Doubly Fed Induction Generator Braking via Rotor DC Component
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Solution Overview
Problem
Wind turbine systems with doubly fed induction generators face challenges in controlled braking, particularly in reducing the rotor speed or bringing it to a stop, due to the complexity and cost associated with existing braking mechanisms.
Innovation Solution
A two-stage power converter system with a line side converter and a rotor side converter coupled by a DC link, utilizing a pulse width modulation scheme to generate a rotor side output with a non-zero DC component, which effectively reduces the rotational speed of the doubly fed induction generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional braking mechanisms are used to reduce rotor speed or bring it to a stop, then the generator can be controlled during braking, but the system complexity and cost increase significantly
Solution Approach 1:
The rotor side converter, originally designed for power regulation during normal operation, is made multi-functional by enabling it to perform braking operations. The converter uses its existing IGBT switches and control circuitry to generate a DC component in the rotor current that produces braking torque, eliminating the need for separate braking mechanisms while maintaining controlled braking capability
Solution Approach 2:
The system uses its own existing power converter infrastructure to perform braking functions. The rotor side converter leverages its built-in DC link capacitor and switching devices to generate the necessary DC current component for braking, allowing the system to brake itself without external braking components
2Reliability
If conventional braking mechanisms are used to reduce rotor speed or bring it to a stop, then the generator can be controlled during braking, but the system cost increases
Solution Approach 1:
The rotor side converter is designed to perform multiple functions: power regulation during normal operation and braking during stop sequences. By making the converter multi-functional, the patent eliminates the need for additional braking hardware, thereby reducing manufacturing costs while maintaining reliable controlled braking capability
Solution Approach 2:
The braking function is merged with the existing power converter system. The rotor side converter's switching devices and control circuitry are used for both power regulation and braking, combining multiple functions into a single integrated system that reduces overall cost
3Speed
If a DC component is added to the rotor side output for braking, then the rotational speed is reduced effectively, but the pulse width modulation scheme becomes more complex
Solution Approach 1:
The pulse width modulation scheme is made dynamic and adaptive. During braking operations, the controller modifies the PWM switching patterns to generate the required DC current component in the rotor, while during normal operation, it uses conventional PWM for power regulation. This dynamic adaptation allows effective speed reduction without requiring a permanently complex PWM scheme
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides a highly repeatable and controlled braking mechanism with minimal additional hardware, simplifying the power system and reducing costs while maintaining the stability of the electrical grid frequency.
Implementation Method 1
The non-zero DC component of the rotor side output can reduce a speed of rotation of the wind-driven doubly fed induction generator
Data Source
AI summary
Systems and methods to provide for the controlled braking of a generator (e.g., a doubly-fed induction generator (DFIG)) in a wind power system are provided. In one example implementation, a method for braking a wind-driven doubly fed induction generator can include: receiving, by one or more control devices, a command to brake a wind-driven doubly fed induction generator; and generating, by the one or more control devices, a pulse width modulation scheme for the rotor side converter to provide a rotor side output to a rotor of the doubly-fed induction generator. The rotor side output includes a non-zero DC component and an AC component. The method includes controlling, by the one or more control devices, the rotor side converter in accordance with the pulse width modulation scheme. The non-zero DC component of the rotor side output can reduce a speed of rotation of the wind-driven doubly fed induction generator.