Three-phase Four-wire Shunt Active Power Filter

With the further development of the industrialisation and electrification, a large number of nonlinear loads are widespread used in the power system。These loads play an important role in saving energy, raising production efficiency, improving people’s life, but at the same time the loads have nonlinear and diversity features, that makes a lot of harmonics and the reactive currents injecting into the electric network,and the problems of the power quality and electronic equipment’s reliability generated by reactive power and harmonics are becoming more and more serious. In order to improve the power quality, various harmonic suppression and reactive compensation methods are used in the field.Active power filter (APF) is paid more attention for it’s special virtue in the harmonic compensation.Three-phase three-wire active power filter has reached the practical stage, Though the prototype machines of three-phase four-wire APF have been developed, there is still not much industrial examples applied is presented.In this dissertation, we focus on the application study of the instantaneous power theory in three-phase four-wire APF.and the design of three-phase four-wire APF, The application characteristics of instantaneous power theory in three-phase three-wire and four-wire systems is analyzed and contrasted. On this basis, instantaneous power theory can be extended from three-phase three-wire to three-phase four-wire system; with the coordinate transformation the fourier decomposition and the symmetry component method, the power components of load of three-phase four-wire system are analyzed in details. In response to that, the influence to d-q method is discussed when the grid voltage is distorted and imbalance. In order to keep the power balance of compensation device, the transformation matrices of positive、negative components in α-β quadrature coordinate is deduced, with the symmetry component method. The synchronous revolution coordinate system is calculated by the positive、negative components. Then the separation of base positive active and base negative active components in load currents is realized and base negative active component in instruction current can be pre-eliminated with the park transform. That makes compensation power in the range of DC bus voltage regulator. At last the analysis and improved method is verified correct by the simulation and experiment results.Based on the above analysis, the design of three-phase four-wire APF is described in details. A small-capacity prototype is trial-produced. The selection of the topology and the main parameters of main circuit, working principles and circuit structure of the functional modules in the control system, Module programming thought and Program Structure of software control systems, The digital realization of APF instruction current signal are described in details. The prototype is debugged and tested in laboratory, and achieved the expected effect.