| The distributed generation(DG)system based on renewable energy is concerned by all countries in the world,and it has been widely used in the world.In order to realize the grid connected operation of DG system,grid connected inverter is required to be connected to the distribution network or microgrid at the point of common coupling(PCC).The early distributed grid connected inverter works at unity power factor and single function.Because of the power electronics penetration into power grid,the using of a large number of modern power electronics devices and unbalanced loads,the load is becoming more and more sensitive to the power quality and puts forward higher requirements.Modern power quality compensation devices,such as dynamic voltage restorer,static synchronous compensator(STATCOM)are widely used in power quality control.However,it is required to install power quality compensation device in the system.In addition,the static synchronous compensator and the grid-connected inverter have similar topology,so integrated it into the grid-connected inverter,and the power quality control can be realized by the reasonable control of the grid-connected inverter.First,the main circuit and drive circuit and filter of voltage source inverter are designed,the mathematical model of voltage source inverter is established,the current loop control is designed,an experimental platform based on DSP was built.In order to realize the synchronization between the voltage of grid connected inverter and the voltage of grid when grid voltage harmonic distortion or unbalanced,using a dual two order generalized integrator phase locked loop for the real-time detection of the grid voltage phase,the inverter can meet the grid-connected function well.When the output current of the inverter is small or the grid-connected current is small,the method of selective harmonic compensation is adopted to compensate the low order harmonics.Aiming at the problem of high frequency harmonics power quality,the mechanism of high frequency harmonics common mode interference is analyzed,a novel grid connected inverter circuit is proposed to solve the problem of high frequency harmonics interference and the simulation is carried out.Secondly,we focuses on two kinds of voltage quality problems,namely voltage riseand voltage dip,discuss the effect of voltage quality adjustment strategy and compensation in the line impedance is resistive,inductive and Resistor-inductance conditions,and the theoretical analysis is carried out by Matlab/Simulink simulation and experimental verification.At last,the voltage adjustment strategy in the line impedance is resistive,inductive and Resistor-inductance conditions in the case of unbalanced voltage is analysed.For grid connected inverter under unbalanced grid voltage conditions in operation will occur the active / reactive power fluctuation,grid current distortion problem,starting from the perspective of complex power theory,a control strategy of grid connected inverter based on complex power stationary coordinate system is proposed,and the six variables are controlled by the combined active / reactive power fluctuation component.Using the two adjustment to combine the control target to achieve a coordinated control with the function of current limiting,which under unbalanced grid voltage conditions of grid connected inverter output active / reactive power continuously adjustable,and the peak of the grid current maintained at rated current range,and the proposed method's feasibility and effectiveness are verified by experiments. |
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