Control of Large Salient-Pole Synchronous Machines Using Synchronous Optimal Pulsewidth Modulation

• Published in: IEEE transactions on industrial electronics (1982) Vol. 62; no. 6; pp. 3372 - 3379
• Main Authors: Holtz, Joachim, da Cunha, Gilberto, Petry, Norton, Torri, Paulo Jose
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-06-2015; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Copper; Grinding mills; Harmonic analysis; Inverters; Mills; Modulation; Motors; Optimization; Pulse width modulation; Stators; Switches; Switching; Synchronous; Synchronous motors; Windings; ball milling; pulse width modulation inverters; software algorithms; Fourier transform; Alternators; variable speed drives; gradient methods
• ISSN: 0278-0046; 1557-9948
• DOI: 10.1109/TIE.2014.2378732

High-power grinding mills are used in the cement and mining industries to crush clinker or copper ore and grind these materials to fine powder. The multimegawatt speed-controlled mill drives operate at a very low angular speed. Synchronous motors with a high number of pole pairs are used as the prime movers. They are traditionally fed by load-commutated thyristorized cycloconverters. These are prone to failure modes that can lead to excessive torque pulsations and high overcurrents. The huge stator, which was built as a separate ring-shaped structure around the tubular mill, may then get mechanically displaced, and the operation of the plant is interrupted. A novel and reliable direct drive uses a voltage source inverter that operates at the unity power factor for increased efficiency. Synchronous optimal pulsewidth modulation ensures a low harmonic current distortion and reduced switching losses at a very low switching frequency. The optimization of the pulse patterns takes the anisotropic magnetic properties of a separately excited synchronous motor into account. The implementation in a 23-MW semiautonomous grinding mill installed in a Zambian copper mine is intended.