Excited Induction Generator Research Articles

00/01360 An experimental investigation of self-excitation in capacitor excited induction generators

00/01360 An experimental investigation of self-excitation in capacitor excited induction generators

An experimental investigation of self-excitation in capacitor excited induction generators

Abstract Self-excitation process in induction generators is a complex physical phenomenon, that has been studied extensively in the past. In-depth coverage of methods of steady-state analysis and models for simulation of transients is provided in the existing literature. Reports regarding experimental investigation of dynamics are however much less detailed. Usually, their only purpose is to prove the theoretical concepts. This paper attempts to fill in this gap by providing a purely experimental treatment of the self-excitation process in induction generators. The emphasis is placed on situations that lead to voltage collapse and total demagnetisation of the machine, and on variable speed operation of the induction generator with a fixed capacitor bank. Operation with capacitors connected in star and delta under no-load conditions, connection of the purely resistive load, and connection of the resistive load with short-shunt compensation are elaborated. It is shown that some of the commonly quoted features of a self-excited generator operation do not necessarily hold true, while others are confirmed.

Analysis of parallel-operated self excited induction generators

The paper presents an iterative solution for the problems related to steady state performance of self-excited induction generators operating in parallel. The analysis is based on voltage and current balance equations derived from an inverse-model for the steady state equivalent circuit of induction machines. The nonlinearity in the magnetization characteristics has been taken into account by piecewise linearisation. The proposed method is general and can be applied for analysis of any number of parallel connected machines. Theoretical predictions and experimental results are presented to study different performance characteristics of the system.

Voltage-frequency control of a self-excited induction generator

A new strategy for controlling voltage and frequency of a self excited induction generator (SEIG) is presented. The SEIG operates in the linear region of the core magnetizing curve, so that efficiency and performance are upgraded. An external excitation circuit, comprising permanently connected capacitors and electronically switched inductances is used. The external circuit allows to compensate for the generator reactive demand. A detailed analysis is performed, showing some salient aspects related to the connection of the external excitation circuit on the control performance. Asynchronous switching is used, but some important considerations must be taken into account related to the instantaneous phase angle between stator voltage and external inductor current at the switching instant, if good transient response is desired. Sliding mode controllers are proposed, showing good dynamic response and robust behavior upon changes in load and generator parameters. Computer simulations are used to demonstrate the validity of the proposed scheme.

Voltage stabilization system for induction generator in stand alone mode

A problem of terminal voltage stabilization for self excited induction generator (SEIG) in stand alone mode is studied. Some means of SEIG terminal voltage stabilization implementing different designs of control schemes are observed. A method for tuning of digital control block by using an optimisation technique is proposed. The method is based on looking for minimum of criterion function that is weighted sum of some system' parameters. Factors of control equation have been obtained and computer modelling was done in order to check out system behaviour in different transient modes. Data of experimental investigations of a prototype are given which confirm the results of simulation. An overall method is based on well established theory for the time domain modelling of induction machines and affords to take into account nonlinearities of induction machines and digital control blocks and seems to be reliable and accurate.

Stand Alone Bio-Gas Power Plants with Induction Generator and PWM Voltage Source Inverter

Biogas energy conversion scheme using bio-gas engine driven self excited induction generator as voltage AC source and PWM Voltage Source Inverter (VSI) have been modeled and investigaded. In remote locations where the utility grid doei not exist, stand alone biogas energy conversion scheme can be used to feed local electrical load. Paper presents the mathematical model which enable the direct calculation of the load currents from PWM VSI. The method make use of Laplaces and of the Z-transformation for calculation transient and steady state components of load currents

ANALYSIS OF SELF-EXCITED INDUCTION GENERATORS UNDER UNBALANCED CONDITIONS

This paper presents general mathematical models for various generator-load configurations that accurately determine the conditions for self-excitation and performance characteristics of an isolated, three-phase, self excited induction generator operating under balanced or unbalanced excitation and/or load conditions. The models are derived using symmetrical components theory along with the generator sequence equivalent circuits. The theoretical predictions obtained from the proposed models have been verified experimentally for several balanced and unbalanced configurations.

Transient performance of the self regulated short shunt self excited induction generator

A detailed investigation is carried out on the transient behaviour of the short shunt self-excited induction generator (SEIG) system subjected to different dynamic conditions. An analytical model incorporating the cross-saturation effect has been used to predict the performance of the SEIG. Experimental results are presented along with the simulated values. Response of the system to disturbances reveals excellent transient performance. The system has good overload capability and is free from operational problems related with short circuits and loss of excitation. By presenting typical results of a 3.7 kW, three-phase squirrel cage machine, the suitability of the short shunt SEIG for a simple, rugged and self regulated stand-alone generating system, is established. >

Selection of capacitors for the self regulated short shunt self excited induction generator

The self regulating feature of a self-excited induction generator (SEIG) by connecting additional capacitors is examined. A system consisting of both shunt and series capacitors has been analyzed. A methodology has been explained to choose an appropriate set of values of these capacitors for desired voltage regulation. Performance of short and long shunt configurations has been compared which shows the superiority of the short shunt connection. The results of a detailed investigation on a conventional 3.7 kW induction motor operated as a SEIG are presented to illustrate the effectiveness of the proposed method. Close agreement between predicted and test results has been observed, thereby establishing the validity of the analysis carried out and the criterion adopted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of self excited induction generator feeding induction motor

The paper assesses the suitability of a self excited induction generator (SEIG) to supply dynamic loads like induction motors. An algorithm is proposed to predict the steady state performance of an SEIG feeding an induction motor (IM). The computed and experimental results are presented for different operating conditions of an SEIG-IM system. A good agreement reached between the predicted and test results validate the effectiveness of the proposed algorithm. Experimentally recorded transients of an SEIG during a series of switching operations are presented to demonstrate the ability of an SEIG to sustain the starting of an IM. By analyzing the performance of a typical 7.5 kW, 3-phase SEIG feeding induction motors of different ratings, useful guidelines are proposed for the design of an SEIG-IM system in autonomous applications like agricultural pumpsets.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Parallel Operation of Self-Excited Induction Generators

This paper discusses steady state analysis and performance characteristics of three-phase self excited induction generators operating in parallel arvd supplying a balanced load. It is shown that induction machines with similar or different parameters and speeds can be operated in parallel and their steady state performance characteristics can be accurately predicted using the proposed method. The performance characteristics of such machines are influenced by the excitation capacitance, load resistance as well as speeds and parameters of the individual machines. Typical cases have been investigated for a number of test machines operating in parallel. Predictions of the proposed method have been verified experimentally.

Voltage control of parallel operated self excited induction generators

Two methods of analysis are proposed for use in the control of the common bus voltage of any number of parallel self-excited induction generators (SEIGs) under steady state balanced conditions. The methods are general and can be used for a single SEIG or a group of SEIGs employing similar or different machines with equal or unequal prime mover speeds. Theoretical predictions of the two models have been verified experimentally. Using these methods, effects of various parameters on the voltage control characteristics are examined for a number of cases employing similar and different SEIGs at equal and unequal speeds. >

A step towards improvements in the characteristics of self excited induction generator

Improvements of voltage regulation characteristics of self-excited induction generators (SEIGs) are investigated. Typical results of the sensitivity studies performed are presented and conclusions are drawn to suggest guidelines for design of such generators.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparative study on the performance of a commercially designed induction generator with induction motors operating as self excited induction generators

The paper presents the performance characteristics of different induction machines of various ratings operating as a capacitor self-excited induction generator. Their computed performance is compared with commercially designed line excited induction generators operating as self excited induction generators. An algorithm, using the Newton-Raphson method and steady state equivalent circuit for the machine, is developed to compute the excitation requirement for maintaining a constant terminal voltage at different loads. This technique is also used to compute the number of capacitor steps required to load the machine, from no load to full load, while maintaining terminal voltage within specified limits. The optimum output power of the machine is computed without exceeding the rated stator current for its rated speed. The voltage range within which the machine is expected to operate at or above its rated capacity in stand alone mode, but without being overloaded, is also obtained. The effect of speed on excitation requirements is studied.

A novel self-induced self-regulated single phase induction generator. I. Basic system and theory

This paper describes a newly developed single phase capacitor self excited induction generator with self regulating features, suitable for oil engine driven portable gen-sets for autonomous/standby power generation. The system is also suitable for microhydel and wind energy systems. The generator has two specially designed stator windings in quadrature, connected externally to a shunt and a series capacitor respectively. It employs a standard die-cast squirrel cage rotor. Special features, advantages and theoretical concepts of the system are highlighted. >

Influence of the terminal capacitor on the performance characteristics of a self excited induction generator

The influence of the excitation capacitor on the steady state performance characteristics of an isolated self-excited induction generator feeding a balanced load is examined. It is shown that the terminal capacitor must have its value within a certain range to sustain self-excitation. If the value of the excitation capacitor is outside this range, self-excitation will not be possible. Moreover, if the load impedance is below a certain value, self-excitation will not be achieved irrespective of the value of the excitation capacitor. In the capacitance range where self-excitation is possible, it's value strongly influences the induction generator performance characteristics. The value of capacitance can be selected so that the terminal voltage is constant, regardless of the generator output power. It is further shown that under such condition, the value of capacitance is influenced by the load as well as by the load power factor. The generator performance is however independent of the load power factor and is only affected by the magnitude of the load impedance.

Performance characteristics and optimum utilization of a cage machine as capacitance excited induction generator

The performance characteristics of a cage induction machine operating as a self-excited induction generator (SEIG) in stand-alone mode are presented. A static capacitor bank is considered to self-excite the machine and to maintain its terminal voltage constant. The lagging reactive power requirement of self-excited induction generator is obtained for different load values. The effect of speed on the excitation requirement of the cage machine has also been studied. An algorithm is developed to achieve these characteristics using the Newton-Raphson method and a steady-state equivalent circuit of the machine. The developed analytical technique is extended to evaluate the number of steps of switching capacitors for loading the machine up to its full load rating while maintaining the terminal voltage within desired limits. The selection of an optimum terminal voltage corresponding to the maximum output of the machine for its optimum utilization is also made using single-variable optimization.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Random input generation system based on secondary excited induction generator for isolated small power network.

Random input generation system based on secondary excited induction generator for isolated small power network.

Capacitance Requirements for Isolated Self Excited Induction Generators

Capacitance requirements for isolated self excitd induction generators are discussed. It is shown that numerical methods based upon the steady state as well as operational equivalent circuit give similar predicted values. An analytical method is proposed to compute, Cmin, the minimun capacitance value required for self excitation under no load conditons. It is shown that Cmin is inversely proportional to the square of the speed. Furthermore, it is inversely proportional to the maximum saturated magnetizing reactance. The theoretical results are verified experimentally for a number of test machines and a good agreement is observed between the theoretical and the experimental values. The influence of load impedance and its power factor on the terminal capacitance required to maintain self excitation under steady state is also examined and it is shown that when machine is loaded, the terminal capacitance should be several times that required at no load. Furthermore, the influence of terminal capacitor upon the maximum available output power fron isolated induction generators is also examined.

Stratégie de commande pour un système de conversion de l'énergie éolienne à vitesse variable

Discusses a method of calculating an optimal control strategy for a variable speed wind power generation scheme, incorporating a squirrel cage induction machine, operating in a self excited induction generator mode. This scheme also uses a conventional three phase thyristor rectifier, a line commutated inverter and an economical auxiliary commutated voltage source inverter. The three regulated variables are: drive speed as a function of available mechanical energy by manipulating the resistive torque developed by induction generator; induction motor power consumption during startup of the wind machine of vertical axis type: and operating slip of induction machine, thereby limiting start-up and braking currents. The developed strategy is also suitable for any other variable speed drive system incorporating an induction machine.