Effect of motor current sampling method on motor torque ripple in high torque permanent magnet synchronous machine drives

High torque low speed direct drive permanent magnetic synchronous machines (PMSM) powered by variable speed drives are increasingly used in applications traditionally reserved for standard induction motors with gear-boxes. Our application experience shows that in such motors resonant frequency of the common mode current path can have unusually low value (comparable with the inverter switching frequency) which is for at least a decade lower than that normally expected in standard induction machines. Thus the drive inverter switchings can excite large common mode currents which appear as a strong low frequency disturbance in the motor currents causing significant errors in the motor current measurements and related motor torque ripple induced by the drive itself. Rejection of such strong low frequency disturbance in the motor current measurements appears to be far more problematic that the rejection of the standard motor current switching ripple or high frequency noise caused by the inverter switching. Our goal in this paper is to point out to this issue and investigate practically available options appropriate for its mitigation. It will be shown and experimentally demonstrated that the averaging sampling method is suitable for this purpose.

[1]  J. Richardson,et al.  Implementation of PWM regular sampling strategy for AC drives , 1989, 20th Annual IEEE Power Electronics Specialists Conference.

[2]  D. Schlegel,et al.  High frequency modeling of current sensors , 1999, APEC '99. Fourteenth Annual Applied Power Electronics Conference and Exposition. 1999 Conference Proceedings (Cat. No.99CH36285).

[3]  Ann C. Mertens,et al.  Voltage and current sensing in power electronic converters using sigma-delta A/D conversion , 1996, IAS '96. Conference Record of the 1996 IEEE Industry Applications Conference Thirty-First IAS Annual Meeting.

[4]  V. Blasko,et al.  Sampling of discontinuous voltage and current signals in electrical drives: a system approach , 1997, IAS '97. Conference Record of the 1997 IEEE Industry Applications Conference Thirty-Second IAS Annual Meeting.

[5]  Seung-Ki Sul,et al.  Current measurements in digitally controlled AC drives , 2000 .

[6]  Takashi Sukegawa,et al.  A high accuracy current component detection method for fully digital, vector-controlled PWM VSI-fed AC drives , 1988, PESC '88 Record., 19th Annual IEEE Power Electronics Specialists Conference.

[7]  Seung-Ki Sul,et al.  Analysis and compensation of current measurement error in vector controlled AC motor drives , 1996, IAS '96. Conference Record of the 1996 IEEE Industry Applications Conference Thirty-First IAS Annual Meeting.

[8]  Shaotang Chen,et al.  Controller induced parasitic torque ripples in a PM synchronous motor , 2000, Conference Record of the 2000 IEEE Industry Applications Conference. Thirty-Fifth IAS Annual Meeting and World Conference on Industrial Applications of Electrical Energy (Cat. No.00CH37129).

[9]  Lasse Laurila,et al.  Analysis of torque and speed ripple producing non-idealities of frequency converters in electric drives , 2004 .

[10]  E. Persson.  A new approach to motor drive current measurement , 2001, 4th IEEE International Conference on Power Electronics and Drive Systems. IEEE PEDS 2001 - Indonesia. Proceedings (Cat. No.01TH8594).