Grid-connected Induction Generator Research Articles

A Grid Connected Open-End Winding Induction Generator System With Series Compensation

This article presents a new grid connected induction generator (IG) system having open-end stator windings with a series reactive power compensator. The proposed scheme consists of a two-level capacitor fed voltage source inverter (VSI) connected to one side of the stator windings of the IG while the other ends of the windings are directly connected to the grid. A current phasor oriented rotating reference frame based control scheme is developed to control the operation of the VSI to ensure that it compensates the reactive power required by the IG. Thus, the IG system can supply active power to the grid without drawing reactive power from it for excitation. Unlike the shunt compensated IG systems, the proposed scheme does not require an interfacing inductor for connecting to the grid thereby reducing the hardware footprint. The proposed scheme is validated by simulation using PLECS software and the simulation results are presented in the article. A prototype of the system was developed in the laboratory to experimentally verify the proposed scheme and the experimental results are also presented in this article.

Optimal Power Management and Control of Hybrid Photovoltaic-Battery for Grid-Connected Doubly-Fed Induction Generator Based Wind Energy Conversion System

Optimal Power Management and Control of Hybrid Photovoltaic-Battery for Grid-Connected Doubly-Fed Induction Generator Based Wind Energy Conversion System

PSO based controlled six-phase grid connected induction generator for wind energy generation

This paper deals a detailed performance investigation of asymmetrical six-phase grid connected induction generator (GCIG) in two proposed configurations in variable speed operation. During the system development, regulation of DC-link voltage has been proposed using particle swarm optimization (PSO) based PI controller, ensuring the power flow to utility grid through back to back converters. The closed loop operation of asymmetrical six-phase GCIG using indirect field oriented control in different configurations has been carried out in Matlab/Simulink environment. Analytical results have been verified using real time test results on virtual platform of Typhoon HIL supported with some experimental validation.

Performance characteristics and reliability assessment of self‐excited induction generator for wind power generation

The paper presents the performance analysis-based reliability estimation of a self-excited induction generator (SEIG) using the Monte-Carlo simulation (MCS) method with data obtained from a self-excited induction motor operating as a generator. The global acceptance of a SEIG depends on its capability to improve the system's poor voltage regulation and frequency regulation. In the grid-connected induction generator, the magnetizing current is drawn from the grid, making the grid weak. In contrast, in the SEIG stand-alone operation, an external capacitor arrangement is implemented to render the reactive power support. This capacitor arrangement is connected across the stator terminals during the stand-alone configuration of SEIG. The capacitor serves two purposes, which include voltage build-up and power factor improvement. Therefore, the paper deals with obtaining the minimum capacitor value required for SEIG excitation in isolated mode applications, including stand-alone wind power generation. The SEIG performance characteristics have been evaluated for different SEIG parameters. The simulation and experimental results are then compared and found satisfactory. Then, SEIG reliability is estimated considering the MCS method utilizing SEIG excitation's failure and success rates during experimental work in the laboratory. Finally, the SEIG reliability evaluation is performed considering different wind speeds.

Modeling and stability analysis of three- and six-phase asymmetrical grid-connected induction generator

This paper presents the development of linearized model of asymmetrical six-phase grid-connected induction generator (GCIG) for small-signal stability. The developed linearized model has been used to obtain the eigenvalue to evaluate generator stability with respect to parameter variation of the machine in comparison with its three-phase counterpart. During the analysis, suitability of six-phase induction generator for higher output power has been accessed. Instability tendency during low electrical output power can be avoided through closed loop operation of the machine. Hence, the indirect field-oriented control scheme for asymmetrical six-phase GCIG has been proposed for stable operation with higher reliability. The key analytical results have been demonstrated with its experimental validation.

Maximizing the Output Power of Wind-Driven Grid-Connected Cage Induction Generator through Pole and Voltage Control

Objectives: A new cheap wind-driven grid-connected cage induction generator has been used to generate electrical power. The performance of the generator has been ameliorated through multiple change of its number of poles using pole amplitude modulation to comply with the wind speed. The generator stator voltage has been adjusted via voltage controller for better performance. Methodology: Circuit and mathematical models have been developed to represent the generator system. An algorithm has been developed and implemented through computer programs to determine the performance characteristics of the turbine-generator system. The performance has been judged by comparing it by the performance when feeding the generator through a rectifier-inverter set in the stator side, which is costly but leads to a generator with ideal performance. Findings: Complete performance characteristics of the new proposed system have been computed. The obtained results have been used to establish a control protocol to guarantee maximizing the output electrical power. The suggested method has been with those of the case of using a rectifier-inverter set in the stator side to achieve ideal operation of the generator. The comparison has proved that the suggested method, being cheap, is very efficient as the proposed technique led to driving the generator and consequently the wind-turbine at speeds close or equal to those realizing the maximizing tip-speed ratio, which results in extracting the greatest mechanical energy from the wind. The output power applying the presented method closely approaches the output power of the generator when ideally controlled by the aid of a rectifier-inverter set inserted in the stator side. Applications: The very good performance obtained with the suggested control technique besides its low cost encourages its application in case of small and moderate size wind-driven grid-connected induction generator systems. Keywords: Induction Generator, Pole Amplitude Modulation, Wind Energy

Enhancing the Performance of a Wind-Driven Grid-Connected Induction Generator

Objectives: optimizing the performance of wind-driven grid-connected cage induction generators for constant torque, constant mechanical power and constant wind speed conditions. The optimization aimed to maximize the power factor, minimize the total losses, minimize the input reactive power, minimize the output current or maximize the efficiency. Methodology: Closed form formulas for the optimizing slips based on a circuit model having linear parameters have been derived for constant driving torque and constant input mechanical power conditions. Optimizing slips have been derived for many performance indices. Also, computer-implemented algorithms, which scan the performance characteristics of the generator, and determine the optimizing slips, have been developed for the constant torque, constant mechanical power and constant wind-speed conditions. With the aid of these algorithms, the electromagnetic saturation effects have been considered. Closed loop system utilizing micro-controller has been suggested for automatic optimization of the induction generator. Experimental tests have been carried out on a laboratory setup, and the computed results have been compared with the measured ones. Findings: The computed results when compared to the experimental measurements confirm the feasibility of the presented optimization theoretical techniques and the derived formulas. The experimental work assured that the proposed optimization technique is easy to be achieved through simply variation of the applied terminal voltage. Application/Improvements: The presented technique has improved the performance of the induction generator. Thus, it could be used to enhance the performance of small and moderate size wind-driven grid-connected constant speed cage induction generator system. The suggested control technique will enrich utilization of wind energy. Keywords: Induction Generator, Performance Optimization, Wind Energy

Nonlinear Controller with Rotor Crowbar and DC-Chopper Fault Ride Through Technique for Grid-Connected Doubly-Fed Induction Generator

The most significant drawback of the Doubly Fed Induction Generator (DFIG) is its susceptibility to grid fault due to its stator windings being directly connected to the grid. The stator and rotor of the DFIG are electromagnetically coupled, therefore, the resulting stator current surge during low voltage dip provokes inrush current at the delicate back-to-back converters and an overcharge of the DC-link capacitor. In this paper, a robust nonlinear controller, under the context of Lyapunov stability theory, is first employed to control the Rotor and Grid Side Power Converters under normal grid conditions. Under grid fault, the nonlinear controller is then coupled with Active crowbar and DC chopper protection schemes to ameliorate the performance of the DFIG system to ride through fault. Simulation of a 1.5MW wound rotor induction generator under MATLAB/SIMULINK is carried out using the PI-controller (PIC) and Adaptive Backstepping Controller (ABC). Analysis and comparisons are made for different operating scenarios: speed variation, grid fault, grid fault with protection schemes activated.

Fault Analysis of Grid Connected Induction Generator Driven By Wind Power Generation

Fault Analysis of Grid Connected Induction Generator Driven By Wind Power Generation

Adaptive PI Control Strategy for a Self-Excited Induction Generator Driven by a Variable Speed Wind Turbine

In this paper, an adaptive proportional-integral (API) control strategy is developed to extract the maximum power from a variable wind speed turbine and to regulate the DC-link voltage, rotor flux and AC load voltage in a three-phase grid-connected self-excited induction generator (SEIG) system. The resulting controller associated to the flux-oriented control technique can be easily implemented in practice since finite time estimators for the unknown time-varying rotor resistance, rotor flux (nonmeasurable signal) and stator electrical angular position required for the online implementation of the proposed algorithm are provided. Comparative results with a conventional nonadaptive proportional-integral regulator have shown the superiority of the proposed strategy in terms of robustness with respect to online variation of the rotor resistance (up to 100%) and large varying load condition. The computing results are obtained using relatively low wind speed profile. Thus, the generating system with the proposed control strategy is suitable for variable wind speed turbine installation for grid-connected and remote-area power supply where the wind speed profile is relatively low.

Robust direct power control based on the Lyapunov theory of a grid-connected brushless doubly fed induction generator

This paper deals with robust direct power control of a grid-connected brushless doubly-fed induction generator(BDFIG). Using a nonlinear feedback linearization strategy, an attempt is made to improve the desired performances by controlling the generated stator active and reactive power in a linear and decoupled manner. Therefore, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability. Thus, an optimal operation of the BDFIG in sub-synchronous operation is obtained as well as the stator power flows with the possibility of keeping stator power factor at a unity. The proposed method is tested with the Matlab/Simulink software. Simulation results illustrate the performances and the feasibility of the designed control.

A New Robust Decoupled Control of the Stator Active and Reactive Currents for Grid-Connected Doubly-Fed Induction Generators

This paper addresses the grid-connected variable speed doubly-fed induction generator, and proposes a new decoupled control to replace the conventional decoupled active and reactive powers (P-Q) control. The proposed decoupled control is based on decoupling the stator active and reactive currents, in contrast with the conventional decoupled P-Q control, which is based on decoupling the stator active and reactive powers by forcing the stator d- or q-voltage to zero. The proposed decoupled control has all the advantages of the conventional decoupled P-Q control such as constant switching frequency and robustness against slip angle inaccuracy, and it has some additional advantages: The proposed control requires less machine parameters; for the controller design, it requires the stator-to-rotor turns ratio only; for the online calculation, it does not requires any machine parameter. The proposed decoupled control is more flexible and robust since the control is independent of the grid voltage orientation. It is robust against variation in the grid voltage amplitude. Several experiments are carried out using a 1.1 kW doubly-fed induction generator (DFIG), and the results support the proposed decoupled control and demonstrate some of its advantages.

An Energy-efficient Switching Scheme with Reduced Switching Transients for a Wind-driven Induction Generator

This article presents a scheme for improving the power output of grid-connected induction generator commonly used in wind energy conversion systems. Generally, the stator of the induction generator is connected in a star with a line voltage of √3 times the rated winding voltage to reduce the line current and, hence, conductor size. To extend the generating operation over a wider speed range, delta-star switchable stator windings are also in vogue. In such cases, the stator is star connected in the lower speed range and switched to a delta connection above a threshold speed. In this study, a new switching scheme is proposed wherein the stator coils are always connected in a star, while the stator is connected to different voltages in low- and high-speed conditions. At low wind speeds, nominal winding voltage is applied to the stator, whereas at higher speeds, the stator applied voltage is √3 times higher than the rated winding voltage. The efficacy of the scheme is demonstrated experimentally with a suitable microcontroller-based switching arrangement. Typical results indicate an increase in output with reduced switching transients. A case study on a 3-Φ, 50-kW induction generator is presented to emphasize the performance improvement with the proposed scheme.

Sensorless Vector Control of Induction Motors for Wind Energy Applications Using MRAS and ASO

Speed sensorless modes of operation are becoming standard solution in the area of electric drives. This paper presents flux estimator and speed estimator for the speed sensorless vector control of induction motors. The proposed sensorless methods are based on the model reference adaptive system (MRAS) observer and adaptive speed observer (ASO). The proposed speed estimation algorithm can be employed in the power control of grid connected induction generator for wind power applications. Two proposed schemes are verified through computer simulation PSIM and compared their simulation results.

An Insightful Steady-State Performance of a Squirrel Cage Induction Generator Enhanced with STATCOM

Abstract This paper presents the regulation of the terminal voltage and reactive power of a grid-connected squirrel cage induction generator. A shunt connected voltage source inverter (VSI) with a capacitor in the DC side operating as a Static Compensator (STATCOM) and a shunt capacitor are used for regulating the generator terminal voltage and limit the reactive power demand from the grid. Simulation results for steady-state operation for a wide variation of speed in the super-synchronous region are presented as well as the dynamic stability of the system. Closed-form steady-state characteristics equations for the system are used to determine key variables and to demonstrate how the operation of the system depends on various parameters. This characteristics curve which contains all of the equations of the system provides the all in one insightful view to the inherent characteristics of the system and the effect of the parameter variation on the terminal voltage plane.

Optimization of the Performance of a Grid-Connected Induction Generator

Optimization of the Performance of a Grid-Connected Induction Generator

Effect of Modeling of Induction Generator Based Wind Generating Systems on Determining CCT

Transient stability of wind generation system is evaluated in terms of critical clearing time (CCT) of fault. CCT of a wind generation system connected to grid is calculated based on the maximum amount of time that the wind generation system remains connected to grid, without becoming unstable, when the grid is subjected to a fault. In the literature, the wind turbine model has been used for steady state analysis alone, that is, it is used for finding the initial operating mechanical torque output of the turbine. The turbine model is then completely neglected in case of transient stability analysis by assuming constant mechanical torque output for a particular wind speed. This may not be true, as the mechanical torque-speed characteristic of a wind turbine depends not only on the wind speed but also on the slip of the induction generator connected to the wind turbine. This paper explains the necessity of considering the wind turbine model for the transient stability and steady state analysis of grid connected induction generator based wind generation system. A detailed analysis has been done on the effect of various electrical and mechanical factors on CCT determination and the simulation results are presented.

Robust control based on the Lyapunov theory of a grid-connected doubly fed induction generator

This paper discusses the robust control of a grid-connected doubly-fed induction generator (DFIG) controlled by vector control using a nonlinear feedback linearization strategy in order to ameliorate the performances of the control and to govern the developed stator active and reactive power in a linear and decoupled manner, in which an optimal operation of the DFIG in subsynchronous operation is given, as well as the control stator power flow with the possibility of keeping stator power factor at a unity. The use of the state-all-flux induction machine model gives place to a simpler control model. So, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability and the robustness of the parametric variations.

Application of fuzzy logic control algorithm as stator power controller of a grid-connected doubly-fed induction generator

This paper discusses the power outputs control of a grid-connected doubly-fed induction generator (DFIG) for a wind power generation systems. The DFIG structure control has a six diode rectifier and a PWM IGBT converter in order to control the power outputs of the DFIG driven by wind turbine. So, to supply commercially the electrical power to the grid without any problems related to power quality, the active and reactive powers (Ps, Qs) at the stator side of the DFIG are strictly controlled at a required level, which, in this paper, is realized with an optimized fuzzy logic controller based on the grid flux oriented control, which gives an optimal operation of the DFIG in sub-synchronous region, and the control of the stator power flow with the possibility of keeping stator power factor at a unity.

Modeling and Power Quality Improvement of Grid Connected Induction Generators Driven by Turbo-Expanders

Nowadays, the energy crisis has forced the need to recover the energy which is normally wasted in industrial processes. Gas pressure reducing process in city or power plant gas stations is one of these processes in which the energy is wasted. This work is done by turbo-expanders in parallel with gas regulating valves. In electrical industry, these devices drive generators to produce electrical power from the main process. In this paper a model for turbo-expander is presented. This model which utilizes an online calculation method is more efficient and simpler than the older offline model which surmounts the need for making complicated lookup tables prior to calculation. Because of instantaneous varying of domestic consumptions, environment temperature and other effective parameters, turbo-expander inlet gas pressure and mass flow-rate vary with time and consequently the extracted power has time variant specification and causes some power quality issues such as voltage flicker, voltage sag, etc. So, this system is simulated and power quality issues are investigated for a fault occurring at the point of common coupling (PCC). Then, the flicker in electrical waveforms due to change in input pressure or mass flow rate is investigated. Since the power quality problems due to disturbances are considerable, a D-STATCOM is designed and connected at PCC and it is shown that the STATCOM has improved the power quality problems of the system.