INCREASING POWER OF WIND TURBINE PERMANENT MAGNET SYNCHRONOUS GENERATORS BY UTILISING THERMAL DESIGN MARGINS

Abstract

Wind generation plays a pivotal role in facilitating our move towards net-zero ambition and carbon-free electrical power generation. The design and development of high power wind turbine (WT) generators have been continuously increasing over the last 50 years and continue to grow, with the current state-of-the-art WTs rated at up to 15 MW output power. In this thesis, an alternative, lower-cost possibility for increasing the amount of generated wind power is presented that explores the prospect for a more intelligent utilisation of already installed wind capacity. Existing, in-service, WT generators have the potential to increase their electrical output power to higher levels than stipulated by their pre-installation design rating, capturing more of the energy attainable in the wind stream, without replacing major key components. This could facilitate the increase in in-service WT capacity, enabling both the increased long term energy yield and the usage of additional capacity for short term grid support. Exceeding the stated nominal ratings of the generator, however, needs further research to understand the possibilities and requirements in this context. The utilisation of the generator design margins is a key factor that needs to be researched to this end, along with appropriate bespoke control schemes able to extend the operational envelope in a fully controllable manner which does not detrimentally affect the asset integrity. This thesis proposes a new enhanced power recovery through controlled overload (EPRO) scheme for WT permanent magnet (PM) generators. The enhanced power recovery through controlled overload is implemented by integrating the WT pitch angle controller in a specific manner with a bespoke PM generator’s field weakening controller to enable a controlled overspeed/overload operation. The proposed scheme maintains the generator voltage at the rated condition while increasing the generator current above the nominal design rating by utilising its thermal rating margins. To allow an improved understanding of the existing thermal conditions, the experimental work employs advanced fibre optic sensing, for monitoring in-situ the critical generator winding hot spots when the proposed control algorithm is in place. The resulting scheme increases electrical output power and hence yields extra energy. A novel WT generator coupled electromagnetic and thermal model is developed in Matlab/Simulink and MotorCAD. The co-simulation is performed using an ActiveX interface programmed in Matlab. The coupled model represents the electromagnetic and thermal variables under both fixed wind speed and realistic field-measured wind speed profiles in nominal and overload conditions, covering the maximum power point tracking 14 (MPPT) and constant power regions. The development of the enhanced power recovery through controlled overload scheme is tested on a 1.1 kW permanent magnet synchronous generator (PMSG) in simulation, and then experimentally validated on a 5.5 kW PMSG WT emulator test rig, with different field-measured variable wind speed profiles applied to the emulator. Two distinct research contributions of the enhanced power recovery through controlled overload scheme are separately evaluated: the first aimed at facilitating long-term harvesting of additional output power through controlled thermal overload and the second focused on facilitating grid support through rapid short-term overload. The simulation and experimental results show good agreement and indicate that the proposed scheme has the ability to allow increased electrical output power in a controlled fashion, at a cost of increased general thermal stress and the need for a higher inverter current rating. The scheme is demonstrated to have the ability to manage winding hotspots to a level where these do not exceed set critical thresholds. The results of long-term enhanced power recovery through controlled overload showed a significant increase in WT PMSG energy yields of up to ≈20% for the examined test machine and the field-measured wind speed profiles used in this thesis. The short-term enhanced power recovery through controlled overload results demonstrated an active power boost of up to ≈40% of the pre-defined design rating on the examined test system. This can be exploited to contribute to the power system stability when needed as a primary and secondary ancillary frequency support service in line with the current national grid ESO standards.

Date of Award	16 Oct 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Sinisa Durovic (Main Supervisor) & Judith Apsley (Co Supervisor)