Study On Distribution Transformer Reactive-harmonic Tap Injecting Compensation Model And Its Control Method

With the rapid development of national economy, power load keeps increasing. The use of reactive power load and nonlinear power load has brought serious problems to the utility grid, including insufficient reactive power compensation capacity and harmonic pollution. When facing complicated power quality problems, single compensation device has limited effect. Combining compensation device with transformer to achieve a better effect is one of the research and developing trends of power quality improvement. Distribution transformer integrated with static synchronous compensator(DT-STATCOM) is a new solutions to power quality problems. DT-STATCOM injects compensation currents through winding taps. It has the advantage of flexible connection point selection.First, from the point of filed and circuit, this paper builds circuit model and finite element model of tap injecting compensation of DT-STATCOM. Using the magnetomotive force balance principle, equivalent T circuit model is derived. Comparision of the equivalent circuit calculation and simulation results verifies its correctness. Ansoft Maxwell is used to build finite element model of transformer tap compensation, field-circuit coupling method is adopted to carry out the simulation. Feasibility and effectiveness of reactive power compensation, harmonic compensation and reactive-harmonic comprehensive compensation are verified.Secondly, reactive and harmonic compensation control method of DT-STATCOM is studied. Due to the use of power electronic load such as rectifiers and inverters, characteristic harmonic waves are relatively common in power grid. If too many harmonic waves are needed to be compensated, proportional resonant(PR) controller should be configured for each harmonic wave, thus control system and computation complexity will also be increased accordingly.This paper proposed double rotating coordinates transformation harmonic compensation control method of DT-STATCOM, without reducing the compensation effect, proportional resonant controller configuration number can be reduced by half. Based on reactive power compensation control, reactive and harmonic comprehensive compensation control method of DT-STATCOM is put forward. Matlab/Simulink software is used to build simulation model to verify its correctness.Finally, model-based-design method is introduced to complete pulse generation mod-ule and embedded target design of DT-STATCOM. Based on analysis of state transitions during carrier phase-shifting modulation, pulse generation module of DT-STATCOM is designed with Matlab/Stateflow toolbox. Embedded target design of reference current calculation module and pulse generation module of DT-STATCOM is completed with Matlab/RealTimeWorkshop(RTW), generating object code for TMS320F28335. Correctness of the generated code is verified through hardware experiments.