An investigation into the use of real-time simulation and hardware-in-the-loop techniques for studying the dynamic performance of adjustable speed drives under fault conditions.

Abstract

Sophisticated adjustable speed drives (ASDs) have for decades been an ever-increasing part of industrial automation and control systems. The control schemes in the drives themselves have been continually developed to exploit improvements made in electrical machine, control system and powerelectronic technologies to fulfil application requirements in industry. One particular trend is the emergence of active front-end type drives, in which advanced control techniques aim to allow ASDs to exhibit increased immunity to power quality problems, in particular voltage sags. The ability to test the impact of power quality events on such drives, as well as the interaction of the drives themselves with other protection and control equipment elsewhere in the system during such events, will be of obvious importance in future, in particular with the increased penetration of such technology in future into both industry and utility systems, and, very importantly, because of the unique characteristics of such controls in each drive manufacturer’s proprietary implementations. This thesis describes a study into the use of real-time digital simulators as a tool for hardware-in-loop (HIL) testing of commercial adjustable speed drive control hardware in order to evaluate the performance of these drives under realistic fault contingencies in an upstream utility power system supply network, rather than relying on limited and simplistic voltage sag tests that are currently often used in such testing. The results of the investigations in the thesis show that, provided key components of the plant in the drive system are modelled in appropriate detail, very accurate results can be obtained from HIL testing of drive controls interfaced to a real-time simulation model of the electrical supply system and of the drive converters and motor plant. The investigations in the thesis also show how different types of adjustable speed drive technology not only respond differently to the same power system disturbances, but also how they can interact differently with the power system, resulting in different degrees of harmonic distortion, fault currents, and depths of voltage sag within the utility power system itself during upstream fault conditions. These results further emphasize the value of being able to test the response of actual drive controller hardware using detailed and realistic real-time simulation models of the supply system when carrying out power quality studies. This real-time simulation approach considered in the thesis constitutes a full, closed-loop test of the actual drive control hardware, but has the advantage of allowing the inclusion of far more detailed representations of the plant in the ASD system itself, and in the utility power supply system, as well as

the inclusion of representations of neighbouring plant fed off busbars in the vicinity of the drive, than is possible in a small-scale laboratory hardware test system such as that which has been used in this thesis for initial validation purposes. However, with the necessary confidence established in the method as a result of the investigations in this thesis, the HIL approach to testing adjustable speed drive controls has potential applications in future for studying the impact of power quality issues on various types of drive system equipment in much larger-scale representations of utility supply networks.