By Asma Jlassi |
26/05/2022
Permanent Magnet Wind Turbine Generators
Permanent magnet synchronous generators are the ideal technology for low-speed primary movers applications such as wind turbines and micro-hydro-turbines. They are usually used in small-scale wind turbines as well as in large MW applications, up to 7-10 MW. They are characterized by high efficiency, high power density, and robust rotor structure compared to induction generators and switched reluctance machines.
A typical wind turbine [1]
Direct-drive Wind Turbine Generator Type
Most wind turbine drive trains currently use generators that are connected to gearboxes. The latter accelerates the rotation from the relatively slow speed of the turbine’s blades to the high speeds needed to generate electricity using a fixed-speed induction generator. Considering its many moving parts, the gearbox is one of the highest-maintenance components of a wind turbine. Direct- drive generator, is an alternative solution to generate electricity at much slower speed with fewer moving parts and reduced transmission losses; thus allowing flexible control and quicker response to wind fluctuations and load variations for variable speed wind turbines.
A 120 slots, 116 poles surface-mounted PMSM for wind turbine
Electric Machine Solution Package
The design of direct-drive generators is a challenging endeavor, especially for high Megawatt applications, where their size grows rapidly larger and heavier due to high torque requirements. To meet the design challenges of such machines and study the phenomena related to high-torque and low-speed generators, such as electromagnetic, thermal, mechanical, losses, and concentrated forces stress performances, a comprehensive and accurate Solution for electric machines is required. EMWorks motor simulators EMS, EMWorks2D, and MotorWizard are used to perform both 2D and 3D analyses of the wind turbine generator. The on-load analysis results of the wind turbine generator modeling are shown below.
For a fully resistive load, the magnetic flux and current density distributions at the base speed of 51.7 rpm are presented in the animation plots below.
Magnetic flux density plot
Current density plot
For the same speed, the generator produces a high electromagnetic torque which achieves a maximum value around 4800 N.m.
Electromagnetic torque for a generator at base speed (51.7 rpm)
EMWorks2D simulator computes and plots all losses within the entire generator. The following figures illustrate the plots of core and winding losses versus time steps. Evidently, high losses resulted in the stator region generate a high temperature in the steel.
Stator and rotor core loss versus time at the base speed (51.7 rpm) of generator
Winding loss result versus time of generator at base speed (51.7 rpm)
Steady-state stator temperature distribution for phase A coils
Permanent magnet synchronous generators offer unparalleled efficiency and reliability for wind turbine applications, ensuring optimal performance even at low speeds. By eliminating the need for gearboxes, direct-drive generators reduce maintenance and transmission losses, while providing flexible control over variable wind conditions. EMWorks' comprehensive electric machine solution enables designers to accurately analyze and optimize generator performance, addressing challenges related to torque, thermal management, and mechanical stress for efficient renewable energy generation.