Patent ID: 6353302
Filing Date: 2002-03-05
Classification: F04D,H02P,Y02B

Abstract:
A method of implementing a speed computation function in an automatic controller of an induction motor/blower system that provides a specified flow output, comprising the steps of:providing an induction motor/blower system having an induction motor coupled to a blower such that a motor-torque by rotor-speed product (TmÃ—Nm) of the induction motor substantially corresponds to a blower-torque by impeller-speed product (TbÃ—Nb) of the blower at steady state and where the ratio of rotor-speed to blower-speed (Nm/Nb) is known; providing a controller linked to a motor drive that adjusts motor speed Nm in response to control signals from the controller corresponding to a voltage-frequency index R; serving the controller information corresponding to flow command information F; serving the controller information corresponding to dc bus current I of the motor drive and solving for rotor speed Nm by a polynomial equation expanded through at least second order terms and such that the rotor-speed equation's coefficients vary with the voltage-frequency index R according to: Nm=C0R+C1RI+C2RI+2. . . , including extracting the rotor-speed equation's coefficients C0R, C1R, C2R. . . , from a database according to the voltage-frequency index R;solving for impeller speed Nb by the known ratio Nm/Nb; solving for required blower torque Tb by another polynomial equation expanded through at least second order terms and such that the blower-torque equation's coefficients vary with the flow command information F according to: Tb=A0F+A1FNb+A2FNb2+. . . , including extracting the blower-torque equation's coefficients A0F, A1F, A2F. . . , from a database according to the flow command value F;solving for delivered motor torque Tm by a further polynomial equation expanded through at least second order terms and such that the motor-torque equation's coefficients vary with the most recent voltage-frequency index R according to: Tm=B0R+B1RNm+B2RNm2+. . . , including extracting the motor-torque equation's coefficients B0R, B1R, B2R. . . , from a database according to the most recent voltage-frequency index R;comparing, in cases of the ratio Nm/Nb being substantially unity, the required blower-torque (required-Tb) to the delivered motor-torque (delivered-Tm), otherwise the product of required blower-torque by impeller-speed (required-TbÃ—Nb) to the product of delivered motor-torque by rotor-speed (delivered-TmÃ—Nm and, in any case, responding to inequality by signaling the motor drive with a succeeding most recent voltage-frequency index R which is modified to adjust the motor speed correspondingly.