DC Capacitor Voltage Control in Power Conversion Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-voltage DC power transmission systems, when a power conversion device stops, existing technologies require expanding the operation range of DC voltage to continue power transmission, necessitating larger power conversion devices to maintain stability and prevent voltage variations.
Innovation Solution
A power conversion system with self-excitation-type devices interconnected via DC buses, utilizing semiconductor switching elements for bidirectional power conversion, includes a control device that detects and compensates DC capacitor voltage and current to maintain constant DC voltage, allowing another normal device to take over power transmission without expanding the operation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage control methods are used when a power conversion device stops, then voltage stability can be maintained, but the operation range of DC voltage must be expanded requiring larger device size
Solution Approach 1:
The invention changes the control parameter from DC voltage to DC current. When a power conversion device stops, the remaining devices maintain voltage stability by controlling DC current instead of expanding the DC voltage operation range. This parameter substitution allows normal-sized devices to maintain reliability without size increase.
2Productivity
If another power conversion device takes over when one stops, then operation continuity is improved, but voltage variation occurs requiring larger capacity devices
Solution Approach 1:
The invention implements feedback control where remaining power conversion devices detect DC voltage variations and adjust their DC current output accordingly. This feedback mechanism enables operation continuity without requiring increased device capacity, as the system dynamically balances the load among functioning devices.
3Stability of the object's composition
If DC voltage command value is corrected to maintain stability, then voltage variation is suppressed, but the DC voltage operation range expands requiring larger devices
Solution Approach 1:
Instead of correcting DC voltage command values to maintain stability (which expands operation range), the invention inverts the approach by controlling DC current to maintain stability. This inversion keeps the DC voltage operation range within normal limits while achieving the same stability objective.
Data Source
AI summary
In a power conversion system in which self-excitation-type power conversion devices performing bidirectional power conversion are mutually interconnected by direct current, when the power conversion device serving for power transmission is stopped, in the first power conversion device, a DC capacitor voltage control unit calculates a current amount for compensating capacitor voltage in accordance with voltage variation in a DC capacitor. A high-voltage-side DC current control unit determines that an electricity amount supplied from a power supply system to the first power conversion device is a predetermined value or higher, and subtracts the current amount for compensating the capacitor voltage from a DC current command value. Thus, while the DC voltage is kept to be constant, the power flow direction is changed and power transmission to a second DC system is continued.