Abstract
The direct axis (d-axis) stator winding and field winding of a wound-rotor synchronous motor (WRSM) are mutually coupled much like the primary and secondary windings in a transformer are. As the field winding has a large number of turns, small variations of the stator d-axis current can induce a great electromotive force (EMF) in the field windings. This induced EMF voltage disturbs field current regulation, invokes an unwanted field current response, and distorts the stator d-axis flux. In this work, a novel field current control strategy for the WRSM is proposed for compensating the disturbance by d-axis current in field winding. The coupling effect between the stator d-axis winding and field winding is analyzed by using a polynomial regression of the stator d-axis flux linkage. Based on an analysis of the coupling effect, the proposed strategy combines two control methods. First, feedforward control is applied to decouple the field current response from the coupled change in the stator d-axis current flux. Second, a method is used to adjust the d-axis current to ensure that the field inverter voltage is not saturated. Simulations and experiments are presented to verify the proposed control method, proving that the proposed field current control strategy successfully compensates for the field current ripples caused by variations in the coupled stator d-axis current flux.
Highlights
Wound-rotor synchronous motors (WRSM) are widely used in electric vehicles (EVs) because they require no rare-earth magnets and provide a broad range of operating speeds with good high-speed efficiency. These advantages make WRSMs well-suited for use in EV propulsion motors [1]–[5] and integrated starter generators (ISGs) [6]–[8]
If the calculated compensation voltage is greater than the DC link voltage, the d-axis current command is adjusted and the transient field current is completely reduced by feedforward control
Owing to the coupling between its field and stator windings, the WRSM is prone to faults when the field current is influenced by rapid changes in the d-axis current
Summary
Wound-rotor synchronous motors (WRSM) are widely used in electric vehicles (EVs) because they require no rare-earth magnets and provide a broad range of operating speeds with good high-speed efficiency. A field current ripple induced by variation in the stator d-axis current flux can delay the change of stator d-axis flux linkage, which limits field-weakening control and causes torque ripples To address this problem, a coupling inductance look-up table is used to compensate for d-f cross coupling in [3]. Because of the high turns ratio between the stator d-axis and field winding, a small change in the d-axis current flux would invoke a large field control voltage demand; field-inverter voltage saturation was not considered in [12]–[14]. To compensate for the effects of this coupled EMF in field current control, at first, the d-axis flux linkage with magnetic saturation is modeled in a polynomial equation with the d-axis current and field current. The effects of the coupled flux linkage on the field current controller are analyzed and an appropriate compensation method is proposed
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