Networked brushless DC motor control system based on DSP

　　As everyone knows, DC motors have the most superior speed regulation performance, which is mainly reflected in convenient speed regulation (stepless speed regulation possible), wide speed regulation range, good low-speed performance (large starting torque, small starting current), balanced operation, Low noise, high efficiency, etc. At present, brushless DC motors have been widely used in feed drives of CNC machine tools, servo drives of robots, and variable speed drives of new generation household appliances.

　　In order to further improve the comprehensive performance of the control system, in terms of controllers for brushless DC motor control systems, in recent years some large foreign companies have launched DSP (digital signal processor) single-chip motor controllers with superior performance compared to MCUs. Such as ADI's ADMC3xx series, TI's TMS320C24 series and Motorola's DSP56F8xx series. They all integrate a DSP-based core with peripheral functional circuits required for motor control into a single chip, which greatly reduces the price, reduces the size, compacts the structure, is convenient to use, and improves reliability. Its maximum speed can reach 20 to 40 MIPS, and the instruction execution time or the time to complete an action is only tens of nanoseconds. Compared with ordinary MCUs, the computing and processing capabilities are increased by 10 to 50 times, ensuring superior control of the system. performance.

　　1 Overview of system principles

　　In the brushless DC motor control system designed in this article, TI's TMS320LF240x chip is used as the controller. As a new member of the DSP controller 24x series, the TMS320LF240x chip is a fixed-point DSP chip under the TMS320C2000 platform. In terms of structural design, the 240x series DSP provides low-cost, low-consumption, high-performance processing capabilities, and has a very prominent role in digital control of motors. In the brushless DC motor control system based on TMS320LF240x shown in Figure 1, TMS320LF240 DSP is used as the controller to process the collected data and send control commands. The TMS320LF240 controller first captures the high-speed pulse signals of the Hall elements H1, H2, and H3 on the DC motor through three I/O ports, detects the rotational position of the rotor, and sends out corresponding control words according to the position of the rotor to change the PWM signal. The current value is used to change the conduction sequence of the power tubes in the DC motor drive circuit (full-bridge control circuit MOSFET) to control the motor speed and rotation direction. The motor's code plate signals A and B are captured through the CAP1 and CAP2 ports of the DSP controller. The captured data is stored in the register. By comparing the captured A and B phase pulse values, the current forward and reverse rotation status and speed of the motor can be determined. During the operation of the system, the drive protection circuit will detect the current operating status of the system. If an overcurrent or undervoltage situation occurs in the system, the PWM signal driver IR2130 will activate the internal protection circuit to lock the output of subsequent PWM signals. At the same time, the FAULT pin will pull down the PDPINT pin voltage of the DSP controller and start the DSP controller. Power driver protection. At this time, all EV module output pins will be set to a high-impedance state by hardware to protect the control system. The protection circuit designed in this system is mainly used to protect the DSP controller and the drive circuit of the motor. Figure 2 Full-bridge motor drive circuit control schematic. The following mainly introduces the rotor position detection circuit, drive circuit, system protection circuit, etc. of the system.

　　2 Rotor position detection circuit

　　2.1 Detection circuit application principle

　　When controlling a brushless DC motor, the DSP controller mainly issues corresponding control words based on the current rotation position of the rotor, and controls the motor by changing the duty cycle of the PWM pulse signal. The rotor position of the brushless DC motor is detected by a position sensor. In this design, three photoelectric position sensors (Hall elements) are used. This kind of sensor is made by using the photoelectric effect and consists of a light shield that rotates with the motor rotor, a fixed light source, a photoelectric tube and other components. The light shield is opened with 180% electrical angle gaps, and the number of gaps is equal to the number of pole pairs of the brushless DC motor rotor magnetic poles. When the gap faces the phototransistor, the light source strikes the phototransistor, producing a "bright current" output. Other phototransistors only have "dark current" output because the light shield blocks the light. Under the action of "bright current", one phase winding of the three-phase winding has current conduction, and the other two phase windings do not work. The shading plate takes turns outputting "bright current" or "dark current" signals as the rotor rotates to detect the position of the rotor's magnetic poles and control the three-phase windings of the motor's stator to conduct in turn, so that the three-phase windings are energized in a certain sequence to ensure The brushless DC motor operates normally.

　　As the motor rotor rotates, the photoelectric tube intermittently receives the light emitted from the light source and is continuously turned on and off, thereby generating a series of "0" and "1" signals. These pulse signals are transmitted to the DSP through the I/O port. The DSP reads the status value of the Hall element, determines the current position of the rotor, controls the drive circuit by changing the high or low efficiency of the PWM signal output, and changes the conduction of the MOSFET tube. sequence to achieve good control of motor commutation; at the same time, change the PWM signal duty cycle to adjust the motor speed. The conduction sequence of the motor drive circuit control bridge power tube is Q1Q2, Q2Q3, Q3Q4, Q4Q5, Q5Q6, Q6Q1, which is a pair-by-two energization method. Each time the motor rotor rotates, the Hall elements H1, H2, and H3 will appear in six states. The DSP sends a corresponding control word to each state to change the power-on phase sequence of the motor to achieve continuous operation of the motor. The motor drive circuit control schematic diagram and motor forward conversion phase table are shown in Figure 2 and Table 1.

　　Table 1 Motor forward conversion phase table PWM6 PWM5 PWM4 PWM3 PWM2 PWM1 H1H2H3 ACTR Q12Q 00 11 11 11 11 10 101 0X03FE Q2Q3 00 11 11 10 11 11 100 0X03EF Q3Q4 11 11 11 10 00 11 110 0X0FE3 Q4Q% 11 10 11 11 00 11 010 0X0FE3 Q%Q6 11 10 00 11 11 11 011 0X0E3F Q6Q1 11 11 00 11 11 10 001 0X0F3E

　　2.2 Hall element signal processing

　　The timing sequence of the Hall element signal on the motor is shown in Figure 3. The Hall element signals generated by DC motors usually cover each other with high and low levels. The control of the motor drive bridge needs to trigger the controller to enter an interrupt response based on each detected transition of the three Hall elements, and at the same time record the status of the Hall elements. Therefore, the three Hall elements are processed in two steps in the design: first, the signals of the three Hall elements are connected to the three I/O pins of TMS320LF240, and the current status is recorded; then the Hall element signals are used as three The input is connected to the I/O port of the CPLD, and a continuous narrow pulse output is realized through programming, which is connected to the CAP3 pin of TMS320LF240. Each pulse triggers an interrupt, controls the conduction sequence of the drive bridge circuit, and controls the motor's speed and forward and reverse rotation based on the current Hall element status information.

　　3 drive circuit

　　The motor control driver uses the IR2130 chip. IR2130/IR2132(J)(S) is a high-voltage, high-speed power MOSFET and IGBT driver with an operating voltage of 10~20V and three independent high-side and low-side output channels. The logic input is compatible with CMOS or LSTTL output, and the minimum logic voltage can reach 2.5V. The ground-referenced operation amplifier in the peripheral circuit provides an analog feedback value of the full-bridge circuit current through an external current detection potentiometer, if it exceeds the set or adjusted reference current value. The internal current protection circuit of the IR2130 driver starts to turn off the output channel to achieve the function of current protection. The IR2130 driver reflects the state of a high pulse current buffer, with propagation delays matched to high frequency amplifiers. The floating channel can be used to drive N-channel power MOSFETs and IGBTs up to 600V. The IR2130 chip can control the turn-on and turn-off sequence of six high-power tubes at the same time. Through the output HO1, 2, and 3, it controls the turn-on and turn-off of the upper half-bridge Q1, Q3, and Q5 of the three-phase full-bridge drive circuit respectively. The IR2130 The outputs LO1, 2, and 3 respectively control the on and off of the lower half bridge Q4, Q6, and Q2 of the three-phase full-bridge drive circuit, thereby achieving the purpose of controlling the motor speed and forward and reverse rotation. Figure 4 Typical circuit of IR2130 There is a current comparison circuit inside the IR2130 chip, which can set the motor comparison current. The set value can be used as a reference value for the software protection circuit, which can make the circuit suitable for controlling motors with different powers. The typical circuit of IR2130 is shown in Figure 4.

　　4 System protection circuit

　　In the brushless DC motor control system, the protection circuit occupies a very important position. Its main function is to protect the core component DSP of the control system from high voltage and overcurrent impacts, and also to protect the motor drive circuit from damage. The protection circuit of the entire system mainly consists of three parts: circuit isolation circuit, signal isolation circuit, and drive protection circuit. The circuit isolation circuit uses a voltage module with an internal isolation transformer to isolate the voltage of the motor drive voltage control part and divide it into two power supply systems: a 5V power supply system and a 24V power supply system. In this way, when an abnormality occurs in the driving circuit part, the control circuit will not be affected from the power supply part, thereby achieving the protection function of the control circuit. The signal isolation circuit mainly isolates the control and drive signals between the control circuit and the drive circuit through a photoelectric isolator to realize signal transmission between different voltages. Since the output frequency of the PWM pulse signal in this system is relatively high, in order to avoid signal loss and distortion, a 6N137 photoelectric isolator is used here.

　　The system's drive circuit protection function is mainly implemented by the IR2130 driver. The IR2130 driver protection circuit mainly consists of two parts: self-protection circuit and over-current and under-voltage protection circuit. The self-protection circuit is shown in Figure 5. The reference ground operational amplifier in the peripheral circuit compares the set value of the pin VsO with the voltage generated on the feedback resistor by the current flowing into the CA- pin. If it exceeds the set or adjusted VsO reference value, the internal current of the IR2130 driver The protection circuit starts and turns off the output channel to realize the current protection function. There is also a hardware protection circuit inside the IR2130 chip. If there is overcurrent or undervoltage in the load or drive circuit, the FAULT pin of the IR2130 driver will output a braking signal. Usually, this output signal is connected to the PDPINT pin of the DSP, and the input level of the PDPINT pin is pulled down and turned off. All outputs of the DSP are cut off and placed in a high-impedance state to protect the entire control circuit. 　　

　　5 Principles of Networked Interface Design

　　In order to adapt to the requirements of network development, microprocessor control equipment must be required to provide various network communication interfaces. Traditional microcontrollers have insufficient network support, and the new generation of microprocessors has begun to embed network interfaces. In addition to supporting TCP/IP protocols, some also support USB, CAN, BLUETOOTH and other communication interfaces, and also provide corresponding communication groups. Network protocol software and physical layer driver software. Controlling the operation of the brushless DC motor through the network can be said to be a feature of the control system. Usually the control system of the brushless DC motor is controlled by a single machine or dual controllers, and is rarely controlled through the network. This control system uses RS485 communication interface for networked data transmission. The main network transmission diagram is shown in Figure 6. The host computer or PC assigns an address to each control module software and sends data to each module. When sending data, the host mainly identifies the sending object through the address assigned to each module. After the network system is powered on and before network initialization, except that the group address and address of the host can be determined, all drive module group addresses and addresses are 0xFF.

　　Indicates that the driver module is only in the overall group 0xFF, and the address has not been initialized. Determined by the connection method of the hardware, at this time, the next driver module on the network is waiting for the network initialization command. The host should send an address allocation command to allocate the address to the drive module. Once the address of the drive module is allocated successfully, it passes information to the next drive module through hardware, indicating that it has been allocated. The host's next address allocation command will then act on the next drive module. This process will continue until the host receives feedback information that the allocation is successful after sending the address allocation command. At this time, it means that there are no drive modules that need to be allocated. At this point, the network initialization is completed. When the network has been established, the host can reset all drive modules to the state just after power-on by sending a network reset command, and then initialize them again, which provides the network "hot" reconstruction capability. The brushless DC motor is equipped with a speed regulating device composed of a high-performance, high-speed real-time digital controller. The entire system has relatively simple control, low cost, balanced speed and low noise. It is especially suitable for application in household electrical products. At the same time, it can also be extended to other industrial application fields, such as machine tools, robots and elevator drives.