M. Mengoni

Control of Multiphase Induction Motors With an Odd Number of Phases Under Open-Circuit Phase Faults

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.

Stator Flux Vector Control of Induction Motor Drive in the Field Weakening Region

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.

High-Torque-Density Control of Multiphase Induction Motor Drives Operating Over a Wide Speed Range

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.

A Comparison of Four Robust Control Schemes for Field-Weakening Operation of Induction Motors

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.

Detection and Localization of Stator Resistance Dissymmetry Based on Multiple Reference Frame Controllers in Multiphase Induction Motor Drives

Multiphase drives are receiving increasing attention by the research community in high-power applications. In this paper, the behavior of multiphase induction machines with an odd number of phases is investigated under the assumption that the resistances of the stator winding are unbalanced owing to poor connections. A high-resistance connection can cause overheating and supply voltage unbalance, which may reduce the efficiency and increase the fire hazard. The main contribution of this paper is a control scheme that can detect the stator resistance unbalance, that can localize the faulty phase, and, at the same time, that can keep the drive behavior unchanged, both in transient and steady-state operating conditions. The control scheme is based on an analytical model that shows the effect of the unbalance on the current components related to the high-order spatial harmonics of the air-gap magnetic field. The theoretical analysis and the feasibility of the control scheme are confirmed by experimental tests.

Minimization of the Power Losses in IGBT Multiphase Inverters with Carrier-Based Pulsewidth Modulation

Nowadays, there is an increasing interest toward multiphase drives, particularly for medium- and high-power applications. In this paper, some modulation strategies for multiphase voltage-source inverters are compared and the modulation strategy with the minimum switching losses is determined. If the switching devices of the inverter are insulated-gate bipolar transistors or bipolar junction transistors, this modulation strategy turns out to be the one with the minimum total power losses. Simulation and experimental results confirm the validity of the analytical approach and the feasibility of the proposed modulation strategy.

Space Vector Modulation for Multiphase Inverters Based on a Space Partitioning Algorithm

Since the late 1990s, multiphase drives have become a serious alternative to three-phase drives in some particular applications such as electric ship propulsion, locomotive traction, electric vehicles, and high-power industrial applications. Nowadays, the research activity is focused on the development of control strategies that can exploit the degrees of freedom that exist in multiphase machines. As known, a multiphase motor cannot be analyzed using the space vector representation in a single d -q plane, but it is necessary to introduce multiple d-q planes. In this paper, the problem of the space vector modulation (SVM) of multiphase inverters is solved extending the theory of SVM used for traditional three-phase voltage source inverters and introducing the concept of reciprocal vector. The proposed approach, confirmed by experimental tests, allows the full exploitation of the dc input voltage and the simultaneous modulation of voltage space vectors in different d-q planes.

On-Line Identification of Winding Resistances and Load Torque in Induction Machines

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.

A Control Scheme With Energy Saving and DC-Link Overvoltage Rejection for Induction Motor Drives of Electric Vehicles

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.

Optimal fault-tolerant control strategy for multi-phase motor drives under an open circuit phase fault condition

In this paper an optimal disturbance-free control strategy suitable for open-phase fault operation of multi-phase current regulated motor drives, is presented and tested. The proposed strategy, which is based on the multiple space vector representation of multi-phase systems, minimizes the stator copper losses either in transient or steady-state operating conditions. The effectiveness of the proposed fault tolerant control strategy is verified for a five-phase permanent magnet motor using a finite element analysis. Furthermore, some experimental tests have been carried out on a seven-phase asynchronous motor drive prototype available in laboratory.