Gong-kuang zidonghua (Aug 2022)
High-frequency isolated variable frequency speed regulation sensorless vector control in mine
Abstract
In the coal mine's medium and high voltage and limited occasions, the frequency converter is connected to the power grid by power frequency transformer. Most of the controlled motors are controlled by open-loop control, which has the problems of narrow working space, complex structure and poor robustness of motor control. In order to solve the above problems, a speed sensorless vector control strategy based on high frequency isolated variable frequency speed regulation topology is proposed. This paper analyzes the topology and power transmission of the main circuit of high-frequency isolated variable frequency speed regulation in mine. The input three-phase power frequency AC power supply is rectified into DC power supply through an uncontrollable rectification link. The pulsating DC power supply is smoothed and filtered to obtain a stable DC power supply. The DC power supply is transformed through high-frequency isolation (DC-DClevel). Then, through the three-phase inverter stage, the DC power supply is converted into AC power supply with adjustable voltage and frequency. In order to reduce IGBT switching loss, save the overall cost and reduce the complexity of its overall structure, the three-phase rectifier stage adopts a diode uncontrolled rectification strategy. The equal pulse width modulation (EPWM) strategy is adopted for the high-frequency isolated DC-DC stage. The speed sensorless vector control strategy is adopted in the three-phase inverter stage. In this control strategy, the model reference adaptive system (MRAS) is used to estimate the speed of the asynchronous motor. A 0.75 kW three-phase asynchronous motor is used as the tested motor to verify the speed sensorless vector control strategy of high-frequency isolated variable frequency speed regulation for mine. The results show the following points. ① The voltage fluctuation of the DC bus on both sides of the high-frequency isolation DC-DC level is less than 10 V and the high-frequency square wave voltage is equal. The voltage waveforms of the primary single-phase inverter square wave and the high-frequency transformer coupled square wave are smooth and the overall steady-state performance is good. ② The three-phase inverter voltage and current waveform sine degree are good. The waveform is symmetrical and smooth. The three-phase inverter level stability performance is good, which meets the requirements of motor operation. ③ With the increase of time, the excitation current change is stable. The torque current responds quickly at startup. The torque current is large at the start-up stage, which can generate large torque. ④ The speed fluctuation of the motor is small in the stable phase. The waveforms of acceleration and deceleration phases tend to be a linear function, and the motor can start and stop smoothly. When the motor is just started, the maximum torque can reach more than 5 times of the stable torque, and the motor can be started quickly to work.
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