Abstract: A method for detecting a voltage disturbance in a utility having a micro-grid. The method transforms current and voltage measurements into first and second voltage values and first and second current values in a stationary reference frame, and transforms the first and second voltage values and the first and second current values to third and fourth voltage values and third and fourth current values in a rotating reference frame, where the third voltage value defines an average magnitude of the three-phase power signals. The method multiplies the third current value by the third voltage value to obtain an instantaneous power value and multiplies the fourth current value by the third voltage value to obtain an instantaneous volt-ampere reactive (VAR) value. The method opens the switch if the VAR value has a magnitude above a predetermined value and a direction indicating the fault is outside of the micro-grid in the network.

Abstract: A method for detecting a voltage disturbance in a utility having a micro-grid. The method transforms current and voltage measurements into first and second voltage values and first and second current values in a stationary reference frame, and transforms the first and second voltage values and the first and second current values to third and fourth voltage values and third and fourth current values in a rotating reference frame, where the third voltage value defines an average magnitude of the three-phase power signals. The method multiplies the third current value by the third voltage value to obtain an instantaneous power value and multiplies the fourth current value by the third voltage value to obtain an instantaneous volt-ampere reactive (VAR) value. The method opens the switch if the VAR value has a magnitude above a predetermined value and a direction indicating the fault is outside of the micro-grid in the network.

Abstract: A method for detecting a voltage disturbance on an electrical line coupled to a utility that provides three-phase electrical AC power signals to a critical load that includes a transformer. The method includes reading instantaneous voltage measurements at a high sample rate of each of the three-phase power signals, and calculating a flux in the transformer at the sample rate for each of three-phase power signals by adding the instantaneous voltage measurements at the current sample point and at a previous sample point. The method includes calculating a flux error for each of the three-phase signals at the sample rate as a difference between the newly calculated flux and the oldest calculated flux. The method determines whether the flux error for any of the three-phase power signals is greater than a first predetermined percentage or less than a second predetermined percentage, and if so, identifies a voltage disturbance.

Abstract: A method for detecting a voltage disturbance on an electrical line coupled to a utility that includes calculating a sliding window actual root mean squared (RMS) voltage for each three-phase power signal, calculating a sliding window filtered RMS average voltage for each actual RMS voltage to identify normal changes in the voltage of the power signals from a nominal voltage, and obtaining a difference between the actual RMS voltage and the RMS average voltage for each of the power signals. The method determines whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is greater than a first predetermined percentage, or whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is less than a second predetermined percentage, and if so, disconnects a load from the utility.

Abstract: Electrical systems and related operating methods are provided. One exemplary electrical system includes a sensing arrangement coupled to an electrical grid interface to measure an electrical characteristic of the electrical grid interface, a power conversion module having an output coupled to the electrical grid interface, and a control module coupled to the sensing arrangement and the power conversion module. The control module determines an estimated frequency of the electrical characteristic based on a phase error corresponding to a measured value of the electrical characteristic obtained from the sensing arrangement, determines a frequency correction power command based on a difference between the estimated frequency and a target frequency, and operates the power conversion module in accordance with the frequency correction power command.

Abstract: A method for detecting a voltage disturbance on an electrical line coupled to a utility that provides three-phase electrical AC power signals to a critical load that includes a transformer. The method includes reading instantaneous voltage measurements at a high sample rate of each of the three-phase power signals, and calculating a flux in the transformer at the sample rate for each of three-phase power signals by adding the instantaneous voltage measurements at the current sample point and at a previous sample point. The method includes calculating a flux error for each of the three-phase signals at the sample rate as a difference between the newly calculated flux and the oldest calculated flux. The method determines whether the flux error for any of the three-phase power signals is greater than a first predetermined percentage or less than a second predetermined percentage, and if so, identifies a voltage disturbance.

Abstract: A method for detecting a voltage disturbance in a utility having a micro-grid. The method transforms current and voltage measurements into first and second voltage values and first and second current values in a stationary reference frame, and transforms the first and second voltage values and the first and second current values to third and fourth voltage values and third and fourth current values in a rotating reference frame, where the third voltage value defines an average magnitude of the three-phase power signals. The method multiplies the third current value by the third voltage value to obtain an instantaneous power value and multiplies the fourth current value by the third voltage value to obtain an instantaneous volt-ampere reactive (VAR) value. The method opens the switch if the VAR value has a magnitude above a predetermined value and a direction indicating the fault is outside of the micro-grid in the network.

Abstract: A method for detecting a voltage disturbance on an electrical line coupled to a utility that includes calculating a sliding window actual root mean squared (RMS) voltage for each three-phase power signal, calculating a sliding window filtered RMS average voltage for each actual RMS voltage to identify normal changes in the voltage of the power signals from a nominal voltage, and obtaining a difference between the actual RMS voltage and the RMS average voltage for each of the power signals. The method determines whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is greater than a first predetermined percentage, or whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is less than a second predetermined percentage, and if so, disconnects a load from the utility.

Abstract: Electrical systems and related operating methods are provided. One exemplary electrical system includes a sensing arrangement coupled to an electrical grid interface to measure an electrical characteristic of the electrical grid interface, a power conversion module having an output coupled to the electrical grid interface, and a control module coupled to the sensing arrangement and the power conversion module. The control module determines an estimated frequency of the electrical characteristic based on a measured value of the electrical characteristic from the sensing arrangement, adjusts a commanded reactive power for the power conversion module to increase a difference between the estimated frequency and a reference frequency, operates the power conversion module in accordance with the adjusted reactive power command, and thereafter initiates a remedial action when the difference between the estimated frequency and the reference frequency exceeds a threshold amount.

Abstract: An electrical system includes a sensing arrangement coupled to an electrical grid interface to measure an electrical characteristic of the electrical grid interface, a power conversion module having an output coupled to the electrical grid interface, and a control module coupled to the sensing arrangement and the power conversion module. The control module determines a reference value for the electrical characteristic, identifies an islanding condition based on a difference between a value for the electrical characteristic and the reference value, determines a target output value for the power conversion module based on the difference, and in response to the islanding condition, operates the power conversion module to provide the target output value for the electrical characteristic at the output. The target output value reduces the difference while a connection arrangement is being opened to achieve islanding.

Abstract: Apparatuses and methods are provided for restoring flux in a startup of an uninterruptible power supply device. The uninterruptible power supply device passes voltage to loads while offline. Upon occurrence of a utility disturbance, the output voltage is adjusted while maintaining RMS voltage within a pre-specified window in order to restore flux during startup of the uninterruptible power supply device.

Abstract: Electrical systems and related operating methods are provided. One exemplary electrical system includes a sensing arrangement coupled to an electrical grid interface to measure an electrical characteristic of the electrical grid interface, a power conversion module having an output coupled to the electrical grid interface, and a control module coupled to the sensing arrangement and the power conversion module. The control module determines an estimated frequency of the electrical characteristic based on a phase error corresponding to a measured value of the electrical characteristic obtained from the sensing arrangement, determines a frequency correction power command based on a difference between the estimated frequency and a target frequency, and operates the power conversion module in accordance with the frequency correction power command.

Abstract: Electrical systems and related operating methods are provided. One exemplary electrical system includes a sensing arrangement coupled to an electrical grid interface to measure an electrical characteristic of the electrical grid interface, a power conversion module having an output coupled to the electrical grid interface, and a control module coupled to the sensing arrangement and the power conversion module. The control module determines a reference value for the electrical characteristic, identifies an islanding condition based on a difference between a value for the electrical characteristic and the reference value, determines a target output value for the power conversion module based on the difference, and in response to the islanding condition, operates the power conversion module to provide the target output value for the electrical characteristic at the output. The target output value reduces the difference while a connection arrangement is being opened to achieve islanding.

Abstract: Electrical systems and related operating methods are provided. One exemplary electrical system includes a sensing arrangement coupled to an electrical grid interface to measure an electrical characteristic of the electrical grid interface, a power conversion module having an output coupled to the electrical grid interface, and a control module coupled to the sensing arrangement and the power conversion module. The control module determines an estimated frequency of the electrical characteristic based on a measured value of the electrical characteristic from the sensing arrangement, adjusts a commanded reactive power for the power conversion module to increase a difference between the estimated frequency and a reference frequency, operates the power conversion module in accordance with the adjusted reactive power command, and thereafter initiates a remedial action when the difference between the estimated frequency and the reference frequency exceeds a threshold amount.