The Simulation Research Of Parallel Active Power Filters

Along with the rapid development and gradual ripeness of power and electron technique, the power and electron equipments are used diffusely in the course of industry- agriculture production and human daily life. The power and electron equipments have the characteristic of non-line load, though they can improve the efficiency of industry- agriculture production and life level of human, they can make much harmonics and reaction power current into power grid. They might make power grid appear the problems of power quality: flash, frequency variety, three-phase imbalance and harmonics. They influence the efficiency of transmit electricity and safe function of equipments.Now two methods are used in the compensation of harmonics and reaction power: traditional LC passive power filters and active power filters. LC passive power filters only can absorb the harmonics of steady frequency and easily make parallel resonance. Active power filters can overcome the shortcoming of LC passive power filters, and achieve the function of harmonics and reaction power compensation. Among lots of kinds of active power filters, parallel active power filters are used most widely. They have the characteristic different from LC passive power filters: even if the frequency and amplitude of compensated objects harmonics, parallel active power filters have fine compensation characteristic.Parallel active power filters are used widely in the system of three-phase three-wire, and the research of this typed filters structure and control methods is ripe. Presently, computers, television, electric ballast and microwave oven are single phase load, and the amount is much bigger, so the harmonics and three-phase imbalance influence made by them is not ignored. Three-phase four-wire system is used in factory power supply, civilian house and city power supply. The research to compensation of three-phase imbalance and harmonics in three-phase four-wire system is realistically significative.First, the control methods of traditional load-current harmonics detection (with harmonics detection) and DC voltage detection(without harmonics detection) are discussed detailedly for three-phase three-wire system, the entitative relation between them is shown, and a new control method is given, which has a good dynamic characteristic like the control methods of detecting load current harmonics and the sententiousness like the control methods of DC voltage detection .Second, the two kinds of topology structures (capacitance- midpoint and four-arms )for three-phase four-wire system are given,and their control methods are showed amply. Third, the technique about active power filters is discussed, which includes the anti-aliasing technique for load current detection, the design of digital LPF for harmonics detection, the design of output filters and the analysis of influence to the active power filter system and the analysis of big compensation current product and restrain. PSIM and MATLAB models corresponding to all control methods and arithmetics mentioned in this paper are given, their validity and feasibility are validated by simulation.