With the rapid development of modern industry, equipment that signifies a nation's industrial strength, such as precision machine tools and industrial robots, places increasingly higher demands on their "drive sources"—electric servo drive systems. Permanent magnet synchronous motors (PMSMs) based on sinusoidal back electromotive force have gradually become the "mainstream" actuators in electric servo systems due to their superior performance. With the rapid development of supporting technologies such as modern power electronics, microelectronics, and computer technology, the development of AC servo drive systems using PMSMs as actuators has made significant progress. However, servo control technology is one of the key technologies determining the performance of AC servo systems and is a major area where foreign AC servo technology is restricted. As domestic hardware technologies such as AC servo motors and drivers mature, servo control technology, existing in software form within control chips, has become a bottleneck restricting the development of high-performance AC servo technology and products in my country. Researching high-performance AC servo control technology with independent intellectual property rights, especially the most promising PMSM servo control technology, has significant theoretical and practical value. Basic Structure of Permanent Magnet Synchronous Motor Servo System A permanent magnet synchronous motor servo system mainly consists of a servo control unit, a power drive unit, a communication interface unit, a servo motor, and corresponding feedback detection devices. Its structure is shown in the attached diagram. The servo control unit includes a position controller, a speed controller, and torque and current controllers. The fully digital permanent magnet synchronous motor servo control system integrates advanced control technology and strategies, making it highly suitable for servo drive applications requiring high precision and performance. Furthermore, intelligence and flexibility have become a development trend in modern electric servo drive systems. Current Status of PWM Modulation and Dead-Zone Compensation Technology: PWM modulation often employs asynchronous modulation methods, including hysteresis modulation, sinusoidal modulation, and space vector modulation (SVPWM). Zhenyu Yu et al. from TI analyzed the digital implementation technology of various PWM modulation methods based on DSP. Hysteresis modulation is simple to implement, but it has large waveform harmonics and poor performance. The signal wave of sinusoidal PWM modulation is a sine wave, and its pulse width is formed by the intersection of a sine wave and a triangular carrier wave, representing natural sampling. In digital implementation, various regular sampling methods have been developed. Some literature, based on the characteristics of motors, superimposes higher harmonics onto sine waves to suppress certain harmonics and optimize the current waveform. In the 1980s, Dr. Broeck proposed a new pulse width modulation method—space vector PWM modulation—introducing space vectors into pulse width modulation. It has advantages such as a wide linear range, fewer higher harmonics, and ease of digital implementation, and has been widely used in new types of drivers. This paper analyzes the principle of space vector PWM for three-phase AC motors and discusses the voltage output capability of a three-phase bridge voltage-source inverter using space vector PWM. A comparative analysis of SVPWM and carrier-based SPWM is conducted, highlighting the connection between SVPWM and SPWM with superimposed third harmonics. Different placement of the zero-sequence vector can lead to different SVPWM modulation methods; inserting only one zero-sequence vector per PWM cycle can reduce the number of switching operations by 1/3, thus achieving SVPWM modulation with minimal switching losses. The dead time of devices such as IGBTs is one of the causes of inverter nonlinearity, leading to current waveform distortion and deteriorating control performance. Much research has been conducted on various dead-time compensation techniques. The literature analyzes the influence of dead zone on current waveform and gives two compensation circuits. The literature analyzes the usual current feedback compensation and voltage feedback compensation, and proposes a feedforward compensation scheme based on the dq rotating coordinate axis. Its correction is not affected by the voltage amplitude and current distortion of the inverter output, and it compensates well for the distortion of the inverter output voltage. The literature analyzes the role of dead zone, and only gives a dead zone when the current crosses zero, which can reduce the distortion caused by dead zone. The literature adopts time delay control, estimates the interference voltage caused by dead zone online in real time, and feeds it back to the reference voltage to compensate for its influence. In the SVPWM modulation control of induction motor, the literature [14] predicts the stator current, calculates the influence of dead zone, and proposes a predictive compensation algorithm. The literature [15] analyzes the characteristics of inverter dead zone through simulation, establishes the mathematical model of dead zone and the nonlinear model of the whole system, and adopts an adaptive variable structure control strategy to eliminate the influence of inverter dead zone. It does not require the measurement of dead zone parameters, has strong robustness, and can make the system globally stable and achieve accurate position tracking. Current Status of Sensorless Control Technology Sensorless control technology is one of the most active areas in permanent magnet AC motor drive technology in recent years. Because the cost of sensors used to determine the rotor position can account for almost one-third of the total cost of the controller, and the axial length of the sensor is almost one-third of the axial length of the permanent magnet motor. Therefore, the scheme of extracting current or voltage signals to estimate the rotor position and realize the self-synchronous operation of the motor by means of some advanced control algorithms without position sensors has aroused great interest among researchers. This idea is particularly applicable to brushless DC motors, because it only needs to provide a commutation signal every 60° electrical angle. This requirement can be completely met by detecting the back EMF signal of the unenergized phase in the three-phase winding to provide the commutation signal. References [16] to [18] have proposed a series of algorithms to achieve this purpose. By detecting the back EMF to determine the commutation time and sequence, the original Hall sensor is eliminated. The algorithm in reference [18] has been successfully applied to integrated circuits and has become a commercial product. Removing position sensors in permanent magnet synchronous motor drive systems is more challenging because the three phases of the motor are always energized, there is no back EMF signal available, and the required position information is not limited to the six commutation points of a brushless DC motor. This necessitates the design of more complex observers that use measured phase voltages and phase currents to estimate accurate position information [19]-[21]. Reference [19] designed a flux linkage observer by establishing flux linkage equations. References [20] and [21] utilized the position information contained in harmonic reactive power. Salient-pole permanent magnet synchronous motors have an advantage over non-salient-pole permanent magnet synchronous motors in utilizing sensorless technology [22]-[26] because the inductance of a salient-pole motor changes sinusoidally with the rotation of the rotor, and this characteristic can be used to detect the rotor position at low speeds. Also for cost reduction considerations, reducing current sensors in permanent magnet synchronous motor drive systems has received attention. For example, Reference [27] provides a method that uses only one current sensor to detect the bus current instead of three current sensors to detect the three-phase current separately. For current detection of brushless DC motors, reference [28] proposes a method to replace the separate current sensor with a current sensor integrated in the inverter. This method can also reduce the overcurrent phenomenon during motor commutation. Current Status of PMSM Robust Control Development Various robust control methods applied to permanent magnet synchronous motors have also attracted great interest from researchers. This is because traditional PID control is likely to cause the dynamic characteristics of the control system to deteriorate when the motor load or motor parameters change. Such changes in motor load or motor parameters are unavoidable. Therefore, it is necessary to design a robust controller to suppress the influence of parameter changes on control performance. To meet this demand, reference [29] proposes a sliding mode variable structure control scheme, while references [30] and [31] propose an adaptive control strategy to design the position and speed controller of permanent magnet synchronous motors. Fuzzy control strategy, as an optimistic alternative to PID control, has also been introduced into permanent magnet synchronous motor controllers to improve the robustness of permanent magnet synchronous motors when facing load torque changes [32]. Reference [33] proposes a robust controller for permanent magnet synchronous motor position control to improve system stability and enhance its anti-disturbance performance. In addition, using space vector modulation technology, references [34] and [35] proposed relatively complex current control strategies for the current control of permanent magnet synchronous motors. These advanced current controllers introduce predictive control methods and provide all-digital control schemes to improve the characteristics of the current loop. Neural network methods have also been introduced into permanent magnet synchronous motor controllers as a means to realize self-learning current control [36] and optimal inverter control [37]. Various torque and speed observers have also been used in the design of robust control systems for permanent magnet synchronous motors. Reference [38] designed a torque observer that only uses speed information, but the speed information is obtained indirectly from the position sensor. The speed information calculated by the number of pulses rotated per unit sampling time will introduce delay and noise into the system [39]. Because this delay and noise phenomenon is particularly obvious at low speeds, the observer proposed in reference [38] cannot be used in a wide speed range. Lorenz detailed the method of using a linear observer for instantaneous speed estimation in reference [40]. Conclusion Looking at the current research status of permanent magnet synchronous motor (PMSM) servo systems, scholars both domestically and internationally have conducted extensive research and practice from different perspectives, achieving considerable results. In particular, recent years have seen bold explorations and research into system control strategies aimed at improving servo control performance and reducing costs, proposing new ideas, adopting advanced intelligent control strategies, and achieving some practically significant results. However, the PMSM itself is a "system" with certain nonlinearity, strong coupling, and time-varying characteristics. Furthermore, the servo object also exhibits strong uncertainty and nonlinearity, and the system is subject to varying degrees of interference during operation. Therefore, conventional control strategies are insufficient to meet the control requirements of high-performance PMSM servo systems. Thus, combining new developments in control theory with the introduction of advanced "composite control strategies" to improve the performance of the "controller," a core component of the PMSM servo system, and to compensate for the "hard constraints" inherent in the system, should be a major "breakthrough" in the development of high-performance PMSM servo systems.