A simple fault-tolerant induction motor drive for auxiliary equipment of railway locomotives

This work was supported by Italian Ministry of Research.
divided into two groups, each one supplied by a power converter. The frequency of the output voltage of one converter is variable within a limited range with a v/f law, while the other is constant. The system is already endowed with a certain degree of fault tolerance. For example if a converter is out of order the essential auxiliary equipment is supplied by the working converter while other less important loads are excluded. A proposal for system fault-tolerance improvement is to make both the power converters supplying the auxiliary equipment fault-tolerant. This allows each converter to operate, even if with reduced performance, also in case of a fault occurrence, causing therefore the degraded operation of only the auxiliary equipment supplied by that converter. Electrical auxiliary equipment includes cooling fans, air compressors, pumps, battery chargers, cabin auxiliaries (such as air conditioning). The most important loads are constituted by induction motors, therefore the auxiliary equipment system can be considered as an induction motor drive. In this paper a simple induction motor drive employing v/f control with fault-tolerant features is proposed. Only the fault tolerance of the converter is considered. The first step in fault tolerance implementation is fault diagnosis. Many diagnosis methods are proposed in the literature [1]. In case of a fault resulting in an open switch there are many methods based on the analysis of the current space vector [2], [3], [4] and a few ones based on the analysis of a voltage error [5]. In this paper a very simple diagnosis method based on the analysis of the current vector is proposed. After a fault occurrence many different remedial topologies are possible [6], [7], but most of them are applied to electric drives with a control system using current regulators or direct torque control [7], [8]. Since the goal of this paper is to provide a simple v/f motor drive with fault-tolerant performances, the simplest solution is considered, that is in presence of a fault the control system isolates the faulty leg and connects the stator winding neutral point to the dc-link middle point through a switch S [8], as represented in Fig.1. In this situation a v/f law is still used to control the motor speed, but it is modified in order to keep the amplitude of the rotating m.m.f. constant and therefore to minimize the torque ripple.
SPEEDAM 2008 International Symposium on Power Electronics, Electrical Drives, Automimple Fault-Tolerant Induction Motor Drive for Dependable Electrical Auxiliary Equipment of Railway Locomotives
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Abstract -- A simple fault-tolerant induction motor drive with v/f speed control included in the electrical auxiliary equipment of railway locomotives is presented in the paper. The employment of fault tolerant on-board electrical auxiliary equipment increases the dependability and then the quality of the railway service. The fault tolerance technique consists of some emergency countermeasures applied in case of fault. It includes a fault diagnosis procedure based on the analysis of the current vector, the connection of the stator winding neutral point to the dc-link middle point and the variation of the v/f law, taking into account the contribution of the zero-sequence impedance and the need for a flux weakening in order to avoid saturation. Some experimental results are reported showing the improved performance of the motor drive under fault conditions by means of the proposed remedial strategy. Index Terms -- Fault diagnosis, fault tolerance, induction motor drives.
I. NOMENCLATURE Rs, Rr stator and rotor phase winding resistances, Ls, Lr stator and rotor self inductances, stator leakage inductance, Lσs magnetizing inductance, Lm s rotor slip, peak value of the rotor flux. Λr II. INTRODUCTION Fault tolerance is a fundamental requirement for dependable electric drives used in safety-critical applications or industrial processes where the very high costs of unplanned stops are unacceptable. Nevertheless nowadays the demand for systems with improved performances makes fault tolerance more and more important also in electric drives used for less critical applications. An example of such an application is represented by the electrical on-board auxiliary equipment of railway rolling stock, the dependability of which is essential to respect the requirements on the quality of service. For instance in one of the latest locomotives (the E464) in use on the Italian railway network, the auxiliary equipment is
Fig. 1. Induction motor drive with connection of the stator winding neutral point to the dc-link middle point in case of fault.
S. Castellan, M. Favot, R. Menis, and A. Tessarolo
Department of Electrical, Electronic and Computer Engineering, University of Trieste, via A. Valerio, 10 - Trieste (Italy)