Abstract: A motor drive comprises a rectifier circuit portion arranged to receive an externally supplied AC voltage and to generate a DC bus voltage. An inverter circuit portion is arranged to receive the DC bus voltage (VDC_Bus) and to generate an AC output voltage (Vout) for supply to an external load. A DC bus portion is connected between the rectifier and the inverter. An inductor (L1) is connected in series along a bus conductor between the rectifier and inverter, and a DC link capacitor (C1) is connected in parallel between the bus conductors. A voltage across the DC link capacitor (C1) is input to a tuneable notch filter arranged to supply a filtered signal. A controller varies the resonant frequency of the notch filter to a plurality of values across an operational range and modulates a supply current provided by the inverter with a probe current signal at the resonant frequency.

Abstract: A filter for motor speed measurement signals includes one or more resonators configured to filter signals having a frequency that is proportional by a predetermined factor to the frequency of the motor whose speed is measured.