Dynamic Voltage Stability Comparison of Thermal and Wind Power Generation with Different Static and Dynamic Load Models

This paper presents a static and dynamic voltage stability analysis of a power network with thermal and wind generation considering static and dynamic load models. The thermal plant was modeled as a synchronous machine and the wind farm as a variable speed induction generator based on a doubly-fed induction generator. The load considered the ZIP, exponential recovery, induction motor, and frequency-dependent load models. The bifurcation points were found by continuation power flow and sensitivity analyses. In addition, dynamic voltage stability assessments were performed considering changes in the moment of inertia and the frequency parameters. All simulations were carried out in a 4-bus power system and using the power system analysis toolbox (PSAT) and MATLAB script code. The results show that the thermal generator had difficulties to maintain stability under dynamic load variations and frequency changes, the wind generator had difficulties to maintain voltage for the load with induction motors, and both generators had difficulties when the moment of inertia is increased

Real time implementation of STATCOM to analyze transient and dynamic characteristics of wind farm

In this paper, a grid connected wind farm with a static synchronous compensator (STATCOM) is modeled in Real Time Digital Simulator (RTDS) environment to analyze its dynamic and transient characteristics in real system. This work is also a part of future power hardware-in-loop (PHIL) test and therefore, individual components are models considering practical viewpoints. Wind turbines and generators of a wind farm, power grid, and control system are realized in the large time-step main network. However, 2-level voltage source converter based STATCOM is modeled in RTDS small time-step environment to adapt with higher switching frequency, where interface transformer is used to link the different time step sub-networks. Suitable control strategy for STATCOM is developed to augment the stability of wind farm considering that capacitor connected at the terminal of wind generator is reduced up to certain percentage. Option for integrating anemometer for dynamic characteristics analysis, difficulties of STATCOM switching schemes for implementing PHIL testing in RTDS environment are discussed. Results are compared with Laboratory standard power system software PSCAD/EMTDC and the advantages of using RTDS in dynamic and transient characteristics analyses of wind farm are also demonstrated clearly

Simultaneous analysis of frequency and voltage control of the interconnected hybrid power system in presence of FACTS devices and demand response scheme

This work confers the simultaneous analysis of voltage and frequency control of the 3-area interconnected hybrid power system (IHPS) consisting of parabolic-trough solar power system (PSP), wind power system (WPS) and dish-stirling solar power system (DSP) under the paradigm of microgrid. The speculated result of the IHPS is presented and analyzed considering real and reactive power as the function of both voltage and frequency. 9The proposed IHPS under investigation has been mathematically modeled for direct coupling like active power-frequency and reactive power-voltage relationships and cross coupling like active power-voltage and reactive power-frequency? relationships. The system responses under different operating conditions have been investigated to see the cross-coupling behavior of the proposed IHPS in the presence of voltage compensating devices like dynamic voltage restorer (DVR) and Static Synchronous Compensator (STATCOM). Further, Demand Response Scheme (DRS) as a frequency control strategy has been considered to enhance the system stability. System responses have been critically analyzed under Mine Blast Algorithm (MBA) based proportional-integral-derivative (PID) controllersThis work was made possible by NPRP grant # [ 13S-0108-20008 ] from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors".Scopu

Integration of wind farms into weak AC grid

Large wind farms are usually located in remote and offshore areas. High voltage transmission systems that have long transmission distances are used to deliver the wind power to main grids. Weak AC grids have high impedance, low short circuit ratio (SCR) and/or low inertia compared to strong AC grids. The voltage stability of weak AC grids is a challenging issue that needs to be considered. This thesis compares weak and strong AC grids based on the voltage stability analysis. The steady-state characteristics of the weak AC grids are investigated. The power transfer characteristics of the wind farms that are connected to weak AC grids are studied under different voltage control technologies. The mitigation of the voltage recovery problems for weak AC grids is proposed by supplementary voltage control. The main characteristics of a weak AC grid are determined using P-V and V-Q curves. Different short circuit levels of the AC grid are presented with an increase in grid load and active power generation. Weak AC grid has a poor voltage stability limit and a low reactive power margin, which make the grid close to voltage instability. A static model is developed to study a test system including wind farm, AC grid, and reactive power compensators. Variable-speed wind turbines are examined under different control modes (power factor control, AC voltage control and reactive power control) using full power converters to increase the limit of transferred wind power to weak AC grids. Reactive power compensators of STATCOM, SVC, and fixed capacitor are compared to the full power converters. The capability of transferring power using STATCOM and SVC is greater than the full power converters. A dynamic model for the wind farm connected to the AC grid is developed and a STATCOM. The AC grid is modelled using two methods: as an ideal voltage source behind a Thevenin impedance and as a synchronous generator. A reactive power versus AC voltage droop is designed in STATCOM. The effectiveness of the STATCOM control is tested to increase the power transferred to the weak AC grids. The new supplementary voltage control is proposed using the full power converters with DC chopper considering three-phase to ground fault. Although the DC chopper is inadequate to keep the transient stability, a fast voltage control of the STATCOM is utilized to support the DC chopper in weak AC grids. The voltage recovery is improved using this controller after fault clearing

Development of PSO Based Control Algorithms for Maximizing Wind Energy Penetration

In this paper, new methodologies have been proposed for attaining the maximum safe instantaneous wind energy penetration. Various types of control algorithms namely, load increase, generation displacement and the combined load increase and generation displacement have been developed to obtain the maximum penetration. Wind Turbine used is DFIG and dynamic model of the system by considering Turbine governor (TG), Automatic voltage regulator (AVR) have been considered. Grid stability at high penetration level is obtained by conducting eigenvalue analysis of the complete power system grid. All the control algorithms are powered by Particle Swarm Optimization Algorithm (PSO) which adjusts the grid parameters for achieving maximum wind penetration. The developed algorithms have been tested with 25-bus, 220kV practical system. The results have shown the maximum safe instantaneous wind energy penetration limit possible by various methodologies proposed

Grid forming converters in renewable energy sources dominated power grid : control strategy, stability, application, and challenges

The renewable energy sources (RESs) dominated power grid is an envisaged infrastructure of the future power system, where the commonly used grid following (GFL) control for grid-tied converters suffers from lacking grid support capability, low stability, etc. Recently, emerging grid forming (GFM) control methods have been proposed to improve the dynamic performance and stability of grid-tied converters. This paper reviews existing GFM control methods for the grid-tied converters and compares them in terms of control structure, grid support capability, fault current limiting, and stability. Considering the impact of fault current limiting strategies, a comprehensive transient stability analysis is provided. In addition, this paper explores the typical applications of GFM converters, such as AC microgrid and offshore wind farm high-voltage direct current (OWF-HVDC) integration systems. Finally, the challenges to the GFM converters in future applications are discussed

Synchrophasor Sensing and Processing Based Smart Grid Security Assessment for Renewable Energy Integration

With the evolution of energy and power systems, the emerging Smart Grid (SG) is mainly featured by distributed renewable energy generations, demand-response control and huge amount of heterogeneous data sources. Widely distributed synchrophasor sensors, such as phasor measurement units (PMUs) and fault disturbance recorders (FDRs), can record multi-modal signals, for power system situational awareness and renewable energy integration. An effective and economical approach is proposed for wide-area security assessment. This approach is based on wavelet analysis for detecting and locating the short-term and long-term faults in SG, using voltage signals collected by distributed synchrophasor sensors. A data-driven approach for fault detection, identification and location is proposed and studied. This approach is based on matching pursuit decomposition (MPD) using Gaussian atom dictionary, hidden Markov model (HMM) of real-time frequency and voltage variation features, and fault contour maps generated by machine learning algorithms in SG systems. In addition, considering the economic issues, the placement optimization of distributed synchrophasor sensors is studied to reduce the number of the sensors without affecting the accuracy and effectiveness of the proposed approach. Furthermore, because the natural hazards is a critical issue for power system security, this approach is studied under different types of faults caused by natural hazards. A fast steady-state approach is proposed for voltage security of power systems with a wind power plant connected. The impedance matrix can be calculated by the voltage and current information collected by the PMUs. Based on the impedance matrix, locations in SG can be identified, where cause the greatest impact on the voltage at the wind power plants point of interconnection. Furthermore, because this dynamic voltage security assessment method relies on time-domain simulations of faults at different locations, the proposed approach is feasible, convenient and effective. Conventionally, wind energy is highly location-dependent. Many desirable wind resources are located in rural areas without direct access to the transmission grid. By connecting MW-scale wind turbines or wind farms to the distributions system of SG, the cost of building long transmission facilities can be avoid and wind power supplied to consumers can be greatly increased. After the effective wide area monitoring (WAM) approach is built, an event-driven control strategy is proposed for renewable energy integration. This approach is based on support vector machine (SVM) predictor and multiple-input and multiple-output (MIMO) model predictive control (MPC) on linear time-invariant (LTI) and linear time-variant (LTV) systems. The voltage condition of the distribution system is predicted by the SVM classifier using synchrophasor measurement data. The controllers equipped with wind turbine generators are triggered by the prediction results. Both transmission level and distribution level are designed based on this proposed approach. Considering economic issues in the power system, a statistical scheduling approach to economic dispatch and energy reserves is proposed. The proposed approach focuses on minimizing the overall power operating cost with considerations of renewable energy uncertainty and power system security. The hybrid power system scheduling is formulated as a convex programming problem to minimize power operating cost, taking considerations of renewable energy generation, power generation-consumption balance and power system security. A genetic algorithm based approach is used for solving the minimization of the power operating cost. In addition, with technology development, it can be predicted that the renewable energy such as wind turbine generators and PV panels will be pervasively located in distribution systems. The distribution system is an unbalanced system, which contains single-phase, two-phase and three-phase loads, and distribution lines. The complex configuration brings a challenge to power flow calculation. A topology analysis based iterative approach is used to solve this problem. In this approach, a self-adaptive topology recognition method is used to analyze the distribution system, and the backward/forward sweep algorithm is used to generate the power flow results. Finally, for the numerical simulations, the IEEE 14-bus, 30-bus, 39-bus and 118-bus systems are studied for fault detection, identification and location. Both transmission level and distribution level models are employed with the proposed control strategy for voltage stability of renewable energy integration. The simulation results demonstrate the effectiveness of the proposed methods. The IEEE 24-bus reliability test system (IEEE-RTS), which is commonly used for evaluating the price stability and reliability of power system, is used as the test bench for verifying and evaluating system performance of the proposed scheduling approach