Research On Active Damping Control Of The LCL-type Grid Connected Inverter

As an important interface between new energy power generation and the power grid,the LCL-type grid connected inverter has an important position in the distributed power generation system.However,the resonance of the LCL filter affects the stability of the system.In order to solve the problem,the active damping methods for LCL filter-based inverter have been studied,and a virtual capacitor current feedback control method is proposed as well.Firstly,the frequency domain mathematical model of the system is established and analyzed,which involves control delay.The frequency domain characteristics of the system under the control of GCF(grid-side current feedback)is revealed,and the allowable gain margin is provided.Furthermore,the relationship between the gain margin and the resonance characteristics,as well as the effectiveness of active damping approaches are studied.The active damping characteristics of the common coupling point voltage vpcc feedforward are revealed as well,and the relationship between the system gain margin and the filter parameters is discussed.Secondly,since the vpcc feedforward cannot effectively expand the system allowed control gain,the capacitor current feedback control is studied,and its damping characteristics is analyzed,as well as the unified evaluation standard for active damping is provided.Furthermore,the effect of the low-pass filter in the feedback channel is studied.Finally,due to that the capacitor current sampling is susceptible to frequency aliasing,a virtual capacitor current feedback control method is proposed in this paper.The method consists of two parts:the current reshaping based on the GCF channel and the active high-frequency damping link integrated in the controller.The implementation of virtual capacitor current feedback alleviates the stability problem caused by grid impedance fluctuations.It can expand the value space of low-frequency control gain without introducing any resonant controller,and the grid-connected current waveform quality in low frequency bands is thereby improved.The research methods were first verified by simulation in MATLAB/Simulink.Furthermore,the DSP-based experimental platform is development.Based on which,the proposed method and analysis approaches are verified as well.The simulation and experimental results show the correctness and effectiveness of the virtual capacitor current feedback control.