Control strategy of the hottest permanent magnet s

Permanent magnet synchronous motor servo system control strategy

Abstract: PWM modulation and dead time compensation technology, sensorless control technology and robust control technology of permanent magnet synchronous motor are one of the key technologies that determine the performance of AC servo system, and are the main part of foreign AC servo technology blockade

with the rapid development of modern industry, the corresponding equipment that marks a country's industrial strength, such as precision machine tools and industrial robots, have put forward higher and higher requirements for its "driving source" - electric servo drive system. The permanent magnet synchronous motor (PMSM) based on sine wave back EMF has gradually become the "mainstream" of the executive motor of the electric servo system because of its excellent performance [1]. With the rapid development of modern power electronics technology, microelectronics technology and computer technology, the development of AC servo drive system with permanent magnet synchronous motor as actuator has been greatly advanced. However, servo control technology is one of the key technologies that determine the performance of AC servo system, and it is the main part of foreign AC servo technology blockade. With the gradual maturity of domestic AC servo motor and driver hardware technology, the servo control technology in the form of software in the control chip has become a bottleneck restricting the development of High-Performance AC servo technology and products in our country. Research on High-Performance AC servo control technology with independent intellectual property rights, especially the most promising permanent magnet synchronous motor servo control technology, has important theoretical significance and practical value

basic structure of permanent magnet synchronous motor servo system

permanent magnet synchronous motor servo system is mainly composed of servo control unit, power drive unit, communication interface unit, servo motor and corresponding feedback detection devices. Its structure is shown in the attached figure. The servo control unit includes position controller, speed controller, torque and current controller, etc. The fully digital permanent magnet synchronous motor servo control system integrates advanced control technology and control strategy, making it very suitable for the servo drive field with high precision and high performance requirements. At the same time, intelligence and flexibility have also become a development trend of modern electric servo drive system [2][3]

pwm modulation technology and dead time compensation technology development status

pwm modulation mostly adopts asynchronous modulation mode, including hysteresis modulation, sine wave modulation, space vector modulation (SVPWM), etc. Zhenyu Yu of TI company and others analyzed the digital implementation technology of various PWM modulation methods based on DSP [4]. The implementation of hysteresis modulation is simple, but the waveform harmonic is large and the performance is poor. Sine PWM modulated signal wave is sine wave, and its pulse width is formed by the intersection of sine wave and triangular carrier wave. It is natural sampling, and a variety of regular sampling methods are changed in digital implementation. In some literatures, according to the characteristics of the motor, higher harmonics are superimposed in the sine wave to suppress some harmonics and achieve the purpose of optimizing the current waveform. In the 1980s, Dr. Broeck proposed a new pulse width modulation method - space vector PWM modulation, which introduced space vector into pulse width modulation [5]. It has the advantages of wide linear range, less high-order harmonics and easy digital implementation, and has been widely used in new drivers. Reference [6] analyzes the principle of space vector pulse width modulation of three-phase AC motor, and discusses the voltage output capacity of three-phase bridge voltage source inverter using space vector pulse width modulation. Literature [7] compares and analyzes SVPWM and carrier based SPWM, and points out the relationship between SVPWM and SPWM superimposed with third harmonic. Different placement of zero sequence vectors can lead to different SVPWM modulation methods. Inserting only one zero sequence vector in each PWM cycle can reduce the switching times by 1/3, and realize SVPWM modulation with minimum switching loss [8]

development status of sensorless control technology

sensorless control technology is the most active field in permanent magnet AC motor drive technology in recent years. Because the cost of the sensor used to determine the rotor position can account for almost one-third of the cost of the whole controller, and the axial length of the sensor is almost one-third of the axial length of the permanent magnet motor. Therefore, with the help of some advanced control algorithms, in the case of no position sensor, only the current or voltage signals are extracted to estimate the rotor position and realize the self synchronous operation of the motor, which has aroused great interest of researchers. This assumption is particularly applicable to brushless DC motors, because it only needs to provide a commutation signal every 60 ° electrical angle. This requirement can give the commutation signal by detecting the back EMF signal of the non energized phase in the three-phase winding. References [16] to [18] have proposed a series of algorithms to achieve this intention. The commutation time and sequence are determined by detecting the back EMF, which cancels the original Hall sensor. The algorithm in reference [18] has been successfully applied to integrated circuits and become a commercial product

it is more challenging to remove the position sensor in the permanent magnet synchronous motor drive system, because the three phases of the motor are always energized, there is no back EMF signal to use, and the required position information is not limited to the six commutation points of the brushless DC motor. In this way, it is necessary to design a more complex observer to estimate the accurate position information by using the measured phase voltage and phase current [19]-[21]. Reference [19] designed the flux observer by establishing the flux equation. References [20] and [21] make use of the position information contained in harmonic reactive power. Salient pole permanent magnet synchronous motor has more advantages in using sensorless technology than non salient pole permanent magnet synchronous motor [22]-[26], because the inductance of salient pole motor changes sinusoidally with the rotation of rotor, which can be used to detect the rotor position at low speed

also for the sake of cost reduction, the reduction of current sensors in permanent magnet synchronous motor drive systems has also attracted attention. For example, reference [27] gives a method that only one current sensor is needed to detect the bus current by using an appropriate method, rather than using three current sensors to detect the three-phase current respectively. For the current detection of Brushless DC motor, reference [28] proposed a method of using the current sensor integrated in the inverter to replace the separate current sensor, which can also reduce the overcurrent phenomenon during motor commutation

pmsm robust control development status

various robust control methods applied to permanent magnet synchronous motor have also attracted great interest of researchers. This is because the traditional PID control is likely to deteriorate the dynamic characteristics of the control system when the motor load or motor parameters change. However, the change of motor load or motor parameters is inevitable. So it is necessary to design a robust controller to suppress the influence of parameter changes on the control performance. To meet this demand, reference [29] proposed a sliding mode variable structure control scheme, and references [30] and [31] proposed an adaptive control strategy to design the position and speed controller of permanent magnet synchronous motor. As an optimistic alternative to PID control, fuzzy control strategy has also been introduced into the permanent magnet synchronous motor controller to improve the robustness of the permanent magnet synchronous motor in the face of load torque changes [32]. Reference [33] proposed a robust controller for permanent magnet synchronous motor position control to improve the stability of the system and enhance its anti-interference performance

in addition, using space vector modulation technology, literature [34] and [35] proposed a relatively complex current control strategy for permanent magnet synchronous motor current control. These advanced current controllers introduce the predictive control method, and give a full digital control scheme to improve the characteristics of the current loop. The neural network method is also introduced into the permanent magnet synchronous motor controller as a means to realize self-learning current control [36] and optimal inverter control [37]

various torque and speed observers are also used in the design of permanent magnet synchronous motor robust control system. Literature [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 turned per unit sampling time will introduce delay and noise to the system [39]. Because this delay and noise phenomenon is particularly obvious at low speed, the observer proposed in document [38] cannot be used in a wide speed range. Lorenz detailed the method of using linear observer for instantaneous velocity estimation in reference [40]

conclusion

throughout the research status of permanent magnet synchronous motor servo system, domestic and foreign scholars have carried out a lot of research and practice from different angles, and achieved rich results; Especially in recent years, around improving the performance of its servo control and reducing the cost, we have made bold exploration and Research on the system control strategy, put forward some new ideas, adopted some intelligent advanced control strategies, and achieved some practical results. However, permanent magnet synchronous motor itself is a "system" with certain nonlinearity, strong coupling and timely variability. At the same time, its servo object also has strong uncertainty and nonlinearity. In addition, the system is also subject to varying degrees of interference when running. Therefore, it is difficult to meet the control requirements of high-performance permanent magnet synchronous motor servo system according to the conventional control strategy. Therefore, how to combine the new development of control theory and introduce some advanced "compound control strategies" to improve the performance of the "controller" as the core component of the permanent magnet synchronous motor servo system, so as to make up for the "hard constraints" in the "hard form" of the system, should be a major "breakthrough" in the current development of high-performance PMSM servo system

references

[1] Li Ye, Yan Xinping Research status and application prospect of permanent magnet synchronous motor servo system Micromotor, 2001, 34 (4):

[2] Qin Yi Modern AC servo system Wuhan: Huazhong University of Technology Press, 1995

[3] Tang Renyuan Theory and design of modern permanent magnet motor Beijing: China Machine Press, 1997

[4] Yu, Z., Mohammed, A., Panahi, I. A review