Protection System Design Of Active Power Filter

In recent years, the degree of modernization of the world is improving continuously, and the national economy is developing rapidly, so the requirement of electric energy quality is more and more high. In view of the existence of nonlinear equipment and load in power system, waveform distortion of the power system appears. Harmonics on the power system has lots of Harmfulness to the operation of the power grid, such as causing the misoperation of relay protection and automatic device, shortening the life of electrical equipment, increasing the network loss of lines and causing communication interference and so on.APF is a new type of power electronic equipment, it can inhibit harmonics of the system dynamically, and can track and compensate different size and frequency of harmonics. "Active" is relative to "passive" LC filter, it makes up for shortcomings of the passive filter which can only absorb the fixed size and frequency harmonics, and it can control and output the size, frequency and phase of current initiatively. APF has characteristics of response quickly, resonance with the system uneasily and good filtering effect. Therefore, the research on active power filter has great practical value.How to ensure the normal operation of APF is the precondition of engineering application. This paper first introduces the basic principle of APF, the system structure and the method of APF compensation harmonic current detection, then put forward the overall design scheme of APF protection. The protective scheme involves three aspects, respectively is when the protection design of fault APF of their own; protection design of APF external short circuit fault; APF in the no normal state(such as overload protection design); to validate the APF model finally, using Matlab/Simulink simulation platform for three-phase three wire system the proposed protection scheme, the simulation results prove that the experiment over current can not only effectively limit APF equipment, make it in the in the power grid running safety and can play the maximum compensation in power abnormal operation condition.