| In recent years, as the technique of power electronics develops, the load with nonlinear, impactive, unbalanced characteristics have been increasingly used in power network. They generate lots of harmonics. The harmonic pollution in public supply network becomes more and more severely, and influences the quality of electric energy supply and the safety of use to consumers, so it is increasingly important to harness the harmonic pollution.Firstly, to the problems that caused by harmonics, this dissertation depicts the reason of harmonic's bringing and the harm, then introduces the methods of harmonic restraining. Active power filter is one of the most effective methods to depress harmonics. This filter can track in the harmonic whose frequency and amplitude are both variant to compensate, and its compensation character is not influenced by power line impedance, so it is taken premium widely. Secondly, the theory, the class and the basic composing of the active power filter are described in detail.Based on the analysis of various harmonic current detection methods and the drawback of instantaneous reactive power theory, the concept of power factor is introduced into the control system of active power filter. The harmonic and reactive current detection technique based on unity power factor is described. The transient characteristic of the detection method is analysed and the detailed method of shortening the detection delay is provided.This dissertation analyses the basic operation principle of the active power filter,provides the foundation of design for filter in theory ,discusses the mutual relation of foundation formal, capability, direct current voltage and main circuit inductance while using hysteretic loop current control. At last, the real-time and dynamic simulation of active power filter based on unity power factor is implemented in Simulink environment of Matlab software, the simulation result shows that theproposed method is feasible and this theory is correct. |
PDF Full Text Request