Research On Theory And Application Of New Injection Type Hybrid Active Power Filter

With the development of national economy and the enhancement of people's living standard, more and more strict requirements for power quality are needed by electrical power users because the problems caused by voltage quality and harmonics are becoming increasingly serious. As we all know, the main reason resulting in voltage quality contamination and harmonics is the backward technologies of power transmission and distribution, as well as the lack of controlling and compensating reactive power and harmonics effectively and flexibly. Hence, it is imperative to promote the research process of eliminating harmonics and compensating reactive power together by an integrated equipment in the power transmission and distribution system.Based on a project of harmonics suppression and reactive power compensation in a copper foil factory in Jiang Xi province, this dissertation studies a new injection type hybrid active power filter (HAPF) including its topology structure, functional principle, systematic stability, detection and control method, synthesis compensation technology, as well as the optimum design means of main parameters and some important realizing technologies, etc. The emphasis and achievement of this paper mainly manifests in the following aspects:(1) According to the demand put forward by the copper foil factory, which the integrated equipment could compensate large-capacity reactive power just with small-capacity active power filter (APF) in high-voltage and large-capacity engineering environments, this paper proposes a new injection type HAPF. By adding an equivalent harmonic impedance in the branch circuit of power grid, this HAPF could force all the harmonic currents flow into passive power filters (PPF), which resulting in eliminating harmonic contamination more effective. And using the capacitive feature of PPF in the fundamental frequency, this HAPF could compensate fixed-capacity reactive power without increasing APF's burden. Moreover, in order to decrease APF's cost, the fundamental voltage will largely be endured by capacitor in view of the series resonance circuit tuned at the fundamental frequency, so the APF just bears little harmonic voltages. In this paper, we also analyze some steady-state characteristics such as damping the resonance probability between power grid and PPFs, enhancing the filtering effects of PPFs and enriching the system robustness. For better harmonic suppression effects, the amplification parameter of APF should be bigger, but it is restricted by system time delay, the inductance of power system, and parameters of PPFs. Complying with safe, reliable and economical principles, we take detecting grid current as control strategy which result in instability because of forming a closed loop. By careful analysis, this paper studies the system stability problem on the basis of mathematical model. On the basis of conclusions from stability analysis, this paper presents an on-line self adjustment technique to obtain perfect effects for harmonic suppressions under different operation conditions.(2) It is well known that whether the APF could or not get desirable harmonic eliminating effects, it mainly depends on the detecting method. Based on the discussion of sequence extractors of positive and negative fundamental wave, this paper proposes two types of methods for detecting current with reactive power, harmonics and negative sequence, which are the improved synchronous reference frame method and the detecting method based on sequence extractor of positive and negative fundamental wave. By synchronizing the grid voltage vector with positive sequence, the improved synchronous reference frame method is very simple without the phase locked loop and calculations for sinusoidal function. And the detecting method based on sequence extractor of positive and negative fundamental wave can further omit the transformation from theαβcoordinate to the dq coordinate, as well as its inverse transformation.(3) After obtain reference signals by the improved synchronous reference frame method, this paper studies the current tracking control algorithm. By establishing mathematical model with switching functions, we propose a new synthesis control method which combines the speedy performance of traditional double hysteresis control method with the zero steady-state error of recursive integral control algorithm. The main functional principle of synthesis control method could be concluded to taking outer-loop control strategy to decrease error greatly, then making inner-loop control strategy reduce error and energy loss, at last realizing zero steady-state error by recursive integral control algorithm.(4) In order to effectively compensate nonlinear characteristics in the voltage-source-inverter (VSI) and to efficacious eliminate switching ripples caused by the VSI. According to some problems arisen in the engineering project, this paper studies the cause, negative influence of DC-side voltage ripple and optional methods to hold DC-side voltage; analyzes some adverse effects of dead-time on output voltage, together with effective dead-time compensation method; proposes an approach to eliminate asymmetric problem caused by voltage drop on the switches by judging the directions of output currents; put forward to several ways to inhibit high-frequency burr such as the synthesis current tracking control algorithm, a non-dead-time SVPWM strategy based on randomized pulse position PWM, and a optimum designed LC filter. At last, we give a synthesis compensation technology to settle problems including DC-side voltage ripple, dead-time, as well as voltage drop on the switches and high-frequency burr.(5) In view of the lack of research on high-capacity APF's engineering application in china, this paper studies the optimum design means of main parameters and some important realizing technologies. Firstly, we discusses the general design principle of PPFs, as well as some considerations on safety and reliability of injection branch, hence multi-objective genetic algorithm has been needed to design PPFs with excellent performances. Secondly, on consideration of the coupling transformer performing a role in electrical isolation and voltages as well as currents matching between APF and PPFs, so the parameters of coupling transformer to be decided are rated voltage, current, volume and turns. After choosing switching frequency, the design of output filter should take APF's compensating properties, tracking reference signals and the safety of switches into consideration. In order to save time of developing and debugging, intelligent power module (IPM) has been used as high-capacity inverter in the new injection type hybrid APF. Then, some design and using problems such as optical shutter, power supply of controller, heat sink, interface circuits for driver and the size selecting of DC-side capacitor have been analyzed in detail. System composition of the new injection type hybrid APF is also introduced. At present, the new injection type hybrid APF, which eliminating harmonics and compensating reactive power together, is in commission and operation. The detecting result shows that the injection type hybrid APF meets all the requirements, and the harmonic suppression effect is obvious. It is worth to extend and use this integrated equipment in the power transmission and distribution system.In a word, taking the new injection type hybrid APF as example, this paper studies its topology, stability, detecting method and current tracking control algorithm, proposes a synthesis compensating technology to settle problems including DC-side voltage ripple, dead-time, as well as voltage drop on the switches and high-frequency burr, successfully designs an integrated equipment with eliminating harmonics and compensating reactive power together. The method for theoretical analysis and relative conclusion can be used as reference for another type HAPFs to accelerate research process for cleaner electric circumstances.