Part Number:DRV8303
Hello, this is a general question in relation to commutation of 3 phase permanent magnet brushless motors.
When commutating using the traditional 6 step square wave method, an acoustic "tick" is heard once for every AC cycle, eg at half the pole count of the motor. For example a 22 pole motor will create an audible tick at a regular frequency 11 times per motor rotation. The volume of the tick increases with voltage/current.
I believe it is to do with the rapidly increasing current caused by the square wave creating a mechanical movement in the winding. Is this correct ? If not can somebody explain please the root cause for the noise ?
What approaches can be used to minimise it's size/volume ?
Related to this issue, I have an application whereby I am commutating using a variety of sine and space vector wave commutation patterns, and find that on some occasions the motor will commutate completely silently, but then later under the same circumstances begin to "tick" intermittently (not necessarily every AC cycle). The intermittent "ticks" occur at the same frequency as the above 6 step commutation, however the output is a simulated sine wave running at 42kHz PWM outputting 1,000 duty cycle steps per second. It would seem that the ticks are common to both commutation types, albeit with the sine drive they on occasion disappear completely which is what I'm hoping to achieve with the sine driven system.
Any assistance on ways to reduce or eliminate the ticking on either 6 step or sinusoidal drive would be greatly appreciated.
Thanks