Abstract: This paper details a brushless DC motor speed control system based on a DSP (TMS320F2812) and a dedicated control integrated chip (MC33035), and comprehensively utilizes PID and filtering algorithms. The actual hardware circuit design and software control strategy of the control system are presented. Experimental results show that the control system operates stably, has a reasonable control algorithm, and high control accuracy, demonstrating strong application and promotion value.
introduction
Brushless DC motors began to attract the attention of scholars engaged in motor and drive systems in the late 1970s. There are many forms of motor drive control structures, and in recent years, foreign scholars have focused their research on the torque ripple and control problems of DC motors. Digital control circuits based on microcontrollers have strong speed control capabilities, but can only achieve outer-loop digital control of the system, while DSPs can achieve fully digital control.
The TMS320C28x series is the latest 32-bit fixed-point DSP chip launched by TI. It has both digital signal processing capabilities and powerful time management capabilities and embedded control functions, making it particularly suitable for measurement and control applications involving large-scale data processing [1].
In the speed control system of a brushless DC motor, in order to enable the commissioner to understand the system's operating information in real time, it is necessary to collect information such as motor speed and armature current in real time and perform data analysis and processing [2]. The control process is complex and the control algorithm has a large amount of computation. Therefore, this system selected the DSP chip TMS320F2812 with strong data processing capabilities as the control core, and combined it with the MC33035 dedicated control integrated chip to design and manufacture a brushless DC motor speed controller.
1 System Structure
This system is designed for high-speed brushless DC motors. In principle, there is no upper limit to the motor speed. The maximum speed of the motor used in the experiment was 50,000 rpm, and the motor power was 5 kW.
The system was designed with two modes for user convenience: communication and JOG (manual). Communication mode allows users to easily operate the motor from their computer, setting its maximum speed, acceleration, and displaying its current actual speed. In JOG mode, users can also operate the motor via keyboard to set its speed when a computer is unavailable.
Funding: National Natural Science Foundation of China (70271001)
This system designs and controls a brushless DC motor using Hall effect sensors as the position feedback mechanism, obtaining position and speed information from the feedback pulse signals. The core DSP adjusts the control speed based on the acquired actual speed, achieving closed-loop control of the motor speed. Additionally, the system obtains current information from the motor's IGBT driver. By integrating these three pieces of information, the entire motor speed control system operates safely, stably, and reliably.
2 System Hardware Design
The signal lines between different parts are isolated by optocouplers, as shown in Figure 3. The optocoupler used here is a TLP521, with an isolation voltage of 2500V. In this system, the maximum voltage of the driver section is 300V; 2500V ensures absolute safety during system operation. The optocouplers in Figure 3 are connected according to positive logic, meaning an input of 1 corresponds to an output of 1. In addition to the TLP521, several high-speed 6N127 optocouplers are used at the communication line connections.
2.1 Control Section
The core component of the control section is the TMS320F2812. During the fabrication, an ICETEK-2812-B board (a DSP development board with a 2812) was used. In addition to the DSP, there is also a power management chip that converts the external 5V to 3.3V to power the system.
The 2812 acquires speed, current, and position feedback signals from the motor. The DSP integrates these three signals and outputs external control signals. The overcurrent signal fed back from the drive section is a 0/1 signal. The DSP constantly monitors this signal during operation. Once it detects a 1, indicating that the motor is overloaded, it immediately issues a signal to stop the motor to prevent damage to the motor and speed controller.
The speed control signal output by the DSP is a digital quantity. This digital quantity is converted into a voltage quantity by a D/A converter and fed to the MC33035 for speed regulation. The system uses a 12-bit serial D/A converter (TLV5616), followed by an amplifier stage (LM358) to amplify the output voltage according to the requirements of different motors.
Communication between the TMS320F2812 and the PC is accomplished via the 485 bus. The 485 bus is widely used in industrial control due to its long transmission distance and stable performance; therefore, this system chooses the 485 bus for transmission.
2.2 Driver Section
The core control unit of the drive section is the MC33035, and the driving devices are the IR2183 and IRGP50B60PD1. As the core control unit of the drive section, the MC33035 determines the position of the motor rotor based on the position signal fed back by the motor Hall effect sensor, and controls the switching of the IGBTs.
Although IGBTs have superior on-state characteristics, it is still not easy to completely turn them off instantaneously. During debugging, it was found that even a slight spike when the IGBT is turned off can cause the motor to overheat or even burn out. This requires corresponding measures in the circuit design, such as connecting a resistor in series at the connection between the IR2183 output and the IGBT; and more careful attention must be paid to the PCB layout, ensuring symmetry.
The motor speed is adjusted by receiving the control voltage from the control section at pin 11 of the MC33035 (the non-inverting input of the error signal amplifier). Depending on the voltage, a pulse width modulation (PWM) signal is generated internally to control the three lower drive outputs. By changing the output pulse width, the conduction time of the IGBT is changed, thereby adjusting the motor speed.
2.3 Display Section
The main control element for the display section is the AT89C51. The display section and the drive section exchange commands via the serial port of the AT89C51 and AT2812 (i.e., communication method). Meanwhile, the 5V power supply required by the display section is provided by the control section.
Here, the rotational speed is acquired by using the counting pin of the AT89C51 to acquire the pulse signal output by the Hall effect sensor. This signal is then converted into frequency and sent to a seven-segment display. In this case, the AT89C51 functions as a frequency meter.
