An AC servo system consists of two parts: an AC servo motor and a controller. Permanent magnet synchronous motors (PMSMs) have become the preferred choice for AC servo motors in CNC machine tools, industrial robots, aerospace, and other applications due to their advantages such as simple structure, small size, light weight, and high power density, and have gained widespread use. The controller, as the core of the servo system, directly affects the operating state of the servo motor. With the application of high-speed digital signal processors (DSPs), servo systems are developing towards miniaturization, digitalization, and intelligence. The goal of this paper is to design a fully digital AC servo system control platform, utilizing the high-speed signal processing capabilities of the DSP to achieve vector control of the permanent magnet synchronous motor. Based on this, various advanced control strategies, such as optimal control and adaptive control, will be tested to assess their application effects in the AC servo system, further improving the system's control performance. PMSM Digital Control Hardware Platform A typical fully digital AC servo system usually consists of the controlled object, servo motor, power module, controller, and measurement and detection modules. Various control strategies and algorithms are implemented by a control system based on the DSP. The system platform adopts a semi-closed-loop control method, and its structural block diagram is shown in Figure 1: [align=center] Figure 1 Semi-closed-loop servo system diagram Figure 2 Servo system hardware structure diagram[/align] The hardware platform design structure diagram is shown in Figure 2, which is divided into two parts: control circuit and power circuit. The control core needs to have high-speed computing power and rich functional modules. Modern DSPs meet these requirements well and realize the digitization of the servo system. The peripheral circuits of the control core include phase detection circuit, JTAG simulation interface, user interface, serial asynchronous communication interface, core power supply, PWM module, digital-to-analog and analog-to-digital conversion circuits, etc. The power part mainly includes inverter, current detection circuit, position and speed detection circuit, protection circuit and auxiliary power supply, etc. DSP56F8346 control circuit DSPs used in control systems are a product of combining traditional DSPs with MCUs (microprocessors). On the one hand, it has the high-speed processor core of traditional DSPs to achieve high-speed computing; on the other hand, it integrates the rich peripheral resources of MCUs, which makes DSP chips the mainstream control chips for modern servo control. Key Features of the DSP56F8346 [align=center]Appendix: Performance Comparison of Two DSPs[/align] The appendix compares the performance of the TI TMS320LF2407A and the Freescale DSP56F8346, both commonly used in servo systems. The comparison shows that the Freescale DSP56F8346 is more suitable for AC servo systems with high real-time performance and control precision requirements, demonstrating a higher cost-performance ratio. JTAG Emulation Interface Another advantage of the Freescale DSP8346 compared to other companies' DSP products is that Freescale's 56800/E series DSPs require very few, if any, additional functional modules for development, meaning no dedicated emulator is needed. Using JTAG requires almost no hardware support; connecting to a PC only requires a 5V to 3.3V level conversion. Ideally, optocoupler isolation should be used to isolate the power supply of the host computer's parallel port and the DSP, ensuring the safety of both. Therefore, a small optocoupler isolation circuit board was specifically designed for the JTAG interface, and the D/A conversion circuit discussed later is also implemented on this circuit board. This simple interface enables online program debugging and simulation, and allows the program to be downloaded to the DSP chip. User Interface To facilitate on-site debugging and experimental verification, a user interface was designed to connect to the motion controller or motion control board via the DSP's I/O ports and counter interface. The motion controller issues command pulses, start, stop, reset, and other signals. The command pulses include two signals: PLU and DIRT. PLU provides a series of pulses, where the number of pulses represents the distance traveled and the pulse frequency represents the speed. The DIRT signal uses high and low levels to indicate the direction of motion. Figure 3 shows the selected motion controller, SC100: [align=center] Figure 3 SC100 Motion Controller[/align] This motion controller is freely programmable, has a rich instruction set, and can execute various unidirectional, cyclic, reciprocating, and delayed actions. Speed, length, and acceleration can be arbitrarily set. It uses opto-isolation, has strong anti-interference capabilities, and features an LCD display to show corresponding commands and data, making it a powerful device. This system uses this controller as the position and speed input, achieving excellent results. The DSP56F8346 has two SCI serial communication modules. The host computer control program is written in VBScript using the PC Master software included with CodeWarrior, and communicates with the DSP via RS232. The PC Master provides a user-friendly interface, easily enabling real-time motor control and displaying the required electrical parameters or test waveforms. The D/A conversion circuit in this design consists of the DSP's SPI port and a Maxim Integrated D/A conversion chip, MAX5251, providing 10-bit, 4-channel D/A conversion. The circuit diagram is shown in Figure 4: [align=center] Figure 4 D/A Circuit Schematic[/align] The core power supply, the DSP, has high requirements for power supply stability. Unstable power supply voltage will cause DSP instability, making the program prone to crashing, and more seriously, shortening its lifespan or even damaging it. The DSP's I/O power supply is a digital 3.3V, generated by a digital 5V supply from an auxiliary power source via a low-output-dropout voltage regulator module, TPS76833. The ADC's analog 3.3V power supply is generated by a TPS7333. To monitor the DSP's power supply online, a power management chip, TPS3823-33, is used. When the digital 3.3V voltage drops below 2.93V, the TPS3823-33 sends a reset signal to automatically reset the DSP. This chip also has a manual reset function. Power Main Circuit The power main circuit uses a full-bridge uncontrolled rectifier. The output, after filtering capacitors, serves as the bus voltage for the three-phase bridge inverter, i.e., an AC-DC-AC structure. Inverter Circuit The inverter 's frequency conversion circuit uses a Cyntec intelligent power module, IM23400. This IPM can drive a 2.2kW/220V motor, with a typical switching frequency of 15kHz. The internal integrated functions include: a drive circuit, a bootstrap circuit powered by a single power supply, short-circuit protection, undervoltage protection for the control power supply, and an error signal logic output circuit. The module integrates drive and protection circuits, making the circuit simple and reliable. The six PWM signals from the DSP are sent to the IPM drive circuit via high-speed optocoupler isolation, while a braking signal is output from another I/O port to control the switching transistor of the energy-consumption braking circuit, i.e., the brake signal. An overcurrent detection resistor shunt is connected between the IPM's N pin and ground to provide overcurrent protection for the IPM. The circuit is shown in Figure 5: [align=center] Figure 5 Inverter IPM peripheral diagram[/align] Here, fo (fault output) is the error protection signal, which is input to the enable pin of the three-state linear drive/receiver 74HC244 via optocoupler isolation, realizing the system's hardware protection. Current Detection Circuit The function of the current detection circuit is to filter, adjust the amplitude, bias the voltage, and limit the signal obtained from the current Hall sensor before sending it to the DSP's AD conversion interface. This circuit uses a domestically produced Hall current sensor, CSM025NPT, to detect the current. It employs the Hall effect closed-loop principle, with a linearity εl < 0.1%, response time tr < 500ns, and bandwidth of DC ~ 200kHz, fully meeting the system requirements. The downstream stage of the Hall current sensor is an AD conditioning circuit, which reflects the current change range as a voltage range of 0 ~ 3.3V, satisfying the voltage input range of the DSP's AD pin, thus forming a current closed loop. Position and Speed ​​Detection Circuit The goal of the servo system is to quickly and accurately follow a given position or speed, thus requiring closed-loop position and speed control. The encoder interface receives incremental position sensor signals (A, B, Z) and Hall element signals (Halla, Hallb, Hallc) from the non-power output end of the motor. After filtering, these signals are input to the DSP's phase detector and three general-purpose I/O ports. Based on the six states of the three Hall elements, the rotor's stationary position is determined. An algorithm is used to achieve the initial positioning of the motor rotor, thereby emitting a corresponding voltage vector to start the motor. The z-signal provides the reference position point. When the rotor passes the z-position for the first time, the position is corrected, and the actual motor vector control begins. The rotation direction and speed of the motor rotor are obtained from the phase relationship and frequency of the a and b signals. The DSP captures the rising and falling edges of the a and b pulse sequences, achieving a fourfold frequency multiplication of the encoder pulses, which improves positioning accuracy. Its waveform is shown in Figure 6. The counter counts its pulses to obtain the position of the motor rotor. [align=center] Figure 6 Encoder Output Signal[/align] Protection Circuit The system samples the three-phase current and bus voltage of the motor. Since the three-phase currents are sinusoidal quantities with a 120° phase difference, their sum is zero. Only two phases need to be detected to determine the current of the other phase. The sampled value is compared with the set value by a comparator, and a protection signal is output. Different colored LEDs are used to represent different error protection signals. The undervoltage signal is implemented via software sampling of the bus voltage. The overcurrent protection signal and overvoltage protection signal are ORed and input to the enable pin of the MC74HC244. When a protection condition occurs, all PWM outputs of the MC74HC244 are disabled. Simultaneously, this protection signal is input to the fault pin of the DSP. By configuring the corresponding register, the DSP's PWM output is disabled, achieving dual hardware and software protection. Auxiliary Power Supply The entire system requires multiple DC power supplies of different voltage levels. For example, the DSP control circuit and AD conditioning circuit require a digital 5V power supply, the SCI communication interface, encoder interface, and user interface require another analog 5V power supply, and the IPM inverter requires a +15V drive power supply, etc. Therefore, this system uses a flyback circuit as a multi-output auxiliary power supply. Figure 7 shows the designed AC servo hardware platform. [align=center]Figure 7 AC Servo Hardware Platform[/align] Conclusion This design uses the DSP56F8346 as the main control chip, fully utilizing its high-speed computing power and abundant on-chip resources. Combined with an intelligent power module, this not only makes the entire hardware platform simpler but also greatly improves reliability. The application of the high-performance DSP also provides a foundation for the implementation of various advanced algorithms. Experiments have shown that the hardware circuit works normally and has high reliability.