This paper investigates the use of different techniques for fault detection in voltage-fed asynchronous machine drive systems. With the proposed techniques it is possible to detect and identify the power switch in which the fault has occurred. Such detection requires the measurement of some voltages and is based on the analytical model of the voltage source inverter. Simulation and experimental results are presented to demonstrate the correctness of the proposed techniques. The results obtained so far indicate that it is possible to embed some fault-tolerant properties for the voltage-fed asynchronous machine drive system.

This paper shows how to integrate fault compensation strategies into two different types of configurations of induction motor drive systems. The proposed strategies provide compensation for open-circuit and short-circuit failures occurring in the converter power devices. The fault compensation is achieved by reconfiguring the power converter topology with the help of isolating and connecting devices. These devices are used to redefine the post-fault converter topology. This allows for continuous free operation of the drive after isolation of the faulty power switches in the converter. Experimental results demonstrate the validity of the proposed systems.

A general pulsewidth modulation (PWM) method for control of four-switch three-phase inverters is presented. The proposed vector PWM offers a simple method to select three or four vectors that effectively synthesize the desired output voltage, even in presence of voltage oscillations across the two dc-link capacitors. The method utilizes the so called space vector modulation, and includes its scalar version. Different vector combinations are compared. The effect of Wye and delta motor winding connections over the pulse width modulator is also considered. The common mode voltage generated by the four-switch three-phase converter is evaluated and compared to that provided by the standard six-switch three-phase inverter. Simulation and experimental results are presented to demonstrate the feasibility of the proposed approach

The digital scalar pulse-width modulation (DSPWM) gathers the characteristics of simplicity of implementation found in the regular sampling with the flexibility of manipulation of the switching patterns in the space vector modulation (SVPWM). This paper establishes a correlation between the SVPWM and DSPWM techniques. It also shows how to make the DSPWM strategy equivalent to the SVPWM technique without losing its simplicity of implementation. By using such an equivalence concept a microprocessor-based scheme, which uses standard timer circuits and a simple software algorithm, is proposed to implement the DSPWM technique. The introduction of the "distribution ratio" in this technique, allows the development of a systematic approach for implementing either conventional or any modified vector strategies without changing the modulator scheme. This corresponds to generating any attractive nonsinusoidal modulating signals (NSMS) in the carrier-based modulation techniques. Furthermore, the simple digital blocks can be easily implemented as a specialized integrated circuit. Simulated and experimental results demonstrate the validity of the proposed methods.

The vector modeling approach is employed to describe the behavior of unbalanced three-phase (three-wire), unbalanced two-phase and single-phase systems. In the case of single-phase systems, a fictitious circuit is introduced in order to create the vector model. Continuous-time and discrete-time current controllers based on the vector approach are presented. The current control scheme is based on two controllers, one for the positive sequence and another for the negative sequence. The controllers are implemented in the synchronous reference frame and in the stationary reference frame. In the stationary reference frame, the use of the same integral gains for both controllers simplifies the equations of the control law especially for single-phase systems. Simulation and experimental results obtained with a pulsewidth modulation voltage-source inverter supplying unbalanced systems are presented.

This paper investigates the utilization of a simplified topology that permits the fault-tolerant operation of a three-phase induction motor drive system. When one of the inverter legs is lost, the machine can operate with only two stator windings by connecting the machine neutral to a fourth converter leg. The structure and the operation principle of the system are presented. The machine model corresponding to the asymmetric two-windings machine is developed and a suitable controller is proposed. Experimental results are presented.