Brushless DC motors are increasingly widely used due to their ease of control, commutator-free operation, simple structure, high speed, and high efficiency. The continuous introduction of various dedicated chips has further promoted their application and development. The C50x is a microcontroller control chip launched by Siemens specifically for brushless DC motors. It features an internal hardware commutation circuit, simplifying the hardware structure of the brushless DC motor controller and enhancing reliability. The C504 can control one motor, while the C508 can control two. This article uses the C504 as an example to introduce the design method of a brushless DC motor control and speed regulation system.
Structure and Function of Brushless DC Motor Speed Control System
The structure of the brushless DC motor speed control system is shown in Figure 1. The system mainly consists of a microcontroller, a 1GBT drive circuit, a 1GBT bridge circuit, a three-phase brushless DC motor rotor position detection circuit, a protection circuit, an LCD display, and an operation circuit. The three-phase brushless DC motor rotor position detection circuit converts the rotor magnetic pole position into an electrical signal for processing by the C504. This signal triggers commutation of the three-phase 1GBT bridge, and the 1GBT drive circuit completes the conversion between low-voltage and high-voltage signals.
Working principle of brushless DC motor and characteristics of C504
Figure 2 is the main circuit diagram of the brushless DC motor speed control system, and Figure 3 is the rotor position and commutation relationship diagram. Corresponding to different rotor positions, only two of the six transistors in the main bridge arm are switched on at any given time.
The C504 chip integrates a hardware commutation circuit. When the three-phase rotor detects a position signal change and sends it to the C504, the C504 switches the commutation control signal of the main circuit without requiring software processing. This significantly reduces development difficulty and increases commutation reliability.
The C504 features unique internal hardware protection circuitry. To effectively protect the IGBT and motor in the main control circuit, overvoltage and overcurrent detection circuits are included. When overvoltage or overcurrent occurs, the protection detection circuit sends the detected signal to pin P6 of the C504, which has a capture and lock-up function. This pin immediately blocks the main circuit trigger control signal, cuts off the main circuit current, protects the components, and then notifies the C504 to perform fault interruption processing. This method is highly effective and reliable.
The actual motor speed can be calculated from the rotor position detection signal. When the speed needs to be reset or when there is interference, the chip can be programmed to change the duty cycle of the control output signal, which can easily adjust the motor speed to achieve the desired value.
System software design
The system software adopts a modular structure, and the main program flow is shown in Figure 4.
Conclusion
By utilizing the hardware commutation circuit and interrupt protection circuit of the C50x series dedicated MCU controller, a brushless DC motor speed control system can be easily, reliably, and economically constructed.
