Study On Three-phase Parallel Active Power Filter

Active power filter(APF) is an advanced power electronic equipment used to dynamically eliminate harmonic and compensate reactive power.Compared with some conventional measures,APF has many advantages and wide prospect.In china, the studies and exploitations in APF are at its beginning stage, and mature products of large capacity have not been coming out yet, so the studies in active power filers have important significance. The principle of power energy flows between AC power and nonlinear load is discussed in this paper, and the basic principle, main circuit structure and mathematic model of APF are expatiated also. In this paper, the distorted current detecting methods based on the p -q and i p -iqalgorithm are systemically analyzed and discussed firstly, then a novel detecting method based on synchronous reference frame transformation is presented. Through theoretical analysis and simulation, the conclusion is that the detecting method based on synchronous reference frame transformation can be used to calculate the compensating current reference accurately even under the unsymmetrical and non-sinusoidal supply voltage conditions. In this paper,two control methods of current compensation are analysed and their advantages and disadvantages are also presented.On the basis of theoretical analysis for the triangular carrier linear control, a new PWM arithmetic based on asymmetric regular sampling is brought forward, which is more close to natural sampling and easy to use on-line calculation method. The main circuit of 3-phase parallel APF with 50kVA is designed and its design method of main parameters is explained in detail. A full digital APF based on DSP and singlechip is designed. Computing of distorted current and controlling of system are realized by TMS320LF2407A DSP, and the function of human computer interface is implemented by AT89C52 singlechip. The design of hardwave interface and flowchart of software are given in this paper. To examine the validity of the controlling measure of the active power filter and understand the controlling rules furthermore, the simulink model of the parallel APF system is built with SimPowerSystems Blockset and simulinked in MATLAB/ SIMULINK. The simulation results show the precision of the proposed approach and also proved the availability of the parallel APF system, the validity of the distorted current detecting method and the feasibility the controlling strategy. This research project belongs to one financed project of science and technology office, Fujian Province in 2005. The experiment equipment will be applicated in the future.