Several issues to be considered in the application of permanent magnet AC servo motor
Because permanent magnet AC servo motor has the characteristics of fast response, high power density, high efficiency and stable operation, it has been widely used in industrial fields such as automation. However, in the application, many engineers have: how to determine the phase sequence of the permanent magnet AC servo motor winding phase sequence and the encoder signal phase; the meaning of the key parameters of the motor kt and ke and how to effectively use these two parameters in engineering calculation; how to understand the motor Power; there are confusions about how to use these parameters in engineering applications. Therefore, this paper elaborates on these issues from the perspective of engineering application for the reader's reference.
Basic principle of permanent magnet AC servo motor
The stator winding structure of pmsm is a three-phase symmetrical winding. The rotor structure is a surface-mounted permanent magnet structure or an in-line permanent magnet structure. The winding back electromotive force is a sine wave. When a three-phase symmetrical sine wave is applied to the stator winding of the motor. At current, the motor will produce continuous electromagnetic torque. The rotor permanent magnet of pmsm produces a magnetic field close to a sine wave in the working air gap, so that the back electromotive force close to the sine wave is induced on the armature winding when the rotor rotates. The three-phase armature winding of pmsm is connected to a 180-conducting half-bridge inverter circuit, and the driving voltage is a pulse voltage modulated by a space vector pulse width. When the motor is running, the three-phase armature windings are turned on at the same time, creating a "continuous" circular rotating magnetic field in the working air gap. In order to realize servo control, the position sensor of PMMS can use rotary transformer or photoelectric encoder. At present, industrial applications are more incremental photoelectric encoders. Servo-driven encoders typically require two sets of signals:
1) a, b, z signals, where a, b two-way pulse phase difference 90, so that the motor can be easily judged; z signal, then one pulse per revolution, used for reference point positioning (currently, the Rayleigh servo does not need z signal).
2) u, v, w signals: The three-way pulse signals are out of phase with each other by 120, and the number of pulses emitted per revolution is consistent with the number of poles of the motor. According to the high-low relationship of the u, v, w signals, the current position of the motor rotor can be judged.
Before the motor is started, the current position of the motor pole can be estimated based on the level of the three-way pulse signal levels of u, v, and w. Once the motor rotates, the a, b signal accurately detects the rotor position angle.
The current mainstream pmsm servo drives basically adopt vector control technology, and the system block diagram is shown in Figure 1.
How to define or judge the phase sequence of permanent magnet AC servo motor
In the production process of pmsm servo motor, an important assembly and debugging process is required to ensure the proper phase relationship between the back electromotive force of the three-phase winding of the motor and the encoder signals u, v, w. The specific explanations are shown in Figures 2, 3, 4 and 5. Show.
Kt and ke of permanent magnet AC servo motor
1) Back electromotive force constant of permanent magnet motor ke
As long as the motor is rotating, there will be a coil cutting magnetic line, so there will be a counter electromotive force. For a specific type of motor, the faster the rotation speed, the higher the back electromotive voltage generated. That is, the back electromotive force voltage is proportional to the motor speed.
2) Torque constant kt of permanent magnet DC motor
For a specific type of motor, the greater the motor winding current, the greater the torque generated by the motor shaft. That is, the torque of the motor is proportional to the motor winding current.
Rotor inertia of permanent magnet AC servo motor
The requirement of the servo drive for the load inertia of the servo motor is that the applicable load inertia is less than 5 times the rotor inertia of the motor. Therefore, the larger rotor inertia of the motor can carry a larger load inertia, but the mechanical time constant of the motor will be When the motor is increased, the response of the motor to the speed is reduced; the smaller the rotor inertia of the motor, the mechanical time constant of the motor is small, and the response of the motor to the speed is fast, but the load inertia of the motor is not allowed to be large. Www.
Torque and power of permanent magnet AC servo motor
The rated torque of the permanent magnet AC servo motor refers to the torque that the motor can continuously and safely output. When the ambient temperature is 25 °C, it will make the winding temperature of the motor reach the maximum allowable value. The rated power of the motor refers to the mechanical power output by the motor at rated speed and rated torque.
Since the servo motor is closed-loop control operation, in the control mode of id=0 (vector control), the magnitude of the motor torque is proportional to the magnitude of the current supplied to the motor. The torque output of the motor changes with the load. When the load is constant, the torque output of the servo motor is also constant. The servo motor can be overloaded for a short period of time. The overload factor is determined by the overload current output by the driver. The overload time is determined by the capacity of the driver and the temperature rise of the servo motor. The general overload factor is 3 times.
Insulation class of permanent magnet AC servo motor
