The Digital Control On Current Of Parallel Active Power Filter

Being the fast, potent, and economical control means to industrial devices, power electronics, however, have also deteriorated power quality by injecting the non-negligible harmonics and reactive current to the network. Among those technologies in harmonic suppression and reactive compensation, the active power filter (APF) is the most famous one. This thesis, first of all, has introduced the harmonic reference generation of APF and the typical hysteresis control based on the design and realization of the three-phase three-wire parallel APF, and then chosen digital control as its centre content with detailed analysis on PI conditioner and repetitive control.Firstly, this thesis has presented the system structure and operation principles of three-phase three-wire parallel APF. Specified introductions of the instantaneous reactive power theory are given, and a sliding window recursive method as the low pass filter is proposed which is supposed to depart the fundamental current from the load and get the harmonic reference.The influence on the compensation current, caused by the inductance connecting to the network, is given in this thesis after the establishment of mathematic model of APF. Typical hysteresis control on current is introduced and its simulation results have depicted its compensation characteristics, which are followed by two improved methods in brief as to overcome the inner deficiencies of traditional hysteresis control.Taking the digital control as its centre content, this thesis has proposed a PWM control way on current. The control plant with a RC filter placed on the AC side of APF is established. What's more, the thesis has analyzed how PI parameters affect the system of APF and pointed out the limitation of simple PI conditioner in active filtering. In order to achieve better characteristics in the steady state of APF, this thesis has proposed a way of adding the repetitive control technology to the digital current loop. Detailed procedures of designing every block of the repetitive controller are given, and the simulation model of an improved current controller with PI conditioner and repetitive controller working in parallel is presented in this thesis. The simulation results are provided after that. In the end, experiments have been carried out in different conditions which are discussed in this thesis, and their results have proved the effectiveness of this digital control method.