Excitation Capacitance Research Articles

Experimental Analysis of Harmonic Distortion in Isolated Induction Generators

The use of induction generator, replacing the continuous and synchronous generators, has proved to be an interesting solution for the supply of electricity in remote areas where the supply through a distribution network is not economically viable. In some cases the use of this machine type is appropriate in these areas, with the same associated with non-conventional systems of electricity, such as wind and hydro generation small. In these isolated systems is common to use cage induction generators with excitation capacitors, known as self excited induction generators. Allied to this, there has been an increase in the number of non-linear loads, at all levels of electricity consumption. Thus, it becomes necessary to study experimentally the harmonic distortion of voltage and current in this type of generator, which can supply non-linear loads that may be present in these remote areas.

A Single-Sensor-Based MPPT Controller for Wind-Driven Induction Generators Supplying DC Microgrid

In this paper, a simple method of tracking the maximum power (MP) available in the wind energy conversion system (WECS) for dc microgrid application is proposed. A three-phase diode bridge rectifier along with a dc–dc converter has been employed between the terminals of a wind-driven induction generator and dc microgrid. Induction generator is being operated in self-excited mode with excitation capacitor at stator. The output current of the dc–dc converter, i.e., dc-grid current is considered as a control variable to track the MP in the proposed WECS. Thus, the proposed algorithm for maximum power point tracking (MPPT) is independent of the machine and wind-turbine parameters. This algorithm has been implemented using dsPIC30F4011 controller. Furthermore, a method has been developed for determining the duty ratio of the dc–dc converter for operating the proposed system in MPPT condition using wind-turbine characteristics, steady-state equivalent circuit of a induction generator, and power balance in power converters. Circuit simplicity and simple control algorithm are the major advantages of the proposed configuration for supplying power to the dc microgrid from the proposed small-scale WECS. The successful working of the proposed algorithm for MPPT has been demonstrated with extensive experimental results along with the simulated values.

Performance of synchronous reluctance generator for DG set based standalone supply system

This paper presents the performance of a SyRG (Synchronous Reluctance Generator) for DG (Diesel Engine Driven Generator) set based standalone generating system. A STATCOM (Static Compensator) is used for its voltage control, harmonics reduction and load balancing on a SyRG based DG set. The proposed system consists of a diesel engine driven specially designed SyRG with a rating of 3-phase, 3.7kW, 50Hz, 4-pole, 230V line voltage SyRG, an excitation capacitor bank of 6.25kVAr and a STATCOM of 5kVA. The modified PBT (Power Balance Theory) based control algorithm is used to estimate the reference source currents for control of STATCOM. A DSP (dSPACE) is used to implement this control algorithm of STATCOM. The performance of the proposed system is studied using STATCOM which improves the performance by exchanging the reactive power with the system. The source of reactive power is a capacitor bank and VSC (Voltage Source Converter) with a DC link capacitor used as STATCOM. The gating signals of VSC of the STATCOM are generated using PBT based control algorithm. The energy stored in the DC link is exchanged with the system to eliminate harmonics, voltage regulation and load balancing. The performance of the SyRG based standalone DG system is observed under a linear load of 3.19kW with power factor of 0.8 and a nonlinear load of 2.99kW under both balanced and unbalanced conditions. The proposed system has maintained fixed terminal voltage at 220V, voltage and current harmonics within 5% under highly nonlinear load and balanced source currents under highly unbalanced load currents.

Analysis of self-excitation and performance characteristics of a single-phase self-excited induction generator by field-circuit method

Purpose – The purpose of this paper is to present analysis of an influence of rotor slots opening on self-excitation process, terminal voltage and performance characteristics of the single-phase self-excited induction generator (SPSEIG). Design/methodology/approach – The paper presents field analysis of the self-excitation problem in the SPSEIG and performance characteristics on the base of two-dimensional field-circuit model of the generator. Findings – The carried out field computations of the tested SPSEIG with closed rotor slots showed that only an initial voltage across the excitation capacitor of about nominal value (230 V) causes successful self-excitation of the generator. It was also proved that the suitable opening of the rotor slots, beside remnant flux density in the rotor core, facilitates self-excitation in the generator. Since in working applications initially charging of the capacitor to almost nominal voltage may cause a problem, therefore employment of semi-closed rotor slots in the SPSEIG would be proper solution. Originality/value – The conducted simulations, validated by laboratory tests showed that not only suitable excitation capacitor capacitance and rotor speed are needed to obtain desired terminal voltage of the generator, but also suitable initial voltage across the capacitor in auxiliary stator winding is very important and necessary for reliable self-excitation of the single-phase induction generator with closed rotor slots. The employment of semi-closed rotor slots in the SPSEIG makes the self-excitation more effective.

Analysis and control of capacitor‐excited induction generators connected to a micro‐grid through power electronic converters

A system consisting of a capacitor-excited induction generator (CEIG) with associated power electronic converters has been developed for supplying power to a micro-grid. The power fed to the grid from the CEIG is controlled using a diode bridge rectifier (DBR) and a pulse width modulated (PWM) inverter, connected between the generator terminals and the grid. A simple analog based hysteresis current control (HCC) technique has been employed in which the current control of the PWM inverter alone needs to be carried out by sensing the current and voltage at the grid terminals. The successful working of the system has been demonstrated for three different patterns of feeding power to a micro-grid, by experiments conducted on a three-phase 230 V, 3.7 kW CEIG, with a 100 µF delta connected excitation capacitor bank and employing the controllers fabricated in the laboratory. The grid power is represented as an equivalent load resistance in the steady-state equivalent circuit of the CEIG and the technique of genetic algorithm (GA) has been adopted for the analysis of the proposed system. The predetermined performance characteristics of the system and the results of Matlab/Simulink simulation studies have also been presented.

English

The depletion of fossil fuels in the world, has given rise to the importance of non-conventional energy sources. Wind turbines and micro hydro generators with induction generators are considered as an alternative choice. Wind turbines with Self-excited Induction Generators (SEIGs) are increasingly being used to generate clean renewable energy. SEIGs are widely being used in isolated areas (rural areas) to generate electrical energy. Capacitor banks are used with a purpose to provide reactive power for its excitation. The nonlinearity of the magnetizing inductance and the varying rotor speeds necessitates the calculation of excitation capacitance required for voltage build up in a SEIG. This paper presents the various approaches for determining the excitation capacitance and evaluates the value of excitation capacitor for 220/380V, 12.4/7.2A, 4 pole, 50Hz induction machine through various approaches, to build-up voltage for isolated operation of a self-excited induction generator.

Models to investigate the performance of self-excited induction generator under switching operations

The performance of self-excited induction generator can be analysed by applying switching operations in terms of variation in load resistance, excitation capacitance and rotor speed on steady state and transient models of self-excited induction generator. To investigate the effects of these switching variations, models are simulated in Matlab/Simulink and results hence obtained are validated experimentally on two test machines. The effect of disturbance due to these switching operations, on performance of machine is also discussed in this paper, which will be helpful to the researchers in designing various controllers both for transient state and steady state of same machine.

Minimising losses of SEIG using constrained particle swarm optimisation considering voltage regulation

Induction generators are widely used in various applications since they offer distinct advantages over conventional synchronous machines, like a simplified design, installation at lower capital cost and substantial savings in operation and maintenance expenses. The wind turbine induction generator systems are proposed to supply isolated loads under widely varying conditions. These conditions are the wind speed and load variations. Under these varying conditions, there will be some changes in the terminal generated voltage. The terminal voltage can be regulated by adapting the value of excitation capacitance required for the induction generator. This paper presents a constrained particle swarm optimisation technique for minimising the power losses of self–excited induction generator with terminal voltage control under operating conditions by selecting the suitable capacitance required for generator excitation. Testing of the proposed technique over conventional particle swarm optimisation technique is performed. Results signify the supremacy of the proposed technique over conventional particle swarm optimisation technique.

Parameter Design and Static Performance of Dual Stator-Winding Induction Generator Variable Frequency AC Generating System With Inductive and Capacitive Loads

In this paper, the design methods of the auxiliary excitation capacitors and the filter inductances are investigated for the dual stator-winding induction generator (DWIG) variable frequency ac (VFAC) generating system with inductive and capacitive loads, and the system static performance is presented as well. For this generating system, the proper selection of the auxiliary excitation capacitors and the filter inductances can minimize the reactive power capacity of the control winding, reduce the capacity of the static excitation converter (SEC) and improve the system static performance of the output voltage. The corresponding design principles and methods are proposed based on the change law of the control-winding reactive power and the requirements of the control-winding current. The experimental results show that the proposed design methods are correct and valid, and the DWIG VFAC generating system has a good static performance with the minimum-capacity control-winding reactive power and a compact-size SEC.

Coordination Control of an AC-to-DC Converter and a Switched Excitation Capacitor Bank for an Autonomous Self-Excited Induction Generator in Renewable-Energy Systems

This paper proposes a novel coordination control scheme for effectively controlling an ac-to-dc converter and a switched excitation capacitor bank of an autonomous self-excited induction generator (SEIG) using a digital signal processor. The aim of the proposed control scheme is to maintain the dc voltage at the output terminals of the ac-to-dc converter under various operating conditions. A three-phase system model is established to simulate the dynamic performance of the studied system. The experimental results based on a laboratory 2.2-kW induction generator driven by a brushless dc motor are also carried out. It can be concluded from the simulated and experimental results that the proposed coordination control scheme can be applied to various SEIG-based renewable-energy systems based by maintaining the output dc voltage of the ac-to-dc converter under different operating conditions.

Optimisation of voltage and frequency regulation in an isolated wind-driven six-phase self-excited induction generator

This paper presents a constant voltage operation of a Six-Phase Self-Excited Induction Generator (SPSEIG) driven by a fixed speed wind turbine using an Ant colony optimisation (ACO) technique to predict the behaviour of a the machine. In this paper, an attempt has been made to estimate the excitation capacitance requirements of a SPSEIG for maintaining rated terminal voltage and frequency. The range of capacitance variation required for maintaining constant terminal voltage while supplying a load of variable magnitude is evaluated. Analytical approaches, suitable for all the configurations of shunt capacitances such as variable excitation capacitance connected across (i) single three-phase winding set only and (ii) both the three-phase winding sets of an SPSEIG for operation as a simple shunt on no load and pure resistive load, are presented. The mathematical model developed is based on loop impedance method using graph theory. It is shown that the proposed technique is very effective and useful for making the SPSEIG feasible for remote areas with wind potential. The proposed approach is tested and compared with Genetic Algorithm (GA) and Fmincon technique.

Adaptive voltage regulation of self excited induction generator using FACTS controllers

This paper introduces an adaptive terminal voltage regulation of a standalone self excited induction generator using flexible AC transmission systems (FACTS). FACTS in the form of static VAR compensator (SVC) is introduced. SVC is used to regulate the terminal voltage of self excited induction generator-based (SEIG) wind generator working with variable speed and load. Since, the wind generator operates over a wide range of operating conditions; the terminal voltage of the induction generator is not regulated. This terminal voltage is controlled by adapting the value of the excitation capacitance of SVC using artificial neural networks (ANN) and adaptive neuro-fuzzy inference systems (ANFIS). Changing the excitation capacitance is performed by controlling the firing angle of SVC under different operating conditions to control the terminal voltage. A mathematical model of SEIG with variable load and speed along with SVC is developed and simulated in MATLAB to get the excitation capacitance required for voltage control. Simulation results are used to train both ANN and ANFIS for on-line prediction of the suitable firing angles required to control the terminal voltage of the system under these operating conditions. Results signify the supremacy of ANFIS over ANN in terms of performance measures.

A New Electronic Load Controller for the Self-excited Induction Generator to Decrease Stator Winding Stress

Constant voltage and frequency can be generated by a Self-Excited Induction Generator (SEIG) driven with a fixed-speed low-head hydro-turbine when a constant electrical load is maintained by an Electronic Load Controller (ELC). In the Conventional-ELC (C-ELC), usually a chopper with a dump load is used in parallel with the consumer loads to provide regulation of voltage and control of frequency. In the C-ELC configuration a high degree of stress can be experienced by stator windings and excitation capacitors resulting from chopper operation, since in each chopping period the dump load is connected to the stator winding for a short period then disconnected. A new ELC topology is proposed to reduce this stress. Compared with the C-ELC, the main dump load has been divided into two separated parts. A part of the dump load can be connected in parallel with the consumer loads, resulting in less variation in the total load seen by the SEIG and less stress on the stator windings and excitation capacitors. This proposed topology can be utilized per-phase using bi-directional power switches, hence it can operate with unbalanced consumer loads. Simulation results demonstrate that even with unbalanced three-phase loads (assisted with bi-directional switches per-phase), the proposed topology has the capability to regulate voltage from no-load to full load. Moreover, the Total Harmonic Distortion (THD) analysis for output (stator) current shows a 9% improvement compared with the most recent results in the literature.

Backstepping control of DFIG generators for wide-range variable-speed wind turbines

In this paper, we have presented a general study of self excited induction generator used in isolated renewable energy conversion source. Tthe behaviour of generated voltage under variable load, rotor speed and excitation capacitance is presented. Also, we have proposed a robust controller suitable in order to control the terminal DC voltage under different speed and AC load conditions for supplied an isolated DC load. The experimental characteristic curve of the generator and simulation result of proposed control scheme are presented.

STATCOM-based voltage and frequency regulator for stand-alone asynchronous generator

This paper presents a STATCOM-based voltage and frequency regulation for stand-alone asynchronous generator feeding linear and nonlinear loads. The SEIG have inherent poor voltage and frequency regulation. The voltage and frequency depend upon the load current and power factor of the load with fixed excitation capacitor employing unregulated turbines. The changing consumer load requires variable reactive power compensation for excitation requirement. Consumer load contains harmonics and performance of SEIG is largely affected by these load harmonics. A current controlled voltage source inverter working as STATCOM is used for harmonic elimination, load balancing and variable reactive power compensation. A DC chopper with dump load is connected across DC bus capacitor to regulate varying consumer load. The control algorithm has been first co-simulated with processor in the loop (PIL) and then experimentally validated. The transient behaviour of developed prototype system for application and removal of balanced, unbalanced, nonlinear load is investigated.

Survey and Performance Evaluation of Jamgodrani Hills and Nagda Hill Wind Farm in Madhya Pradesh, India – A Case Study

Today, most of the electricity generated comes from fossil fuels (coal, oil, and natural gas). These fossil fuels have finite reserves and will run out in the future. The negative effect of these fossil fuels is that they produce pollutant gases when they are burned in the process to generate electricity. Fossil fuels are a non-renewable energy source. However, renewable energy resources (solar, wind, hydro, biomass, geothermal and ocean) are constantly replaced, hence will not run out, and are usually less polluting. Due to an increase in greenhouse gas emissions more attention is being given to renewable energy. As wind is a renewable energy it is a clean and abundant resource that can produce electricity with virtually no pollutant gas emission. Induction generators are widely used for wind powered electric generation, especially in remote and isolated areas, because they do not need an external power supply to produce the excitation magnetic field. Furthermore, induction generators have more advantages such as cost, reduced maintenance, rugged and simple construction, brushless rotor (squirrel cage) and so on. This paper presents the detailed survey on performance of wind farms situated at Jamgodrani hills and Nagda hill, near Dewas city in Madhya Pradesh, India. Variation of various performance indices such as total yearly generation, total availability of grid, total availability of wind generator, total generating units per wind generator and capacity utilization factor is discussed for wind farm on Jamgodrani hills and Nagda hill respectively.Latter, it introduces a simple and direct formula based on complex impedance matrix method to calculate the minimum excitation capacitance (Cmin) and corresponding maximum frequency (fmax)required for successful voltage build up across the terminal of three phase dual winding induction generator when operating on 225kW rating, used as wind generator in wind farm and variation of minimum excitation capacitance as well as corresponding maximum frequency is also being plotted for various conditions of load and speed.

Design and Implementation of a Prototype Underwater Turbine Generator System for Renewable Microhydro Power Energy

This paper presents the installation and field measurements of a prototype microhydro power (MHP) generation system based on an underwater turbine generator. The studied MHP system employs the energy of flowing water in the agricultural irrigation of one of the irrigation ditches of the Yunlin Farmland Irrigation Association, Taiwan. The irrigation ditches are basically used for distributing irrigation water to different farmlands. To design the prototype, the MHP unit has to meet practical conditions of the selected ditch such as depth, width, water flow rate, total days of water flowing in a year, etc. The designed MHP unit consists of an underwater turbine, a gearbox, a three-phase self-excited induction generator with a switchable excitation capacitor bank, a three-phase diode bridge rectifier, a dc-to-dc buck converter, and a dc-to-ac inverter. A monitoring and control system based on an embedded system is also designed to measure the electrical data of the MHP unit.

Conditions for stable joint operation of asynchronous machines of different types in an autonomous electromechanical system

To ensure stable joint operation of asynchronous machines in an autonomous system under extreme conditions, separation of excitation capacitances and their distribution between branches of a unified electric circuit that are separate for the motor and the generator and not interrelated by the condition of the voltage resonance are proposed using an isolated induction generator with internal capacitive excitation.

Voltage and Frequency Control of Wind Driven Stand-Alone Self-Excited Induction Generator Using DCMLC Based STATCOM

This paper describe the methods employed to control voltage and frequency of a 3-O stand-alone self-excited induction generator (SEIG) driven by a variable speed wind turbine. An attempt made to control the terminal voltage of SEIG by using a 3-O diode clamped multilevel converter (DCMLC) based STATCOM operation. A 3-O diode bridge rectifier with a d.c chopper circuit is employed to control the frequency of generated voltage. The VAr required by the load and the machine owing to changes in magnetizing reactance’s are compensated by DCMLC–STATCOM operate with full load excitation capacitance. To emphasis the controller characteristics, mathematical model of the controller is developed and implemented in MATLAB / SIMULINK software.

Dynamic behavior of a single-phase self-excited induction generator using a three-phase machine feeding single-phase dynamic load

This paper is motivated to analyze the transient behavior of a single-phase self-excited induction generator (SEIG) using a three-phase machine due to switching of single-phase dynamic load like induction motors. The generator consists of a three-phase star connected induction machine excited with three-capacitors and a single-phase induction motor (IM) load. The developed dynamic models of the SEIG and the motor are based on stationary reference frame d–q axes theory incorporating the effect of cross-saturation in the magnetic circuit of the machine and the equations of excitation capacitors are described by three-phase abc model. The system suffers from heavy transients during switching of induction motor and becomes unstable. These problems may be due to resonance caused by series capacitors and the inductive motor load. The use of damping resistors across one series capacitor is proposed to damp out the starting transients for the stable operation. The motor can be started up successfully using the damping resistor. The variation of the damping resistance with the increase in load on the motor after successful starting to maintain constant terminal voltage has been presented. The eigenvalue technique is also employed to examine the transient conditions in the studied SEIG-IM system. The simulated and experimental results are presented for both the unsuccessful and successful starting of the motor. These results are in close agreement with each other, which show the effectiveness of the approach.