First, the ordinary asynchronous motor are designed by constant voltage constant voltage, can not fully meet the requirements of frequency control. The following is the impact of the inverter on the Special Electric Motors
1, the efficiency of the motor and the temperature rise
Regardless of the form of the inverter, in the operation are produced in varying degrees of harmonic voltage and current, so that the motor in the non-sinusoidal voltage, current running. Refused to introduce the data, the current commonly used sine wave PWM inverter, for example, the lower harmonics is basically zero, the remaining than the carrier frequency about twice the high harmonic components: 2u + 1 (u For modulation ratio).
Higher harmonics can cause the motor stator copper consumption, rotor copper (aluminum) consumption, iron loss and additional loss increases, the most significant is the rotor copper (aluminum) consumption. Since the asynchronous motor rotates at a synchronous speed corresponding to the fundamental frequency, the high harmonic voltage causes a large rotor loss after cutting the rotor bar with a large slip. In addition, the additional copper consumption due to the skin effect needs to be taken into account. These losses will make the motor additional heat, reduce efficiency, reduce the output power, such as the ordinary three-phase asynchronous motor running in the inverter output of non-sinusoidal power conditions, the temperature rise generally increased by 10% - 20%.
2, the motor insulation strength problem
At present, small and medium-sized inverter, many of the PWM control mode. His carrier frequency is about a few thousand to ten kilohertz, which makes the motor stator windings to withstand a high voltage rise rate, equivalent to the motor to impose a steep impulse voltage, so that the motor interturn insulation to withstand more Harsh test. In addition, the rectangular chopper impulse voltage generated by the PWM inverter is superimposed on the motor operating voltage, which poses a threat to the insulation of the motor. The insulation of the ground will accelerate aging under repeated high pressure.
3, harmonic electromagnetic noise and vibration
Ordinary asynchronous motor with inverter power supply, will make by the electromagnetic, mechanical, ventilation and other factors caused by the vibration and noise become more complex. The frequency harmonics contained in the frequency conversion power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces. When the frequency of the electromagnetic force wave and the motor body of the natural vibration frequency of the same or close, will resonate, thereby increasing the noise. As the motor operating frequency range, the speed range of change, a variety of electromagnetic force wave frequency is difficult to avoid the motor components of the natural vibration frequency.
4, Special Electric Motors on the frequent start, the ability to adapt to the brake
As a result of the use of inverter power supply, the Special Electric Motors can be very low frequency and voltage to the way without impact current start, and can use the inverter for a variety of braking methods for fast braking, in order to achieve frequent start and system The mechanical system and the electromagnetic system are in the role of alternating alternating force, to the mechanical structure and insulation structure to bring fatigue and accelerated aging problem.