Device and process for detecting and mitigating reverse power-flow

A device for mitigating reverse power flow to a power source providing an alternating current to a load, said alternating current alternating according to a current waveform and having a cyclically varying voltage alternating between a minimum and a maximum at a frequency that defines a cycle duration, wherein said varying voltage has a voltage waveform, whereby changes in current flow direction define current middle crossing points, whereby said load changes said current waveform so said current waveform fluctuates, may vary in periodicity, and may differ from said voltage waveform, and whereby noise is introduced into said alternating current by extraneous sources or said device, comprising:

• a power supply having a power supply positive voltage and a power supply negative voltage that creates a reference voltage midway between said power supply positive voltage and said power supply negative voltage;
• a voltage sensor connected to said power source, whereby said voltage sensor senses said varying voltage and outputs in real time a voltage-representative voltage signal with approximately said voltage waveform, scaled and biased to be centered between said power supply positive voltage and said power supply negative voltage and with crossing points over said reference voltage defining voltage middle crossing points at the ends and midpoint of each cycle;
• a current sensor connected to said load, whereby said current sensor senses said alternating current and outputs in real time a current-representative voltage signal with approximately said current waveform, scaled and biased to be centered between said power supply positive voltage and said power supply negative voltage and also scaled to be able to be compared with said reference voltage;
• a voltage any to square wave converter that has a voltage converter propagation delay, to receive said voltage-representative voltage signal and compare said voltage-representative voltage signal with said reference voltage, having a hysteresis circuit to generate a high voltage trigger point voltage in response to a voltage-representative voltage signal higher than said voltage middle crossing point plus said noise, and a low voltage trigger point voltage in response to a voltage-representative voltage signal lower than said voltage middle crossing point minus said noise, and that outputs voltage square waves that are high in response to said high voltage trigger point voltage and low in response to said low voltage trigger point voltage, whereby a voltage square wave that transitions from low to high and back to low again constitutes a voltage pulse;
• a current any to square wave converter that has a current converter propagation delay, to receive said current-representative voltage signal, and to compare said current-representative voltage signal with said reference voltage, having a hysteresis circuit, to generate a high current trigger point voltage in response to a current-representative voltage signal higher than said current middle crossing voltage plus said noise, and a low current trigger point voltage in response to a current-representative voltage signal lower than said current middle crossing voltage minus said noise, and that outputs current square waves that are high in response to said high current trigger point voltage and low in response to said low current trigger point voltage, whereby a current square wave that transitions from low to high and back to low again constitutes a current pulse having a leading edge and a trailing edge, that has a current pulse length;
• wherein said voltage converter propagation delay and said current converter propagation delay are substantially identical;
• a polarity checker that compares said voltage square waves and said current square waves that generates a polarity pulse when said voltage square wave is high and said current square wave is low, and also when said voltage square wave is low and said current square wave is high;
• a pulse extender connected to said current any to square wave converter that extends a current pulse for a pulse duration time and continues to extend said pulse duration time if a subsequent current pulse arrives in less than a cycle duration, whereby an extended current pulse indicating reliable current for said pulse duration time is created;
• a switch control leading to an output operably connected to said pulse extender and said polarity checker that enables said polarity checker only for said pulse duration time, whereby when said polarity pulse is high, reverse power flow is considered to be possibly present, and when said polarity pulse is low, reverse power flow is not considered to be possibly present, but said polarity checker is enabled only if said extended current pulse indicates reliable current, whereby said switch control indicates to said output reverse power flow when reliable current is indicated and reverse power flow is considered to be possibly present, and said switch control indicates to said output no reverse power flow when reliable current is not indicated or when reverse power flow is not considered to be possibly present.