Servo technology is a crucial pillar of modern industry. With its continuous development in recent years, AC servo technology has gradually replaced traditional DC servo technology in many applications. The three-phase AC permanent magnet synchronous motor (PMSM) is a type of AC permanent magnet servo motor. With the improvement in permanent magnet performance and the decrease in price, and the advantages brought by replacing the excitation windings in wound rotors with permanent magnets—such as no rotor overheating, simpler control systems, higher operating efficiency, and higher operating speeds—it has gained widespread application in low-power applications such as CNC machine tools and robots. As modern industry continues to demand precision, high speed, and high performance, traditional controllers are no longer sufficient for high-requirement applications. In many applications requiring high real-time performance and high efficiency, dedicated digital signal processors (DSPs) are necessary to replace some functions of traditional controllers. The unique rapid calculation capabilities of DSPs are particularly evident when control algorithms are complex or require improvement and optimization. Furthermore, with the advancement of integrated circuit manufacturing technology and the development of power electronics technology, AC servo technology has also made significant progress. The intelligent power module, integrating three-phase inverter, protection circuit, isolation circuit, and energy-saving braking circuit functions, along with advanced power electronic devices, makes AC servo control more convenient, consumes less power, has shorter switching time, a wider frequency range, and superior performance. These advantages make AC servo significantly superior to DC servo. System Overview The hardware of the AC servo digital system uses a DSP as the signal processor, a rotary encoder and a current sensor to provide feedback signals, and an intelligent power module (IPM) as the inverter. Signals from the sensors are filtered and shaped before being fed back to the DSP for calculation. The DSP processes the reference and feedback signals to adjust the current loop, speed loop, and position loop of the servo system. Finally, the output PWM signal drives the isolated IPM module to achieve closed-loop servo control of the motor. The system hardware structure is shown in Figure 1. [align=center] Figure 1 Hardware Structure Diagram[/align] The system uses a three-loop control method: position control is the outer loop, which is also the final target; speed control is the middle loop; and current control is the inner loop. To ensure dynamic response speed and prevent oscillations during positioning, both the current loop and speed loop employ PID regulation, while the position regulator uses PI regulation. The system control block diagram is shown in Figure 2: [align=center] Figure 2 Control System Block Diagram[/align] The actual rotor position signal detected by the encoder is compared with the system's given position signal. The difference is then adjusted by the PI regulator to output a rotor speed command signal. This command speed signal is then compared with the actual speed signal detected by the encoder. The difference is adjusted by the speed regulator to output a given current command value, which is then compared with the actual current feedback value for PWM control. Vector Control In synchronous motors, the spatial angle between the excitation magnetic field and the armature magnetomotive force is not fixed. Therefore, adjusting the armature current cannot directly control the electromagnetic torque. By using an external control system for the motor, spatial orientation control is performed on the armature magnetomotive force relative to the excitation magnetic field, maintaining a fixed angle between them. Simultaneously, the amplitude of the armature current is also controlled. This control method is called vector control. Vector control essentially controls the three-phase current of the armature by controlling the current along the two-phase rotor reference coordinate dq axis. This equivalence can be clearly understood through the previous system control block diagram, and can be expressed by the following formula: (1) The encoder installed on the non-load shaft end of the motor continuously detects the position of the rotor magnetic poles and continuously obtains the position angle information. By detecting in real time, θ is known, that is, real-time coordinate changes can be performed. The transformed current controls the inverter and generates a PWM waveform to control the motor. Position and speed detection The AC servo motor is equipped with an encoder for measuring position and speed. In most cases, the signal waveform directly from the encoder is irregular and cannot be directly used for control, signal processing and long-distance transmission. Therefore, the signal needs to be shaped and filtered into a rectangular wave before being fed back to the DSP. The two mutually orthogonal encoder signals A and B after processing are directly sent to the QEP pin of the DSP after voltage transformation. The decoding logic unit generates a direction signal and a 4 times frequency pulse signal. The direction signal is determined by the phase lead and lag of the two signals. Because of the problem of forward and reverse rotation, the counter is required to be reversible. Therefore, the general timer 2 is set to the directional increment/decrement counting mode. The quadrature encoded pulse after frequency multiplication is used as the input clock of timer 2 for counting. The counting direction is determined by the direction signal. If the input phase of QEP1 is ahead, the count is incremented, and vice versa. The position and speed can be determined by the number of pulses and the pulse frequency. The total number of pulses per revolution is represented by M. The number of pulses at time T1 is m1. The angle through which the motor rotates can be calculated according to the following formula. (2) If it is a multi-revolution case, the count value of the encoder's Z-phase zero-position pulse and the corresponding timer 2 are used to determine how many revolutions and how many angles the motor shaft has rotated. The motor rotor speed can be calculated according to the MT speed measurement method. The encoder speed formula is as follows: (3) M1—the number of encoder pulses recorded by the counter within a certain time; M2—the number of DSP clock pulses recorded within a certain time; N—the number of encoder lines, that is, the number of encoder pulses before frequency multiplication; Fclk—the DSP clock pulse frequency. Conclusion In summary, the digital AC servo drive studied in this paper adopts a modular design, with a simple hardware structure and easy software programming. It can easily achieve communication between a PC or PLC and the controller, thus enabling the host computer to receive real-time parameters from the control system and transmit parameters to the servo control system, allowing direct control of the servo system.