AC200MAX fan speed

Never heard it before, but with a load of about 1.5kw on the ac200max, I noticed the fan noise was going up and down. It is very hot here right now, but I’d never noticed this before. Is it it normal for the fan speed to go up and down, or should it be constant speed, whether that’s low or high???

I have asked such an option as a Suggestion

@Kingkong AC200MAX has two fans. If the output power is greater than 1500W, two fans will be activated, and if the output power is lower than 1500W, only one fan will be activated. If the output power is 1500W (little difference allowed), it is possible to activate one fan or two fans at times.