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This paper analyzes carrier-signal voltage injection zero-sequence current-based sensorless control techniques for delta-connected three-phase ac machines. The analysis will focus on rotor position estimation (tracking of rotor-position-dependent saliencies), but the method applies equally well to flux position estimation (tracking of flux-dependent saliencies). The paper first develops a theoretical model and then provides analysis of relevant implementation aspects, such as selection of carrier-signal frequency and voltage magnitude, measurement of the zero-sequence carrier-signal current, measurement and compensation of saturation-induced saliencies, and the signal processing needed for position/flux angle estimation. A similar implementation to that proposed in this paper, and with practically the same performance in terms of accuracy and estimation bandwidth, can be obtained for the case of wye-connected machines using the zero-sequence carrier-signal voltage, as shown in IEEE Trans. Ind. Appl., vol. 41, no. 6 pp. 1637-1646, Nov./Dec. 2005.