A distribution feeder of an electricity grid comprises a substation and a plurality of nodes with at least one controllable reactive power resource. A method is provided for locally controlling delivery of electrical power along the distribution feeder, wherein for a feeder segment in the distribution feeder the method comprises: obtaining an actual voltage magnitude at an upstream node and at a downstream node of the feeder segment, and a real power value at the upstream node; setting a target voltage phasor at the downstream node as a value when a power flow across the feeder segment is maintained, and when equal reactive power is injected at the upstream and downstream nodes that consumes all the reactive power in the feeder segment; and adjusting operation of the at least one controllable reactive power resource so that the actual voltage magnitude at the downstream node moves towards a target voltage magnitude of the target voltage phasor.

A distribution feeder of an electricity grid comprises a substation and a plurality of nodes with at least one controllable reactive power resource. A method is provided for locally controlling delivery of electrical power along the distribution feeder, wherein for a feeder segment in the distribution feeder the method comprises: obtaining an actual voltage magnitude at an upstream node and at a downstream node of the feeder segment, and a real power value at the upstream node; setting a target voltage phasor at the downstream node as a value when a power flow across the feeder segment is maintained, and when equal reactive power is injected at the upstream and downstream nodes that consumes all the reactive power in the feeder segment; and adjusting operation of the at least one controllable reactive power resource so that the actual voltage magnitude at the downstream node moves towards a target voltage magnitude of the target voltage phasor.

A phase sequence adjustment system includes a power conversion circuit and a control circuit. The power conversion circuit is connected to a main power supply with a phase sequence. The control circuit respectively provides a first and a second excitation signals to the power conversion circuit, so as to short the power conversion circuit with the main power supply twice. The control circuit includes a current detection circuit and a control unit. The current detection circuit obtains two current signals respectively during two short-circuit operations. The control unit calculates two current phase angles respectively according to these two current signals and determines whether the phase sequence is positive or negative accordingly. The control unit selects one from the two current phase angles, calculates a voltage phase angle of the main power and a phase angle difference there-between to adjust a feedback phase sequence accordingly.

A phase sequence adjustment system includes a power conversion circuit and a control circuit. The power conversion circuit is connected to a main power supply with a phase sequence. The control circuit respectively provides a first and a second excitation signals to the power conversion circuit, so as to short the power conversion circuit with the main power supply twice. The control circuit includes a current detection circuit and a control unit. The current detection circuit obtains two current signals respectively during two short-circuit operations. The control unit calculates two current phase angles respectively according to these two current signals and determines whether the phase sequence is positive or negative accordingly. The control unit selects one from the two current phase angles, calculates a voltage phase angle of the main power and a phase angle difference there-between to adjust a feedback phase sequence accordingly.

A method of detecting phase loss of a three-phase AC power source includes steps of: acquiring any two line voltages of the AC power source with a first cycle period, acquiring a first digital signal and a second digital signal, performing an exclusive OR operation between the first digital signal and the second digital signal to generate a level signal, accumulating a high-level time count value, or accumulating a low-level time count value, resetting the low-level time count value when the high-level time count value is accumulated, or resetting the high-level time count value when the low-level time count value is accumulated, and determining that the AC power source occurs a phase-loss abnormality when the high-level time count value is greater than or equal to ⅓ of the first cycle period or the low-level time count value is greater than or equal to ⅙ of the first cycle period.

The present invention provides an apparatus and method enabling to perform a 2-dimensional trajectory analysis applicable for a three-phase system. A signal analysis apparatus generates a three-row and N-column waveform matrix constituted by three N dimensional row vectors having respectively N samples of first to third phase current values obtained from three-phase current signals measured in a three-phase system, where N is the number of samples of each of the three-phase current signals in one cycle of an AC power supply; applies transformation to the waveform matrix to obtain a two-row and N-column matrix constituted by the first and second N dimensional row vectors; performs normalization in amplitude of the first and second N dimensional row vectors, respectively; selects a grid size based on the sample number N; and maps a two dimensional trajectory made up from the first and second normalized N dimensional row vectors on a grid with the grid size selected.

The present invention provides an apparatus and method enabling to perform a 2-dimensional trajectory analysis applicable for a three-phase system. A signal analysis apparatus generates a three-row and N-column waveform matrix constituted by three N dimensional row vectors having respectively N samples of first to third phase current values obtained from three-phase current signals measured in a three-phase system, where N is the number of samples of each of the three-phase current signals in one cycle of an AC power supply; applies transformation to the waveform matrix to obtain a two-row and N-column matrix constituted by the first and second N dimensional row vectors; performs normalization in amplitude of the first and second N dimensional row vectors, respectively; selects a grid size based on the sample number N; and maps a two dimensional trajectory made up from the first and second normalized N dimensional row vectors on a grid with the grid size selected.

A method and a system sense at least one phase difference between at least two phases of a group of parallel connected three phase AC output terminals (e.g., a first phase AC output terminal, a second phase AC output terminal, or a third phase AC output terminal). The parallel connected AC output terminals may be three parallel connected DC to AC three phase inverters. Features of the parallel connected three phase AC output terminals enable wiring of conductors to one phase of an AC output terminal to be swapped with wiring of conductors of one phase of another phase AC output terminal. A sign of at least one phase difference is verified different from signs of other phase differences thereby the system determining the lateral position of the at least one three phase inverters relative to at least one other of the three phase inverters.

A method of detecting phase loss of a three-phase AC power source includes steps of: acquiring any two line voltages of the AC power source with a first cycle period, acquiring a first digital signal and a second digital signal, performing an exclusive OR operation between the first digital signal and the second digital signal to generate a level signal, accumulating a high-level time count value, or accumulating a low-level time count value, resetting the low-level time count value when the high-level time count value is accumulated, or resetting the high-level time count value when the low-level time count value is accumulated, and determining that the AC power source occurs a phase-loss abnormality when the high-level time count value is greater than or equal to ⅓ of the first cycle period or the low-level time count value is greater than or equal to ⅙ of the first cycle period.

A system for energy metering for a building, such as a data center.