Smart meter voltage and current sensing using optically coupled isolators

摘要

A transformer-less method and system for voltage and current sensing using voltage drops across resistors is disclosed. Using optically coupled isolators, the sensed voltages in the high voltage power lines are optically coupled and electrically isolated to the low voltage circuits. The circuit designs for voltage and current sensing's and electrical isolation are disclosed.

主权项

1. A method of sensing current within a smart meter comprising:
coupling a first resistor to a high voltage portion of the smart meter; and optically coupling the high voltage portion to a low voltage portion; wherein the optical coupling is provided by an infrared (IR) emitting diode on the high voltage portion and an optical transistor on the low voltage portion; wherein the IR emitting diode and the optical transistor comprises a optically coupled isolator; wherein a second resistor (RD) coupled to the IR emitting diode provides a bias condition to the IR emitting diode; wherein the second resistor (RD) is determined by the equationRD=VB-VFIF,wherein VB is a bias voltage source, VF is a forward voltage of the IR emitting diode and IF is a forward current of the IR emitting diode; and wherein current is sensed based upon a voltage measured across the first resistor.