Research And Design On Shunt Active Power Filters With Double Parallel Connection

With the development of power electronics technology, non-linear loads, are in large-scale use. While at the same time, massive harmonic components generated by the non-linear loads are leading to distortion of the grid voltage and current and have threatened power quality and power utilization safety seriously. Therefore, harmonic suppression has become one of the most important methods to improve power quality and ensure the reliable operation of electrical equipment. Active power filters (APF) as a new type of electrical equipment in order to suppress harmonics and compensate reactive power, are able to track harmonic components dynamically and compensate them together with the reactive power. Compared with the traditional passive power filter, the APF has the characteristics of adaptive compensation, continuous control, no sensibility for the grid frequency and less causing of resonance.At present, the shunt APF accomplishes both harmonic suppression and reactive power compensation only through one set of inverter circuit. It’ll result that the state of inverter switching changes frequently. On one hand, the switching endurance will decrease and more losses will be generated. On the other hand, the control difficulty of the filter will be increased greatly. To solve the above problems, the thesis designs the shunt APF with double parallel connection, whose characteristics lies in the design of principal and subordinate inverter circuits. The principal one is used for harmonic suppression of the grid separately, equivalent to the high frequency filter; while the subordinate one is used for reactive power compensation of the grid separately, equivalent to the low frequency filter. The main works of the thesis are shown as follow:(1) A method for harmonics detection based on the adaptive FIR (finite impulse response) digital low pass filter (LPF) is proposed to solve the weakness of big crinkle, poor precision, slow response in the traditional ip-iq method based on the instantaneous reactive power theory, which can improve the dynamic characteristics and static characteristics as well as the respond speed and control precision of the system.(2) For three-phase three-wire grid and three-phase four-wire grid, the mathematical models of the inverter circuits in the filter are set up respectively. The thesis also discusses the control strategy for both two-level inverter based on space vector PWM and the dc-link voltage based on fuzzy PI instantaneous conservation of energy. The general system design for the shunt APF with double parallel connection and relevant hardware circuits based on DSP controller are proposed in the thesis.(3) Topology of the inverter circuits based on the soft switching technology of ZVS-PWM (Zero Voltage Switching-Pulse Width Modulation) is proposed in the thesis to solve the problems of great switching losses and strong additional switching noise in the APF which uses hard switching technology when the switching frequency is high. The topology is put into the principle inverter circuit. Simulated and experimental results verify the effect of research.