Variable Gain Current Regulator for DFIG Sub-Synchronous Stability
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Solution Overview
Problem
Power generation systems, particularly wind-driven doubly fed induction generator (DFIG) systems connected to series compensated transmission lines, experience sub-synchronous instability due to insufficient damping at low frequency ranges, leading to unintentional tripping.
Innovation Solution
A method and system that monitor the rotor speed of a generator and adjust the regulator gains in the current regulators based on a gain scaling factor, increasing damping and enhancing system stability by modifying the gains as the rotor speed decreases below synchronous speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power generation system uses fixed regulator gains in the current regulators, then the system operates normally at synchronous speed, but the system experiences sub-synchronous instability when connected to series compensated transmission lines
Solution Approach 1:
The patent applies dynamics by making the regulator gains variable rather than fixed. The controller dynamically adjusts the regulator gains in the current regulators based on the operating conditions, specifically adapting them to provide appropriate damping across different frequency ranges including sub-synchronous frequencies. This dynamic adjustment resolves the contradiction by enabling the system to maintain stability both at synchronous speed and during sub-synchronous oscillations.
Solution Approach 2:
The patent changes the parameters of the current regulators by adjusting their gains. The controller modifies the regulator gain parameters to enhance damping capability in the sub-synchronous frequency range while maintaining proper operation at synchronous speed. This parameter adjustment directly addresses the instability issue without compromising normal system operation.
2Reliability
If the electrical system control components use standard damping, then the system is simple to operate, but the damping is insufficient at low frequency ranges causing instability
Solution Approach 1:
The patent makes the existing electrical system control components multi-functional by enabling them to provide both standard damping for normal operation and enhanced sub-synchronous damping when needed. The controller achieves this by dynamically adjusting the regulator gains to adapt to different operating conditions, allowing the same control components to handle both synchronous and sub-synchronous frequency requirements without adding separate dedicated damping devices.
Solution Approach 2:
The control components are made dynamic through gain scheduling, where the regulator gains are adjusted based on the operating frequency and system conditions. This dynamic behavior allows the control components to automatically provide appropriate damping levels for both standard operation and sub-synchronous stability, resolving the contradiction between simplicity and effectiveness.
3Adaptability or versatility
If the DFIG operates with negative equivalent resistance at frequencies below nominal frequency, then the generator can produce power in variable frequency range, but the system experiences sub-synchronous instability
Solution Approach 1:
The patent changes the effective resistance characteristic of the DFIG by adjusting the regulator gains in the current regulators. By modifying these gain parameters, the controller compensates for the negative equivalent resistance effect that causes instability, while allowing the generator to continue operating across the variable frequency range. This parameter adjustment maintains both the adaptability of the DFIG and the stability of the system.
Solution Approach 2:
The patent converts the harmful effect of negative equivalent resistance into a beneficial outcome by using the same control mechanism to provide positive damping. The controller adjusts the regulator gains to counteract the negative resistance effect, transforming the potential source of instability into an opportunity for enhanced system control and stability across the full operating frequency range.
Data Source
AI summary
In one aspect, a method for controlling the operation of a power generation system configured to supply power to an electrical grid may generally include monitoring a rotor speed of a generator of the power generation system and determining a gain scaling factor based on the rotor speed, wherein the gain scaling factor increases with decreases in the rotor speed across a range of rotor speeds. In addition, the method may include adjusting a regulator gain to be applied within a current regulator of the power generation system based on the gain scaling factor and applying the adjusted regulator gain within the current regulator in order to generate a voltage command signal for controlling a power converter of the power generation system.