The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Sensorless Control of AC Drives Equipped with an Inverter Output Filter

Janne Salomäki

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 21st of December, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9130-4)   [1153 KB]
Dissertation is also available in print (ISBN 978-951-22-9129-8)

Abstract

In this thesis, new sensorless control methods are developed for AC motor drives equipped with an inverter output filter. A three-phase LC filter with a cut-off frequency well below the switching frequency of the inverter enables nearly sinusoidal supply voltage for the motor. Induction motors and permanent magnet synchronous motors are typically connected directly to the frequency converter. In some applications, however, it is necessary to add a filter between the inverter and the motor in order to mitigate the harmful effects of the pulse-width modulated (PWM) voltage. The control methods proposed in this thesis take an LC filter into account. Besides the conventional stator current control, two nested control loops are added to control the stator voltage and the inverter output current. A full-order observer of the motor dynamics is augmented with the filter dynamics. The observer enables the vector control without any additional current or voltage measurements. Furthermore, the drive should preferably work without a speed sensor. A speed adaptation mechanism is added to the observer enabling the speed-sensorless operation. The selection of the observer gain and adaptation parameters is based on the linearization analysis of the system. Speed-sensorless control methods are known to have stability problems at low speeds. Similar problems occur when the inverter output filter is used. To enhance the stability at low speeds, the speed-adaptive observer is augmented with a high-frequency signal injection method for permanent magnet synchronous motor drives equipped with an LC filter. The signal injection enables sustained operation even at zero speed under load changes. Field-weakening methods are also developed for AC motor drives equipped with an inverter output filter. Computer simulations and experiments validate the performance of the proposed control methods in wide speed and load ranges. In addition, the influence of the inverter output filter on the selection of the PWM method is investigated. If a common-mode filter is used, discontinuous PWM methods may cause excessive vibration in the common-mode current. A conventional space vector PWM is suitable method, because it does not generate significant harmonics near the resonance frequency of the common-mode filter. The cost-effective filter design is also considered. Filtering requirements and the limitation caused by the vector control are taken into account in the filter design.

This thesis consists of an overview and of the following 8 publications:

  1. Salomäki, J. and Luomi, J. (2006). Vector control of an induction motor fed by a PWM inverter with output LC filter. European Power Electronics and Drives Association Journal, 16 (1), pp. 37-43. © 2006 European Power Electronics and Drives Association. By permission.
  2. Salomäki, J., Hinkkanen, M., and Luomi, J. (2006). Sensorless vector control of an induction motor fed by a PWM inverter through an output LC filter. IEEJ Transactions on Industry Applications, 126 (4), pp. 430-437.
  3. Salomäki, J., Hinkkanen, M., and Luomi, J. (2006). Sensorless control of induction motor drives equipped with inverter output filter. IEEE Transactions on Industrial Electronics, 53 (4), pp. 1188-1197. © 2006 IEEE. By permission.
  4. Salomäki, J., Hinkkanen, M., and Luomi, J. (2006). Influence of inverter output filter on the selection of PWM technique. In Proceedings of the 2006 IEEE International Symposium on Industrial Electronics (ISIE 2006), Montreal, Canada, pp. 1052-1057. © 2006 IEEE. By permission.
  5. Salomäki, J., Piippo, A., Hinkkanen, M., and Luomi, J. (2006). Sensorless vector control of PMSM drives equipped with inverter output filter. In Proceedings of the 32nd Annual Conference of the IEEE Industrial Electronics Society (IECON 2006), Paris, France, pp. 1059-1064. © 2006 IEEE. By permission.
  6. Salomäki, J., Hinkkanen, M., and Luomi, J. (2008). Influence of inverter output filter on maximum torque and speed of PMSM drives. IEEE Transactions on Industry Applications, 44 (1), in press. © 2008 IEEE. By permission.
  7. Piippo, A., Salomäki, J., and Luomi, J. (2007). Signal injection in sensorless PMSM drives equipped with inverter output filter. In Proceedings of the Fourth Power Conversion Conference (PCC 2007), Nagoya, Japan, pp. 1105-1110. © 2007 IEEE. By permission.
  8. Salomäki, J., Hinkkanen, M., and Luomi, J. (2007). Cost-effective design of inverter output filters for AC drives. In Proceedings of the 33rd Annual Conference of the IEEE Industrial Electronics Society (IECON 2007), Taipei, Taiwan, pp. 1220-1226. © 2007 IEEE. By permission.

Keywords: inverter output filter, induction motor, permanent magnet synchronous motor, sensorless control

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© 2007 Helsinki University of Technology

Last update 2011-05-26