A Study On The PWM Inverter Input-Terminal And Output-Terminal Filter

Harmonic is existed in electric power systems universally .It may cause serious damage to the operating safety of the electric power system and the electric power utilization and becomes a serious threaten to the electric environment, which is the basis of human living .It has become a common viewpoint to manage harmonic pollution and limit the harmonic in a reasonable level .The root of harmonic pollution is the harmonic current produced by non-linear loads and injected into the power system .An important method for harmonic management is to suppress the harmonic current injected into the power system.PWM inverter AC motor bring the harmonic current, It pollute electric power systems. Theoretically, active power niter can suppress load harmonic current effectively and it is one of the most promising methods to solve the harmonic problem. Most of the active power filters used to suppress harmonic current is parallel ones. But parallel active power filer has disadvantages, such as difficult to be implemented and having ordinary compensation performance etc .So it is practically utilized as a secondary choice. Therefore, it is important to enhance the research of active power filer, push the process of its industrial application and improve the capability of harmonic management. A novel active power niter based on theoretical and experimental research of active power filtering technology is resented in the paper to overcome the disadvantages of parallel active power filter and accelerate the development of active power filtering technology.The operating principle of parallel active power filter is analyzed in the paper. It shows that the harmonic current injecting idea leads the weakness of traditional parallel active power filter. Because the goal of harmonic management is to keep the line current sinusoidal, a compensating idea, which is based on the direct control of line current, is proposed in this paper. So the injection of harmonic current may be changed to the control of fundamental current.To realize the filtering idea of this paper, novel main-circuit topology should be designed to Et the line current control. The filter mainly includes a voltage-source inverter and three identical control inductors that are connected in series with the power-line. So the inductor currents arc the line currents and can be controlled by adjusting the voltages across. Therefore the line current can be controlled through regulating the inverter outpl1t voltages according to the characteristics of the line voltages. Then, compensating principle of the proposed filter is analyzed based on the different requirements of harmonic current management and the configuration of the filter.PWM inverter AC motor are resulted in some problems when long motor cables are required, such as over voltage and damped high frequency ringing at motor terminals which contribute to winding failure, leakage current to ground, Shaft voltage and baring current, etc. These problems can be eliminated by some passive filtering techniques. On the basis of installation position, the filters can be divided into motor terminal filters and inverter output filters. In this paper, voltage reflection is analyzed. The results show that over voltage is depends on the PWM pulse rise time. Furthermore, three inverter output filters are discussed. These filters all can reduce the over voltage and ringing at motor terminals, but only the improved second-order low-pass inverter output filter can suppress bearing current and shaft voltage. So the development of this type of filter is most prospective. so the paper research the optimal design of this type of inverter output filter, so it has better versatility.