Energy supporting device
An energy supporting device for a high voltage direct current, HVDC, transmission system includes an energy supporting device for providing grid forming and/or virtual synchronous machine, VSM, capabilities to the HVDC transmission system. The energy supporting device comprises a plurality of cells configured to be connected to the HVDC transmission system, and a cell includes a full-bridge arrangement of power switches, an energy storage device electrically connected to the full-bridge arrangement, a resistor electrically connected between the plurality of cells and an electrical reference potential, and a bypass switch configured to allow the resistor to be bypassed. The energy supporting device is configured to be operated in a dissipation mode, in which the bypass switch is in an open state for allowing the resistor to dissipate electrical energy from the HVDC transmission system, and in which the energy storage devices of the plurality of cells are bypassed.
1 . An energy supporting device for providing grid forming and/or virtual synchronous machine (VSM) capabilities to a high voltage direct current (HVDC) transmission system, wherein the energy supporting device comprises:
a plurality of cells configured to be connected to the HVDC transmission system, wherein a cell includes:
a full-bridge arrangement of power switches; and
an energy storage device electrically connected to the full-bridge arrangement;
a resistor electrically connected between the plurality of cells and an electrical reference potential; and
a bypass switch configured to allow the resistor to be bypassed;
wherein the energy supporting device is configured to be operated in a dissipation mode, in which the bypass switch is in an open state for allowing the resistor to dissipate electrical energy from the HVDC transmission system, and in which the energy storage devices of the plurality of cells are bypassed.
2 . The energy supporting device according to claim 1 , wherein the energy supporting device is further configured to operate in:
a charging mode, in which the bypass switch is in a closed state for allowing the resistor to be bypassed, and in which the energy storage device of at least one cell of the plurality of cells is receiving electrical energy from the HVDC transmission system; and
an energy release mode, in which the energy storage device of at least one cell of the plurality of cells is discharging electrical energy to the HVDC transmission system to thereby provide the grid forming and/or VSM capabilities.
3 . The energy supporting device according to claim 2 , wherein the energy supporting device is further configured to operate in:
an idle mode, in which the full-bridge arrangement of at least one of the plurality of cells is configured to block electrical energy from the HVDC transmission system from passing through the energy supporting device.
4 . The energy supporting device according to claim 2 , wherein the full-bridge arrangement of a cell of the plurality of cells is configured to:
in the charging mode, allow the energy storage device of the cell to receive electrical energy;
in the dissipation mode, allow the energy storage device of the cell to be bypassed; and
in the discharging mode, allow the energy storage device of the cell to discharge electrical energy.
5 . The energy supporting device according to claim 1 ,
wherein the energy storage device of a cell of the plurality of cells comprises a super-capacitor and/or a battery.
6 . The energy supporting device according to claim 1 , further comprising a control unit configured to control the power switches of the full-bridge arrangements of the plurality of cells and the bypass switch.
7 . The HVDC transmission system comprising the energy supporting device according to claim 1 , the HVDC transmission system being configured as a symmetrical monopole HVDC transmission system or a bipolar HVDC transmission system.
8 . The HVDC transmission system according to claim 7 , further comprising:
a control system configured to control the power switches of the full-bridge arrangement of the plurality of cells and the bypass switch; and
at least one sensor configured to sense a current and/or a voltage of the HVDC transmission system and communicatively coupled to the control system;
wherein the control system is further configured to cause the energy supporting device to assume a mode based on the sensed current and/or voltage of the HVDC transmission system.
9 . The HVDC transmission system according to claim 1 , further comprising a first HVDC converter and a second HVDC converter connected to each other via the HVDC transmission system, wherein the first HVDC converter is coupled to a first AC network and the second HVDC converter is coupled to a second AC network.
10 . The HVDC transmission system according to claim 9 , wherein the first AC network comprises a power plant based on a renewable source or that is part of an AC grid.
11 . A method for providing grid forming and/or virtual synchronous machine (VSM) capabilities to a high voltage direct current (HVDC) transmission system, wherein the grid forming and for virtual synchronous machine, VSM, capabilities are provided by means of an energy supporting device comprising:
a plurality of cells connected to the HVDC transmission system, wherein a cell includes:
a full-bridge arrangement of power switches; and
an energy storage device electrically connected to the full-bridge arrangement;
a resistor electrically connected between the plurality of cells and an electrical reference potential; and
a bypass switch configured to allow the resistor to be bypassed;
the method comprising the steps of:
dissipating a surplus of electrical energy from the HVDC transmission system by opening the bypass switch of the energy supporting device and transmitting the surplus of electrical energy to the resistor of the energy supporting device.
12 . The method according to claim 11 , further comprising:
charging, in which the bypass switch is in a closed state for allowing the resistor to be bypassed, and in which the energy storage device of at least one cell of the plurality of cells is receiving electrical energy from the HVDC transmission system; and
releasing energy, in which the energy storage device of at least one cell of the plurality of cells is discharging electrical energy to the HVDC transmission system to thereby provide the grid forming and/or VSM capabilities.
13 . The method according to claim 12 , further comprising absorbing electrical energy from the HVDC transmission system by closing the bypass switch of the energy supporting device and transmitting the electrical energy into an energy storage device of at least one cell of the plurality of cells of the energy supporting device.
14 . The method according to claim 13 , wherein the step of absorbing electrical energy further comprises transmitting the electrical energy into a number of energy storage devices of the plurality of cells, wherein the number is based on a sensed level of charge of the energy storage devices.
15 . The method according to claim 11 , wherein the step of dissipating the surplus of electrical energy further comprises dissipating the surplus of electrical energy from the HVDC transmission system if a level of the surplus electrical energy of the HVDC transmission system is above a predetermined threshold.
16 . The method according to claim 11 , comprising:
performing the step of dissipating a surplus of electrical energy in response to a first support request; and
performing the step of discharging a surplus of electrical energy in response to a second support request.
17 . The method according to claim 11 , further comprising:
controlling, by a control system, the power switches of the full-bridge arrangement of the plurality of cells and the bypass switch;
sensing, by at least one sensor, a current and/or a voltage of the HVDC transmission system and communicatively coupled to the control system; and
causing, by the control system, the energy supporting device to assume a mode based on the sensed current and/or voltage of the HVDC transmission system.
18 . The method according to claim 11 , wherein a first HVDC converter and a second HVDC converter are connected to each other via the HVDC transmission system, wherein the first HVDC converter is coupled to a first AC network and the second HVDC converter is coupled to a second AC network, and wherein the first AC network comprises a power plant based on a renewable source or that is part of an AC grid.
19 . The method according to claim 11 , further comprising in an idle mode, the full-bridge arrangement of at least one of the plurality of cells blocking electrical energy from the HVDC transmission system from passing through the energy supporting device.
20 . The method according to claim 11 , further comprising controlling, by a control unit, the power switches of the full-bridge arrangements of the plurality of cells and the bypass switch.