Research of Scalar Control System of Two Traction Induction Motors From by One Inverter

Abstract

Most adjustable-speed AC drive systems are constructed in such a way that one motor receives power from one inverter and uses vector control as the basic control principle. However, in some cases there is a need to power several motors in parallel from a single inverter, that minimizes the size, weight and cost of such a system. The most common examples of such systems are rail and urban electric vehicles, where two to four induction motors are connected to drive in parallel. Control of such a system is a difficult task, especially in conditions of unbalanced loads on the motors, that can occur in conditions of different adhesion of wheels with rails. The inability to provide individual control of the motor when powered by a single inverter can lead to a decrease in the safety level of such a vehicle due to the loss of stability when changing the current value of the adhesion coefficient of individual wheel pairs. Mechanical processes in the traction system are analyzed, in which each wheel pair is driven by a separate motor powered by a common inverter. It is shown that the identity of the values of the adhesion coefficients is an important condition for the stability of such a system, that cannot be guaranteed in the actual practice of the operation of the vehicle. Therefore, the development and research of control systems that are capable of operating the system in a variety of rail / road conditions is an important direction for the further development of such systems. The structure of mathematical model of traction electromechanical system consisting of two induction motors powered by one inverter is proposed. The adjustable-speed control is based on the scalar control system, that is the easiest to implement because it does not require the estimation of the state variables of the system components. Sinusoidal pulse width modulation is selected as the switch control signal method. Operation of traction electromechanical system with scalar frequency control law is investigated by mathematical modeling. It has been proven that changing the characteristics of a single wheel pair's adhesion can lead to a loss of stability by a system that is unacceptable in terms of providing a comfortable and safe operation of the vehicle. Keywords: traction electric drive, scalar control, adhesion, mathematical model, frequency control