HVDC Converter Control Using Virtual Voltage for Multi-AC Grids
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Solution Overview
Problem
High voltage direct current (HVDC) power transmission networks require multiple converters for AC-DC conversion, leading to increased capital costs and space requirements, and existing control methods struggle to manage over-voltages and maintain stable AC network voltages, especially in weak grids and wind farm integrations.
Innovation Solution
A power transmission network utilizing a single power converter with primary and secondary controller configurations to establish a virtual voltage, allowing control of multiple AC network voltages, reducing the need for additional converters and maintaining voltages within predetermined limits by adjusting the AC converter voltage, while accounting for conduit reactance and cross-coupling effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple converters are used for AC-DC conversion in HVDC power transmission networks, then the conversion reliability is improved, but the capital cost and space requirements increase
Solution Approach 1:
The patent combines multiple converter functions into a single power converter by establishing a virtual voltage that represents multiple AC network voltages. The single converter controls multiple AC transmission conduits through this virtual voltage mechanism, merging what would traditionally require multiple separate converters into one integrated device.
Solution Approach 2:
The single power converter is designed to perform multiple functions simultaneously - it converts AC to DC for the HVDC network while also controlling multiple different AC network voltages across different transmission conduits. This multi-functionality eliminates the need for dedicated converters for each AC network connection.
2Device complexity
If conventional control methods are used for AC converter voltage, then the system simplicity is maintained, but the ability to manage over-voltages and maintain stable AC network voltages deteriorates
Solution Approach 1:
The control system continuously monitors the virtual voltage, which represents the state of multiple AC network voltages, and adjusts the AC converter voltage accordingly. This feedback mechanism enables the single converter to maintain stable voltages across multiple AC networks and prevent over-voltage conditions by automatically responding to changes in the virtual voltage parameter.
Data Source
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AI summary
In the field of high voltage direct current (HVDC) power transmission networks, there is a need for improvements to allow a single power converter to control individual AC network voltages carried by multiple AC transmission conduits to multiple AC network elements, such as respective wind parks. A power transmission network (10; 100) comprises a power converter (12) which has first and second DC converter terminals (14, 16) that are for connection, in use, to a DC network. The power converter (12) also includes an AC converter terminal (22) which is electrically connected to a plurality of AC transmission conduits (241, 242, 24n), each of which is for connection, in use, to a respective AC network element (261, 262, 26n) that is configured to operate at a respective individual AC network voltage. The power converter (12) further includes a primary converter controller (34) which is programmed, in use, to control the transfer of power through the power converter (12) and thereby between the DC network and the plurality of AC network elements (261, 262, 26n). The primary converter controller (34) is further programmed, in use, to control each individual AC network voltage by establishing a virtual voltage which is representative of the plurality of AC network voltages and altering a single AC converter voltage produced by the power converter (12) at the AC converter terminal (22) to adjust the virtual voltage and thereby adjust each individual AC network voltage.