Power Dissipating Converter Control for HVDC Energy Balancing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In HVDC power transmission networks, the continuous DC power generation from offshore wind parks can cause challenges for onshore AC networks, particularly when the AC network is unable to accept the power, leading to energy imbalances and potential faults, which may result in the isolation of power conversion schemes and interruption of power transfer.
Innovation Solution
A power dissipating converter with a controller that selectively causes a balancing current to flow through chain-link modules, allowing for energy balancing without high energy losses, by modifying voltage references and utilizing subharmonic or superharmonic frequencies to avoid interference, and determining current flow direction to ensure accurate energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large discharge current is used to balance energy in chain-link modules, then energy balancing is achieved, but energy losses increase significantly
Solution Approach 1:
The system dynamically adjusts the current magnitude based on the balancing needs of chain-link modules. Instead of using a fixed large discharge current, the controller modulates the current to provide only the necessary balancing amount, reducing energy losses while maintaining reliability.
Solution Approach 2:
The invention changes the parameter of current magnitude from a fixed high value to a variable value that adapts to the actual energy imbalance conditions. This allows the system to use minimal current for balancing, significantly reducing I²R losses while achieving the required energy distribution.
2Stability of the object's composition
If the AC network cannot accept continuous DC power, then power transmission stability is maintained, but power transfer is interrupted
Solution Approach 1:
The power dissipating converter acts as an intermediary buffer between the DC network and AC network. It temporarily absorbs excess DC power when the AC network cannot accept it, preventing instability while maintaining continuous power transfer capability without requiring isolation of the entire system.
Solution Approach 2:
The system temporarily discards excess power through the dissipating converter when AC network capacity is unavailable, then recovers the power transfer capability once the AC network can again accept power. This maintains overall system stability while minimizing interruption to power transfer.
3Object-generated harmful factors
If subharmonic or superharmonic frequencies are used for balancing current, then interference with fundamental frequency is avoided, but control complexity increases
Solution Approach 1:
The system employs periodic action at subharmonic or superharmonic frequencies for the balancing current. This periodic modulation at frequencies distinct from the fundamental frequency allows energy balancing while avoiding interference with the main power transmission frequency, and the periodic nature simplifies the control implementation compared to arbitrary waveforms.
Data Source
Figure 1~2
AI summary
In the field of high voltage direct current (HVDC) power transmission, there is a need for an improved power dissipating converter (30). A power dissipating converter (30) for use with a power converter (10) configured to convert between AC power and DC power, comprises first and second DC terminals (12, 14) for connection to a DC network (20). The power dissipating converter (30) also includes a converter limb (32) that extends between the first and second DC terminals (12, 14) and which includes first and second limb portions (34, 36) that are separated by a ground terminal (38) for connection to ground (40). Each limb portion (34, 36) includes a chain-link converter (44) which is connected in series with a power dissipating resistor (46). Each chain-link converter (44) includes a plurality of series-connected chain-link modules (48), and each chain-link module (48) includes a plurality of switching elements (50) that are connected in parallel with an energy storage device (52) whereby each chain-link module (48) is selectively operable to provide a voltage source and the corresponding chain-link converter (44) is selectively operable to provide a stepped variable voltage source. The power dissipating converter (30) further includes a controller (70) which is programmed to operate the power dissipating converter (30) in first and second modes, the first mode being an inactive mode in which the power dissipating converter (30) is prevented from exchanging current with a DC network (20) connected in-use to the first and second DC terminals (12, 14) and no power from the DC network (20) is dissipated by either power dissipating resistor (46), and the second mode being an active mode in which the power dissipating converter (30) exchanges a discharge current with the DC network (20) and power from the DC network (20) is dissipated by each power dissipating resistor (46). The controller (70) is further programmed to operate the power dissipating converter (30) in a third mode, the third mode being a balancing mode in which the controller (70) causes a balancing current (I) smaller than the discharge current to flow through each chain-link converter (44).