Research On Digital Realization Of DC Side Active Power Filter Based On Coupling Transformer

Harmonics pose a grave threat to power quality and the reliability of grid. As an effective device to suppress harmonics, APF (Active Power Filter) is able to compensate harmonics and reactive power, which may vary in both amplitude and frequency. APF can solve the problems of passive power filters whose performance depend on the system's impedance and can be easily affected by the change of temperature.The rectifier loads become the commonest ones among several harmonic sources. Focusing on the rectifier loads, the DC side series APF which has a strong ability to harness voltage harmonic source had been presented by some researchers. But the traditional DC side series APF doesn't isolate with the grid and the voltage of storage capacitor and switch components will be very high when the line voltage rises. In order to solve these problems the follow work has been done in this paper.After introducing the generation, the harm and the suppression methods of harmonics, the workings of shunt APF and series APF are analyzed, and their compensation characteristics for different harmonic sources have been discussed. It is indicated that traditional DC side series APF doesn't isolate with the grid and the voltage of storage capacitor is higher than that of the line and the output voltage, which not only increases the cost of circuit and the ratings of storage capacitor, but also boosts the voltage of switches and lowers the reliability of the circuit.Focusing on these problems, a new topology of DC side series APF based on coupling transformer is presented. This topology can isolate with the grid and reduce the voltage of switch through a coupling transformer. The theory and energy flow of the proposed topology have been analyzed. Simulation results are also presented for validation proposes.Then, this topology is applied to three-phase system, and the three-phase DC side series APF based on coupling transformer is also proposed. Its working theory is analyzed and the simulation study has been done.Lastly, focusing on the problems of traditional circuit, such as complexity of the control circuit, difficulty of debugging, inconvenience of changing arithmetic and parameters, the digital realization method for DC side series APF has been researched. A 100VA prototype of single-phase DC side series APF based on TMS320F2812 is designed, including the designation of hardware system and software system. the prototype has been debugged successfully in the laboratory. Experimental results verify that the DC side series APF with a coupling transformer based on DSP not only compensate harmonics well caused by rectifier loads, but also lower the voltage of storage capacitor and increase the system's stability and the ability to avoid disturbance.