Control Strategy Of Brushless DC Motor

The structure diagram of a general self synchronous brushless DC motor inverter and drive is shown in Figure 1. The drive system shown in the figure is usually more commonly used for voltage source inverters (VSIs). The corresponding voltage source inverter is the current source inverter (CSI). The reason why VSI is widely used is because its cost, weight, dynamic performance, and ease of control are superior to CSI. The difference in weight and cost between the two inverters is due to the fact that VSI uses capacitors for DC coupling, while CSI requires a bulky reactor to be connected between the rectifier and inverter. VSI also differs from CSI in terms of dynamic response capability. Due to the function of a large reactor to meet the needs of CSI as a constant current source with a large commutation overlap angle, it prevents rapid changes in current in the motor winding and suppresses high-speed servo operation of the motor. This will increase the size of the damper in the drive system. The expected constant current control and constant torque control performance of CSI can also be approximated in VSI by hysteresis current control in its internal current control loop.