Rigid Bipole HVDC Energization Control for Low Ground Current
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Solution Overview
Problem
In rigid bipole HVDC systems, uncoordinated energization of converters leads to energy imbalances between DC electrical poles, causing ground currents that induce electromagnetic interference, equipment damage, and corrosion, which existing technologies fail to adequately address.
Innovation Solution
A control logic is implemented to modulate the DC voltage output of converters during energization, balancing energy levels by adjusting the charging rate of converter valve capacitors and switching submodules, ensuring synchronous energization and minimizing ground currents to near-zero levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If converters are energized simultaneously without coordination, then energization speed is improved, but energy imbalance between poles causes ground currents that lead to electromagnetic interference and equipment damage
Solution Approach 1:
The control logic is activated before the converters are fully energized, during the deblocking phase. It preliminarily adjusts the DC voltage output and energization rate of each converter based on their individual states, preventing energy imbalance before it occurs. This preliminary coordinated control ensures that when the converters reach full energization, their energy levels are balanced and ground currents are minimized.
Solution Approach 2:
The control logic continuously monitors the energy levels and DC voltage outputs of both converters, and adjusts their energization rates in real-time based on this feedback. The system compares the actual energy balance with the desired balance and dynamically modifies the charging rate of valve capacitors and switching of submodules to maintain equilibrium, thereby preventing harmful ground currents while achieving fast energization.
2Object-affected harmful factors
If converter energization is coordinated to balance energy levels, then ground current is reduced, but energization time increases due to sequential control
Solution Approach 1:
The control logic dynamically adjusts the energization rate of each converter based on real-time energy balance requirements. Rather than using fixed sequential energization, the system continuously modifies the charging rate of valve capacitors and the switching timing of submodules to maintain energy equilibrium. This dynamic coordination allows both converters to be energized in parallel at optimized rates, reducing total energization time while keeping ground currents below threshold levels.
3Object-affected harmful factors
If DC voltage outputs of converters are made equal through precise control, then ground current is minimized, but control complexity increases
Solution Approach 1:
The control logic is designed to automatically detect energy imbalances and self-adjust the energization parameters without external intervention. It monitors the DC voltage outputs and energy levels of both converters, and autonomously modifies the charging rates and switching sequences to maintain equality. This self-regulating mechanism minimizes ground currents while avoiding the need for complex external control systems or manual coordination.
Data Source
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AI summary
There is provided a method (800) of energising electrical poles of a rigid bipole power transmission network, the rigid bipole power transmission network comprising a first pair of converters connected to a second pair of converters via first and second electrical poles, and further comprising a ground return path. The method (800) comprises determining (810) one or more parameters associated with either of the first or second pair of converters, wherein the one or more parameters indicate a difference in energy between the first and second electrical poles. The method (800) further comprises controlling (820), based on the one or more parameters, at least one converter of the associated first or second pair of converters to regulate the difference in energy between the first and second electrical poles such that a ground current flowing in the ground return path is below a predetermined threshold value.