Abstract: A high-performance, fully functional, all-digital AC servo system for a permanent magnet synchronous motor (PMSM) was developed using digital signal processors (DSPs), large-scale programmable gate arrays (CPLDs), and intelligent power modules (IPMs), with rotor field-oriented vector control and voltage space vector pulse-width modulation (SVPWM) technology as the core control algorithms. Experimental results show that the AC servo system has fast response speed and high stiffness, meeting industrial requirements. Keywords: digital; PMSM; vector control; SVPWM [align=center][b]Design of PMSM Digital Servo System AN Jiao, HU Xiehe, HU Haiyan[/b][/align] Abstract: A PMSM digital servo system based on DSP TMS320LF2407, CPLD and IPM was introduced. Field-oriented Control (FOC) method and Voltage Space Vector PulseWidthModulation method were adopted in the system. The experimental results veri2fies that the fast response and accuracy meet the industrial needs. Keywords: Digital; PMSM; FOC; SVPWM 0 Introduction With the rapid improvement of computer technology, electronic technology, communication technology and control technology, permanent magnet synchronous motor servo systems with full digital control have gradually replaced traditional stepper servo, DC servo and AC servo systems with analog control, becoming the mainstream of contemporary servo control, and are widely used in high-precision CNC machine tools, robots, special processing equipment and precision feed systems[1]. The authors of this paper use the TI TMS320LF2407 DSP chip, which is dedicated to motor control, to implement the PID real-time tracking technology of vector transformation control current loop, speed loop and position loop in software; Mitsubishi's intelligent power module IPM is used as the power conversion device; with the addition of a simple operation panel and other necessary peripheral circuits, a complete permanent magnet synchronous motor all-digital AC servo system is formed. 1 System Design Specifications The main technical specifications of the all-digital AC servo system with DSP as the core are as follows: (1) Command input mode: pulse train input mode, digital input mode, analog input mode; (2) Working mode: position, speed and torque control mode; (3) Speed ​​ratio: 1:5000; (4) Response time ≤20ms; (5) Maximum speed: 3000 r/min, rotational positioning accuracy 1/10000 r; (6) Protection: automatic protection against overcurrent, overvoltage, undervoltage, motor stall, stall, overload, position deviation and other issues. 2 Regulator Design The AC servo system adopts position loop, speed loop and current loop control[2] to ensure the high performance and high reliability of the servo system. All control operations in the servo system are completed by DSP. Current regulation is achieved by adjusting the armature current, that is, adjusting the IGBT duty cycle. The relationship between armature current and IGBT duty cycle is[3] [img=127,64]http://www.chuandong.com/uploadpic/THESIS/2009/5/2009051112281954491W.jpg[/img] Where: I0 is the average load output current; D is the chopper duty cycle; R is the armature resistance; E is the motor back EMF; Ud is the DC voltage. The three-phase PWM circuit in the DSP chip can easily generate the required IGBT duty cycle modulation signal[4]. It can be achieved by setting the PWM switching frequency, dead time, minimum pulse width and compensation time through software. The IGBT duty cycle adjustment flowchart is shown in Figure 1. [img=284,225]http://www.chuandong.com/uploadpic/THESIS/2009/5/2009051112300174288W.jpg[/img] Figure 1 IGBT Duty Cycle Adjustment Flowchart 3 System Hardware Design Scheme The system design is based on TI's TMS320LF2407 (DSP), a new generation microcontroller specifically designed for motor control. It features a high-performance C2XLP core, an improved Harvard architecture, and four-stage pipelined operation. The on-chip integrated event managers EVA and EVB each include three independent bidirectional timers, supporting the generation of programmable dead-time PWM outputs. Two of the four capture ports can be directly connected to orthogonal encoding pulses from photoelectric encoders. Two independent 10-bit eight-channel A/D converters can simultaneously and in parallel complete the conversion of two analog inputs. The on-chip integrated serial communication interface (SCI) and serial peripheral interface (SPI) can be used for communication with the host computer, peripherals, and multiprocessors. The 40 independently programmable multiplexed I/O ports can be configured as keyboard input and oscilloscope display input/output ports. These features of the TMS320LF2407 provide a feasible solution for motor control. 3.1 System Board Design The servo driver system board mainly consists of a DSP minimum system, position and speed detection circuits, current detection circuits, and communication modules. The TMS320LF2407 minimum system consists of a DSP chip, a 313V power supply, a 20MHz crystal oscillator, an external 64K static RAM, and external wiring pins. The system can be connected to an emulator via a JTAG interface for online debugging. A composite incremental photoelectric encoder is used as the position detection device, with six output signals: two are orthogonal A and B pulse signals, one is a zero-position detection pulse signal Z, and the other three are Hall position signals U, V, and W with a 120° phase difference. This effectively solves the problem that incremental photoelectric encoders cannot provide initial absolute position. The three Hall signals can have 6 states, each representing a 60° electrical angle. When the system is powered on, the three Hall signals can provide the 60° position range of the rotor. In order to reduce the error, the middle value of each position is taken as the initial position of the rotor. In this way, when the motor starts, the conduction angle and the actual rotor position have an error of up to 30° electrical angle. After theoretical analysis and experimental proof, in the worst case, the motor can generate enough torque to start. During normal operation, the relative angular displacement of the rotor can be obtained by accumulating the orthogonal A and B pulse signals. The motor speed is calculated by calculating the change in position per unit time. The method of 4 times frequency is used to improve the positioning accuracy of the photoelectric encoder. The orthogonal pulse coding (QEP) circuit in the event management module of TMS320F2407 can perform 4 times frequency decoding and calculation on the two pulse signals generated by the incremental photoelectric encoder [4], thereby realizing the reading of the rotor position and speed information of the motor in the rotating working state. The encoder signals A and B are directly connected to the QEP1 and QEP2 pins of the DSP after being denoised by the CPLD. The main circuit current signal is detected by a Hall element with a transformation ratio of 1:1000. The TMS320LF2407 has two 10-bit A/D converters, each of which can connect to 8 analog signals. The A/D input signal range of the TMS320LF2407 is 0 to 5V. The small current signal output by the Hall is first converted into a voltage signal, and then amplified and filtered before entering the A/D channel inside the DSP for feedback control. Only two current signals need to be detected to control the motor current [4]. The traditional analog control interface of the servo drive is easily affected by external signal interference and has a short transmission distance. The pulse control interface currently widely used in servo drive devices in my country is not a true digital interface. This interface is limited by the pulse frequency and cannot meet the requirements of high-speed and high-precision control. The TMS320F2407A includes a high-speed C2XXDSP CPU core and an SCI communication module, which provides convenience for real-time communication. The system uses SCI for the design of the control interface [4]. [img=447,345]http://www.chuandong.com/uploadpic/THESIS/2009/5/20090511123031963549.jpg[/img] Figure 2 Communication hardware interface diagram As shown in Figure 2, MAX3223 is used for level conversion. The communication between TMS320LF2407 and PC adopts a three-wire system. During communication, both parties are regarded as terminal devices and full-duplex mode is adopted. 3.2 Main Circuit Design [img=401,369]http://www.chuandong.com/uploadpic/THESIS/2009/5/2009051112332523110F.jpg[/img] Figure 3 Main Circuit The main circuit mainly consists of rectifier and filter circuits, Mitsubishi's intelligent power module IPM (PS212552E), switching power supply, protection circuit, etc. The IPM module encapsulates six IGBTs together to form a three-phase full-bridge inverter circuit. It is small in size and light in weight, and has an internal drive circuit. It is designed with overvoltage, overcurrent, overheat, and undercurrent protection circuits. The DSP output PWM signal is input to the input terminal of the IPM through opto-isolation; fault signals such as overcurrent, overvoltage, overheat, overload, encoder feedback disconnection, and communication failure are also isolated and sent to the DSP. When a fault signal occurs, the DSP immediately blocks the PWM output, thereby ensuring safe operation. The main circuit design is shown in Figure 3. 4. System Software Design The TMS320LF2407 DSP supports C language programming and mixed programming, and has a JTAG interface. The written program can be easily debugged using a simulator and TI's CC2000 simulation software. To improve the real-time performance of the control, the software uses interrupt services to implement AD conversion, QEP capture, and PI regulation. [img=396,284]http://www.chuandong.com/uploadpic/THESIS/2009/5/20090513212818831333.jpg[/img][align=center] Figure 4 [/align][img=401,402]http://www.chuandong.com/uploadpic/THESIS/2009/5/2009051112483232662V.jpg[/img] Figure 5 The system software works as follows: DSP initialization, including GPIO, ADC, EV, then core interrupts are enabled; the initial position of the rotor magnetic poles is determined using U, V, and W signals, then the PWM signal is triggered to make the motor rotate; after obtaining the Z signal, the system enters the main loop. The DSP samples the phase current in each PWM cycle and performs current adjustment; when the current loop cycle count value is equal to the given value, speed adjustment is performed. The main program of the system is shown in Figure 4. The main loop performs communication between the host computer and the DSP, as shown in Figure 5. 5. Physical Experiments The parameters of the motor used in the experiment are listed in Table 1. Figure 6 shows the speed step response characteristics when the target speed is 200 r/min under no-load conditions. Figure 6 shows that the response time is 10ms, the steady-state error is less than 1%, and the maximum overshoot is less than 5%, indicating that the system has good dynamic performance. Figure 7 records the system stability test process. At 115 s, the system was suddenly subjected to a 50% load, and it can be seen that the system quickly recovered to a stable state. Figure 8 shows the results of the system following performance test. With the system at zero speed, a step command corresponding to the rated speed was input, showing that the system has a fast response speed and excellent following performance. In the position following test, by inputting pulse commands of different frequencies (0 < F < 500kHz) and observing the position offset pulse monitor on the system panel operator, it can be seen that the positioning accuracy of the system is ±1 pulse. [img=202,144]http://www.chuandong.com/uploadpic/THESIS/2009/5/20090511124950371128.jpg[/img]Figure 6 Speed ​​Response Curve[img=332,193]http://www.chuandong.com/uploadpic/THESIS/2009/5/2009051112524561409Q.jpg[/img] 6 Conclusion The AC servo system composed of a permanent magnet synchronous motor, DSP, CPLD, IPM, and photoelectric encoder has the advantages of simple hardware structure, high reliability, high control accuracy, and fast dynamic response. The current loop sampling frequency can reach above 10kHz, providing sufficient bandwidth to achieve a high-precision, fast-response servo system. Experiments show that all indicators of this vector control system meet the engineering design requirements and have good dynamic performance. References [1] Wang Jian. Overview of modern AC servo system technology and market development [J]. Servo Control, 2007 (1). [2] Guo Qingding, Wang Chengyuan. AC Servo System [M]. Beijing: Machinery Industry Press, 1994. [3] Liu Nianzhou, Liu Xiaolin, Wang Jianqiang. Design of permanent magnet synchronous motor control system based on DSP [J]. Marine Electrical Technology, 2004 (2). [4] Liu Heping, Yan Liping, Zhang Xuefeng, Zhuo Qingfeng. Structure, principle and application of TMS320LF240XDSP [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 200213.