Design and Analysis of Controller with Selective Harmonic Compensator for Grid Connected PV System

Harmonics produced by distributed power generation systems (DPGS) is a main power quality issue, particularly due to the number of these systems connected to the grid is always increasing. This means that, it is significant to control the harmonics caused by these inverters to limit their contrary effects on the grid power quality. This paper has proposed a new proportional current controller (P Resonant Current Controller) with selective harmonic compensator for grid connected photovoltaic (PV) systems. The proportional resonant current controller (PRCC) can have a significant effect on the quality of the current supplied to the grid by the PV inverter, and hence it is essential that the controller provides a highquality sinusoidal output with negligible distortion to avoid generating harmonics. The effectiveness of the proposed framework has been verified using simulation results in MATLAB/Simulink.


Introduction
Recently, due to environment pollution the distribution generation system using renewable energy sources like solar, wind power and micro-hydro power have become the main power generation systems. Solar powered electrical generation depend on photovoltaic (PV) system. PV system uses one or more solar panels to convert solar energy into electricity. The most collective way to produce solar energy is to conversion of photon energy to HOHFWULFDO HQHUJ\ 1RZ D GD\ ¶s photovoltaic system has greatly contribution to generate the electric power when it compares with the other renewable energy sources it has more abundance and sustainability [1]. Basically, PV system converts sun light into electricity by using photovoltaic modules. By using different maximum power point tracking [MPPT] techniques it is possible to extract the maximum power from photovoltaic modules [2]- [3]. The PV system generates DC, and it can be converted in to AC with desired frequency through inverter and it tied with grid is called Grid Tie inverter [GTI] [4][5]. Grid tie Normally, synchronization is required for grid tied inverter of the voltage such as fundamental frequency and phase must be unique to send power to the load. Harmonics generated by the distributed power generation system is major power quality issue. It is very important to control the harmonics generated by these inverters to limit their adverse effects on the grid power quality [6].

Grid Connected System
Single phase grid connected configuration is shown in fig.1. The main elements that can be included in a system of photo voltaic conversion are the photo voltaic modules, dc link capacitor, Inverters, loads, utility grid. The most common PV-technologies used nowadays are the single-crystalline silicon and the multi-crystalline silicon modules [8]. Power electronics has a significance role in the field of solar photovoltaic system. The enhancement of efficiency of the solar PV system is mainly depends on the power electronics-based devices like converter and inverter. The conversion efficiency and losses have significantly reduced by the application of these devices.

A. Modeling of PV system
Basically, solar cell is a p-n junction diode that directly converts light energy into electricity. The equivalent circuit of the general model which consists of a photon current, a diode, a parallel resistor and series resistor it express leakage current, an internal resistance to the current flow respectively as shown in Fig 2. The current source IPh represents the cell photo current. RSh and RSe are representing the intrinsic shunt and series resistance of the solar cell.

Fig.2. Equivalent circuit models of generalized PV
The basic equation is taken from theory of semiconducto r [9], mathematically describes the I-V characteristic of the PV cell is, The current-voltage characteristic equation of a solar cell is given as The ideal factor A is dependent on PV technology [10]. Photon current is mainly depending on the outer environment irradiance and temperature of the sunlight is represented as Where,

B. Selection of DC-LINK capacitor
The selection criteria of dc-link capacitor based on the optimal ac line current regulation strategy for the single-phase grid-connected photovoltaic (GCPV) system. The expression for dc-link capacitance can be derived as [11].

C. Inverter
For processing the DC power generated from solar PV panels to obtain AC power, inverters are used. Inverters are classified into three broad types [12]. Single-phase full bridge inverter circuit is shown in fig.3. Grid-tied inverters are designed to provide up to 99% MPPT efficiency and after converting DC power to AC power it feeds the electricity into the grid system [13].

D. Filters
The L-filter is the first order filter with attenuation 20 dB/decade over the whole frequency range. The LCfilter is second order filter, and it has better damping manner than L-filter. This simple configuration is easy to design, and it works mostly without any problems. The second order filter provides 12 dB per octave of attenuation after the cut-off frequency of Transfer function of the LC-filter is, The attenuation of the LCL-filter is 60 dB/decade for frequencies above resonant frequency, therefore lower switching frequency for the converter can be used. The LCL filter has good current ripple attenuation even with small inductance values.

Control Scheme for Grid-Connected Inverter
The main important elements of the PV System for control structure are: a maximum power point tracker (MPPT), a synchronization is obtain by using the phaselocked-loop (PLL), based on delay, the input power control using the dc voltage controller and power feedforward, and the grid current controller implemented through a P-Resonant(PR) Control as shown in fig  4.The most common control structure for the dc-ac grid converter is a current-controlled H-bridge PWM inverter having a low-pass output filters. The drawback is its resonance frequency which can produce stability problems and special control design is required [15]. The control structure of the PV energy conversion system is shown in fig.4. The highly most elements of the control structure are the synchronization algorithm based on the MPPT, the input power control, PLL and the grid current controller.

A. Phase locked loop
The phase locked loop (PLL) is used to bringing into a unity power factor operation which involves synchronization of the inverter output current with the grid voltage. The PLL structure is also used for grid voltage monitoring [15]. The general form of the PLL structure is presented in Fig.5.   Fig. 5. Generalized structure of a 1-PLL

B. Perturbation and Observation Based MPPT Algorithm
The Perturbation and Observation (P&O) MPPT algorithm is easy to implement, it works based on the photovoltaic array which is perturbed of a radiation of orientation. If the power extraction from the array increases, the operating point varies towards the MPP which in turn suits therefore the working voltage in the similar direction.

C. Input Power Control
The control strategies of input power in the case of a power configuration of PV system without dc-dc converter are presented in the following section. A new control strategy of input power is proposed in Fig.7. The new element introduced is the power feed-forward. The computed value of the current amplitude reference using the PV power (PDc) and the RMS value of the ac voltage (Ug_rms) is added to the output value of the dc voltage controller (Id) resulting in the ac current amplitude reference (I*Ref) Using the input power feed-forward the dynamic of the PV system is improved being known the fact that the MPPT is rather slow. The dc voltage controller ensures a quick response of the PV system at a sudden change of the input power [16].

D. Grid current controller
Classical PI control with grid voltage feed-forward (Ug) as depicted in fig.8 is commonly used for currentcontrolled PV inverters. Where, pi G is Proportional Integral control, Kp is the Proportional gain, Ki is the Integral gain. Alternative solution for the improperly performances of the PI controller is the PR controller. The current loop of the Photovoltaic inverter with PR controller is shown in Fig. 9. The PR current controller GPR(s) is defined as [17], [19].
Where, Kp is the Proportional gain, Ki is the Integral gain Ȧ o is the resonance frequency Gf(s) represent the low pass filters and Gd(s) represents t he processing delay of the microcontroller,which is typic allyequal to the time of one sample Ts and is represented by reduced such as the3rd, 5th,7th. This compensation can be used to reduce the current THD.

Simulation Results
In this section, discussed about the system configurations and the performance of the single phase grid connected system is verified in MATLAB/SIMULI NK at temperature 25 c q and irradiance 2 1000w / m  Fig.11. shows the grid voltage and inverter output current of the gridconnected system. Synchronization between grid voltage and current is obtained by using the PLL. The Vpcc is given to the PLL block to control the voltage and current of the system. The harmonic analysis of the current is shown in fig.12. By using the P-resonant controller the total harmonic distortion is 11.82%. To reduce the current THD by adding the 3 rd , 5 th and 7 th harmonic compensators to the p-resonant current controller. Fig.13 (a). shows the inverter output current by adding the different harmonic compensators to the P-resonant controller. Fig.13. (b) shows the THD analysis of the current with adding selective harmonic compensators to the resonant controller. By adding the different compensators, the THD value is reduced to 5.85%.

Conclusions
This paper presented a design of single-phase gridconnected PV system with proportional resonant controller. A complete analysis is passed out in order to estimate the effect of the PR current control https://doi.org/10.1051/e3sconf/202130 E3S Web of Conferences 309, 01009 (2021) ICMED 2021 901009 characteristics on the PV inverter performance. A set of design adjustments relating harmonic injection and grid synchronization. The design of PR current control and reduse the effective harmonics from inverter output current is done by using matlab/simulink. The design procedure is also formulated according to the IEEE standard requirement for grid interconnection.