Derivation of motor mean phase currents in PMSM drives operating with low switching-to-fundamental frequency ratio

Leszek Jarzębowicz

doi:10.2478/pead-2019-0003

Derivation of motor mean phase currents in PMSM drives operating with low switching-to-fundamental frequency ratio

Abstract

Pulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase cur-rents to consist of distinctive ripples. In order to provide suitable feedback for the motor current con-trollers, the mean value must be extracted from the currents’ waveforms in every PWM cycle. A com-mon solution to derive the mean phase currents is to sample their value at the midpoint of a symmetrical PWM cycle. Using an assumption of linear current changes in steady PWM subintervals, this midpoint sample corresponds to the mean current in the PWM cycle. This way no hardware filtering or high-rate current sampling is required. Nevertheless, the as-sumption of linear current changes has been recently reported as over simplistic in permanent magnet syn-chronous motor (PMSM) drives operating with low switching-to-fundamental frequency ratio (SFFR). This, in turn, causes substantial errors in the repre-sentation of the mean phase currents by the midpoint sample. This paper proposes a solution for deriving mean phase currents in low SFFR PMSM drives, which does not rely on the linear current change as-sumption. The method is based on sampling the cur-rents at the start point of a PWM cycle and correct-ing the sampled value using a model-based formula that reproduces the current waveforms. Effective-ness of the method is verified by simulation for an exemplary setup of high-speed PMSM drive. The re-sults show that the proposed method decreases the error of determining the mean phase currents approx-imately 10 times when compared to the classical midpoint sampling technique.

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Leszek Jarzębowicz dr hab. inż.

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artykuły w czasopismach

Published in:

Power Electronics and Drives no. 4, pages 95 - 102,
ISSN: 2451-0262

Language:

English

Publication year:

2019

Bibliographic description:

Jarzębowicz L.: Derivation of motor mean phase currents in PMSM drives operating with low switching-to-fundamental frequency ratio// Power Electronics and Drives -Vol. 4,iss. 39 (2019), s.95-102

DOI: