Application Of Active Power Filter Based On H∞ Robust Control Theory

Active Power Filter (APF) is a novel power electronic device, to be dynamically used to eliminate harmonic and to compensate reactive power. Compared with the conventional measures, APF has many advantages and wide prospect, and it is considered as one of most effective means to resist the power pollution. In china, the study and exploitation in regard to APF are at their initial stage, and mature products have not been coming out yet, so the study regarding APF has important significance. The paper researches systemically and deeply on shunt APF, analyses its various sections and derives its mathematic model.Harmonic current detection technology is one of the critical technologies of traditional APF. Its development has directly effect on the development of APF technology, so to improve the harmonic current detection technology is very significative to promote the property of APF. The paper firstly studies the harmonic detection methods in APF based on FFT digit analyzing, single-phase harmonic fast detection and the adaptive noise cancelling technology; then the paper makes simulation in use of last harmonic detection method, and the results show that this method has not only high detecting precision but also better adaptability.The control strategy of APF is another vital technology. To aim at the characteristic of APF being subject to external interference and at model uncertainty, the paper applies H_∞control theory to control the output of APF. On the basis of illustrations above, H_∞robust controllers have been designed to aim at quintuple and septic harmonic current, respectively. The digital simulation results prove that the feasibility and effectiveness of the robust controlling method, both of the H_∞controllers are independent of the model of APF system and the effect from the system uncertainty and external disturbance can be greatly eliminated. The robust controlling method can ensure the internal stability and robustness of the system, which confirms the validity and performance of the method.Finally, the paper compares the adaptive harmonic current detecting method based on the adaptive noise canceling technology with H_∞robust control method, and the results show the previous method is of higher detection precision. However, the method need several periodic time, and its detection precision is at the cost of sacrifice dynamic characteristic; the latter method is of equivalent precision, but only after one periodic time, the system can be stabilized. Thereby this shows H_∞robust control method is of unexampled predominance.