Synthetic Inertia Control Research Articles

Assessment of inertial and primary frequency control from wind power plants in the Mexican electric power grid

AbstractLarge‐scale integration of converter‐based renewable energy sources into power systems, such as wind generation, can lead to frequency stability issues due to the variable nature and lack of inertia of these technologies in combination with the gradual replacement of conventional generating units. However, wind turbine generators (WTGs) can be exploited to provide frequency support and keep system frequency stability requirements. A case study considering the Mexican Electric Power System is presented in this study to highlight both the impact of large‐scale deployment of inverter‐interfaced wind energy generation on system frequency response, and the participation of WTGs in inertial and primary frequency control (IPFC) as a mitigation approach. By incorporating synthetic inertia and droop control functions into the active power control loop of WTG converters, IPFC by wind generation is assessed for several wind shares, different active power modulation strategies based on the rate of change of frequency and frequency deviation, and several IPFC contribution levels under critical contingencies for generation outage. Simulation results show the combination of increasing share of wind energy generation in the study system and retirement of conventional generation has a clearly negative impact on system frequency dynamics. However, the incorporation of IPFC functions into wind power generators of the sample system, with appropriate control gain values, may contribute to effectively achieve an improved system performance in terms of grid frequency response under high wind power penetration scenarios.This article is characterized under: Wind Power > Science and Materials Wind Power > Systems and Infrastructure Energy Research & Innovation > Science and Materials

Influence of PLL on synthetic inertia of DFIG wind turbine in droop controlled microgrids

Islanded microgrids allow for a continuous supply of customers even when there is an outage in the bulk power system. The frequency control and stability in microgrids is an ongoing field of research. This work investigates the influence of synthetic inertia control of doubly-fed induction generator wind turbines on the dynamics of inverter dominated microgrids with droop control. A special focus is placed on the impact of the phase-locked loop dynamics.

Wide-area synthetic inertia control of multiple resources incorporating primary frequency control of wind turbines

With a large proportion of renewable energy sources integrated through the power electronics interface, power systems are challenged with decreased inertia threatening the system stability. Synthetic inertia control aims to emulate inertial response of various available resources. A wide-area synthetic inertia control strategy for multiple resources is proposed in this paper. The offshore wind farm composed of DFIG wind turbines is interconnected by the VSC-HVDC link. Synchronous condensers are installed to improve the system dynamic characteristics. Synthetic inertia control is designed for DFIG wind turbines, VSC-HVDC link and synchronous condensers, respectively. Wide-area frequency signal is employed to overcome the limitation of local signal. Primary frequency control support by DFIG wind turbines is incorporated to improve the control effect of the strategy. Simulation results on New England 39-bus system verify the effectiveness of the proposed wide-area synthetic inertia control strategy.

Accurate Power Sharing and Synthetic Inertia Control for DC Building Microgrids With Guaranteed Performance

Direct current (DC) building microgrids allow the integrations of DC distributed energy resources (DERs) and loads with a simpler topology and the elimination of alternating current (AC) system issues, such as frequency transients and harmonics. Because of the domination of power-electronics-interfaced generators, islanded DC microgrids in general present very low inertia, which reveals subtle stability threats to the systems. In addition, the conventional droop-based DER power-sharing mechanisms may suffer from poor power-sharing accuracy and DC bus voltage deviations that require secondary restorations. In this paper, a novel control scheme for building-scale islanded DC microgrids is proposed based on finite control set model predictive control (FCS-MPC). A new DER power-sharing mechanism is devised by introducing a current-sharing vector in the controller formulation, which eliminates bus voltage deviation during load/DER fluctuation and offers plug-and-play capabilities. Moreover, for the first time, virtual capacitance control for DC microgrids is implemented in an FCS-MPC manner to enhance the adaptive synthetic inertia of DC bus. Both the simulation and experimental case studies are carried out to provide verification for the promising performance of the proposed method.

Design and Implementation of a Variable Synthetic Inertia Controller for Wind Turbine Generators

The increasing penetration of Renewable Energy Sources (RES) and, more in general, of converter connected power generation is progressively reducing the overall inertia of the electricity system introducing new challenges in the network Frequency Support (FS). Therefore, FS strategies for RES are becoming an important aspect to be developed in order to en-sure the secure operation of the electricity power grid. The aim of the present paper is to propose an innovative approach for the inertial emulation of Wind Turbine Generators (WTGs) in order to ensure a positive effect on the system frequency avoiding unstable operations of the WTG and reducing the negative impact of the rotor speed recovery on the secondary frequency drop. Moreover, the paper provides a detailed definition of the triggering logics adopted to activate and deactivate the FS making it suitable for implementation in available industrial controllers. The proposed controller is firstly tested on a simplified configuration to show its enhanced performances with respect to previously developed approaches. Then, simulations are carried out in a more realistic network to assess the positive impact of the controller on the system frequency. Results highlighted a 40% reduction of the system Rate of Change of Frequency while the frequency deviation at the transient nadir is improved by 35%.

Synthetic inertia control based on fuzzy adaptive differential evolution

The transformation of the traditional transmission power systems due to the current rise of non-synchronous generation on it presents new engineering challenges. One of the challenges is the degradation of the inertial response due to the large penetration of high power converters used for the interconnection of renewables energy sources. The addition of a supplementary synthetic inertia control loop can contribute to the improvement of the inertial response. This paper proposes the application of a novel Fuzzy Adaptive Differential Evolution (FADE) algorithm for the tuning of a fuzzy controller for the improvement of the synthetic inertia control in power systems. The method is validated with two test power systems: (i) an aggregated power system and its purpose is to understand the controller-system behavior, and (ii) a two-area test power system where one of the synchronous machine has been replaced by a full aggregated model of a Wind Turbine Generator (WTG), whereby different limits in the tuning process can be analyzed. Results demonstrate the evolution of the membership functions and the inertial response enhancement in the respective test cases. Moreover, the appropriate tuning of the controller shows that it is possible to substantially reduce the instantaneous frequency deviation.

Electric power system inertia: requirements, challenges and solutions

The displacement of conventional generation by converter connected resources reduces the available rotational inertia in the power system, which leads to faster frequency dynamics and consequently a less stable frequency behaviour. This study aims at presenting the current requirements and challenges that transmission system operators are facing due to the high integration of inertia-less resources. The manuscript presents a review of the various solutions and technologies that could potentially compensate for reduction in system inertia. The solutions are categorized into two groups, namely synchronous inertia and emulated inertia employing fast acting reserve (FAR). Meanwhile, FAR is divided into three groups based on the applied control approach, namely virtual synchronous machines, synthetic inertia control and fast frequency control. The analytical interdependency between the applied control approaches and the frequency gradient is also presented. It highlights the key parameters that can influence the units’ response and limit their ability in participating in such services. The manuscript presents also a trade-off analysis among the most prominent control approaches and technologies guiding the reader through benefits and drawbacks of each solution.

Synthetic Inertia Control Strategy for Doubly Fed Induction Generator Wind Turbine Generators Using Lithium-Ion Supercapacitors

To address the system operability challenges due to the continuous reduction of system inertia by increasing penetration of renewable power generation, this paper proposes a new synthetic inertia control (SIC) strategy for doubly fed induction generator (DFIG)-based wind turbine generators. The proposed SIC scheme enables individual DFIG generators to contribute an effective inertial response which helps to stabilise the rate of change of frequency and minimize the maximum frequency deviations in particular under severe disturbance conditions. To achieve the proposed SIC, lithium-ion supercapacitors are required in the dc link of the DFIG power electronic conversion system to increase extra energy storage capability. The DFIG's dc voltage operates at various levels following the derived SIC algorithms for energy exchange with the connected ac grid, and the conventional control system for DFIG is modified to implement the algorithms. The functions and system benefits of SIC scheme are verified using a DFIG model connected to a power system and compared with the simulations of conventional DFIG control scheme. Practical issues such as size, cost, weight, connection configuration, and charging/discharging rate of lithium-ion capacitors for the SIC are discussed and relevant recommendations are presented.

Two-Level Damping Control for DFIG-Based Wind Farm Providing Synthetic Inertial Service

Equivalent inertia of the power system is reducing with the increasing wind power penetration. To alleviate this issue, more and more countries have put forward grid codes that require wind farms (WFs) to provide inertial response as traditional synchronous generation does. It is found in this paper that the synthetic inertial control of the WF in a weak grid deteriorates drive-train torsional oscillation of wind turbine generators (WTGs). Furthermore, the WF emulating inertial response is involved in power system oscillations and induces a new critical low-frequency oscillation. The above oscillations threaten small-signal stability of the WF and the power system, which restricts the WF to fulfill grid code requirements. To overcome this problem, this paper proposes a two-level damping control scheme consisting of a WTG level torsional oscillation damping control and a WF level low-frequency oscillation adaptive damping control to enhance damping characteristic of the WF. Simulation results show that the two-level damping control can simultaneously counteract these concerned multiple oscillations under various operating conditions, which facilitates the WF to meet grid code requirements, and improves dynamic stability of the WF and the power system.

Comparison between synthetic inertia and fast frequency containment control based on single phase EVs in a microgrid

The increasing share of distributed and inertia-less resources entails an upsurge in balancing and system stabilisation services. In particular, the displacement of conventional generation reduces the available rotational inertia in the power system, leading to high interest in synthetic inertia solutions. The objective of this paper is twofold: first, it aims to implement and validate fast frequency control and synthetic (virtual) inertia control, employing single phase electric vehicles as flexibility resources. Second, it proposes a trade-off analysis between the two controllers. The interdependency between frequency containment and synthetic inertia control on the transient frequency variation is shown analytically. The capabilities and limits of series produced EVs in providing such services are investigated, first on a simulation based approach and subsequently by using real hardware. The results show that fast frequency control can improve the transient frequency behaviour. However, both on the simulation and on the experimental level, the implementation of synthetic inertia control is more challenging. In fact, due its derivative nature and the system dynamics, its performance is limited. Furthermore, the crucial importance of the EVs’ response time for both controllers is highlighted.

Equivalent inertial time constant of doubly fed induction generator considering synthetic inertial control

The integration of large-scale doubly fed induction generators (DFIGs) into power system leads to the deterioration of the dynamic frequency characteristics in case of power shortage. One effective way to address this deterioration is through synthetic inertial control. However, a quantitative representation of the synthetic equivalent inertial time constant of DFIG (Heq) is greatly needed for research on the dynamic frequency characteristics of wind power-incorporating systems. This study introduces the traditional synthetic inertial control technique of DFIG, and reveals that the dynamic inertial response process is influenced by both the inertial controller and the speed controller. Expressions of Heq in the frequency and time domains were mathematically derived, and the accuracy of Heq was verified by comparing the calculated and simulated values. The 3-stage time varying characteristics of Heq are detailed, and the resulting mechanisms are analyzed.