Digital Control And Implementation Of High Frequency AC/DC/AC Converter For UPS System

With the vigorous development of new energy vehicles by the country,the onboard uninterruptible power supply(UPS),as a key power supply device for internal equipment in automobiles,has been widely studied and used.As the core module of on-board UPS,the AC/DC/AC converter has important research significance and value.The AC/DC/AC converter in traditional UPS usually has low power factor,large volume and weight,and low power density,making it difficult to apply to the automotive industry.Therefore,this thesis studies and designs a high power factor,high-frequency,and small lightweight digital control AC/DC/AC power converter for on-board UPS.The main research content is summarized as follows:In response to the design requirements of small and lightweight on-board UPS,this thesis has designed and selected from three aspects: topology structure,switching frequency,power switching devices,and energy storage components.In terms of topology,the AC/DC/AC system designed in this thesis adopts a Double Boost rectifier topology without a diode rectifier bridge in the front stage,and a T-type three-level half bridge inverter topology in the rear stage.This topology scheme has the characteristics of fewer rectifier diodes,fewer power switches,smaller filter volume,and higher power density.In terms of switching frequency,this thesis adopts a high switching frequency scheme to reduce the inductance and capacitance values of energy storage components in the system.In terms of power switching devices and energy storage components,in order to achieve high frequency and reduce the significant losses and electromagnetic interference caused by high-frequency conversion,this thesis adopts a new Cool MOS power device with faster switching speed,lower switching losses,and better electromagnetic interference resistance.At a high switching frequency of 120 k Hz,parameter calculations and device selection were conducted on the inductance,capacitance,and LC filter of the system’s front-end rectifier circuit and back-end inverter circuit.For the high-frequency AC/DC/AC system mentioned above,this thesis has carried out digital controller design,mainly including system modeling,controller and modulation strategy design.In terms of system modeling,this thesis uses the small signal perturbation analysis method to derive the transfer function of the system.In terms of controller and modulation strategy design,in order to achieve a higher power factor in the system,this thesis designs a dual closed-loop controller based on the average current method and PI at a high switching frequency of 120 k Hz,which basically achieves unit power factor correction of the system.In order to improve the steady-state accuracy of the system output voltage and its ability to resist load disturbances,this thesis adopts quasi proportional resonance control and load disturbance current feedforward control based on the three-level sine pulse width modulation strategy,achieving high-quality inverter output voltage with constant voltage and frequency.The simulation results show that at a high switching frequency of 120 k Hz,the power factor of the system is about 0.995,and the total harmonic distortion of the inverter output voltage under linear load is about0.19%.The dynamic characteristics are good and basically meet the design specifications.Finally,this thesis constructs a high-frequency AC/DC/AC digital control experimental prototype with Cool MOS as the core power device and TMS320F28035 as the main control chip through the selection of digital signal processors and semiconductor devices,as well as the design of peripheral hardware circuits.This achieves the design requirements of high power factor,high frequency,and small lightweight of the system.