US-12627153-B2 - Control of power converters in power transmission networks

US12627153B2US 12627153 B2US12627153 B2US 12627153B2US-12627153-B2

Abstract

A method of controlling a power converter in a power transmission network. A first amplitude limit value for a first AC current output from an AC side of the power converter is received. A second amplitude limit value for a negative phase sequence component of the first AC current is received. The negative phase sequence component is measured to provide a measured second amplitude. The negative phase sequence component is regulated to flow with a second amplitude that is the lesser of the measured second amplitude and second amplitude limit value. A positive phase sequence component of the first AC current is regulated to flow with an amplitude not exceeding a regulated third amplitude. The third amplitude is set using a function such that the second amplitude and the third amplitude provide a first amplitude for the first AC current that is substantially equal to the first amplitude limit value.

Inventors

Andrzej Adamczyk
Carl Barker
Li Zou
Huy Quoc Si DANG

Assignees

GE INFRASTRUCTURE TECHNOLOGY LLC

Dates

Publication Date: 20260512
Application Date: 20240529
Priority Date: 20230609

Claims (17)

1 . A computer-implemented method of controlling a power converter in a power transmission network, the power converter having an alternating current ‘AC’ side electrically connected to an AC network at a point of connection, the method comprising: receiving a first amplitude limit value for a first AC current, the first AC current being output from the AC side of the power converter; receiving a second amplitude limit value for a negative phase sequence component of the first AC current, wherein the second amplitude limit value is less than or equal to the first amplitude limit value; measuring the negative phase sequence component of the first AC current to provide a measured second amplitude; regulating the negative phase sequence component to flow with a regulated second amplitude by: if the measured second amplitude is less than the second amplitude limit value, setting the regulated second amplitude to be the measured second amplitude; if the measured second amplitude is equal to or greater than the second amplitude limit value, setting the regulated second amplitude to be the second amplitude limit value; regulating a positive phase sequence component of the first AC current to flow with an amplitude not exceeding a regulated third amplitude by: setting the regulated third amplitude as a function of the first amplitude limit value and the regulated second amplitude, such that the regulated second amplitude and the regulated third amplitude, when combined, provide a first amplitude for the first AC current that is substantially equal to the first amplitude limit value.
2 . The computer-implemented method of claim 1 , comprising: measuring the negative phase sequence component to provide a measured second phase angle; measuring the positive phase sequence component to provide a measured third amplitude value and measured third phase angle; wherein the function is further a function of an angular difference between the measured second phase angle and the measured third phase angle.
3 . The computer-implemented method of claim 2 , wherein the regulating the positive phase sequence component to flow with the regulated third amplitude further comprises: projecting the measured negative phase sequence component to at least one second phase vector in a reference frame of a fundamental frequency of the first AC current; and projecting the measured positive phase sequence component to at least one third phase vector in the reference frame.
4 . The computer implemented method of claim 3 , wherein: the first AC current is a multi-phase current; the at least one second phase vector comprises a second phase vector for each electrical phase of the multi-phase current; and the at least one third phase vector comprises a third phase vector for each electrical phase of the multi-phase current.
5 . The computer implemented method of claim 4 , wherein the regulating the positive phase sequence component to flow with the regulated third amplitude further comprises: calculating, for each electrical phase of the multi-phase current, a nominal angular difference between the measured second phase angle and measured third phase angle of the corresponding second and third phase vectors, thereby generating a plurality of nominal angular differences; and selecting, as the angular difference, a minimum nominal angular difference from the plurality of nominal angular differences.
6 . The computer implemented method of claim 5 , wherein the function is: I lim + = ( I ph , lim ) 2 - ( I ltd - ) 2 · ( sin 2 ( φ min ) ) - I ltd - ⁢ cos ⁡ ( φ min ) wherein I lim + is the regulated third amplitude, l ph,lim is the first amplitude limit value, I ltd - is the regulated second amplitude, Amin is the angular difference.
7 . The computer-implemented method of claim 1 , wherein: the first amplitude limit value is a predetermined first amplitude limit value ; and/or the second amplitude limit value is a predetermined second amplitude limit value.
8 . The computer-implemented method of claim 1 , wherein the power converter comprises a voltage sourced converter ‘VSC’.
9 . The computer-implemented method of claim 1 , wherein the power transmission network is a high voltage direct current ‘HVDC’ power transmission network.
10 . The computer-implemented method of claim 1 , wherein the AC network is an AC power grid.
11 . The computer-implemented method of claim 1 , for use in synchronous grid forming ‘SGFM’.
12 . A controller for controlling a power converter in the power transmission network, the controller comprising: a memory; and at least one processor; wherein the memory comprises computer-readable instructions which when executed by the at least one processor cause the controller to perform the method of claim 1 .
13 . The power converter for the power transmission network, comprising: an AC side for electrically connecting to the AC network at a point of connection; and a DC side for electrically connecting to a DC network; and the controller of claim 12 .
14 . The power transmission network comprising: the AC network; the DC network; and the power converter of claim 13 , wherein the AC network is connected to the AC side of the power converter and the DC network is connected to the DC side of the power converter.
15 . A computer program comprising instructions which when executed by a processor of a controller for the power converter, cause the controller to perform the method of claim 1 .
16 . The computer-implemented method of claim 1 , wherein: the first amplitude limit value is a maximum instantaneous total current limit for the power converter; and/or the second amplitude limit value is a maximum negative phase sequence current limit for the power converter.
17 . The computer-implemented method of claim 1 , wherein the power converter comprises a modular multi-level converter ‘MMC’.

Description

FIELD The subject matter herein relates generally to the field of power transmission networks and more specifically to the control of power converters in power transmission networks. INTRODUCTION 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 kilometre 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 utilised 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 effect 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. The dynamic exchange of active and reactive power between a power electronic converter interfaced system, such as an HVDC transmission link and the AC power system or grid itself, is primarily governed by a control algorithm employed by the power electronic converter. More specifically, synchronous grid forming (SGFM) control is gaining in interest and popularity owing to its strengthening effect on the stability of the overall power system. SUMMARY A typical characterization of SGFM control is to make a power electronic converter behave as a three-phase, positive phase sequence, AC voltage source, that resides behind an impedance. The power electronic converter operates at a frequency that is synchronous with other SGFM sources connected to the same power system. The use of SGFM control brings benefits in scenarios where an AC power system perturbation materializes. In response to such a perturbation, the power electronic converter would inherently exchange transient current that would counteract the voltage and/or frequency change experienced at the point of connection of the converter to the AC power system. However, unlike other SGFM sources such as synchronous generators, power electronic interfaced systems, including power converters in HVDC converter stations, need to obey much stricter current limits. Hence, SGFM converter control methods and apparatus must not allow steady state or transient currents to exceed these limits. In order to achieve this, SGFM control methods and apparatus must act to modify the output voltage profile of the power converter should a risk of non-compliance with the current limits arise. An example of a scenario whereby the current limits of a power electronic converter could be exceeded is that of an insulation fault occurring in a connected AC power system. This may result in a relatively large voltage deviation at the point of connection of the power electronic converter and the AC power system. The larger the voltage difference between the point of connection and the voltage behind the converter impedance, the higher the current exchange will be. A three-phase system is designed to operate as a balanced system comprising only positive phase sequence voltage/current. However, when an AC power system undergoes an asymmetric fault, such as a single-phase to earth fault, a large negative phase sequence voltage component may be introduced and experienced at the converter point of connection to the AC power system. In addition, a substantial reduction of the positive phase sequence voltage component may be experienced. If the converter was to maintain purely the positive phase sequence AC voltage profile, as desired, for instance, in SGFM control modes, the negative and positive phase sequence voltage components resulting from the fault would likely drive large negative phase and positive phase sequence current flows within the circuit. Combined with other current components, this could potentially overload at least a portion of the semiconductor devices within the power converter. More specifically, with regard to modular, multi-level voltage sourced converters (MMC VSC) that are typically employed in HVDC systems, this unmitigated exchange of negative phase and positive phase sequence AC currents, combined with the DC and converter circulating currents, could overload the transistors (insulated-gate bipolar transistors (IGBT), for instance) in the sub-modules of a converter valve or group of valves. T