Johannes H. J. Potgieter

Torque and Voltage Quality in Design Optimization of Low-Cost Non-Overlap Single Layer Winding Permanent Magnet Wind Generator

The main focus of this paper is cost-effective techniques to reduce the cogging torque in permanent magnet (PM) wind generators. However, there are also certain limits with which other machine design aspects need to comply. These aspects include ease of manufacturing, mass, load torque ripple, and voltage quality. In this paper, a low-cost single layer PM wind generator with an irregular, parallel slotted stator is analyzed. The sensitivity of average torque and cogging torque to machine dimension variations is investigated, as well as the effects imposed upon the load torque ripple and the voltage quality. Methods are proposed whereby regions of low cogging torque can be identified more quickly in the design optimization. Furthermore, an interesting observation is made regarding the effects imposed upon the cogging torque by varying the yoke heights. Finite element calculated results are validated by practical measurements on a 15-kW PM wind generator.

Design of New Concept Direct Grid-Connected Slip-Synchronous Permanent-Magnet Wind Generator

This paper deals with the modeling, the design, and the construction of a new concept slip-synchronous permanent-magnet (PM) wind generator for direct-drive direct grid connection. This generator is a variation of the conventional PM induction generator concept as proposed and analyzed in literature. The use of nonoverlap windings is proposed for the first time for this type of generator. Combined analytical and finite-element calculation and design-optimization methods are developed and used in the design of the generator. Load torque ripple and no-load cogging torque are identified as very important design parameters and are minimized to an absolute minimum in the design optimization. The modeling and the design are verified with measurements on a 15-kW prototype wind generator system.

Design of new concept permanent magnet induction wind generator

The construction and design of a new concept permanent magnet induction wind generator for direct grid-connection is proposed and evaluated in this paper. The use of non-overlap windings in this type of generator is proposed for the first time and analysed. Combined analytical and finite element calculation and design-optimisation methods are developed and used in the design of the generator. The cogging ripple torque is very important and is minimised to an absolute minimum in the design optimisation. An overall efficiency of higher than 92 % over a wide load range is obtained of a 15 kW permanent magnet induction wind generator.

Grid-connected VSC-HVDC wind farm system and control using permanent magnet induction generators

In this paper the use of the permanent magnet induction generator (PMIG) as a direct drive, direct online solution for wind energy conversion is considered. A wind farm system with several PMIGs connected to a single voltage source converter (VSC) is proposed. This VSC forms part of a utility grid-connected HVDC transmission system. A PMIG model and control strategies for the VSCs are derived. A 3 MW wind farm consisting of ten 300 kW PMIGs are simulated to demonstrate the dynamic operation of the system.

Calculation Methods and Effects of End-Winding Inductance and Permanent-Magnet End Flux on Performance Prediction of Nonoverlap Winding Permanent-Magnet Machines

Due to the short end windings of nonoverlap winding permanent-magnet (PM) machines, the end-winding inductance component is generally ignored in the design. In most cases, the end-flux fringing effects in PMs are also not taken into account. It is shown in this paper that these end effects have a significant influence on the performance parameters of the machine. In this paper, several nonoverlap winding PM machines are considered with respect to the effects of end-winding inductance and PM end-flux fringing. A number of calculation methods for the per-phase end-winding inductance of the machines are compared. A new simple analytical calculation method is proposed, which is shown to give a relatively good prediction of the end-winding inductance compared with 3-D finite-element (FE) results. It is proposed in this paper that the PM strength should be reduced by a certain fringing factor to take the end-flux fringing effects into account in the 2-D FE analysis. Practical measurements are also presented to validate the FE calculations and to give an indication on the effects that are caused by the end-winding inductance and the PM end-flux fringing.

Modelling and dynamic performance of a direct-drive direct-grid slip permanent magnet wind generator

In this paper a transfer function model is developed to evaluate the dynamic performance of the direct-drive direct-grid connected slip permanent magnet wind generator system. The modelling of the generator is done in the dq reference frame fixed to the PM-rotor, for both the grid frequency and slip-frequency generator components. The transient response of a single, 15 kW grid-connected system to changes in turbine torque and grid voltage and frequency is evaluated. It is shown that the generator is very stable under transient turbine-torque conditions and that it acts as a filter to prevent voltage flickering. The dynamic performance is confirmed by laboratory measurements on a 15 kW direct drive slip permanent magnet generator.

Cogging torque sensitivity in design optimisation of low cost non-overlap winding PM wind generator

Low cost and low cogging torque are the most important aspects in the design of direct drive PM wind generators. In this paper a low cost PM wind generator with an irregular, parallel slotted stator is analysed with respect to cogging torque. The sensitivity of average torque and cogging torque to machine dimension variations are investigated. From this a method is proposed whereby regions of low cogging torque can be identified more quickly in the design optimisation. Finite element analysis is used to determine the cogging torque. Calculated results are validated by practical measurements on a 15 kW PM wind generator.

Optimum Design and Comparison of Slip Permanent-Magnet Couplings With Wind Energy as Case Study Application

With eddy-current couplings proposed for and applied in several industrial applications, it is essential that these types of electrical machines be more thoroughly evaluated. In this paper, the feasibility of replacing the classical eddy-current coupling topology with a toothed slip permanent magnet coupling (PMC) is investigated. The case study application in this paper for the slip PMC is for a new type of wind generator concept known as a slip synchronous permanent magnet generator. Several different slip PMC technologies are evaluated, and a number of interesting novel concepts are introduced. These different topologies are optimized by means of finite element (FE) analysis for minimum active mass. The FE results are verified with practical measurements on several different prototypes.

Design specifications and optimisation of a directly grid-connected PM wind generator

This paper forms part of a broader study on the design and implementation of a slip-synchronous permanent magnet wind generator. This is a gearless, direct-drive generator connected directly to the utility grid without a power electronic converter. The system consists of two integrated generating units, a directly turbine connected slip permanent magnet generator and a conventional grid-connected permanent magnet synchronous generator. The focus of this study is to define the exact design requirements of the directly grid connected synchronous generator unit from the relevant grid code specifications, and to find the optimum design subject to these requirements. Due to the direct grid connection there are clear differences in the design requirements of this machine and those of conventional PM wind generators connected to the grid via a converter. Different generator topologies are evaluated with regard to ease of manufacturing, active mass, PM content and suitability for direct grid connection. Simulation results are presented and measured results are given for an existing directly grid-connected PM generator to confirm the FE-calculations.

Optimum design and technology evaluation of slip permanent magnet generators for wind energy applications

Recently a new type of wind generator concept known as a slip-synchronous permanent magnet generator was proposed. This is a gearless direct-drive generator which also connects directly to the grid, thus omitting the need for a power electronic converter. This generator consists of two machine units, a directly grid connected generator operating at synchronous speed and a directly turbine connected short-circuited generator unit. With the theory of designing the grid-connected permanent magnet generator unit well known, the focus in this study is on the identification and finite element design of the optimum turbine connected generator unit. Several different slip permanent magnet generator technologies are evaluated and a number of interesting novel concepts are introduced. These different generator units are optimised by means of finite element analysis for minimum mass, and very good results are obtained. The finite element results are verified by means of practical measurements.