Search

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 as for an equivalent three-phase machine. The main alternative to the VSD is the multistator (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 article 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 nonstandard spatial shift between windings. Experimental results are presented for a nine-phase PMSM prototype with a triple-three-phase stator winding configuration. [ABSTRACT FROM AUTHOR]

This article presents a generalized approach toward the dc-link voltage switching ripple analysis in the two-level multiphase pulsewidth modulation (PWM) voltage source inverters with a balanced load. Since the voltage ripple is one of the crucial sizing criteria for a dc-link capacitor, a 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 the 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 by increasing the number of phases up to seven. However, from the point of view of the 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 are derived with an aim to provide the precise dc-link capacitor sizing and hence improve the power density of the whole system. The comparison of different phase numbers has been made. Proposed theoretical developments are verified by the simulation and experimental tests. [ABSTRACT FROM AUTHOR]

Testing the high-power machines in general is not an easy task. One of the standard tests is the full-load test. This test typically requires another machine, of the same or higher power rating, to be coupled to the tested one. For multiphase machines, which are commonly designed for high-power applications, this test can be conducted in a different way. In order to simplify full-load test, this paper proposes a new method that is applicable for multiple three-phase machines with even number of neutral points. The method is based on indirect rotor-field oriented control. It enables evaluation of the efficiency and the thermal design in the case of synchronous machines and the segregation of the constant and stator variable losses for induction machines, without the need for coupling another machine as a load. In the presented method, the full-load test conditions on the stator are obtained by circulating the rated active power flow in a closed loop from one winding set to another. The only power used during the test is to cover machine and converter losses. The proposed control scheme is unique and is based around y-component from the vector space decomposition subspace. It is validated through the simulation and experimental results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study discusses the space vector pulse-width modulation (SVPWM) scheme for an eleven-phase two-level voltage source inverter, aimed at producing a sinusoidal output voltage waveform. Generalised space vector theory is used to realise the SVPWM. As per the general inverter switching theory, there are 211 = 2048 switching states that yield 2046 active voltage space vectors and one zero voltage vector, which results with two switching states. Out of the total of 2046 active voltage vectors, the most suitable set comprising 110 active voltage vectors is identified and is utilised in the implementation of the SVPWM. The sinusoidal voltage is obtained by controlling the duty cycles of the applied voltage space vectors in such a way that the non-zero reference voltage in the first (d-q) plane is achieved, while simultaneously zeroing the average voltage in the other four (x-y) planes in accordance with the zero references. The theoretical results are verified by experimentation using a passive resistive-inductive load. Finally, experimentally obtained total harmonic distortion values of the phase voltage and current for the eleven-phase SVPWM are compared with the corresponding values obtained using SVPWM for other odd phase numbers. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulation strategy for a seven-phase three-level inverter, aimed at variable-speed drive applications. Developed space vector pulsewidth modulation (SVPWM) strategy is based on vector space decomposition (VSD) approach and an analysis of multidimensional space vector projections in mutually orthogonal planes. The algorithm represents an extension of a recently developed five-phase three-level SVPWM algorithm and is considerably more complex, due to the existence of three mutually orthogonal planes in a seven-phase system. The difficulties of generalization of space vector strategies, which stem from the nature of the multiphase systems, are highlighted. Increasing the number of phases from five to seven increases the number of switching states from 3 ^5 = 243 to 3^7 = 2187 and the number of orthogonal planes from two to three. This considerably affects the complexity of the offline calculations. However, the final implementation of the algorithm is simple. Developed SVPWM algorithm is compared to an equivalent carrier-based strategy and it is shown that they yield identical performance. The complexity of the algorithms for real-time implementation is compared. Simulation and experimental results, obtained using neutral-point clamped inverter, verify the theoretical developments. [ABSTRACT FROM AUTHOR]