Permanent Magnet Brushless DC Motor Digital Controller

1. Overview

Permanent magnet brushless DC motor (PM-BLDC), due to its many inherent characteristics and my country's abundant rare earth resources, is considered by many motor experts to be a new generation of products in the 21st century. With the development of semiconductor integrated circuits, power electronic devices, control principles and rare earth material industries, it can be predicted that this product will gradually replace the traditional structure of AC motor plus variable frequency speed regulator.

In the literature currently available, the controller generally uses Motorola's MC33035, MicroLinear's ML4425/4428 or general PWM chips such as SG3524, TL494, etc. Although these ASIC chips can realize wireless speed regulation of the motor, there are still some problems, such as the inability to directly interface with the computer, many more complex control algorithms cannot be implemented without increasing hardware costs, and the controller's computer interface is not ideal. In general, the controller is not intelligent enough. Although the cost of using general PWM chips to achieve stepless speed regulation of the motor is low, when the controller adds various additional functions for different applications, it is not flexible enough and increases the cost of hardware.

In the design of the controller of electric automatic vehicles, if the above traditional control scheme is adopted, the control characteristics of both the current loop and the speed loop are not satisfactory. For the speed loop, sudden stalling will cause damage to the power device, and for the current loop, when measuring the speed, additional hardware overhead will be added. In the electric bicycle controller, we use the embedded single-chip microcomputer C504 to perform dual-loop control of the PM-BLDC Motor for speed and current, which meets the requirements of electric vehicle characteristics.

2. PM-BLDC digital controller solution

The block diagram of the PM-BLDC digital controller is shown in Figure 1.

The core component is the embedded microcontroller C504 from Infineon. The reason for choosing C504 is that there is a CCU unit inside C504 that can generate three-phase PWM waves. When the SFR of CCU is set to Block Communication Mode, the CCU unit can automatically generate a 6-phase PWM chopping signal suitable for the PM-BLDC Motor 1200 conduction mode according to the phase of the three interrupted signals without adding software unlocking. At this time, it is required to directly connect the three HALLs with a phase difference of 1200 electrical degrees to INT0, INT1, and INT2 of C504.

In addition, C504 has high anti-interference performance and can work normally in harsh electromagnetic environments. C504 is easy to develop, fully compatible with the MCS-51 series microcontrollers commonly used in China and has an acceptable price [1].

As can be seen from the controller schematic, the speed of the PM-BLDC can be directly preset digitally or controlled by software, implementing different control algorithms to meet various application requirements.

Conclusion

This digital controller has achieved satisfactory results in controlling PM-BLDC electric automatic vehicles.

In the design of electric vehicle controller, there is a problem of slow start, which can only be achieved by digital method. When users start, they usually open the throttle signal to the maximum, which is extremely detrimental to the life of the motor and control. In our controller using C504, this problem is well solved and smooth start is achieved.

It can be seen that as long as the MCU has a field programmable function (ISP Function), various control schemes can be implemented by only changing the software at the application site without readjusting the hardware, which provides great convenience for on-site debugging.

At present, we have used this solution to implement a tension control system, using the C504 MCU, high-power MOSFET (CoolMOS), high-voltage IGBT and SFH series high-speed optocoupler provided by Infineon, replacing the traditional induction motor, variable frequency speed regulator and tension controller. It has certain advancedness and price advantages and has the prospect of popularization and application.