Electrical angle-detecting apparatus and driving system of synchronous

Abstract

The present invention provides a system for detecting a rotational orientation or electrical angle of a rotor without any specific sensor so as to efficiently control a synchronous motor even while the rotor is at a stop or rotates at a relatively low speed. An electrical angle of a rotor (50) is determined according to a previously stored relationship between inductances of different interphases and electrical angles. At a first step, an electrical angle .phi. is calculated either in a range of 0 through .pi. or in a range of .pi. through 2.pi. by approximation. At a second step, a range where the electrical angle .phi. belongs to is specified by taking advantage of asymmetrical property of a maximum current in response to a voltage applied to each interphase. An equivocal electrical angle .theta. is then determined in a range of 0 through 2.pi.. In order to control the driving current of a three-phase synchronous motor (40) at better efficiency, a preferable system of the invention determines the electrical angle according to the above method while the rotor (50) is under inactivating condition or rotates at a speed of less than a predetermined rotating speed, and detects the electrical angle with a reverse electromotive voltage while the rotor (50) rotates at a speed of not less than the predetermined rotating speed.