Research On Model Predictive Power Control Algorithm For Single-phase Cascade H-Bridge Rectifier Without AC-side Voltage Sensors

The traction power density of high-speed trains can be increased by lightweight design.Obtaining higher acceleration and running speed under the same traction power is the development trend of high-speed trains.The traction drive system as the source of power for high-speed trains is the key to achieving light weight.Non-power frequency traction transformer is mainly used to achieve the light weight of the traction drive system,which is named as the technology of power electronic transformer.The cascade H-bridge structure is usually used as the front stage of the power electronic transformer,and the model predictive power control can significantly improve the dynamic and static performance of the controlled object.Therefore,the study of the single-phase cascade H-bridge rectifier model predictive power control has important theoretical significance and engineering value.First,the topology and working principle of single-phase cascaded H-bridge rectifier is analyzed in the article,and the working principle and mathematical model of predictive power control of finite set model is introduced.Secondly,Unbalanced voltage on the DC side of the single-phase cascade H-bridge rectifier is caused by unequal load on the DC side of the sub-modules.Based on the analysis of the causes of unbalanced voltage on the DC-side,in order to achieve balanced voltage on DC-side,the finite control set model predictive control has the problem of too many mathematical calculations and logical judgments and the number of cycles when selecting the appropriate switching state.An improved voltage balancing algorithm is given to reduce complexity of algorithm.In order to achieve fixed frequency control,a model predictive power control algorithm with power error minimization is introduced.A voltage control algorithm based on modulation ratio incremental adjustment is adopted,when the load is extremely unbalanced,the control will can not achieve balance of voltage on the DC side.For this purpose,a improved voltage control algorithm based on the injected voltage compensation component is used to ensure that balance of voltage on the DC side even when the load is extremely unbalanced.Subsequently,based on realizing the balance of voltage,in order to reduce the hardware cost and solve the complicated wiring design problem,grid voltage sensorless is studied and the virtual flux is introduced and the mathematical predictive power control mathematical model based on virtual flux is established.In the process of acquiring virtual flux of the gridside voltage,there are problems of phase shift and amplitude attenuation between virtual flux and the actual flux of the grid-side voltage.And an improved phase-compensated first-order low-pass virtual flux observer is proposed to ensure the accuracy of virtual flux of grid-side voltage.During the startup of the rectifier,in order to ensure that the observed virtual flux of grid-side voltage is consistent with the actual flux,the grid-side current is used to estimate the virtual flux during the uncontrolled phase.Aiming at the problem of starting current shock,the nonlinear function of starting current is added to the evaluation function to obtain a better suppression effect.Finally,in order to verify the effectiveness and correctness of the proposed improved voltage balance algorithm and the improved virtual flux observer based on first-order lowpass with phase compensation,a single-phase cascade seven-level H-bridge rectifier model is builded on the RT-LAB platform in this paper.The control algorithm based on DSP controller is constructed.And a hardware-in-the-loop semi-physical experiment is carried out.The experimental results prove the correctness and effectiveness of the proposed algorithm.