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The large synchronous motor application was started in early 90’s, currently the wound-field synchronous motors (SM) are getting old, and they are being replaced with a larger motor, being installed to an existing motor-mount basement. And then large motors require higher magnetic flux than conventional motors, this led another issue, magnetic saturation inside of SM. Then our conventional SM control needed time to find suitable parameters related to flux for each motors. This paper introduces a method to improve an adjustment of flux parameters by using simplified matrix table.

This paper provides a theoretical and experimental discussion on ac-inductors design for a modular multilevel triple-star bridge-cell (TSBC) converter, or shortly a TSBC converter. This converter requires multiple ac inductors for controlling nine cluster currents. This paper proposes three three-legged, six-winding, "inter-zigzag" inductors for the TSBC converter. Since each leg of the individual inductor has two windings, the three inductors have 18 windings in total. The wire leads are zigzagged among the three inductors. This unique structure of the "inter-zigzag" windings leads to the following feature: Both three-phase supply and motor currents produce no magnetic flux in each of the nine legs. This feature makes each inductor smaller in size and lighter in weight. A specially-designed downscaled motor drive system rated at 400 V and 15 kW is constructed and tested to confirm the validity of a design of the proposed inductors, as well as to verify transient motor-drive performance during four-quadrant operation.

This paper proposes a three-phase AC-DC converter topology used for a front-end converter of medium-voltage (MV) motor drives suitable for inverter with a common DC-link bus, such as modular multilevel converters (MMCs) or others. A multilevel cascaded H-bridge inverter is traditionally used for the MV drives which has distributed DC-link buses. For the purpose of the reduction of harmonics and the production of the distributed DC-voltage sources, the multilevel cascaded H-bridge inverter is generally used with a phase-shifted multi-winding transformer and diode rectifiers. However, the phase-shifted multi-winding transformer has many secondary windings, resulting in complex structure, bulky and costly. The MMC is one of the most expected topologies as a next-generation inverter for the MV drives. However, the front-end converter topology still consists of the phase-shifted multi-winding transformer and the diode rectifiers. Besides, the diode rectifiers have no capabilities of boosting DC-link voltage and suppressing the influence of the voltage sags. By contrast, cascaded single-phase three-level boost-type rectifiers and an open-end winding transformer can provide less harmonics, high functionality and capabilities of boosting DC voltages and suppressing the influence of the voltage sags. This paper presents the circuit configuration, the operation principle, and the simulation results with the input voltage of 6.6 kVAC and the output voltage of 12 kVDC, where a novel control method by a third-order harmonic current injection to reduce the harmonics is proposed. The simulation results verify the validity of the proposed configuration and the proposed control method.

This paper provides theoretical, numerical, and experimental comparisons in electrical-drive performance between a double-star chopper-cells (DSCC) inverter and a triple-star bridge-cells (TSBC) converter. The inverter and converter are two of the most promising members of the modular multilevel cascade converter (MMCC) family. Two sets of downscaled electrical drives using the DSCC inverter and the TSBC converter are designed, constructed, and tested, along with the common three-phase four-pole induction motor rated at 380 V, 15 kW, and 50 Hz. This paper presents experimental waveforms of the electrical drives loaded with a quadratic torque-to-speed profile and at the rated torque.