Research On Control Strategy Of Three-phase To Single-phase Matrix Converter

The three-phase to single-phase matrix converter can provide the frequency-adjustable and voltage-variable electricity energy for single-phase loads.It can be used for the airport power supplies,electrified railways,single-phase motor drives,and many single-phase power supplies that require the voltage regulation or frequency conversion.Moreover,this has all the advantages of ordinary matrix converters.Thus,the three-phase to single-phase matrix converter possesses good promising prospects and practical significance.However,the output side of this matrix converter is single-phase AC power,and the output power is pulsating power which will affect the quality of the input current waveform and the output voltage,and make the system control complicated.Meanwhile,the converter may have practical problems such as the power imbalance or the switching element failure in the actual operation process.In this paper,three-phase to single-phase matrix converter with power decoupling inductance is taken as the research object,the steady-state control under normal operating conditions,the control strategy under unbalanced input voltage conditions,and the system control under fault conditions are studied and designed.The control strategies and algorithms designed under the above three working conditions are verified theoretically through system simulation,and then prototype experiments are performed to verify the effectiveness of the proposed control strategies.The main research work and content are as follows:(1)The power decoupling of the three-phase to single-phase matrix converter is analyzed,and the inductor is employed to act as the pulsating power compensation unit which can construct the average signal model and small signal model for BUCK three-phase to single-phase matrix converter.Then,according to the system modeling,this paper proposes three control strategies based on the instantaneous power control,the virtual rectifier and virtual inverter independent control,and the dual current closed-loop control of the virtual DC bus current,respectively.Simulations and experiments are conducted to analyze the three different control strategies.The results illustrate that all the three strategies can achieve excellent control to systems.There into,the control strategy built on the instantaneous power control possesses the characteristics of the explicit meaning and clear logic,however,the transformation of the control segment is more complicated and the speed of the dynamic response is slower.The strategy on the basis of the virtual rectifier and virtual inverter independent control has the advantages of the clear control relation and simple control logic.The dual current closed-loop control strategy based on the virtual DC bus current can avoid the decoupling calculation of the instantaneous power,the system is easy to be implemented,the response of the system is faster,and this study of the control strategy under steady state operating condition can offer the research foundation for the control under following abnormal operating condition.(2)Under the input voltage imbalance working condition,this paper studies the system control strategy to make the three-phase to single-phase matrix converter work well.In order to optimize the waveform of the input current and reduce the harmonics of the input current on the basis of the steady output voltage,a novel closed-loop control strategy of the output voltage and input voltage is presented based on analyzing the different voltage stable controlling methods and current waveform optimized modulation strategies.Furthermore,the proposed closed-loop control strategy combines the dynamic modulation ratio with the input current reference vector which is provided by the positive-sequence component of the input voltage.Additionally,simulations and experiments of the proposed control strategy are performed under the input voltage imbalance condition,and the results validate the effectiveness of the system control.(3)The fault diagnosis and fault tolerant control of the three-phase to single-phase matrix converter are studied.According to the two common open circuit and short circuit fault types of the switching elements,the short circuit fault is transformed into the open circuit fault by using the fast acting fuse,and then the above two type of faults are merged into the open circuit fault.Subsequently,the judgment,the recognition and the current properties of the open circuit faults are studied,and then this paper proposes the open circuit fault diagnosis strategy.The proposed diagnosis strategy can provide the criterion for the fault tolerant control strategy.Due to the open circuit faults generated by different bridge-arms of the three-phase to single-phase matrix converter,the topological structures are divided into three fault modes.According to the aforementioned three fault modes,the corresponding fault tolerant control strategy of each fault mode is designed,and the designed strategies can make the system keep on working on the basis of changing the main circuit least when the switching tube occurs the open fault.The designed fault tolerant control strategies optimize the quality of the input current waveform with the fault case when these strategies can guarantee the output voltage steadily.Finally,simulations and experiments of the fault tolerant control strategies are conducted.