Ultra-Low Inductance PMSM Drive Using a DC Current Sensor

This article presents a single shunt current sensing drive method for ultra-low inductance PMSMs that can reliably reconstruct phase currents even at very low speeds. Single current shunt inverters using dc current measurement entail the problem of having dead zones where the phase currents cannot be reconstructed. Voltage injection at the switching frequency can be a solution to avoid this, but at the expense of the newly introduced current ripple. That current ripple is exacerbated in ultra-low inductance motors and can cause drive failure, especially at low speeds. To rule out voltage injection, this article presents a drive scheme that combines sequential two-phase excitation with a dc current averaging method using an RC low-pass filter. This permits three-phase current reconstruction from the average of dc current measurements per half-switching period, regardless of the active vector duration. Experimental demonstrations in this article show that the proposed driving method allows reliable current reconstruction at both startup and low speed without a significant current ripple. The current reconstruction and dynamic control performance are demonstrated with both steady-state and transient experiments.