Chain-Link Converter Fault Current Control With Switched Discharge Resistors
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Solution Overview
Problem
High voltage direct current (HVDC) power transmission systems face challenges in efficiently and reliably converting power between AC and DC networks, particularly in managing fault currents to optimize energy storage capacity without compromising normal operation, leading to increased costs and hardware requirements.
Innovation Solution
A converter system with a controller that switches discharge resistors into and out of switching modules at different voltage levels during normal and fault modes, dividing fault currents between resistors and energy storage devices to limit voltage and reduce energy storage capacity, allowing for smaller, more cost-effective designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the energy storage device capacity is increased to accommodate fault current charging, then the converter can handle fault conditions, but the converter size, cost, and hardware requirements increase
Solution Approach 1:
The discharge circuit is segmented from the main power conversion circuit, with dedicated discharge switching elements and resistors that can be independently controlled. This allows the energy storage device to serve dual purposes: normal voltage support and fault current dissipation, eliminating the need for oversized capacity
Solution Approach 2:
The system dynamically switches between normal operation mode and fault mode by controlling the discharge switching elements. During faults, the discharge circuits are activated to dissipate fault current, preventing excessive voltage rise and allowing smaller energy storage devices to suffice
2Reliability
If the energy storage device capacity is increased to limit voltage during fault conditions, then voltage rating requirements are met, but the converter becomes more expensive and complex
Solution Approach 1:
Discharge resistors act as intermediary elements between the energy storage device and the fault current. These resistors provide a controlled path for fault current dissipation, limiting voltage rise across the energy storage device without requiring increased capacity or complex protection circuits
Solution Approach 2:
The energy storage device serves itself by incorporating integrated discharge circuits within each switching module. The same energy storage device that provides voltage support during normal operation also handles fault conditions through its built-in discharge paths, eliminating the need for separate protection hardware
3Power
If discharge resistors are switched in at higher voltage levels during normal operation, then energy storage voltage is maintained, but fault current division is less effective
Solution Approach 1:
The control system dynamically adjusts the switching state of discharge resistors based on operating conditions. During normal operation, resistors remain disconnected to maintain efficiency. Upon detecting a fault condition, the control system rapidly switches discharge resistors into the circuit to divert fault current, optimizing performance for each operational state
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 optimizes energy storage capacity, reduces converter size and costs, and enhances reliability by managing fault currents efficiently while maintaining normal operation efficiency.
Implementation Method 1
a discharge circuit, the or each discharge circuit including a discharge switching element and a discharge resistor
Data Source
AI summary
A converter including a first terminal and a second terminal, the first terminal configured for connection to a first network, the second terminal configured for connection to a second network; at least one switching module arranged to interconnect the first terminal and the second terminal, the switching module including at least one module switching element and at least one energy storage device, the module switching element and the energy storage device arranged to be combinable to selectively provide a voltage source, the switching module switchable to control a transfer of power between the first and second networks; the switching module including a discharge circuit, the discharge circuit including a discharge switching element and a discharge resistor, the discharge switching element switchable to switch the corresponding discharge resistor into and out of the corresponding switching module; and a controller configured to selectively control the switching of the discharge switching element.