The Control Method Of Inverter Based On The H_? Repetition Control In The Unbalanced Grid

In case of the global energy shortage,a lot of distributed power with solar energy,wind energy or hydroenergy as source of energy has emerged,which is connected to the power grid by the inverter.The inverter connects the distributed power and the power grid,and increases the probability of unbalanced grid.This paper considers the output current,active power and reactive power of the inverter in case of the unbalanced grid as the object of study,and studies the positive and negative sequence signal extraction method,design of repetitive controller and suppression of the grid-connected power fluctuation.The main contributions of this paper can be summarized as follows:First,by analyzing the working principle of the traditional Second order generalized integrator-Frequency locked loop(SOGI-FLL)in the positive and negative sequence signals extraction method,the interaction between DC offset and output accuracy of SOGI-FLL is obtained.Accordingly,an enhanced SOGI-FLL which can suppress the DC offset is designed in this paper.The enhanced SOGI-FLL uses a low pass filter to estimate the DC component in the input signal,so as to eliminate the influence of DC component on the output.The proposed SOGI-FLL is more robust in the presence of DC offset.Then aiming at the resonance problem of LCL filter,based on the active damping scheme using inductor current on the inverter side,the state space model of LCL inverter considering inductor current feedback on the inverter side is established.Based on the state space model,a standard H? model for resonance suppression problem of LCL filter is constructed.Accordingly,the transfer function of resonance suppression compensator is obtained and the stability of LCL filter closed-loop system with compensator is analyzed.Finally,by analyzing the correlation between power and current in the unbalanced grid,it was concluded that there is a contradiction between the two control objectives of keeping the injected power constant and reducing the current harmonic content.For the contradictory relation,a power-current cooperative control strategy was proposed.It was ensured that the harmonic content of current complied with the standard.At the same time,the fluctuation of the grid-connected power was suppressed as much as possible.In the proposed power-current cooperative control strategy,the multi SOGI parallel resonant decoupling network is used to calculate THD of the grid-connected current.The calculation accuracy of THD was ensured.At the same time,the overall efficiency of the system was improved.Based on the above theory,the control system of grid connected inverter in unbalanced power grid is established.Using PSCAD software to build the simulation platform and carry out simulation test on the proposed theory.The simulation test was mainly done for the modified positive and negative sequence signal extraction module,repetitive controller designed according to H? theory,and power-current cooperative control strategy.The correctness of the theory proposed in this paper was verified.