Research Of Key Technologies For Multiplexed Active Power Filter

With the extensive application of power electronic equipments, the problem of power grid harmonic pollution has become more and more serious. Active Power Filter(APF) is an effective tool to improve electric energy equality. It can compensate the harmonic current and reactive power in power grid. In order to effectively enhance the compensation capacity of active power filter, this thesis takes three-phase three-wire shunt multiplexed APF as the research object, intended to address some of its key technical problems at runtime.As to active power filter, the harmonic detection part has a significant impact on the filter’s performance. In this thesis, the traditional harmonic detection methods are classified, and the widely used ip-iq harmonic detection algorithm is highlighted. Due to the use of low-pass filter, the delay of the system will increase in ip-iq method. When harmonics change rapidly, this method can not work efficiently. This thesis describes a harmonic detection algorithm based on discrete Fourier transform. The traditional sliding window iterative discrete Fourier harmonic detection algorithm is improved in three areas, which can track the fundamental signal faster than ip-iq detection algorithm.For multiplexed active power filter, the mathematical models are established in three-phase stationary coordinate system, two-phase stationary coordinate system and two-phase rotating coordinate system respectively in this thesis. Besides, the mathematical expression of the zero-sequence current is deduced.Since the DC side using common bus capacitor, it would produce a certain amount of zero-sequence current. In this thesis, the path of zero-sequence current is analyzed in detail, and the mechanism of zero-sequence circulation formation is deduced. The circulation will influence some aspects of the filter’s performance. The loss of zero-sequence current is discussed, and the effects of zero-sequence current are showed in an equivalent way on filtering device filtering performance. According to the mathematical model of multiplexed active power filter, a circumfluence suppression strategy is introduced based on deadbeat control and current balance control. Deadbeat control is mainly based on its mathematical model by adjusting the zero vector in next operation period. The current balance control is used to cooperate with the deadbeat control strategy. The main idea is to re-adjust the current of α/β axis. The combination of these two control strategies can be implemented to inhibit the circulation of zero sequence effectively, and improve the performance of APF to some extent.Finally, the relevant content of this thesis are verified by MATLAB simulation and experiment.