Control Strategy for Dual Three-Phase Machines With Two Open Phases Providing Minimum Loss in the Full Torque Operation Range

Dual three-phase machines (D3PMs) are particularly attractive due to their fault-tolerance capability. In general, under open-phase (OP) faults, the current references are adapted following a minimum-loss strategy (MLS) or a maximum-torque strategy (MTS). The MLS offers lower copper loss than the MTS for any given torque, but a smaller torque operation range. The full-range MLS (FRMLS) has recently been proposed, providing minimum copper loss, for each torque value, in the whole torque operation range (the MTS torque operation range); however, only one OP was considered. Furthermore, neither the torque operation range of the MLS nor the copper loss of the MLS or MTS have been assessed with two OPs. Consequently, it is difficult to infer a priori the relevance that the FRLMS may have for two OPs. This letter evaluates the extension of the FRMLS to D3PMs with two OPs. First, the procedure to carry out this extension is described. Then, the convenience of the FRMLS for two OPs is studied for different situations. It is concluded that for two OPs in most cases, the FRMLS is substantially better than the MTS and MLS in terms of copper loss and torque operation range. Experimental results verify the theory.

I. Introduction

Dual three-phase machines (D3PMs), a.k.a. asymmetrical six-phase machines, are an attractive alternative to three-phase ones [1]–[20]. An important reason is their capability to operate under one or more open phases (OPs) [1]–[4], [7]– [17]. OP faults occur due to numerous causes, such as mechanical failure of a connector, internal winding rupture, failure in an inverter leg, or certain remedial actions [16], [21], [22].