A Novel Approach for Controlling the Electric Drives Used in Electric Trains

Abstract

Nowadays, the DC motors have been replaced by induction motors in most of the industrial applications. Substantially, Induction motors are single speed, but they can produce high power density in a wide range of speed by applying new drive controllers based on constant V/f, DTC and vector control theory. Electric motors control is mainly accomplished by power electronic drives based on control schemes like constant v/f. However, the challenge of torque generation with fast time response and high accuracy was met by using the controllers based on vector control and DTC. In applications like electric train, generation of torque with rapid time response is so vital. As an example, in Anti skid-Anti slid system, the generated torque should vary between zero and the desirable value quickly to prevent the electric train from slip and the wheels from skidding on the rail. However, the accuracy of the torque magnitude due to its high value is not an important issue and most of the time, errors up to 3 percents in the generated torque is acceptable. In this paper, the control systems used in constant v/f drives are modified in order to generate torque with fast time response and acceptable accuracy. Control systems stability is an essential concern in electric drives and is arisen from the complexities in the controller's process and the time delays. In the proposed system, by simplification of the drive controllers, the instability problem of the control units is eliminated which in turn reduces the calculation time delays and results in torque generation with appropriate time response. Furthermore, the overall cost of the drive system is reduced considerably.