Nonlinear transient and steady state analysis for self-excited single-phase synchronous reluctance generator

With today\u27s trend for distributed generation and the need for alternative and renewable energy sources, self-excited induction and synchronous reluctance generators have attracted more attention for wind, tidal and hydro power generation applications. Compared to synchronous and DC generators, they have the advantages: they are brushless, they are robust, they do not need DC excitation and they are relatively low cost.;Compared with SEIG, the self-excited reluctance generator (SERG) not only has the advantages of simplicity and ruggedness, but can also have enhanced steady-state characteristics and high efficiency over a wide range of operation. Moreover, its output frequency is determined only by the prime mover speed, rather than by both the load and the prime mover speed as in an induction generator, so SERG can be easily integrated with power electronic devices to implement a control scheme.;Most of the current analyses deal with three-phase reluctance generators, but insufficient attention has been paid to single-phase self-excited reluctance generators (SPSERG). Their unbalanced loads make their analysis more difficult. This research is motivated by the fact that SPSERG provides a good alternative to single-phase induction generators used in stand-alone generation applications. A general methodology is suggested for transient response prediction and steady state performance analysis for the SPSERG type of electric machine.;To establish a design environment, finite element method is an effective tool, which can be integrated in machine modeling to obtain good performance prediction. In this work, an off-line FEM approach is proposed to obtain the saturation characteristics for state space simulation. During the process, transformation between instantaneous inductance and average inductance is investigated. Off-line FEM + SS approach is proved to be a simple and economic method and can fit the experimental results in good accuracy.;Moreover, a steady state model has to be built to reveal the parametric dependence and provide good design guidance. However, because of the unbalanced load and nonlinear feature of the machine, existing models are not suitable for analysis. In this dissertation, a novel inductance-oriented steady state model based on the harmonic balance technique is introduced. The idea is that starting from the inductance determination under certain load, the fluxes can be attained by a nonlinear relationship, after that, the machine variables can be solved according to the fluxes. Comparison between simulation and experiment validates this approach

Alone Self-Excited Induction Generators

In recent years, some converter structures and analyzing methods for the voltage regulation of stand-alone self-excited induction generators (SEIGs) have been introduced. However, all of them are concerned with the three-phase voltage control of three-phase SEIGs or the single-phase voltage control of single-phase SEIGs for the operation of these machines under balanced load conditions. In this paper, each phase voltage is controlled separately through separated converters, which consist of a full-bridge diode rectifier and one-IGBT. For this purpose, the principle of the electronic load controllers supported by fuzzy logic is employed in the two-different proposed converter structures. While changing single phase consumer loads that are independent from each other, the output voltages of the generator are controlled independently by three-number of separated electronic load controllers (SELCs) in two different mode operations. The aim is to obtain a rated power from the SEIG via the switching of the dump loads to be the complement of consumer load variations. The transient and steady state behaviors of the whole system are investigated by simulation studies from the point of getting the design parameters, and experiments are carried out for validation of the results. The results illustrate that the proposed SELC system is capable of coping with independent consumer load variations to keep output voltage at a desired value for each phase. It is also available for unbalanced consumer load conditions. In addition, it is concluded that the proposed converter without a filter capacitor has less harmonics on the currents

Power management of islanded Self-Excited Induction Generator reinforced by energy storage systems

Self-Excited Induction Generators (SEIGs), e.g., Small-Scale Embedded wind generation, are increasingly used in electricity distribution networks. The operational stability of stand-alone SEIG is constrained by the local load conditions: stability can be achieved by maintaining the load’s active and reactive power at optimal values. Changes in power demand are dependent on customers’ requirements, and any deviation from the pre-calculated optimum setting will affect a machine’s operating voltage and frequency. This paper presents an investigation of the operation of the SEIG in islanding mode of operation under different load conditions, with the aid of batteries as an energy storage source. In this research a current-controlled voltage-source converter is proposed to regulate the power exchange between a direct current (DC) energy storage source and an alternating current (AC) grid, the converter’s controller is driven by any variation between machine capability and load demand. In order to prolong the system stability when the battery reaches its operation constraints, it is recommended that an ancillary generator and a dummy local load be embedded in the system. The results show the robustness and operability of the proposed system in the islanding mode of the SEIG under different load conditions

Analysis of the dynamic performance of self-excited induction generators employed in renewable energy generation

Incentives, such as the Feed-in-tariff are expected to lead to continuous increase in the deployment of Small Scale Embedded Generation (SSEG) in the distribution network. Self-Excited Induction Generators (SEIG) represent a significant segment of potential SSEG. The quality of SEIG output voltage magnitude and frequency is investigated in this paper to support the SEIG operation for different network operating conditions. The dynamic behaviour of the SEIG resulting from disconnection, reconnection from/to the grid and potential operation in islanding mode is studied in detail. The local load and reactive power supply are the key factors that determine the SEIG performance, as they have significant influence on the voltage and frequency change after disconnection from the grid. Hence, the aim of this work is to identify the optimum combination of the reactive power supply (essential for self excitation of the SEIG) and the active load (essential for balancing power generation and demand). This is required in order to support the SEIG operation after disconnection from the grid, during islanding and reconnection to the grid. The results show that the generator voltage and speed (frequency) can be controlled and maintained within the statuary limits. This will enable safe disconnection and reconnection of the SEIG from/to the grid and makes it easier to operate in islanding mode

Sensored and sensorless speed control methods for brushless doubly fed reluctance motors

The study considers aspects of scalar V/f control, vector control and direct torque (and flux) control (DTC) of the brushless doubly fed reluctance machine (BDFRM) as a promising cost-effective alternative to the existing technological solutions for applications with restricted variable speed capability such as large pumps and wind turbine generators. Apart from providing a comprehensive literature review and analysis of these control methods, the development and results of experimental verification, of an angular velocity observerbased DTC scheme for sensorless speed control of the BDFRM which, unlike most of the other DTC-concept applications, can perform well down to zero supply frequency of the inverter-fed winding, have also been presented in the study

Effects of POD control on a DFIG wind turbine structural system

This paper investigates the effects power oscillation damping (POD) controller could have on a wind turbine structural system. Most of the published work in this area has been done using relatively simple aerodynamic and structural models of a wind turbine which cannot be used to investigate the detailed interactions between electrical and mechanical components of the wind turbine. Therefore, a detailed model that combines electrical, structural and aerodynamic characteristics of a grid-connected Doubly Fed Induction Generator (DFIG) based wind turbine has been developed by adapting the NREL (National Renewable Energy Laboratory) 5MW wind turbine model within FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. This detailed model is used to evaluate the effects of POD controller on the wind turbine system. The results appear to indicate that the effects of POD control on the WT structural system are comparable or less significant as those caused by wind speed variations. Furthermore, the results also reveal that the effects of a transient three-phase short circuit fault on the WT structural system are much larger than those caused by the POD controller

Analysis of the Transient Response of a Capacitor-Excited Induction Generator for Unity Power Factor Load Condition using MATLAB/SIMULINK

Advantageous features of an induction generators are widely used in a single system like wind or micro turbo etc. It is operated in a capacitor excited or self excited mode to generate electrical energy in remote areas. The Main drawbacks of a CEIG under variable load conditions are poor voltage and frequency regulation .The aim of this paper is to provide a better understanding of the dynamic response of a capacitor-excited, squirrel cage induction generator that is carried out for determining the change in performance under the running condition from no-load to full-load. Voltage control, frequency control and temperature rise due to continuous running of the machine are evaluated using transient analysis. This assessment would hopefully help to develop a better controlled required for CEIG system, operated in remote areas