| 摘要 |
PROBLEM TO BE SOLVED: To provide a digital filter capable of removing PWM noise without equipping it with an analog prefilter and even when a lower sampling frequency than a PWM drive frequency is used.SOLUTION: The digital filter includes an averaging filter 21 for calculating an average value of sampling data obtained by most recent m times of sampling on inputted sampling data (m: an integer greater than or equal to 2). Regarding a frequency fdn of fundamental wave component and harmonic component (n: 1, 2, 3, and so on) of a PWM noise to be removed, a sampling frequency fs and an average number m of the averaging filter 21 are set for a removal frequency fdn so that a difference in absolute value between a frequency k fs that is k times the sampling frequency fs (k: 0, 1, 2, 3, and so on) and the removal frequency fdn becomes equal to a frequency that is an integral multiple of fs/m (except a multiple 0) in a frequency region from 0 to a Nyquist frequency fs/2. |
