Research On Brushless DC Motor Control System Based On Soft Switch Inverter

Because of the simple structure and electronic commutation, the brushless dc motor(BLDCM) has a wide spread use in compare with traditional dc motor. But in the traditional BLDCM control system, hard switched inverter will create larger switching loss and EMI problems, so this paper use soft switched inverter to the BLDCM control system to solve the hard switched inverter problems. After using the soft switched inverter in the BLDCM control system successfully, this paper proposed a pulse width modulation way using the auxiliary resonant circuit through in-depth analysis of the resonant circuit, and then The simulation and experimental verification has been done.Firstly, this paper deducts the mathematic model of BLDCM and gives the equivalent circuit when the motor is operating at six states, and then the paper deducts the different commutating tables when the motor rotates in the forward direction or in the reverse direction. After that, this paper analyses and compares four kinds of typical resonant dc link inverter to illustrate the PRDCLI2’s advantages. After that, the paper analyzes the working principle and working process of this soft switch inverter in detail. The simulation verification has been done when the load is constant-current source.Secondly, the timing change affection on the resonant process is studied, including the inductance charge time change and the SL break over time change. Then the conclusion is drawn that as long as the inductance charge time is longer than threshold value, the resonant circuit can work well. The influence of resonant component parameters’ change to the resonant process is studied to give the way of ensuring the resonant circuit work properly when these parameters change. The influence of the load current change to the resonant process is studied. At last, this paper studies the output voltage deviation caused by the bus voltage groove, and the compensation way is given.Thirdly, this paper studies the way to combine the soft switch technology with the BLDCM control, and the zero voltage switching realization of the inverter’s switches is given. The difference of the resonant process with motor load and constant load is studied, and the current flow of the motor is explained when the resonant voltage is zero. Based on the above theory, this paper finishes the simulation of the BLDCM control system based on the soft switch inverter and verifies the above conclusion. Lastly, this paper proposes a way to modulate the bus voltage using the resonant circuit, and the simulation verification is done. The duty cycle restriction of the modulation voltage is deduced.Finally, this paper designs the main circuit schematics of the whole control system and completes the debugging of the hardware circuit and software programs. The zero voltage switching of the main power switch is realized. Finally, this paper verifies the bus voltage modulation using the resonant circuit by the experiment.