DC Link Voltage Control for SSCI Damping in Wind Turbines
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Solution Overview
Problem
Wind turbine power systems experience control instabilities due to sub-synchronous control interactions (SSCI) when power-electronic converter controls interact with series-compensated transmission lines, leading to potential control margin issues if not properly tuned.
Innovation Solution
A method for controlling the voltage of a DC link in a power converter that involves setting an optimum voltage set point and immediately increasing it to a higher set point upon detection of transient events indicative of SSCI, optimizing voltage control and increasing the available voltage control margin by adjusting the modulation index limit and using rotor DC current regulator outputs to determine the voltage command.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the voltage set point is increased to dampen SSCI, then control stability is improved, but the risk of overvoltage and equipment stress increases
Solution Approach 1:
The control system applies periodic modulation to the voltage set point based on detected SSCI conditions, using oscillating control signals at sub-synchronous frequencies to dampen the instability without maintaining a continuously elevated voltage that would cause overvoltage stress
Solution Approach 2:
The system dynamically adjusts voltage control parameters including the voltage set point, modulation index, and damping coefficients based on real-time detection of SSCI conditions, changing these parameters adaptively to stabilize control while preventing overvoltage damage
2Adaptability or versatility
If the modulation index limit is increased to enhance voltage control margin, then control flexibility is improved, but the risk of exceeding safe operating limits increases
Solution Approach 1:
The modulation index limit is made dynamic rather than fixed, allowing the system to adjust the control margin adaptively based on operating conditions and SSCI detection, providing flexibility when needed while maintaining safety limits under normal conditions
Solution Approach 2:
The control system uses feedback from voltage and current measurements to continuously monitor operating conditions and adjust the modulation index limit accordingly, ensuring flexibility is provided only when safe operating margins allow
Data Source
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AI summary
A method (100) for controlling voltage of a DC link (244) of a power converter (210) of an electrical power system (200) connected to a power grid (242) includes operating the DC link (244) to an optimum voltage set point that achieves steady state operation of the power converter (210). The method (100) also includes monitoring the power grid (242) for one or more transient events that may be an indicator of one or more sub-synchronous control interaction (SSCI) conditions occurring in the electrical power system (200). Upon detection of the transient event(s) occurring in the power grid (242), the method (100) also includes immediately increasing the optimum voltage set point to a higher voltage set point of the DC link (244). Moreover, the method (100) includes operating the DC link (244) at the higher voltage set point until the sub-synchronous control interaction(s) is damped, thereby optimizing voltage control of the DC link (244).