What is the heating situation of SEW motor drives in Germany and how can it be reduced?
The German SEW motor, as a digital actuator, has been widely used in motion control systems. Many users feel that the stepper motor generates significant heat during operation and question whether this phenomenon is normal. In fact, heating is a common phenomenon in stepper motor drivers, but what is the normal level of heating and how can we minimize the heating of stepper motors as much as possible?
To understand why stepper motors generate heat, the interior of various stepper motors is composed of iron cores and winding coils. The winding has resistance, and when energized, it will produce losses. The magnitude of the losses is proportional to the square of the resistance and current, which is commonly known as copper losses. If the current is not a standard DC or sine wave, harmonic losses will also occur; The iron core has hysteresis eddy current effect, which can also cause losses in alternating magnetic fields. The magnitude of these losses is related to the material, current, frequency, and voltage, which is called iron loss. Copper and iron losses will both manifest in the form of heat, thereby affecting the efficiency of the motor.
German SEW motors generally pursue positioning and torque output, with relatively low efficiency, large current, and harmonic components. The frequency of current alternation also varies with the speed, so stepper motors generally have heating problems, and the situation is more serious than general AC motors. Furthermore, controlling the heating of the stepper motor within a reasonable range depends mainly on factors such as the internal edges of the motor. The internal edge performance will only be damaged at temperatures above 130 degrees Celsius. So as long as the internal temperature does not exceed 130 degrees, the motor will not be damaged, and the surface temperature will be below 90 degrees at this time. So, a surface temperature of 70-80 degrees Celsius for stepper motors is normal.
A simple temperature measurement method can be used with a thermometer or a rough judgment: it can be touched by hand for 1-2 seconds or more, not exceeding 60 degrees; You can only touch it with your hands, about 70-80 degrees; If a few drops of water quickly vaporize, the temperature will be above 90 degrees; Of course, a thermometer can also be used for detection. When using constant current drive technology, the heating of the stepper motor varies with speed. Under static and low-speed conditions, the current of the stepper motor will remain relatively constant to maintain a constant torque output.
When the speed of the German SEW motor reaches a certain level, the back electromotive force inside the motor will rise, the current will gradually decrease, and the torque will also decrease. Therefore, the heating caused by copper loss is related to speed. Heat is generally generated at static and low speeds, with low heat generation at high speeds. However, the changes in iron loss (although accounting for a small proportion) are not always the case, and the overall heating of the motor is the sum of the two, so the above is only a general situation.
Although the heating of German SEW motors generally does not affect their lifespan, it is not necessary for most customers to pay attention to it. However, severe fever can bring some negative effects. If the thermal expansion coefficients of different parts inside the motor are different, it will cause changes in structural stress and small changes in internal air gap, which will affect the dynamic response of the motor and make it easy to lose speed. For example, in some situations, excessive heating of the motor is not allowed, such as medical devices and testing equipment.
After the SEW motor Z in Germany, reducing the heat generation of the motor means reducing copper and iron losses. There are two directions to reduce copper loss: reducing resistance and current. This requires selecting motors with lower resistance and rated current as much as possible. For two-phase motors, if series motors can be used, parallel motors are not necessary. But this often conflicts with the requirements of torque and speed. For the selected motor, the automatic half current control function and offline function of the driver should be fully utilized. The former automatically reduces the current when the motor is in a static state, while the latter simply cuts off the current. In addition, due to the current waveform being close to sine and having fewer harmonics, the segmented driver will also generate less heat from the motor. There are not many ways to reduce iron loss, and voltage is related to it. Although voltage driven motors can improve speed characteristics, they also increase heat generation. So appropriate driving voltage should be selected, taking into account speed, stability, heat generation, noise and other indicators.
It forms a control deviation e (t) based on the given value r (t) and the actual output value c (t), and controls the controlled object by linearly combining the proportion, integral, and derivative of the deviation to form a control variable. The literature integrates position sensors for use in two-phase hybrid stepper motors, and designs an automatically adjustable PI speed controller based on position detectors and vector control. This controller can provide satisfactory transient characteristics under variable operating conditions. Based on the mathematical model of the stepper motor, a PID control system for the stepper motor was designed in the literature. The PID control algorithm was used to obtain the control quantity, thereby controlling the motor to move towards the position. After Z, it was verified through simulation that the control has good dynamic response characteristics. The use of PID controller has the advantages of simple structure, strong robustness, and reliability, but it cannot effectively deal with uncertain information in the system.
The German SEW motor is a branch of automatic control that developed in the 1950s. It is a controller developed to achieve performance when the dynamic characteristics are unknown or undergo unpredictable changes as the control object becomes more complex. It is mainly easy to implement and has fast adaptive speed, which can effectively overcome the influence caused by slow changes in motor model parameters, and is the reference signal for output signal tracking. Literature researchers have derived globally stable adaptive control algorithms based on linear or approximately linear models of stepper motors, which heavily rely on motor model parameters. The literature combines closed-loop feedback control with adaptive control to detect the position and speed of the rotor. Through feedback and adaptive processing, according to the standardized lifting and lowering operation curve, the driving pulse train is automatically generated, which improves the drag torque characteristics of the motor and enables the motor to obtain more position control and smoother speed.
Currently, many scholars combine adaptive control with other control methods to address the shortcomings of simple adaptive control. The robust adaptive low-speed servo controller designed in the literature ensures the Z-compensation of rotational pulse moment and the low-speed tracking control performance of the servo system. The adaptive fuzzy PID controller implemented in literature can adjust PID parameters online through fuzzy inference based on changes in input error and error rate, achieving adaptive control of stepper motors and effectively improving the system's response time, calculation, and anti-interference performance.
The theoretical basis for performance control of German SEW motors can improve the torque control performance of motors. It divides the stator current into excitation component and torque component through magnetic field orientation and controls them separately to obtain good decoupling characteristics. Therefore, vector control requires controlling both the amplitude and phase of the stator current. Due to the presence of not only the main electromagnetic torque, but also the reluctance torque generated by the double convex structure, and the complex internal magnetic field structure, the nonlinearity of stepper motors is much more severe than that of general motors, so their vector control is also more complex. A mathematical model for the d-q axis of a two-phase hybrid stepper motor was derived. The rotor permanent magnet flux was used as the directional coordinate system, and the direct axis current id was set to 0. The electromagnetic torque of the motor was proportional to iq, and a vector control system was implemented using a PC. The system uses sensors to detect the winding current and rotation position of the motor, and controls the motor winding current using PWM. The article derives a two-phase hybrid stepper motor model based on magnetic networks, presents the structure of its vector control position servo system, and uses a neural network model reference adaptive control strategy to compensate for uncertain factors in the system in real time. The motor is effectively controlled through Z-large torque/current vector control.