Research On Single-phase PWM Rectifier Based On DC-Split-Capacitor Roboust Power Decoupling

At present,single-phase PWM rectifier is widely used in PV grid-connected,electric vehicles,energy storage and electric locomotive traction system and other fields due to its advantages of realizing unit power factor and working in rectifier and inverter state.However,there are secondary ripple power flowing between the AC side and the DC side of single-phase PWM rectifier due to its topological characteristics,reduces power quality,shortens the service life of the device,and affects the stable operation of the system.The traditional solution is to use large capacity electrolytic capacitors for power decoupling,but the power density of rectifier is reduced,and the life of rectifier is limited because of the short life of electrolytic capacitors.In order to solve the above problems,more and more attention has been paid to the active power decoupling technology with additional switching devices on the DC side.Based on the mathematical model of single-phase PWM rectifier,this paper analyzes the mechanism and harm of secondary ripple on DC bus voltage,and studies a power decoupling topology based on DC-split-capacitor.In this topology,a symmetrical half-bridge circuit is added to the DC side of the single-phase PWM rectifier to transfer all the secondary ripple power to the symmetrical half-bridge circuit,so as to maintain DC side voltage constant.However,under the ideal condition that the capacitance of the split capacitor is completely equal,the current studies on the circuit topology do not consider the capacitance drift caused by environmental factors such as temperature,humidity and time effect,resulting in a deviation between the capacitance of two capacitors.This paper studies the working principle and control strategy of the circuit topology,and the analysis shows that the capacitance deviation will produce the first power component which cannot be offset by the power decoupling circuit,and the simulation verifies the effect on the power decoupling performance.In order to solve the problem that power decoupling circuit is affected by capacitance deviation,a control strategy based on DC-split-capacitor robust power decoupling is studied in this paper,superior power decoupling effect can be achieved regardless of whether the capacitance is equal or not.A phase-locked loop based on frequency-fixed second order generalized integrator for system phase-locking is analysised to achieve accurate phase-locking.The parameters of the single-phase PWM rectifier system are designed,and the circuit topology is simulated in Matlab/Simulink to verify the effectiveness of the power decoupling control strategy.According to this,the software and hardware of the single-phase PWM rectifier system are designed in this paper,part of hardware has mainly completed design of the main circuit,drive protection circuit,sampling circuit and controller,part of software has completed the digital control system design.On this basis,a single-phase PWM rectifier prototype with rated power of 2k W based on DC-split-capacitor robust power decoupling is builted.The experimental results have verified the feasibility of the control strategy.The capacitance value of the DC side is significantly reduced,well power decoupling effect which is not affected by the capacitance deviation,which obviously improves the robustness of power decoupling in the actual operation of the system,and at the same time reduces the cost and volume of the system.