Sensorless Control And Four-switch Inverter Control Strategy Of Brushless DC Motor

Brushless DC (BLDC) motor has found widespread applications in the fields of servo systems, electrical vehicle, robot control and household appliance etc, due to its extensive speeding range, high power density, light electromagnetic pollution and high reliability. To further improve performance of BLDC motor drive, the thesis makes deep investigations on the following aspects, including intelligent control, sensorless control and new topological structure of inverter.To improve the reliability of sensorless BLDC motor drive, relationship between line back EMF and commutation instant is analyzed to improve ordinary back-EMF method, and a novel rotor position detection method withoutπ/3 phase angle shift is proposed. Position detecting circuit is improved, commutation rules are re-arranged and error from filtering is compensated. It can be drawn from simulation and experimental results that the method avoids the error introduced by phase shifting of measured signals, and improve precision and rapidity of position detection. .Recently, cost reduction of BLDC motor drive has drawn more and more attention of researchers. Four-switch inverter can reduce cost of drivers by replacing power devices with capacitors. This work designs four-switch inverter for three phase BLDC motor. The relationship between current of phase C and working mode of motor is analyzed. Control strategy based on two phase current measurement is improved. A novel control strategy based on single current sensor is proposed and implemented for four-switch three phase BLDC motor drive. The proposed method achieves good performance with reduced cost, which proves it a new valuable research direction.Despite its simplicity and good steady performance, traditional PID controller could hardly meet the requirement of precision and fast responding when used in controlling nonlinear system. In this work, a novel approach of compound control for BLDC motor using Cerebella Model Neural Network controller and PID strategy is proposed and researched. Based on strong mapping capability of neural network, the parameters of controller can be adjusted online so that the motor speed can track reference value very fast and exactly under different working conditions. Simulation and experiment results prove that the proposed intelligent controller has excellent dynamic and steady performance with very short setting time, extremely reduced overshot, and dramatically restrained effect of load disturbance. Elevator door drive is one of important applications of BLDC motor. A sensorless BLDC motor control system is designed for it in this work. The system uses TMS320F2812 DSP as core control unit, and includes power circuits, drive circuits, inverter, signal measurement circuits, protection circuits, optically coupled isolation circuits, and so on. The major functions, such as self-learning of door width, smooth track of speed reference curve, and protective action when blocked, are totally implemented with reduced cost, low noise, and high operational reliability.