The increasing popularity of brushless DC motors stems not only from the actual use of the motors themselves, but also from the application of related technologies, such as sinusoidal drive technology. So, what exactly is sinusoidal drive technology for brushless DC motors? What are its functions? Let's delve deeper into this topic.
The sinusoidal drive technology of brushless DC motors involves applying a certain voltage to the brushless motor windings to generate a sinusoidal current. By controlling the amplitude and phase of this sinusoidal current, the motor torque can be controlled. Compared with traditional square wave control, the phase current of a brushless DC motor is sinusoidal and changes continuously without sudden changes in commutation current, resulting in lower motor operating noise.
Based on the complexity of control, the sinusoidal drive technology of brushless DC motors can be divided into: simple sinusoidal wave control and complex sinusoidal wave control.
Simplified sinusoidal wave control achieves motor current control by adjusting the amplitude and phase of the sinusoidal phase voltage of the motor. This is typically done by applying a specific voltage to the motor terminals to generate a sinusoidal phase voltage across the windings. Common generation methods include sinusoidal PWM and space vector PWM. Because sinusoidal PWM is simple in principle and easy to implement, it is commonly used as the PWM generation method in simplified sinusoidal wave control. Figure 1 shows the BLDC control structure diagram, where Ux, Uy, and Uz are the bridge arm voltages, and Ua, Ub, and Uc are the phase voltages of the motor windings. The following introduction to different types of PWM modulation methods will be based on this structure diagram.
Figure 1: Control block diagram of a brushless DC motor
(1) Three-phase sinusoidal modulation PWM
Three-phase SPWM is the most common method for generating sinusoidal PWM. It involves applying sinusoidal voltage signals with a 120-degree phase difference to the three terminals of the motor. Since the neutral point is 0, the motor phase voltages are also sinusoidal, and their phases are the same as the applied sinusoidal voltages. See Figure 2. Three-phase modulated SPWM terminal voltages.
(2) Minimum switching loss sinusoidal PWM
Unlike common SPWM, when using sinusoidal PWM with minimal switching losses, the voltages Ua, Ub, and Uc applied to the motor terminals are not sinusoidal voltages. In this case, the voltage at the motor's center point is not zero, but the motor phase voltages remain sinusoidal. Therefore, this type of control is line voltage control. See Figure 3:
