HVDC Bipole Converter Control for DC Current Distribution
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Solution Overview
Problem
In high voltage direct current (HVDC) power transmission networks, existing bipole power transmission schemes face challenges in efficiently controlling the distribution of DC current between transmission conduits, leading to suboptimal power transmission efficiency and increased maintenance needs.
Innovation Solution
A bipole power transmission scheme is implemented with a first and second converter station connected by transmission conduits and a return conduit. The scheme includes power converters with converter controllers that adjust the operating phase angles of AC voltages presented to a point of common coupling, allowing for controlled distribution of DC current between the conduits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the distribution of DC current between transmission conduits is not controlled, then the system structure remains simple, but power transmission efficiency decreases and maintenance needs increase
Solution Approach 1:
The converter station controller continuously monitors the distribution of DC current between the first and second transmission conduits and automatically adjusts the operating phase angles of the power converters to optimize current distribution. This closed-loop feedback control minimizes power transmission losses by dynamically responding to changing system conditions without requiring manual intervention or complex external control systems.
Solution Approach 2:
The system uses the existing converter stations and their control capabilities to automatically manage DC current distribution. The converter station controller leverages the phase angle control already present in the power converters to achieve optimal current distribution, eliminating the need for separate dedicated control devices or complex additional infrastructure.
2Productivity
If DC current distribution is controlled by adjusting phase angles, then power transmission efficiency improves, but the control system complexity increases
Solution Approach 1:
The converter station controller performs multiple functions: it manages the conversion between AC and DC power, controls the operating phase angles of power converters, monitors DC current distribution, and optimizes power transmission efficiency. By consolidating these functions into a single control system that leverages existing converter capabilities, the patent avoids adding separate dedicated control devices, thereby improving operational efficiency without proportionally increasing system complexity.
3Ease of repair
If the return conduit is used extensively for current carry, then the transmission scheme remains simple, but maintenance requirements increase
Solution Approach 1:
The converter station controller monitors the current distribution between the transmission conduits and the return conduit, and automatically adjusts the operating phase angles to minimize the current carried by the return conduit. This feedback control reduces wear and maintenance needs on the return conduit by optimizing current distribution, without requiring complex manual intervention or additional control infrastructure.
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 solution enables efficient control of DC current distribution between transmission conduits, reducing power transmission losses and minimizing the use of return conduit components, thereby enhancing operational efficiency and reducing maintenance requirements.
Implementation Method 1
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, converters (i.e. power converters) are required at each interface between AC and DC power to effect the required conversion from AC to DC or from DC to AC.
Data Source
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Figure 3(a)
AI summary
In the field of high voltage direct current (HVDC) power transmission networks there is a need for improvements in relations to bipole power transmission schemes. A bipole power transmission scheme (10) comprises a first converter station (12) that is positioned, in-use, remote from a second converter station (14). First and second transmission conduits (18, 20) and a return conduit (22) interconnect, in-use, the first converter station (12) with the second converter station (14) and thereby permit the transfer of power (PDC1, PDC2) between the first and second converter stations (12, 14). The first converter station (12) includes a first power converter (30) which has a first DC terminal (32) that is connected with the first transmission conduit (18), a second DC terminal (34) which is connected with the return conduit (22), and at least one first AC terminal (36) that is electrically connected with a point of common coupling (40) for connection to an AC network element which operates at a reference phase angle. The first power converter (30) further has a first converter controller (46) which is programmed to control the transfer of power between the first transmission conduit (18) and the point of common coupling (40) by having the first power converter (30) provide a first AC voltage (VAC1) at the or each first AC terminal (36) which is presented to the point of common coupling (40). The first converter station (12) also includes a second power converter (48) which has a third DC terminal (50) that is connected with the return conduit (22), a fourth DC terminal (52) which is connected with the second transmission conduit (20), and at least one second AC terminal (54) that is electrically connected with the point of common coupling (40). The second power converter (48) further has a second converter controller (56) that is programmed to control the transfer of power between the second transmission conduit (20) and the point of common coupling (40) by having the second power converter (48) provide a second AC voltage (VAC2) at the or each second AC terminal (54) which is presented to the point of common coupling (40). Also included in the first converter station (12) is a converter station controller (58) that is arranged in operative communication with each of the first and second converter controllers (46, 56) whereby the first and second power converters (30, 48) are controlled as grid forming converters such that the first and second AC voltages (VAC1, VAC2) presented to the point of common coupling (40) manage the AC frequency (f) and AC voltage (V) at the point of common coupling (40). The converter station controller (58) is programmed to operate the first converter station (12) in a current distribution mode (78) in which the distribution of DC current (IDC1, IDC2) between the first and second transmission conduits (18, 20) is controlled. The converter station controller (58), when operating the first converter station (12) in the current distribution mode (78), is programmed to instruct the first converter controller (46) to adjust the operating phase angle of the first AC voltage (VAC1) provided at the or each first AC terminal (36) in a first direction relative to the reference phase angle at the point of common coupling (40) and instruct the second converter controller (56) to adjust the operating phase angle of the second AC voltage (VAC2) provided at the or each second AC terminal (54) in a second direction opposite to the first direction relative to the reference phase angle at the point of common coupling (40).