3. However, the control principle of the frequency converter is not to output a standard sine wave to the asynchronous motor, but to output a series of pulsed square waves in the form of PWM chopping, using the mathematical principle of calculus to achieve the same effect area. The effect of the equivalent sine wave. It is conceivable that when the motor speed of the inverter is low, the output pulse density is relatively low, so it is difficult to simulate the sine wave effect. If the inverter is equipped with an ordinary asynchronous motor, it is necessary to avoid working in a low frequency state. So Tesla cars are smarter, let the motor work in a high frequency state (first of all, the bearings must be excellent), and then decelerate through gears, so as to avoid letting the asynchronous motor work in a low frequency state, for some industrial control systems that require a speed regulation range , can also refer to this control idea.
4. The frequency converter realizes the on-off control of the motor coil through the two states of the high-power switch tube switch, and the coil is an inductive load, and the current cannot be abruptly changed. During the forced switching process of the switch tube, di/dt will inevitably be generated. The instantaneous high voltage caused by these high-frequency on-off will inevitably impact the insulation system of the motor, and repeated on-off will cause some power loss, resulting in motor vibration and heat, which will inevitably shorten the service life of the motor. Frequent switching on and off will also generate electromagnetic waves, causing various types of interference.
5. In the low-speed and low-frequency state, the motor itself generates more heat, while the ordinary asynchronous motor is a self-cooling air-cooling system, which is mainly cooled by a fan at the rear. The speed of this fan is the same as the speed of the motor. At times, the speed of the fan is also low, and the cooling effect cannot be achieved, so the asynchronous motor running at low frequency can change the fan to the external drive mode, such as adding a fan to drive the cooling fan to meet the heat dissipation requirements.
6. It is unavoidable to encounter interference problems when using the inverter. You can separate the strong and weak currents through power isolation. Do not touch the strong and weak current wiring together, pay attention to grounding, and use some magnetic ring filter lights to avoid. For occasions with high precision requirements, variable frequency motors or even synchronous motors can be used to meet the requirements.
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