Hybrid PV/Wind System Modeling & its Control in Grid Connected Mode

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1 Hybrid PV/Wind System Modeling & its Control in Grid Connected Mode S.Krishnaveni 1 (12HU1D5607), M.Balachandar 2, R.Lakshmi 3 1 M.Tech Scholar, Dept. of EEE, Chebrolu Engineering College, Guntur (A.P), India. 3 Asst. Prof, Dept. of EEE, Chebrolu Engineering College, Guntur (A.P), India. ABSTRACT: This paper presents a modeling and control of grid connected Hybrid wind photovoltaic array. Hybrid energy system consists of two or more renewable/nonrenewable energy sources. In this paper the hybrid energy system is formed by the combination of wind and photovoltaic array. There are some constraints in harnessing power from Renewable energy sources like wind and photovoltaic power systems. Variation in environmental condition will cause variation of power output from renewable energy sources. Power electronic converters play a major role in utilizing these RES. A proper control scheme is required to operate power converters to match the up the grid-connection requirements. This paper consists of modeling and simulation of Hybrid Wind/PV energy system inter-connected to electrical grid through power electronic interface. Power conditioning system is implemented and modeled to control power electronic interface. Performance of modeled hybrid system is evaluated for different input power levels and load variation. INTRODUCTION chemical pollution. Thus connecting the PV array and Wind directly to the Grid is a method to make use of the energy that is produced. PHOTOVOLTAIC ARRAY MODULE A photovoltaic system converts sunlight into electricity. The basic device of a photovoltaic system is the photovoltaic cell. Cells may be grouped to form panels or modules. Panels can be grouped to form large photo voltaic arrays. PV arrays can either be designed as stand-alone and grid-connected systems. Mathematical modeling of PV array Hybrid Energy Systems Inter-connection of two or more of Renewable Generations like wind power, photovoltaic power, fuel cell and micro turbine generator to generate power to local load and or connecting to grid/micro grid forms Hybrid Energy Systems. Because of the characteristic nature of the solar energy and the wind energy, the electric power generation of the PV array and the wind turbine are corresponding. The reliability of combined power generation is much higher when compared to the Power generated by an Individual source. A sizable battery bank is required for a load so that maximum power is drawn from Wind and Photovoltaic array. Nonetheless, the usage of battery is not an environmental friendly and there are some drawbacks like, heavy weights, bulky size, high costs, limited life cycles, and MATLAB/Simulink Modeling of PV Array A typical KC-200GT PV module is considered here [Appendix (i)]. The module has 54 cells in series. For desired output voltage and ISSN: Page 1

2 current, the proposed solar PV power generation system (6kW) consists of 30 PV modules with 10x3 series-parallel arrangements. Each module can produce 200W of DC electric power. Typical electrical characteristics of a KC-200GT PV module are shown in Table 1 at solar radiation of 1000W/ and cell temperature of 25ºC (STC). MaximumPower ( ) 200W(+10%/-5%) MaximumPowerVoltage ( ) MaximumPower Current ( ) 26.3 V 7.61 A OpenCircuitVoltage( ) 32.9 V ShortCircuitCurrent ( ) 8.21 A Wind Turbine Modeling The wind turbine (WT) converts wind energy to mechanical energy by means of a torque applied to a drive train. A model of the WT is necessary to evaluate the torque and power production for a given wind speed and the effect of wind speed variations on the produced torque. The torque T and power produced by the WT within the interval [, ], where is minimum wind Where, ρ=air density, Vwind=Wind speed, A=Turbine swept area, =Tip speed ratio, R=Radius of turbine blades, Cp =Coefficient of performance, =Mechanical output power, T = Torque of wind turbine, ω =Angular frequency of rotational turbine, β =Blade pitch angle. The performance coefficient Cp (λ, β), which depends on tip speed ratio λ and blade pitch angle β, determines how much of the wind kinetic energy can be captured by the wind turbine system. A nonlinear model describes Cp (λ, β) as: Where, C1=0.5176, C2=116, C3=0.4, C4=5, C5=21and C6= (Eqn.3.11) Modeling of PMSG: speed and is maximum wind speed, are functions of the WT blade radius R, air pressure, wind speed and coefficients and (Jitendra Kasera et al. 2012). Is known as the power coefficient and characterizes the ability of the WT to extract energy from the wind. Is the torque coefficient and is related to according to: MATLAB/SIMULINKMODEL OF WECS MODELING OF GRID TIE WIND/PV HYBRID SYSTEM Hybrid energy system usually consists oftwoor more renewable / nonrenewable energy sources. Presently two kinds of wind power ISSN: Page 2

3 hybrid systems are in focus: wind power with fuel cell and wind power with photovoltaic power. The main purpose of such hybrid power systems is to overcome the intermittency and uncertainty of wind energy and to make the power supply more reliable. (Chen Wang et al. 2007).Wind power and solar energy are always combined into a hybrid system, especially for the power supply for remote areas where the cost of transmission line is too high. Also, another advantage of this kind of hybrid system is that they are both renewable energies, which is compatible to the environment. Table 4: Component parameters of the Proposed Hybrid Energy System Schematic of DC/DC Boost converter The Proposed System Configuration Configuaration for the proposed hybrid system The details of the system component parameters are listed in Table 4 WIND TURBINE Rated Power 20 kw Rated wind speed 12 m/s Rated Rotor speed rad/sec Blade Radius 2.7 m PMSG Rated Power 20 kw Rated line Voltage V rms Stator phase inductance Mh Stator phase Resistance 2.7 Ω No. of poles 36 Rated mechanical speed 211 rpm PV Module Unit 54 cells, 200 W@1kW/m 2,25ºC Module numbers 10*3=30 Power rating 30* W PI controller ofdc/dc Boost converter DC/DC Boost Converter parameters of PV system Input voltage (V in ) Power rating (P) Output voltage (V out ) Switching frequency (f) Output voltage ripple factor (V r ) Inductor (L) V 20 kw 480 V 20 khz 2% mh Capacitor (C) Determination of DC Link Voltage : The dc bus voltage is mainly determined by the inverter ac output voltage and the voltage drop across the filter. A lower bound on the dc bus voltage can be determined from the following relation at a unity power factor [N.Mohan et al.2003]. ISSN: Page 3

Where, =Line-Line RMS voltage on inverter side, =Filter Inductance, =Maximum possible RMS value of the ac load current, =Modulation Index of the Inverter.

4 Where, =Line-Line RMS voltage on inverter side, =Filter Inductance, =Maximum possible RMS value of the ac load current, =Modulation Index of the Inverter. Three Phase Inverter: The regulated DC output of boost converter feeds the VSI which will then connect to the grid through LC filter. The inverter is of typical three phase six switch pulse width modulation (PWM) voltage source inverter. The VSI converts the power from the dc voltage source to three phase ac outputs with 120º phase displacement. PWM is modulation technique used to control and shape of the VSI output voltage. In order to control the magnitude, phase angle and frequency of the output voltage of VSI, PWM is used to generate switching pulses to control the six switches in VSI.In PWM three balanced sinusoidal control voltages are compared with the triangular voltages. The triangular waveform is at a switching frequency, which is generally much higher than the frequency of the control voltages and is called as carrier frequency. The three phase sinusoidal control signals with the same frequency are used to modulate the duty ratios of switching pulses from the switches. The Figure 4.5 shows power flow between a VSI and grid, where the impedance represents the combined filter, transformer and transmission line inductance. The active and reactive power flows from the converter are controlled by magnitude and phase of the converter output voltages relative with grid parameters. The active power flow is controlled by varying the phase difference and reactive power flow is by varying the magnitude of inverter output. The phase difference and amplitude are varied with reference of constant grid voltage. The control of modulation index controls amplitude, and synchronization and phase angle control of modulating sine wave controls the phase variation. The real and reactive power delivered to the utility is given by following relations (Santhosha kumar A 2010). Fig Power flow between a VSI and Grid Parameters of Inverter Input Voltage Output Voltage SwitchingFrequency V DC 230 V AC 8 khz Modeling and Control of Grid side converter: Since the machine is grid connected the grid voltage as well as the stator voltage is same, there exists a relation between the grid voltage and DC link voltage. The main objective of the grid side converter is to maintain DC link voltage constant for the necessary action. The voltage oriented vector control method is approached to solve this problem. The detail mathematical modeling of grid side converter is given below. The control strategies are made following the mathematical modeling and it is shown in Fig The PWM converter is current regulated with the direct axis current is used to regulate the DC link voltage whereas the quadrature axis current component is used to regulate the reactive power. The reactive power demand is set to zero to ensure the unit power factor operation [R.Pena et al.1996]. Fig. 4.6 shows the schematic diagram of the grid side converter. The voltage balance across the line is given by Eq. (4.8), where R and L are the line resistance and reactance respectively. With the use of d-q theory the three phase quantities are transferred to the two phase quantities. Schematic diagram of grid side converter ISSN: Page 4

5 for the voltage loop. The plants for the current loop and the voltage loop are given in below equations. For the grid side converter mathematical modeling can be represented as Where and are the two phase voltages found from using d-q theory. Since the DC link voltage needs to be constant and the power factor of the overall system sets to be unity, the reference values are to be set consequently. The active and reactive power is controlled independently using the vector control strategy. Aligning the axis of the reference frame along the stator voltage position is found by Eq. (4.13), v q = 0, since the amplitude of supply voltage is constant the active power and reactive power are controlled independently by means of i d and i q in the following Equations. The d and q reference voltages are found from the below eqns. MATLAB / Simulink Model of WIND/PV Hybrid System Control block diagram of Grid side converter 20 kw WIND Energy Conversion System 6 kw PV System 480 V DC Link Voltage 230 V 50 Hz Grid The control scheme utilizes current control loops for i d and i q with the i d demand being derived from the dc-link voltage error through a standard PI controller. The i q demand determines the displacement factor on the grid side of the choke. The i q demand is set to zero to guarantee unit power factor. There are two loops for the control design, i.e. inner current loop and outer voltage loop to provide necessary control action. Line resistance and reactance decide the plant for the current loop, whereas DC link capacitor is taken as the plant ISSN: Page 5

6 RESULTS: Model of wind turbine coupled with PMSG and model of Photovoltaic energy system are inter-connected with grid through full scale power electronic devices by using MATLAB/Simulink. The performance study is done for the simulatedsystem under input variations at RES s and load variations. Case-I: Constant Generation & Constant Load In this case the inputs like irradiation, temperature, and wind speed are kept constant with a constant ac load near Grid are considered for simulation. The irradiation 900 W/m 2, temperature 25ºC, for PV and wind speed of 8 m/s are given as inputs to the simulated Hybrid model and load parameters as 7.5 kw active power, kvar Inductive reactive power connected to 230 V, 50 Hz Grid. The system is simulated for 1 second and load is connected through a breaker which closes at 0.5 second. The results are as follows: Active Power distribution Grid Voltage Case I Grid current Case I Load Current case I DC Link Voltage case I Power of Hybrid System case I Inverter Output Voltage casei Inverter Output Current case I Case-II: Variable Generation & Change in Load In this case both the inputs parameters like irradiation and wind speed are varied with a change in ac load near Grid are considered for simulation. Change in Generation is achieved by changing the irradiation of PV system and Wind speed of WECS. In our simulation we consider a change of irradiance from 900 W/m 2 to 600 W/m 2 at 0.5 second, Similarly for WECS the change in speed from 6m/s to 8m/s at 0.5 second. Change in Load is illustrated by connecting a Load 1 of 7.5 kw active power, kvar Inductive reactive power at 0.4 second, here the breaker 1 closes and at 0.8 second the breaker is opened. Load 2 of 4 kw active power, kvar connected through breaker 2 at 0.6 second. So from 0.4 second to 0.6 second the Load will be 7.5 kw, kvar; from 0.6 second to 0.8 second the Load will be 11.5 kw, kvar and from 0.8 second to 1 second the Load will be 4 kw active power, kvar. These local ac loads are connected to ISSN: Page 6

7 230 V, 50 Hz Grid. The system is simulated for 1 second. The results are as follows: DC Link Voltage case II Case-II: Variable Generation & Change in Load In this case Hybrid Wind/PV generation the input parameters are varied, irradiance of PV is changed from 900 W/m 2 to 600 W/m 2 at 0.5 second, Similarly for WECS the change in speed from 6m/s to 8m/s at 0.5 second. Change in Load is achieved by using 2 Breakers for connecting Loads. The Power required by the Load is supplied by the Hybrid system and remaining power is fed in to the Grid. CONCLUSIONS AND SCOPE FOR FUTURE WORK Power of Hybrid System case II Active Power Distribution case II Observations : Load Current case II Case-I:Constant Generation & Constant Load In this case both Hybrid Wind/PV generation as well as ac load is constant. Load of 7.5 kw active power, kvar is connected to ac grid at 0.5 second by a breaker. The Power required by the Load is supplied by the Hybrid system and remaining power is fed in to the Grid. So Hybrid Wind/PV active power generation remains constant, wind reactive power is maintained at zero as controller has restricted the Hybrid model to generate it and at common point of coupling inverter, grid and load voltage remains at Peak voltage V, 50Hz. Conclusions The modeling of hybrid Wind/PV for power system configuration is done in MATLAB/SIMULINK environment. The present work mainly includes the grid tied mode of operation of hybrid system. The models are developed for all the converters to maintain stable system under various loads and resource conditions and also the control mechanism are studied. The dynamic performance of Hybrid Wind/photovoltaic power systems are studied for different system disturbances like load variation, wind speed variation and different irradiation and temperature inputs. The simulation results shows that, using a VSI and PQ control strategies, it is possible to have a good response of grid-connected hybrid energy system. The hybrid grid can provide a reliable, high quality and more efficient power to consumer. The hybrid grid may be feasible for small isolated industrial plants with both PV systems and wind turbine generator as the major power supply. Scope for future work The control strategy which is implemented in this work is grid-connected RES hybrid energy system. Implementation of control strategy for islanding operation of RES can be done to operate hybrid energy system to supply local loads during islanding. Also, connecting BSES (Battery storage Energy system) across the DC link can be modeled to increase the reliability and efficiency during peak conditions. ISSN: Page 7

8 REFERENCES Alejandro Rolan, Alvaro Luna, Gerardo Vazquez and Gustavo Azevedo, (2009). Modeling of a Variable Speed Wind Turbine with a Permanent Magnet Synchronous Generator, IEEE International Symposium on Industrial Electronics. B. M Hasaneen and Adel A. Elbaset Mohammed, (2008). Design and Simulation of DC/DC Boost Converter, IEEE. Chen Wang, Liming Wang, Libao Shi and Yixin Ni, (2007). A Survey on Wind Power Technologies in Power Systems, IEEE. D. Kastha, S. N. Bhadra, S. Banerjee, Wind Electrical Systems, Oxford University Press, New Delhi, Fei Ding, Peng Li, Bibin Huang, Fei Gao, Chengdi Ding and Chengshan Wang, (2010). Modeling and Frede Blaabjerg and Zhe Chen, (2006). Power Electronics for Modern Wind Turbines, A Publication in the Morgan & Claypool Publishers Series. IEEE 1547 (2008). IEEE Standard for Interconnecting Jitendra Kasera, Ankit Chaplot and Jai Kumar Maherchandani, (2012). Modeling and Simulation of Wind-PV Hybrid Power System using Matlab/Simulink, IEEE Students Conference on Electrical, Electronics and Computer Science. Kiam Heong Ang, Gregory Chong and Yun Li, (2005). PID Control System Analysis, Design, and Technology, IEEE Transactions on Control Systems Technology, vol. 13, no. 4. K. T. Tan, P. L. So, Y. C. Chu, and K. H. Kwan, (2010). Modeling, Control and Simulation of a Photovoltaic Power System for Grid-connected and Stand-alone Applications, IEEE- IPEC. Mehmet Tumay K.Çagatay Bayindir Mehmet Ugraş Cuma and Ahmet Teke, (2004). Experimental Setup for a DSP Based Single-Phase PWM Inverter IEEE. N. Mohan, T. M. Undeland and W. P. Robbins, Power Electronics: Converter, Applications and Design, John Wiley & Sons, New York, ISSN: Page 8

Dynamic Modeling and Control of Grid Connected Hybrid Wind/PV Generation System

International Journal of Engineering Research and Development e-issn: 2278-067X, p-issn: 2278-800X, www.ijerd.com Volume 10, Issue 5 (May 2014), PP.01-12 Dynamic Modeling and Control of Grid Connected