DC servo drive based on single chip microcomputer

1 Introduction

DC servo drives are widely used in the fields of industry, medical treatment, and national defense due to their excellent driving performance. The structure of a typical DC servo drive is shown in Figure 1-1. The entire system is a multi-loop control system consisting of a current loop, a speed loop, and a position loop. Traditional servo drives use analog circuits with op amps as the core, which have the disadvantages of complex structure, difficulty in parameter adjustment, and system performance being easily affected by the environment. With the rapid development of microprocessor technology, analog digital interface technology, and power semiconductor technology, modern DC servo drives generally use digital control systems with microprocessors as the core. Servo drives with microprocessors as the core can not only easily implement control algorithms that could not be implemented with analog circuits before, but also have the advantages of simple structure, convenient parameter adjustment, and system performance being insensitive to environmental parameters. At the same time, digital control systems can also make full use of mature network connection technology to achieve multi-machine parallel operation.

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2. Introduction to Chip Features

SPMC752313A is a new member of μ'nSP™ series products, and is a 16-bit microcontroller specially designed for motor drive launched by Sunplus Technology. It has excellent timer and PWM signal generator. It can easily realize various motor servo drive solutions.

SPMC75F2313A has an operating speed range of 0~24MHz within the operating voltage range of 4.5V~5.5V, and has 2K words of SRAM and 32K words of flash ROM; up to 33 programmable multi-function I/O ports; 4 general-purpose 16-bit timers/counters (including a motor drive dedicated PWM waveform generator and a position detection interface timer), and each timer has a PWM event capture function; 2 dedicated timing programmable cycle timers; programmable watchdog; low voltage reset/monitoring function; 8-channel 10-bit analog-to-digital conversion. With the support of these hardware peripherals, SPMC75F2313A has a very good performance in the field of motor control. The characteristics of SPMC75F2313A are as follows:

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3. Introduction to the overall system solution

This servo driver is mainly composed of Lingyang SPMC75F2313A, a power full bridge composed of IRF540 and various interface modules. Its structural block diagram is shown in Figure 3-1. The driver uses a position servo structure with a current loop, in which the position servo loop can be connected to the system as needed. The driver uses a 20KHz bipolar PWM to ensure good dynamic performance of the system.

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The flow of the core service subroutines of each control loop is shown in Figure 5-2. These parts are the core of the entire system, and their performance also determines the performance of the entire drive. Therefore, these parts are written in pure assembly, and the corresponding PID algorithms are also adjusted in structure and optimized in performance according to the characteristics of different control loops. This ensures the performance and real-time performance of these parts of the program to the maximum extent.

Figure 5-2 PWM period interrupt service subroutine flow chart

The system control part is the heart of the whole system coordination. The whole system works in an orderly manner under its coordination. This part mainly gives corresponding control information according to the system settings and the current system status to ensure the reliable operation of the system.

The human-machine interface program mainly provides users with a simple and easy-to-use interactive interface to facilitate users to reliably control the drive. The start and stop of the drive and the setting of various operating parameters are all carried out at this level.

6 Conclusion

Usually, in the process of developing servo drive equipment, it is necessary to write real-time and highly readable code, and then hybrid programming is needed. However, Sunplus' m'nSP™ IDE has a good programming environment, which can easily and easily perform hybrid programming (calling the assembler in the C program and calling the C program in the assembler).

The system uses three timers and about 30 IO port resources of SPMC75F2313A. In fact, the resources of SPMC75F2313A are quite rich. Because it has professional motor drive hardware support, the development of motor drive system becomes relatively simple. Therefore, the motor servo drive system based on SPMC75F2313A has broad application prospects in the fields of industry, medical treatment, national defense, etc.