The Voltage Balance Strategy Of Single-phase Cascaded Rectifier Based On SVPWM Modulation

With the development of high-speed railway,the weight reduction of high-speed train has became an important developing trend.Power electronic traction transformer(PETT)has been receiving increased attention due to its advantages on weight and volume.The cascaded rectifier is employed in the front end of PETT,its stable operation plays a vital role in the normal operation of PETT.First of all,the topology of single phase cascaded rectifier,along with its working principle and mathematical model have been analyzed.After a detailed study of the transient direct current control strategy,the overall control strategy of single-phase cascaded rectifier has been designed.A PI-based voltage balance control strategy and its capability limitations have been discussed,referring to the voltage imbalance problem between the cascaded modules.The validity of the transient direct current control strategy and the PI-based voltage balance control strategy have been verified by simulation and experiment.In order to achieve a faster and broader voltage balance control,the causes of voltage imbalance problem has been analyzed.It has been realized that the redundant voltage vectors have significant influence on the voltage balance control.Considering the abundant voltage vectors in one-dimention SVPWM modulation,which could be taken good advantage of in process of voltage balance control,the combanition method of voltage balancing control and the one-dimention SVPWM modulation has been discussed.Furthermore,a voltage balance control algorithm based on one-dimension SVPWM modulation has been proposed.The proposed method is able to balance the dc-link voltages by making full use of all the redundant voltage vectors.The proposed method pre-calculates the optimal voltage vector for voltage balance control according to the realtime voltage and current parameters of the single phase cascaded rectifier.As a result,the computational complexity has been greatly decreased,and the transient performance has been improved.At the same time,a voltage level switching principle has been set up to avoid voltage step jump on the input terminal of each cascaded module.Through MATLAB/Simulink,the validity of the proposed method has been verified,and its ultimate voltage balancing capacity has been explored.Last but not least,the topology of single phase cascaded rectifier,along with its working principle and mathematical model have been verified by experiment.The program of the voltage balancing algorithm based on one-dimension SVPWM modulation has been designed on FPGA control chip.The proposed control strategy has been verified on a low power single-phase cascaded rectifier experimental platform.On this basis,the ultimate voltage balancing capacity of the proposed control strategy has been verified by experiment.