Wind Power Integration into Power Systems: Stability and Control Aspects

Power network operators are rapidly incorporating wind power generation into their power grids to meet the widely accepted carbon neutrality targets and facilitate the transition from conventional fossil-fuel energy sources to clean and low-carbon renewable energy sources. Complex stability issues, such as frequency, voltage, and oscillatory instability, are frequently reported in the power grids of many countries and regions (e.g., Germany, Denmark, Ireland, and South Australia) due to the substantially increased wind power generation. Control techniques, such as virtual/emulated inertia and damping controls, could be developed to address these stability issues, and additional devices, such as energy storage systems, can also be deployed to mitigate the adverse impact of high wind power generation on various system stability problems. Moreover, other wind power integration aspects, such as capacity planning and the short- and long-term forecasting of wind power generation, also require careful attention to ensure grid security and reliability. This book includes fourteen novel research articles published in this Energies Special Issue on Wind Power Integration into Power Systems: Stability and Control Aspects, with topics ranging from stability and control to system capacity planning and forecasting

Stability analysis of VSCs connected to an AC grid

As a typical renewable energy resource, wind power has been extensively exploited in the past years. With the continuous growth of wind power installed capacity, power electronic devices are widely used due to their good control performances. However, the interaction between power electronic devices and the power grid will lead to power system stability problems. Subsynchronous interaction (SSI) between wind farms and AC grids, as one of the most severe power system stability problems, has aroused great concerns. Different from the SSI between wind turbine generator (WTG) controllers and fixed series compensation or between generators and high voltage direct current (HVDC) controllers, recently, a new type of SSI is detected which is caused by the interactions between power electronic devices of WTGs and weak AC grid. The work in this thesis focuses on the mechanism and characteristics of this new type of SSI. A simplified system model with permanent magnet synchronous motors (PMSGs) connected to weak AC grids is established to investigate the new SSI. The linear impedance model of the studied system is conducted. The correctness of the proposed impedance model is validated by the comparison between the analysis in MATLAB and time-domain simulations in PSCAD/EMTDC. In the model of a single VSC connected to an AC grid, the mechanism of the SSI is investigated. The characteristics of the studied system under various conditions are analysed. The effects on system stability of different factors have been studied including the number of connected WTGs line reactance, Phase-locked loop (PLL), feed-forward voltage low-pass filter, current loop and outer loop of the VSCs. Time-domain simulation results verify the correctness of the analysis. An equivalent model of multiple VSCs connected to an AC grid is presented to investigate the characteristics when VSCs with different control systems and control parameters are connected to an AC grid. A new approach based on the Generalised Nyquist Criterion (GNC) is proposed to analyse the system stability. Compared to the existing traditional criteria, the new criterion has the advantages of better accuracy and simplicity. The new approach is validated in time-domain simulation. The study of this research work contributes to the stability analysis of power systems in the subsynchronous frequenc

Reduction of torsional vibrations due to electromechanical interaction in aircraft systems

With the growth of electrical power onboard aircraft, the interaction between the electrical systems and the engine will become significant. Moreover, since the drivetrain has a flexible shaft, higher load connections can excite torsional vibrations on the aircraft drivetrain. These vibrations can break the shaft if the torque induced is higher than the designed value, or reduce its lifespan if the excitation is constant. To avoid these problems, the electromechanical interaction between the electrical power system and the drivetrain must be evaluated. Past studies have identified the electromechanical interaction and introduced experimental setups that allow its study. However, strategies to reduce the excitation of the torsional vibrations have not been presented. This thesis aims to analyse the electromechanical interaction in aircraft systems and develop an advanced electrical power management system (PMS) to mitigate its effects. The PMS introduces strategies based on the load timing requirements, which are built on the open loop Posicast compensator. The strategies referred as Single Level Multi-edge Switching Loads (SLME), Multilevel Loading (MLL), and Multi-load Single Level Multi-edge Switching Loads (MSLME) are applied to different loads, such as pulsating loads, ice protection system, and time-critical loads, such as the control surfaces. The Posicast based strategies, eliminate the torsional vibrations after a switching event, by the addition of zeros that cancel the poles of the system. For this reason, the knowledge of the natural frequencies of the mechanical system is necessary. Experimentally, the system parameters are obtained through Fourier analysis of the step response and the strategies are applied. A robust analysis of the strategies allows the establishment of the range of uncertainty on the frequencies that allow the proper operation of the strategies. Simulation and experimental results show that the torsional vibrations can be reduced to values close to zero by the application of the strategy. Therefore, the PMS mitigates the electromechanical interaction between the electrical power system and the aircraft drivetrain

Reduction of torsional vibrations due to electromechanical interaction in aircraft systems

With the growth of electrical power onboard aircraft, the interaction between the electrical systems and the engine will become significant. Moreover, since the drivetrain has a flexible shaft, higher load connections can excite torsional vibrations on the aircraft drivetrain. These vibrations can break the shaft if the torque induced is higher than the designed value, or reduce its lifespan if the excitation is constant. To avoid these problems, the electromechanical interaction between the electrical power system and the drivetrain must be evaluated. Past studies have identified the electromechanical interaction and introduced experimental setups that allow its study. However, strategies to reduce the excitation of the torsional vibrations have not been presented. This thesis aims to analyse the electromechanical interaction in aircraft systems and develop an advanced electrical power management system (PMS) to mitigate its effects. The PMS introduces strategies based on the load timing requirements, which are built on the open loop Posicast compensator. The strategies referred as Single Level Multi-edge Switching Loads (SLME), Multilevel Loading (MLL), and Multi-load Single Level Multi-edge Switching Loads (MSLME) are applied to different loads, such as pulsating loads, ice protection system, and time-critical loads, such as the control surfaces. The Posicast based strategies, eliminate the torsional vibrations after a switching event, by the addition of zeros that cancel the poles of the system. For this reason, the knowledge of the natural frequencies of the mechanical system is necessary. Experimentally, the system parameters are obtained through Fourier analysis of the step response and the strategies are applied. A robust analysis of the strategies allows the establishment of the range of uncertainty on the frequencies that allow the proper operation of the strategies. Simulation and experimental results show that the torsional vibrations can be reduced to values close to zero by the application of the strategy. Therefore, the PMS mitigates the electromechanical interaction between the electrical power system and the aircraft drivetrain

Aeronautical Engineering: a Continuing Bibliography with Indexes (Supplement 243)

This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics