Research On Operation Control Of Permanent Magnet Synchronous Motor System Based On Triple Converter

With the increase of the power level of the permanent magnet synchronous motor system,the topology of the traditional power device can not meet the high voltage and high power applications.In practical engineering,the technology of multiple convertor is recognized by many scholars.The multiplexed variable current technology refers to the technique in which a plurality of existing topologies are combined in series or in parallel to obtain a novel topology.When the topology is constructed with a certain power level and combined with multiple variable current technologies,the overall power level of the system can be greatly improved to meet the needs of high voltage and high power applications.This thesis studies on a triple line-voltage cascade converter,which takes an traditional two-level six-switch voltage-source converter(VSC)as the basic power unit and using line-to-voltage cascade.According to its structural characteristics,the working principle of the converter is analyzed.An equivalent switching circuit model of transmission power equalization and unbalance is established in this thesis based on the integrated control theory.In addition,the problem of large AC line-voltage spike caused by traditional carrier phase shift modulation is analyzed.According to the topology characteristics,a new carrier phase shift space vector modulation strategy is proposed to reduce the AC side line-voltage spike.In terms of control algorithm,this thesis analyzes the advantages and disadvantages of traditional fixed-frequency model prediction current control and traditional proportional resonance control(PR),combining the advantages of the two control algorithms.According to the Gauss distribution function in Bell curve,a new dynamic variable-weight fixed-frequency model predictive current control is designed and realizes smooth conversion of two algorithms,which weakens the influence of double-frequency fluctuation in the DC side bus voltage on the performance of the controller,and ensures the control system has good performance in both dynamic and steady processes.Because the new fixed-frequency model predictive current control still adopts the theory of integrated control,there are also problems such as unequal DC side capacitance voltage and asymmetric three-phase input current of AC side,when control system under the condition of unbalanced transmission power.In order to solve the problem of unbalanced transmission power,an inner-loop compensation control method is proposed based on the characteristics of the new modulation mode.At the same time,in the triple converter system with Proportional Integral(PI)controller as the voltage external loop controller,the PI controller can achieve good steady state performance,but it has a certain hysteresis in the dynamic process.Therefore,the three groups of DC side voltages will fluctuate greatly when the load changes.In order to solve this problem,this thesis introduces the load current feedforward compensation link on the basis of voltage outer loop,which to reduce the influence of load change on DC side voltage.Finally,an experimental platform was built to verify the algorithm.The experimental results show that the proposed control strategy is correct and effective.