[Abstract] This paper introduces a dual-CPU PMSM position servo system based on DSP and IRMCK201, focusing on the system architecture and hardware/software design scheme. Experimental results show that the hardware/software design is reasonable, with good real-time performance, high control accuracy, and good dynamic performance. Furthermore, this AC servo scheme boasts superior performance, simple design, minimal programming workload, and short development cycle, and can also be used in other AC servo control systems, making it highly valuable for widespread application.
Permanent magnet servo motors (PMSMs) possess unparalleled advantages over other motors, including low rotor inertia, fast response speed, high efficiency, high power density, small size, reduced noise due to brush elimination, and reduced maintenance. In the field of high-performance position servo systems, servo systems composed of PMSMs are increasingly widely used. PMSMs come in two forms: square wave and sine wave. This paper primarily studies servo systems using PMSMs as servo motors. Currently, the control of permanent magnet synchronous motors mainly employs three approaches: DSP, DSP+FPGA, and DSP+ASIC. The first two methods require significant programming for position control. To address the requirements of high-performance AC servo drives, International Rectifier (IRMCK201) has developed a complete closed-loop current control and speed control servo system single-chip solution based on FPGA technology. Based on this digital motion control chip, this paper designs an AC servo control system using DSP and IRMCK201. This system also boasts advantages such as superior performance, simple structure, minimal programming workload, and short development cycle, making it highly promising for widespread adoption.
1IRMCK201 Chip Introduction
To address the need for high-performance AC servo drives, International Rectifier (IR) has designed a complete servo drive control solution based on FPGA technology—the IRMCK201 chip. Unlike traditional motion control-specific DSP chips, the IRMCK201 not only includes peripheral functions for motion control (such as PWM, encoder counting circuits, and current sensing interfaces), but also hardware-implemented FOC and speed control algorithms, thus eliminating the need for programming and simplifying the design of high-performance AC servo systems. Furthermore, it is suitable for various types of permanent magnet motors or induction motors, thus showing great application potential.
The main features of the IRMCK201 chip are as follows: ① Complete current closed-loop control and speed closed-loop control; ② Space vector PWM with dead time; ③ Maximum clock input 33.3MHz, maximum PWM carrier frequency 83.3kHz, current loop bandwidth 5.5kHz, speed loop update rate 5/10kHz; ④ Interfaces with high-voltage linear current sensor IR2175, high-voltage driver chip IR213x, Hall A/B/C signals, photoelectric encoder, RS232 or RS422, and fast SPI; ⑤ Configurable photoelectric encoder line count range of 200PPR～10000PPR; ⑥ Can monitor DC bus voltage; ⑦ Can be configured with analog reference input; ⑧ 2MHz counter improves low-speed performance; ⑨ Has a 4-channel sample/hold A/D conversion interface; ⑩ The AT24C01A can initialize internal data/parameters through the host register interface; ⑩ Intelligent IGBT protection blocking control. As can be seen from the above, as a motion control chip, the IRMCK201 possesses the necessary control units for servo control in its hardware, such as space vector PWM with dead-time setting, PARK and Clark transforms, current loop PI regulators, speed loop PI regulators, and speed measurement units. This saves users the task of writing code and simplifies the complex design process.
2 System Implementation
The control circuit of this AC servo system mainly consists of a TMS320LF2407, an IRMCK201, and a small number of peripheral circuits. The TI DSP TMS320LF2407 is used as the main control chip, responsible for processing the servo motor position loop, starting and stopping the motor, responding to keyboard inputs and displaying data, and initializing the IRMCK201. The internal hardware circuitry of the IRMCK201 handles the system's current and speed loop control, ultimately generating SVPWM drive signals to control the switching of the power module. It also monitors the bus voltage via an A/D interface to provide overvoltage protection. The system uses a 2000PPR incremental photoelectric encoder and a Hall effect sensor to measure motor position and speed signals, and an IR2175 current sensor to sample the phase current. Since the IRMCK201 provides an IR2175 interface, the sampled current signal can be directly sent to the IRMCK201 as current feedback for the control section. To enhance the system's anti-interference capability, a high-speed optocoupler is used to isolate the control and power sections of the system. The main circuit consists of a three-phase bridge full-wave rectifier circuit, filters, and inverters. The system hardware design block diagram is shown in Figure 1.
3 System Hardware Design
3.1 Position ring design
The vector control system for a permanent magnet synchronous motor requires precise rotor pole position and speed information for adjusting the control voltage. To improve the accuracy of the control system, a hybrid photoelectric encoder can be used as the rotor position detector. This system uses a hybrid photoelectric encoder, outputting six signals (A+, A-, B+, B-, Z+, Z-). After filtering, to improve the anti-interference capability of the feedback signal, the signals are sent to an orthogonal linear receiver DS3486, finally outputting digital signals A+, B+, and Z+ related to speed, direction of rotation, origin position, and relative angular displacement. The output three signals (HALLA/B/C) provide the initial precise positioning and initial absolute position of the motor rotor. A hybrid photoelectric encoder is used to sample the position of the servo motor to obtain the position feedback signal. The position feedback signal is sent to the event management module of the TMS320F2407A for post-processing. The event management module has an orthogonal decoding pulse circuit (QEP circuit). When the QEP circuit is enabled, it decodes and counts the orthogonal encoded input pulses on pins QEP1 and QEP2. This method of position detection requires no additional external circuitry, resulting in a simple and reliable circuit. As can be seen from the above, the hardware design of the position loop is simple and reliable. In this system, the position loop design is primarily implemented in the DSP using simple software, which will be described in detail in the software design section.
3.2 Speed Loop Design
The A and B signals output from the photoelectric encoder are two pulse sequences with a 90° difference between them. The motor speed and direction of rotation can be calculated from these two signals. A hybrid photoelectric encoder is used to sample the servo motor speed to obtain a speed feedback signal. This speed feedback is directly fed into the IRMCK201 chip for speed closed-loop processing. The speed loop is mainly handled by the IRMCK201; by setting the corresponding value in the IRMCK201 speed loop register, speed closed-loop can be achieved. Therefore, it can be seen that the speed loop design is entirely hardware-based, requiring no software design and saving a significant amount of work.
3.3 IR2175 and Hall Current Sensor to Implement Current Loop
The IR2175 is a monolithic linear current sensor designed for motor drive applications. When implementing a servo system using the IRMCK201 chip, current feedback is achieved using a sampling resistor combined with the IR2175 as the current feedback loop. The sampling resistor samples the phase current of the servo motor, outputting a sampling voltage signal within 260mV. This signal is input to the IR2175 current sensor, which processes it internally and outputs a pulse signal whose duty cycle changes with the current amplitude. This pulse signal is then opto-isolated and sent to the IRMCK201 as the current feedback signal for the servo motor. Since the input voltage of the IR2175 is limited to ±260mV, the maximum current in the main circuit is limited when the sampling resistor is constant, thus limiting the system's power level and making it difficult to implement a high-power servo system. In this solution, a Hall effect current sensor combined with a sampling resistor and the IR2175 is used to address the power level limitation, ultimately enabling a high-power position servo system. A Hall effect current sensor (selected according to power rating requirements) is used to sample the motor phase current. The output is connected to a sampling resistor to obtain a voltage between ±260mV. This voltage is used as the input to an IR2175, and the output of the IR2175 is fed into an IRMCK201 for calculation via an optocoupler. A schematic diagram of one current feedback circuit is shown in Figure 2.
3.4 Communication Interface Design between DSP and IRMCK201
The lower 8 data lines of the DSP are connected to the 8 parallel data lines of the IRMCK201, which is used as the peripheral interface expansion chip of the DSP. The I/O space selection signal and the three high-bit signals of the parallel port are decoded by GAL to serve as its chip select signal.
During motor operation, the DSP needs to access and configure the registers of the IRMCK201 in real time, thus requiring high reliability and speed in their communication. This solution uses a parallel port approach, employing GAL16V8B decoding to achieve accurate and reliable communication between the DSP and the IRMCK201. Figure 3 shows the communication interface circuit between the DSP and the IRMCK201.
4 System Programming
Since the current loop, speed loop control, and overcurrent, overvoltage, and undervoltage protection functions of the system are all implemented by the internal hardware of the IRMCK201, the system software mainly uses a DSP to implement the control of the AC servo system's position loop and communication with the IRMCK201. In comparison, the program design is relatively simple. As a position servo system, the following three requirements must be guaranteed in positioning control: positioning accuracy, requiring zero steady-state error; positioning speed, requiring the system to have the highest possible dynamic response speed; and no overshoot in the system's position response. In this system, the position loop adopts feedforward control: control is performed according to a given change. When the given change occurs, the regulator immediately controls the controlled parameter according to its nature and magnitude, so that the controlled variable can follow the change of the given value in a timely manner, greatly reducing control lag. After introducing feedforward control into the servo system, the equivalent structure of the position loop controller transfer function model of the permanent magnet AC servo system is shown in Figure 4. Adding a feedforward compensation element to the proportional regulator, where KPP is the position loop proportional coefficient, KPR is the feedforward coefficient, and TR is the feedforward filter time constant, this structure can meet the performance requirements. Adding a low-order filter to the feedforward stage can effectively suppress fluctuations and reduce overshoot.
After the motor parameters are measured, appropriate controller parameters can be selected based on the actual needs of the motor. By adopting feedforward control, the position tracking lag error can be reduced to approximately 20%, thereby significantly improving position control accuracy. The position loop interrupt handling subroutine is shown in Figure 5.
5. Experimental Waveforms and Conclusions
The motor used is a surface-mount permanent magnet synchronous motor. Figure 6 shows the position following curve without feedforward, Figure 7 shows the position following curve with feedforward control, and Figure 8 shows the motor's speed response curve after the position is given. Experiments show that the position feedforward control system achieves a fast dynamic response while ensuring high positioning accuracy and no overshoot.
This system utilizes the IRMCK201 chip, combined with TI's TMS320LF2407 DSP chip, significantly simplifying the system's hardware and software design, shortening the development cycle, and improving reliability, thus achieving a high-performance AC servo system. This system has been successfully applied to elevator door operator servo systems and power servo systems. Practice has proven that this position servo system is reliable and high-performance. With corresponding modifications, this position servo system can be applied to other servo systems, making its application scenarios very wide.
References
1. Guo Qingding, Wang Chengyuan. AC Servo Systems [M]. Beijing: Machinery Industry Press, 1994;
2. ToshioTakahashi.HighPerformanceACDrivebySingleChipMotionControlEngineIC.IRCorporation, 2003;
3.IRCorporation.IRMCK201DataSheet,2003;
4.IRCorporation.IR217xDateSheet,2003;
5. Han Antai, et al. DSP Controller Principles and Their Applications in Motion Control Systems [M]. Beijing: Tsinghua University Press, 2003;
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
