Stator Harmonic Currents in VSI-Fed Synchronous Motors With Multiple Three-Phase Armature Windings

Abstract

Electric motors equipped with multiple three-phase windings are often used for the advantages they offer in terms of reliability, performance, and inverter power segmentation. When the windings are fed by independent voltage-source inverters (VSIs), circulation harmonic currents can occur in stator phases. If the motor is an induction machine, circulation currents are known to originate form transient imbalances in the applied voltages due to inverter switching. This paper investigates the problem when a synchronous machine is used and shows how additional (and possibly major) sources for circulation currents can arise in this case (even with a round-rotor design) due to the nonsinusoidal air-gap flux distribution. The phenomenon is illustrated for a 45-MW quadruple three-phase synchronous motor supplied by four medium-voltage (MV) multilevel VSIs. Its circulation currents are predicted with two alternative methods, i.e., analytically and from time-stepping finite-element simulation. The results obtained in both ways are shown to well match measurement results collected on the actual motor during full-load system testing.

Sensorless speed control of symmetrical triple-star nine-phase Interior Permanent Magnet machines

“…To remove these coupling terms, a new reference frame transformation which is a combination of the rotor reference frame transformation and a second transformation is determined to diagonalize the impedance matrix in equation (2) [6][7]. The inductance matrix is separated into two components comprising of a diagonal matrix of the leakage inductances and inductance matrix equation qd L (3). The diagonalization of equation (3) is possible since it has distinct eigen-values [8].…”

“…To further increase the reliability and fault tolerance of multi-phase machines, the stator windings have been connected as double, triple, quadruple and higher three phase machines with separate and unconnected neutral (star) points [1][2][3][4]. For the nine-phase IPM machines, instead of one single neutral point for all nine-phases of the stator phases, they are connected as three isolated three-phase machines with three isolated star (neutral) points [5].…”

A high-performance 640-kW 10.000-rpm Halbach-array PM slotless motor with active magnetic bearings. Part II: Manufacturing and testing

“…One more point regards the use of intermediate manufacturing checks: due to its low leakage reactance and double three-phase winding, potentially harmful circulation currents can arise in stator phases as an effect of back-EMF harmonics [16]. To avoid such risk, some intermediate rotor flux symmetry checks have been developed.…”

Modeling of split-phase machines in Park's coordinates. Part II: Equivalent circuit representation

“…The purpose of this paper, along with its companion one (Part I, [12]) is to investigate the detailed dq0 equivalent circuit topology for split-phase synchronous machines equipped with more than two stator three-phase sets (N>2), given their growing importance in the field of today's drive technology and research [6], [13], [14], [15], [16], [17].…”