Modular HVDC Current Source Converter for Load Flow Control
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Solution Overview
Problem
In high voltage direct current (HVDC) power transmission systems, existing series converters face challenges in controlling load flow congestion, harmonic filtering, and protection against faults, leading to increased costs and complexity due to the need for costly protection equipment and additional reactors.
Innovation Solution
A multilevel current source converter (CSC) is introduced, comprising a series connection of modular cells with switches that inject voltage in series with the HVDC transmission line, reducing harmonic filtering needs and allowing for lower current-rated components, and featuring a thyristor diverter or bi-directional switches for efficient operation in all quadrants, along with antiparallel configurations for fault protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a series converter is inserted in a congested HVDC network to control load flow, then the ability to control load flow congestion is improved, but the device complexity and cost increase due to the need for filters and protection equipment
Solution Approach 1:
The series converter is divided into multiple modular units (first series converter unit and second series converter unit) that can be independently controlled. Each unit has its own control system and can operate autonomously, allowing the complex function to be segmented into manageable modules that reduce overall system complexity while maintaining full load flow control capability
Solution Approach 2:
The series converter units are designed to perform multiple functions: they can control active power flow, provide fault protection, and operate in all four quadrants (bipolar operation). The same hardware structure serves both normal operation and fault protection functions, reducing the need for separate dedicated equipment and thereby reducing device complexity
2Adaptability or versatility
If a series converter is used to control load flow, then the harmonic content and power quality issues arise, necessitating filters on both DC and AC sides
Solution Approach 1:
The converter is segmented into multiple independent units with separate control systems. Each unit generates fewer harmonics individually, and the segmented structure allows for better harmonic management. The modular design enables selective operation of units to minimize harmonic generation while maintaining load flow control
Solution Approach 2:
Each series converter unit is equipped with its own control system that monitors and adjusts operation to minimize harmonic generation. The control systems use feedback mechanisms to detect harmonic content and adjust switching patterns accordingly, reducing power quality issues while maintaining the ability to control load flow
3Reliability
If protection equipment and additional reactors are added to protect the series converter from faults, then the reliability is improved, but the cost and device complexity significantly increase
Solution Approach 1:
The series converter units serve dual purposes: they perform normal load flow control during healthy operation and automatically provide fault protection when needed. The same converter units that control power flow also detect and respond to faults (such as cable faults) by adjusting their operation or isolating themselves, eliminating the need for separate dedicated protection equipment and reactors
Solution Approach 2:
The converter system is designed to protect itself through inherent control mechanisms. Each converter unit has control systems that continuously monitor operating conditions and automatically take protective action when faults are detected, such as adjusting voltage injection or isolating from the line. This self-protection capability reduces reliance on external protection equipment
Data Source
AI summary
A multilevel current source converter (CSC) for controlling electrical power transmission in a high voltage direct current (HVDC) transmission system includes an alternating current (AC) side for input/output of AC to/from the CSC; a direct current (DC) side for input/output of DC to/from the CSC; and a plurality of modular CSC cells connected in parallel with each other between the AC side and the DC side of the CSC, each modular cell comprising a plurality of switches. The CSC is configured for being connected in series with an HVDC transmission line and for injecting a voltage in series with the HVDC transmission line at the DC side of the CSC.