Current-Scaling Gain Compensation of Motor Drives Under Locked-Rotor Condition Considering Inequality of Phase Resistances

This article proposes a current-scaling gain-compensation algorithm for motor drive applications under the locked-rotor condition. In heavy industrial applications, such as elevators and cranes, initial commissioning tests are performed with the rotor locked. To compensate for errors in the current-scaling gain, the proposed method controls the current in the d-q axis using two-phase current-sensing methods in a stationary reference frame. The three-phase scaling gains are then estimated using the resulting d-axis current command and output voltage and are compensated for using these estimations. The proposed method delivers accurate compensations by considering the inequality between phase resistances. The effectiveness of the proposed algorithm is verified through simulations and experiments.

I. Introduction

Vector control is a general control method for ac motors and it is implemented by using current-control techniques. To effectively control the currents in an ac motor, three-phase currents must be measured accurately. Currents are measured with current-measuring circuits, which consist of current sensors and analog interfaces that include analog filters and analog/digital (A/D) converters. An A/D converter (ADC) delivers digital values to a digital controller. Measurement errors are introduced due to the quantization and nonideal elements of the current-measuring circuits [1].