Frequency Trajectory Planning Based Transient Frequency Support of D-PMSG

As the wind power penetration increases, the frequency stability of the power system is deteriorating. Thus, it is expected that the wind power plants (WPPs) will be required to produce the inertial response during the short-term large-scale frequency disturbances. To study the effects of the inertial response of the WPP, the dynamic equivalent model (DEM) of the WPP should be able to emulate the inertial response of the actual WPP. Otherwise, the simulated system frequency would be different from the actual one. Therefore, the inertial response identification algorithm (IRIA) is proposed in this paper. The IRIA is able to identify the values of the droop gain and the inertia constants of the WPP according to the actual system frequency and the active power output of the actual WPP. The simulation results demonstrate that the DEM of the WPP and the actual WPP have similar responses of the active power output and the rotor speed under two frequency disturbances. In addition, the FNs of the simulated and actual system frequencies are very close. As a results, the effectiveness of the IRIA is successfully proved.

As the wind power penetration increases, the frequency stability of the power system is deteriorating. Thus, it is expected that the wind power plants (WPPs) will be required to produce the inertial response during the short-term large-scale frequency disturbances. To study the effects of the inertial response of the WPP, the dynamic equivalent model (DEM) of the WPP should be able to emulate the inertial response of the actual WPP. Otherwise, the simulated system frequency would be different from the actual one. Therefore, the inertial response identification algorithm (IRIA) is proposed in this article. The IRIA is able to identify the gain of the inertial controller and the inertia constants of the WPP according to the actual system frequency and the active power output of the actual WPP. In this article, the actual WPP is represented by the detailed model. In order to prove the effectiveness of the IRIA, three cases with different gains of the inertial controller are studied. The simulation results demonstrate that the proposed IRIA allows the DEM of the WPP to generate similar response of the active power and lead to close response of the system frequency as the actual WPP does in three different scenarios.

Due to a large number of grid-connected wind turbines don't have the ability to respond to system frequency changes, problems on frequency stability of power system have become increasingly prominent. At present, the primary frequency regulation of wind turbines is mostly based on the method of additional frequency regulation control to change the reference value of electromagnetic power, so as to realize that wind turbines can participate in the system frequency regulation. However, the method of additional frequency regulation control does not t consider the conflict of power increment between the power tracking controller and the frequency regulation controller, which lead to the power increment required for the primary frequency regulation can't reach the target value. Based on this issue, the paper combines the original power tracking technology of wind turbines with the existing frequency regulation technology, and change the signal of frequency deviation by the power tracking curve of the wind turbine, which realize the inertial response and primary frequency regulation of the unit through the fast active power control of the wind turbine. That the purpose of frequency regulation is realized and the power tracking curve is changed, by converting the active output required for the frequency regulation control into the increment load reduction. The simulation results show that, based on the control method in the paper, the double-fed wind turbine can fully achieve the target increment needed for primary frequency regulation, which makes the wind turbines more reliable and effective to participate in system of frequency regulation.

Stable wind power generation can ensure the quality of power transmitted by the grid. The application of large-scale grid-connected wind power systems will induce problems such as grid oscillation and frequency instability. In order to solve the problem of abnormal power system interaction caused by large-scale wind power access and improve the stability of grid-connected doubly-fed wind power generation, this paper proposes a stability modeling analysis of grid-connected doubly-fed wind power generation based on small signal model. First, the operating conditions of the grid-connected DFIG are analyzed, and the vector diagrams of the three operating conditions are given. When the grid-connected DFIG is in the super-synchronous working state, the sub-synchronous working state and the synchronous working state. According to the operating conditions of the grid-connected doubly-fed generators, the grid-connected doubly-fed wind power generation system is linearized. According to the relationship between the actual speed and the synchronous speed of the doubly-fed generator, the operating conditions of the doubly-fed generator are analyzed. By introducing the small-signal model, we analyze the small-signal of the grid-connected doubly-fed wind power generation system. The indirect current control circuit is used to perform reactive power compensation for grid-connected doubly-fed wind turbines. By calculating the reactive power loss of the grid-connected DFIG and the reactive power loss of the transmission line, the compensation capacity of the grid-connected DFIG is calculated. The transient voltage of the wind turbine is controlled by the rotor-side frequency converter, combined with the pitch angle control model. So far, this paper has realized the modeling analysis of grid-connected doubly-fed wind power generation stability. The simulation results show that the modeling analysis in this paper is reasonable for the small-signal analysis results of the stability of grid-connected doubly-fed wind power generation. In the rotor voltage simulation test, after the oscillation occurs for 1 s, the model starts to simulate and eliminate the fault. During the simulation period of 0.7 s∼1.0 s, the output voltage of the converter decreased to 168 V, and the voltage waveform did not fluctuate greatly after 1.0 s. The experimental results show that this method can improve the stability of grid-connected doubly-fed wind power generation.

With the increasing wind power penetration level (WPPL), the frequency regulation support capacity of traditional power systems is insufficient, which seriously affects the safety and stability of system frequency. Aiming at this problem, this paper proposes a robust control strategy of wind turbines based on second-order sliding mode to support the frequency stability of the power system. Firstly, in order to reflect the dynamic behavior of wind turbines participating in frequency regulation support, the wind turbine linearization model is deduced. Secondly, a second-order sliding mode algorithm, namely the super-twisting algorithm, is introduced into the wind turbine frequency regulation support control, and the stability of the proposed strategy is proved by the Lyapunov method. Finally, the effectiveness of the proposed strategy and its advantages are verified by simulation results.

As wind power generation technology rapidly advances, the threat of wind turbine failures to the secure and stable operation of the power grid is gaining increasing attention. Real-time monitoring of operation status and predicting potential failures in wind turbines are indispensable requirements for the safe integration of wind power. In this paper, a model based on the least squares support vector machine (LSSVM), whose parameters are optimized by the Big Bang–Big Crunch algorithm, is constructed to improve the monitoring of wind turbine operation status and fault prediction accuracy. The research methodology consists of several key stages. Firstly, the initial wind turbine sensing data are preprocessed, utilizing factor analysis to reduce dimensionality and obtain the main influencing factors of wind turbine operation. Then, an improved failure prediction model for wind turbines, based on the least squares support vector machine, is developed using the preprocessed data. The model parameters are optimized by utilizing the Big Bang–Big Crunch optimization algorithm to enhance the prediction accuracy of wind turbine failures. Finally, the feasibility and accuracy of the proposed method are validated through a case study conducted on a regional power grid with wind farm integration.

Due to the increasing penetration of wind power, operating characteristic of wind turbines may cause great concerns to frequency stability of the power system with large-scale wind power integration. Wind power plant participation in frequency regulation and the coordination with stored energy of the power system will be a trend in the future. However, the traditional wind turbines may not have the capability of frequency regulation. The issue of how wind power plants can participate in frequency regulation becomes research hotspot in recent years. Currently, most of frequency control methods of wind turbines are designed to have a new control loop from the existing control modules, such as speed control, droop control and pitch angle control. Theses novel control methods could realize the frequency support in some cases. However, these single-functional control loops have some drawbacks and could not solve the issues of frequency control effectively. For instance, the speed control could only work under the rated wind speed and the pitch control may not have fast-speed response ability to support the frequency control when the system frequency starts to fall. In this paper, a comprehensive review is presented regarding the latest studies about the multi-controller method of variable speed wind turbines in order to solve the problems of primary and secondary frequency control.

The frequency stability of the power system gradually decreases with the increasing share of wind power integration. Virtual inertia control (VIC) can be used to control the wind turbine (WT) to release rotor kinetic energy for providing fast frequency response (FFR). However, WTs need to absorb energy for speed recovery after participating in FFR, which easily causes a secondary frequency drop (SFD) if too much energy is absorbed from the grid. This paper proposes a coordinated control method for multiple WTs to effectively avoid the SFD while ensuring the frequency support effect. The number of WTs required for FFR is dynamically selected by the real-time disturbance power and the rotor speed of each WT. Then, the parameters of VIC are adaptively adjusted according to the frequency and the rotor speed changes of the WTs involved in FFR, which ensures the frequency support requirements. The unchosen WTs are controlled to release their kinetic energy to support the speed recovery of selected WTs, thus lowering the extra energy absorbed from the grid. This therefore reduces the possibility of the SFD and an excessive fall of the WT’s speed. The feasibility and superiority of the proposed method are validated through simulations in MATLAB/Simulink.

Advanced control of large-scale wind turbines: Structural load reduction and lifetime control

Analysis on the inertia and the damping characteristics of DFIG under multiple working conditions based on the grid-forming control

Experimental and numerical study of dynamic responses of a new combined TLP type floating wind turbine and a wave energy converter under operational conditions

This paper discusses a data-driven, cooperative control strategy to maximize wind farm power production. Conventionally, every wind turbine in a wind farm is operated to maximize its own power production without taking into account the interactions between the wind turbines in a wind farm. Because of wake interference, such greedy control strategy can significantly lower the power production of the downstream wind turbines and, thus, reduce the overall wind farm power production. As an alternative to the greedy control strategy, we study a cooperative wind farm control strategy that determines and executes the optimum coordinated control actions for maximizing the total wind farm power production. To determine the optimum coordinated control actions of the wind turbines, we employ a data-driven optimization method that seeks to find the optimum control actions using only the power measurement data collected from the wind turbines in a wind farm. In particular, we employ the Bayesian Ascent (BA) algorithm, a probabilistic optimization method constructed based on Gaussian Process regression and the trust region concept. Wind tunnel experiments using 6 scaled wind turbine models are conducted to assess (1) the effectiveness of the cooperative control strategy in improving the power production; and (2) the efficiency of the BA algorithm in determining the optimum control actions of the wind turbines using only the input control actions and the output power measurement data.

With the construction of interconnected power grid and the rapid development of clean energy, the frequency problem of power system is becoming increasingly prominent. The problem of ultra-low frequency oscillation affects the stability of system frequency. In order to analyze the frequency regulation characteristics of the system, it is necessary to study the local active power control link and stability calculation model of the hydropower plant computer monitoring system. In this paper, the influence of the local active power control link of the monitoring system on the system frequency small signal stability is studied, and the model is built in the simulation program. Through the simulation of 4-machine-2 regional power grid, the influence characteristics of local active power control on frequency dynamic damping level are verified. In the example of large power grid, the coordination between the local active power control of the monitoring system and the speed regulation system of hydropower units is comprehensively considered, the suggestion of coordination of multi-level frequency modulation resources to system frequency regulation is put forward.

The increasing integration of renewable energy sources into the grid causing increasingly problems in maintaining frequency stability of the power system. The participation of wind turbines in frequency regulation service for the power system is a necessary and expected condition for future energy systems. Deloading control for wind turbines can ensure a power reserve for participation in frequency regulation. This study presents the design of a constant deloading control technique for a direct drive permanent magnet wind turbine generation system, utilizing rotor overspeed control across various wind speed ranges. The efficacy of the suggested strategy is validated by simulation via Matlab/Simulink for varying power output of the turbine at different wind speed.

This paper is to investigate the inertial dynamics of virtual-synchronous-controlled (VSynC) doubly fed induction generator (DFIG)-based wind turbines (WTs). VSynC, different from the conventional synchronization method based on phase-locked-loop (PLL) synchronizing technique, makes DFIG-based WT synchronize with power grid via the active power control (APC), and thus provide the desired inertial support to power grid. Further, an effective approach for describing the inertial dynamics of DFIG-based WT with VSynC is proposed by establishing the WT's electromechanical motion equation. The approach synthetically considers the impacts of the WT's different controller parameters, operating points, and, in particular, the variations of mechanical power caused by the rotational speed or pitch angle changes during the inertial response period. It also makes the essential of DFIG-based WT's inertia clearer, which, as a matter of fact, is controllable and manifests frequency-dependent characteristics, and noticeably differs from the fixed inertia time constant featured in synchronous generator (SG). The impacts of different controller parameters and operating points on single WT's frequency response characteristics are studied. Simulated results also validate the superiority of VSynC on inertial support capability and operation stability to the typical PLL-based vector control (VC), especially for weak grid conditions. Finally, the frequency response on wind power plant (WPP) level is initially explored and further research to improve VSynC is discussed.