There is the effect of freewheeling in the inductor. The larger the inductance value, the stronger the freewheeling capability. When a reverse voltage is applied, the winding may continue to freewheel in the forward direction, which may cause commutation failure. Power electronics technology has an explanation for this.
23. Question: Can increasing the PWM frequency of the driver improve the heating of the permanent magnet synchronous motor? What are the ways to improve the heating of permanent magnet synchronous motors?
Answer: Increasing the PWM frequency can limit and reduce the fluctuation of the winding current, which is definitely beneficial, but I don't know how much it can improve the heating problem.
I think the PWM frequency should have a suitable value. If it is too low, it will definitely not work. If it is too high, there will definitely be greater losses on the driver side. Since the speed of the switch tube opening and closing is limited and fixed, when the switching time takes up After a large portion of the entire on time, this side of the drive will be very inefficient.
Answer: If the pwm carrier frequency is high, the temperature rise of the motor will be beneficial, but the temperature rise of the inverter will be greater.
Question: Now PWM work is above 10K. Can the temperature rise be improved through the design of the motor itself? What measures are available?
Answer: If you want to design a motor with a low temperature rise, you must optimize the motor plan, such as changing to a higher grade of silicon steel sheet, reducing the number of turns, increasing the wire diameter, etc. In short, only by reducing the electrical density, line load, and magnetic density can the temperature rise be reduced.
24. Question: What is the relationship between the initial phase angle in space corresponding to the fundamental wave of the motor's air gap magnetomotive force and the phase of the current in the winding? What is the relationship between the spatial initial phase angle corresponding to the fundamental wave of the air gap magnetomotive force generated by the motor torque winding and the phase of the current flowing in the torque winding?
Answer: The torque winding you are talking about should be a three-phase symmetrical armature winding, right? The two angles you mentioned, one is the space angle and the other is the time angle, are not strictly speaking concepts within the same category, but they are unified in the space-time phase vector diagram of the synchronous motor. If the initial angle in space is taken as the axis of the winding of a certain phase (such as phase A), and the time axis coincides with the phase axis, then there is an answer to this question, which is 0°. The basis is that when the current of a certain phase reaches, the resulting magnetomotive force The axis coincides exactly with the axial direction of the phase winding.
25. Question: Does anyone use weftless tape to wrap the outer circumference of the rotor magnet, or does it use a cylinder liner? Is there any other way? How to store the magnet-glued rotors after mass production? If you put them too densely, they will be sucked together, and too much is a waste of space.
Answer: Bolts, stainless steel sleeves, weftless belts, carbon fiber, and titanium alloys are mainly these.
26. Question: Nowadays, more and more high-power permanent magnet generators are used in the field of wind power generation. It is well known that the rotor of high-power permanent magnet generator is the key to the design of permanent magnet motors. For high-speed permanent magnet motors, medium-speed permanent magnet motors and What are the rotor structures and magnet fixing methods of low-speed direct-drive permanent magnet motors? Does the rotor need to be cooled? What is its heat dissipation method and structure?
Answer: When the current source is used, the induced voltage is indeed smaller than the actual supply voltage. The difference lies in the resistance and terminal leakage voltage drop, but this value is relatively small, about 2-3%. Therefore, your motor does not have such a large load output capability, of course, provided that your other simulation settings are correct.
28. Question: Why is the rotor of the squirrel cage asynchronous machine not insulated?
Answer: Because the induced voltage and voltage drop on the cage bars of the squirrel cage are balanced, and any two points on the cage bars are at equal potential, there is no need for insulation.
29. Question: When a three-phase asynchronous motor runs with constant torque, how will the voltage and current change when the voltage is increased? How will the voltage and current change when the voltage is reduced? Why?
Answer: Increase the voltage - the torque increases - the speed increases - the torque returns to its original value - the active current decreases - the magnetic density increases - the iron loss increases - the reactive current increases - the power factor decreases and the total current How it changes depends on the ratio of active and reactive currents. Generally speaking, for heavy loads, the total current will decrease, and for light loads, the total current may increase.
30. Question: How to calculate mechanical friction loss and wind wear loss?
Answer: Some data are obtained based on experience. For example, we have done many experiments on motors, and there will be empirical data in them. Secondly, we need to look at some standards. The proportion is mentioned in the NEMA standard, you can check it.
31. Question: In the 2D model automatically generated by the RM model, the angle of voltage excitation and the torque angle are equal, but the power factor angle is calculated to be greater than the torque angle. When giving incentives, which angle in RM RESULT should be used?
Answer: It depends on whether you are a voltage source or a current source. The two angles are different. The angle of the voltage source is the power angle, while the angle of the current source is the internal power factor angle.
32. Question: Are there any operating time limits for peak torque and peak power? Are there any assessment conditions for peak torque and power regarding temperature rise?
33. Question: Why is the squirrel cage rotor of asynchronous motor not insulated?
Answer: Because the induced voltage and voltage drop on the cage bars of the squirrel cage are balanced, and any two points on the cage bars are at equal potential, there is no need for insulation.
34. Question: Please help me, how can I measure the rotor temperature? Are there any more mature methods currently?
Answer: Wired rotor - when measuring resistance, the temperature coefficient of copper wire is basically -0.04/K.
Permanent magnet rotor - measure the back electromotive force. The temperature coefficient of magnetic steel Br is basically -0.1%/K, and the back electromotive force is basically the same as Br.
35. Question: How to set up maxwell for sine wave magnetization?
Answer: When defining the material of the magnetic ring, just define R as cos (p*phi) and Phi as -sin (p*phi) or sin (p*phi). In addition, the radiation magnetization process of the magnetic ring is very difficult. , there are not many good ones, and there are size restrictions.
36. Question: After establishing the simulation model of the motor, do I need to set the set Y connection for the excitation source? Or is the three-phase winding Y connected by default?
Answer: For 2d voltage excitation, Y is connected, of course it must be set! Otherwise, there will be an unreal 3rd harmonic in the current, which will have an impact on your losses, etc.! For 3d and y connections, this cannot be set and can only be achieved using the connection topology of the external circuit.
37. Question: Let’s discuss, under what circumstances can ordinary ferrite permanent magnets be demagnetized? All I can think of is: running at low temperatures, with on-stop-on-stop. In operating mode, the operating environment temperature is higher than the Curie point temperature. What other situations?
Answer: Different magnets have different demagnetization characteristics. Rare earth permanent magnets have a positive temperature coefficient and demagnetize at high temperatures. Ferrite has a negative temperature coefficient and demagnetize at low temperatures.
38. Question: What are the advantages of opening holes in the rotor core? Will this result in less yoke on the rotor? Motor performance deteriorates?
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