A Current Reconstruction Scheme for Low-Cost PMSM Drives Using Shunt Resistors

This paper presents a novel phase current reconstruction scheme using the information obtained from shunt resistors (in series with low-side switches in a conventional three-phase inverter) for closed-loop current control in low-cost PMSM drives. A state observer is developed for reconstructing phase currents when they cannot be directly measured only in a portion of fundamental period due to the limitation of the bandwidth of signal conditioning circuits and minimum turn-on time of low-side switches. The observer is adaptive to variation of motor parameters and operation condition. By means of an integrating approach, i.e. using direct measurement at low MI and estimated currents from the observer at high MI, the reconstructed current feedback is sufficiently accurate for closed-loop current regulation. In addition, a fuzzy logic function is designed to achieve smooth transitions using trapezoidal weighting functions based on the instantaneous duty ratio of each phase, i.e. switching function. The proposed reconstruction algorithm is verified by experimental testing.