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This paper presents a technique for predicting phase currents in vector-controlled pulsewidth-modulated (PWM) inverters using single dc-link current sensor. There is a limitation for current measurements in the inverters. The measurements are executed in the effective voltages, not in the zero voltage. The current measured in the dc-link and then reconstructed to the phase value is used as a feedback value for controlling an ac machine. Here, there is a difference between the reconstructed current and measured currents at the top or bottom of PWM carrier such as in the conventional inverters. It changes according to the reference voltages, load conditions, noises, and disturbances. Next, it can cause deterioration of the performance of current control by increasing ripples in currents and torque. This paper analyzes the difference in the drives of a permanent magnet synchronous motor and proposes a method for reducing it. The proposed method predicts the currents measured at the fixed sampling points from those measured in the dc-link and the PWM patterns of voltage outputs. It can reduce current ripples and the experimental results verify it. It is applicable to the vapor compression refrigeration process with the low-cost and high-performance feature.
Date of Publication: Feb. 2010