| In the aerospace applications,such as control moment gyro motor,high-precision and high-efficiency of motor drives are demanded.The switching inverters are efficient,but the pulse mode voltage with lots of harmonics brings extra fluctuations of speed and torque which influence the control accuracy of motor.In the other hand,the linear power amplifiers output high precocious signals,however the circuits work in DC power supply,the huge power losses of transistors make the system unefficient.Therefore,a multilevel-switching-linear hybrid(MSLH)scheme and its control strategies for the permanent magnet synchronous motor(PMSM)drives are studied in this paper.Firstly,the three-phase MSLH scheme is proposed.The H-Bridge cascaded multilevel inverter,LC filter and linear power amplifier are connected in series which makes the system have high efficiency and high accurate outputs.The simplified model,the power factor of circuit,the ripple voltages of outputs and system efficiency are analyzed.The modulation of multilevel-switching inverter and the control strategy of linear amplifier dirves are studied.The ripple voltages and power losses of different modulations are analyzed.To reduce the tracking errors of outputs,the methods of compensating voltage phase and voltage-closed-loop control are studied.Secondly,the mathematical model of PMSM is studied and a control strategy based on the vector control with speed,current and voltage closed-loop control is studied.To ensure the motor starting up reliably at low speeds,the simplified motor motion model is analyzed and an optimal open-loop variable-frequency starting-up method is proposed.Combining to the open-loop starting-up method and the speed-sensorless algorithm based on back EMF,the control strategy studied.Finally,the simulation models have been built and experiments have also been executed on a laboratory prototype.The effectiveness of this scheme is validated by the simulation and experiment results. |
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