Research On MMC-APF Control Strategy Based On Improved Quasi-PR And ELM Optimization

Now a large number of power electronic devices are used in the micro grid.These rectifying inverters and nonlinear loads are used in the grid,which will cause harmonic pollution and affect the power quality of the grid.At the same time,with the development of industry,the power system has higher requirements on voltage and power.In order to meet the requirements of high power and voltage,this paper adopts the APF of modular multi-level(MMC)structure for harmonic suppression to improve the power quality of the system.In this paper,the basic principle and topological structure of the modular multi-level APF structure are introduced in detail.In order to improve the ability of the MMC APF to detect and compensate harmonics,an adaptive algorithm with improved momentum factor is proposed to optimize the ip-iq detection method and improve the tracking speed and precision of harmonic detection.This method can detect the harmonic current accurately and improve the detection accuracy greatly.Since each sub-module in the MMC structure has a capacitor,the initial energy storage of the capacitor is different,resulting in different capacitance voltage of each module,which will generate a circulation within the bridge arm.In order to suppress the circulation in the MMC module,the analysis of the circulation in the MMC shows that the circulation is mainly composed of dc component and double frequency component.The second order generalized integrator(SOGI)and direct current integrator were used to extract the double frequency circulations,and then the quasi-pr controller was used to control the double frequency circulations.In order to eliminate the disturbance of the capacitor voltage in the submodule,a feedforward compensation method is proposed to compensate the disturbance and suppress the circulation in the MMC.In this way,the frequency doublescale component can be suppressed,and it is easy to realize.For the current inner loop control for the traditional PI control system running state can’t online real-time setting PI control parameters,leading to problems such as control accuracy is not high and the stability is not enough,is presented based on the extreme learning machine(ELM)repeat PI control strategy,through a real-time online learning setting ELM PI control parameters,and then get the effective value of real-time compared to the traditional PI control,the optimized control strategy not only improve the response speed of the system operation and the compensation accuracy,also greatly improve the stability of the system.The APF experimental platform with MMC structure is built to verify the method adopted in this paper.The experimental results show that the improved harmonic detection method and control strategy can better realize the regulation function of APF with MMC structure for power quality of micro grid.The paper has 56 pictures,7 tables and 60 references.