Excitation Capacitance Research Articles

Multi-port network based modeling and selection of capacitor for desired voltage regulation of a standalone six-phase short-shunt induction generator for application in remote areas

This paper gives a straightforward method to determine the values of excitation capacitors of a standalone short-shunt six-phase induction generator (SPIG) to maintain the voltage profile within predetermined percentage of voltage deviation (VD). In this envisioned study, the value of the capacitor is meticulously chosen to optimize the number of capacitor switching, ensuring minimal system cost and complexity. The theory of multi-port network analysis has been applied for modelling of the SPIG, thus, the complex mathematical derivation to obtain the model equations is avoided. The system is expressed as a multivariable nonlinear optimization problem. The resultant admittance of the SPIG is calculated from its per phase equivalent circuit and is used as an objective function, which is solved using Binary Search Algorithm (BSA). The main novelty of this work is the determination of the model equations of the SPIG system in an efficient and simple way using the multi-port network analysis approach. Along with this, the BSA is employed for optimal selection of excitation capacitors because of its simplicity and less computational time. The results, on a 3.7 kW induction machine, reveal that to maintain a 4 % VD, a fixed series capacitor of 140 µF and two switched shunt capacitors (34.4 µF, 91.8 µF) are required. For 2 % VD, four shunt capacitors (24.2µF, 36.2µF, 64.7µF, 91.2µF) are necessary. The performance of the machine is evaluated with the help of magnetic characteristics and other equations obtained from its per phase equivalent circuit. The experimentation has been carried out in a hardware prototype system developed in the laboratory. The experimental and the simulated results are compared and found that both are nearly same for different operating conditions, which indicates the efficacy of the proposed approach.

АСИНХРОННІ ГЕНЕРАТОРИ В АВТОНОМНИХ ДЖЕРЕЛАХ ЖИВЛЕННЯ ЗВАРЮВАЛЬНОЇ ДУГИ. СТАН І ПЕРСПЕКТИВИ

The article is aimed at generalizing the results of the study of asynchronous generators (AG) of autonomous welding arc power sources (AWPS) obtained in the Department of Electromechanical Systems of the Institute of Electrodynamics of the NASU. The proposed classification of AG of autonomous welding systems is considered, mathematical models are developed, the results of computational and experimental studies of such systems with AG with capacitor excitation and an uncontrolled rectifier, in the DC circuit of which high-frequency inverters, pulse-width regulators or half-bridge inverters are connected, as well as generators with valve and valve-capacitor excitation. The design features and experimental samples of welding arc power sources with AG are considered. The directions of further research are determined. Ref. 42, fig. 5.

The Behavior of Terminal Voltage and Frequency of Wind-Driven Single-Phase Induction Generators under Variations in Excitation Capacitances for Different Operating Conditions

This paper assesses the behavior of output voltage and frequency of wind-driven self-excited induction generators with variable excitation capacitances connected to the main and auxiliary windings under different operating conditions. The optimum values of the main winding excitation capacitance for fixed terminal voltage operation under different values of shunt capacitance, load, and speed are also evaluated. The obtained results show that the terminal voltage is highly affected by changing the main winding excitation capacitance. In addition, the frequency is greatly affected by changing the auxiliary winding excitation capacitance. However, under different operating conditions, variation in the output frequency under different values of the main winding capacitance, with fixed auxiliary winding capacitance, is acceptable. Extensive simulations were conducted and the results are discussed in this publication.

Development of modified P&O algorithm based simple controller for constant voltage and frequency operation of three-phase IIG for micro-hydro application

This paper introduces Modified Perturb and Observe (MP&O) based MPPT algorithm for constant frequency and voltage operation of a three-phase Isolated Induction Generator (IIG) coupled to an ungoverned hydro turbine. The generator is operated at maximum output power point corresponding to the excitation capacitance connected across the Point of Common Coupling (PCC) of the IIG. The output power of the generator is always maintained constant. With a fixed capacitor bank connected across the stator terminals, the IIG simultaneously supplies power to both ac load (main load) and controlled dc load (dump load). This modified MPPT algorithm not only tracks the maximum output power point, but also diverts power from main load to dump load and vice-versa as per requirement to maintain the voltage and frequency at constant value. The electronic circuit is realized using an uncontrolled rectifier-chopper (diode-IGBT) combination connected across the IIG terminals supplying the controlled dc load. The IIG has been modeled based on stationary reference frame d-q axes theory. The proposed control algorithm has been experimentally implemented on a three-phase, 415 V, 2.2 kW induction machine using dSPACE 1104 platform and the effectiveness of the algorithm has been tested for various transient conditions, such as, sudden ac load application as well as removal.

Optimization algorithms for steady state analysis of self excited induction generator

The current publication is directed to evaluate the steady state performance of three-phase self-excited induction generator (SEIG) utilizing particle swarm optimization (PSO), grey wolf optimization (GWO), wale optimization algorithm (WOA), genetic algorithm (GA), and three MATLAB optimization functions (<em><span lang="EN-US">fminimax</span></em><span lang="EN-US">, </span><em><span lang="EN-US">fmincon</span></em><span lang="EN-US">, </span><em><span lang="EN-US">fminunc</span></em><span lang="EN-US">). The behavior of the output voltage and frequency under a vast range of variation in the load, rotational speed and excitation capacitance is examined for each optimizer. A comparison made shows that the most accurate results are obtained with GA followed by GWO. Consequently, GA optimizer can be categorized as the best choice to analyze the generator under various conditions.</span>

Persistent Voltage Control of a Wind Turbine-Driven Isolated Multiphase Induction Machine

The growing concern about the energy crisis and environmental protection has caused a growing interest in wind power generation systems. Researchers and engineers urgently need to create new multiphase induction machines for the production of wind energy, since they are essential parts of wind turbines. This study offers control and stability analysis of a multiphase induction machine based on the entropy stability requirements for its linearized model. The generated model was used to assess the on-load properties of the multiphase induction machine and calculate its steady-state parameters under each operating circumstance. According to the analysis, the eigenvalues depend on the machine parameters, with the excitation capacitance and speed variation being the most important. Stabilization of the multiphase induction machine is the main focus of the singular values, which vary according to its variables. The simulated results include an examination of a multiphase induction machine steady state for voltage build-up at various types of load.

A Novel Control Scheme for Induction Generator Based Stand-alone Micro Hydro Power Plants

A system comprising of a hydraulic turbine (HT) driven induction generator with excitation capacitor (IGEC) has been proposed for providing electricity to the residents living in remote areas and steep terrains, wherein the grid connection is unviable. The available water resource in such locations is effectively utilized and the load on the generator terminals is set, based on the requirement of the consumer demand. A method has been formulated for the estimation of excitation capacitor and rotor speed for ensuring nominal voltage and frequency at the generator terminals, regardless of variation in the consumer load. This design procedure is based on the analysis of IGEC employing the binary search algorithm (BSA). The logical way of arriving at the range of per unit (pu) speed to start the BSA has also been illustrated. A closed-loop control scheme has also been formulated, by taking generator voltage as the feedback variable and comparing the voltage set limits Vmin and Vmax. Accordingly, a controller action is initiated to add or disconnect the flexible loads. An available mathematical modeling of HT has been modified suitably and by using this model, the functioning of the proposed system with respect to the HT characteristics and generated frequency of IGEC has also been investigated. Using a MATLAB/Simulink software, the successful functioning of the proposed system has been demonstrated with typical operating conditions. The predetermined values and simulated observations are amply supported with the laboratory results conducted on a 3-phase, 3.7 kW IGEC.

Research on Excitation Control and Energy Feedback Control of Brushless Doubly‐Fed Air‐Core Pulse Alternator

Brushless doubly‐fed air‐core pulse alternator (BDAPA) is a new type of pulse alternator. It does not need a brush and slip ring, improving the reliability of the system. Moreover, the field winding and rotor winding have good compensation effect, which can significantly improve the discharge performance of the pulse alternator. As a high‐power pulse power supply, BDAPA must have a set of corresponding excitation power supplies to control its excitation. Pulse alternator and excitation power supply constitute the pulse alternator power supply system. The excitation power supply of pulse alternator usually adopts a pulse capacitor, the field winding of pulse alternator is excited by the pre‐charged capacitor before the pulse alternator discharges the load. After discharging, the excitation capacitor must be charged again before the next work of pulse alternator. This requires an additional set of DC power supply to charge the excitation capacitor. It not only increases the volume of the whole system and reduces the energy storage density of the system, but also makes the control of the system more complex. Taking the BDAPA as the research object, this paper proposes a control method with energy feedback, which is combining self‐excitation and separate excitation. Using the inertial energy storage of the pulse alternator and the inductive energy storage of the field winding and rotor winding, the excitation capacitor can be recharged through proper control methods, which can save the DC excitation power supply and improve the energy storage density of the system. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Wind Energy Conversion System Using Advanced Speed Control and Model-Based Loss Minimization

This paper presents a new optimization strategy for a stand-alone wind energy conversion system (WECS). The WECS is comprised of a variable-speed wind turbine (WT) with a vector-controlled self-excited induction generator (SEIG), a three-phase full-bridge converter, and a DC-bus containing the excitation capacitor, batteries, and a load. The control strategy incorporates an advanced model-based SEIG loss minimization and fuzzy-logic WT optimization. The latter utilizes a hedge-algebra speed controller to ensure fast response with practically no overshoot in the whole WT operating range, which cannot be achieved with the conventional proportional-integral (PI) controller. Consequently, the WT optimization time step is shortened and its convergence accelerated. The proposed SEIG loss minimization is based on the corresponding mathematical model that accounts for magnetic saturation and variable stray load and iron losses. Simultaneous optimization of the WT and SEIG is enabled, which results in greater total energy output compared to the successive WT-SEIG optimization. The proposed control strategy is run in real-time using the DS1103 board (dSpace) with a 1.5 kW SEIG driven by an emulated WT. It is experimentally evaluated over a wide WT operating range and compared with several competing strategies involving successive optimization, PI speed control and/or less elaborate SEIG models.

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>

A grid forming control for wind energy conversion systems

This paper presents an effective and practical structure to improve voltage and frequency regulation in grid-forming control of self-excited induction generator-based wind energy conversion systems. In the proposed control structure, in addition to a fixed parallel excitation capacitor, a small wound rotor synchronous generator is also used as a reactive power compensator. The excitation voltage of the small synchronous generator is controlled in such a way that by injecting the required amount of reactive power, this generator maintains the balance between the inductive and the capacitive reactive powers in the isolated system, and thus, improves the system voltage regulation. In addition, an active power control is proposed in which the speed of the prime mover of the self-excited squirrel cage induction generator is adjusted in such a way that the active power of the small synchronous generator is maintained at zero value. The proposed power controller, by creating the balance between the generated and the consumed active powers, improves the frequency regulation of the wind energy conversion system. The validity and effectiveness of the proposed structure are demonstrated through both simulation studies and experimental implementation. The obtained results confirm that the poor regulation of voltage and frequency, which is one of the major drawbacks of self-excited induction generator-based wind energy conversion systems, has been significantly mitigated by using the proposed method.

A hardware-based novel approach for parallel operation of two differently rated SEIGs

The application of Self-Excited Induction Generator (SEIG) for micro/mini hydro power generation running under standalone mode is an emerging topic for research. Therefore, investigation of parallel operation for two or more SEIGs imitating two separate generating units under standalone mode is highly needed. This paper presents a hardware-based new approach for running two SEIGs in parallel without considering any constraints and without use of any power electronic components. Separate excitation capacitor banks are required for two differently rated machines while sharing of loads has been discussed, along with simple and novel parallel steps using starting resistive load are also being presented. Three phase 2.2 kW and 5.5 kW SEIGs of the same number of poles are being used for this experiment. Results are observed in a power analyser (Tektronix PA4000) and are being advocated with graphs which showcases load sharing between these two machines. In the proposed method, separate excitation capacitor banks are used for individual machines to overcome the unwanted disadvantages of existing method of paralleling, and, it is observed that the proposed method performs better, provided an individual starting resistive load must be connected. The hardware result indicates that there is a decrease in load sharing current for 2.2 kW machine by 78% and increment in load sharing current by 19.79% for 5.5 kW machine when compared with the existing method.

An accurate dynamical model of induction generator utilized in wind energy systems

Due to the advantages of a self-excited induction generator (SEIG), it plays a main role in sources of renewable energy, such as wind turbines (WT). The regulation of terminal voltage and frequency is poor under variable rotor speed and load conditions at stand-alone operation mode. The generator terminal voltage depends on the excitation capacitance which can be controlled by a capacitor bank and static voltage compensator. The dynamical model of the machine is described by differential equations in D-Q axes transformations of the synchronously rotating frame. Many models of analysis are proposed in the literature. In those models, several approximations are used to simplify the process of calculations, such as neglecting the iron core resistance, stray load resistance, stator and rotor leakage reactance, and magnetic saturation. In this work, a comprehensive dynamic model of the SEIG-WT is performed to analyze the system performance under transient and steady-state conditions. This dynamic model considers the effect of all machine parameters variation. New analytical formulas are used for to accurate calculation of minimum and maximum values of excitation capacitance and generator rotor cut-off and maximum speed. The dynamic model results are partially compared with experimental results, and accurate agreement is shown.

Capacitively-excited single-phase asynchronous generator for autonomous applications

The need to decentralize power generation and decarbonize the earth in order to have a sustainable global economy are the major reasons for the development of this paper. Considering the flaws of grid-connected power system, the autonomous system becomes a better alternative in rural and isolated areas. Analysis of stand-alone single-phase Asynchronous generator based on d-q model in a stationary reference frame is presented. Asynchronous generator does not have the capability to produce reactive power necessary for excitation and this must be provided by external means. Capacitive method has been considered in this paper due to its simplicity and its economic viability. The effects of magnetic saturation in the airgap has been considered by using the nonlinear relationship between the magnetizing inductance and the magnetizing current of the machine. Under this approach, the mutual inductance varies continuously. The results have shown that steady state condition of the generated voltage is not fixed but depends on the suitable combination of excitation capacitance and the rotor speed.

Performance Analysis of Synchronous Reluctance Generator

Abstract: The synchronous reluctance generators are a species of self-excited generators such as the induction generators. The self-excited synchronous reluctance generator (SynRG) has become a promising and viable replacement of self-excited induction generator because of the supply frequency dependence on the prime speed and not load. The self-excited synchronous reluctance generator has high reliability, low cost and robustness and capacity of variable speed operation. The aim of this research is to carry out performance analysis of shunt connected three-phase synchronous reluctance generator feeding an R-L load. The dynamic analysis is based on the classical d-q model where equations for electrical quantities were derived and implemented using a computer simulation tool, MATLAB®. The equations for steady state analysis were derived from the dynamic equations by setting all time variables to zero. The dynamic analysis was carried out on a 4-pole, speed of 1500 rpm with connected load at a fixed excitation capacitor value of 50uF for a 2.5kVA machine. Effect of excitation-capacitance variation and loadingconditions variation on the generated output voltage and frequency are presented and discussed. The load variations were done based on energy-current perturbation at a fixed power factor of 1.0. The load variations were done at several points and result shows that with the variations in the connected loads, the output frequency of the synchronous reluctance generator remains constant, which makes it a good alternative for induction generator. On the steady state analysis, it was discovered that on increasing the excitation capacitor, the terminal voltage increases as well as the output power. The result specifically revealed that when the capacitance increases from 25uF to 45uF, the terminal voltage and the output power increases from 200volts to 300volts; and 200watt to 1700watt. Therefore, it is recommended that to ensure machine excitation, the capacitor should not be reduced below a certain value. The study is beneficial for operation of an isolated power supply. Keywords: Synchronous Reluctance Generator, Direct Current and Indirect Current

High precision, low excitation capacitance measurement methods from 10 mK to room temperature.

Capacitance measurement is a useful technique in studying quantum devices, as it directly probes the local particle charging properties, i.e., the system compressibility. Here, we report one approach that can measure capacitance from mK to room temperature with excellent accuracy. Our experiments show that such a high-precision technique is able to reveal delicate and essential properties of high-mobility two-dimensional electron systems.

Dynamic Modeling of Wound-Rotor Slip-Ring Induction Generator with Switched-Excitation Capacitance and Chopper Resistance Across Bridge Rectifier in the Rotor Circuit

This paper presents a novel external secondary self-excitation capacitance and chopper resistance across the diode bridge rectifier in the rotor circuit to control the voltage and frequency of 3-phase, wound-rotor, slip-ring, induction generator (WRSRIG). The problem related to the excitation- capacitance from the rotor side is the required large excitation capacitance to enhance the generator performance in a wide - range. In the present proposed method, a dynamic excitation capacitance is used in the H-Bridge inverter circuit connected in series with a chopper resistance across a 3-phase diode bridge rectifier in the rotor circuit. The duty ratios of the H-bridge thyristor elements and the thyristor chopper element are varied to emulate the excitation-capacitance as well as external-rotor resistance values dynamically, and to be used as terminal voltage and its frequency control. The dynamic excitation-capacitance is used to control the terminal voltage, while the dynamic external rotor resistance is used to control the generator speed (frequency). To study the performance of the WRSRIG a dynamic model is presented in this paper in D-Q axes rotating synchronously in a reference frame. The dynamic model takes into account all the machine parameters, such as stator and rotor - iron core losses, stator and rotor - stray load losses, dynamic saturation of the magnetizing inductance, rotor harmonic losses generated due to switching action of the bridge rectifier, reduction voltage in the rotor circuit due to the over-lap phenomenon and rotor external resistance losses. The new proposed equivalent circuit of the WRSRIG will become an efficient method for studying the performance characteristics of the generator and to be used as a suitable tool for an algorithm of the vector control analysis.

Experimental Investigations on Loading Capacity and Reactive Power Compensation of Star Configured Three Phase Self Excited Induction Generator for Distribution Power Generation

Self excited induction generator (SEIG) is gaining popularity for off-gridpower generation due to the inherent advantages. This paper presents a pri-mary experimental investigative study on the performance of three-phase starconfigured SEIG (Y-SEIG). The aim of the experimental work is to identifya simple and cost-effective scheme of self-excitation and reactive power(VAR) compensation among the six possible operational configurations.From the investigated results, it is found that the capacitor excitation and VAR compensation in the delta connection scheme give the better performance.Experimental test procedure and obtained values of steady state analysis ofSEIG for calculation of minimum excitation capacitance are also highlightedin this paper.

Review of Literature on Self-Excited Induction Generators and Controllers

Abstract: Wind energy is one of the most important and promising sources of renewable energy all over the world. Throughout the globe, in the last, three- or four-decades generation of electricity from wind energy has created a wide interest. At the same time, there has been a rapid development of wind energy-related technology. The control and estimation of wind energy conversion systems constitute a vast subject and are more complex than those of dc drives. Induction generators are widely preferable in wind farms because of their brushless construction, robustness, low maintenance requirements, and self-protection against short circuits. Low cost, robustness, and ease of maintenance are attractive features of induction generators. With wind turbine and micro/mini-hydro generators as an alternative energy source, the induction generators are being considered as an alternative choice to well-developed synchronous generators because of their simplicity, ruggedness, little maintenance, price, brushless (in squirrel cage construction), absence of separate dc source, self-protection against severe overloads and short circuits. In isolated systems, squirrel cage induction generators with capacitor excitation, known as self-excited induction generators (SEIGs), are very popular. This paper presents a review of literature related to the present status of research work on self-excited induction generators (SEIG), their terminal voltage control strategies, and over the past years discussing the classification of induction generators, steady-state and transient analysis, voltage control aspects, and parallel operation of SEIG.

Grey wolf optimizer algorithm for the performance predetermination of variable speed self-excited induction generators

PurposeThis paper aims to apply grey wolf optimizer (GWO) algorithm for steady state analysis of self-excited induction generators (SEIGs) supplying isolated loads.Design/methodology/approachTaking the equivalent circuit of SEIG, the impedances representing the stator, rotor and the connected load are reduced to a single loop impedance in terms of the unknown frequency, magnetizing reactance and core loss resistance for the given rotor speed. This loop impedance is taken as the objective function and minimized using GWO to solve for the unknown parameters. By including the value of the desired voltage as a constraint, the formulated objective function is also extended for estimating the required excitation capacitance.FindingsThe experimental results obtained on a three phase 415 V, 3.5 kW SEIG and the corresponding predetermined performance characteristics agree closely, thereby validating the proposed GWO method. Moreover, a comparative study of GWO with genetic algorithm and particle swarm optimization techniques reveals that GWO exhibits much quicker convergence of the objective function.Originality/valueThe important contributions of this paper are as follows: for the first time, GWO has been introduced for the SEIG performance predetermination and computation of the excitation capacitance for attaining the desired terminal voltage for the given load and speed; the predicted performance accuracy is improved by considering the variable core loss of the SEIG; and GWO does not require derivations of lengthy equations for calculating the SEIG performance.