DC Slack Bus Control for Variable Power Transmission
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Solution Overview
Problem
The integration of variable power sources, such as renewable energy farms, into power grids leads to power variability, causing grid instability and economic issues due to intermittent energy production, which existing technologies struggle to manage effectively.
Innovation Solution
A power transmission network with a control system that operates converters in DC voltage control mode as a DC slack bus to vary DC voltage and in AC voltage control mode as an AC slack bus, facilitating stable power transfer and reducing transmission losses by optimizing voltage levels and accommodating power variations from variable sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable power sources are integrated into the power grid to increase renewable energy utilization, then energy sustainability is improved, but grid stability deteriorates due to power variability
Solution Approach 1:
The patent introduces a DC transmission link as an intermediary between variable power sources and the AC power grid. This DC link acts as a buffer that decouples the variability of renewable energy generation from the grid, allowing power to be transmitted without directly transmitting instability. The DC slack bus further serves as a mediator that absorbs power fluctuations through voltage adjustments.
Solution Approach 2:
The control system dynamically adjusts the DC voltage at the DC slack bus to accommodate variations in power generation from variable sources. By changing the voltage parameter in response to power fluctuations, the system maintains grid stability while fully utilizing the generated power, resolving the contradiction between renewable energy utilization and grid stability.
2Loss of energy
If all generated power from variable sources is transmitted to the grid instead of controlling generation amount, then energy waste is reduced, but power variability increases causing transmission instability
Solution Approach 1:
The DC slack bus performs self-regulation by automatically adjusting its voltage in response to power generation variations. This self-service mechanism allows the system to accommodate all generated power without active control of the variable power sources, preventing energy waste while maintaining transmission stability through autonomous voltage adjustments.
Solution Approach 2:
The system transitions from static voltage control to dynamic voltage adjustment. The DC voltage at the slack bus is continuously varied based on real-time power generation conditions, enabling the transmission system to adapt to all power variations from variable sources while maintaining stability, thus eliminating the need to curtail generation.
3Reliability
If DC voltage is maintained at constant level for stable transmission, then transmission reliability is improved, but transmission losses increase when power generation varies
Solution Approach 1:
The patent implements dynamic DC voltage control at the DC slack bus, where the voltage level is continuously adjusted according to power generation conditions. This dynamic approach replaces constant voltage maintenance, allowing the system to optimize transmission efficiency by varying voltage to match power flow conditions while maintaining reliable transmission through controlled adjustments.
Solution Approach 2:
The DC voltage parameter is changed dynamically in response to power generation variations. By adjusting the voltage level according to actual power conditions, the system reduces transmission losses during low-generation periods while maintaining transmission reliability through controlled voltage variations, resolving the contradiction between constant reliability and variable losses.
4Stability of the object's composition
If converters are operated in AC voltage control mode only, then AC grid stability is maintained, but DC voltage becomes uncontrolled leading to transmission inefficiency
Solution Approach 1:
The converter system is designed with multi-functionality, capable of operating in both AC voltage control mode and DC voltage control mode. The same converter infrastructure serves dual purposes: maintaining AC grid stability through AC voltage control while simultaneously optimizing DC transmission efficiency through DC voltage control at the slack bus, eliminating the need for separate control systems.
Solution Approach 2:
The control functions are segmented between different converters: one converter is designated as the DC slack bus for DC voltage control to optimize transmission efficiency, while other converters maintain AC voltage control for grid stability. This functional segmentation allows both AC stability and DC efficiency to be achieved simultaneously without conflict.
Data Source
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AI summary
A power transmission network, for interconnecting at least one variable power source (28) and at least one AC electrical network (30), comprises: at least one DC transmission link (20) for DC power transmission between at least one network side converter (24) and at least one source side converter (24); at least one AC transmission link (26) for AC power transmission from the or the respective variable power source (28) to at least one source side converter (24); at least one source side converter (24) including: a DC connecting point operably connected to the or the respective DC transmission link (20); and an AC connecting point operably connected to the or the respective AC transmission link (26); at least one network side converter (22) including: an AC connecting point for connection to the or the respective AC electrical network (30); and a DC connecting point operably connected to the or the respective DC transmission link (20); and a control system (32a,32b,34), wherein at least one network side converter (22) is designated as a first converter, and the control system (32a,32b,34) is configured to operate the or each first converter in a DC voltage control mode as a DC slack bus to vary a DC voltage at its DC connecting point with respect to the power generated by the or the respective variable power source (28).