AC/DC Converter Power Control for Frequency Mismatch
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Solution Overview
Problem
Existing power control systems, such as those employing FACTS devices, fail to operate effectively when system frequencies between different points of a transmission line vary, preventing the by-pass switch from being thrown and thus inhibiting the operation of voltage source converters as var compensators.
Innovation Solution
A power control system comprising AC/DC converters and switches connected across transmission lines with different system frequencies, where a control device manages the operation of these converters and switches to enable flexible power control by switching between Back to Back and reactive power compensation modes, ensuring appropriate power control across systems with varying frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a by-pass switch is used to connect transmission lines in existing power control systems, then the system can operate as static var compensators when the switch is closed, but the switch cannot be thrown when system frequency varies between different points of the transmission line, resulting in failure to operate as var compensators
Solution Approach 1:
The patent divides the power control system into two independent AC/DC converter units (first and second voltage source converters), each capable of operating independently. This segmentation allows each converter to handle different frequency systems separately, eliminating the need for a by-pass switch that would need to connect systems with different frequencies. Each converter can be controlled independently to achieve both power transmission and reactive power compensation functions.
Solution Approach 2:
Each AC/DC converter unit is designed with multi-functionality, capable of operating in multiple modes: as a power transmission converter in BTB configuration, and as a static var compensator for reactive power compensation. The control device enables flexible switching between these operational modes for each converter unit, allowing the system to adapt to different operational requirements without requiring physical by-pass switches.
2Power
If voltage source converters are configured to operate in BTB mode for power transmission, then active power can be transmitted between power systems, but the system lacks the flexibility to simultaneously provide reactive power compensation when frequency varies
Solution Approach 1:
The control device provides dynamic operational mode switching for each AC/DC converter unit. The system can dynamically transition between power transmission mode (BTB operation) and reactive power compensation mode (var compensator operation) based on system requirements and frequency conditions. This dynamic adaptability allows the same hardware configuration to serve multiple functions without requiring separate dedicated equipment for each function.
Solution Approach 2:
The control device acts as an intermediary that coordinates the operational modes of the AC/DC converter units. It monitors system conditions including frequency differences and automatically adjusts the operational state of each converter, enabling seamless transition between power transmission and reactive power compensation functions based on real-time system requirements.
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
Enables flexible and appropriate power control in multiple power systems with different system frequencies, allowing for effective reactive power compensation and active power transmission while maintaining system stability.
Implementation Method 1
a first AC/DC converter; a second AC/DC converter... When the first and second AC/DC converters are caused to operate as AC/DC converters in a BTB (Back to Back) method
Data Source
AI summary
A power control system includes: a first AC/DC converter; a second AC/DC converter; a first switch connected between a first transmission line of a first power system having a first system frequency and the first AC/DC converter; a second switch connected between the first transmission line and the second AC/DC converter; a third switch connected between a second transmission line of a second power system having a second system frequency and the first AC/DC converter; a fourth switch connected between the second transmission line and the second AC/DC converter; a fifth switch connected between the first AC/DC converter and the second AC/DC converter; and a control device. When the first and second AC/DC converters are caused to operate as AC/DC converters in a BTB (Back to Back) method, the control device controls at least the fifth switch to be in a closed state.