LBOOST coil inductance is done considering a 5% ripple current from the maximum current through the IGBT. Hence, the peak-to-peak value of current ripple is

The minimum LBOOST coil inductance is calculated with

Considering (17), the minimum inductance is computed as 0.89 mH, so a 1 mH boost inductor is chosen. An input capacitor in necessary for the boost converter's stability. Considering the power involved, a 100 micro F input capacitor is selected [16].

5 THE FLOWCHART OF THE PHOTOVOLTAIC SYSTEM DESIGN:


Fig 3: The flowchart of the photovoltaic system design 6 SIMULATION OF ONE 360 KW PHOTOVOLTAIC ARRAY GENERATOR

RESULTS By using the designing parameters of the PV park presented below and the data from datasheet, a simulation of a field with PV cells corresponding to one of the 28 inverters was done in the Simulink module which belongs to MATLAB. The Simulink model of the PV field is built by using elements from the library SimPowerSystems. The solving method is of discrete type and uses a fix step of 1 􀈝s. The control system operates at a sampling step of 100 􀈝s, in order to reproduce as accurate as possible the digital control and respectively to be appropriate for loading in microcontrollers and in developing platforms as dSPACE is. The Simulink model of the generating PV system includes: - an instrument to build signals related to solar radiation and panels temperature (Signal Builder Tool), in order to test the generation system's reactions in different contexts; - the field with PV cells; - the DC-DC converter, along with the dedicated control system MMPT (Maximum Power Point Tracking); - the three-phase inverter along with the dedicated control system; - the step-up transformer for connection to the network, of 0.4/20 kV; - the network of 20 kV toward which the generated electric power is transferred. The model of PV field includes the configuration of the number of PV cells in series and in parallel, as well as the possibility to access different predefined models of panels from several manufacturers. The module Sanyo HIP- 225HDE1 was selected. The control system MPPT allows for a maximal energy recovering, irrespective to temperature and illumination. The voltage VPV and the current IPV are continuously measured in order to deduce the power extracted from the panel. The power is compared to its previous value. After comparison, the voltage at panel’s terminals is increased or reduced by means of the duty cycle from the input of the PWM generator. The control of the three-phase inverter is performed such as to export the power provided by the PV field in the AC network of 0.4 kV, respectively of 20 kV and to preserve a constant voltage of 400 V at the output terminals, along with a constant voltage of 700 V across the DC bars, irrespective to the operating conditions (power of PV panels). It consists of a block for test and transformation into the d-q coordinates, a DC voltage regulator, a current regulator, a reference voltage generator and a PWM generator for 2-Level three-phase inverters. The model of the network in which the PV generating system exports power includes a MV load, step-up transformers, models for long lines and an equivalent generator of 24 kV connected by using a step-up transformer 24/120 kV.

Fig.4: The evolution of the solar irradiance (top) and PV cell temperature (bottom) during simulation. The inverter’s control pulses are inputs for a block used to introduce switching outages of 3 microseconds, in order to avoid the short-circuits between the IGBT-s from the same side. The chain of events was selected to last 4 seconds, as follows (Fig. 4): - the solar radiation has an initial value of 1000 W/m2, (regular value), than falls up to 250 W/m2 , smoothly along 0.5 seconds in order to simulate the apparition of some clouds; - in the 2nd second, the solar radiation comes back to 1000 W/m2 along a period of 0.5 seconds; - the temperature of the PV cells is increased from 25°C up to 75°C beginning with the 3rd second, along 0.5 sec.

Fig 5: The waveforms at the boost converter side during simulation: the output power (top), the input voltage (middle) and the duty cycle (bottom). The evolution of voltage and power of the PV field is depicted by Fig. 5. The panels’ power decreases from 360 kW (corresponding to maximum solar radiation) up to 80 kW at 250 W/m2. One can notice that the voltage does not decrease significantly. It means that the control algorithm MPPT operates in a correct manner by limiting the current injected into the network. Close to the end of the simulation period, the input voltage decreases up to 320 V because the PV cells increases. The duty cycle increases to 0.6 to keep the output voltage constant (Fig. 5). The waveforms at the inverter side during simulation aredepicted by Fig. 6. No large deviations from the DC-Link reference voltage or the RMS standard 400 V voltage value on the LV bus are observed.

Fig.6: The waveforms at the inverter side during simulation. From top to bottom: the reference and measured DC-Link voltage, the duty cycle, the RMS line voltage, the RMS phase current

Fig 7: The evolution of the active powers during simulation, from the PV array to the MV grid

Fig 8: Detail of the waveforms of the phase voltages (top) and currents (bottom) at the output of the inverter 

The active powers in the conversion chain are depicted by Fig. 7. The efficiency of the power conversion depends greatly on the boost and coupling inductors resistances. An efficiency of 0.88 is obtained for the boost converter and an efficiency of 0.94 is obtained for the inverter. In order to estimate the harmonic distortion level for thevoltage in the 0.4 kV bars, as well as the current injected into the network, a special analysis tool was used (FFT Analysis Tool) from the user graphic interface "Power GUI". By using this instrument one can notice the efficiency of the coil used for coupling to the network with the switching frequency 2.5 kHz and small values for the harmonic distortion of voltage(2.3%) and respectively for current (0.8%). The waveforms of the phase voltages and currents at the output of the inverter are depicted in Fig. 8. In the 20 kV the total harmonic distortion is even smaller (< 1%) because of the transformer’s inductance.

CONCLUSION The simulation of the designed PV park by using Simulink made possible the testing and observation of its stability and efficiency. The PV generation system behaves well in different conditions of solar radiance and temperature of PV panels, preserving its stability and succeeding in extracting the maximum power from the PV panels owing to the control algorithm MPPT. 

         REFERENCES

J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. C. P. Guisado, Ma. A. M. Prats, J. I. Leon, N. Moreno-Alfonso, “PowerElectronic Systems for the Grid Integration of Renewable Energy Sources: A Survey”, IEEE Trans. on Ind. Electr., Vol. 53, Issue 4, June 2006, pp. 1002 – 1016. M, A. Green, K. Emery, Y. Hishikawa and W. Warta , „Solar cell efficiency tables (version 37).” Progress in Photovoltaics: Research and Applications, vol. 19, pp. 84-92 (2011). B. J. Szymanski, K. Kompa, L. Roslaniec, A. Dmowski and J. Szymanski, “Operation of photovoltaic power systems with energy storage”, 2011 7th International Conference-Workshop on Compatibility and Power Electronics (CPE), Tallinn, 2011, pp. 86-91. N. O. Cherchali, A. Morsli, M. S. Boucherit, L. Barazane and A. Tlemçani, "Comparison of two maximum power point trackers for photovoltaic systems using robust controllers," 2014 3rd International Symposium on Environmental Friendly Energies and Applications (EFEA), St. Ouen, 2014, pp. 1-5.




s Design and Simulation of a 10 MW Photovoltaic Power Plant 

Miss. Sonawane Kalyani D.

ME Student, Department of Electrical Engineering Miss. Sonawane Vidya D. BE Student, Department of Electrical Engineering Department of Electrical Engineering SND COE &RC


Abstract- The paper deals with the components design and the simulation of a photovoltaic power generation system using MATLAB and Simulink software. The power plant is composed of photovoltaic panels connected in series and parallel strings, a DC-DC boost converter and a three-phase inverter which connects to a 0.4 KV three-phase low voltage grid and a 20 KV medium voltage grid by means of a step-up transformer. The DC-DC boost converter uses a MPPT controller and the inverter uses a control method based on d-q theory with a PI current regulator. Some cases for which the dynamic behavior of the configured photovoltaic system presents interest are simulated. They address the solar irradiance and temperature change.

Keywords- 


                Ⅰ. INTRODUCTION
In todays, The production of electrical energy without polluting actions and on the environment and depletion of its resources is a very topical problem. The solar energy radiation, considered relative to the life on Earth, seems to be inexhaustible. The photovoltaic solar energy relies on the direct generation of electricity by means of silicon cells. Under favorable climate conditions, when shining, the sun provides a power of 1 kW/m2. The photovoltaic panels allow for direct conversion in electricity of 10-15% from the above mentioned energy. The efficiency of PV system is a permanent concern.

The irradiance energy of the sun to electrical energy can be converted through photovoltaic (PV) power generation systems. If the power generation system does not include batteries to store the DC energy, instead including a common capacitor between the DC-DC and DC-AC converters to store the energy on the side of DC-Link, then a fully non-polluting source is obtained. To get an optimization of the power supplied to the network, depending on the irradiance intensity of the sun, it is preferred to select a configuration in which the photo-voltaic power generation system uses an efficient controller such as Maximum Power Point Tracking (MPPT).

Ⅲ.SYSTEM DESIGN 1 DESIGN OF THE PV POWER GENERATION SYSTEM: The design of a PV power generation system, with an installed power of 10 MW, is proposed which follows. The electric power supplying by using a PV equipment is made according to the requirements imposed by the electric energy provider who operates at the PV site, two options being available: the low voltage connection (400 V) and the medium voltage connection (20 kV), by means of the step-up transformer (LV/MV) The designed PV power generation system is composed of following 1) A PV array of PV panels grouped in series and/or parallel strings such as to obtain a maximum power of 10 MW; 2) A DC-DC boost converter used as a load regulator and respectively to convert the output voltage of the PV array to a suitable voltage for the inverter; 3) A three-phase DC-AC converter (i.e. inverter) to export the electrical energy to the three-phase grid; 4) A three-phase step-up transformer to adapt the 0.4 kV low voltage output of the inverter to the 20 kV voltage of the grid; 5) The PV power generation system controller, which contains the MPPT controller for the DC-DC boost converter and the inverter's controller. DESIGN OF THE PV ARRAY Every panel (module) used by the designed installation consists in cells of series connected polycrystalline cells. The front side of the PV module includes a highly transparent glass sheet, characterized by a significant resistance against mechanic shocks. The frame of anodized aluminum (covered through electrolysis by a layer of protective oxide), forms the structural support of the module. All these provide an adequate protection against atmospheric agents like hail, snow, ice and storm. Each module contains by-pass diodes introduced in the connection (distribution) box. These diodes will allow the “off-lining” of the modules where the sunshine does not reach, in order to prevent their behavior as consumers for the panels getting radiation from sun and therefore avoiding their undesired heating.The technical specifications for one module are given in Table I. Cell type Silicon Polycrystalline Number of cells per module: 60 Open circuit voltage VOC 41.79 V Current at maximum power point IMP 6.63 A Short-circuit current ISC 7.13 A Voltage at maximum power point VMP 33.9 V Temperature coefficient of VOC -0.105 V/°C Temperature coefficient of ISC 0.00214 A/°C Temperature coefficient of VMP -0.101 V/°C Temperature coefficient of IMP -0.0006634 A/°C

Table 1 :-Technical Specifications Of One Sanyo Hip-225hde1 Pv Module

The number of necessary series-connected modules per string and parallel strings is determined by the DC-DC boost converter input voltage value and the inverter power. The rated DC input voltage for the boost converter is normally chosen half the output voltage, i.e. the DC-Link voltage. Considering that the output voltage of a string of series connected PV modules is the sum of the component modules, and also considering the minimum DC-Link voltage for the inverter, one can obtain the number of PV modules connected in series NSER based on:

N_SER=V_(dc-link)/V_mp Where: NSER = Number of necessary series connected modules; VDC-LINK = The DC-Link voltage at the inverter input; VMP = PV module voltage at maximum power point;

Fig.1. The basic schematic of one 360 kW photovoltaic array generator A lower voltage can be selected for the inverter input, but as the voltage decreases (keeping the output voltage constant), a higher current will flow through the DC-DC boost converter. Therefore higher rated IGBT-s are needed The minimum DC-Link voltage for the inverter can be computed with Vdc-link ≥ 2√2 VPHASE Where VPHASE = the RMS value of the phase voltage at the inverter's output Hence, the DC link voltage must be greater than 653V. PMP is located at the intersection between the voltage-current characteristic curve of the PV array is shown in Fig. 2. In Fig. 2, VOL is the open-load voltage of the PV cell, ISC represents its short-circuit current value. IMP and VMP are the current and voltage corresponding to the maximum power.

Fig. 2:-. The Voltage-Current characteristic of a PV cell Thus, in order to obtain an installed power of 10 MW, we need a number of inverters NINV and PV arrays NARRAYS given by: NINV=NARRAYS = PTOTMAX/ PINV where; PTOT MAX = desired installed power for the PV park. The design of the DC-DC-AC converter is done backwards: firstly the inverter and then the DC-DC boost converter. SIZING THE DC-AC INVERTER:

Inverter’s sizing is done considering the PV array's peak output power for a 2-level inverter offered by IGBT manufacturer Semikron. The specialized Semisel online application is used, having the RMS output voltage, output power, efficiency, switching frequency and overload factor as input. For the maximum power of 360 kW and a worst-case efficiency of 85%, the RMS current through inverter is equal to 611.3 A: I_(INV-RMS)=P_inv/〖3.V〗_PHASE The PWM coils inductance is calculated with

Where:- δ= the overload factor fcom = the switching frequency of the inverter. The overload factor 􀄯 generated by transients varies within the range [120...180]% [5]. One selected a value of 150% for δ and a switching frequency of 2.5 kHz, considering a compromise between the high cost and bulkiness of the PWM coils for a low switching frequency and the higher losses at a high switching frequency. Also, a higher switching frequency offers a lower THD for the injected current and PCC voltage. The value of the DC-link capacitor is computed to limit the DC-link voltage ripple to 5% of the DC-Link voltage. For a sinusoidal waveform, the average value of the current IAVG is 63.6% from the peak value or 0.9 from the RMS value: The capacitor’s value CDC-LINK can now be determined with


4 SIZING THE DC-DC BOOST CONVERTER: The parameters imposed for the DC-DC boost converter are centralized in Table II.

Rated input voltage 350 V Minimum input voltage VMIN 300 V Rated output voltage VDC-LINK 700 V Rated output voltage IOUT_RMS 611 A Switching frequency fCOM_BOOST 2 kHz

Table 2: Technical Specifications Of The Dc-Dc Boost Converter

Considering the boost converter's coil resistance of 35mΩ and the IGBT and diode losses, the efficiency of the converter is estimated to be 90% . The duty cycle DMAX at the minimum input voltage VMIN can be computed with

The maximum current through the IGBT can be computed with

Sizing the LBOOST coil inductance is done considering a 5% ripple current from the maximum current through the IGBT. Hence, the peak-to-peak value of current ripple is

The minimum LBOOST coil inductance is calculated with

Considering (17), the minimum inductance is computed as 0.89 mH, so a 1 mH boost inductor is chosen. An input capacitor in necessary for the boost converter's stability. Considering the power involved, a 100 micro F input capacitor is selected [16].

5 THE FLOWCHART OF THE PHOTOVOLTAIC SYSTEM DESIGN:


Fig 3: The flowchart of the photovoltaic system design 6 SIMULATION OF ONE 360 KW PHOTOVOLTAIC ARRAY GENERATOR

RESULTS By using the designing parameters of the PV park presented below and the data from datasheet, a simulation of a field with PV cells corresponding to one of the 28 inverters was done in the Simulink module which belongs to MATLAB. The Simulink model of the PV field is built by using elements from the library SimPowerSystems. The solving method is of discrete type and uses a fix step of 1 􀈝s. The control system operates at a sampling step of 100 􀈝s, in order to reproduce as accurate as possible the digital control and respectively to be appropriate for loading in microcontrollers and in developing platforms as dSPACE is. The Simulink model of the generating PV system includes: - an instrument to build signals related to solar radiation and panels temperature (Signal Builder Tool), in order to test the generation system's reactions in different contexts; - the field with PV cells; - the DC-DC converter, along with the dedicated control system MMPT (Maximum Power Point Tracking); - the three-phase inverter along with the dedicated control system; - the step-up transformer for connection to the network, of 0.4/20 kV; - the network of 20 kV toward which the generated electric power is transferred. The model of PV field includes the configuration of the number of PV cells in series and in parallel, as well as the possibility to access different predefined models of panels from several manufacturers. The module Sanyo HIP- 225HDE1 was selected. The control system MPPT allows for a maximal energy recovering, irrespective to temperature and illumination. The voltage VPV and the current IPV are continuously measured in order to deduce the power extracted from the panel. The power is compared to its previous value. After comparison, the voltage at panel’s terminals is increased or reduced by means of the duty cycle from the input of the PWM generator. The control of the three-phase inverter is performed such as to export the power provided by the PV field in the AC network of 0.4 kV, respectively of 20 kV and to preserve a constant voltage of 400 V at the output terminals, along with a constant voltage of 700 V across the DC bars, irrespective to the operating conditions (power of PV panels). It consists of a block for test and transformation into the d-q coordinates, a DC voltage regulator, a current regulator, a reference voltage generator and a PWM generator for 2-Level three-phase inverters. The model of the network in which the PV generating system exports power includes a MV load, step-up transformers, models for long lines and an equivalent generator of 24 kV connected by using a step-up transformer 24/120 kV.

Fig.4: The evolution of the solar irradiance (top) and PV cell temperature (bottom) during simulation. The inverter’s control pulses are inputs for a block used to introduce switching outages of 3 microseconds, in order to avoid the short-circuits between the IGBT-s from the same side. The chain of events was selected to last 4 seconds, as follows (Fig. 4): - the solar radiation has an initial value of 1000 W/m2, (regular value), than falls up to 250 W/m2 , smoothly along 0.5 seconds in order to simulate the apparition of some clouds; - in the 2nd second, the solar radiation comes back to 1000 W/m2 along a period of 0.5 seconds; - the temperature of the PV cells is increased from 25°C up to 75°C beginning with the 3rd second, along 0.5 sec.

Fig 5: The waveforms at the boost converter side during simulation: the output power (top), the input voltage (middle) and the duty cycle (bottom). The evolution of voltage and power of the PV field is depicted by Fig. 5. The panels’ power decreases from 360 kW (corresponding to maximum solar radiation) up to 80 kW at 250 W/m2. One can notice that the voltage does not decrease significantly. It means that the control algorithm MPPT operates in a correct manner by limiting the current injected into the network. Close to the end of the simulation period, the input voltage decreases up to 320 V because the PV cells increases. The duty cycle increases to 0.6 to keep the output voltage constant (Fig. 5). The waveforms at the inverter side during simulation aredepicted by Fig. 6. No large deviations from the DC-Link reference voltage or the RMS standard 400 V voltage value on the LV bus are observed.

Fig.6: The waveforms at the inverter side during simulation. From top to bottom: the reference and measured DC-Link voltage, the duty cycle, the RMS line voltage, the RMS phase current

Fig 7: The evolution of the active powers during simulation, from the PV array to the MV grid

Fig 8: Detail of the waveforms of the phase voltages (top) and currents (bottom) at the output of the inverter 

The active powers in the conversion chain are depicted by Fig. 7. The efficiency of the power conversion depends greatly on the boost and coupling inductors resistances. An efficiency of 0.88 is obtained for the boost converter and an efficiency of 0.94 is obtained for the inverter. In order to estimate the harmonic distortion level for thevoltage in the 0.4 kV bars, as well as the current injected into the network, a special analysis tool was used (FFT Analysis Tool) from the user graphic interface "Power GUI". By using this instrument one can notice the efficiency of the coil used for coupling to the network with the switching frequency 2.5 kHz and small values for the harmonic distortion of voltage(2.3%) and respectively for current (0.8%). The waveforms of the phase voltages and currents at the output of the inverter are depicted in Fig. 8. In the 20 kV the total harmonic distortion is even smaller (< 1%) because of the transformer’s inductance.

CONCLUSION The simulation of the designed PV park by using Simulink made possible the testing and observation of its stability and efficiency. The PV generation system behaves well in different conditions of solar radiance and temperature of PV panels, preserving its stability and succeeding in extracting the maximum power from the PV panels owing to the control algorithm MPPT. 

         REFERENCES

J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. C. P. Guisado, Ma. A. M. Prats, J. I. Leon, N. Moreno-Alfonso, “PowerElectronic Systems for the Grid Integration of Renewable Energy Sources: A Survey”, IEEE Trans. on Ind. Electr., Vol. 53, Issue 4, June 2006, pp. 1002 – 1016. M, A. Green, K. Emery, Y. Hishikawa and W. Warta , „Solar cell efficiency tables (version 37).” Progress in Photovoltaics: Research and Applications, vol. 19, pp. 84-92 (2011). B. J. Szymanski, K. Kompa, L. Roslaniec, A. Dmowski and J. Szymanski, “Operation of photovoltaic power systems with energy storage”, 2011 7th International Conference-Workshop on Compatibility and Power Electronics (CPE), Tallinn, 2011, pp. 86-91. N. O. Cherchali, A. Morsli, M. S. Boucherit, L. Barazane and A. Tlemçani, "Comparison of two maximum power point trackers for photovoltaic systems using robust controllers," 2014 3rd International Symposium on Environmental Friendly Energies and Applications (EFEA), St. Ouen, 2014, pp. 1-5.

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