Fixed Speed Induction Generator Research Articles

TCSC Application for Transient Stabilization of Wind Turbine with Fixed Speed Induction Generator

Wind turbines (WTs) are a desirable alternative to traditional nonrenewable power resources as a result of recent environmental concerns. Some of them are fixed speed wind generator (FSWG) and have been integrated to power system by squirrel cage induction generator (SCIG). Induction machine absorbs reactive power during all operating conditions, especially at fault condition may result in severe voltage drop which can lead to generator outage. This outage disconnects a significant amount of active power and consequently leads to frequency instability. In order to prevent induction generator (IG) outages in short circuit failures, this paper investigates thyristor-controlled series capacitor (TCSC) device as a candidate solution. TCSC compensates the IG terminal voltage drop by adjusting transmission line impedance at fault condition. In the proposed method, a metaheuristic technique means that shuffled frog leaping algorithm (SFLA) has been utilized to optimize the TCSC controller gains. The proposed scheme can be applied for both SCIGs and wound rotor induction generators (WRIGs) which is another advantage of this method. Single-machine infinite bus system is considered as case study, and various operating conditions and disturbances have been considered to verify the effectiveness of the proposed method.

Enhancement of fault ride-through capability of grid-connected wind farm

The distributed power generation (DPG) at low and medium voltage demands that the renewable generation system is always grid connected during fault condition to ensure the stability of wind power system. The DPG consist of wind turbines (WT) along with fixed speed induction generator (FSIG) does not provide accurate reactive power control and hence, there is need for dedicated compensation. Due to fault condition, the negative sequence component is affected and there is direct impact on DPG with reduction in life expectancy. This paper proposes the application of distributed static compensator (DSTATCOM) for fault ride through (FRT) and reactive power compensation. It has been observed that the compensation of negative sequence component improves the performance of FSIG-based WT. Also, the compensation of positive sequence component avoids the collapsing of voltage and improved the stability of WT. The simulation is done in MATLAB and various tests are considered under fault condition in which results are presented. The FRT enhancement of grid connected WT by using DSTATCOM is 30% and hence, 30% additional wind power is penetrated to the grid.

Hybrid virtual impedance‐based control strategy for DFIG in hybrid wind farm to disperse negative sequence current during network unbalance

When a hybrid wind farm based on doubly fed induction generator (DFIG) and fixed speed induction generator (FSIG) is connected to an unbalanced network, most of the negative sequence current caused by the unbalanced grid will be centralised at the FSIG for its inherent small negative sequence output impedance (NSOI). The centralised negative sequence current can cause significant torque pulsation in the drive train of FSIG, which may go beyond the pressure endurance of the drive train and cause some damages. Meanwhile, losses and risks of overcurrent and grid code violation can also be increased. This study presents a control strategy for DFIG in hybrid wind farm during network unbalance, which can disperse the negative sequence current and the consequent pressure among the three parallel power sources without communication, i.e. among the DFIG stator, the grid side converter (GSC), and the FSIG, rather than centralising the pressure at any of them. In order to achieve this target, a novel hybrid virtual impedance method is proposed to flexibly control the NSOI of the DFIG stator and the GSC from zero to infinity. Theoretical analysis and simulation results are provided to verify the operation performance of the proposed strategy.

SFCL-SMES Control for Power System Transient Stability Enhancement Including SCIG-based Wind Generators

The resolution of the environment pollution depends on renewable energy sources, such as wind energy systems. These systems face transient and voltage stability issues with wind energy employing fixed-speed induction generators to be augmented with resistive type Superconducting Fault Current Limiter (SFCL) and Superconducting Magnetic Energy Storage (SMES) devices. The use of a combined model based on SFCL and SMES for promoting transient and voltage stability of a multi-machine power system considering the fixed-speed induction generators is the primary focus of this study. Our contribution is the development of a new model that combines the advantages of SFCL and SMES. The proposed model functions assure flexible control of reactive power using SMES controller while reducing fault current using superconducting technology-based SFCL. The effectiveness of the proposed combined model is tested on the IEEE11-bus test system applied to the case of a three-phase short circuit fault in one transmission line.

Steady State and Transient Analysis of FSIG and DFIG Integration to Grid for Different Penetration Levels using VSC-HVDC

Among all the Renewable Energy Sources Wind energy is the fastest growing energy source over the last decade mainly due to crucial developments of technology in wind energy. Nowadays, the penetration of wind energy is increasing in many countries in the world including India. The power system stability with large penetration of wind power is a concern for many electrical utilities. The common technical issues with increased penetration of wind energy are voltage and reactive power control, frequency control and Low Voltage Ride Through (LVRT) capability. The VSC-HVDC system with its benefit of independent control of active and reactive power promises to enhance the system stability at high penetration levels. The maximum wind penetration levels in to the grid is analysed for Fixed Speed Induction Generator (FSIG) & Doubly Fed Induction Generator (DFIG). The penetration levels are further enhanced by considering the evacuation of wind power with VSC-HVDC system without losing system stability. Different controllers for VSC-HVDC system are used to improve the stability and LVRT capability. Standard Benchmark System is considered, and the simulations are performed by using power system simulation software SIMPOW. Results shows that wind power evacuated through VSC-HVDC system has better stability and LVRT Capability compared to AC system at high wind penetration levels.

Effects of Fault Current Limiters in Transient Stability Performance of Hybrid Wind Farm

Low voltage ride through capability is an ability of the wind farm to stay connected with grid at the time of disturbance in the power system. The penetration of wind based renewable energy resources is increasing and the low voltage ride through consideration is vital for systems studies. The literature available demonstrates the improvement in low voltage ride through either by using fault current limiters or by implementing a control strategy for induction generator based wind farms. In this paper the low voltage ride through capability enhancement of the fixed speed induction generator is presented with various fault current limiters. The authors have presented the effects of fault current limiters in the aggregated hybrid wind farm consisting the combination of fixed speed induction generators and doubly fed induction generators which is not available in literature so far. A transient fault is simulated using PSCAD/EMTDC software in both the cases and the results are presented and discussed.

Short-Term Voltage Stability Improvement via Dynamic Voltage Support Capability of ESS Devices

Modern power systems are undergoing a steady increase in the loading level and higher penetration of renewables. Induction motor (IM) loads and fixed-speed induction generator (FSIG) based wind turbines (WTs) are broadly used in many power systems. Both IMs and FSIGs draw high amounts of reactive power during large disturbances, which pose major problems for short-term voltage stability (ST-VS). In this paper, the effects of IMs, FSIG-based WTs, and over-excitation limiter (OEL) of synchronous generators on ST-VS are analyzed and illustrated. Then, the use of energy storage systems (ESSs) to provide dynamic voltage support (DVS) to power system during and after large disturbances is investigated, as a countermeasure against short-term voltage instability. To implement ESS's DVS capability, the required power injection by the ESS is dynamically determined and then tracked after the occurrence of a disturbance. The effects of implementing fault ride through and time-overload capabilities of ESS's inverter, on ST-VS of the system, are also analyzed. Optimal power factor adjustment for power injection by ESS, from an ST-VS viewpoint, is discussed as well. It is shown that the DVS capability of an ESS can be effectively used against detrimental effects of IMs, FSIGs, and OELs on ST-VS.

New unified NR power flow algorithm for initialising fixed speed wind generation system with turbine characteristics

Fixed speed induction machine-based wind generators are widely used. Proper initialisation of the models representing fixed speed induction machine-based wind generators connected to grid is of primary concern for stability analysis. The initialisation of fixed speed induction generators (FSIG) has been performed using conventional power flow techniques, but there exists a reactive power mismatch which makes initialisation imprecise. Moreover, turbine characteristics along with control mechanisms are not properly included for initialising the dynamics for stability analysis. A unified Newton–Raphson (NR) method was proposed in literature to include turbine characteristics and control methods for accurate initialisation of FSIG. However, this method creates an extra node for every induction machine causing an increase in the size of the Jacobian and time of execution of power flow algorithm. A new unified-NR method, which does not need an extra node, for initialisation of grid-connected FSIG is proposed in the present work. The proposed unified NR method has been validated on 14-bus, 41-bus, 203-bus, and 1336-bus test systems. The results of the proposed new unified-NR method are compared with existing unified-NR method. The results clearly demonstrate that the proposed method initialisation is accurate with considerably less computational time as compared to existing unified-NR.

Smart Loads for Improving the Fault-Ride-Through Capability of Fixed-Speed Wind Generators in Microgrids

In this paper, the smart load formed by the back-to-back electric springs (ES-B2B) is evaluated for improving the fault-ride through (FRT) capability of the wind turbine generation system with fixed speed induction generator (FSIG) for the first time. The characteristic of the ES-B2B in providing fast reactive power compensation is found to be highly useful in recovering the rotor speed of FSIGs when a fault event occurs. This is a new function in addition to the original function of stabilizing mains voltage against renewable generations. A simple and yet effective controller is then developed for the ES-B2B in order to ensure fast response. The ES-B2B-based smart load and the proposed control have been tested in MATLAB/Simulink and real-time digital simulator to evaluate: 1) the reactive power compensation capability of ES-B2B; 2) the effectiveness of the proposed control of ES-B2B for FRT support; and 3) the comparison of distributed ES-B2Bs with centralized STATCOM in providing distributed FRT support in different grid topologies.

A New Wind Turbine Generating System Model for Balanced and Unbalanced Distribution Systems Load Flow Analysis

Wind turbine generating systems (WTGSs), which are conventionally connected to high voltage transmission networks, have frequently been employed as distributed generation units in today’s distribution networks. In practice, the distribution networks always have unbalanced bus voltages and line currents due to uneven distribution of single or double phase loads over three phases and asymmetry of the lines, etc. Accordingly, in this study, for the load flow analysis of the distribution networks, Conventional Fixed speed Induction Generator (CFIG) based WTGS, one of the most widely used WTGS types, is modelled under unbalanced voltage conditions. The Developed model has active and reactive power expressions in terms of induction machine impedance parameters, terminal voltages and input power. The validity of the Developed model is confirmed with the experimental results obtained in a test system. The results of the slip calculation based phase-domain model (SCP Model), which was previously proposed in the literature for CFIG based WTGSs under unbalanced voltages, are also given for the comparison. Finally, the Developed model and the SCP model are implemented in the load flow analysis of the IEEE 34 bus test system with the CFIG based WTGSs and unbalanced loads. Thus, it is clearly pointed out that the results of the load flow analysis implemented with both models are very close to each other, and the Developed model is computationally more efficient than the SCP model.

An Integrated Electromechanical Model of the Fixed-Speed Induction Generator for Turbine-Grid Interactions Analysis

When wind turbine is connected to the power grid, the turbine-grid interactions restrict its lifespan and produce adverse effects to the grid. Electrical or mechanical oscillations caused by turbine-grid interactions could gradually be weakened or amplified seriously at a certain frequency. This article discusses all types of interactions between a wind turbine and the grid and the influence of the initial operating point, the parallel capacitor, and the series capacitor on the stability of system. Firstly, an integrated dynamic electromechanical model of a single fixed-speed induction generator (FSIG) wind generation system is derived based on the small signal model of each element. Then, a method of stability analysis based on Kharitonov theorem is introduced. Then, the model details the frequency and damping ratio of oscillation mode and classifies those modes' interactions according to participation factors, followed by time domain simulations by the single FSIG generation system to testify the results. Finally, the article studies all the oscillation modes when the initial operating point, the parallel capacitor, or the series capacitor change in the integrated model, which can be verified by Kharitonov polynomials. The indicative findings help to design the damping control to mitigate turbine-grid interactions.

A dynamic strategy to improve the ride-through capability of a fixed speed induction generator

A dynamic strategy to improve the ride-through capability of a fixed speed induction generator

Security region-based small signal stability analysis of power systems with FSIG based wind farm

Based on the Security Region approach, the impact of fixed-speed induction generator based wind farm on the small signal stability of power systems is analyzed. Firstly, the key factors of wind farm on the small signal stability of power systems are analyzed and the parameter space for small signal stability region is formed. Secondly, the small signal stability region of power systems with wind power is established. Thirdly, the corresponding relation between the boundary of SSSR and the dominant oscillation mode is further studied. Results show that the integration of fixed-speed induction generator based wind farm will cause the low frequency oscillation stability of the power system deteriorate. When the output of wind power is high, the oscillation stability of the power system is mainly concerned with the inter-area oscillation mode caused by the integration of the wind farm. Both the active power output and the capacity of reactive power compensation of the wind farm have a significant influence on the SSSR. To improve the oscillation stability of power systems with wind power, it is suggested to reasonably set the reactive power compensation capacity for the wind farm through SSSR.

Output Power Smoothing and Voltage Regulation of a Fixed Speed Wind Generator in the Partial Load Region Using STATCOM and a Pitch Angle Controller

The output power and terminal voltage of the fixed speed induction generator fluctuate in the partial load region where the wind speed is below the rated vale, resulting in fluctuations in the grid frequency and voltage. In this paper, a novel pitch angle control strategy has developed by introducing an exponential moving average (EMA) concept from which the controller reference power (signal) can be set for below-rated wind speeds. Therefore, the employed pitch angle controller together with static synchronous compensator (STATCOM), named the unified voltage and pitch angle controller (UVPC), addresses the objective of smoothing the output power and terminal voltage regulation of a wind generator, subjected to below-rated wind speed variations. Moreover, an interval type-2 fuzzy logic technique has incorporated in the pitch angle controller design, since it is more efficient in handling the uncertainties in membership functions and rules than its traditional fuzzy logic counterparts. Simulation results clearly show that the proposed UVPC effectively smoothens out the generator output power and also regulates the terminal voltage at its constant magnitude.

An optimization methodology of susceptance variation using lead-lag controller for grid connected FSIG based wind generator system

In wind power system, low frequency oscillations are observed due to imbalance between mechanical input and electrical output. Hence, variable susceptance controllers are being adopted to mitigate these oscillations. However, improper modulation of control parameters also leads to system instability. Therefore, we propose an optimization methodology for mitigating low frequency oscillations in wind power generation system. To visualize our methodology, we use a lead-lag type variable susceptance controller for fixed speed induction generator (FSIG) based wind generation system. Then, we optimize gain and time constants of lead-lag controller using three optimization algorithms: particle swarm optimization (PSO), genetic algorithm (GA), and flower pollination algorithm (FPA). Later, we perform non-linear time domain simulation and quantitative analysis to find average fitness, standard deviation, run time, and iteration number for these optimization algorithms. Moreover, non-parametric statistical analysis, such as Kolmogorov–Smirnov and Wilcoxon signed-rank tests are employed for identifying statistically significant differences among these algorithms.

Subsynchronous Torsional Interaction of Wind Farms with FSIG Wind Turbines Connected to LCC-HVDC Lines

High-voltage direct current (HVDC) lines with line-commutated converter (LCC) are being increasingly employed to transmit bulk wind power over long distance. However, this may cause the sub-synchronous torsional interaction (SSTI) between the wind farms and the LCC-HVDC system. The SSTI characteristics of wind farms with fixed-speed induction generator (FSIG) wind turbines connected to LCC-HVDC are investigated in this paper. To simplify the calculations, a modular modeling method is proposed for building the small-signal mathematical model of the investigated system. Small-signal analysis, participation factor analysis, and impact of dominant factors analysis are then applied to investigate the SSTI characteristics under different operating conditions. Three oscillation modes associated with the SSTI are identified in the entire system through small-signal and participation factor analysis, comprising two torsional modes and an electromechanical mode. Impact of dominant factors analysis shows that the system becomes less stable as the wind farm capacity grows and the distance between FSIG wind farm and the rectifier station increases. Moreover, the above analysis suggests that wind farms with FSIG connected to LCC-HVDC lines may not cause unstable SSTI. The electromagnetic transient simulations based on PSCAD/EMTDC (Power Systems Computer-Aided Design/Electromagnetic Transients including DC) verify these results.

Coordinated control of a hybrid wind farm with PMSG and FSIG during asymmetrical grid fault

This paper investigates a coordinated control of a hybrid wind farm with permanent magnet synchronous generator (PMSG)-based and fixed-speed induction generator (FSIG)-based wind turbines during asymmetrical grid fault. According to the boundary conditions of asymmetrical grid fault, the coupling relationship between positive- and negative-sequence grid voltages is presented in detail. Furthermore, the impact of the operation and equivalent impedance of the hybrid wind farm on the grid voltage components during asymmetrical grid fault are analyzed. A coordinated low voltage ride through (LVRT) control strategy for a hybrid wind farm without communication equipments is then developed based on the impact analysis. The proposed strategy supports the grid voltage recovery with the reactive power provided from the PMSG systems. Meanwhile, by using the extra current capacity of the PMSG systems to provide the negative-sequence current, the negative-sequence grid voltage can be suppressed. As a result, performance and output power quality of the FSIG-based wind farm are both improved with the coordinated control of PMSG-based wind farm. Finally, the simulation results of a hybrid wind farm under different asymmetrical grid fault conditions and a phase-phase short circuit fault experimental results of laboratory-scale test rig both validate the proposed coordinated control strategy.

Capacity Configuration and Coordinated Operation of a Hybrid Wind Farm With FSIG-Based and PMSG-Based Wind Farms During Grid Faults

This paper mainly proposes a capacity configuration strategy for a hybrid wind farm with fixed-speed induction generator (FSIG)-based and permanent magnet synchronous generator (PMSG)-based wind farms during grid faults. In this paper, FSIG-based wind farm realizes low voltage ride through (LVRT) with the associated control of nearby PMSG systems as StatComs to provide the required reactive power. By establishing the mathematical model of hybrid wind farm containing network parameters, the operation characteristics of the FSIG-based wind farm during grid faults are analyzed in detail. Based on the characteristics and the critical clearing time of FSIG-based wind farm, a novel capacity configuration method for the hybrid wind farm is proposed to calculate the required reactive power of FSIG-based wind farm for a LVRT operation. Based on the capacity configuration result, the minimum installed capacity of PMSG-based wind farm could be determined. Taking into account the impact of reactive power compensation capacity and grid transmission line parameters, the coordinated LVRT capability of the hybrid wind farm is then analyzed. Finally, simulation and experimental results demonstrate the effectiveness of the proposed capacity configuration method and the coordinated operation performance of the hybrid wind farm respectively.

A Methodology to Synthesize Gearbox and Control Design for Increased Power Production and Blade Root Stress Mitigation in a Small Wind Turbine1

Large wind turbines typically have variable rotor speed capability that increases power production. However, the cost of this technology is more significant for small turbines, which have the highest cost-per-watt of energy produced. This work presents a low-cost system for applications where cost and reliability are of concern. The configuration utilizes the fixed-speed squirrel cage induction generator. It is combined with a variable ratio gearbox (VRG) that is based on the automated-manual automotive transmission. The design is simple, low cost and implements reliable components. The VRG increases efficiency in lower wind speeds through three discrete rotor speeds. In this study, it is implemented with active blades. The contribution of this work is a methodology that synthesizes the selection of the gearbox ratios with the control design. The design objectives increase the power production while mitigating the blade stress. Top-down dynamic programming reduces the computational expense of evaluating the performance of multiple gearbox combinations. The procedure is customizable to the wind conditions at an installation site. A case study is presented to demonstrate the ability of the strategy. It employs a 300 kW wind turbine drivetrain model that simulates power production. Two sets of wind data representing low and high wind speed installation sites were used as the input. The results suggest a VRG can improve energy production by up to 10% when the system operates below the rated wind speed. This is also accompanied by a slight increase in the blade-root stress. When operating above the rated speed, the stress decreases through the optimal selection of gear combinations.

Effect of ECS low‐pass filter timing on grid frequency dynamics of a power network considering wind energy penetration

This study investigates the effect of wind energy penetration on the frequency response of a multi-machine power network considering different time constants of a low-pass filter (LPF) in the DC chopper of an energy capacitor system (ECS). The power network is made up of wind farm composed of fixed speed induction generator interconnected to a steam and hydro synchronous power plants. Heavy and light loads were connected in the system. The ECS is connected at the terminal of the wind turbine. The LPF time constant parameter was varied for different cases considering the same wind speed for the wind turbine. Scenarios with and without considering the synergy of a series dynamic braking resistor (SDBR) connected to the stator of the wind turbine and the ECS were investigated. The results obtained were compared to a case where no frequency control was employed in the power network. Simulations were carried out in power system computer aided design and electromagnetic transient including DC. The results show that a higher time constant of the LPF effectively damp the oscillations of the grid variables and restores quickly the system during network disturbance. The SDBR was used to further enhance the performance of the ECS.