Method and apparatus for sensing load current in a motor control

Details Method and apparatus for sensing load current in a motor control Method and apparatus for sensing load current in a motor control

1997-06-11

1999-02-23

Masih, Karen

Electricity: motive power systems

Limitation of motor load, current, torque or force

318254, 318138, 318599, 318280, 363 17, 363 18, H01R 3946

Patent

active

058748180

ABSTRACT:
The approach to measuring load current in a multi-phase bridge inverter circuit connected to a multiphase load involves placing a single current sense resistor in series with the inverter circuit and power supply. The current flow through the sense resistor is sampled during a portion of the switching cycle wherein the inverter is configured to enable current flowing through the multi-phase load to flow through the sense resistor. Typically, this will occur during a portion of the switching cycle (e.g. PWM cycle) wherein the load is being actively driven. For a 120.degree., 3-phase, 6-step commutation sequence typically used to control a d.c. brushless servo motor, the sampled current is a time-multiplexed measure of the current flow through each load phase. The same sense resistor is also used for indicating a short circuit condition by comparing the voltage across the resistor to a reference voltage.

REFERENCES:
patent: 4980838 (1990-12-01), Daggett et al.
patent: 5343382 (1994-08-01), Hale et al.
patent: 5639970 (1997-06-01), Schulz
patent: 5689162 (1997-11-01), Li
Konopoka and Twitchell, "Higher Voltage Servo Redesign Requires Current Sensing Re-Evaluation", Power Conversion and Intelligent Motion, Feb. 1997, pp. 12-19.
Unitrode Integrated Circuits Corporation, Products and Applications Handbook, 1995-1996, pp. 10-97 to 10-101 (UC3620), 10-150 to 10-156 (UC3625), and 10-247 to 10-259 (UC3625).

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