Design And Simulation Study On PWM Converter Of Active Power Filter

PWM converter is becoming a hot research topic in the field of power electronics because of its wide range of applications. In the dissertation, the active power filter is selected as object of study, its main circuit structure is based on single-phase PWM converter, the three-phase three-wire PWM converter and the three-phase four-wire PWM converter separately. The relationships among the parameters in the main circuit are analyzed and two calculation methods of the parameters are given. The calculation of parameters mainly refers to determine the values of circuit parameters, including filter inductance at the AC side, the storage capacitance and voltage at the DC side, the rated voltage and current of the switching devices and so on. Grid side harmonics are filtered by inductance, voltage at the DC side is stabilized by capacitance, and the more important is that these two parameters affect the dynamic response of the entire system.Firstly, the dissertation analyzes the relationship between load current and compensation current of the single-phase shunt active power filter system in which the single-phase voltage source PWM converter acts as the main circuit, and then the rated current of the switching devices is determined; and the rated voltage of the switching devices is decided according to the maximum value of voltage at the DC side. On this basis, the appropriate switching devices are selected under considering switching frequency. The value of capacitance is calculated according to two indexes, which are the largest storage energy and voltage fluctuation ratio at the DC side. Considering from the different point of views, the mathematical model of inductance parameter calculation is established. Based on the analysis above, two methods of parameter calculation are proposed, and the high-pass power filter is introduced to eliminate higher harmonics of several times time switch frequency which are generated in the process of turning on and off the switching device.Secondly, the dissertation investigates the relationships among the currents of the three-phase three-wire active filter in which three-phase three-bridge arm voltage source PWM converter acts as the main circuit, laying the groundwork for determining the rated value of the switching device. The parameter design idea of the DC side energy storage component in the single-phase PWM converter is applied into three-phase three-wire system, and the values of the voltage and capacitance at the DC side are determined. The three-phase three-wire active filter is transformed equivalently into three single-phase branches separately, considering the three branches as the research object to determine each parameter.Thirdly, the mathematical model of quadrupole active power filter under the three-phase four-wire system with three-phase four-bridge arm voltage source PWM converter as the main circuit is established, the decoupling of the fourth leg is realized under the stationary αβ0coordinate system, that is to say the arm inductance values of the first three bridge and the fourth bridge are calculated separately. The design methods in the three-phase three-wire system are still applied in the design of other parameters.Finally, a visual parameter design interface convenient for user handling is set up based on the analysis and design above, and simulation models for single-phase and three-phase three-wire active power filter are built, the correction of parameter design ideas and feasibility of further application are verified with the combination of the theoretical analysis and simulation experiment.