Recent developments in power electronics are making the multiphase machines a competitive alternative to conventional three-phase counterparts. Due to their fault-tolerant features, multiphase drives represent a robust technology in high power/high current, safety-critical applications. Besides, their introduction into transportation electrification is gaining on importance. Among the multiphase solutions, the multi-three-phase machines are receiving a lot of the attention by the industry since they use the well-consolidated three-phase technology, thus reducing the design time and also the cost. Therefore, this paper proposes a modular vector control scheme for multi-three-phase permanent magnet synchronous motors. The proposed solution uses a modular modeling approach for the independent and decoupled torque control of each three-phase unit, allowing the implementation of torque-sharing strategies among the three-phase sets of the machine. The developed modular control has been validated on a nine-phase permanent magnet machine.

In multiphase machine drives, accuracy of the estimated machine parameters is crucial for effective performance prediction and/or control. While a great amount of work has been done on parameter estimation for three-phase machines, corresponding discussions for six-phase machine remain scarce. It has been proven in the literature that the effect of mutual leakage inductance between different winding layers has a significant impact on the equivalent machine reactance, which challenges the standard separation method of stator and rotor leakage inductances from the measured locked-rotor impedance. In this paper, parameter identification of an asymmetrical six-phase induction machine using six-phase no-load and locked-rotor tests is discussed. A zero-sequence test using an improved equivalent circuit is proposed to improve the accuracy of the estimated parameters. The concept is verified using experimental results obtained from a low-power prototype asymmetrical six-phase machine.

When multiphase drives are used for specific applications, the modular solutions are preferred as they use consolidated power electronics technologies. The literature reports two modeling approaches for multiphase machines having a modular configuration of the stator winding. The first approach is the vector space decomposition (VSD) that models the energy conversion like an equivalent three-phase machine. The main alternative to the VSD is the multi-stator (MS) modeling that emphasizes machine modularity in terms of torque production. Both approaches have advantages and disadvantages for multiphase machines with a modular structure. Therefore, this paper aims to combine the VSD and MS approaches, defining a new matrix transformation and hence developing a new modeling approach for multiphase machines with a modular structure. The proposed transformation allows a decoupled and independent torque control of the sets composing the machine, preserving the torque regulation's modularity. Together with a new vector control scheme, it has been applied to a modular permanent magnet synchronous machine (PMSM) with a non-standard spatial shift between windings. Experimental results are presented for a nine-phase PMSM prototype with a triple-three-phase stator winding configuration.

A space vector pulse-width modulation (SVPWM) algorithm for a three-level symmetrical six-phase drive, based on a vector space decomposition approach, is, for the first time, presented and experimentally proven in this paper. The process how to correctly select the optimal switching sequences, based on several starting requirements and conditions for the analyzed topology, such that the output phase voltage waveforms do not contain any low-order harmonics, is explained in detail. The developed SVPWM algorithm is verified experimentally using a three-level neutral-point-clamped converter and a symmetrical six-phase induction machine. Obtained results prove the validity of the developed SVPWM algorithm. The performance of the SVPWM algorithm is compared with the corresponding carrier-based modulation strategy, and it is shown that the two techniques yield identical performance. Finally, both simulation and experimental analysis of the voltage and current total harmonic distortion (THD) are reported.

This paper presents a generalized approach towards the dc-link voltage switching ripple analysis in two-level multiphase PWM voltage source inverters with balanced load. Since voltage ripple is one of the crucial sizing criteria for dc-link capacitor, simple and practical equation for designing the dc-link capacitor based on the maximum (peak-to-peak) value of the dc-link voltage ripple has been proposed for multiphase inverters. The amplitude of the dc-link voltage switching ripple is analytically derived as a function of operating conditions. The effect of the number of phases on the dc-link capacitor size is investigated as well. It is found that considering the same total output current, the dc-link capacitor size is reduced increasing the number of phases up to seven. However, from the point of view of dc-link capacitor size, there are no benefits of further increasing the number of phases. Reference is made to two commonly used modulation strategies – sinusoidal PWM and continuous symmetric centered PWM (i.e., space vector). The mathematical models derived aim to provide precise dc-link capacitor sizing and hence improve the power density of the whole system. Comparison within different phase numbers has been made. Proposed theoretical developments are verified by simulations and experimental tests.

This work presents a modelling approach and a control strategy for a multiphase surface mounted Permanent Magnet Synchronous Machine (PMSM) drive. The mathematical model is completely general with respect to the machine parameters and to the winding configuration. It also intrinsically considers the effects of eventual constraints for the phase currents, generated from the electrical connections among the phase windings or resulting from faults. The current controller is entirely formalized in the phase variables domain. It is based on a pseudo-inverse decoupling algorithm and on a linear decoupled controller. The current references are computed by means of a Maximum-Torque-Per-Ampere (MTPA) strategy, which can be also easily adapted for torque sharing purposes. The proposed controller requires minimum changes with respect to system reconfigurations or parameters variations and, therefore, it is suited both for healthy and for faulty operations. An extensive set of experimental results has been conducted to validate the proposed approach in several testing scenarios.