Research On Control Strategy Of Modular Power Electronic Transformer

With the development of power electronics technology,the performance of static var generator is becoming more and more powerful.High-voltage parallel static var generator with H-bridge cascade as its main circuit topology has been greatly developed because of its advantages in boosting capacity,output harmonic characteristics and easy expansion.At the same time,due to the rapid development of digital signal processor,high-performance floating-point DSP chip has rapidly replaced the traditional one.The traditional floating-point DSP greatly improves the detection and control performance of high-voltage parallel SVG.Therefore,the design of signal detection and control system for high-voltage parallel static var generator based on high-performance floating-point DSP-TMS320F28335 is studied in this paper.Firstly,the research background and significance of this topic are expounded,the development history of reactive power compensation device and the research status of static var generator based on DSP at home and abroad are introduced,then the basic topology structure of the main circuit of the static var generator is analyzed,and the realization method of capacitance and boost of the high voltage parallel static var generator is introduced.The ideal of the high voltage parallel static var generator is also presented.The working principle of high voltage shunt static var generator is analyzed in detail,and the dynamic mathematical model of high voltage shunt static var generator is established.Then the definition of generalized instantaneous reactive power theory in single-phase circuit and the definition of generalized instantaneous reactive power in three-phase three-wire circuit in dqO coordinate system and alpha-beta coordinate system are introduced.On this basis,detection algorithms such as PQ method,ip-iq method and DQ method are studied.The total harmonic current,the sum of harmonic component and fundamental reactive component of the detected current,reactive current and specific sub-harmonic are obtained.Weight.Two control strategies,direct current control and indirect current control,are introduced.A feedforward decoupling control strategy based on SVG output indirect current for high voltage and high power is adopted.The principle of feedforward decoupling control is introduced in detail,and the decoupling control model of SVG is established.Based on the analysis of the causes of unbalanced capacitor voltage on DC side,a voltage equalization method of PI control on DC side is proposed.Then the principle and implementation method of single-stage frequency doubling CPS-SPWM are introduced.Finally,the basic parameters of the main circuit IGBT,series reactor and DC-side capacitor of the experimental principle machine are designed.The hardware circuit design including signal detection,protection,drive and human-computer interaction is given.At the same time,the main program,signal detection,output control,protection and interruption subroutines of the control system are designed and written.The simulation model is built with the help of MATLAB software.A high-voltage parallel SVG experimental principle machine is set up.The validity of the detection and control strategy is verified by simulation and experiment.