PMSM and IM rotational sensorless technologies specialized for railway vehicles traction

Rotational sensorless control methods which are particular to the railway vehicle applications are presented in this paper. An induction motor speed sensorless control method for railway vehicle traction is introduced, including the re-powering control method. Especially, a mechanical simulator method which is utilized for stating induction motors at zero speed condition are presented. A permanent magnet permanent magnet synchronous motor (PMSM) rotor angle sensorless control method with the induced voltage are also introduced, including harmonics current injection method for starting at zero speed condition. A modified inverter short circuit method for re-powering control method of PMSMs is presented in this paper.

I. Introduction

As traction motors for railway vehicles, induction motors have been mainly utilized for these thirty years. In many cases, the rotor speed is detected by pulse sensors for the indirect type vector control. In some cases, speed sensorless control is employed to improve the reliability against the troubles of sensors and their cables and to reduce the length of the traction motor or increase the power density per volume. Even in the lower speed range, traction induction motors are required to output enough torque to start the vehicles by the required acceleration. In the lower speed range, the induced voltage is too low to utilize the frequency information included in the rotor induced voltage. Thus, other method than using the rotor induced voltage must be applied, such as a kind of feed forward strategy. A mechanical simulator method is introduced in this paper as a rotor speed estimation method in the ultra lower speed range, which is a kind of feed forward rotor speed estimation. Traction inverters with IGBTs for electrical motive units (EMUs) are designed as small as possible for the underfloor installation. Thus, the inverters are not designed under the continuous rating, but a few minutes rating. They are designed under the condition that the switching of IGBTs stops at the coasting condition after the powering mode or before the regenerative brake mode. Therefore, the inverter must start the speed sensorless control procedure under the rotor rotating condition. This means that the speed estimation must be conducted without the rotor flux, though the rotor frequency is needed to establish the rotor flux and to identify its direction of the rotational coordinates. To cope with these technical issues, the rotor speed must be estimated right after the switching of IGBTs starts. This is called re-powering control and this is a particular control function for railway traction applications. In a method which is presented in this paper, the rotor induced voltage is utilized to estimate the initial rotor frequency, as well the frequency estimation procedure in the normal condition. The estimated frequency at the re-powering is obtained by the oscillation of the rotor induced voltage with high gains on its compensator.