Bipolar HVDC Converter Station Power Coordination
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Solution Overview
Problem
Line-commutated converters in bipolar HVDC transmission systems experience high losses and sudden real power changes when switching on or off, which can cause undesirable voltage fluctuations in weak AC grids, and existing methods to mitigate these issues either increase losses or require costly compensation measures.
Innovation Solution
A converter station with two line-commutated converters operating in antiparallel mode on the same pole, where one converter acts as a rectifier and the other as an inverter, or operating on different poles as rectifiers or inverters, allowing for controlled real power exchange to minimize sudden real power changes and reduce transmission losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If line-commutated converters are operated with minimum flow of current to avoid intermittent flow, then converter reliability is improved, but transmission losses increase and sudden real power changes occur during switching
Solution Approach 1:
The invention changes the operating parameters of the converters by coordinating the real power of multiple converters at a converter station. By adjusting the real power settings of individual converters relative to each other, the system achieves reduced sudden real power changes during switching while maintaining minimum current flow to prevent intermittent operation. This parameter coordination allows operation below the traditional 5-10% minimum transmission power threshold without causing intermittent flow.
Solution Approach 2:
The invention introduces dynamic control of real power distribution among converters at a station. The control system continuously adjusts the real power of individual converters based on system conditions, enabling the station real power to be made lower than the minimum transmission power of individual converters. This dynamic coordination allows the system to respond to changing conditions while maintaining reliable operation without intermittent flow.
2Stability of the object's composition
If DC voltage is lowered to decrease sudden real power change during switching, then voltage stability is improved, but transmission losses increase
Solution Approach 1:
Instead of changing the DC voltage parameter, the invention changes the real power distribution parameter among converters. By coordinating the real power of multiple converters at a station, the system achieves reduced sudden real power changes during switching operations while maintaining the DC voltage at levels that minimize transmission losses. This approach decouples voltage stability from transmission loss considerations.
Solution Approach 2:
The invention segments the real power control function across multiple converters at a converter station. Rather than controlling a single converter's real power, the system divides the control among multiple converters, coordinating their individual real power outputs. This segmentation allows the station real power to be made lower than the minimum transmission power of individual converters, reducing sudden changes during switching without affecting DC voltage and transmission losses.
3Stability of the object's composition
If bipolar HVDC link transmits real powers in opposite directions to reduce sudden real power change, then voltage stability is improved, but transmission losses increase due to transmission via both poles
Solution Approach 1:
The invention segments the real power control function across multiple converters at a converter station, allowing independent control of each converter's real power. This enables the station real power to be made lower than the minimum transmission power of individual converters by coordinating converter real powers, reducing sudden changes during switching without requiring transmission via both poles and thus avoiding the associated transmission losses.
Solution Approach 2:
The invention changes the real power parameter distribution among converters at a station rather than changing transmission topology or voltage levels. By coordinating the real power of individual converters, the system achieves reduced sudden real power changes during switching while maintaining efficient single-pole or bipolar operation, avoiding the transmission losses that would result from utilizing both poles for opposite direction power transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for reduced or eliminated sudden real power changes during switching operations, enabling low station real power settings without increasing transmission losses, and supports high power transmission by controlling real power stipulations, thus enhancing operational efficiency and stability.
Implementation Method 1
These converters operate on the principle of reciprocal current commutation between individual valve units that each have one thyristor or multiple series-connected thyristors. The continuous flow of current is maintained by inductances.
Data Source
AI summary
A converter station has two line-commutated converters for energy transmission via a bipolar high voltage direct current transmission line. In a first operating mode of the converter station the two converters are electrically connected in an anti-parallel circuit to the same pole of the high voltage direct current transmission link and one of the converters is operated as a rectifier and the other converter is operated as an inverter in an network. In a second operating mode the two converters are connected to different poles of the high voltage direct current transmission link and both converters are operated as either rectifiers or inverters in the AC network. In both operating modes a station active power exchanged between the converter station and the AC network is controlled by active power specifications for converter active powers which are exchanged between the converters and the AC network.