Smart grid sensor with power harvesting from low line currents

A system for sampling current in a power line, comprising:

• a current measurement frontend circuit configured to receive current from the power line;
• wherein the current measurement frontend circuit is configured to provide a low analog channel and a high analog channel responsive to the received current, each of the low and high analog channels having a different gain but a similar time response;
• a multi-channel analog to digital circuit (ADC);
• wherein a low ADC channel is connected to the low analog channel and a high ADC channel is connected to the high analog channel;
• and
• a processor configured to select a channel of the multi-channel ADC, receive ADC samples and process the ADC samples;
• wherein the processor is configured to continuously sample the low ADC channel, check the level of each sample, and switch to the high ADC channel when the level of a sample is at an edge of the ADC range and provide a value of the sample multiplied by a gain ratio between the low and high analog channels.

A system for sampling current in a power line, comprising:

• a current measurement frontend circuit configured to receive current from the power line and produce a current level output signal;
• a peak detector configured to receive the current level output signal and configured to provide a peak output;
• a multi-channel analog to digital converter (ADC) with a first channel configured to receive the current level output signal and a second channel configured to receive the peak output;
• a processor configured to select a channel from the multi-channel ADC, receiving ADC samples, and processing the ADC samples;
• wherein the processor is further configured to measure a battery level of the system and a current level in the power line, and when the battery level is low and the current in the line does not supply power for normal operation of the system, the processor instructs the multi-channel ADC to stop sampling the current level signal and to begin sampling the peak detector output, at a lower rate.

A system for measuring AC current in a power line comprising:

• a current measurement frontend circuit configured to measure current in the power line;
• an ADC;
• a processor for controlling a sampling rate of the ADC;
• wherein the processor is configured to sample an output of the ADC, measure a difference ΔI(n) between a most recent sample I(n) and previous samples, and compare the difference to a predetermined threshold, wherein when ΔI(n) is larger than a predetermined threshold the processor instructs the ADC to switch to a higher sampling rate relative to a rate it used prior to comparing.

A system for sensing power in a power line, comprising:

• a power storage device to serve as a backup power storage for the system;
• a processor and circuit configured to analyze the current sensed in the power line and/or the level of power stored by the power storage device;
• a switch configured to connect or disconnect the power storage device from the processor and circuit of the sensor system;
• a latch circuit configured to maintain a state of the switch until it is changed by the processor or when an indication of a sufficient amount of available current in the power line is detected;
• wherein the processor senses the power in the power line and the power storage device periodically and when the power is not sufficient to power the processor and circuit the processor closes the switch, which enters an OFF state that is maintained by the latch circuit, and the power storage device is disconnected, when current in the power line rises and charges the processor and circuit, the processor opens the switch automatically, the switch enters an ON state, and the power storage device is reconnected.

A method of harvesting power from AC current in a power line, comprising:

• enclosing the power line by combining two halves of a split magnetic core around the power line;
• wherein a coil is wrapped around one or two halves of the magnetic core, with a first end and a second end of the coil configured to provide current from the coil;
• connecting an input of a power harvesting circuit to the first end and second end of the coil to harvest current from the AC current in the power lines;
• wherein said power harvesting circuit comprises:
• a rectifier;
• at least one voltage multiplier electrically connected in parallel to the rectifier;
• and
• wherein an output of the power harvesting circuit is configured to supply voltage and current to load circuits.