Abstract: A method for transferring power between medium voltage feeders via a direct current link in a power distribution network includes setting an iteration step value for each of a set of power reference quantities of the link, setting an initial value of each reference quantity, iteratively changing values of each reference quantity, and selecting one changed value of the set by: changing a present value of each reference quantity with the set iteration step value into a new value, measuring a total active power at a substation of the power distribution network for each new value, and selecting the new value that provides the lowest measured total active power at the substation. A next iteration is performed with the selected new value as present value for the one of the set of power reference quantities and with the present value for the other of the set of power reference quantities.

Abstract: A method for restoration of a fault isolation in a medium voltage, MV, network having a plurality of feeders and a plurality of normally open, NO, switches possibly in parallel with MV direct current, DC, links is presented. The method is performed in a control device of the MV network. The method includes closing at least two NO switches in parallel with MVDC links of the plurality of NO switches, being connected to a fault isolated feeder of the plurality of feeders of the MV network, and opening the closed at least two NO switches in parallel with MVDC links except one. A control device, a computer program and a computer program product for restoration of a fault isolation in a MV network are also presented.

Abstract: A method for transfer of power between medium voltage, MV, feeders via a MV direct current, MVDC, link in a power distribution network is presented.

Abstract: One embodiment is a system comprising a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter. The first AC-DC converter is electrically coupled with a first alternating current (AC) feeder. The second AC-DC converter electrically coupled with a second AC feeder. A battery charger electrically coupled with the MVDC link via a converterless connection. A first electronic controller is operatively coupled with the first AC-DC converter. A second electronic controller is operatively coupled with the second AC-DC converter. During operation of the battery charger to charge a battery the first electronic controller is configured to control power flow between the first AC feeder and the second AC feeder and the second electronic controller is configured to control the voltage of the MVDC link.

Abstract: A method for restoration of a fault isolation in a medium voltage, MV, network having a plurality of feeders and a plurality of normally open, NO, switches possibly in parallel with MV direct current, DC, links is presented. The method is performed in a control device of the MV network. The method includes closing at least two NO switches in parallel with MVDC links of the plurality of NO switches, being connected to a fault isolated feeder of the plurality of feeders of the MV network, and opening the closed at least two NO switches in parallel with MVDC links except one. A control device, a computer program and a computer program product for restoration of a fault isolation in a MV network are also presented.

Abstract: Unique systems, methods, techniques and apparatuses of fault mitigation are disclosed. One exemplary embodiment is a fault mitigation system for a medium voltage alternating current (MVAC) distribution network including a direct current (DC) link and a control system. The DC link is coupled to a first feeder line and a second feeder line. The control system is structured to determine a first feeder line is deenergized, operate the DC link so as to receive MVAC from a second feeder line and output low voltage alternating current (LVAC) to the first feeder line, operate a plurality of isolation devices, measure the LVAC in response to operating the plurality of isolation devices, determine a fault is isolated from a healthy portion of the first feeder line using the received LVAC measurements, and reenergize the healthy portion of the first feeder line.

Abstract: Unique systems, methods, techniques and apparatuses of a distribution system are disclosed. One exemplary embodiment is an alternating current (AC) distribution system including a first substation including a first transformer and a protective device; a first distribution network portion coupled to the first transformer; a second substation; a second distribution network portion; a DC interconnection system coupled between the first distribution network portion and the second distribution network portion; and a control system. The control system is structured to detect a fault in the first transformer or the transmission network, isolate the first distribution network from the fault, determine a set point of the DC interconnection system, and operate the DC interconnection system using the set point so as to transfer a portion of the MVAC from the second distribution network portion to the first distribution network portion.

Abstract: Systems, methods, techniques, and apparatuses of a medium voltage alternating current (MVAC) network are disclosed. One exemplary embodiment is a direct current (DC) interconnection system for an MVAC distribution network including an AC/AC power converter including a first AC terminal and a second AC terminal; a plurality of switching devices structured to selectively couple a first AC terminal to a plurality of feeder line points in the MVAC network; and a control system structured to receive a set of measurements, calculate a headroom value for each feeder line point using the set of measurements, select a first feeder line point using the calculated headroom values, operate the plurality of switching devices so as to couple the first AC terminal to the first feeder line point, and operate the AC/AC power converter so as to transmit MVAC power from the first AC terminal to the first feeder line point.

Abstract: One embodiment is a system comprising a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter. The first AC-DC converter is electrically coupled with a first alternating current (AC) feeder. The second AC-DC converter electrically coupled with a second AC feeder. A battery charger electrically coupled with the MVDC link via a converterless connection. A first electronic controller is operatively coupled with the first AC-DC converter. A second electronic controller is operatively coupled with the second AC-DC converter. During operation of the battery charger to charge a battery the first electronic controller is configured to control power flow between the first AC feeder and the second AC feeder and the second electronic controller is configured to control the voltage of the MVDC link.

Abstract: Systems, methods, techniques and apparatuses of feeder line fault response are disclosed. One exemplary embodiment is a method for operating an alternating current (AC) distribution network including a first feeder line, a second feeder line, and a third feeder line. The method includes isolating a faulted portion of the first feeder line from a healthy portion of the first feeder line; closing a tie switch coupled between the healthy portion and the second feeder line in response to isolating the faulted portion from the healthy portion; determining the second feeder line is experiencing an overload condition after closing the tie switch; and transferring AC power including transferring AC power using a direct current (DC) interconnection system coupled to the third feeder line effective to remove the overload condition from the second feeder line.

Abstract: Systems, methods, techniques and apparatuses of feeder line fault response are disclosed. One exemplary embodiment is a method for operating an alternating current (AC) distribution network including a first feeder line, a second feeder line, and a third feeder line. The method includes isolating a faulted portion of the first feeder line from a healthy portion of the first feeder line; closing a tie switch coupled between the healthy portion and the second feeder line in response to isolating the faulted portion from the healthy portion; determining the second feeder line is experiencing an overload condition after closing the tie switch; and transferring AC power including transferring AC power using a direct current (DC) interconnection system coupled to the third feeder line effective to remove the overload condition from the second feeder line.

Abstract: Unique systems, methods, techniques and apparatuses of a distribution system are disclosed. One exemplary embodiment is an alternating current (AC) distribution system including a first substation including a first transformer and a protective device; a first distribution network portion coupled to the first transformer; a second substation; a second distribution network portion; a DC interconnection system coupled between the first distribution network portion and the second distribution network portion; and a control system. The control system is structured to detect a fault in the first transformer or the transmission network, isolate the first distribution network from the fault, determine a set point of the DC interconnection system, and operate the DC interconnection system using the set point so as to transfer a portion of the MVAC from the second distribution network portion to the first distribution network portion.

Abstract: Systems, methods, techniques, and apparatuses of a medium voltage alternating current (MVAC) network are disclosed. One exemplary embodiment is a direct current (DC) interconnection system for an MVAC distribution network including an AC/AC power converter including a first AC terminal and a second AC terminal; a plurality of switching devices structured to selectively couple a first AC terminal to a plurality of feeder line points in the MVAC network; and a control system structured to receive a set of measurements, calculate a headroom value for each feeder line point using the set of measurements, select a first feeder line point using the calculated headroom values, operate the plurality of switching devices so as to couple the first AC terminal to the first feeder line point, and operate the AC/AC power converter so as to transmit MVAC power from the first AC terminal to the first feeder line point.

Abstract: Unique systems, methods, techniques and apparatuses of fault mitigation are disclosed. One exemplary embodiment is a fault mitigation system for a medium voltage alternating current (MVAC) distribution network including a direct current (DC) link and a control system. The DC link is coupled to a first feeder line and a second feeder line. The control system is structured to determine a first feeder line is deenergized, operate the DC link so as to receive MVAC from a second feeder line and output low voltage alternating current (LVAC) to the first feeder line, operate a plurality of isolation devices, measure the LVAC in response to operating the plurality of isolation devices, determine a fault is isolated from a healthy portion of the first feeder line using the received LVAC measurements, and reenergize the healthy portion of the first feeder line.

Abstract: The invention concerns a switchyard for interconnecting direct current power networks and a direct current power transmission system comprising such a switchyard. The switchyard comprises a number of interconnected entities comprising at least two main circuit breakers and a number of transfer switches, where each network has two connections to the switchyard, at least one via a transfer switch, each main circuit breaker has four connections in the switchyard, two at each end of the main circuit breaker and at least one via a transfer switch, and each network is joined with every other network via a corresponding path through at least one main circuit breaker as well as via a corresponding path bypassing all main circuit breakers.

Abstract: The invention concerns a switchyard for interconnecting direct current power networks and a direct current power transmission system comprising such a switchyard. The switchyard comprises a number of interconnected entities comprising at least two main circuit breakers and a number of transfer switches, where each network has two connections to the switchyard, at least one via a transfer switch, each main circuit breaker has four connections in the switchyard, two at each end of the main circuit breaker and at least one via a transfer switch, and each network is joined with every other network via a corresponding path through at least one main circuit breaker as well as via a corresponding path bypassing all main circuit breakers.

Abstract: An exemplary Multi-Terminal High Voltage Direct Current (MTDC) system includes at least three terminals, where each terminal including a Voltage Source Converter (VSC) controlled by a VSC controller. A method for controlling the MTDC system includes providing a converter schedule including at least one of a desired power flow value and a DC voltage; determining, by a MTDC master controller, a present state of the MTDC system including a dynamic topology of the MTDC system; determining, by the MTDC master controller, based on the present state of the MTDC system, based on the schedule and based on MTDC system constraints, VSC controller parameters including droop settings for local control by the VSC controllers; and transmitting the VSC controller parameters to the VSC controllers.

Abstract: A DC grid (100) comprising a plurality of AC/DC converters (105) which are interconnected via DC lines (115) is provided, wherein, in order to limit the effects of a fault in the DC grid, the DC grid is divided into at least two zones (200) by means of at least one current limiter (205) in a manner so that a current limiter is connected in each of the DC line(s) (115z) by which two zones are interconnected. A method of limiting the effects of a fault in a DC grid by dividing the DC grid into at least two zones is also provided.

Abstract: A breaker failure protection system for a high voltage direct current, HVDC, circuit breaker is provided. The circuit breaker is arranged for interrupting a DC circuit upon reception of a trip signal. The protection system includes a current sensor, at least one inductor, and a breaker failure detection unit. The current sensor is arranged for measuring a current I(t) through the DC circuit. The at least one inductor is connected in series with the DC circuit. The breaker failure detection unit is arranged for assessing, whether the circuit breaker has failed, and sending, if the circuit breaker has failed, a trip signal to an adjacent circuit breaker. The assessment is based on the measured current. The stability of HVDC grids may be improved by sending, in case of a breaker failure, a trip signal to adjacent circuit breakers. Further, a method of breaker failure protection for an HVDC circuit breaker is provided.

Abstract: An exemplary Multi-Terminal High Voltage Direct Current (MTDC) system includes at least three terminals, where each terminal including a Voltage Source Converter (VSC) controlled by a VSC controller. A method for controlling the MTDC system includes providing a converter schedule including at least one of a desired power flow value and a DC voltage; determining, by a MTDC master controller, a present state of the MTDC system including a dynamic topology of the MTDC system; determining, by the MTDC master controller, based on the present state of the MTDC system, based on the schedule and based on MTDC system constraints, VSC controller parameters including droop settings for local control by the VSC controllers; and transmitting the VSC controller parameters to the VSC controllers.