Review of Literature on Self-Excited Induction Generators and Controllers

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.

Optimization of synchronized frequency and voltage control for a distributed generation system using the Black Widow Optimization algorithm

A distributed generation network could be a hybrid power system that includes wind–diesel power generation based on induction generators (IGs) and synchronous generators (SGs). The main advantage of these systems is the possibility of using renewable energy in their structures. The most important challenge is to design the voltage-control loop with the frequency-control loop to obtain optimal responses for voltage and frequency deviations. In this work, the voltage-control loop is designed by an automatic voltage regulator. A linear model of the hybrid system has also been developed with coordinated voltage and frequency control. Dynamic frequency response and voltage deviations are compared for different load disturbances and different reactive loads. The gains of the SG and the static volt-ampere reactive compensator (SVC) controllers in the IG terminal are calculated using the Black Widow Optimization (BWO) algorithm to insure low frequency and voltage deviations. The BWO optimization algorithm is one of the newest and most powerful optimization methods to have been introduced so far. The results showed that the BWO algorithm has a good speed in solving the proposed objective function. A 22% improvement in time adjustment was observed in the use of an optimal SVC. Also, an 18% improvement was observed in the transitory values.

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

Purpose This paper aims to apply grey wolf optimizer (GWO) algorithm for steady state analysis of self-excited induction generators (SEIGs) supplying isolated loads. Design/methodology/approach Taking 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. Findings The 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/value The 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.

Modeling and Validation of the Switching Techniques Applied to Back-to-Back Power Converter Connected to a DFIG-Based Wind Turbine for Harmonic Analysis

Most power quality problems for electrical grids connected to Doubly-Fed Induction Generators (DFIGs) include flicker, variations of the RMS voltage profile, and injected harmonics because of switching in power converters. These converters have different topologies with the back-to-back (B2B) topology being the most exploited in high-powered three-phase systems. Therefore, in this article a model of a DFIG connected to the B2B power converter is proposed to which different switching techniques are implemented for interharmonic propagation studies. The switching techniques that are implemented include the Sinusoidal PWM (SPWM), the third harmonic injection PWM (THIPWM), and the space vector PWM (SVPWM), to reduce the Total Harmonic Distortion (THD) index of voltage and current in both windings of the machine. MATLAB-Simulink® software is used for modeling and simulating the B2B power converter and the switching techniques. The proposed model is validated with an experimental prototype that includes a 3-kW DFIG, a 10 HP motor, a gear-box with a transmission ratio of 4.5: 1, a B2B power converter, and a three-phase transformer connecting the system to the electrical grid. Finally, it is shown that the results obtained from the experimental tests corroborate the correct operation of the proposed model.

Enhanced Inertial Response Capability of a Variable Wind Energy Conversion System

An inertial response emulated control strategy of doubly-fed induction generators (DFIGs) is able to arrest their frequency decline following a severe frequency event. Nevertheless, the control coefficient is unchanged, so as to limit the benefit potentiality of improving the inertial response capability for various disturbances and provide less of a benefit for boosting the frequency nadir. This paper addresses an enhanced inertial response emulated control scheme for a DFIG to improve the maximum frequency deviation and maximum rate of change of frequency for various disturbances. To this end, the control coefficient is coupled with the system frequency deviation so as to regulate the control coefficient according to the system frequency deviation (i.e., sizes of the disturbance). Results clearly indicate that the proposed inertial response emulated control strategy provides better performance in terms of improving the maximum rate of change of frequency and maximum frequency deviation under various sizes of disturbance and random wind speed conditions.

Transient stability analysis of IEEE 9-bus system integrated with DFIG and SCIG based wind turbines

Electricity is in high demand with a fast-growing population; hence it is advisable to turn towards green energy. In this research, Wind Turbine (WT) is modelled with two different types of induction generators (IGs), which are the Doubly-Fed Induction Generator (DFIG) and Squirrel-Cage Induction Generator (SCIG) and implemented to IEEE 9-Bus system to assess the transient stability. MATLAB/ Simulink R2019a platform was considered to carry the whole examination. DC1A excitation system was applied to Synchronous Generators (SGs) as well as Power System Stabilizer (PSS). The transmission line7-5 was found to suffer from a high peak value of a relative power angle of approximately 130 degrees. As for the settling time, without PSS it was 20.69 s and with PSS it became 6.23 s. A wind farm with a rated capacity of 60 MW was used in the system. WT integrated with DFIG has the lowest peak value of 127 degrees at Bus locations 4 and 5 and for SCIG, Bus 5 with a peak value of 136 degrees. Thus, it can be propelled as the perfect location. Moreover, this is due to the three-phase fault was located at the transmission line7-5 which is far away from Buses 4 and 5. In the end, the WT integrated with DFIG provides a lower peak value of relative power angle compared to SCIG, whereas for settling time, it is the opposite.

An Improved Droop Control Scheme of a Doubly-Fed Induction Generator for Various Disturbances

Doubly-fed induction generators (DFIGs) participate in the system frequency regulation using a fixed-coefficient droop control scheme. Nevertheless, the frequency-supporting capability of this control scheme with fixed gain is limited for different disturbances. This paper suggests an improved droop control scheme for a DFIG that can both alleviate the frequency nadir and maximum rate of change of frequency (ROCOF) during the frequency regulation. To achieve this, an adaptive droop control coefficient based on the ROCOF is suggested. The proposed droop control coefficient is a linear function of the ROCOF. Therefore, the proposed scheme can adjust the control coefficient according to the varying ROCOF. Simulation results clearly demonstrate that the proposed droop control scheme shows better effectiveness in improving the maximum ROCOF and frequency nadir under various sizes of disturbance, even in a varying wind speed.