Self-excited Reluctance Generator Research Articles

Performance analysis of a stand-alone synchronous reluctance generator under unbalanced conditions

<span lang="EN-US">A stand-alone self-excited wind energy conversion system (WECS) is considered commonly used in remote areas due to its simple control and low cost. This paper introduces the performance analysis of a stand-alone self-excited reluctance generator (SERG) under balanced and unbalanced operations. An asymmetrical component is proposed to obtain the positive and negative sequence components of voltages and currents in addition to the unbalanced voltage factor of SERG. The obtained results have been validated and compared with experimental results obtained from a laboratory prototype of a 5.5 kW synchronous reluctance generator driven by a dc motor as a prime-mover under unbalanced excitation capacitors and unbalanced loads. The comparison verifies the applicability of the proposed model.</span>

Voltage and frequency control of standalone wind-driven self-excited reluctance generator using switching capacitors

This paper presents a methodology for voltage and frequency (V–f) control of a standalone wind-driven self-excited reluctance generator (WDSERG). The methodology is based on proposing two different compensation configurations using two switching capacitors (short-shunt and long-shunt compensation) for (V–f) control. The dynamic and steady-state performances of the two configurations are discussed under different operating conditions: wind speeds, load currents and power factors. This analysis is done by developing a complete dynamic model of WDSERG including the excitation capacitors and load. Therefore, complete equivalent circuits are proposed. The values of capacitors are controlled by adjusting the duty cycle of H-bridge circuits with PI controllers. To validate the proposed configurations and their dynamic models and equivalent circuits, simulation results for a 1.5-kW standalone WDSERG and experimental results for 0.2 kW reluctance generator driven by a DC motor, emulating the wind turbine, are carried out. The results show a significant enhancement in voltage and frequency regulation with the selected optimal capacitances for each configuration; however, short-shunt compensation is the preferred configuration as it controls the output voltage and frequency with minimum values of capacitances and minimum required duty variation.

Analysis of Self-Excited PM-Assisted Reluctance Generators

Induction machines and reluctance machines have been proposed to the self-excited generating system as isolated power supply in the past few decades. On the other hand, they show either poor voltage regulation or difficulty in excitation. In this paper, the self-excited PM-assisted reluctance (PMAREL) generator is investigated, aiming at overcoming such drawbacks. An analytical model in the $dq$ reference frame is developed to identify the steady-state performance of the self-excited PMAREL generator. Experimental results using a laboratory PMAREL machine are compared to the predicted results. The characteristics of the self-excited PMAREL generator are presented, based on the experimental results. The effects of design parameters (including stator resistances, $d$ -axis inductance, and $q$ -axis inductance) on the generator performance are investigated by using the analytical model. The performance comparisons with a self-excited reluctance generator are also carried out. It is verified that the self-excited PMAREL generator exhibits not only the improvement in terminal voltage, output power, and power factor but also achieves inherently a stable self-excitation process.

Investigation of Self-Excited Synchronous Reluctance Generators

In this paper, an analytical model in the $dq$ reference frame is developed to recognize the steady state of the self-excited reluctance generator considering no-load and resistive load conditions. A fast method to estimate the minimum capacitance requirement is proposed. Experiments have been carried out to verify the analytical results. After that, attention is paid to the capability of self-excitation in the reluctance generator with different residual magnetisms in the rotor. Different levels of residual rotor magnetism are achieved by different magnetizing dc currents. An indicative value of phase current is defined to determine the self-excitation and the required minimum residual rotor magnetism for self-excitation in the reluctance generator connected with different capacitances is discussed. At last, the capability of self-excitation in the reluctance generator by connecting charged capacitors is investigated.

Steady state analysis of wind-driven self-excited reluctance generator for isolated applications

This paper presents the steady state analysis of Wind-Driven Self-Excited Reluctance Generator (WDSERG) under various operating conditions of wind speeds, excitation capacitances, load, and power factor. A steady state mathematical model is developed from the dynamic model of self-excited reluctance generator (SERG) and phasor diagram. This model is used to compute and analyse various steady state performances under different wind speed, terminal operating conditions and variation of critical machine parameters. The model is extended to determine the range of wind speed within which the WDSERG excitation and stable operation is possible under a given load and excitation conditions. The critical capacitances and the maximum load limit under different operating conditions are also determined. It is found that for any specified WDSERG configuration and connected load, there exist a capacitance value below which no cut-in wind speed exist and therefore excitation and operation of WDSERG is impossible. This paper could aid the development of optimum capacitance selection for best operation of WDSERG under intermittent wind speed and changing load condition. The results also show a considerable effect of power factor on the operating characteristics of the WDSERG.

Optimal capacitance selection for a wind-driven self-excited reluctance generator under varying wind speed and load conditions

This paper presents a methodology to determine and select a suitable excitation capacitance value for a wind-driven self-excited reluctance generator (WDSERG), which would produce a constant output voltage under changing wind speed and connected load. A steady state mathematical model of WDSERG is developed from the dynamic model of self-excited reluctance generator (SERG) and phasor diagram. This model is used to develop an algorithm that searches for the optimum excitation capacitance which produces a desired output voltage level for any given wind speed and load within the operating limits of the WDSERG. Different scenarios of variable speed, load and power factor are considered and an optimal capacitance value is determined and selected for each cases. Published experimental data was utilised to validate the developed model. The results show that there is a distinct capacitance value that would produce a constant output voltage under any given operating conditions of wind speed and terminal load. The procedure presented can form a basis for the design of a variable excitation capacitor to maintain a constant output voltage under varying wind speed and load, which will invariably offer an effective and low-cost solution for output voltage control of WDSERG.

Self-Excited Reluctance Generator: State of the Art and Future Trends

This paper is a road map for the new generation of graduate students who are interested in reluctance generator research work. Recent research work on two-pole single phase self-excited reluctance generator (2PSPSERG) has been evaluated. The coverage extends over three decades of time, and covers more than eighty pages of reported pioneering research work. Topics addressed include: converting synchronous motor into reluctance generator (RG), types of rotors used especially axially laminated anisotropic (ALA), existence of mutual coupling, negative mutual coupling, time variation of windings inductances, d-axis and q-axis inductance variations with flux, rotor saliency ratio variation with flux, relationship between electrical frequency of stator windings voltages and currents and rotor mechanical frequency of rotation, unbalanced loading of RG, stability of RG under rotor speed fluctuations, stability of RG under load power factor changes, and efficiency of RG. Findings extracted from literature-cited matrix are reported, as well as gaps revealed by the same matrix. Facts in SERG literature are collected and listed. Questions raised during the study are documented. Guidelines for clear experimental future research work are outlined. Finally, suggestions for future research are then discussed.

Influence of Rotor Cage on the Performance of a Synchronous Reluctance Generator

The influence of rotor cage on the performance of an autonomous self-excited reluctance generator supplying loads of different power factors is presented. It is seen that for the same excitation capacitance, terminal load connection, and speed, the self-excited reluctance generator with a cage exhibits a better ability to preserve the voltage waveshape following a sudden addition or removal of load than does a cageless self-excited reluctance generator. This is because during the transient disturbance, the rotor cage supports some DC current in the d-axis, making it act as a field winding. The solution of steady-state model equations formulated directly from the dynamic model are solved using the MATLAB® (The MathWorks, Natick, Massachusetts, USA) optimization technique ‘fsolve.’ The cageless self-excited reluctance generator is only capable of yielding less than half the rated power, while the self-excited reluctance generator with a cage is able to produce more than two-thirds of the rated power. This is due to the inability of the cageless machine to excite at capacitance values high enough to circulate the rated current in the machine windings.

Dynamic Analysis of a Self-Excited Single-Phase Reluctance Generator

This article presents a mathematical model by which the dynamic behavior of a self-excited single-phase reluctance generator (SESPRG) can be successfully predicted under different operating conditions. The proposed analysis is based on the d-q axis model. Self-excitation is achieved via capacitors connected across the terminals of both the main and auxiliary windings. Dynamic stability of the proposed generator is studied using the linearized model. In order to achieve maximum damping characteristics, the machine parameters are optimized using the torque decomposition algorithm. An improved dynamic stability with well-damped hunting oscillations has been achieved using the present approach. Excellent agreement between experimental and simulated results have been observed, which supports the validity of the proposed analysis.

マルチプルバリアロータを用いた自励同期リラクタンス発電機の性能解析

マルチプルバリアロータを用いた自励同期リラクタンス発電機の性能解析

Single-Phase Self-Excited Reluctance Generator, Part I:Steady-State Analysis

A method of steady-state analysis of a single-phase, self-excited reluctance generator based on a qd model and harmonic balancetechnique is proposed. A necessary constraint function is derived to reveal the parametric dependency of the system which has a combination of self-excitation and nonlinear characteristics. Moreover, the proposed method can be used to reconstruct the machine waveforms, which can provide a better understanding ofthe system. The comparison between experiment and simulation shows a good agreement. This method not only offers guidance for the design of a single-phase, self-excited reluctance generator, but also provides a general methodology for other self-excited generator steady-state analysis under unbalanced terminal conditions.

Single-Phase Self-Excited Reluctance Generator, Part II: Transient Analysis

An offline finite element analysis plus state space method isintroduced for transient analysis of a single-phase, self-excited reluctance generator (SPSERG). A transform from the instantaneous inductances obtained from the finite element method to the average inductances for a short runtime simulation is studied. This approach reduces the computational effort and is suited for a total design environment. There is good agreement between experiment and simulation.

Unbalanced Switching Effects on Dynamic Performance of an Isolated Three-Phase Self-Excited Generator

This paper presents dynamic performance of an isolated three-phase self-excited reluctance generator (SERG) under sudden disconnection of single-phase loads and excitation capacitors. A novel approach based on three-phase reluctance machine model is employed to derive dynamic equations of a stand-alone SERG under different unbalanced conditions. Experimental results obtained from a laboratory 0.37 kW reluctance machine driven by a DC motor are also performed and compared with the simulated results to validate the effectiveness of the proposed method. It can be concluded from the analyzed results that the stator current unbalanced factor for the loaded SERG under switching off one excitation capacitor is much larger than the one under switching off one or two resistive loads. The voltage unbalanced factors for the loaded SERG under switching off one excitation capacitor or switching off one or two resistive loads are very similar. Moreover, the terminal voltage of a loaded SERG cannot be generated when two excitation capacitors are simultaneously switched off.

Minimum loading resistance and its effects on performance of an isolated self-excited reluctance generator

An approach based on eigenvalue and eigenvalue sensitivity to determine minimum loading resistance of an isolated self-excited reluctance generator (SERG) is presented. A d–q axis equivalent-circuit model is employed to derive dynamic equations of the SERG studied. Both transient and steady-state characteristics of the SERG subject to minimum loading resistance are investigated. Experimental results obtained from a laboratory 0.37 kW reluctance machine driven by a DC motor are compared with simulated results to validate the feasibility of the proposed method.

Steady-state analysis of a three-phase self-excited reluctance generator

The author presents a general method for analyzing the steady-state performance of a three-phase, self-excited reluctance generator which supplies an isolated R-L load. The two-axis theory is employed to account for the saliency effect. In the analysis, magnetic saturation is assumed to be confined to the direct-axis and is accounted for by a variable direct-axis magnetizing reactance. It is shown that for a given load impedance and excitation capacitance, the direct-axis magnetizing reactance that satisfies the circuit conditions can be determined by solving a simple quadratic equation. Based on the same equation, the maximum permissible value of capacitive reactance to secure self-excitation can also be directly computed. The experimental results in general verify the validity of the circuit model and the theoretical analysis. >

Steady-state operating limits of three phase self-excited reluctance generator

The performance of three phase self-excited reluctance generators is analysed under a wide range of different operating conditions. The validity of the analysis is verified by comparing some of the theoretical results with their corresponding experimental measurements. The impact of varying different system parameters on the performance is also presented.

Capacitance requirements for three phase self-excited reluctance generators

A direct method to find the capacitance requirements for a three phase self-excited reluctance generator under any load or speed is introduced. Expressions for the load angle as well as for the minimum value of the excitation capacitance are derived. It has been found that there is a cut off speed, above which no excitation is possible no matter what the terminal capacitance value. Expressions for the value of this speed under open circuit, resistive and pure inductive loads are also derived and presented.

Analysis of a Three-Phase Self-Excited Reluctance Generator

A three-phase, self-excited reluctance generator with capacitive excitation is described and analyzed using the two-axis theory developed for synchronous machines, magnetic saturation being accounted for by the use of a variable direct-axis magnetizing reactance. Experimental results are found to be in close agreement with theoretical calculations.

Steady-state performance of self-excited reluctance generators

The paper discusses the steady-state performance of an isolated self-excited reluctance generator. A computer model based on the Park transformation has been made. Results have shown good agreement with those obtained from experimental models using both salient and segmental rotors. The study has been extended to cover the effect of machine parameters.

The Reluctance Machine as a Self-Excited Reluctance Generator

ABSTRACT The test described in this paper show that the reluctance machine may be operated as an independent or isolated generator at a predetermined voltage and frequency, with sinusoidal wave form, by moans of capacitive excitation. Further, proper choice and arrangement of the capacitors will result in a practically flat external load-voltage characteristics. The performance analysis based on a developed equivalent circuit is given with experimental verification.