Compensated feedforward voltage for a PWM AC motor drive
AssigneeAllen-Bradley Company, Inc.
InventorsRussel J. Kerkman, David Leggate
Life of this patent
Estimating the term…
Abstract
An AC motor drive includes a PWM voltage inverter which is responsive to voltage commands from a synchronous current regulator to control motor armature current and rotor speed. A feedforward voltage is also applied as input to the PWM voltage inverter and it is compensated to boost the effective gain of the inverter when it is operated in the pulse dropping region. The compensation values are precalculated and stored in a table from which they are read during drive operation.
Claims7
In an AC motor drive having a PWM inverter which controls motor armature current in response to a sine wave voltage command and is operationally characterized by an operating point and an effective gain, the improvement comprising:
- means for producing a feedforward voltage which is proportional to the voltage command applied to the PWM inverter;
- means for determining the operating point of the PWM inverter when it is operating within a pulse dropping region in which the PWM inverter gain drops below its nominal gain;
- means for producing a compensation factor value which comprises an addressable compensation factor table including a plurality of compensation factor values which have been generated off-line as functions of different modulation index values and means for reading a compensation factor entry value therefrom by reading out a value from an address location determined as a function of the PWM inverter operating point;
- and
- a multiplier for magnifying the value of the feedforward voltage by the compensation factor providing a compensated sinusoidal voltage command to the PWM inverter that substantially maintains the effective gain of the PWM inverter at its nominal value throughout its pulse dropping region of operation.
Dependencies are inferred from the claim text.