Most of the inverters are in the form of PWM modulation for the inverter. That is to say, the voltage output from the inverter is actually a series of pulses, and the width and interval of the pulses are not equal. Its size depends on the intersection of the modulated wave and the carrier, which is the switching frequency. The higher the switching frequency, the greater the number of pulses in a cycle, the better the smoothness of the current waveform, but the greater the interference to other devices. The lower the carrier frequency or the poor setting, the motor will make an unpleasant noise. By adjusting the switching frequency, the noise of the system can be minimized, the smoothness of the waveform is best, and interference can be minimized. 1. Overview of low frequency inverter carrier frequency
For inverters with voltage ≤500V, almost all of the main circuits of AC-DC-AC are used today. The control mode is sinusoidal pulse width modulation (SPWM). Its carrier frequency is adjustable, generally from 1~15kHz, which is convenient. Make artificial choices. However, in actual use, many users only follow the original set value of the inverter manufacturing unit, and do not adjust according to the actual situation on site. As a result, the carrier frequency value is improperly selected, which affects the correct effective working state. How to correctly select the carrier frequency value of the inverter during the use of the inverter is also important. This article provides considerations for the following aspects and as a basis for the correct selection of carrier frequency values.
2, carrier frequency and inverter power consumption
The power loss of the power module IGBT is related to the carrier frequency, and the carrier frequency is increased, the power loss is increased, such that the efficiency is reduced, and the second is that the power module generates heat, which is disadvantageous for long-term operation, of course, the inverter The higher the operating voltage, the greater the impact on power loss.
The larger the carrier frequency, the greater the loss of the inverter and the smaller the output power. If the ambient temperature is high, the dead zone of the upper and lower inverter tubes of the inverter bridge will become smaller during the alternate conduction process. In severe cases, the bridge arm may be short-circuited and damage the inverter.
3, carrier frequency and ambient temperature
When the frequency converter requires high carrier frequency and the ambient temperature is high, it is very unfavorable for the power module. At this time, the frequency of the carrier frequency of the different power inverters and the ambient temperature are used. The size and the allowable constant output current of the inverter should be appropriately reduced to ensure safe, reliable and long-term operation of the power module IGBT.
4, carrier frequency and motor power
If the motor power is large, the relative carrier frequency is lower. The purpose is to reduce the interference (the influence on the use of other devices) and reduce the power consumption and heat generation. Generally, this principle is followed, but the specific values of different manufacturers are different.
5. The relationship between the carrier frequency and the length of the secondary output (U, V, W) of the inverter.
Generally, as the output line grows, the leakage current of the inverter will increase. Therefore, if the output line is long, the carrier frequency should be appropriately reduced.
Carrier frequency: 15kHz 10kHz 5kHz 1kHz
Line length: <50m>50~100m>100~150m>150~200m