Yes, using square waves instead of sine waves can be done.  As you suspected, it will be less efficient.  Think of it in frequency space.  The fundamental component of the square wave will do all the work.  The remaining harmonics will heat the motor without adding useful torque, will add mechanical stresses, and can cause more audible noise.

You say you can't get a PWM frequency fast enough to produce a reasonable sine wave, but that is hard to believe.  Surely the AVR can do 25 kHz or so PWM?  I have done this a few times with Microchip PICs, some of which even have a special PWM module intended for this application.

drive 3 phase induction motor with only DC (not pwm) thru each phase
I've got a 2010 Kia Soul, and I was wondering if I should get a reusable/washable air filter, such as the K&amp;N 33-2960.

The reasons I would think to get such an air filter would be:


Save on the cost of replacement filters
Less waste for the environment
Better for the engine
A bit more power


How much of a benefit am I likely to see in each of the above categories from using a washable air filter? Are there other benefits?

Thanks!
