In this paper, a control scheme for multiphase induction motor drives is presented and assessed. This control scheme ensures the operation of a multiphase drive under an open-circuit phase fault that can occur in one or more phases at the same time. A fault-tolerant control strategy is developed. The mathematical analysis is based on the space vector representation of the multiphase system and is valid either in transient or steady-state operating conditions. The feasibility of the drive is verified by means of experimental tests carried out on a prototype of seven-phase induction motor.

The high-order harmonics of the magnetic field can be used in some typologies of multiphase machine to improve the torque density. However, maximizing the torque capability depends on the thermal, voltage, and current constraints of the machine and the inverter. In this paper, a rotor-flux-oriented control scheme, which is capable of exploiting the maximum torque at any speed, is presented for multiphase induction motor drives. Below the base speed, the torque improvement is obtained by adding a third harmonic component to the fundamental component of the air-gap magnetic field. At high speeds, the amplitude of the field harmonics is progressively reduced to ensure the widest possible operating speed range. The validity of the proposed control scheme is confirmed by experimental tests.

Four sensorless control schemes for the operation of induction motors in the field-weakening region are compared and assessed in terms of performance and complexity. These four control schemes fully utilize the maximum available voltage and current and can produce the maximum possible torque in the entire field-weakening region. For comparison, the four control schemes are implemented on the same experimental platform, i.e., the same DSP board, power inverter, and motor drive. In this way, it is possible to assess not only the performance of each solution, but also its requirements in terms of computational time, tuning complexity, parameter knowledge, and stability of operation.

A torque control scheme that utilizes the stator flux components as control variables, applied to a speed-sensorless induction motor drive, is presented. The proposed scheme allows the motor to exploit the maximum torque capability in the whole speed range, and shows a reduced dependence on the motor parameters. It is based on a control algorithm that decreases the d-component of the stator flux as soon as the voltage corresponding to the maximum torque exceeds the available voltage. The control scheme produces a smooth transition into and out of the field weakening region and preserves the torque dynamic. The feasibility of the field weakening technique is confirmed by computer simulations and experimental tests.

Rotor and stator resistances along with load torque are typically uncertain quantities in induction machines. The machine heating makes the winding resistances vary during operation whereas the load torque strictly depends on the application. All those variables need to be on-line estimated to improve the drive performances and in particular to minimize the power loss at steady state. A new adaptive observer is designed in this brief. It is able to exponentially estimate the motor fluxes and to identify the aforementioned critical parameters from stator currents/voltages and rotor speed measurements. In contrast to other solutions proposed in the literature, rotor and stator resistances are not estimated on the same time scale. New insights on the behavior of an intuitively inspired observer are thus given through a detailed stability proof, which does not rely on linearization arguments around constant operating conditions. Persistency of excitation conditions, which only depend on exogenous signals to the estimation error system, are analyzed in detail and a clear physical interpretation is presented. Key features of the proposed solution are the overall simplicity of the estimation scheme, the low dimension of the regressor matrix (being exactly related to the number of unmeasured or uncertain quantities) and the exponential convergence to zero of the estimation errors. Simulations confirm the correctness of all the mathematical derivations. Experimental results show the effectiveness of the proposed approach in implementing an advanced version of the indirect field oriented control scheme: the uncertain rotor flux modulus reference that minimizes the power loss at steady state can be actually estimated and imposed.

This paper presents a control scheme for an induction motor that integrates, within a coherent solution, some of the features that are commonly required from an electric vehicle drive. The main features of the proposed control scheme are the capability to exploit the maximum torque in the whole speed range, a weak dependence on the motor parameters, a good robustness against the variations of the dc-link voltage, and, whenever possible, the maximum efficiency. The performance of the control scheme is verified by experimental tests.