Research On The Photovoltaic Grid-connected Power Conditioner System

The photovoltaic technology is a new-energy technology, which converts solar energy directly into electrical energy with the photovoltaic effect. The research about photovoltaic technology is very important for solving the world’s energy crisis and environmental issues. However, with the development of the domestic’s industrialization process, a large number of nonlinear loads appeared, harmonies and reactive current from nonlinear load make power quality deteriorate increasingly. This thesis compares the working theory, topology and control strategy of the PV grid-connected generation and APF is proposed. Based on the existing function of PV grid-connected generation, the function of the new system is further expanded. The main research contents of this thesis include:1) The detection of harmonic and reactive current method based on instantaneous reactive power theory is discussed in details in the thesis. Based on the ip-iq detection of harmonic current method, grid-connected current is added to the current for compensating harmonic. In sense of vector, command current can be obtained by analyzing the fundamental positive-sequence active current of load and the command current of voltage loop.2) The combined system’s control strategy including compensatory current control and DC control is analyzed in detail. Two strategies of control, hysteresis comparison control and triangle wave comparison control, are proposed for compensatory current control. DC voltage control adopts PI closed loop control. Based on mathematical and circuital model of photovoltaic cell, after discussing the principle of MPPT(maximum power point tracking), two common control methods of MPPT are proposed. The mechanism of islanding is analyzed, including its risk, detecting methods and coping strategies.3) The topology of photovoltaic grid-connected power conditioner system is proposed. By analyzing several photovoltaic grid-connected inverters, a grid-connected system is proposed, which adopts BOOST DC and three-phase voltage inverter. The topology and working principle of BOOST are discussed in details. The value ranges of grid-connected reactance and energy storage capacitor are analyzed, in which system can be in its normal operation.4) In the end of thesis, based on MATLAB/Simulink, the researched system is modeled and simulated respectively, including three main functions:MPPT, grid-connected function and APF. Finally the unified control system proposed is analyzed and verified by simulation with MATLAB.