Patent ID: 8917040
Filing Date: 2014-12-23
Classification: H02P

Abstract:
1. An AC motor control apparatus for a system, which includes a three-phase AC motor having a first phase, a second phase and a third phase, an inverter for driving the AC motor and a current sensor for sensing a current flowing in the first phase, the AC motor control apparatus comprising: a current estimating part for calculating a current phase relative to the first phase from an α-axis current and a β-axis current in a fixed coordinate system set with an α-axis and a β-axis, the α-axis extending in a same direction as an axis of the first phase extends, the β-axis being perpendicular to the axis of the first phase, and calculating an estimated current in at least the second phase from the current phase relative to the first phase and the sensed current in the first phase; and a controlling part for controlling electric power supply to the AC motor by square wave control for applying square wave voltages to each phase of the AC motor by switching on and off switching elements of each phase at switching time points, wherein the current estimating part is configured to calculate the α-axis current from the sensed current in the first phase at each switching time point and an intermediate time point between every two successive switching time points, and the current estimating part is further configured to calculate a first differentiated value of the α-axis current from a variation quantity of the α-axis current during an interval between every two successive switching time points, calculate the β-axis current from the first differentiated value, calculate a second differentiated value of the α-axis current from a variation quantity of the α-axis current during an interval between every two successive intermediate time points, and calculate the β-axis current from the second differentiated value.