Excitation Capacitance Research Articles

Design and simulation of an RCN Controller to improve steady state behavior of a self-excited induction generator

Self-excited induction generators (SEIG) are gaining importance as compared to conventional generators due to their capability toconvert wind energy into electrical energy for a wide range of variation in operating speed. The performance of such a generator depends upon the load, rotor speed and excitation capacitance. Therefore, depending upon the operating conditions, the output voltage and frequency of this machine goes on changing and this imposes a restriction on its usage. In order to maintain constant voltage and frequency, it need controllers, which make the circuit complicated and also increases the overall cost of power generation. This paper presents a simple controller to regulate the output voltage and frequency of SEIG for variation in its operating conditions due to any change in load, rotor speed and excitation capacitance (R, N, C) and their combination. The controller presented is simple in design, user friendly and is also less expensive, as the elements used in the controller are only resistors, inductors and capacitors. A block of SEIG for steady state operation is also modeled and presented in this paper. SEIG, Controller and other components are modeled and simulated using Matlab/Simulink.

A Method for Balancing a Single-Phase Loaded Three-Phase Induction Generator

When a three-phase induction generator (IG) supplies unbalanced loads, its terminal voltages and line currents are also unbalanced, which may cause the IG to overheat and need to be derated. A single-phase loaded self-excited induction generator (SEIG) works under most unfavorable load unbalance conditions. This paper proposes a three-capacitor circuit scheme and a method to find the values of the self-excitation capacitors that allow the SEIG to be balanced. The SEIG is modeled by a two-port network equivalent circuit that resolves the SEIG into its positive- and negative-sequence circuits associated with the self-excitation capacitors and the load. The network can then be analyzed by common AC circuit analysis techniques. Successful results for balancing the SEIG supplying a single-phase load have been achieved by properly choosing the values of the excitation capacitors. The proposed method has also been validated by experiments on a 0.37 kW SEIG.

Voltage and frequency regulation of aluminium- and copper-rotor SEIGs incorporating proximity effect

Self-excited induction generators (SEIGs) will play an important role in off-grid wind power generation. To advance understanding of the significance and prospects of SEIGs, this paper elucidates the significance of incorporating the proximity effect in the conventional model of self-excited induction generators. The researchers offer an analytical model to incorporate the proximity effect in the rectangular rotor bars of the SEIG. The model’s accuracy relies on a computer program. The calculated results are experimentally verified in the case of two 7.5 hp aluminium- and copper-rotor SEIGs under open-circuit and static loading conditions, through an exclusive qualitative analysis of terminal voltage build-up at no-load, variation in terminal voltage and frequency, as a function of the proximity effect. The paper examines also the voltage regulation, frequency regulation and excitation capacitance requirements of both aluminium- and copper-rotor SEIGs.

GeneticAlgorithm based Analysis of Six-phase Self-excited Induction Generators for Wind Energy Conversion

paper presents the application of genetic algorithm for the analysis of six-phase self-excited induction generators (SPSEIG) by means of series compensation. A new, simple and generalized mathematical model for the steady-state analysis of SPSEIG with series compensation is proposed. The mathematical model is formed directly from the equivalent circuit of SPSEIG using nodal admittance method based on inspection. The proposed model completely avoids lengthy derivations of nonlinear equations which are followed so far. Since the model results in matrix form, inclusion or elimination of any equivalent circuit elements can be carried out easily. Moreover, this model can be used to find any combination of unknown quantities of the equivalent circuit. The matrix equation is solved by Genetic Algorithm (GA) to predict the steady-state performance of SPSEIG with three capacitor excitation configuration such as simple shunt, short shunt and long shunt. Comparative performance evaluation of SPSEIG with simple shunt, short shunt and long shunt configurations is also presented. Computed results are experimentally verified to validate the analytical approach presented in the paper.

Different Self Excitation Techniques for Slip Ring Self Excited Induction Generator

paper discusses the different possible techniques to self excite the slip ring induction machine working as self excited induction generator. The generated voltage due to self excitation is initiated and sustained with constant value of power capacitors connected across the stator windings. Attention is focused on the influence of different techniques on generator voltage and output power capabilities. The generated voltage of the wind driven self - excited induction generator (SEIG) is mainly depending on the wind velocity fluctuations and load variations. By choosing the proper value of the self excitation capacitor banks achieves the reactive power requirements. In case of squirrel cage induction generator only the excitation capacitance at stator is used to achieve the reactive power requirements. But in case of slip ring induction generators with the different self excitation techniques at the rotor are used to achieve the reactive power requirements and improvement in the voltage build up. In previous literature there is no discussion about the different techniques of self excitation and its effects on the induction generator. These are the new methods proposed for the improvement in voltage build up and can also controls the slip. MATLAB/SIMULINK based work is carried out for 3.5kW machine. Proposed methods may be used for low cost variable speed wind energy conversion systems.

Current Control of the Isolated Self-Excited Induction Generator using Shunt Active Filter

The Self Excited Induction Generator (SEIG) is an isolated power source whose terminal voltage and frequency are controlled by the excitation of the capacitance or the load impedance. This paper presents a method for calculating the minimum excitation capacitance using the equivalent circuit approach for analyzing the steady state operation of SEIG. A new strategy based on an active power filter (APF) for controlling the current and power quality of the self excited induction generator (SEIG) is also presented in this paper. The shunt active power filter was implemented using a three phase PWM current controlled voltage source inverter (VSI) and connected to the wind generator and loads in order to compensate the current harmonics and reactive power. The PWM-VSI gate control signals are derived from hysteresis band current controller. The proposed active filter proved to play an important role and give good dynamic response and robust behavior upon changes in load parameters. This investigation demonstrated that power average control strategy can facilitate the improvement of the power quality. The proposed control method extracts fundamental (reference) components of the source current for the shunt active power line conditioners for nonlinear and unbalanced loads. The Power average approach additionally maintains the voltage of the capacitor (of the PWM inverter) nearly constant without any external control circuit. The shunt APF in conjunction with the proposed controller performs perfectly under different steady state and transient conditions. The simulation results with nonlinear loads and unbalanced loads have showed the effectiveness of the proposed scheme for harmonic reduction in Wind based Power Generation.

A reliable and accurate calculation of excitation capacitance value for an induction generator based on interval computation technique

A squirrel cage induction generator (SCIG) offers many advantages for wind energy conversion systems but suffers from poor voltage regulation under varying operating conditions. The value of excitation capacitance (C exct ) is very crucial for the selfexcitation and voltage build-up as well as voltage regulation in SCIG. Precise calculation of the value of C exct is, therefore, of considerable practical importance. Most of the existing calculation methods make use of the steady-state model of the SCIG in conjunction with some numerical iterative method to determine the minimum value of C exct . But this results in over estimation, leading to poor transient dynamics. This paper presents a novel method, which can precisely calculate the value of C exct by taking into account the behavior of the magnetizing inductance during saturation. Interval analysis has been used to solve the equations. In the proposed method, a range of magnetizing inductance values in the saturation region are included in the calculation of C exct , required for the self-excitation of a 3-? induction generator. Mathematical analysis to derive the basic equation and application of interval method is presented. The method also yields the magnetizing inductance value in the saturation region which corresponds to an optimum C exct(min) value. The proposed method is experimentally tested for a 1.1 kW induction generator and has shown improved results.

Direct Voltage Control for a Stand-Alone Wind-Driven Self-Excited Induction Generator With Improved Power Quality

An improved direct voltage control (DVC) strategy is proposed for the control of terminal voltage and frequency of a stand-alone wind-driven self-excited induction generator with variable loads. The DVC strategy, including a proportional-integral (PI) regulator, lead-lag corrector, and a feed-forward compensator, is designed based on the system transfer function matrix. The PI regulator can eliminate the steady-state tracking errors of the terminal voltage. The lead-lag corrector is employed to enlarge the phase stability margin of the dominant loops while the feed-forward compensator is adopted to mitigate the voltage harmonics resulting from the cross-coupling dynamics. The procedures for capacity design of the excitation capacitors, the voltage source inverter, and the consumer load are also presented. The simulation and experimental results verify that the proposed strategy has a fast dynamic response and can effectively control the generated voltage with low harmonic distortions under different linear or nonlinear loads.

Control of Self Excited Induction Generator using ANN based SVC

This paper presents a terminal voltage control of a wind turbine Self Excited Induction Generator (SEIG). The wind turbine induction generator system is proposed to supply an isolated static load under widely varying conditions. The terminal voltage had been regulated by adapting the value of the excitation capacitance from Static VAR Compensator (SVC) using Artificial Neural Network (ANN) controller. The wind turbine operates over a wide range of operating conditions, which means that the terminal voltage of the induction generator is not constant. Changing the value of excitation capacitance by controlling the firing angle of SVC under different operating conditions can handle this problem. It is proved that SVC in the form of Fixed Capacitor -Thyristor Controlled Reactor (FC- TCR) is used not only provide capacitive excitation for the isolated induction generator, but also it controls its terminal voltage at all different loads with variable speeds of the windmill prime-mover. ANN is used for on-line prediction of the suitable firing angles required to control the terminal voltage of the system under different operating conditions.

Analysis, voltage control and experiments on a self excited induction generator

In this paper dynamic analysis, closed loop voltage control and experiments on a self excited induction generator are presented. Electromagnetic torque, active power and reactive power are controlled under dynamic conditions of varied load, excitation capacitance and shaft speed, A closed loop voltage control scheme using a PWM Voltage Source Converter (VSC), dc link capacitor and a P-I voltage controller is proposed and implemented. This scheme generates constant voltage and variable frequency using the converter which also acts as a reactive power compensator. The frequency of stator voltage and current is varied by changing the error proportional gain making it attractive for wind energy conversion system. The simulation is done using MATLAB environment and the experimental results are also presented in this paper.

Enhancement of Measurement Efficiency for Electrical Capacitance Tomography

This paper presents a new sensing method to improve the efficiency of electrical capacitance tomography. Instead of applying one excitation signal to one electrode at a time, the multiple excitation capacitance polling (MECaP) method progressively applies an increasing number of multiple excitations to multiple electrodes and simultaneously measures the capacitance values, thereby significantly increasing the image scanning speed. The performance of a MECaP-based sensor system is numerically simulated and analyzed using the finite element method. Experimental evaluation of the numerical results demonstrates the effectiveness and efficiency of the new sensing technique and its applicability to a broad range of commercial and industrial applications where permittivity determination through capacitance measurement provides an effective means for noninvasive dynamic processes monitoring in an enclosed environment.

An Excitation-Capacitor-Optimized Dual Stator-Winding Induction Generator With the Static Excitation Controller for Wind Power Application

This paper presents an optimal scheme of excitation capacitor to decrease the capacity of static excitation controller (SEC) for dual stator-winding induction generator (DWIG) system applied in wind power generation. The investigations into reactive excitation power released by the excitation capacitor and SEC illustrate that the optimal excitation capacitor is not only related to generator parameters, speed range, and load, but also affected by wind turbine power curve. Based on the objective of minimizing the capacity of SEC, several methods are employed here to select an appropriate excitation capacitor. Through the analysis of DWIG control mechanism and model of SEC in the stator-voltage-orientation synchronous d-q frame, a decoupling control strategy using the space vector modulation is obtained. On the basis of this, the simulation and experimental works from the prototype of 18-kW six/three-phase DWIG wind power system are carried out to verify the optimal scheme. The results demonstrate the correctness and effectiveness of this optimization scheme.

Electronic Load Controller for a Parallel Operated Isolated Asynchronous Generator Feeding Various Loads

This paper presents an investigation on a voltage and frequency controller (VFC), which functions as an improved elec-tronic load controller (IELC) for parallel operated isolated asynchronous generators (IAGs) in an autonomous hydro power generation system. In such type of hydro scheme whole generating system is isolated from the grid and supply electricity to the remote communities. The single point operation of these generators is realized, in such a manner that excitation capacitors, speeds, load, voltage, currents of generators remain constant under various operating conditions. The proposed controller consists of a 3-leg IGBT (Insulated Gate Bipolar Transistor) based voltage source converter (VSC) and a DC chopper with an auxiliary load at the DC bus of the VSC. The IELC controls the reactive and active powers simultaneously for controlling the voltage and frequency under varying consumer loads. Along with voltage and frequency control through single point operation of IAGs driven by uncontrolled pico hydro turbines, the IELC meets the power quality standard an IEEE-519 and it keeps the total harmonic distortion (THD) of the terminal voltage and currents within the limit of 5%. Here the proposed electrical system along with its controller is modeled in MATLAB along with Simulink and PSB (Power System Block-set) toolboxes. Simulation results are presented to demonstrate the capability of proposed controller for an isolated generating system.

Analysis and Investigation of Skew Effect on Behavior and Performance of a Small Scale Three-Phase Self-Excited Induction Generator

This paper presents analysis and investigation of the skew effect on behavior and performance of a three-phase, 220/380V, 8.7/5.0A, Δ/Y connected, 4 poles, 2.2kW self-excited induction generator (SEIG) with different angles rotor skewing. A 2D finite element analysis (2D-FEA) is used to consider core loss, flux density and circuit parameters. Analysis of excitation capacitor values for the SEIG based on a steady-state equivalent circuit model including rotor skew effect is given. Skewed rotor slots with angle of 0° (non-skew), 5° and 10° for the SEIGs are employed. Testing and performance comparisons under steady-state operation with a pure resistive load have been conducted. Obtained results can be guidelines and recommendations for development of effective wind induction generators.

Performance analysis of a simple shunt and series compensated six-phase self-excited induction generator for stand-alone renewable energy generation

This paper describes a new generalized and efficient model for performance analysis of a six-phase self-excited induction generator (SPSEIG) with three capacitor excitation topologies; simple shunt, short shunt and long shunt. Mathematical model of SPSEIG is formulated using nodal admittance method based on graph theory. Attention is focused on the influence of the different capacitor connections on the generator overload and output power capabilities. The generator voltage with simple shunt excitation connection collapses when it is overloaded while with either the short shunt or long shunt excitation connection; generator is able to sustain the load at a lower operating voltage and larger load current. The matrix equation developed by nodal admittance method is solved by Genetic Algorithm (GA) technique to predetermine the steady-state performance of SPSEIG. The experimental and theoretical results are found to be in good agreement.

Design of a Microcontroller Based Electronic Load Controller for a Self Excited Induction Generator Supplying Single-Phase Loads

The generation of electric power using self excited induction generation (SEIG) is a viable option in remote and rural areas where grid electricity is not available. The generated voltage and frequency of these machines, however, varies with varying loads. This characteristic can be resolved either by adjusting the values of the excitation capacitance or by controlling the prime mover speed. Further, in a single-point constant power application, where the machines deliver a fixed amount of power, the electronic load controller (ELC) can be used to switch-in or switch-out a dump load whenever the consumer load decreases or increases respectively. This paper presents a detailed analysis and the design of a microcontroller based SEIG -ELC system intended for stand-alone pico hydro power generation. The simulated performance of the controller is supplemented by experimental results.

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.

Performance analysis of salient-pole self-excited reluctance generators using a simplified model

A simple, direct mathematical model is developed for steady-state analysis of salient-pole, self-excited synchronous reluctance generators. The model does not require either the power consumed by the load or the ratio of the load to excitation current to be estimated which are prerequisite assumptions of previous analysis techniques. The model is verified by experiment which includes assessment of critical speed, excitation capacitance, no-load terminal voltage and voltage regulation on load. The experiments are performed using a prototype synchronous reluctance generator. The analysis technique is then used to investigate the effect that saliency, stator resistance and power factor have on the performance of the self-excited system.

A Novel Unified Approach for the Analysis and Design of Wind-Driven SEIGs Using Nested GAs

A unified procedure for the design optimization and performance predetermination of wind-driven three-phase Self-Excited Induction Generators (SEIGs) has been attempted using Genetic Algorithm (GA) twice, in two nested loops. The outer loop is meant for the calculation of the values of turns per coil of the stator winding and the excitation capacitor which would meet the specified performance constraints of the generator. The inner loop applies the GA tool for the first time, for a straightforward predetermination of these performance quantities. Further, additional schemes such as, switching of the stator connection from delta to star, at times of lower wind speed and short shunt arrangement suitable for lagging power loads, have also been included. Method of estimating the ranges for the variables, required to be given as input data into each of these two loops for the application of GA, has been explained. Experimental results obtained on a test machine and performance values predicted employing Genetic Algorithm, have been shown to agree closely, validating the comprehensive methodology proposed for the first time for the economical design of SEIGs for wind-driven applications.

The Capacity Optimization for the Static Excitation Controller of the Dual-Stator-Winding Induction Generator Operating in a Wide Speed Range

The dual-stator-winding induction generator (DWIG) designed to achieve wide-speed-range operation with reduced capacity of the static power controller is presented. The DWIG consists of a standard squirrel-cage rotor and a stator with two separate windings wound for the same number of poles. This generator has a diode bridge rectifier load connected across to the power winding and a static excitation controller (SEC) to the control winding. Investigations into the reactive power released by the fixed excitation capacitor bank versus rotor speed under various loads represent that the minimal capacity of SEC can be achieved by an appropriate selection of excitation capacitor bank. With the help of instantaneous power theory, the control mechanism for the DWIG system working with a variable rotor speed is analyzed. Moreover, the system control strategy which is fit for the wide-speed-range operation using the stator flux orientation is consequently proposed. An 18-kW DWIG system with a 270-V high voltage DC output is developed. The simulation and experimental results illustrate a desirable performance, and the compact implementation of SEC is obtained.