DFIG Rotor Current Damping for Sub-Synchronous Oscillation Control
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Solution Overview
Problem
Inverter-based resources, such as wind turbine power systems, connected to series-compensated networks experience sub-synchronous oscillations, leading to instability and equipment damage due to negative resistance presented by doubly-fed induction generator (DFIG) wind turbines under sub-synchronous conditions.
Innovation Solution
The method involves determining rotor current commands for the power converter and applying stator current components to provide active damping, thereby mitigating sub-synchronous power oscillations. This is achieved by reducing the effective rotor resistance through the placement of a virtual resistance in parallel, compensating for the negative resistance under sub-synchronous conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If inverter-based resources are connected to series-compensated networks, then power transmission capability is improved, but sub-synchronous oscillations occur leading to instability
Solution Approach 1:
The patent converts the harmful negative resistance effect into a beneficial damping effect by injecting a damping current that is proportional to the stator current. The controller calculates the damping current based on the relationship idamping = -k * istator, where the negative sign transforms the harmful negative resistance into positive damping, thereby eliminating sub-synchronous oscillations while maintaining the series compensation benefits
Solution Approach 2:
The patent implements a feedback mechanism where the controller continuously monitors the stator current and adjusts the rotor current accordingly to maintain damping. The damping current is calculated in real-time based on the measured stator current, creating a closed-loop control system that actively suppresses sub-synchronous oscillations as they occur
2Adaptability or versatility
If DFIG wind turbines operate under sub-synchronous conditions, then power conversion flexibility is improved, but negative resistance is presented causing oscillations
Solution Approach 1:
The patent transforms the harmful negative resistance characteristic of DFIG under sub-synchronous conditions into a beneficial damping effect. By injecting a rotor current component that is proportional and opposite to the stator current (idamping = -k * istator), the system converts the destabilizing negative resistance into positive damping that suppresses oscillations while preserving power conversion flexibility
3Loss of energy
If series compensation is applied to the network, then transmission efficiency is improved, but sub-synchronous oscillations are excited
Solution Approach 1:
The patent employs a feedback control mechanism where the controller measures the stator current and generates a damping current in response. This real-time feedback loop (idamping = -k * istator) allows the system to maintain series compensation for improved transmission efficiency while actively counteracting the sub-synchronous oscillations that the compensation excites
Data Source
AI summary
A method for mitigating sub-synchronous power oscillations in an inverter-based resource connected to an electrical grid via a series-compensated grid connection includes determining, via a controller, one or more rotor current commands for a power converter of the inverter-based resource. The method also includes applying, via a software module of the controller, at least one stator current component to the one or more rotor current commands to provide active damping to mitigate the sub-synchronous power oscillations in the inverter-based resource. Further, the method includes determining, via the controller, at least one voltage command for the inverter-based resource as a function of the one or more rotor current commands and the at least one stator current component. Moreover, the method includes controlling, via the controller, the inverter-based resource, based at least in part, on the voltage command.