Ghanshyam Shrestha

Structural Flexibility: A Solution for Weight Reduction of Large Direct-Drive Wind-Turbine Generators

This paper looks into a new concept for reducing the structural weight of large direct-drive generators used in wind turbines. The concept uses magnetic bearings to position the rotor of the generator. The use of magnetic bearings allows structural flexibility in the generator. The weight of the rotor using the new concept is compared to the weight of a rotor designed with conventional methods. For a 5-MW generator, the result is that the structural weight of the rotor reduces by 45%.

Comparative design of radial and transverse flux PM generators for direct-drive wind turbines

The aim of this paper is to assess the radial flux permanent magnet (RFPM) and transverse flux permanent magnet (TFPM) generators for large direct-drive wind turbines. For the assessment, the electromagnetic design of RFPM and TFPM generators is done. The analytical design result of a TFPM generator is compared with the experimental result. A RFPM machine concept and four different TFPM machine concepts are designed electromagnetically for 5 MW direct-drive wind turbines. These machines are assessed with criteria such as the cost, the mass, the copper loss, the power/mass ratio, the power/cost ratio, the cost/mass ratio and the mass/torque ratio.

Design of a Lightweight Transverse Flux Permanent Magnet Machine for Direct-Drive Wind Turbines

The aim of this paper is to design a lightweight transverse flux permanent magnet (TFPM) machine for large scale direct-drive wind turbines. The requirements for suitable generator systems for wind turbines are discussed. Analytical modeling of TFPM machines is discussed by considering the machine parameters and the magnetic circuit. The proposed analytical model is verified by comparing it to results of finite element analysis and experiments. A new lightweight TFPM machine is designed for a 10 MW direct-drive wind turbine and it is compared to the RFPM machine.

Ring-shaped transverse flux PM generator for large direct-drive wind turbines

A ring-shaped transverse flux permanent magnet (TFPM) generator with double-sided axial flux configuration is proposed in this paper. The ring-shaped TFPM generator does not use a shaft and arms to transfer the torque and to support both the rotor and the stator. The active part of the proposed generator consists of multiple-segment structure. This new generator configuration can remarkably reduce the mass, and can make the construction easy in manufacturing and handling. Analytical design model is developed for the TFPM generator. The analytical model is verified by the experimental analysis of the downscaled generator. The design results of 5 MW ring-shaped TFPM generators are compared with two different generators, namely a conventional radial flux PM generator and a single-sided air gap TFPM generator.

Scaling laws for direct drive generators in wind turbines

Upscaling of wind turbines affects the individual components in the wind turbine. In order to assess the effects of upscaling on the direct drive generator used in wind turbines, the weight and size of the generator sub-components should be estimated. A method to estimate the weight is either by designing the generator analytically, or by using finite element method or by building the machine. These methods can be time consuming and complicated. The objective of this paper is to find the scaling laws for the weight of both electromagnetic and structural material used in direct drive generator specifically for wind turbine application. The scaling laws can be used to quickly estimate the weight of direct drive machine of any required size. The scaling laws for electromagnetic material and structural material are derived for various power levels and aspect ratios. Then the reference turbine Zephyros (now Harakosan) Z72 is used to find the generator weight of up to 20MW machine and different aspect ratio.

Promising Direct-Drive Generator System for Large Wind Turbines

Abstract The aim of this paper is to review direct-drive generators and to propose promising direct-drive generator concepts for large wind turbines. Different large direct-drive generators are compared based on the mass and the torque rating. Features of different PM machines are investigated to find a suitable machine type for direct-drive. Some promising solutions are proposed for both electromagnetic and mechanical design.

A new concept for weight reduction of large direct drive machines

This paper looks into a new concept for reducing the structural weight of large direct drive generators used in wind turbines. The concept uses magnetic bearings to position the rotor of the machine. The weight of the rotor using the new concept is compared to a rotor designed with conventional methods. The comparison of a 5 MW generator rotor structural material shows about 45% reduction of weight of the rotor.

Cell voltage balancing of a series-connected multiphase BLDC motor drive

Brushless DC operation with a trapezoidal waveform of permanent magnet machines provides a simple, robust and cost effective method to drive the motor. In this paper, the proven technology is applied to a motor drive system with series-connected multiphase windings and converter cells. The proposed topology provides a modular approach and enables MOSFET, which is more cost-effective and efficient, to replace the IGBT which is typically used in 3-phase motor drives. Cell voltage balancing in this topology is also studied and the result shows that the cell voltages have a potential to self balance. A 2 kW prototype has been built and tested to validate the conclusion.