Power drive module
In a control system, the control signal cannot directly drive the actuator, the motor, because it does not provide enough power for the motor to operate. The control signal must pass through the power amplifier unit to drive the motor. It can be said that the power amplifier component turns the power supply having a fixed voltage into an energy source controlled by the control signal, and the voltage, current or other parameters vary with the control signal. There are three types of DC power amplifiers that are the most widely used in servo systems: linear (proportional) power amplifiers, switching power amplifiers, and thyristor power amplifiers. The switching power amplifier is modulated by a pulse width modulation converter, which is called a PWM modulation method.
1. PWM speed principle
The PWM drive uses the switching characteristics of high-power transistors to modulate the fixed voltage of the DC power supply, turn it on and off at a fixed frequency, and change the length of the "on" and "off" times in a cycle as needed. The speed of the motor is controlled by changing the "duty cycle" of the voltage on the armature of the servo motor to change the magnitude of the average voltage. Figure 3 shows the PWM control schematic.
2. current detection circuit
The stator three-phase motor of the motor is tested by a chip IR2277 produced by IR Company to detect the phase current in the motor controller. The chip has a signal terminal that is synchronized with the DSP. The stator current is detected by the chip, and is output to the AD converter of the DSP, and the current of the two phases is detected, thereby obtaining the information of the three-phase current of the stator. The figure shows the block diagram of the motor control system.
3. speed detection circuit
The speed is detected using an incremental photoelectric encoder. It outputs two square wave signals A and B with a phase difference of 90 degrees, and non-signal PA, PB and zero pulse PZ signals. The photoelectric encoder is detected by the orthogonal coding unit of the event manager in the control system, and A and B are respectively connected to the two channels QEP1 and QEP2 of the orthogonal decoding pulse unit. The quadrature decoding pulse unit QEP has a direction detecting function whose direction detecting logic discriminates which of the two sequences is a preamble sequence, and then can generate a direction signal as a direction input of the selected timer. Note that both edges of the two columns of quadrature input pulses are counted by the quadrature decoding pulse unit, thus producing a clock frequency that is four times that of each input sequence.
4. Conclusion
The control structure of DSP is adopted in the hardware of the system. The current design is simple and compact, which can meet the requirements of system vector control. At the same time, the full digital control can greatly improve the control accuracy, function and anti-interference ability of the system. From the control algorithm of the typical closed-loop control system, the analog circuit is difficult to implement complex control algorithms. The walking robot has higher requirements on the drive system. Therefore, the DSP-based all-digital motor control system is selected, and the chip used is fast. High bit number, large on-chip memory capacity, special motor control module and CAN bus communication function, with A/D conversion module, which satisfies the control requirements.
