<abstract xmlns="http://www.w3.org/1999/xhtml"><p>Pulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase currents to consist of distinctive ripples. In order to provide suitable feedback for the motor current controllers, the mean value must be extracted from the currents’ waveforms in every PWM cycle. A common 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 assumption of linear current changes has been recently reported as over simplistic in permanent magnet synchronous motor (PMSM) drives operating with low switching-to-fundamental frequency ratio (SFFR). This, in turn, causes substantial errors in the representation 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 assumption. The method is based on sampling the currents at the start point of a PWM cycle and correcting the sampled value using a model-based formula that reproduces the current waveforms. Effectiveness of the method is verified by simulation for an exemplary setup of high-speed PMSM drive. The results show that the proposed method decreases the error of determining the mean phase currents approximately 10 times when compared to the classical midpoint sampling technique.</p></abstract>

Pulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase currents to consist of distinctive ripples. In order to provide suitable feedback for the motor current controllers, the mean value must be extracted from the currents’ waveforms in every PWM cycle. A common 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 assumption of linear current changes has been recently reported as over simplistic in permanent magnet synchronous motor (PMSM) drives operating with low switching-to-fundamental frequency ratio (SFFR). This, in turn, causes substantial errors in the representation 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 assumption. The method is based on sampling the currents at the start point of a PWM cycle and correcting the sampled value using a model-based formula that reproduces the current waveforms. Effectiveness of the method is verified by simulation for an exemplary setup of high-speed PMSM drive. The results show that the proposed method decreases the error of determining the mean phase currents approximately 10 times when compared to the classical midpoint sampling technique.

Derivation of Motor Mean Phase Currents in PMSM Drives Operating with Low Switching-to-Fundamental Frequency Ratio

Faculty of Electrical and Control Engineering

Power Electronics and Drives

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Pulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase currents to consist of distinctive ripples. In order to provide...

Derivation of Motor Mean Phase Currents in PMSM Drives Operating with Low Switching-to-Fundamental Frequency Ratio

Published Online: Nov 26, 2019

Page range: 95 - 102

Received: Sep 27, 2018

Accepted: Dec 27, 2018

DOI: https://doi.org/10.2478/pead-2019-0003

Keywords
Electric drives, High-speed drives, Current control, Current measurement, Permanent Magnet Synchronous Drives, Digital Signal Processing

© 2019 Leszek Jarzebowicz, published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Derivation of Motor Mean Phase Currents in PMSM Drives Operating with Low Switching-to-Fundamental Frequency Ratio

Published Online: Nov 26, 2019

Page range: 95 - 102

Received: Sep 27, 2018

Accepted: Dec 27, 2018

DOI: https://doi.org/10.2478/pead-2019-0003

KeywordsElectric drives, High-speed drives, Current control, Current measurement, Permanent Magnet Synchronous Drives, Digital Signal Processing

© 2019 Leszek Jarzebowicz, published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
Electric drives, High-speed drives, Current control, Current measurement, Permanent Magnet Synchronous Drives, Digital Signal Processing