Research On The Detection And Control Strategy Of Three-phase Four-wire Active Power Filter With Three Level Structure

Harmonic, a serious problem that has bothered the power quality constantly, is caused by the nonlinear loads which are connected to the electricity grid. In order to guarantee the security, stability and high-quality operation of the power system, harmonic, the “cancer” of the system, must be eliminated to achieve the goal for green and harmonious power grid. As an effective harmonic compensation device, active power filter is of great significance and necessity to the research. Therefore, this thesis takes the three-phase four-wire three-level shunt active power filter as the research object and makes a systematic and deep research on the detection technology, compensation control technology and device design.According to the entire harmonic detection algorithm for active power filter, this paper researches on the detection method based on Hilbert-Huang transform(HHT) and furthermore the HHT detection method based on ensemble empirical mode decomposition(EEMD) theory is proposed. The simulation shows that using EEMD doesn’t bring up the mode mixing phenomenon in the decomposition process, and overcomes the disadvantage of EMD. Compared with the instantaneous reactive power qpii - theory, EEMD has the adaptive ability and high precision when the load mutates. It also can realize real-time requirements.The simplified space voltage vector modulation method is used as the compensation control method. At the same time, the compound current tracking control of PI+repeated, the control principle of the DC voltage and the solution of mid-point voltage offset are elaborated in this thesis. The corresponding model of APF is carried out in Simulink. The simulation indicates that the compensation effect is both satisfactory for the balance and imbalance three-phase load and the insufficient compensation problem at commutation point has also been improved obviously. As a result, the compensation control of three-phase four-wire three-level active power filter is realized.In the end, three-level active power filter device is designed. The TMS320F28335 chip is adopted as main control unit, the DSP software program is complied, and the corresponding peripheral circuits are prepared. Through the load test, the effective compensation for harmonic current can fully be realized.