Patent ID: 8564916
Filing Date: 2013-10-22
Classification: H02H,Y02E

Abstract:
1. An apparatus for a photovoltaic system, comprising: a hybrid grounding circuit as well as a ground fault monitoring circuit in inverter circuitry with switching devices that are configured to generate three-phase Alternating Current (AC) voltage supplied to a utility power grid interface transformer, where a primary-side common node of the utility power grid interface transformer is connected to Earth ground, where the inverter circuitry includes at least a first inverter circuit and a second inverter circuit, where each inverter circuit has 1) its own set of isolation contacts to connect as well as isolate this particular inverter circuit from the utility grid interface transformer, and 2) control components in the ground fault monitoring circuit for controlling operation of the isolation contacts based off a presence of the ground fault detected by the ground fault monitor circuit for that inverter circuit, where the first inverter circuit receives a first DC voltage supplied from its own set of ungrounded PhotoVoltaic (PV) modules, where the second inverter circuit receives a second DC voltage supplied from its own set of ungrounded PV modules, where multiple solar arrays, each with their one or more inverter circuits, directly couple their three phase AC output to the same utility power grid interface transformer, where each inverter circuit in the grounded system has its own ground fault monitoring circuit, where the ground fault monitoring circuit detects the presence of the ground fault via a change in 1) voltage, 2) current or 3) both and the detection method occurs via a differential sense method, where in the hybrid grounding circuit when in operation producing AC, each inverter circuit gets referenced to 1) the primary-side common node of the utility power grid interface transformer which is connected to Earth ground during the operation of that inverter circuit and 2) referenced to Earth ground by a grounding switching device in an input circuit of that inverter circuit prior to the switching devices of the inverter circuit producing three phase AC power, and where the ground fault monitoring circuit is configured to detect PV array ground leakage before the isolation contacts of the first inverter circuit connect to the utility power grid interface transformer, which prevents disconnecting all of the inverter circuits in the entire system due to a ground fault on a single set of PV modules.