Research Of Three-level Shunt Active Power Filter Based On DSP

The wide use of power electronic equipments makes harmonic problem serious increasingly in power system and harmonic becomes the primary factor influencing power quality. Active power filter has become a key project in power effective method to solve harmonic problem and improve power quality. Active power filter has many advantages, such as fast response, high compensation accuracy, small size and high intelligence, so has been put into practical application in foreign countries. But the research and development on active power filter is still in the laboratory in our country. This project is to design a low-voltage shunt active power filter in collaboration with BIA science and technology.Firstly, the basic principle and main circuit’s diode clamp three-level inverter topologies of active power filter are introduced in this paper. Using multilevel technology, the voltage stress on switches will be reduced, the shape of output waveform will be improved and the rate of voltage and power can be increased too. Multilevel technologies become a trendency in application of active power filter.Methods of harmonic current detection and current tracking control are the keys which ensure good compensation performance of the active power filter. This thesis describes two detection algorithms:detection algorithms based on sliding-window iterative DFT and the d-q detection algorithm based on the instantaneous reactive theory. Both methods have advantages and disadvantages, should be adapted to different applications and compensation requirements. This thesis analyzes the current control strategy, a new dead-beat current based on the predicated cycle is proposed. This control method could achieve accurate current tracking, combined with the SVPWM algorithm. This thesis focuses on dead-beat control algorithm based on cycle prediction and the SVPWM algorithm based on60°coordinate system.The design of the main circuit is one of the keys that direct impact on the actual compensation effect of active power filter. Thorough research has been carried out for the main circuit of the three-level shunt active power filter. The design of inverter circuit, buffer circuits, high frequency filter circuits, charging circuit and EMI filter circuit are discussed detailedly. The selected methods of DC bus voltage value, DC bus capacitance and AC side filtering inductance value are given, using the method of integration of theoretical analysis with simulated experiment based on the mathematical model of main circuit.In this thesis, the design of the control system of the active power filter is also discussed. The realization scheme of full digital control system based on TMS320F28335DSP has been discussed, and the hardware circuit and software design of control system have been studied. Hardware circuits include power module circuit, signal detection and conditioning circuits, hardware protection circuits, IGBT drive circuit and the RS485communication circuit. Software designs include the main program and interrupt programs.The system MATLAB simulation model according to the detection methods and control strategies proposed in this paper is given. The validity and feasibility of the analysis in this thesis are validated by simulation. The simulation model also lays a foundation for subsequent system design of this active power fliter.