Direct Thrust Force Control of Primary Permanent-Magnet Linear Motors With Single DC-Link Current Sensor for Subway Applications

Because both magnets and windings can be mounted in the mover, the primary permanent-magnet linear motor (PPMLM) has a low-cost advantage for subway applications. In this paper, a novel direct thrust force control (DTFC) with single dc-link current sensor is proposed for PPMLM traction system in subway applications. The first phase current is directly measured by the dc-link current sensor. The second phase current is sensed with a limited delay, which is strictly limited by the limited measurement delay principle. The third phase current is calculated based on the condition that the summation of the three phase currents is zero. During the current reconstruction, no motor parameters are required. Because PPMLM may sink in the same phase for a long time and affect the current reconstruction accuracy, the single optimal target is proposed to re-select the original voltage vector. Compared with the conventional DTFC scheme, the proposed one has nearly the same performances; especially, the maximum speed and response time remain nearly unchanged. The effectiveness of the proposed DTFC scheme is verified by experimental results.