Abstract: This paper details the research on a brushless DC motor speed control system based on a DSP (TMS320F2812) and a dedicated control integrated chip (MC33035), comprehensively utilizing 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. Keywords: Brushless DC motor, DSP, TMS320F2812, MC33035 Introduction Brushless DC motors have attracted the attention of scholars engaged in motor and drive systems since the late 1970s. There are many forms of motor drive control structures. In recent years, foreign scholars have focused on the torque fluctuation 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, and is particularly suitable for measurement and control occasions with large-scale data processing [1]. In the speed control system of brushless DC motor, in order to enable the debugger 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, this system does not limit the upper limit of motor speed. The maximum speed of the motor used in the experiment is 50,000 rpm and the motor power is 5 kW. The system design includes two modes: communication and JOG (manual) for user convenience. The communication mode allows users to conveniently operate the motor from their computer, setting the maximum speed, acceleration, and displaying the current actual speed. When a computer is unavailable, users can also operate the motor via keyboard in JOG mode to set the speed. 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 control core DSP corrects the control speed based on the acquired actual speed, achieving closed-loop control of the motor speed. In addition, 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. The entire system consists of four parts: control, drive, display, and power supply. The structural block diagram is shown in Figure 1. 2 System Hardware Design The hardware principle block diagram is shown in Figure 2. The signal lines between the various parts are isolated by optocouplers, and the connections at both ends of the optocouplers are shown in Figure 3. The optocoupler used here is the TLP521, with an isolation voltage of 2500V. In this system, the maximum voltage of the drive section is 300V, and 2500V ensures the absolute safety of the system operation. In Figure 3, the optocouplers are connected according to positive logic, that is, input 1, output is also 1. In addition to the TLP521, several high-speed optocouplers 6N127 are used at the connection of the communication line. Figure 3 Optocoupler Connection Diagram 2.1 Control Section The core device of the control section is the TMS320F2812. During the construction, an ICETEK-2812-B board (a DSP development board with 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 collects speed, current feedback signals and position feedback signals from the motor. The DSP integrates these three signals to output 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 a 1 is detected, it indicates that the motor is overloaded, and an immediate signal is sent 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. A 12-bit serial D/A converter (TLV5616) is selected in the system, 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 a 485 bus. In industrial control, the 485 bus is widely used, with long transmission distances and stable performance, so this system chooses the 485 bus for transmission. 2.2 Drive Section The control core of the drive section is the MC33035, and the driving devices are IR2183 and IRGP50B60PD1. The MC33035 serves as the control core of the drive section. Based on the position signal from the motor's Hall effect sensor, it determines the rotor's position to control the IGBT's switching. Although IGBTs have excellent on-state characteristics, completely turning them off instantaneously is still not easy. During debugging, it was found that even a slight spike during IGBT turn-off can cause the motor to overheat or even burn out. This necessitates appropriate measures in the circuit design, such as connecting a resistor in series between the IR2183 output and the IGBT; and strict attention must be paid to symmetrical layout during PCB routing. Motor speed regulation is achieved by the MC33035 receiving a control voltage from the control section at pin 11 (the non-inverting input of the error signal amplifier). Based on this voltage, the internal circuitry generates a pulse width modulation (PWM) signal, controlling the three lower drive outputs. By changing the output pulse width, the IGBT's on-time is altered, thereby regulating the motor speed. 2.3 Display Section The main control element of the display section is the AT89C51. The display section and the drive section communicate via the serial port (i.e., communication method) between the AT89C51 and the 2812. 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 collect the pulse signal output from the Hall effect sensor. This signal is then converted into a frequency and sent to the seven-segment display. In this case, the AT89C51 functions as a frequency meter. The system allows the user to input the rotational speed via the keyboard, rather than adjusting it via a potentiometer. This is because the potentiometer outputs an analog signal, and acquiring this voltage through the integrated A/D converter of the 2812 is unstable and will drift slightly. This slight drift can cause significant fluctuations in rotational speed. To avoid this fluctuation, this system uses a fully digital keyboard. The AT89C51 reads the digital signal from the keyboard and then transmits this signal to the 2812 via the communication port to achieve fully digital stepless speed control. 3. System Software Design The system software design concept involves continuously collecting motor speed data and comparing it with the given speed command. Using a PID algorithm combined with a filtering algorithm, the speed error is continuously corrected until the collected motor speed matches the system's given speed. At this point, the program considers the system locked. During system control, the motor current and position feedback are constantly monitored. If any abnormality occurs, the corresponding alarm mechanism is activated, and the motor stops rotating. The program software block diagram is shown in Figure 4: [Figure 4: Software Block Diagram] The actual speed is measured by the program reading pulses from the Hall element feedback every 20ms. Each pulse is counted as one revolution, and a total of 10 samples are recorded as one cycle. The program counts the number of pulses within 200ms to calculate the actual motor speed. Using this calculation method, the system's error is 75 rpm, which fully meets the error requirements of high-speed motors. For motor safety, in addition to overcurrent protection, the system also includes a maximum speed over-limit alarm. During operation, the system program continuously compares the actual speed with this maximum speed. Once the actual motor speed is detected to exceed the user-given maximum speed, an overspeed alarm is immediately triggered, and the motor stops rotating. The communication between the control unit and the PC and display unit adopts the following communication protocol: 19200 bps, 8 bit, 1 start, 1 stop, no parity check. In addition, the system has reserved corresponding signal interfaces for the motor cooling device, allowing for the connection of external cooling devices as needed to improve motor safety performance. 4. System Operation Interface The operation interface, as shown in Figure 5, is designed based on the system's functions: [Figure 5: Operation Interface] The operation interface is user-friendly and includes a speed monitoring curve to facilitate observation of motor speed stability. Furthermore, users can easily set and modify parameters through the operation interface. 5. Conclusion This motor speed control system, after actual testing, demonstrates high control accuracy and stable, reliable operation. The control accuracy under load is within a 75 rpm deviation, close to the theoretical value. During actual debugging, overload and overspeed experiments were conducted, and the system responded sensitively, demonstrating safe and reliable control. This system utilizes a powerful DSP (TMS320F2812) chip, providing ample expansion space and allowing for expansion according to actual application needs. The innovations of this paper are: ① This speed control system integrates TMS32F812 and MC33035; ② The manual input of motor speed uses a fully digital keyboard; ③ The control system communicates with the PC via a 485 bus; ④ All signal line connections are completely isolated by optocouplers, so that each part does not affect the other and ensures absolute safety of operation. References [1] TMS320F2812 Data Sheet. TEXAS INSTRUMENTS, 2005 (Revised). [2] Chen Bin, Wu Zhong. Matlab implementation of serial communication between brushless DC motor DSP control system and PC. Microcomputer Information, 2005, 21 (07): 95-117.