Low frequency communication system over power lines
An apparatus and method for transmitting information from an emergency power system (EPS) to control devices of remotely connected loads without any additional hardware or wiring. The EPS causes the frequency, phase or magnitude of an AC power signal to be varied according to an established protocol, that is detected by the remote control device, which operates the load in accordance with the protocol.
1 . An emergency power system configured to automatically provide emergency power to a remote load in the event of a main power failure, comprising:
an emergency power supply device;
a control device configured to be connected to said emergency power supply device and to control the operation of said remote load; and
a main controller configured to detect a condition of a magnitude, a phase, and/or a frequency of a power signal from a main power source, switch from a normal mode of operation in which power is supplied to said remote load from said main power source to an emergency mode of operation in which power is supplied to said remote load from said emergency power supply device, and to send a control signal to a power converter/inverter, of said emergency power supply device, in dependence on said mode of operation;
wherein said power converter/inverter is configured to vary, from a nominal value frequency and for first and second predetermined time periods respectively corresponding to a beginning and an ending of said emergency mode of operation, a magnitude and/or a phase of a fundamental frequency of a power waveform generated thereby and transmit said power waveform to said control device, in accordance with said control signal received from said main controller at said power converter/inverter, to communicate, entirely within a total time period of operation of said emergency mode of operation, said respective beginning and said respective ending of said emergency mode of operation to said control device via said transmitted power waveform;
wherein a variation in said magnitude and/or said phase of said fundamental frequency of said power waveform corresponds to a digital encoding for said emergency mode of operation; and
wherein said control device is configured to, in response to receipt of said power waveform, interpret said variations in said magnitude and/or said phase of said fundamental frequency of said power waveform as each respectively corresponding to a predetermined digital code respectively representing said beginning or said ending of said emergency mode of operation, and to control said remote load in accordance with said beginning or said ending of said emergency mode of operation.
2 . The emergency power system of claim 1 , wherein said predetermined time period comprises two seconds.
3 . The emergency power system of claim 2 , wherein said magnitude and/or phase of said fundamental frequency are varied by pulse width modulation.
4 . The emergency power system of claim 1 , wherein said load is an illumination device.
5 . A method of communication between an emergency power system and a remotely located control device for operating a load, comprising:
varying, from a nominal value frequency and for each of a first and a second predetermined time period entirely within an emergency mode of operation of said emergency power system, a magnitude and/or a phase of a fundamental frequency of a power signal waveform supplied, from a power converter/inverter, of said emergency power system, to said remotely located control device according to a predefined protocol,
wherein said power signal waveform is based on a control signal transmitted to said power converter/inverter from a main controller of said emergency power system,
wherein said remotely located control device detects said variation in said magnitude and/or said phase of a fundamental frequency of said power signal waveform, for each of said first and second predetermined time period, as respectively corresponding to said predefined protocol, determines said predefined protocol according to respective digital coding for said variation, and controls operation of said load in dependence on said predefined protocol, and
wherein said first predetermined time period corresponds to a beginning of said emergency mode of operation and said second predetermined time period corresponds to an ending of said emergency mode of operation.
6 . The method of communication as set forth in claim 5 , wherein said predetermined time period comprises two seconds.
7 . The method of communication as set forth in claim 5 , wherein said load is an illumination device.
8 . The method of communication as set forth in claim 5 , wherein said predefined protocol indicates a mains power outage.
9 . The method of communication as set forth in claim 5 , wherein said predefined protocol indicates a fire emergency.
10 . The method of communication as set forth in claim 5 , wherein said predefined protocol indicates a test mode of said system.