Research On Active Power Decoupling Control Based On New VSI-VB&PDC Topology

Single phase inverter is widely used in the grid connected system of distributed power supply with power level less than 10 k W,such as distributed photovoltaic power generation,energy storage unit,fuel cell and other grid connected systems.However,the single-phase inverter system has the inherent problem of double power frequency fluctuation.The traditional method to solve this problem is to connect large capacity electrolytic capacitors in parallel on the DC side,but the life of electrolytic capacitors is shorter than other components of the system,thus reducing the overall life of the system and increasing the cost of system maintenance.Therefore,the active power decoupling technology which does not depend on the electrolytic capacitor is the research hotspot to solve this problem.Based on the new voltage source inverter with voltage boosting and power decoupling capabilities(VSI-VB&PDC)proposed by the research group,this paper focuses on the active power decoupling control strategy which is not affected by system parameters.The main research contents and innovations are as follows:1.Based on the power decoupling mechanism of single-phase VSI-VB&PDC topology,the small signal model of the system is established and the transfer function of the system is derived.The root locus method is used to analyze the influence of circuit parameter changes on system stability,which lays a foundation for the design of the controller.2.Two indirect power decoupling control strategies are proposed,which are indirect power decoupling control strategy based on decoupling capacitor voltage closed-loop and indirect decoupling control strategy based on decoupling capacitor current feedforward.According to the principle of instantaneous power balance,the two control strategies calculate the power of decoupling capacitor and derive the instantaneous expression of capacitor voltage and capacitor current respectively.By building PSIM11 simulation models,it is verified that the above two indirect power decoupling control strategies can greatly reduce the low-frequency ripple current on the DC side,and the stability of the two control systems are analyzed using Bode diagrams.The analysis results show that,compared with the capacitor voltage closed-loop control strategy,the capacitor current feedforward control strategy is more robust to the decoupling capacitor parameter changes.3.The two indirect power decoupling control strategies above can not eliminate theinstantaneous power consumed by the resistance in the circuit.In order to further improve the decoupling accuracy and enhance the robustness of the control to the circuit parameter drift,the DC side current ripple direct closed-loop decoupling control strategy is further proposed.The simulation results of PSIM11 show that the influence of parameter change can be greatly reduced by direct closed-loop control of DC side current ripple,and the stability of control system is analyzed by Bode diagram.4.In order to further verify the proposed control algorithms,RTLAB is used to build the hardware in the loop simulation system,and DSP control program is written.At the same time,the physical hardware platform is built.It is verified that the new single-phase VSI-VB&PDC topology can realize the function of voltage-boosting and power decoupling under the open-loop decoupling control strategy,and the closed-loop control experiments will be completed after returning to school.