R. Spee

Performance optimization for doubly-fed wind power generation systems

Significant variation of the resource kinetic energy, in the form of wind speed, results in substantially reduced energy capture in a fixed speed wind turbine. In order to increase the wind energy capture in the turbine, variable speed generation (VSG) strategies have been proposed and implemented. However, that requires an expensive AC/AC power converter which increases the capital investment significantly. Consequently doubly-fed systems have been proposed to reduce the size of the power converter and thereby the associated cost. Additionally, in doubly-fed systems, at a fixed operating point (power and speed), power flow can be regulated between the two winding systems on the machine. This feature can be utilized to essentially minimize losses in the machine associated with the given operating point or achieve other desired performance enhancements. In this paper, a brushless doubly-fed machine (BDFM) is utilized to develop a VSG wind power generator. The VSG controller employs a wind speed estimation based maximum power point tracker (MPPT) and a heuristic model based maximum efficiency point tracker (MEPT) to optimize the power output of the system. The controller has been verified for efficacy on a 1.5 kW laboratory VSG wind generator. The strategy is applicable to all doubly-fed configurations, including conventional wound rotor induction machines, Scherbius cascades, brushless doubly fed machines, and doubly-fed reluctance machines.

Two-axis model development of cage-rotor brushless doubly-fed machines

A two-axis model of a cage-rotor brushless doubly-fed machine (BDFM) which is suitable for machine and BDFM drive system dynamics studies is presented. The technique enables the two-axis model to be derived from a detailed model recently developed for investigation of design aspects of the machine. Unlike the conventional approaches to self-cascaded machines analysis, this method permits analysis of the machine characteristics in both dynamic and steady state conditions, and also facilitates machine and drive system design by directly correlating machine performance with machine structure and parameters. The approach allows the machine parameters to be calculated from machine geometry and developed into the model parameters. >

Novel control strategies for variable-speed doubly fed wind power generation systems

This paper presents a novel control strategy for a brushless doubly fed machine (BDFM) applied to variable-speed wind power generation systems. A 7 kW proof-of-concept laboratory prototype is used to investigate the proposed control algorithm. The paper discusses the use of an adaptive maximum power point tracking (MPPT) strategy to implement an efficiency maximization loop in parallel with the regular maximum tip speed ratio tracker, without the measurement of mechanical quantities. The overall power output of the generation system is increased with a minimal increase in controller cost. A 100 kW case study is included to describe the prospects of the proposed control strategy for a typical wind power generation site on the Oregon coast.

Experimental evaluation of a variable-speed, doubly-fed wind-power generation system

The authors evaluate the potential of a brushless doubly fed generation system for wind power applications. A 1.5 kW proof-of-concept laboratory prototype is used to investigate the feasibility of the proposed variable-speed generation principle. Experimental results show that the prototype system can achieve high efficiency over a range of speeds. The system efficiencies achieved at the power levels considered compare favorably with conventional squirrel cage induction machines. It is experimentally demonstrated that the brushless double fed system achieves variable-speed operation with a power converter of reduced rating. For the prototype under consideration, a 2:1 speed range can be covered with a converter rated at approximately 25% of system capacity. While reactive power control can be realized with the proposed system, the magnitude is limited by the desired low converter rating. The prototype system is also shown to exhibit excellent output current waveforms.<<ETX>>

Voltage sag ride-through for adjustable speed drives with active rectifiers

Adjustable speed drives (ASDs) trip due to voltage sags, interfering with production and incurring financial losses. In this paper, a methodology for incorporating voltage sag ride-through in the design of ASDs with active rectifiers is presented. The magnitude of the voltage sag for which ride-through can be provided is determined by the current rating of the active rectifier and load condition of the ASD but a sag of any duration can be compensated for.

The design and development of an axial flux permanent magnet brushless DC motor for wheel drive in a solar powered vehicle

Fig. 1. The “Desert Rose” on the road. presented here is based on a high-performance solar vehicle, many of the issues addressed are applicable to conventional, battery powered vehicles. The paper presents a review of electric propulsion characteristics and wheeled vehicle physics with an emphasis on the solar application. A weight-power tradeoff forms the basis for the in-wheel drive design which is discussed in detail. Experimental results for a 1-kW machine verify the design concepts introduced.

Dynamic simulation of brushless doubly-fed machines

Dynamic and steady-state models for the simulation of the performance of experimental brushless doubly-fed machines (BDFM) are presented. The dynamic simulation results are obtained using a two-axis representation which has been developed from a detailed machine design model. In turn, it is shown that several forms of steady-state equivalent circuit can be developed from the two-axis model for different specific modes of operation. Test data in dynamic conditions are compared with the predictions given by the two-axis model. It is concluded that these simplified models will provide adequate representation of full performance for control, stability, and scoping studies. >

Sensorless current control for active rectifiers

A novel model-based sensorless input current controller for three phase active rectifiers is presented. The proposed algorithm is based upon a load conductance rectifier controller, which was previously implemented using current sensors. The paper presents analytical studies, simulation results and discusses a simple implementation using a low-cost integrated microcontroller. Experimental verification utilizes a 50 kVA active input/output IGBT converter. Simulation and experimental results for the proposed controller are compared to that of the sensor based version to validate the efficacy of this novel algorithm.

Experimental evaluation of a rotor flux oriented control algorithm for brushless doubly-fed machines

The brushless doubly-fed machine (BDFM) has shown potential for adjustable speed drive applications. Although the BDFM is readily applicable for industrial drives requiring only slow speed response, control methods for higher performance operation need to be explored. With the help of a suitable synchronous reference frame dq model, this paper defines a BDFM synchronous angle and employs an electric torque estimator to establish a rotor flux oriented control algorithm. Experimental results show the effectiveness of the proposed controller.

A new unified approach to power quality management

A new control algorithm for a power converter-based device that is capable of alleviating the problems of harmonic interference and voltage regulation on radial distribution lines is introduced. It comprises a relocatable converter in series with a passive filter and is known as the Power Quality Manager. Simulation results based on an existing 88-kV line are presented. Experimental results are presented, based on a three-phase 200-VA scaled model of the existing 88-kV system. It is a cost-effective and flexible solution to improving power quality.