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The urban trams with a low floor are more convenient for the passengers, and with a high floor - more cheaply and more technologically during manufacturing and operation. The combined advantages those and others in themselves are trams with average height of a floor, but for this purpose it is necessary to lower height of tram carriages, that is reached by application of electric motors with a small stator external diameter. It is offered in this the perspective electric drive on the base of the synchronous motor with independent excitation. The salient rotor poles of the motor do not contain windings. The motors stator is carried out on the base of the stator body of regular AC electric motor. The multiphase winding is located in the stator. A winding section, which conductors settle down above the between rotor poles, carry out a role of the excitation winding, and others, which conductors lay above poles, - a role of the armature winding.

Regular induction motors operate at a constant value of voltage. They operate from zero external load to rated value. At low loads, motors works with reserve of the power. At low loads, motor can work with lower voltage, with lower current (lower power losses) and higher power factor (cos φ). In the paper, we consider theoretical basics of reduction of idle current and increase power factor in idle mode operation. We consider speed controller by changing value of motor voltage. With this controller, we can reduce idle current and increase its power factor. In addition, we consider current controller for limiting starting current by decreasing voltage during motor start, and reduction idle current with improved power factor in idle steady state conditions. Voltage change includes controlled (thyristor) rectifier or pulse width modulated converter of voltage. Controllers can include speed or current feedbacks. We consider digital model of induction motor with different controllers.

The problem of increasing the accuracy of determining the torque and the load angle of the permanent magnet synchronous motor of an electric traction drive to the predicted level (2.5...3)% of the full-scale error is solved by an indirect method. We considered the algorithms for calculating the generalized current and voltage of the electric motor, the total power, the instantaneous values of the power factor, and the sine of the phase angle between the first harmonics of voltages and currents. We determined the requirements for the accuracy of determining these values at the level of 1% of the full-scale error. We considered the algorithms for determining the total instantaneous power losses by the indirect method at the predicted level (15...20)% of the full-scale error with the efficiency of the motor (90...95)%.