Research On Back-to-back Two-stage Type Medium Frequency Power Supply Control Technology Based On SiC MOSFET

Medium frequency power supply is a kind of special power supply,which are extensively applied in power supply systems of aerospace,ships,locomotives,etc.More and more application fields put forward stringent requirements to medium frequency power supply technical indicators such as waveform quality,dynamic response,reliability,power density,etc.The traditional 400 Hz medium frequency power supply has some serious shortcomings,such as heavy volume,low efficiency,the waveform quality is not high,Injecting harmonic into power grid,etc.By contrast,this paper designed a novel back-to-back type of medium frequency power supply system consisted of three-phase PWM rectifier and three-phase medium frequency inverter.Waveform control technology is the core technology of medium frequency power supply.In view of defect that the traditional double loop control and state feedback control can't achieve full zero pole assignment,this paper studied a kind of discrete control technology which is PI + full order state feedback control technology based on zero pole assignment,and successfully applied to the control of rectifier and inverter.This paper established a mathematical model of continuous domain of three-phase rectifier and traditional double loop control technology is discussed in the continuous domain.Considering that PWM generation process is equivalent to a zero-order holder and that the loaded modulation wave work only next cycle in digital control which means a cycle delay,accurate mathematical models of zero-order holder and one cycle delay can be established with no any approximation in discrete domain.This paper established the controlled object model of rectifier current loop in discrete domain,and designed the PI + full order state feedback control of the current loop,using zero pole assignment method to set up a direct quantitative relations between the desired performance index and PI parameters and state feedback parameters.In order to speed up the dynamic response of the rectifier voltage loop,this paper studied the influence of the load current feedforward.The mathematical model of three-phase inverter is established in continuous domain and in discrete domain.Through analysis this paper reveals the essential reason that inverter output voltage feedforward can improve the inverter current loop dynamic characteristics,and design a PI + full order state feedback control of the inverter voltage loop.In this paper,the research content above is verified by theoretical analysis,simulation and experiment,the experiment results show that this control method has excellent control performance.Hardware design is a guarantee and foundation of which a prototype can operate efficiently and reliably.In view of the research content a high performance experimental prototype is designed.In this paper,the parameters of the main circuit components are designed in detail,and the general design method is presented.The latest SiC MOSFET is selected,and the MOSFET switch loss calculation and analysis in detail is presented.The results show that the SiC device does have lower switching loss relative to the traditional Si device.Using SiC MOSFET plays a vital role to improve the switching frequency of the medium frequency power supply system.