DC Energy Storage Control for VSC Oscillation Suppression
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Solution Overview
Problem
Direct current power transmission systems experience oscillation instability due to constant power control characteristics of converters and small equivalent resistance of devices, leading to potential system instability and oscillation.
Innovation Solution
A method involving a direct current energy storage apparatus connected in parallel to the sending and receiving terminal VSCs, with the number of energy storage submodules controlled based on acquired power oscillation amounts to adjust and suppress oscillations, utilizing multiple control modes (voltage, current, and active power control) to maintain system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If constant power control is adopted for converters connected to alternating current system, then independent control of active and reactive power is achieved, but system oscillation instability occurs due to negative resistance and reduced damping
Solution Approach 1:
The patent introduces a direct current energy storage apparatus as an intermediary component connected in parallel to the sending and receiving terminal VSCs. This energy storage apparatus acts as a mediator to counteract the negative resistance effect of constant power control, providing additional damping to the system and suppressing oscillations while maintaining the independent control capability of active and reactive power.
Solution Approach 2:
The patent dynamically adjusts the equivalent resistance parameter of the system by controlling the direct current energy storage apparatus. By changing the operating parameters of the energy storage apparatus, the system can modify its damping characteristics to compensate for the reduced damping caused by constant power control, thereby suppressing oscillations.
2Stability of the object's composition
If direct current energy storage apparatus is used to suppress oscillation, then system stability is improved, but energy waste increases if full apparatus is always connected
Solution Approach 1:
The patent employs a dynamic control strategy where the direct current energy storage apparatus transitions between different operating states (connected and disconnected) based on real-time system oscillation conditions. This dynamic adjustment allows the system to activate the energy storage apparatus only when oscillation suppression is needed, minimizing energy waste during normal stable operation while ensuring stability when oscillations occur.
Solution Approach 2:
The control method implements periodic monitoring of system oscillation and correspondingly periodic switching of the energy storage apparatus connection state. The apparatus is connected during periods when oscillation suppression is required and disconnected during periods when the system is stable, creating a periodic on-off pattern that balances stability maintenance with energy efficiency.
Data Source
AI summary
Provided are a method for suppressing direct current oscillation in a power transmission system and the power transmission system. The power transmission system comprises a sending terminal VSC, a receiving terminal VSC and a direct current energy storage apparatus, wherein the direct current energy storage apparatus is connected in parallel between the sending terminal VSC and the receiving terminal VSC, and the direct current energy storage apparatus comprises a plurality of energy storage submodules. The method comprises acquiring a direct current power oscillation amount of the power transmission system; and controlling, according to the direct current power oscillation amount, the number of the direct current energy storage apparatuses connected to the energy storage submodules of the power transmission system.