Research On The Key Techniques Of Shunt Active Power Filter

Active power filter (APF) is one of the most important approaches to control power quality based on advanced power electronic. The shunt active power filter plays the most leading role in the past or future. Domestic filtering market is thirsting for the practical products which have our own knowledge property, core technique and reasonable price. This paper do systemic and deep research on the most fundamental and applied shunt active power filter, including related theoretics and application issues.Compensating strategy should be confirmed when using active filter for nonlinear loads. Two main compensating strategy, including constant source power strategy and sinusoidal source current strategy are studied. Their characteristic, Selection principle and compensation objective is described. The dominant harmonic detecting method is summarized in this paper and a modified technique based on synchronous reference is proposed for accurate harmonic and reactive current detection.The mathematic model of shunt active power filter, including three-leg 3-wire, capacitor midpoint four-wire and four-pole fur-wire topology, are established. Using decomposition of current, the relation between the voltage ripple of dc side capacitor and the characteristic of compensating current are revealed. Moreover, the optimization of dc side capacitance can be done by virtue of the above relation.Main circuit design is one of the core tache in the systematic design. The operation of capacitor midpoint four-wire shunt active filter adopting hysteresis control is studied and analyzed to reveal the relation of main parameters of APF. The main parameters of APF are associated with and are conditional upon each other. Through vector model in 2-phase α-β reference frame and vector graphical aid design method, the critical value of dc bus voltage will be derived. Besides, the selection of ac side inductor is also been discussed.Real-time and accurate harmonic detection and control is the key for practical active filter implementation. An improved design scheme based on fundamental component extraction using DSP is presented in this paper. Phase-compensation strategy of fundamental component, as well as optimal digital low pass filter based on low sampling rate are introduced into harmonic detection algorithm based on synchronous reference frame for delayless harmonic detection with high accuracy.A shunt active power filter prototype based on DSP has been set up in our lab forexperimental study. The dc side voltage of APF and its balance should be well controlled for its practical use. Both the closed loop of dc side voltage and its balancing loop are modeled and analyzed. An applied soft-startup scheme is also been introduced. To improve the compensating performance for rectifier circuit, whose input current often characterized by high THD, crest value and di/dt, the method of series connecting impedance in the ac side of load is investigated. This measure is more simple and practical than hybrid solutions.Through the research and experimental results, it can be verified that the key techniques for APF described in this paper, including control strategy, main circuit design, harmonic detection and application solutions, etc, is viable and effective.