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Doubly fed induction machine (DFIM) has been widely used in variable speed constant frequency electricity generation systems due to its small power converter capacity. Then another machine—brushless doubly fed machine (BDFM)—is widely concerned because of its similar characteristics but better reliability than DFIM. In fact, according to common features of DFIM and BDFM, these two machines can be collectively called doubly fed machine (DFM). Theoretical study on characteristics of these two machines has not formed concise, practical, and all-sided theoretical analysis system. Proceeding from basic theory of DFIM, this paper derived the physical model and established a novel synchronous–asynchronous series equivalent circuit model of DFIM at first. Based on the analysis method of DFIM, a novel equivalent circuit model of BDFM was established. These two models illustrated that the characteristic of DFM is the superposition of synchronous characteristic and asynchronous characteristic. Based on these circuit models, the characteristic under different operation mode was analyzed and corresponding analytical curves were drawn, which revealed the operation mechanism of DFM clearly. To verify the theoretical analysis of two novel equivalent circuit models, simulation models of DFIM and BDFM were established in Simulink and finite element analysis (FEA) software. Corresponding characteristic curves were drawn to compare with that obtained by circuit models. At last, combined with these characteristic curves, practical significance that circuit models and theoretical analysis bring to machine design and control theory was analyzed. [ABSTRACT FROM AUTHOR]

This paper presents a surrogate-model-based optimization of a doubly-fed induction generator (DFIG) machine winding design for maximizing power yield. Based on site-specific wind profile data and the machine's previous operational performance, the DFIG's stator and rotor windings are optimized to match the maximum efficiency with operating conditions for rewinding purposes. The particle swarm optimization-based surrogate optimization techniques are used in conjunction with the finite element method to optimize the machine design utilizing the limited available information for the site-specific wind profile and generator operating conditions. A response surface method in the surrogate model is developed to formulate the design objectives and constraints. Besides, the machine tests and efficiency calculations follow IEEE standard 112-B. Numerical and experimental results validate the effectiveness of the proposed technologies. [ABSTRACT FROM AUTHOR]

In recent years, with the ever increasing penetration of wind generation, great concerns have been raised since the constantly decline of system's inertia may considerably deteriorate the frequency stability of power system. In this regard, an inertial response control technique is proposed to enable wind generators to provide the power system with controlled inertia in need via releasing energy to or absorbing energy from the system. In this paper, an extended state observer (ESO)-based inertia emulation controller (InEC) is proposed for doubly-fed induction generators (DFIGs), which is shown to be robust to measurement noise and changing working conditions. In addition, to mitigate potential adverse impacts of rotor speed recovery control (RSRC) of DFIGs on system frequency, an ESO-based RSRC is derived, allowing a schedulable dynamic of speed recovery. Experiments carried out on a power hardware-in-loop testbed manifest that the proposed controllers outperform the traditional proportional–differential type InEC and proportional–integral type RSRC in performance and robustness. [ABSTRACT FROM PUBLISHER]

This paper presents an unexpected fluctuation of voltage for a 30-kW wound rotor brushless doubly-fed machine (BDFM) in a standalone power generation system. To address this issue, an improved method of harmonic injection is introduced. A voltage and current double closed-loop control strategy, based on control winding (CW) current decoupling, is applied through the entire experiment. Consequently, the experimental outcomes are fairly aligned with the dynamic simulations in most conditions. However, the voltage fluctuation in the power winding (PW) can be observed for a certain speed range. Harmonic analysis is then carried out on experimental data of PW voltage and CW current. A pair of interharmonic waves, which are symmetric with respect to the fundamental wave, is demonstrated to exist in PW voltage and CW current. Due to the analysis, these harmonic conjugate waves are caused by the high-order magnetomotive force tooth harmonics and current harmonics within a specific speed range. Accordingly, the control strategy of harmonic injection is employed to effectively eliminate these harmonic conjugate waves. The experimental results further highlight that the voltage amplitude can be maintained with less harmonic contents by our tailored control scheme. In addition, the formation and presence of harmonic conjugate waves may lead to the voltage amplitude fluctuation of BDFM in the standalone power generation system. [ABSTRACT FROM AUTHOR]

This paper presents the development and experimental results of a supervisor strategy and a sliding mode control setup to improve the performance of hybrid generation systems. The topology in this study is conformed by a core comprising a fuel cell module and a supercapacitor module, in combination with an alternative energy source module and an electrolyzer. In particular, a wind power turbine is considered as alternative power source to attain a hybrid generation system fully relying on renewable energy. First, a supervisor strategy is proposed to manage the power flows of the subsystems and coordinate the system as a whole. Subsequently, a sliding mode control setup for combined operation of the dc/dc power converters of the fuel cell/supercapacitor core is presented to track the power references synthesized by the supervisor control. Both control levels, supervisor strategy and sliding mode controllers, are implemented and assessed through extensive experimental tests under different wind conditions and heavy-load changes. [ABSTRACT FROM AUTHOR]

A full-scale permanent-magnet synchronous generator (PMSG)-based wind turbine with dc-link voltage control via the machine-side converter has the potential to provide inherent low-voltage ride-through (LVRT) performance without additional hardware components. However, several important performance aspects related to this topology are not addressed in this literature. This paper investigates the impacts of the LVRT control on the stability and risk of resonance, successful operation, and fatigue in a full-scale PMSG-based wind power generation system. An analytical model, considering the double-mass nature of the turbine/generator and typical LVRT requirements, is developed, validated, and used to characterize the dynamic performance of the wind generation system under LVRT control and practical generator characteristics. To enhance the operation and reduce the fatigue under LVRT control, two solutions, based on active damping control and dc-link voltage bandwidth retuning, are proposed, analyzed, and compared. The detailed nonlinear time-domain simulation results validate the accuracy of the developed model and analytical results. [ABSTRACT FROM AUTHOR]

The basic idea of the fractional frequency transmission system (FFTS) is to use lower frequency to reduce the effective electrical length of the ac transmission line, thus increasing its transmission capacity. Because the rotational speeds of the generators in hydro and wind power generation systems are very low, the FFTS is particularly suitable for transmitting electricity produced by renewable energy sources. The fractional frequency wind power system (FFWPS) provides an effective approach for integrating the large-scale and long-distance wind power into the grid. A novel method of the integration of the wind turbines in direct-driven FFWPS is introduced in this paper. A full-power ac–dc–ac converter is used as the grid-connection device in the experiment, and the experiment results verify the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFCs) are a promising option for power generation plants, but the design of fault diagnosis methods remains a key challenge. We propose the use of a quantitative model for such a plant (validated by real experiments) with a support vector machine (SVM) to detect and classify possible faults. The adoption of a classification approach as an identification strategy in a model-based fault diagnosis process represents a major innovation in the field of SOFC plants. Constant–voltage and constant–current control strategies are investigated. In both cases, an adequately trained SVM classifier is used to provide a high probability of correct classification when the plant functions at different steady-state operating conditions for random sizes of the considered faults and for realistic magnitudes of the errors affecting the model predictions. In addition, the relative importance of the easy-to-measure residuals, which are used as features in the SVM classification process, are discussed based on an advanced feature selection technique. [ABSTRACT FROM PUBLISHER]

Applications for low-speed high-torque machines include marine propulsion and wind power generation. Since electric machinery size is more directly related to required torque than to required power, high required torque leads to large machines. Mechanical gears increase the speed and lower the required torque of the machine to reduce size. This, however, results in increased noise and maintenance, and decreased reliability. Magnetic gears offer the advantages of mechanical gears without the disadvantages created by physical contact. Integrating magnetic gears into the machine structure offers additional mass savings. This study proposes a novel machine architecture, which integrates magnetic gearing and a permanent magnet synchronous machine to create an inner rotor flux-modulated permanent magnet synchronous machine. Unlike previous arrangements, the proposed machine utilizes a more desirable inner rotor configuration and avoids multiple magnet arrays. This study presents a finite–element-based design model of the proposed machine to be utilized in an optimization-based design environment. A multiobjective design study is presented for a laboratory scale application. The resulting tradeoff between mass and loss is compared with that of a permanent magnet synchronous machine for the same application. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFC) are alternative renewable power sources that can directly produce electricity from biodegradable substances. However, due to their low power and voltage production, power management systems (PMS) are required to process the MFC power to a more readily usable level. For this application, a monolithic PMS with an integrated maximum power extraction algorithm (MPEA) is proposed. The MPEA allows for quick and accurate pin-pointing of the matching conditions for maximum power transfer from the MFC to the PMS. The PMS delivers a regulated fixed voltage from low fluctuating voltages produced by MFC at maximum power point to a supercapacitor from which electronic devices, such as wireless sensors, for extended operation time can be directly powered. Along with the MPEA system, the PMS is composed of a dc–dc boost converter operating in discontinuous conduction mode to maximize efficiency. In addition, a zero current switching tracking loop is proposed to improve overall system efficiency and minimize losses in the PMS through accurate P-type Metal-oxide-semiconductor field-effect transistor on/off timing control. The PMS circuit was fabricated in 0.5-μm CMOS technology. The maximum dynamic efficiency measured was ∼58% for a load of ∼250 μW. [ABSTRACT FROM AUTHOR]