Axial-flux permanent-magnet air-cored generator for small-scale windturbines

The design and development of an axial-flux permanent-magnet air-cored generator for use as a direct drive generator with small-scale wind and water turbines is described. The generator is designed for simplicity and ease of manufacture and consists of two rotor discs each with permanent magnets located around its periphery. The stator is made of plastic and has a number of bobbin-wound armature coils located around its periphery. A three-phase prototype generator has been designed and built with 16 magnets per rotor disc, 12 armature coils (four per phase) and an overall diameter of 495 mm. The generator produces 1000 W at 300 rpm or 2000 W at 500 rpm with an electrical efficiency substantially greater than 90%. The generator performs as predicted by the design process

Equivalent circuit analysis of solid-rotor induction machines with reference to turbocharger accelerator applications

Theoretical, numerical and experimental studies are described that have been carried out to develop a solid-rotor induction machine design for a particularly demanding application as an accelerator drive for a diesel engine turbocharger. In this application the turbo-motor will be required to operate at speeds of up to 130 000 rpm and in temperatures that can exceed 200°C. The results show that the equivalent circuit gives predictions that are of sufficient precision for design purposes and provides a useful design tool. It is shown that the use of a solid rotor affects the value of the stator leakage reactance and influences the motor performance through this effect as well as by presenting a high rotor resistance

Lightweight ironless-stator PM generators for direct-drive wind turbines

A permanent-magnet electrical machine that employs lightweight spoked structures for both rotor and stator is described. The stator is ironless so that there is no direct magnetic attraction between rotor and stator. The lightweight structures are sufficient to carry the small forces due to the interaction of the permanent magnet field with the stator winding current. Despite the absence of stator iron and a large airgap, rare-earth magnets are able to create a working flux density of about 0.25 T at the winding. This is sufficient for an effective generator design because the lightweight structures offer the opportunity to build generators of unprecedented diameter. The outcome is a generator that has a mass typically 20–30% of equivalent designs based on iron-cored magnetic circuits, and with efficiency greater than 90%

Polynomial Modelling of Electromechanical Devices: An Efficient alternative to Look-Up Tables

A technique is described for taking results from complex numerical modelling procedures (such as a finite element model, a dynamic simulation or from experimental data) to create a simple yet accurate mathematical description of a device based on a modest amount of input data. The analytic model is then available for use within design or control programs that need to evaluate many examples quickly. The technique may be applied to a wide range of devices or systems. Examples are given for three applications

Coordinated control of an HVDC link and doubly fed induction generators in a large offshore wind farm

Doubly fed induction generators (DFIGs) are an economic variable-speed solution for large wind turbines while high-voltage dc (HVdc) transmission is being considered for the grid connection of some offshore wind farms. This paper analyzes the need for coordinating the control of the DFIGs and the HVdc link so that the two topologies can work together, giving system designers and operators a choice that may be useful in some applications. It is desired that individual generators be controlled for power tracking in a way similar to that used when they are connected directly to an ac grid, although a grid voltage reference for the DFIG control is no longer available as an independent source in this case. The study shows that machine control should explicitly maintain the flux level, which then allows the HVdc link to regulate the local system frequency and, indirectly, voltage amplitude. Interactions between DFIGs and the HVdc link are investigated and simulations performed to verify the proposed control strategy