Research On Harmonic Power Sharing Strategy Of Parallel Photovoltaic Inverter System

The microgrid,which includes a number of distributed power generation systems and loads,is proposed to reinforce the use of renewable energy and solve the potential problems in the grid.In microgrid,the parallel inverter technology has been widespread concerned because of its redundant power supply and flexible power capacity.With the application and development of industrial and modern technology,the nonlinear loads increase dramatically,and the harmo nic pollution problem needs to be solved urgently.The research on the harmonic power sharing of solar photovoltaic parallel inverter system with the nonlinear loads which use the photovoltaic power generation as the distributed power has become an importa nt direction nowadays..This paper introduces and compares three common inverter topological structure,and selects a non-isolated two-class structure without transformer as the main circuit.The single inverter adopts the double quasi-PR control strategy based on the instantaneous inductor current and the output voltage to improve its working performance,and guarantee the stable operation of parallel inverter systemIn this paper,the fourth-order band-pass filter is utilized to extract the harmonics without delay and distortion.The fundamental power and harmonic power is calculated based on the single phase instantaneous reactive power theory.The influence of the difference of line impedance on the accuracy of active power and reactive power sharing is analyzed.Then the rationale of virtual impedance algorithm is analyzed.The virtual impedance is introduced by two ways based on the droop control to achieve the fundamental and the harmonic power high-precision sharing.One is to introduce the positive virtual impedance,and design a new voltage compensate strategy in order to reduce the influence of the positive virtual impedance on the PCC power quality;the other is to introduce the negative virtual impedance,and design an adaptive selection method o f virtual impedance values based on the linear relationship between the virtual impedance and the fundamental reactive power,harmonic reactive power.On the basis of the above work,the hardware experimental platform of photovoltaic parallel inverter based on DSP28335 is established,and the experimental verification of the two harmonic sharing strategies is completed.The experimental results validate the proposed control strategies can effectively improve the harmonic power sharing accuracy and ensure the power supply quality of the common coupling point(PCC).