Expansion of reconstruction areas for current measurement using three shunt resistors in three leg two-phase inverters

초록

When driving two-phase motors using three leg inverters, phase currents can be measured using shunt resistors inserted between a low-side switch on each leg of the inverter and the negative DC-link terminal. The current measuring scheme using shunt resistors on only two inverter legs has a limited current measurement capability. In addition to this two shunt scheme, the three shunt scheme can reconstruct immeasurable currents utilizing a shunt resistor located on a neutral leg of the inverter. Thus, the three shunt scheme can widen the areas where the currents can be measured when compared to those in the two shunt scheme. However, this scheme cannot appropriately reconstruct currents within operating areas where a sufficient turn-on time for the low-side switches cannot be guaranteed, which results in increased torque ripple of two-phase motors and decreased DC voltage utilization of inverters. In this paper, a simple technique for expanding the reconstruction areas of the currents in the three shunt scheme is proposed. The proposed technique can expand the reconstruction areas by utilizing DPWM (discontinuous pulse width modulation) that can secure the turn-on time of the low-side switches longer than CPWM (continuous PWM), thereby improving the DC voltage utilization.

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