Research On Key Technology Of Control System Of Current Source Grid-connected Photovoltaic Inverter

As an important part of photovoltaic power generation,photovoltaic grid-connected inverters determine the energy transfer efficiency of the entire system.Compared with the voltage source inverter,the current source inverter has the boosting capability,which results in the absence of the cascaded DC-DC boost converter and improves the topology and working efficiency of photovoltaic power generation system.In this thesis,the research object is the three-phase current source photovoltaic grid-connected inverter.And this thesis focuses on the key technology of control system of three-phase current source inverter,including CL filter resonance suppression method and non-ideal grid disturbance suppression method.Firstly,the mathematical models of three-phase current source inverter are established in three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotating coordinate system,respectively.And according to the instantaneous power theory,the instantaneous power models of three-phase current source grid-connected inverter are established respectively when the three-phase grid voltage is unbalanced and contains 6k±1 order harmonic.Then,the space vector modulation technique,the main circuit parameter design method,the maximum power point tracking technology of the photovoltaic array and the CL filter resonance suppression method of the three-phase current source inverter are studied in detail.In the traditional capacitor voltage proportional feedback active damping method,the capacitor voltage is too large relative to the current modulation signal,which affects the dynamic performance of the three-phase grid-connected current source inverter system,and may even saturate the control loop and lead to the system out of control.To solve this problem,this thesis adds a high-pass filter in the capacitor-voltage feedback loop.Considering the influence of the high-pass filter and 1.5-beat delay existed in the digital control system,the stability of the traditional control strategy based the capacitive-voltage proportional feedback active damping method is analyzed in detail,and the value range of the capacitor-voltage proportional coefficient is derived when the closed-loop system is stable.And on this basis,an optimal design method of key parameters is proposed,which gives the concrete design principles and detailed design steps of the key parameters in the control system,making the resonance suppression effect of the system to the CL filter in the optimal state.The simulation and experimental results verify the effectiveness of the proposed method.Aiming at the disadvantages existed in the traditional control method of current source inverter,such as more parameters,complex design process and poor disturbance rejection capacibility against non-ideal power grids,a simple control method based on the optimization theory is proposed in this thesis.The proposed control method is composed of the proportional feedback of the grid-connected current,the proportional feedback of the capacitor voltage and the feedforward of the inverter-side current steady-state value.The proposed control method can effectively suppress the resonance problem of CL filter and current distortion problem caused by non-ideal grid disturbance.In addition,the proportional feedback coefficients of grid-connected current and AC-side capacitor voltage can be determined by only one parameter.On this basis,the key parameters are designed according to the bode diagram of the control system,and the poles position map of the closed-loop control system shows that the proposed method has good robustness to parameter disturbance.The simulation and experimental results verify the effectiveness of the proposed method.