Study On Problems Of Time Delay And Switching Loss Of Active Power Filter

With the increasing seriousness of harmonic pollution in power system, the impact on power quality is greater and greater, which not only causes great economic losses, but also gradually affects people’s daily life, so how to effectively suppress harmonic has important significance. As the most direct and effective means of harmonic suppression, active power filter (APF) has become a research focus in many countries. The performance of APF directly determines whether it can effectively suppress harmonic, and its own system delay and switching loss problems are the main factors affecting its performance, so the problems of time delay and switching loss of APF is mainly studied, and then puts forward ways to solve these problems.The most widely used three-phase three-wire shunt voltage APF is mainly researched, and its working principle is analyed through the study of its topology, which provides a theoretical basis for the analysis of system delay and switching loss. Aiming at the system delay problem, the reason of delay is firstly analyzed, and then analyzes its effects on the performance of the system through the mathematical model. Because the prediction algorithm can effectively solve the system delay problem in signal processing, a prediction link is introduced to the instantaneous reactive power theory as the system’s harmonic current detecting method, and then makes a detail analysis and introduction to it. Due to the traditional fixed step adaptive prediction algorithm is unable to achieve fast convergence and high steady accuracy at the same tine, a variable step size adaptive prediction algorithm is put forward. This algorithm uses the total weighted error and dynamic factor to regulate the step size, which successfully solves the contradiction of the fixed step algorithm. And its effectiveness is finally verified by simulation results.Aiming at the switching loss problem, the reason of switching loss is firstly analyzed through the mathematical model, concluding that switching loss is directly affected by the switching frequency and on-state current, and puts forward a discontinuous PWM control strategy according to these two factors. This control strategy further decreases the switching frequency on the basis of space vector pulse width modulation method, and reduces the average on-state current of switch, so it decreases switching loss in the largest extent. And the feasibility and effectiveness of this method is finally verified through simulation results.At last, the experiment platform of APF system is set up, and finishes the software and hardware design, then verifies the effectiveness of the experimental prototype through experiments. The experimental results show that this prototype can effectively suppress harmonic, achieve the function designed, and satisfy the expected requirement.