Research On Key Techniques Of Dual-module Parallel-connected SAPF

Large-capacity shunt active power filter(SAPF) is the main means to solve the increasingly prominent harmonic issue in current power grid. Traditional APF equipment with smaller capacity is difficult to meet large-capacity industrial field applications. Based on dual-module parallel-connected ideas, this dissertation presented a three-phase three-wire526kVA/380V SAPF and discussed its key technological issues.Firstly, this thesis outlined the reasons for harmonic generation, its hazards and the ways to deal with it. Then it introduced the principle and main circuit topologies of shunt active power filter. Due to limitations of semiconductor devices including power capacity, switching frequency, thermal design, and cost, double SAPF modules in parallel connection topology was adopted in the paper to achieve large capacity goals in a single SAPF equipment. After analyzing and comparing main circuit topologies of currently used dual module SAPF, two-module double-loop with independent DC-link capacitor topology was chosen as the main circuit structure of this equipment.Secondly, in order to meet the special requirements of large capacity SAPF equipment’s main power circuit, the design principles of LCL filter and power unit which was based on the concept of power electronics building block (PEBB) were studied. A filter inductor design method which was based on accurate change rate of load current was proposed. Static and dynamic current sharing between parallel-connected IGBT modules was also discussed and experimentally verified in the paper. Since IGBT turn-off voltage spike and the corresponding EMI problem were severe in large-capacity SAPF, a laminated busbar was designed and its spike suppression performance was demonstrated in the thesis.Thirdly, based on the mathematical model of SAPF, current loop control strategy with high compensation accuracy was proposed. Analysis and simulation verified that simple proportional-integral (PI) control could not realize high precision goals. Repetitive controller was introduced into the current control loop so as to track harmonic reference signals. However, the inherent delay characteristics of repetitive control limit the dynamic response speed of the system. In order to obtain both excellent dynamic performance and accurate compensation precision, a double loop control strategy composed by a PI inner loop and repetitive outer loop was put forward. Simulation and experimental results demonstrated its performance.Finally, DC voltage regulation scheme and DC side soft-start strategy were studied as well.