Inverter ground fault circuit
A batteryless inverter allows for a positive or a negative lead from a photovoltaic array to be attached to a grounding terminal of the inverter. Internally a ground fault voltage is rectified and processed to produce a signal that will shut down the inverter. This signal will be the same whether the ground fault voltage is positive, negative, or AC.
1 . A ground fault detection apparatus for use in an inverter connected to a photovoltaic panel comprising:
a ground conductor that connects a system ground in said inverter to earth ground;
a fuse device in series with said ground conductor;
a rectifier circuit connected in parallel with said fuse device;
a voltage detector that detects a rectified voltage across said fuse device; and
a switch that interrupts an electrical circuit within said inverter when a voltage is detected across said fuse device.
2 . The ground fault detection apparatus of claim 1 wherein said fuse device is a fuse.
3 . The ground fault detection apparatus of claim 1 wherein said fuse device is a circuit breaker.
4 . The ground fault detection apparatus of claim 1 wherein said fuse device is a current sensor and a relay.
5 . The ground fault detection apparatus of claim 1 wherein said fuse device is a relay.
6 . The ground fault detection apparatus of claim 1 wherein said rectifier circuit produces a DC output with a predetermined voltage polarity regardless of the polarity of voltage across said fuse device and regardless of whether the voltage across said fuse device is AC or DC.
7 . The ground fault detection apparatus of claim 6 wherein said rectifier circuit comprises a plurality of diodes arranged to form a passive rectifier.
8 . The ground fault detection apparatus of claim 7 wherein said rectifier circuit is an H bridge circuit.
9 . The ground fault detection apparatus of claim 1 further comprising a signal conditioning circuit that converts said rectified voltage across said fuse to a signal in a different form that is appropriate for input to said voltage detector.
10 . The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises an opticoupler.
11 . The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises a low pass filter.
12 . The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises a Zener diode whereby said switch does not interrupt an electrical circuit within said inverter until said voltage across said fuse device exceeds a predetermined threshold level.
13 . The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises a transistor.
14 . The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit produces a binary signal with predetermined characteristics regardless of the magnitude and waveform of said rectified voltage across said fuse.
15 . A solar generation system comprising: a photovoltaic panel;
an inverter electrically connected to said photovoltaic panel for conditioning the output of said photovoltaic panel; and
a ground fault interrupter in said inverter comprising:
a ground conductor that connects a system ground to earth ground;
a fuse device in series with said ground conductor;
a voltage detector that detects a voltage across said fuse device; and
a switch that interrupts an electrical circuit within said inverter when a voltage is detected across said fuse device.
16 . The solar generation system of claim 15 further comprising a rectifier circuit connected in parallel with said fuse device and wherein the voltage presented to said voltage detector has a polarity that is independent of the polarity and frequency of said voltage across said fuse device.
17 . The ground fault detection apparatus of claim 16 wherein said rectifier circuit comprises a plurality of diodes arranged to form a passive rectifier.
18 . The ground fault detection apparatus of claim 17 wherein said rectifier circuit is an H bridge circuit.
19 . The ground fault detection apparatus of claim 16 further comprising a signal conditioning circuit that converts said rectified voltage across said fuse to a signal in a different form that is appropriate for input to said voltage detector.
20 . The ground fault detector apparatus of claim 19 wherein said signal conditioning circuit produces a binary signal with predetermined characteristics regardless of the magnitude and waveform of said rectified voltage across said fuse.
21 . A method of detecting a ground fault in an inverter comprising the steps of:
providing a system ground within said inverter;
providing a ground conductor between said system ground and earth ground;
providing a fuse device in series with said ground conductor that trips when electrical current in said ground conductor exceeds a predetermined level;
rectifying voltage across said fuse device whereby said rectified voltage is a DC voltage with a polarity that does not depend on the polarity of voltage across said fuse device and does not depend on whether voltage across said fuse device is AC or DC; and detecting said rectified voltage across said fuse device as an indication of a ground fault condition.
22 . The method of claim 21 further comprising the step of conditioning said rectified voltage.
23 . The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of filtering high frequency electrical noise from said rectified voltage.
24 . The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of blocking said voltage when it is less than a predetermined threshold value.
25 . The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of optically isolating said voltage from a circuit that detects said voltage.
26 . The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of converting said rectified voltage into a current signal with predetermined magnitude when said rectified voltage is above a predetermined threshold value.
27 . The method of claim 21 further comprising the step of activating a switch to interrupt a circuit within said inverter when a ground fault condition is detected.