US 6,313,600 B1Granted

Control method and apparatus for insufficient input voltage in an AC drive

AssigneeRobicon Corporation

InventorsPeter W. Hammond, Richard Osman

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Abstract

An electric drive apparatus and method for controlling AC motors wherein the motor output is a function of the AC input power to the electric drive. Means are provided for detecting the voltage being supplied by the source of AC power to a drive circuit, and for controlling the output to the multi-phase AC load based on the detected power level. A controller monitors the motor voltage, current, and speed or frequency while also receiving a command for torque or torque-producing current. The method provides for the operation of the drive circuit in the event of either a partial or complete loss of AC input power. During such an occurrence, the controller will cause the circuit to generate sufficient negative torque to cause a power flow from the motor to the drive circuit to substantially equal the inherent losses in the drive and motor to avoid loss of energy from the DC filter of the drive circuit. Motor torque and speed can be quickly restored when the input power is re-established.

Claims14

Dependent claims

A method of controlling an electric drive for use with an AC motor, said electric drive including means for converting power from an AC power source to a DC voltage, means for storing DC energy, means for converting said DC energy to an AC input source having adjustable voltage and frequency to operate the AC motor, a drive controller, and means for responding to a command for torque or torque-producing current, said control method comprising the steps of:

detecting a voltage level of said AC power source and comparing said detected voltage level with first and second predetermined AC voltage levels;
monitoring the AC motor speed;
providing a normal torque command signal to the drive controller;
estimating a total power loss in the electric drive and the AC motor;
calculating a negative torque command value as a function of said total power loss and said AC motor speed;
and
providing a modified torque command signal by transitioning from said normal torque command signal toward the negative torque command signal when said detected AC voltage level falls below the first predetermined minimum AC voltage level and approaches a second predetermined AC voltage level.

4 more elements

Dependencies are inferred from the claim text.