Wound Rotor Induction Generator Frequency Conversion for Compact Wind Power
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Solution Overview
Problem
Modern variable speed wind turbines with doubly-fed induction generators have limitations due to low power density and high costs, resulting in bulky machines with limited rotational speed and increased electrical losses, necessitating a more compact and efficient power generation solution.
Innovation Solution
A wind turbine electrical power generating system utilizing a wound rotor induction generator with an AC to DC converter and a bi-directional DC to AC converter, allowing operation at higher output frequencies, which reduces the generator size and increases power density by inducing a higher electromagnetic force with a faster changing electromagnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a doubly-fed induction generator is used with nominal operating speed of about 1200 rpm, then the generator can provide electrical power at grid frequency with little slip, but the generator becomes bulky with low power density and high costs
Solution Approach 1:
The patent changes the operating parameters by allowing the generator to operate at speeds significantly higher than the nominal 1200 rpm (up to 3000 rpm or more). This parameter change enables the generator to produce the same grid frequency power through electronic conversion rather than direct mechanical coupling, thereby reducing the physical size and improving power density while maintaining reliability
Solution Approach 2:
The patent replaces the direct mechanical coupling between the wind turbine rotor and the generator with an electronic conversion system. Instead of mechanically coupling the generator to run at grid-synchronized speeds, the system uses power electronic converters to transform the variable-speed mechanical energy into grid-compatible electrical energy, eliminating the need for a bulky synchronous generator design
2Device complexity
If the generator operates at low rotational speed, then the mechanical coupling is simpler, but voltage step-up is required which increases electrical losses and machine size
Solution Approach 1:
The patent replaces the mechanical simplicity of direct coupling with an electronic solution that achieves the same goal more efficiently. Power electronic converters directly convert the variable-speed generator output to grid frequency without requiring intermediate mechanical gearboxes or electrical voltage step-up transformers, thereby reducing electrical losses while maintaining operational simplicity through electronic control
3Volume of moving object
If the rotational speed is increased to improve power density, then the generator becomes more compact, but gearbox limitations prevent efficient speed increase
Solution Approach 1:
The patent eliminates the mechanical gearbox system entirely and replaces it with power electronic speed conversion. The variable-speed generator can operate at optimal high speeds for compactness and power density, while electronic converters handle the speed and frequency transformation that would otherwise require a complex mechanical gearbox system
Solution Approach 2:
The patent introduces dynamic control through power electronic converters that can adaptively adjust the electrical output frequency and voltage to match grid requirements, regardless of the generator's rotational speed. This dynamic electronic control replaces the static mechanical gear ratios, enabling the generator to operate at variable speeds for optimal power density while maintaining grid compatibility
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 configuration enables a smaller, more compact generator with higher power density and lower footprint, achieving cost savings while maintaining efficient power generation, even at varying rotational speeds.
Implementation Method 1
a wound rotor induction generator (WRIG) comprising stator windings and a generator rotor with rotor windings. The generator rotor is configured to be mechanically coupled to a wind turbine rotor of the wind turbine to receive rotational mechanical energy
Implementation Method 2
A first converter is electrically coupled to the stator windings such that in operation, AC (alternating current) electrical power generated by these stator windings and provided to the main load passes through the first converter. The first converter is in particular an AC to DC converter that is configured to provide a conversion of the AC electrical power generated by the stator windings to DC (direct current) electrical power
Implementation Method 3
An AC frequency of the generated AC electrical power is at least partially determined by setting or controlling currents in the rotor windings of the generator rotor by the second converter
Data Source
AI summary
A wind turbine electrical power generating system is provided and is configured to supply generated electrical power to a main load. The system includes a wound rotor induction generator including stator windings and a generator rotor with rotor windings. The generator rotor is configured to be mechanically coupled to a wind turbine rotor of the wind turbine to receive rotational mechanical energy. A first converter is electrically coupled to the stator windings such that in operation, AC electrical power generated by the stator windings and provided to the main load passes through the first converter. A second converter is electrically coupled to the rotor windings of the generator rotor, wherein an AC frequency of the generated AC electrical power is at least partially determined by setting or controlling currents in the rotor windings of the generator rotor by the second converter.