Patent ID: 6483271
Filing Date: 2002-11-19
Classification: H02P

Abstract:
A method of controlling thermal stress in a space vector, PWM, zero state regulator motor drive responsive to motor control commands to provide drive signals to a variable frequency motor, said motor drive having a transistor switch matrix in which the switching frequency is adjustable, each transistor having a junction and being in a combination with a corresponding anti-parallel diode having a junction, said motor drive incorporating selectable zero states in which no differential voltage is applied to the motor, comprising:(A) determining the approximate transistor junction temperature of each of said transistors; (B) comparing the approximate transistor junction temperature, of the one transistor having the highest one of said approximate transistor junction temperatures, to a predetermined transistor temperature threshold, and (a) if said highest approximate transistor junction temperature exceeds said transistor temperature threshold, altering the operation of said motor drive in a manner which will tend to lower switching losses in said transistors, but (b) if said highest approximate transistor junction temperature is less than said transistor temperature threshold, not altering the operation of said motor drive in a manner which will tend to lower switching losses in said transistors; (C) determining the approximate diode junction temperature of each of said diodes; and (D) comparing the approximate diode junction temperature of the one diode having the highest one of said approximate diode junction temperatures to a predetermined diode threshold temperature, and (c) if said highest approximate diode junction temperature exceeds said diode threshold temperature, selecting a pattern of zero states involving a lower duty cycle of said one diode, but (d) if said highest approximate diode junction temperature is less than said diode threshold temperature, selecting a pattern of zero states involving lower switching losses in said transistors; wherein said steps (A) and (C) comprise either (E) measuring the transistor junction temperature of each of said transistors and measuring the diode junction temperature of each of said diodes; or (F) determining, from manufacturer-supplied information concerning said transistor-diode combinations utilized in said motor drive, switching losses and conduction losses of said transistors, conduction losses of said diodes, a thermal resistance and a normalized transient thermal response between a case containing said combination and said junctions of said combination, and determining normalized transient thermal response between said case and a heat sink on which said case is disposed; (G) providing a transistor model and a diode model, incorporating parameters determined in said step (F), respectively indicating (e) approximate temperature of one of said transistors as a function of transistor current, duty cycle, and switching frequency, and (f) approximate temperature of one of said diodes as a function of diode current and duty cycle; (H) determining the approximate transistor junction temperature of each of said transistors by operating said transistor model for each of said transistors in response to current and duty cycle of said each transistor and switching frequency of said matrix; and (I) determining the approximate diode junction temperature of each of said diodes by operating said diode model for each of said diodes in response to current and duty cycle of said each diode.