Voltage Source Converter Overload Current Limiting
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Solution Overview
Problem
Current methods for overload current limiting in voltage source converters, such as reducing DC current or dynamic current limiting, are inadequate for effectively managing arm currents in voltage source converters with monopolar or bipolar topologies, as they fail to completely address thermal losses due to insufficient water-cooling capacity, especially during sustained overloads.
Innovation Solution
The method involves simultaneously adjusting active and reactive power instructions according to a specified slope to reduce the absolute value of arm currents, ensuring active and reactive power fall to zero, thereby reducing thermal losses and preventing converter overload. This is achieved through specific mathematical formulas for changing active and reactive instructions, allowing for independent control of active and reactive power adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If DC current is reduced to limit overload arm current, then thermal loss is reduced, but reactive current component is not addressed so arm current limiting objective cannot be completely achieved
Solution Approach 1:
The patent changes the control parameters from simple DC current reduction to simultaneous adjustment of active and reactive power instructions. By modifying both active power (P) and reactive power (Q) according to specified slopes, the method comprehensively controls the arm current magnitude, addressing both active and reactive current components that contribute to thermal loss.
2Speed
If dynamic current limit control is used for transient current limiting, then rapid response is achieved, but it cannot meet the requirements for current limiting during sustained overload
Solution Approach 1:
The patent implements a dynamic control strategy that adapts to different overload scenarios. By using slope-based adjustment of active and reactive power instructions, the system provides rapid initial response while maintaining sustained control capability. The dynamic nature of the slope parameters allows the system to respond quickly to transient overloads and maintain control during sustained overload conditions.
3Reliability
If water-cooling capacity is increased to handle thermal losses, then converter safety is improved, but system complexity and cost increase
Solution Approach 1:
The patent converts the harmful effect of thermal loss into a controllable parameter by actively managing active and reactive power output. Instead of merely reacting to thermal conditions through increased cooling capacity, the method proactively limits arm current by adjusting power instructions, thereby reducing thermal loss at its source and improving converter safety without requiring additional cooling system complexity.
Data Source
AI summary
According to the overload current limiting method for a voltage source converter, when a pole control system receives a water-cooling overload current limiting instruction, an active and reactive instruction are changed at the same time according to a specified slope, so that an absolute value of an arm current of the converter decreases in a fixed slope, and can be ensured that active power and reactive power fall to zero at the same time, and a water-cooling load limiting aim of the converter can be achieved by reducing the arm current. After a water-cooling overload power limiting instruction received by the pole control system is cancelled, a current value of the active power and the inactive power remain unchanged. When a water-cooling overload power limiting instruction is received again, decrease continues on the basis of current power values until the power falls to zero.