| The research content of this paper is a sub project of Shanxi Key Projects of Coal Based Science and Technology “Technology Development and Research of Large-scale Intermittent New Energy Grid Connection”(MD2014-06),aiming at the power quality problems in the new energy microgrid.Active power filter(APF)is a kind of important device for power quality governing,whose control methods include harmonic and non-harmonic detection controls.The latter one has advantages of more simple control system structure,smaller amount of calculation,good real time performance and more feasible for engineering applications.However,in the actual engineering operation,the DC voltage of APF is vulnerable to the loads fluctuation under the non-harmonic detection control,so that not only the utilization of DC voltage and the stability of APF are reduced,but also the compensating effect is severely influenced.In this dissertation,grid current feed forward control is proposed in the application of APF in stationary reference frame,which is based on the analysis of the control model and algorithm and the processes of power conversation.The proposed control method and algorithm are verified by simulation and experiment.The establishment of physical model and the mechanism of power flow is the foundation of control system design.So,starting from the small signal model of state space equation of APF,the relations of power conversion of non-harmonic detection control method are analyzed in this dissertation,and then the production mechanism of DC voltage fluctuation and principle of AC-DC power conversion are detailed explained.Based on the voltage-current double-loop control mechanism analytical results,it is proposed that APF ought to be considered as a part of loads and aim at harnessing the grid power quality,the grid current forward feed method is added on the traditional non-harmonic detection control method to reduce the dynamic power loss and accelerate the adjustment process.In the design of generating link of the feed forward signal,according to the analysis of the characteristics and requirements of feed forward signal,the Cascaded Delayed Signal Cancellation(CDSC)filter and active current approximation algorithm are designed: on the one hand,based on the finite impulse response(FIR)filter design principle and Delayed Signal Cancellation(DSC)filter design thinking,it is pointed that CDSC filter exists designing problems in application to the unbalanced loads,which is combined the effects analysis of CDSC filter,and the solution is offered by analysis of spectrum characteristics of CDSC filter;on the other hand,considering the properties of power factor under the non-harmonic detection control,the traditional algorithm of instantaneous reactive power is proposed to be replaced by a novel approximation algorithm,which simplifies the calculative process and accelerates the adjustment of dynamic processes.The proposed grid current feed forward control reduces the system power losses of APF,enhances the stability of DC voltage,and optimizes the compensatory effects during the dynamic loads fluctuation processes,unbalance factor is reduced after compensation as well.Having reasonable current loop parameters is a prerequisite for optimizing the control effect and system stability of APF.On the basis of traditional voltage-current double loop control,the simplified quasi proportional resonant controller design method in the stationary coordinate was proposed,which considered the characteristics of proportional resonant controller and the actual demand of discretization algorithm,to realize accurate compensation and rapid response of APF system.Then,combining the dynamic performance of voltage loop and current loop,the influence of the CDSC filter and the grid current approximation algorithm on the dynamic adjustment process is analyzed based on the dynamic process of the current vector.Finally,the application of the improved algorithm in the three-phase four-line system is analyzed.Simulation and experimental results verified the good dynamic property of the proposed improvement scheme that restrained the fluctuation of DC voltage,enhanced the operation stability and compensation effects effectively and be referential to industrial applications of APF. |
PDF Full Text Request