This report presents a survey on generator concepts and power electronic concepts for wind turbines. The report is aimed as a tool for decision-makers and development people with respect to wind turbine manufactures, utilities, and independent system operators as well as manufactures of generators and power electronics. The survey is focused on the electric development of wind turbines and it yields an overview on: State of the art on generators and power electronics; future concepts and technologies within generators and power electronics; market needs in the shape of requirements to the grid connection, and; consistent system solutions, plus an evaluation of these seen in the prospect of market needs. This survey on of generator and power electronic concepts was carried out in co-operation between Aalborg University and Risoe National Laboratory in the scope of the research programme Electric Design and Control. (au)

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Conceptual survey of Generators and Power Electronics for Wind Turbines

In this paper a description and operating principles of a consequent-pole permanent-magnet machine are presented. In addition, a sizing analysis, finite-element analysis, and experimental results for a prototype machine are addressed. Due to its particular configuration, this machine allows for a wide range of control of the air-gap flux with minimum field ampere-turn requirements and without brushes or slip rings. Two components of the field flux are produced. One, which is almost constant, is produced by the permanent magnet located on the rotor surface. The other, which is variable, is produced by a field winding positioned circumferentially in the center of the stator. These two flux components converge in the air gap. The excitation level of the machine is manipulated by controlling the DC field current. Three-dimensional finite-element analysis and experimental results demonstrate that it is possible to vary the flux over a wide range to keep the terminal voltage constant as the speed increases. A 3 kW 1000-3000 r/min eight-pole and 32 VAC generator using this configuration is tested to verify the flux control capability of this structure.

Consequent-pole permanent-magnet machine with extended field-weakening capability

This paper discusses how the switched reluctance generator (SRG) converts energy as directed by a controller. Beginning with a review of the electromechanics of generation, the paper identifies the implications of the energy conversion process on how the SRG is controlled. The structure of the SRG controller for speed-control and power-control applications is discussed. Practical implementation details for commutation of the SRG are reviewed. Concepts are illustrated with a 6-kW SRG designed to serve as a starter/alternator in automotive applications.

Switched reluctance generators and their control

Switched reluctance machines (SRM) offer attractive attributes for automotive applications. These include robustness to harsh operational conditions, rugged structure, fault resilient performance, and a wide range of speed. The main debate over the adequacy of switched reluctance drives in automotive applications has often focused on efficiency and position sensorless control over the entire speed range, adaptation of control algorithms in the presence of parameter variations, and high levels of acoustic noise and vibration. The present paper demonstrates three key technologies developed over the past few years that have resulted in tangible improvements in the performance of SRM/generators (SRM/G) as related to the above areas of interest. This paper intends to illustrate the new possibilities and remaining challenges in applications of SRM in automotive industry. The proposed technologies have been validated by simulation and experimental results

Making the case for applications of switched reluctance motor technology in automotive products

Switched reluctance machines (SRMs) are considered as serious candidates for starter/alternator (S/A) systems in more electric cars. Robust performance in the presence of high temperature, safe operation, offering high efficiency, and a very long constant power region, along with a rugged structure contribute to their suitability for this high impact application. To enhance these qualities, we have developed key technologies including sensorless operation over the entire speed range and closed-loop torque and speed regulation. The present paper offers an in-depth analysis of the drive dynamics during motoring and generating modes of operation. These findings will be used to explain our control strategies in the context of the S/A application. Experimental and simulation results are also demonstrated to validate the practicality of our claims.

A switched reluctance machine-based starter/alternator for more electric cars

This paper presents a new approach for controlling a switched-reluctance generator (SRG). The control objective is to produce the required power using the excitation that produces the highest efficiency. The SRG considered here operates above base speed. The turn-on and the conduction angles are the only control parameters that can be used to optimize the power conversion. The conventional control method that advances the turn-on angle as the speed increases is not enough to produce optimum performance. The turn-on and the conduction angles together are the key elements for optimal excitation. Optimization of the excitation angles is performed using a machine model based on finite element analysis. For all of the operating speeds, all possible turn-on and conduction angles are simulated to get the desired power output. The excitation angles using the minimum RMS phase currents are chosen among those that give the desired output power. The control strategy is experimentally tested using a 6 kW 5000 rpm SRG. The control algorithm is able to provide required power with very good generator efficiency.

http://ieeexplore.ieee.org/iel5/6663/17861/00826128.pdf

Optimal excitation of a high speed switched reluctance generator

This paper presents an approach for adaptive control of the surface mounted permanent magnet synchronous motor (PMSM) over its entire speed range. This requires coordination of direct and quadrature axis currents i/sub d/, i/sub q/. Direct model reference adaptive control is responsible for the control of quadrature axis current. Direct axis current is controlled by an adaptive flux weakening approach at elevated speeds where the inverter is in voltage saturation. The developed adaptive flux weakening scheme is able to determine the right amount of i/sub d/ at any operating conditions without the the knowledge of load torque, motor or inverter parameters.

Adaptive flux weakening control of permanent magnet synchronous motors

Important global efforts are underway toward lowering the cost of electric machines for electric and hybrid vehicles by reducing or eliminating the use of rare-earth materials which have been experiencing significant price increases and volatility. Non-permanent-magnet (non-PM) electric machines are a potential solution and are increasingly investigated by researchers worldwide. This paper presents a DC-biased reluctance machine, which is structurally similar to a conventional switched reluctance machine. This type of machine has a DC field winding and an AC three-phase armature winding. It uses a conventional three phase inverter for the armature and an additional auxiliary DC/DC converter for the field winding. This reluctance machine is designed to achieve hybrid vehicle traction requirements of 55 kW peak at 2800 $\rm{r/min}$ and 30 kW continuous over a speed range going from 2800 to 14 000 $\rm{r/min}$ .

Sinusoidal Reluctance Machine With DC Winding: An Attractive Non-Permanent-Magnet Option

Recent advances in power electronics have significantly promoted the development of more electric aircraft (MEA). This paper presents a review of the power electronic applications in MEA that were presented in the literature in the past decade, ranging from the component level such as power semiconductor devices and solid-state circuit breakers, to various power converter topologies, high-voltage AC (HVAC) and high-voltage DC (HVDC) power system architectures for MEA. Opportunities and challenges of using emerging power semiconductor devices, power converter topologies and various system architectures are discussed.

Recent Advances of Power Electronics Applications in More Electric Aircrafts

Important global efforts are underway toward lowering the cost of electric machines for electric and hybrid vehicles by reducing or eliminating the use of rare earth materials which have been experiencing significant price increases and volatility. Non-permanent magnet electric machines are a potential solution and are increasingly investigated by researchers worldwide. This paper presents a DC biased reluctance machine which is structurally similar to a conventional switched reluctance machine. This type of machine has a DC field winding and an AC three phase armature winding. It uses a conventional three phase inverter for the armature and an additional auxiliary DC/DC converter for the field winding. This reluctance machine is designed to achieve hybrid vehicle traction requirements of 55kW peak at 2800 rpm and 30kW continuous over a speed range going from 2800 rpm to 14000 rpm.

David Allan Torrey

Papers

Optimal excitation of a high speed switched reluctance generator

Adaptive flux weakening control of permanent magnet synchronous motors

Sinusoidal Reluctance Machine With DC Winding: An Attractive Non-Permanent-Magnet Option

Recent Advances of Power Electronics Applications in More Electric Aircrafts

Sinusoidal reluctance machine with DC winding: An attractive non-permanent magnet option