Delta Electronics VFD-EL manual 8kHz, 12kHz, Method A, Frame A, Frame B, Method B

Chapter 4 Parameters
Carrier	Acoustic	Electromagnetic	Heat	Current
Frequency	Noise	Noise or leakage	Dissipation	Wave
		current
2kHz	Significant	Minimal	Minimal	Minimal
8kHz
12kHz	Minimal	Significant	Significant	Significant

From the table, we see that the PWM carrier frequency has a significant influence on the electromagnetic noise, AC motor drive heat dissipation, and motor acoustic noise.

The PWM carrier frequency will be decreased automatically by the ambient temperature and output current of the AC motor drives. It is used to prevent AC motor drive overheat and extend IGBT’s life. Therefore, it is necessary to have this kind of protection method. Take an example of 460V models, assume that the carrier frequency is 12kHz, ambient temperature is 50 degrees C with single AC motor drive. If the output current exceeds 80% * rated current, the AC motor drive will decrease the carrier frequency automatically by the following chart. If output current is around 100% * rated current, the carrier frequency will decrease from 12k Hz to 8k Hz.

Mounting method

Method A
Frame A	Frame B
	150mm
	50mm
	50mm
	150mm
Method B	Frame B
Frame A

4-40 Revision August 2008, 2ELE, V1.02