Study On Novel Hybrid Active Power Filter

During recent 30 years, study on Active power filter (APF) has plentiful achievements, however, it has not been broadly applied yet, especially for high power nonlinear loads, which are normally the most important harmonic source.The research for APF with high ratio between the raings of load and inverter is especially meaningful. Compared with such power electronic equipments as SGSand voltage conditioner with thyristors, the cost of APF, which combines with modern power semiconductor switches (mainly IGBT) and advanced control scheme, is extremely high. The following problem of APF with high capacity exists: efficiency of the inverter with high switching frequency can hardly be increased to exceed 95%; the present power level of fast and self-turnoff switches, such as IGBT and so on, can not match the capacity of the nonlinear loads; reliability of high capacity power electronic equipment requires to be verified. In a word, considering the present status of power electronic technology, active power capacity of APF can not reach the requirement of harmonic suppression for power system with high load capacity, furthermore, the pure active power filter is not cost effective.The purpose of this dissertation is specified as follows: the active part of APF is confined to harmonic procession and accordingly, the ratio between the VA ratings of load and inverter of hybrid APF will be greatly improved. Requirement of normal operation for series hybrid APF with fundamental bypass channel, which is one of the topologies with high ratio between the VA ratings of the load and inverter, is specified. When encountered the asymmetrical loads, the problem that fundamental current resonance between the inverter and the fundamental bypass channel occurs by adopting the original control scheme and results in great increase in the capacity of the inverter or destruction of the whole inverter, is verified by both experiment and simulation, and that the purpose of adding the fundamental current bypass circuit can not be achieved.Dedicated to three-phase three-line system and series hybrid APF with fundamental bypass channel, control scheme based on dual d-q transformation is presented in this dissertation. The harmonic suppression validity of the scheme for the very system with nonlinear loads is verified by simulation and experiment. As for the three-phase four-line system, control scheme based on phase identifying principle is presented in this dissertation, accordingly, the validity is verified by simulation. Experiments are implemented by a 5kVA prototype for hree-phase and three-line system, respectively with symmetrical andasymmetrical load. By adopting the control scheme presenting in this dissertation, problem of fundamental current resonance between the inverter and the fundamental current bypass circuit is avoided and the inverter just passes through the harmonic current. Consequently, the VA rating of the active part is greatly decreased.Operation principle and design consideration of the APF with high ratio between the VA ratings of the load and inverter is presented in this dissertation. By adopting the presented control scheme, inverter capacity of APF with fundamental current bypass circuit is greatly decreased, therefore, cost of series hybrid APF is greatly decreased and the new strategy can be adopted for harmonic suppression of larger nonlinear loads, which contributes to further theoretical research, also accelerates development and broad application of high power harmonic suppression equipment.