Investigation on Control of Voltage Source Inverter Interfacing Domestic PV System to The Grid

Abstract

The integration of renewable energy like the clean solar energy into the grid has become increasingly relevant in the recent epoch due to the current energy demand, the depletion of fossil fuel reserves and their environmental impacts. The responsibility of providing adequate harmonic current compensation to the non-linear loads connected at the point of common coupling(PCC) and achieving the power flow balance in the sys- tem lies solely with the interfacing converter that forms the heart of the grid integrated photovoltaic system (PV). The above tasks can be accomplished by incorporating suit- able control strategies to the interfacing converter, preferably inverter. This thesis is an attempt to provide an insight into the various control strategies adopted for adding shunt active filtering feature to the inverter used to interface a domestic PV system to the grid. To regulate the power exchange between the grid and the PV system, a robust DC- link voltage controller capable of withstanding the intermittent nature of solar energy and sudden variations in load is required. A proportional integral controller (PI) used for DC-link voltage control, exhibits oscillations during steady-state and overshoot dur- ing transients. The conventional sliding mode controller reduces the overshoot at the expense of increased steady-state error. A robust sliding mode controller for the control of DC-link voltage to reduce steady-state error by incorporating integral action to the conventional sliding mode controller is proposed. The harmful effect of the chattering phenomenon seen in the conventional sliding mode controller is minimised by limit- ing the error in the control variable using a signum function. The results of numerical simulations carried out in MATLAB/Simulink platform for various system conditions illustrate that the proposed controller provides superior performance compared to PI controller and conventional sliding mode controller in terms of power flow balance and speed of response at all system conditions. The proliferation of power electronic devices and non-linear loads in grid inte- grated photovoltaic (PV) systems have caused power quality issues to originate in the system. The harmonic current requirement of the non-linear load has to be met to im- prove the system’s performance. A fast, simple and effective algorithm for harmonic current compensation that enhances the dynamic performance of the shunt active power filter under various system conditions for the grid is proposed. The proposed dual non- adaptive concatenated delayed signal cancellation (NACDSC) based algorithm extracts the fundamental component of grid voltage and load current that is used to generate ref- erence current required for the harmonic compensation of non-linear load. Moreover, the control algorithm does not require any tuning of controller parameters to eliminate higher-order harmonic components. The simulation results for various system con- ditions demonstrate that the proposed control algorithm offers enhanced performance compared to existing traditional self-tuning filter (STF) and low pass filter-based meth- ods in terms of speed of response and harmonic current compensation. A laboratory prototype of the shunt active power filter is implemented in which the control algorithm is realised in dSPACE 1202 RTI platform. From the hardware results presented under different operating conditions, it is observed that the control scheme provides a good response in terms of power quality and powe control.