DC Current Sensing Drive Scheme for Ultra-Low Inductance PMSMs with Enhanced Low-Speed Performance

This article introduces a method for driving ultra low inductance permanent magnet synchronous motors (PMSMs) that uses a single shunt current sensing approach to accurately reconstruct phase currents, even at very low speeds. The challenge with single shunt inverters is that they have dead zones where the phase currents cannot be reconstructed, and voltage injection to solve this can cause new problems with current ripple, which can be especially troublesome in ultra-low inductance motors. To avoid these issues, the article proposes a drive scheme that combines sequential two-phase excitation with an RC low-pass filter to average the dc current measurements per half-switching period, enabling three-phase current reconstruction regardless of the active vector duration. Experimental results demonstrate that this approach provides reliable current reconstruction at both startup and low speed without significant current ripple, and the article provides both steady-state and transient experiments to demonstrate the current reconstruction and dynamic control performance.