Control Algorithm And Experimental Platform Of Single-Phase Cascaded H-bridge Rectifiers

With the rapid development of China's high-speed railway,the speed up of passenger train is facing many challenges.Lightweight is one of the key technologies for high-speed train to speed up.In order to reduce the traction drive system weight and realize high power density,the use of power electronic transformer(PET)to replace traditional line-frequency transformer is an important research direction.Structure of single-phase cascaded H-bridge rectifiers(CHBR)combined with isolated DC-DC converters is the main research direction of traction drive system with PET.Therefore,it is very significant to analyze and research single-phase CHBRs for engineering application.This paper focuses on the control algorithms of CHBRs and designing a low-power experimental platform with DSP control programing.Firstly,the topology and operating principle of single-phase CHBRs are analyzed,the mathematical model is deduced,and the causes of DC voltage imbalance are analyzed.Refer to the control method of traditional two-level rectifiers,the control and modulation schemes with voltage balance abilitity of single-phase CHBRs are analyzed.The analysis and simulation results show that instantaneous current control and DQ current decoupling control are suitable for single-phase CHBR systems.Carrier phase-shifted sinusoidal pulse width modulation(CPS-SPWM)can achieve higher equivalent switching frequency at lower carrier frequency,helping to improve harmonic characteristics.The dc-link load imbalance is the main reason for the dc voltage imbalance,and the dc voltage balance control can be achieved by adjusting the modulation ratio increment.Secondly,a 220V/2.2kW experimental platform with three H-bridge modules is designed and developed,which consists of control,drive,detection and power circuits.In addition,pre-charge,filter and protection circuits as auxiliary circuits also have been designed.The circuit design and parameter selection process are discussed.Experimental testing results show that the platform is prefect and can achieve good control effect.Finally,the control program of the single-phase CHBRs is designed.In order to be close to the practical application,control programing of the experimental platform includes the procedures of circuit pre-charge,startup,rated operation and shutdown.Self-test and over-voltage detection programs are designed to ensure safety.The program achieves the rectifier control objectives,with good dynamic response and harmonic performance.The correctness and validity of theoretical analysis are verified.