Split Permanent Magnet Induction Generator for Wind Turbines
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wind energy conversion systems rely on complex and costly gearboxes and power converters, which are mechanically and electrically intensive, and current permanent magnet induction generators (PMIGs) face challenges in construction and stability due to cogging torque at low slip speeds.
Innovation Solution
A split permanent magnet induction generator (S-PMIG) system with two magnetically separated permanent magnet machines, one synchronous and one induction generator, linked by a freely rotating rotor with modular construction, allowing for direct drive and grid connection without gearboxes or converters, utilizing non-overlap windings to minimize cogging torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional wind energy conversion systems use gearboxes and power converters, then they can achieve high speed operation and grid connection, but the system becomes mechanically complex, expensive, and maintenance intensive
Solution Approach 1:
The patent divides the single complex machine into two separate permanent magnet machines: a synchronous generator and an induction generator. Each machine has its own rotor and stator windings, allowing them to operate independently at different speeds. This segmentation eliminates the need for a gearbox while achieving both high-speed and low-speed operation through magnetic coupling between the two machines.
Solution Approach 2:
The patent introduces a freely rotating permanent magnet rotor as an intermediary element that magnetically couples the synchronous generator and induction generator. This intermediary rotor transfers magnetic flux between the two machines without mechanical connection, enabling speed conversion and grid connection without requiring a gearbox or power converter.
2Reliability
If a permanent magnet induction generator uses a freely rotating permanent magnet rotor, then it improves power factor and eliminates magnetizing current requirements, but cogging torque causes stability issues at low slip speeds
Solution Approach 1:
The patent segments the single generator into two separate machines with distinct functions. The synchronous generator handles the power factor correction and operates at synchronous speed, while the induction generator handles the variable speed operation. This segmentation isolates the cogging torque issue to only the induction generator portion, allowing the synchronous generator to maintain stable operation and improve overall system reliability.
Solution Approach 2:
The patent changes the operational parameters by operating the synchronous generator at synchronous speed with fixed frequency, while the induction generator operates at variable slip speeds. This parameter separation allows the synchronous machine to provide stable magnetic flux and power factor correction, compensating for the instability caused by cogging torque in the induction generator at low slip speeds.
3Device complexity
If wind turbines operate at low rotational speeds directly connected to the grid, then gearboxes can be omitted, but induction machines require large magnetizing current which reduces efficiency
Solution Approach 1:
The patent segments the generator system into two parts: the induction generator that operates at low speed without requiring large magnetizing current, and the synchronous generator that provides the necessary magnetic flux at synchronous speed. This segmentation allows the low-speed turbine to connect directly to the grid through the synchronous generator without a gearbox, while the synchronous machine supplies the magnetizing flux efficiently.
Solution Approach 2:
The freely rotating permanent magnet rotor acts as an intermediary that transfers magnetic flux from the synchronous generator to the induction generator. This intermediary magnetic coupling allows the induction generator to operate at low speed without drawing large magnetizing current from the grid, as the synchronous generator provides the necessary magnetizing flux through the shared permanent magnet rotor.
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
The S-PMIG system achieves high efficiency, reduced mass, and stability at low slip speeds, enabling direct grid connection and cost-effective wind energy conversion with improved power factor and reduced maintenance, overcoming construction and stability issues of traditional PMIGs.
Implementation Method 1
a freely rotating rotor housing permanent magnets... the series of magnets on a first rotor portion are configured to excite coils on the stationary stator of the synchronous generator and the series of magnets on a second rotor portion are configured to excite coils on the rotor of the induction generator
Implementation Method 2
The rotating magnetic flux from the stator induces currents in the rotor, which in turn also produces a magnetic field
Data Source
AI summary
The invention relates to an electrical energy conversion system (11) which is particularly suited for use in wind energy conversion systems. The system includes two magnetically separated permanent magnet machines (25, 27) linked by a freely rotating rotor (19) housing permanent magnets (39). The first machine is typically a synchronous generator, and the second an induction generator. The synchronous generator (25) has a stationary stator (21) which is connectable to an electrical system such as an electricity grid, and the induction generator (27) has a rotor (17) which is connectable to a mechanical drive system such as, for example, a wind turbine.