Study On Single-phase Three-level Active Power Filter

As harmonic interference problems generated by bulk thyristor converters become increasingly serious as they are widely used in industrial applications and transmission/ distribution systems, compensation for harmonic and reactive currents becomes important. Traditionally, passive LC filters have been used to eliminate line current harmonics and to increase the power factor. However, in practical applications these passive filters present many disadvantages, such as aging and tuning problems, series and parallel resonances and others. In order to overcome these problems, many compensated methods based on the technique of power electronics have been researched and developed recently, one of them is active power filter, which have gradually been recognized as a feasible solution to the problems created by nonlinear loads.Most previously proposed APF are based on two-level converters and thus are suitable for low voltage use. However, in a high voltage system, APF based on two-level converters cannot meet the need of high voltage and high power. In last years, people made great effort on the research of multilevel and it is proved that multilevel converters are a representative and perfect resolvent. Multilevel converters have been hot points in power clectronics, especially in the research of high voltage and high power. In this paper, the circuit topology and control strategy of multilevel converters previously reported are analysed and compared with each other, and their merits, defects and applications are presented respectively. Further, diode-clamped three-level converter is used to main circuit of APF.One-cycle control method is a nonlinear control method. By controlling the switch duty-ratio, it can make the average value of a switched variable equal to or proportional to the control reference in each cycle, so the stationary and transient errors are eliminated. One-cycle control response fast, it can reject power perturbations and the control circuit is simple and reliable. In this paper, the applications of one-cycle control in active power filter are introduced, and many improved methods are discussed.A three-level single-phase APF based on One-cycle control is presented. Based on the analysis of equivalent average modes in switching period, the key control equations are derived and circuit models are created, the five operation modes of the main circuit and working principle of one cycle controller are analyzed in detail. Simulation is...