US-12620809-B2 - Relating to connecting a DC converter to a DC system in power transmission networks

US12620809B2US 12620809 B2US12620809 B2US 12620809B2US-12620809-B2

Abstract

A method for connecting a DC converter to a DC system using a connection circuit, the connection circuit including a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch. The method includes operating the first switch from the open configuration to a closed configuration, such that a first current is able to flow through the connection circuit; determining the first current flowing through the connection circuit; adjusting a DC converter voltage of the DC converter, as a function of the first current, to reduce the first current through the connection circuit to or below a threshold value; and then operating the second switch from the open configuration to a closed configuration, thereby connecting the DC converter to the DC system.

Inventors

Anthony TOTTERDELL
Omar JASIM

Assignees

GE INFRASTRUCTURE TECHNOLOGY LLC

Dates

Publication Date: 20260505
Application Date: 20241031
Priority Date: 20231115

Claims (15)

1 . A method for connecting a direct current (DC) converter to a DC system using a connection circuit, the connection circuit comprising a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch, wherein the first switch and the second switch are initially in an open configuration, the method comprising: operating the first switch from the open configuration to a closed configuration, such that a first current is able to flow through the resistive component of the connection circuit; determining the first current flowing through the connection circuit; adjusting a DC converter voltage of the DC converter, as a function of the first current, to reduce the first current through the connection circuit to or below a threshold value; and thereafter operating the second switch from the open configuration to a closed configuration in response to the first current being reduced to or below the threshold value, thereby connecting the DC converter to the DC system.
2 . The method of claim 1 , further comprising, before operating the first switch, determining and providing an initial setpoint voltage to the DC converter, wherein the initial setpoint voltage configures the DC converter to output an initial DC converter voltage.
3 . The method of claim 2 , wherein the initial setpoint voltage is based on: a normal operating range of the converter; and/or an assumed pre-defined voltage value; and/or a value provided by an external device such as a DC grid controller.
4 . The method of claim 1 , wherein the adjusting the DC converter voltage of the DC converter as a function of the first current, comprises: processing the first current using a closed loop control system, wherein the first current forms part of a feedback loop of the closed loop control system.
5 . The method of claim 1 , wherein the threshold value is: 10A or 5A; or a percentage of a nominal current value of the second switch or less than or equal to 0.5% of the nominal current value of the second switch, or less than or equal to 0.25% of the nominal current value of the second switch.
6 . The method of claim 1 , wherein before the operating the first switch from the open configuration to the closed configuration, the method further comprises: receiving a first command to connect the DC converter to the DC system.
7 . The method of claim 1 , further comprising: determining if the first current has been reduced to or below the threshold value.
8 . The method of claim 7 , further comprising: responsive to a determination that the first current has been reduced to or below the threshold value, providing a second command, wherein the second command causes the DC converter to stop adjusting the DC converter voltage, such that the DC converter voltage remains constant; and wherein the second command is provided before or after the operating the second switch.
9 . The method of claim 8 , wherein the operating the second switch from the open configuration to the closed configuration, comprises: providing a third command to the second switch, after the second command has been provided to the DC converter.
10 . A non-transitory computer readable storage medium storing thereon a computer program comprising instructions which when executed by a processor of a controller causes the controller to perform the method of claim 1 by controlling the connection circuit and the DC converter.
11 . A controller for controlling a connection circuit and a direct current (DC) converter to connect the DC converter to a DC system, the connection circuit comprising a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch, wherein the first switch and the second switch are initially in an open configuration; the controller comprising: a first connection configured to connect the controller to a node, wherein the node is in series with the first switch; a second connection configured to connect the controller to the first switch; a third connection configured to connect the controller to the second switch; a fourth connection configured to connect the controller to the DC converter; wherein the controller is configured to: operate the first switch via the second connection from the open configuration to a closed configuration, such that a first current is able to flow through the resistive component of the connection circuit; determine via the first connection the first current flowing through the connection circuit; adjust via the fourth connection a DC converter voltage of the DC converter, as a function of the first current, to reduce the first current through the connection circuit to or below a threshold value; and thereafter operate the second switch via the third connection from the open configuration to a closed configuration in response to the first current being reduced to or below the threshold value, thereby connecting the DC converter to the DC system.
12 . A connection circuit comprising the controller of claim 11 for connecting the DC converter to the DC system, the connection circuit comprising: the first switch; the second switch; and the resistive component; wherein the first switch is connected in series between the DC converter and the second switch; the second switch is connected in series between the first switch and the DC system; and the resistive component is connected in parallel with the second switch; the controller being configured to control the DC converter, the first switch, and the second switch to connect the DC converter to the DC system.
13 . A power transmission network comprising the connection circuit of claim 12 , the power transmission network comprising: the DC converter; the DC system; and the DC converter is connected to the first switch and the DC system is connected to the second switch of the connection circuit.
14 . The power transmission network of claim 13 , wherein the DC system is any one of: a DC power transmission network; another DC converter; a DC distribution network; a multi-terminal DC node; a multi-purpose DC network; and/or an interconnection between different DC schemes.
15 . The power transmission network of claim 13 , wherein the DC converter is an AC-to-DC converter or a DC-to-DC converter.

Description

FIELD The subject matter herein relates generally to the field of power transmission networks and more specifically to connecting a DC converter to a DC system in power transmission networks. BACKGROUND In high voltage direct current (HVDC) power transmission networks, alternating current (AC) power is typically converted to direct current (DC) power for transmission via overhead lines, under-sea cables and/or underground cables. This conversion removes the need to compensate for the AC reactive/capacitive load effects imposed by the power transmission medium, i.e., the transmission line or cable, and reduces the cost per kilometer of the lines and/or cables, and thus becomes cost-effective when power needs to be transmitted over a long distance. DC power can also be transmitted directly from offshore wind parks to onshore AC power transmission networks, for instance. The conversion between DC power and AC power is utilized where it is necessary to interconnect DC and AC networks. In any such power transmission network, power conversion means also known as converters (i.e., power converters in converter stations) are required at each interface between AC and DC power to affect the required conversion from AC to DC or from DC to AC. The choice of the most suitable HVDC power transmission network or scheme depends on the particular application and scheme features. Examples of power transmission networks include monopole power transmission networks and bipole power transmission networks. HVDC schemes often have a requirement to provide different operating configurations, for example to facilitate power transfer, or to connect multi-terminal or between multi-purpose schemes, or for static synchronous compensators (STATCOM), etc. To enable different operating configurations, it is often needed to connect a DC converter with a DC system. SUMMARY A connection circuit can be used to connect a DC converter with a DC system. The connection circuit can include a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch. The resistive component is configured to reduce the magnitude of a current which may flow due to a voltage difference between a DC converter side voltage and a DC system side voltage. Conventionally, the connection process tends to require a signal indicative of the DC system voltage in order to facilitate a connection that does not cause an inrush current through the connection circuit, or disturbance on the DC system (for example, a voltage spike as discussed further below). Conventional controllers for connection circuits thus require specialist functionality. There remains scope in providing improvement to existing methods of connecting a DC converter to a DC system in power transmission networks. According to a first aspect, there is provided a method for connecting a direct current (DC) converter to a DC system using a connection circuit, the connection circuit comprising a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch, wherein the first switch and the second switch are initially in an open configuration. The method comprises operating the first switch from the open configuration to a closed configuration, such that a first current is able to flow through the connection circuit; determining the first current flowing through the connection circuit; adjusting a DC converter voltage of the DC converter, as a function of the first current, to reduce the first current through the connection circuit to or below a threshold value; and thereafter operating the second switch from the open configuration to a closed configuration, thereby connecting the DC converter to the DC system. The methods described herein tend to allow for the connecting of the DC converter to the DC system with a minimum voltage difference, whilst not requiring a signal indicative of the DC system voltage. When the first switch is operated into the closed configuration, a current path is established in the connection circuit whereby a current may flow between the DC converter and the DC system, through the resistive component. The flow of current tends to be dependent upon the presence of a voltage difference between the DC converter and the DC system. More specifically, this can occur when the DC converter is regulated to a DC voltage that is not equivalent to the voltage of the DC system. Ensuring the precise control of the DC converter voltage in relation to the DC system voltage can be particularly challenging if direct DC system voltage measurements are unavailable. In the methods described herein, because the current path includes the resistive component, even if there is a