Control method and means for efficient operation of brushless d-c motors over a wide range of operating conditions

Abstract

Method and apparatus for efficient operation of a brushless d-c motor are shown. A brushless d-c motor comprises, essentially, a motor drive source, such as a d-c to a-c converter, in combination with a conventional brushless a-c machine. Generally, the brushless a-c machine includes a polyphase stator for the production of a rotating electric field, and a rotor that produces mechanical power from the rotating field without the need for sliding electrical contacts. For induction motors, the rotor phases are short-circuited and rotor currents are produced by allowing the rotor to "slip" with respect to the rotating stator field, the resulting flux variations in the rotor thereby inducing rotor currents. Motor speed is controlled by frequency control of the a-c output from the motor drive source. The present arrangement includes an efficiency controller responsive to motor input current and voltage for producing a first signal related to motor impedance, and a second signal related to motor impedance required for maximum motor operating efficiency. The difference between said first and second impedance related signals is used to control the motor input voltage for efficient motor operation over a wide range of operating speeds and torques.

Dependencies are inferred from the claim text.