The use of multiphase electric drives in industrial applications has increased in the last few years. These machines’ advantages over the three-phase system make them appropriate for harsh working situations. To increase their inherent reliability, some authors have been working in sensorless control schemes, where the absence of an encoder ensures proper system performance. Nevertheless, these sensorless control systems present some problems due to the uncertainties of the parameters. In this regard, using extended Kalman filters overcomes this situation, since Kalman filters consider the system error and measurement error in the estimation process. However, when the three-phase Kalman filters are extended to the five-phase case of study, the complexity of the problem increases substantially. In this work, the authors propose an extended Kalman filter, which discomposes the original state equation, reducing the complexity of the estimation stage. In addition, the system suppresses the third-harmonic injection, which enhances the overall phase-current quality.

Linear induction motors (LIMs) have been widely used in rail transit. However, Due to the breaking of the primary core and the large air gap, the efficiency and power factor of LIMs are seriously damaged, causing a large amount of energy waste. To improve the efficiency and power factor of LIMs for urban rail transit, we present a new optimization method for the design of a short primary double-sided linear induction motor (SP-DLIM) with a rated speed of 45 km/h and small thrust. The method is based on a steady state equivalent circuit model and the differential evolutionary algorithm (DEA). Moreover, the design constraints and the objective functions are proposed for the optimization problem. Finally, the optimized SP-DLIM is simulated by 2D transient finite element method (FEM). The 2-D transient FEM results verify the accuracy of the optimization method proposed in this paper.

This paper proposes a multilayer analytical model for calculating the magnetic field and equivalent circuit parameters of solid rotor induction motors (SRIM), and the B – H curve of rotor material is used to consider the influence of saturation effect of solid rotor. The equivalent circuit of SRIM based on surface impedance theory can fully consider the influence of rotor material. Then, the magnetic vector potential in the rotor is solved in the three‐dimensional electromagnetic field, and the rotor is segmented along the axial direction to obtain the end coefficient considering the axial non‐linear effect of the rotor. The air gap magnetic field distribution, rotor loss, rotor impedance and torque were analysed by finite element simulation, and the accuracy of the multilayer analytical model and end coefficient was verified. Compared with the finite element method, the analytical method proposed in this paper is time saving, resulting in that it is suitable for the optimised design. Finally, an experimental prototype is developed and tested, confirming the accuracy of both the finite element simulation and the analytical model.

For the reduction in the electromagnetic noise level of three-phase induction motors, many empirical rules and analytical models have been established to select the matching scheme of pole and slot, but they are not fully applicable to five-phase squirrel cage induction motors (FSCIM). In this paper, combined with the slot-number phase diagram (SNPD), and the electromagnetic force-vibration-acoustic analytical model deduced in Part I, the influence of pole-slot schemes, including five-phase regular-size phase-belt and fractional-slot winding, on magnetic noise is analyzed. The feasibility of electromagnetic noise prediction is verified by finite element simulation and experiments. Taking a 4 kW FSCIM as a prototype, noise prediction is carried out for all the slot-number matching schemes with pole pairs not exceeding three. For two noise reduction targets, which reduce the maximum single-frequency noise in the steady-state operation and the average noise during startup, the pole-slot numbers matching rule of FSCIM is given. This improved model is also applicable in different power ranges for the noise reduction design of five-phase motors.

Short primary single-sided linear induction motor (SP-SLIM) exhibits promising potential in maglev rail transit and other fields. However, due to the magnetic field distortion caused by the discontinuous iron core, conventional field analysis models typically neglect the influence of slotting effects on spatial harmonics in both normal and transverse air gap flux density. In practical, however, the slot harmonics exert non-negligible impacts on output characteristics such as thrust fluctuations and vibration noise. Unfortunately, few studies have analyzed the spatial harmonics in SP-SLIMs. To investigate the coupling effects of slot harmonics and longitudinal dynamic end effect in slotted SP-SLIMs, this paper proposes an analytical method for calculating the exact normal and transverse air gap magnetic field under synchronous operation. First, considering the large air-gap of SP-SLIMs, the complex relative permeance is improved by using the finite-slot-depth Schwarz-Christoffel transformation. Second, an equivalent method is constructed, which applies Laplace’s equation, Cauchy-Riemann conditions and 2D slotless magnetic field to acquire the analytical expressions for the exact normal and transverse air gap flux density. Additionally, a spatial harmonic frequency analytical model of SP-SLIM is established. The analytical solutions are compared with finite element method (FEM) results, verifying the effectiveness of the proposed analytical method. Based on the investigations, the major findings include the following:1) For SP-SLIM with large air gaps, the finite slot depth must be considered under some specific conditions; 2). There are four major spatial frequencies in the slotted field, predominantly determined by pole pitch and slot pitch; 3) The thrust ripple can be calculated more precisely by the proposed magnetic field compared with conventional method.

Five-phase induction motors have the advantages of high reliability and strong fault-tolerant performance, so it’s open circuit fault model and fault-tolerant control strategy are widely studied. Based on the normal operation of the five-phase induction motor, the mathematical model of the five-phase induction motor under the conditions of single-phase open circuits, adjacent two-phase open circuits, and non-adjacent two-phase open circuits are established by using the reduced order decoupling transformation. Based on the principle of constant magnetic potential, the relationship between magnetic potential and each phase current is analyzed by using the symmetrical component method (MSC). The fault-tolerant control strategy of a five-phase induction motor with the above three open-circuit faults is designed. Through simulation and prototype experiments, the phase current and speed conversion under three open-circuit faults are analyzed. The results show that after the open-circuit fault of a five-phase motor, the residual phase current is no longer balanced, the motor speed is decreased, and the vibration is increased significantly. After fault-tolerant control, the residual phase current is balanced, the rated speed can be reached, and the vibration of the motor is reduced. Thus, the validity and correctness of the fault-tolerant control strategy for a five-phase induction motor are verified.