Research On Power Decoupling Control Algorithm Of Single-phase Cascaded H-Bridge Converter Based On DC Split Capacitance

Cascaded H-bridge converters are widely used in the field of distributed renewable energy or energy storage because of their advantages such as high modularity,low output harmonics and easy expansion of level number.In this thesis,we propose an optimal control method for split-capacitor-based independent and switch-multiplexed decoupling topologies to achieve effective suppression of dc-side secondary voltage ripple in single-phase cascaded H-bridge rectifiers with the problem of secondary voltage ripple.The method improves the robustness and reliability of the converter and lays a theoretical foundation for the promotion of its active power decoupling technology for practical application in photovoltaic power generation and energy storage unit systems,which has important research significance and application value.Firstly,the circuit topology and working principle of single-phase CHBR are analyzed,and the mathematical model is established.The unipolar frequency-doubled carrier phase-shift modulation algorithm is analyzed,and the dual closed-loop control based on voltage and current as well as the DC-side capacitor voltage equalization control strategy is designed.The simulation results show that the control can output stable DC voltage,realize unit power factor operation and DC-side capacitor voltage equalization,but there is a problem of DC voltage difrequency fluctuation.Secondly,for the problem that the conventional control has the fundamental frequency voltage fluctuation on the dc side when the split capacitor is not matched,this thesis proposes a new control method based on the constructed secondary voltage.The generation mechanism of single-phase CHBR dc bus difrequency voltage ripple is analyzed,the independent type dc split-capacitor decoupling topology is given,and the conventional control method based on the constructed fundamental frequency voltage is designed.Based on different decoupling principles,three implementation methods based on the constructed secondary voltage control are proposed for the optimized control of mismatch coefficient and DC bias coefficient.Simulation and experimental results show that the proposed control method effectively compensates the secondary pulsating power on the AC side compared with the conventional control,and avoids the problem of DC bus fundamental frequency voltage fluctuation derived from the capacitor mismatch,while improving the response speed.Finally,considering that the independent power decoupling topology requires additional switching devices,this thesis investigates the CHBR DC voltage ripple suppression method based on the switching multiplexed decoupling topology.The DC bus voltage demand and modulation demand are analyzed,and the system-related parameters are specified.For the problem that the conventional control based on the constructed fundamental frequency voltage will derive the fundamental frequency voltage fluctuation when the capacitance is not matched,an optimal control method is proposed to introduce an integral link on the decoupled controller to realize the feedback control of the dc bias.The proposed control method can not only effectively suppress the secondary voltage ripple on the DC side,but also compensate the fundamental frequency pulsation power derived from the capacitor mismatch,and still have good dynamic performance and robustness when the capacitor capacitance drifts through the simulation experiment.There are 58 figures,7 tables and 75 references in this thesis.