Search

**Jan 19, 2021

The influence of frequency converter carrier frequency and setting standard

1. Overview of carrier frequency of low-voltage inverter

For frequency converters with voltage ≤ 500V, almost all adopt AC-DC-AC main circuit nowadays, and its control method also uses sinusoidal pulse width modulation (SPWM). Its carrier frequency is adjustable, generally from 1-15kHz, which is convenient It is selected manually. but

In actual use, many users just follow the original setting value of the inverter manufacturer and do not adjust it according to the actual situation on the spot. As a result, the incorrect selection of the carrier frequency value affects the correct and effective working status. Therefore, How to correctly select the carrier frequency value of the inverter during the use of the inverter is also an important matter. This article provides the basis for considering the following aspects and correctly selecting the carrier frequency value.

2, carrier frequency and inverter power consumption

The power loss of the IGBT of the power module is related to the carrier frequency, and with the increase of the carrier frequency, the power loss increases, so that the efficiency is reduced, and the heat of the power module increases, which is detrimental to the operation. Of course, the working voltage of the inverter The higher the value, the greater the power loss. The greater 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 during the alternate conduction process will become smaller. In severe cases, it may cause the bridge arm to short-circuit and damage the inverter.

3, carrier frequency and ambient temperature

When the inverter is in use, the carrier frequency is required to be high, and the ambient temperature is also high, which is very unfavorable to the power module. At this time, it is very unfavorable for the inverter of different power with the carrier frequency used and the ambient temperature. The size, the allowable constant output current of the inverter should be appropriately reduced to ensure the safe, reliable and long-term operation of the power module IGBT.

The influence of frequency converter carrier frequency and setting standard

4, carrier frequency and motor power

The power of the motor should be lower than the carrier frequency. The purpose is to reduce the interference (impact on the use of other equipment). This principle is generally followed, but the specific values are different from different manufacturers. For example, Japan has the following relations for reference carrier frequency 15kHz10kHz5kHz

Motor frequency ≤30kW37-100kW185-300kW example, Finland VACON carrier frequency 1-16kHz1-6kHz Motor power ≤90kW110-1500kW example, Shenzhen Ansheng (formerly Huawei) carrier frequency 6kHz3kHz1kHz

Motor power 5.5-22kW30-55kW75-200kW

Example, Chengdu Jialing Company JP6C-T9 series

Carrier frequency 2-6kHz2-4kHz

Motor power 0.75-55kW 75-630kW

5. The carrier frequency and the length of the secondary outlet (U, V, W) of the inverter

Carrier frequency 15kHz10kHz5kHz1kHz

Line length "50M" 50-100M" 100-150M" 150-200M

6. The influence of carrier frequency on inverter output current

It is well known that the inverter (DC/AC conversion) part of the inverter is formed by the IGBT through the sinusoidal pulse width modulation SPWM and the motor windings to form a sinusoidal current waveform. Then the size of the carrier frequency directly affects the quality of the current waveform, as well as the size of the interference, and the size of the carrier frequency is more sensitive and direct. Therefore, the carrier frequency value must be selected correctly during operation, and then Consider attaching various harmonic suppression devices, such as AC reactors, DC reactors, filters, alternative sequence reactors, and installation wiring, grounding and other measures. This treatment is more reasonable and effective, and must not be inverted. To deal with problems, this is a very important principle. When the carrier frequency is high, the sine of the current waveform is good and smooth. In this way, the harmonics are small and the interference is small, and vice versa. When the carrier frequency is too low, the effective torque of the motor will decrease, the loss will increase, and the temperature will increase. On the contrary, when the carrier frequency is too high, the inverter loss will increase. , The IGBT temperature rises, and the rate of change of output voltage dv/dt increases, which has a greater impact on the motor insulation.

(1) The higher the operating frequency, the greater the duty cycle of the voltage wave, and the smaller the current harmonic components, that is, the higher the carrier frequency, the better the smoothness of the current waveform;

(2) The higher the carrier frequency, the smaller the allowable output current of the inverter;

(3) The higher the carrier frequency, the smaller the capacitive reactance of the wiring capacitance (because Xc=1/2πfC), and the greater the leakage current caused by the high-frequency pulse.