Research On Control Strategies Of Single-Phase DC Side Series Active Power Filter

With the widely application of the power electronic devices, a great amount of harmonic currents is produced in power system, which causes hazard to power system and other electric power equipment. The single-phase rectifier bridge and three-phase rectifier bridge are main harmonic sources, the dc side series active power filter can eliminates this kind of harmonic. When average current control method is applied to the single-phase dc side series active power filter, the input current distortion is serious during low frequency switch turns on or turns off transient. The dissertation analyzes essential causes of this current distortion, and makes research on control strategies to solve this current distortion.Firstly, the dissertation analyzes essential causes of this current distortion when average current control method is applied to single-phase dc side series APF. One of the reasons is that the expected duty-ratio of the high frequency switch needs jumping change during low frequency switch turns on or turns off transient, while the duty-ratio of the high frequency switch can't jumping change, because the output value of PI controller can't jump. Another reason is that the rising slope(downward slope) of inductor current approach zero when the low frequency switch just turns off(turns on), so the inductor current can't follows reference current. The inductor value and switch frequency are relate to current distortion, hereby, the measures are proposed to solve current distortion.Then nonlinear average current control method is applied to the single-phase dc side series APF, this method can solve current distortion during low frequency switch turns on or turns off transient. The dissertation investigates stability characteristics of nonlinear average current control method, points out the system unstable around the zero crossing of the input voltage, and improves the stability of this method.A improved linear average current control method is proposed in the dissertation. this method controls the output logic level of comparator, so it can make the duty-ratio of the high frequency switch jump during low frequency switch turns on or turns off transient to solve current distortion.Finally, the detailed design process of improved linear average current control single-phase dc side series APF experimental prototype, including design of main circuit and control circuit, is given in this dissertation. The average current control method can be applied to experimental prototype. The experiment results verify that the improved linear average current control can eliminate input current distortion.