Control Methods Of Switch-Reduced Inverter For Variable Frequency Speed Regulation

Due to the advantages of the simple structure and fewer devices,the switch-reduced inverter characterized by a reduction in the number of power switches can be applied to the variable frequency speed regulation to reduce the weight,volume,and cost of equipment.Besides,it can be applied to the power switch fault tolerance of normal variable frequency speed regulation system to improve reliability.Based on the model predictive control method,this dissertation takes the switch-reduced inverter three-phase induction motor variable frequency speed regulation system as the object to carry out in-depth research on the control methods of the switch-reduced inverter from two perspectives of variable frequency speed regulation control and fault tolerance control.This dissertation focuses on the variable frequency speed regulation problems such as solving the control difficulties in existing topologies and further reducing the number of power switches,and the fault tolerance problems such as dealing with the failure of multi-power switches and improving the reliability of fault tolerance.The main research contents and results are as follows:Since the problem of the bus capacitor voltage AC fluctuation exists in the capacitor mid-point connected topology,this dissertation proposes a mode switching-based model predictive flux control method under the condition of single motor control.The flux prediction models based on reference flux amplitude and based on reference current are established respectively.The alternating switching strategy of two control modes is designed,and the constraint is analyzed.The effectiveness of the proposed method to suppress the capacitor voltage deviation under the condition of single motor control is verified by the physical experiment results.A dual motor complement-based model prediction flux control method is proposed under the condition of multi-motor control.The dual-motor model and the bus capacitor voltage model are analyzed and established.The synchronous control speed regulator,flux electric angle regulator,and space vector modulation method based on compensation vector are designed.The effective working range of dual motors is analyzed.The effectiveness of the proposed method to suppress the capacitor voltage deviation under the condition of dual motor synchronous control is verified by the physical experiment results.To further reduce the number of power switches,this dissertation proposes a dual motor shared single capacitor mid-point connected inverter topology and its model prediction flux control method.The mathematical model of the topology is established.The control difficulties and constraints are analyzed.The voltage vector synthesis method based on selfadjusting weight and the bus capacitor voltage estimation method without voltage sensor are designed.The effectiveness of the proposed method to further reduce the number of power switches is verified by physical experiment results.To solve the problem of multiple power switch failures in normal inverters,this dissertation proposes a switch-reduced inverter topology that both shares the power leg and is connected to the capacitor mid-point.A non-redundant fault-tolerant control method for multiple fault types is proposed.The hardware switching strategy based on the current signal and the model predictive torque control method based on consistent objective function are designed.The effectiveness of the proposed method to realize any single-leg,double-leg and secondary fault tolerance is verified by physical experiment results.Since the unreliability of the triggers can cause the failure of non-redundant faulttolerant control methods,this dissertation deeply analyzes the fault mechanism of the power switch and designs the fault-tolerant scheme based on mode switching.The anti-misdiagnosis no-reconstruction fault-tolerant control method is proposed.The calculation method of reference stator flux vector in fault-tolerant mode and the smooth switching strategy are designed.The effectiveness of the proposed fault-tolerant method and its anti-misdiagnosis capability is verified by physical experiment results.