Research on Brushless DC Motor Control System Based on DSP

Research on Brushless DC Motor Control System Based on DSP Yan-Hui Hui (College of Mechanical and Electrical Engineering, Guangdong University of Technology, Guangzhou 510090, Guangdong, China) The system interfaces to form a single-chip DSP-controlled motor system. A Hall element is used to detect the rotor pole position to form an electronic commutation logic. The motor speed is controlled by a digital PI speed and current controller. Finally, the experimental results and conclusions are given.

Brushless DC motor as a new type of continuously variable motor, not only has the characteristics of small size, light weight, small inertia, etc., but also has the excellent speed control performance of DC motor, but there is no mechanical commutator. Therefore, it has been widely used. Whether it is in the manufacturing and processing fields of CNC machine tools, robots, etc., or household appliances such as washing machines, computer hard disks and other occasions are increasingly valued 111. The past brushless DC motors are mostly composed of a variety of interface devices attached to the microcontroller. Not only is it complicated, but also the speed is limited. It is difficult to achieve full digital control from the position loop to the speed and current loop, and it is not easy to expand. The use of digital signal processor (DSP) to achieve the motor servo system can only use a single DSP to replace the microcontroller and various interfaces, and because of the DSP chip's fast computing power, can achieve a more complex and more intelligent algorithm 12; System upgrades and expansions can be performed through high-speed network interfaces; full digital control of position, speed, and current loops can be achieved.

This article describes the use of TI's TMS320LF2407DSP controller, composed of brushless DC motor servo control system. Firstly, the principle of brushless DC motor is introduced, then the block diagram of the control system is given, the design method of hardware and software is explained, and the experimental conclusion is given finally.

The principle of a brushless DC motor The body of the brushless DC motor is basically a permanent magnet synchronous motor. The three-phase winding of the stator passes the square wave of AC and the rotor is a permanent magnet. The excitation is provided by the permanent magnets of the rotor, and the alternating current in the three-phase windings of the stator generates a rotating magnetic field. The armature magnetic potential and the rotor magnetic potential act together to produce an electromagnetic torque. In accordance with the characteristics of DC motors, if the two magnetic fields are always vertical, the resulting electromagnetic torque is a maximum of 131. Because the rotor is rotating, its magnetic field direction is also rotated, so the stator magnetic field must be changed by controlling the energizing sequence of the three-phase stators. It is essentially perpendicular to the rotor's magnetic field (ie, the torque angle is 90°). In fact, the stator commutation logic has an average torque angle of 90°. First, we should know the current position of the rotor, and then determine the power sequence of the three-phase stator according to the commutation requirements. This is the reason why the brushless DC motor needs the rotor position sensor. In this experiment, the rotor pole position was detected by a Hall element applied on the stator core surface.

The motor adopts Y type connection and three pairs of bridge type inverter circuit drive (). It works in two-phase conduction three-phase six-state mode. The three Hall elements give 60° electrical angular position information, ie they have a 120° pulse width of 180°. The combination of the three Hall elements can give 6 states in one cycle (the other two states generally do not appear), ie a different state is changed every 60 degrees. According to the sensor status information, the six power transistors of the PWM inverter module connected to the three-phase stator are switched on or off in combination with the commutation logic control output, and the torque angle requirement can be satisfied so that the rotor can obtain a stable electromagnetic torque continuously. Since only two phases are conducting at any one time, their currents are equal in magnitude and opposite in direction, so the effect can be considered equivalent to DC current. As a whole, the stator current is a square wave, so long as the commutation of the magnetic pole position of the rotor is performed in a timely manner, this DC driving characteristic can be maintained, and because the commutation is accomplished by an electronic circuit or software instead of a brush, it is called Brushless DC motor.

The relationship between stator three-phase commutation sequence (forward rotation) and the logic output of Hall sensor can be obtained from Table 1 Zll inverter and stator winding wiring 2 Brushless DC motor experiment control Table 1 Sensor signal and commutation logic Guangdong Industry University Journal System Composition TI's TMS320LF2407 is a digital signal processor specifically designed for motion control applications. It contains all the major functional modules required for motor control applications. Not only does it have a 16-bit fixed-point processor core, but more importantly it integrates many common motor control interfaces into one DSP controller. If you have two event managers, including timer and PWM generator can drive two motors, encoder detection circuit can be directly connected to the motor encoder; standard CAN field bus can communicate with the outside world; synchronous and asynchronous string Line ports SPI and SCI can communicate with a variety of standard serial devices; general-purpose bidirectional I() channels and AD conversion interfaces directly capture field data; these make the motor control system implemented with DSP simple and modular. The system hardware basically includes a DSP board with a TMS320LF2407 processing core, an associated power driver board, and a PM50 motor. The main function of each part is 1) DSP board: This is the core part that realizes the motor control. This system program mainly uses the following functional blocks of the DSP: (1) The SCI interface is used to communicate with the host PC.

The AD conversion interface is used to measure the phase current of the motor, 4. The PWM generator is used to generate the desired PWM signal to drive the PWM inverter on the power module.

1 Generates cycles for current and speed control.

Use the QEP unit and Timer2 to connect the output of the encoder signal. The encoder is mounted on the rotor of the motor and is used to measure the position of the motor and differentiate the motor speed.

Use the universal parallel GPIO interface to get the status of the three Hall elements.

2) Power module The power module is the module between the DSP board and the motor. The main function is to receive the PWM control signal from the DSP, collect the feedback signal from the motor, and send it back to the relevant interface of the DSP. Therefore, there are mainly PWM inverter (see), motor power interface, stator current detection, encoder interface and so on.

Stator current detection is performed by connecting resistors in series with the lower arm of the inverter. Convert the stator current to 0. Benefit to the corresponding squadron. After this check, two% of the C phase current can be obtained by wwx =0. The current detection method is relatively simple but requires the software to ensure that the current of the lower arm of the PWM inverter is simultaneously detected when the command of the PWM inverter is output, so as to ensure the correctness of the current detection.

The program stored in the DSP coordinates the functions of each part. The main program continuously calls the data recording module and the monitoring module for serial communication with the host in a circular manner. During the execution of the main program, T1 interrupts occur continuously, and current reading, scaling encoder reading, and speed conversion are handled in the interrupt service routine. It is more important to complete the current control and speed control loop calculations.

It is a system operation block diagram realized in the program according to the control principle. After reading the two-phase current through the ADC04 and ADC05 ports, combined with the rotor pole position information represented by the Hall element obtained from the GPI0 port, the equivalent DC current flow is calculated according to Table 1. The motor needs only one current regulator like the DC motor. Instead of a sinusoidal permanent magnet synchronous motor, two current regulators are required. The voltage commutation module completed by software realizes the calculation of the phase voltage value applied to the inverter. In fact the DSP controller accepts the three-phase voltage and the square wave pulses required by the six full-comparison PWM output inverter modules. At a given location, only two phases are turned on and only the four transistors of the inverter need to be controlled. It can be seen from the above that there are two closed loops in the system. In actual control, the outer loop speed control cycle is 1ms, while the inner loop current control cycle is 0.1ms. This is because the inner loop current changes faster and shorter. The control period can reduce the torque ripple.

3 Experimental Results The experimental device consists of permanent magnet synchronous motor, power module, DSP board, and PC. The servo motor with a 500-line encoder is used to provide the position of the motor. This system differentiates it to obtain the speed information. The basic parameters of the motor are: Phase resistance:. 25-phase inductance: 0.46mH, back-EMF constant: 2. min) Rated voltage: 19.1V, rated current: 1.16A, rotor moment of inertia 9X10-7kg.m2. Speed ​​tracking effect, (a) Waveform of A-phase current (b) is the equivalent/q current waveform calculated from the A and B phase currents.

The actual speed is shown to track the command speed very well, and shows a small tracking error in both positive and negative operations. The current waveform shows that the DSP control system digitally realizes transient and steady-state control of the stator current. 4 Conclusion The superior performance of the brushless DC motor makes it widely used, while the use of DSP to achieve brushless DC motor control is not only more than traditional The analog circuit has low cost and the structure is simple and convenient to expand. DSP's fast computing capability also enables more sophisticated control algorithms. Both the speed and current loops can be digitally implemented to form an all-digital brushless DC motor control system.