Research On The Combined Multi-level Active Power Filter Key Technology

APF has some problems in the grid harmonic compensation, for example, its detecting method is difficult to achieve; the system has low level of compensatable voltage. In order to solve these existing problems, this paper carries out a thorough study in the harmonic detection algorithm and the APF system topology.This paper focus on the advantages and disadvantages of the two-level and multi-level topology in APF, and proposes a combined multi-level inverter structure by combining them together. This Paper studies the principles of multi-level control, and select the carrier phase shifting SPWM as the basic control methods of the new multi-level topology. It analyzes the control characteristics of the carrier phase shifting SPWM technology exerts to the new topology and establishes a new mathematical model of the topology output voltage. It studies the common harmonic detection algorithm, then proposes a new harmonic detection algorithm which is based on trigonometric orthogonal basis. The new algorithm does not need a digital low-pass filter and phase-locked loop circuit, and if of high precision in the non-phase-locked loop, and has high real-time and demands small amount of computation. It studies the control methods of the DC side capacitor voltage during multi-level inverter's application in the APF, and according to the proposed multi-level inverter topology, it proposes a dual-voltage ring core DC capacitor voltage balancing control strategy. Finally according to mentor projects, I make a systemstic design of the combined multi-level type APF.Simulation results show that the proposed harmonic detection algorithm, multi-level inverter topology and control algorithm can be applied to power system harmonic compensation, which is very progressive.