Research On The Switch Control Strategy Of Three-phase Active Power Filter

With the rapid development of power electronic technologies and power electronicdevices, a large number of non-linear loads are connected to the grid. As a result, a largeamount of harmonic injected by these loads leads to serious power quality problems. As thesize of the grid expands gradually and the requirements of users for power quality continue toincrease, the issues about suppressing harmonic and improving the quality of power isattracting increasingly widespread attention. APF(active power filter) is different from thepassive filtering and other traditional filtering methods. APF is capable of real-time dynamiccompensation and carrying out good harmonic suppression.This thesis studies on the parallel active power filter, which injects the compensationcurrent into the grid to suppress the harmonic. The compensation current is calculated bycorresponding detection method and control strategy.The synchronous detection method without PLL(Phase Locked Loop) is used in thedetection of harmonic current. This method can detect harmonic current accurately when thegrid voltage is distorted. The correctness and feasibility of the synchronous detection methodare verified by the result of simulation. Then the traditional hysteris control method is studied.Burr is found in the tracking wave form produced by simulation, which means the current isout of control partly. Then the system controlled by the hysteresis method is analyzed byvector to find out the reason. As the phase current in the system is associated with each other,the control method aims at controlling the state of single bridge can not guarantee the phasecurrent change along with the desired value. Finally, the dead-beat control strategy based onthe minimum integrated error is analyzed. The prediction mechanism and calculation processis analyzed and verified by simulation.The traditional PI control method is widely used to control the voltage on the DC side,but it needs complex calculation for parameters to achieve better control performance. Thus,the control method based on the balance of active power is applied in the system. This methodis easy to implement and the correctness and feasibility of it is verified by simulation.