Controller Strategy for Open-Winding Brushless Doubly-Fed Wind Power Generator with Common Mode Voltage Elimination

This paper presents the theoretical derivation and implementation of a novel direct power control for open-winding brushless doubly-fed reluctance generator (OW-BDFRG). As one of the promising brushless candidates, the OW-BDFRG is characterized with two stator windings fed by a dual controllable two-level three-phase converters through a common DC bus with common mode voltage elimination. The parameter-free control strategy is designed to obtain maximum power point tracking with variable speed constant frequency (VSCF) for wind energy conversion systems (WECSs). Compared to the traditional three-level converter systems, the DC bus voltage, AC-side voltage and capacity ratings of the proposed converter system are notably high while the reliability, redundancy and fault tolerance are significantly improved. Effectiveness, correctness and robustness of the proposed control strategy and the common mode voltage elimination scheme are evaluated and confirmed through simulation and experimental tests on a 42 kW generator prototype typical for VSCF-WECS

Optimization of AVR in Micro-hydro Power Plant Using Differential Evolution (DE) Method

Micro-hydro Power Plant had three primary components: water (as the energy resource), turbine, and generator. Water that flew in a specific capacity was channeled from a certain height to the installation house (turbine house). In the powerhouse, the water installation pounded the turbine that made the turbine received direct energy from the water and turn it into mechanical energy and caused the turbine shaft to spin. Changes in the loading could cause fluctuation in the system’s frequency and voltage. This problem could damage electrical equipment. Therefore, the Automatic Voltage Regulator (AVR) was used to control and stabilize the voltage. This research used PID controller to obtain the optimized control parameter in the Micro-hydro Power Plant. This research compared the simulations of without control method, with PID-ZN control method, and with PID-DE method to obtain the best control method. The comparison simulations showed that the best response in the micro-hydro plant and the AVR system was from the PID-DE controller. These results might be a reference for future research with other methods that might generate better results.  

Optimised Power Error Comparison Strategy for Direct Power Control of the Open-winding Brushless Doubly-Fed Wind Power Generator

This paper presents the conceptual analysis and comparative simulation and experimental evaluation of a novel power error comparison direct power control (PEC-DPC) strategy of the open-winding brushless doubly-fed reluctance generator (OW-BDFRG) for wind energy conversion systems (WECSs). As one of the promising candidates for limited speed range application of pump-alike and wind turbine with partially-rated converter. The emerging OW-BDFRG employed for the proposed PEC-DPC is fed via dual low-cost two-level converters, while the DPC concept is derived from the fundamental dynamic analyses between the calculated and controllable electrical power and flux of the BDFRG with two stators measurable voltage and current. Compared to the traditional two-level and three-level converter systems, the OW-BDFRG requires lower rated capacity of power devices and switching frequency converter, though have more flexible switching mode, higher reliability, redundancy and fault tolerance capability. The performance correctness and effectiveness of the proposed DPC strategy with the selected and optimised switching vector scheme are evaluated and confirmed through computer simulation studies and experimental measurements on a 25 kW generator test rig

Comparison of doubly-fed induction generator and brushless doubly-fed reluctance generator for wind energy applications

Phd ThesisThe Doubly-fed Induction Generator (DFIG) is the dominant technology for variable-speed wind power generation due in part to its cost-effective partially-rated power converter. However, the maintenance requirements and potential failure of brushes and slip rings is a significant disadvantage of DFIG. This has led to increased interest in brushless doubly-fed generators. In this thesis a Brushless Doubly-Fed Reluctance Generator (BDFRG) is compared with DFIG from a control performance point of view. To compare the performance of the two generators a flexible 7.5kW test facility has been constructed. Initially, a classical cascade vector controller is applied to both generators. This controller is based on the stator voltage field orientation method with an inner rotor (secondary stator) current control loop and an outer active and reactive power control loop. The dynamic and steady state performance of two generators are examined experimentally. The results confirm that the BDFRG has a slower dynamic response when compared to the DFIG due to the larger and variable inductance. Finally a sensorless Direct Power Control (DPC) scheme is applied to both the DFIG and BDFRG. The performance of this scheme is demonstrated with both simulation and experimental results.Engineering and Physical Sciences Research Council (EPSRC) and Overseas Researcher Scholarship (ORS

Data-driven model-based approaches to condition monitoring and improving power output of wind turbines

The development of the wind farm has grown dramatically in worldwide over the past 20 years. In order to satisfy the reliability requirement of the power grid, the wind farm should generate sufficient active power to make the frequency stable. Consequently, many methods have been proposed to achieve optimizing wind farm active power dispatch strategy. In previous research, it assumed that each wind turbine has the same health condition in the wind farm, hence the power dispatch for healthy and sub-healthy wind turbines are treated equally. It will accelerate the sub-healthy wind turbines damage, which may leads to decrease generating efficiency and increases operating cost of the wind farm. Thus, a novel wind farm active power dispatch strategy considering the health condition of wind turbines and wind turbine health condition estimation method are the proposed. A modelbased CM approach for wind turbines based on the extreme learning machine (ELM) algorithm and analytic hierarchy process (AHP) are used to estimate health condition of the wind turbine. Essentially, the aim of the proposed method is to make the healthy wind turbines generate power as much as possible and reduce fatigue loads on the sub-healthy wind turbines. Compared with previous methods, the proposed methods is able to dramatically reduce the fatigue loads on subhealthy wind turbines under the condition of satisfying network operator active power demand and maximize the operation efficiency of those healthy turbines. Subsequently, shunt active power filters (SAPFs) are used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads, which is further to increase the reliability of the wind turbine system

Brushless doubly-fed reluctance machine modeling, desing and optimization

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2015.Esta tese aborda a modelagem, o projeto e a otimização, com validação experimental, de máquinas de relutância duplamente alimentadas sem escovas (BDFRM) para sistemas de geração de energia eólica. O objetivo principal dela é de contribuir para o domínio de técnicas de projeto otimizado para a BDFRM através da proposição de uma metodologia baseada em diferentes níveis de modelagem e em otimização. Discute-se como técnicas de otimização podem ser aplicadas em todas as fases de desenvolvimento com objetivos distintos. Especificamente, a metodologia proposta se concentra na definição e na solução iterativa de problemas de otimização com restrições nas saídas utilizando um algoritmo determinístico acoplado a modelos semi-analíticos de diferentes níveis. Como conclusão geral, pode-se afirmar que a BDFRM é potencialmente uma boa candidata para ser utilizada em sistemas de geração de energia eólica. Contudo, aspectos técnicos e econômicos sobre essa escolha devem ainda ser avaliados, comparando-se as diferentes topologias existentes sob o mesmo enfoque metodológico.Abstract : This thesis addresses the modeling, design and optimization with experimental validation of the Brushless Doubly-Fed Reluctance Machine (BDFRM) for wind power systems. Its main goal is to contribute on mastering the BDFRM optimized design by proposing a methodological approach based on different modeling levels and on optimization. More precisely, it draws its attention on setting the optimization problem and on the iterative solution of a constrained inputs/outputs problem by using a deterministic algorithm. As a general conclusion, the results show that the BDFRM is potentially a good candidate to be used in wind power systems. However, the technical and economic aspects on this choice must be still assessed, analyzing and comparing the overall system solution of distinct topologies within the same framework

Stray magnetic field based health monitoring of electrical machines

PhD ThesisElectrical machines are widely used in industrial and transportation applications which are essential to industrial processes. However, the lack of reliability and unpredictable life cycles of these machines still present opportunities and challenges for condition monitoring research. The breakdown of an electrical machine leads to expensive repairs and high losses due to downtime. The motivation of this research is to improve the reliability of electrical machines and to classify different kinds of failures via non-intrusive methods for condition-based maintenance and early warning of failure. Major potential failure types in electrical machines are winding and mechanical failures, which are caused by dynamic load state, component ageing and harsh working environments. To monitor and characterise these abnormal situations in the early stages, this thesis proposes stray magnetic field-based condition monitoring allowing fault diagnosis with the help of finite element models and advanced signal processing technology. By investigating the interaction between stray flux variations and machine failure, different kinds of faults can be classified and distinguished via numerical and experimental studies. A non-intrusive stray flux monitoring system has been developed and can provide both static and transient stray flux information and imaging. The designed monitoring system is based on a giant magnetoresistance (GMR) sensor used to capture low stray flux fields outside the electrical machine’s frame. Compared with other monitoring systems, its small size, low cost, non-inventive and ease of setting up make the designed system more attractive for in many long-term monitoring applications. Additionally, integration with the wireless sensor network (WSN) means that the latter’s unique characteristics makes the proposed system suitable for electrical machine monitoring in industrial applications replacing existing expensive wired systems. The proposed system can achieve real-time data collection and on-line monitoring with the help of spectrogram and independent component analysis. Three cases studies are conducted to validate the proposed system with different failures and loading states, using load fatigue, winding short-circuit failure and mechanical testing. In these case studies, electrical and mechanical failures and dynamic loads are investigated, collecting stray flux information with different kinds and sizes of electrical machines using both simulation and experimental approaches. Stray flux information is collected for different situations of winding failure, unbalanced load and bearing failures. Comprehensive transient feature extraction using spectrogram is implemented with respect to multiple failures and load variations. Spectrograms of stray flux can provide time-frequency information allowing the discrimination of different failures and load states. Different faults can be distinguished through independent component analysis of stray flux data. Compared with traditional and current detection strategies, stray flux-based monitoring can not only provide failure indicator and better resolution but also gives location information. Additionally, by applying different feature extraction methods, different failure types can be separated based on stray flux information, which is likely to be difficult to achieve using traditional monitoring approaches. However, stray flux monitoring systems suffer from issue of noise and instability, and more case studies and investigations are needed for further refinement

A Doubly-Fed Induction Generator (DFIG)-Based Wind-Power System with Integrated Energy Storage for Remote Electrification

Electrification of off-grid remote communities is commonly accomplished through diesel generators. The method may even be employed in cases where there exists an un­ reliable connection to the power grid. Regardless, the method is environmentally-hostile, typically costly, and likely risky. Therefore, to mitigate the reliance on diesel fuel, uti­ lization of renewable energy resources has been considered in recent years. This thesis investigates the feasibility of and technical considerations involved in the employment of a specific class of variable-speed wind-power systems, integrated with battery energy stor­ age, for remote electrification applications. The wind-power system under consideration is based on the doubly-fed induction gen­ erator (DFIG) technology, which features a number of characteristics that render it at­ tractive for the incorporation of battery energy storage. This thesis identifies the control strategy, different control sub-functions, and the controllers structures/parametes required to accommodate the battery energy storage. The developed control strategy enables the operation of the wind-power/storage system in the off-grid (islanded) mode of operation, as well as the grid-connected mode of operation. Under the developed control strategy, the wind-power/storage system can operate in parallel with constant-speed wind-power units, passive loads, and induction motor loads. The effectiveness of the proposed control strategy has been demonstrated through comprehensive simulation studies enabled by the commercial software package PSCAD/EMTDC. In addition to the control aspects, this thesis studies the reliability aspects of the pro­ posed wind-power/storage system, for an example remote electrification system. Thus, a new reliability assessment method has been developed in this thesis, which combines the existing analytical and simulation-based probabilistic approaches. The reliability analysis conducted indicates that the battery energy storage capacity, the wind magnitude and pro­ file, and the load profile impose remarkable impacts on the reliability of the electrification system. It also indicates that a connection to the power grid, however unreliable, signifi­ cantly mitigates the need for a large battery to achieve a given degree of reliability