Continuous and discontinuous modulation techniques for multiphase drives: analysis and contributions

The study of multiphase machines applications is an emergent field of research mainly because of the high reliability they offer for high power applications. Nowadays, they are predominantly supplied from two-level voltage source inverters (VSIs). For the purpose of the inverter control, both carrier-based and space vector pulse width modulation (PWM) techniques have been developed, for various phase numbers, which are capable of generating required sinusoidal output voltages. Both methods are usually a general extension of modulation methods used in the three-phase case. The relationship between continuous carrier-based and space vector PWM has been reported in the scientific literature for the multiphase case, stating analogies and differences. Discontinuous PWM techniques for multiphase inverters have also received some attention as well, but at a lesser extent than the continuous PWM techniques, always in relation to multiphase systems. In this work for filling aforementioned gap, discontinuous modulation methods are first analysed in multiphase drives. The natural consequence of the existence of different PWM strategies is the inherently different behaviour with regard to the performance indicators that can be used to assess the quality of output waveforms. Among these performance indicators, one of the most interesting used in three phase induction machines for the evaluation of switching characteristics and the current ripple are the ux harmonic distortion factor (HDF). However, HDF has been only very recently introduced in the multiphase case, and for asymmetrical six-phase induction machines that can be considered like two three phase machines in the same case. Consequently, there is quite few work in the scientific literature and the multiphase induction machine case in the evaluation of switching characteristics and the current ripple using HDF. Therefore, the extension of HDF for the evaluation of switching characteristics and the current ripple in the multiphase case is studied and analysed like a second main goal of this Thesis. Notice that SVM has been also extended to the multiphase case. However, most scientific literature relates the general case, where linear operation regions are only considered. A third goal of the work is the extension of the operation region of the SVM-multiphase scheme. In this field, non linear operation in the overmodulation region is also considered, guaranteeing a smooth and linear transition characteristic between linear and overmodulation regions, minimizing the unwanted voltage amplitude of low order voltage harmonic components. Then, a simple algorithm is proposed with the ability to minimize xy voltage and current components in any multiphase induction machine with any odd number of phases. Finally, the reduction of Common Mode Voltage (CMV) is an interesting topic in the modulation techniques field because it is known to be the cause of electromagnetic interference (EMI), breakdown of windings insulation, fault activation of current detector circuits and leakage currents problems that can damage the motor bearings. The commonmode voltage issue is also studied in this Thesis, and a SVM method is proposed to minimize its content in the electromechanical system. Major contributions of this dissertation have been published in seven journal and three conferences papers, although related work have been also published in another four journal papers. The main contributions covered in this work are the following: Paper 1: D. Dujic, M. Jones, E. Levi, J. Prieto, F. Barrero, “Switching Ripple Characteristics of Space Vector PWM Schemes for Five-Phase Two-Level Voltage Source Inverters-Part 1: Flux Harmonic Distortion Factors," IEEE Transactions on Industrial Electronics, vol.58, no.7, pp.2789-2798, July 2011. Paper 2: M. Jones, D. Dujic, E. Levi, J. Prieto, F. Barrero, “Switching Ripple Characteristics of Space Vector PWM Schemes for Five-Phase Two-Level Voltage Source Inverters-Part 2: Current Ripple," IEEE Transactions on Industrial Electronics, vol.58, no.7, pp. 2799-2808, July 2011. Paper 3: J. Prieto, M. Jones, F. Barrero, E. Levi, S. Toral, “Comparative Analysis of Discontinuous and Continuous PWM Techniques in VSI-Fed Five-Phase Induction Motor," IEEE Transactions on Industrial Electronics, vol.58, no.12, pp.5324-5335, Dec. 2011. Paper 4: J. Prieto, F. Barrero, E. Levi, S. Toral, M. Jones, M. J. Duran, \Analytical Evaluation of Switching Characteristics in Five-Phase Drives with Discontinuous Space Vector Pulse Width Modulation Techniques", EPE Journal, vol.23, no.2, pp.24-33, Jun. 2013. Paper 5: J. Prieto, E. Levi, F. Barrero, S. Toral, “Output current ripple analysis for asymmetrical six-phase drives using double zero-sequence injection PWM," Proceedings of 37th Annual Conference on IEEE Industrial Electronics Society (IECON 2011), pp.3692-3697, Nov. 2011. Paper 6: M.J. Dur_an, J. Prieto, F. Barrero, J.A. Riveros, H.Guzman, “Space- Vector PWM With Reduced Common-Mode Voltage for Five-Phase Induction Motor Drives," IEEE Transactions on Industrial Electronics, vol.60, no.10, pp.4159- 4168, Oct. 2013. Paper 7: M.J. Duran, J. Prieto, F. Barrero, “Space Vector PWM With Reduced Common-Mode Voltage for Five-Phase Induction Motor Drives Operating in Overmodulation Zone," IEEE Transactions on Power Electronics, vol.28, no.8, pp.4030-4040, Aug. 2013. Paper 8: J. Prieto, F. Barrero, M. J. Duran, S. Toral, M.A. Perales, \SVM Procedure for n-phase VSI With Low Harmonic Distortion in the Overmodulation Region," IEEE Transactions on Industrial Electronics, vol.61, no.1, pp.92-97, Jan. 2014. Notice that all the proposals were validated using simulation and experimental results, and different five-phase and asymmetrical six-phase induction machines available at the labs of the Liverpool John Moores University and the University of Seville, being the candidate one of the main contributors to the obtained publications.