Research On Crucial Technologies Of Active Power Filter

Various power electronic devices are promoted and applied. However it also makes the serious problems of power quality in power system. With constantly developing of modern power electronics and control technology, Active Power Filter (APF) is one of the most effective methods to improved power quality and solved power system pollution. So this thesis focused to research deeply and meticulously of APF harmonic detection and prediction, tracking control of compensation current. Simultaneously, thesis discussed parallel APF for main circuit structure, classification, mathematical model, main circuit important and basic parameter setting of detection current harmonic methods and strategy of compensation current tracking control.The feature of harmonic detection accurate and real time is one of factors which influence to APF performance critical. Dynamic response characteristics and compensation accuracy are two indicators of measured detecting harmonic current technology. Firstly, this thesis influence of analyzes the system delay performance to the compensation feature and the requirements for compensation performance of harmonic detection problems when frequent load changes. With the poor response problem of dynamic characteristics of traditional harmonic current detection algorithm, based on instantaneous reactive power theory of ip-iq method and transform method, they all are impossible to avoid introduced a low-pass filter link. But the low-pass filter link is easy to affect the dynamic response of the system. Although fast Fourier transformed method and various other intelligent algorithms and its improved make calculation highly accurate, however, there is often large computation and difficult engineering problems to achieve. This thesis presents a new type variable forgetting factor which based on recursive least squares (RLS) algorithm for detection current harmonic. By process occurs setting of judgment dynamic in different conditions of harmonic load current gives the value of forgetting factor. Thus it improved algorithm’s convergence speed and system’s dynamic response characteristics. Followed, this thesis also presents an improved algorithm of variable step size adaptive prediction harmonics. This algorithm according to principle of the older current impact of errors the weaker power-weighted calculation error, with regulator step of the main control factor, achieved weight values updating of step length and rolling optimization module. By introducing a dynamic factor to inhibit the algorithm when converges process, with the sensitive of instantaneous jumps error makes steady-state disorders. This algorithm not only has fast dynamic response characteristics, but also has a high accuracy. Simultaneously, it can make certain compensation of the impact on delays performance system.Compensating current control method is compensating performance is also influence performance factor of active power filter. This thesis base on the principle of APF’s compensating current hysteretic control analysis deeply impact on system’s performance of the nonlinear part hysteretic current control method revealed the necessity to improved nonlinear problems of hysteretic control. Followed, it analysis delays problem of the traditional control method, proposed the use of ITAE (Integral Time Absolute Error) optimal control law to achieve optimal of delay part control. According to run in the opposite law to design the twice optimization parameters, used linearization harmonic method to make nonlinear hysteretic loop of APF’s current predictive control scheme. This control method makes the system to have some of the linear system’s advantages. It also retained good original dynamic characteristics, robustness and anti-perturbations ability, etc. of hysteretic loop.This thesis also discusses DC bus voltage regulation, the negative sequence current of load, harmonic currents, zero sequence currents and negative sequence voltage, harmonic voltage, interaction of zero-sequence voltage easy to make fluctuation of DC bus voltage... of the APF system.In addition during the high power APF startup produces a larger of bus current. The increasing process of bus voltage will appear more substantial fluctuations. Above voltage fluctuation will affect not only to compensating performance but also to tracking current performance. Even result makes APF be not working properly. To this end this thesis presents a APF DC bus voltage’s fuzzy and PI compound control method. It solved bus bar excessive current during APF startup and voltage volatile problem. This thesis also presents a design method of APF’s soft-start circuit. Based on the analysis during startup of DC voltage and current, overvoltage protection circuit has been designed. Thereby it makes the adverse effects of shock current and DC capacitor voltage overshoot of the suppressing during system startup.