Design of steering gear control circuit based on IPM module

The insulated gate bipolar transistor (IGBT) is a device composed of a bipolar transistor and a MOSFET. It has both the gate voltage control fast switching characteristics of the MOSFET and the large current handling capability and low saturation voltage drop of the bipolar transistor. Compared with the IGBT module, the IPM module has the following features: built-in drive circuit, overcurrent protection, short circuit protection, control power undervoltage protection, overheating protection and external output alarm. This article uses the IPM module PM25RLA120 of Mitsubishi Corporation of Japan and the motor control chip UC1637 of TI Corporation of the United States for electric servo control.

1 Design Principle
The servo control principle block diagram is shown in Figure 1.

The servo is a position servo driver. Its working principle is: the control signal is compared with the servo position feedback signal to obtain a DC bias voltage. The bias voltage enters the signal modulation chip to generate a comparison level. After passing through the PWM control chip UC1637, a PWM signal with a certain duty cycle is output to drive the on and off of the IGBT in the IPM circuit, thereby realizing the control of the electric servo position.

2 Servo control system circuit
2.1 Control circuit with UC1637 as the core
UC1637 is a chip designed by TI for DC motor control. This chip is used to replace the usual drive circuit. It contains a triangular wave generator, an error amplifier, a pulse width modulator, an undervoltage protection, and an overcurrent protection circuit, which improves the integration of the motor control circuit and the reliability of the system. The servo control circuit receives the steering signal sent by the control computer, compares it with the servo feedback signal, corrects and amplifies it, and then compares it with the triangular wave signal of a certain frequency and amplitude. The signal is input into UC1637, and an analog error voltage signal is generated in the chip, and two PWM control signals with different polarities are output to achieve the purpose of controlling the servo to produce different steering angles. The UC1637 control circuit is shown in Figure 2. MC2 is the triangle wave output signal, M12 is the UC1637 input control signal, A02 and B02 are the output control signals. The two control signals are photoelectrically isolated to control the on and off of different circuits of the IPM module to control the operation of the servo.

2.2 IPM module drive circuit
The IPM module drive circuit is the interface between the internal circuit of the IPM module and the control circuit. A good external drive circuit is of great significance to the operating efficiency, reliability and safety of the system composed of the IPM module. The device itself contains a drive circuit. Therefore, it is sufficient to provide a PWM signal that meets the drive power requirements, a drive circuit power supply and an electrical isolation device to prevent interference. The peripheral drive circuit of the IPM module PM25RLA120 is shown in Figure 3.

M25RLA120 requires 4 non-common +15 V power supplies. M57140 is a voltage conversion module specially configured by Mitsubishi for its IPM series products, which provides 4 non-common +15 V power supplies for the IPM module. The PWM control signals A02 and B02 output by UC1637 are sent to the input end of the IPM module through the high-speed optocoupler HCPL-0466. The circuit structure of the 6 input signals is the same. The servo controlled here is a DC motor, so only 4 input signals are drawn in the figure. The high-speed optocoupler plays the role of electrically isolating the IPM from the external circuit.

3 Conclusion
The actual operation and debugging results show that the servo control circuit based on the IPM module has the advantages of high integration, fast response speed, and strong driving ability. It greatly improves the reliability of the servo control circuit and reduces the volume of the control system, reduces product costs, and has good application prospects.