Fast Frequency Response Research Articles

Functional flexible photonics-assisted frequency measurement based on combination of stimulated Brillouin scattering and a Mach – Zehnder interferometer

A functional flexible photonics-assisted frequency measurement (PFM) is proposed. Owing to polarisation multiplexing, the electro-optic (O/E) conversion can be performed in a single optical path, which endows the system high stability and concise configuration. Moreover, using a specially designed functional coarse/accurate frequency measurement (C/AFM) module, a large covering range, moderate accuracy, and fast response frequency measurement results can be ensured in a radar warning receiver (RWR), whereas high accurate results can be used in an electronic countermeasures receiver (ECMR). The simulation results show that a strict monotonous amplitude comparison function (ACF) can be constructed based on the structure of a Mach – Zehnder interferometer (MZI) to map the signal frequency, with a measurement error of less than 0.2 GHz in the range of 1 – 31 GHz. This coarse measurement results can be used to perform radar warning. Based on this result, a highly accurate frequency measurement result is achieved through stimulated Brillouin scattering (SBS). The results reveal that the accuracy is improved to better than 20 MHz. Noteworthy, the C/AFM module consists of purely passive devices, which makes this system meet the potential of integration.

Control Hardware-in-the-Loop Simulation on Fast Frequency Response of Battery Energy Storage System Equipped With Advanced Frequency Detection Algorithm

Fast frequency response (FFR) of battery energy storage system (BESS) is an effective way to mitigate the system frequency deviation induced by the fluctuation of power generation from the increased renewable energy resources and the impact of reduced system inertia caused by decreased synchronous generators. However, existing standards referring to technical requirements for the frequency measurement do not sufficiently consider abnormal grid conditions, such as voltage unbalance, frequency sweep, and dynamic voltage step. This article shows the impact of frequency measurement logic on the FFR performance of BESS in grid disturbance conditions by control hardware-in-the-loop (CHIL) testing and proposes improved frequency measurement logic based on a phase-locked loop (PLL). A benchmarking of the proposed PLL was conducted against existing PLL and discrete Fourier transformation-based frequency measurement logics. Finally, the FFR performance of BESS with each frequency measurement logic has been tested in CHIL simulation. This CHIL comprises the actual power plant controller, the actual bidirectional inverter control board, and a real-time simulator. In the CHIL experiments, several system disturbance situations likely to happen in existing power systems were considered as test cases and showed that the frequency measurement accuracy and latency were violated in some frequency measurement logics. Furthermore, this article reveals the effects of frequency measurement accuracy and latency on the FFR performance of BESS by a closed-loop power control simulation with a CHIL environment. In conclusion, considerations for the frequency measurement method used for FFR are proposed.

Enabling hybrid energy storage systems in VSC‐based MTDC grids for decentralized fast frequency response control in low‐inertia AC/DC systems

This paper studies the hybrid energy storage system to provide frequency support for the interconnected AC grid through MTDC systems interfacing renewable resources. A hybrid energy storage structure was created using a supercapacitor (SC) and battery storage systems (BESs). To coordinate the sharing of power between SC and BESS, an improved droop controller based on virtual inductance, capacitance, and resistance gain (VICRC) is suggested. Meanwhile, the droop controller's steady-state deviation of the DC link voltage is immediately suppressed. The SC will be in charge of compensating the high-frequency demand, whereas the BESS will be in charge of compensating the low-frequency power demand, thanks to a decentralized energy management process. In addition, the suggested method aids in the rehabilitation of the SC's SOC. Finally, the simulation results with detailed models of the wind farms and AC–DC grid converters are performed on IEEE tests systems in Simulink/SPS and the results extensively discussed to evaluate the proposed structure.

Gust load alleviation on an aircraft wing by trailing edge Circulation Control

This paper reports an investigation of gust load alleviation using Circulation Control for a three-dimensional wing including aerodynamic and structure interaction. The Field Velocity Method is introduced to the unsteady Reynolds averaged Navier–Stokes solutions for gust response simulations. Structural dynamic equations of motion are coupled with the unsteady Reynolds averaged Navier–Stokes solutions to consider the aeroelastic effects due to the gust response. The effects of gust load alleviation on the BAH wing using Circulation Control are tested under typical ‘one-minus-cosine’ gust profiles from certification specification defined by European Aviation Safety Agency. The results show a promising capability of Circulation Control for gust load alleviation as significant gust load alleviation effects have been achieved for both the rigid and elastic BAH wings in the test cases. For the BAH wing considering aeroelasticity, the displacement oscillations induced by gusts have been effectively suppressed by Circulation Control. The results also show that Circulation Control has the fast frequency response characteristics, where more than 50% of the total change in lift coefficient can be obtained within the non-dimensional time s =U∞tc¯=1.

Effects of COVID19 pandemic on the Italian power system and possible countermeasures

The paper analyses the dramatic effects of the first wave of the COVID-19 pandemic on the Italian power system, considering the impacts on load and generation, market issues and ancillary services provision. During the period between March and May 2020, the Italian scenario was considered as exemplary due to the large reduction of loads and thermal generation caused by the hard lockdown across the Country. Italy has experienced the most severe effects of pandemic in terms of increase of death rates and of pressure on the health system as well as severity of the countermeasures. As a domino effect, the total lockdown of one of the most industrialized countries in the world has created an emergency situation that has put a big stress on the power system, reducing the possibility for the system to recover under contingencies. The weakness of the system in such an extreme situation is analyzed in depth using open data, while some countermeasures for providing resilience to the power systems in such cases are analyzed in simulation. Two technologies are here considered as exemplary countermeasures for providing resilience to the Italian power system: Fast Frequency Response by Photovoltaic and Wind plants with rated power above 10 MVA and the massive implementation of Demand Response programs through Energy communities and aggregation using Blockchain technology. The simulations show, on one hand, that the frequency recovery under contingency seems compromised in the current situation and that the support from such innovative technologies can provide a significant relief bringing the operational features close to those before the COVID-19 pandemic.

Potential of data centers for fast frequency response services in synchronously isolated power systems

Grid frequency support is one of the most challenging issues in wind rich islanded power systems. This problem becomes critical with the displacement of synchronous generators and their associated services (i.e., inertia and primary operating reserve). The services that are lost can be replaced by other sources, such as demand response schemes to enhance the resiliency and security of power system operations. Demand response based on internet data centers is expected to become an increasingly important asset to make a significant contribution to frequency ancillary services. To exploit this resource, internet service companies are expected to combine the capabilities of a variety of data centers to participate as a single provider similar to a virtual power plant. In this context, this work develops a novel framework for cooperative participation of data centers delay-tolerant workloads and backup power supply units to provide effective fast frequency response service. This is achieved by employing the model predictive controller to initiate reference signals to data center resources while respecting device operating conditions and constraints. Various case studies are run on the modified linear model of the 39 Bus system via dynamic simulations for the projected 75 % system non-synchronous penetration. Simulation results demonstrate the potential of different data center configurations to stabilize grid frequency during signal delays and severe cascade failures. The analysis shows that the proposed framework is critical to the adoption of renewable energy and reduces the requirement for an expensive spinning reserve used in a typical power system.

Addressing Frequency Control Challenges in Future Low-Inertia Power Systems: A Great Britain Perspective

The ambitious global targets on decarbonization present the need for massive integration of renewable generation in power systems, resulting in a significant decrease in the system inertia. In addition to the reduction in system inertia, the transmission system in Great Britain (GB) faces some unique challenges owing to its relatively small capacity, while being decoupled from other transmission systems and with the renewable resources largely non-uniformly distributed across the system. This paper presents opinions and insights on the challenges associated with frequency control in a low-inertia system and the potential solutions from a GB perspective. In this paper, we focus on three main techniques that act over different time scales: synchronous condensers, inertia emulation, and fast frequency response. We evaluate their relative advantages and limitations with learnings from recent research and development projects in GB, along with the opinions on their roles in addressing the frequency control challenges in future low-inertia systems.

Event-Driven Fast Frequency Response for Energy Storage System Considering State of Charge

The increasing penetration of renewable energy sources reduces the equivalent inertia and spinning reserve. Power systems are becoming more and more vulnerable when subjected to active power deficits. With the trait of quick response and flexible ramp, the energy storage system (ESS) offers a promising capability to counter frequency decline after large disturbances. This paper proposes an event-driven fast frequency response (EFFR) approach for the ESS to sustain frequency stability. A centralized EFFR control framework is established, in which the wide area information is collected, and the disturbance power is broadcasted to ESSs under contingencies. Moreover, a fuzzy logic controller (FLC) is employed to determine the power set-point of the ESS based on the disturbance power and state of charge (SOC). A case study is presented to validate the feasibility and effectiveness of the proposed approach.

Effect of pore size in activated carbon on the response characteristic of electric double layer capacitor

The effect of pore size on the response characteristic of an electric double layer capacitor (EDLC) was closely examined. A series of phenol-resin-based activated carbon (AC) samples was prepared as average pore size from 0.94 to 1.68 nm by KOH activation by varying the activation temperature and KOH/carbonized phenol-resin ratio. The impedance properties of pouch-type EDLC cells prepared using AC samples were evaluated by applying an alternating current at 3 V between 10 mHz and 100 kHz for confirming the response characteristic. The cell based on the AC with a largest pore size (1.68 nm) showed fast response frequency, and had a high dielectric relaxation time constant as calculated from the response frequency value. The AC with the largest pore size, which consisted of both micropores (>1 nm) and mesopores (2–4 nm), was confirmed to facilitate extremely low electrolyte-diffusion resistance during the formation of the electric double layer, implying that the large pores lead to fast and stable response frequency. The presented findings suggest that AC with a largest pore size as the electrode leads to superior capacitance and response frequency characteristics in the alternating current than those of an AC with a smaller pore size.

Gust load alleviation by normal microjet

This paper presents an investigation on the capability of gust load alleviation by normal microjet. The numerical method integrates the unsteady Reynolds averaged Navier-Stokes (URANS) solutions, structural dynamic equations of motion and the Field Velocity Method. The method is verified for gust responses of rigid and elastic models. The numerical results of microjet are validated against experimental and previous numerical data. Load control capabilities of normal microjet are evaluated on the 2D NACA0012 airfoil and the 3D BAH wing with constant and dynamic momentum coefficients under steady subsonic and transonic incoming flow conditions. Thereafter, gust load alleviation effects using microjet are tested on the airfoil and the BAH wing with and without the consideration of aeroelasticity. The results show that normal microjet has a strong capability for load control for transonic incoming flow. This is due to the jet effect on the shock strength on the airfoil upper surface. For the 3D BAH wing, significant load control effects can be shown for jet deployment on the span near the wing tip. Load reduction has also been observed near the wing root away from the jet region. The test cases show that normal microjet is a promising approach for gust load alleviation with a fast frequency response characteristic. A near constant lift response under gust condition can be achieved by adaptively adjusting the blowing momentum coefficients.

Analytical Approach to Understanding the Effects of Implementing Fast-Frequency Response by Wind Turbines on the Short-Term Operation of Power Systems

The significant presence of variable-speed wind turbines in worldwide power systems has led to planners and grid operators requiring them to participate in frequency control tasks. To address this demand, a large number of wind frequency control proposals have been reported in the literature in recent years. Many of these solutions have been tested by specific experiments carried out in computer simulation environments. This paper proposes a methodology to evaluate the effects of enabling frequency support by wind turbines on the magnitudes that characterize the inertial response of a power system by using an analytical approach. The derived formulation and the illustrations are designed to provide a better understanding of both the mechanisms that determine the frequency stability indices and the improvement achieved by enabling the inertial response of wind turbines by implementing a virtual inertia-based method on the active power controllers of these machines. To facilitate the comprehension of the results obtained, the analytical approach is complemented with time-domain simulations in a predefined test system implemented in MATLAB/Simulink®. The proposed methodology achieves a generalization of the results and can be used for the assessment of any power system configuration.

The impact of spatial variation of inertial response and flexible inter-area allocation of fast frequency response on power system scheduling

The impact of the spatial variation of inertial response and fast frequency services has not been fully investigated in power system scheduling models incorporating constraints on network security. This paper demonstrates the importance of acknowledging the variety of local frequency dynamics in the aftermath of a generation loss. It proposes a novel scheduling methodology that enables the system security in all areas of the system thus preventing potential tripping of distributed generation triggered by locally-measured high rates of change of frequency. The proposed methodology highlights the positive contribution to local frequency dynamics from an HVDC link, whose capacity is optimally dispatched to allocate power flow and fast-frequency services. The novel power system scheduling model is applied to analyze a typical 2030 GB low-carbon scenario. Results show that there are changes in the commitment decisions compared to the solution obtained with a one-area formulation when local security is taken into account. These changes translate into additional operational cost.

The Role of Fast Frequency Response of Energy Storage Systems and Renewables for Ensuring Frequency Stability in Future Low-Inertia Power Systems

Renewable generation technologies are rapidly penetrating electrical power systems, which challenge frequency stability, especially in power systems with low inertia. To prevent future instabilities, this issue should already be addressed in the planning stage of the power systems. With this purpose, this paper presents a generation expansion planning tool that incorporates a set of frequency stability constraints along with the capability of renewable technologies and batteries to support system frequency stability during major power imbalances. We study how the investment decisions change depending on (i) which technology—batteries, renewable or conventional generation—support system frequency stability, (ii) the available levels of system inertia, and (iii) the modeling detail of reserve allocation (system-wide versus zone-specific). Our results for a case study of Chile’s system in the year 2050 show that including fast frequency response from converter-based technologies will be mandatory to achieve a secure operation in power systems dominated by renewable generation. When batteries offer the service, the total investment sizes are only slightly impacted. More precise spatial modeling of the reserves primarily affects the location of the investments as well as the reserve provider. These findings are relevant to energy policy makers, energy planners, and energy companies.

Simultaneous Provision of Dynamic Active and Reactive Power Response From Utility-Scale Battery Energy Storage Systems in Weak Grids

Utility-scale battery energy storage system (BESS) technologies have huge potential to support system frequency in low-inertia conditions via fast frequency response (FFR) as well as system voltage via dynamic reactive power response. However, technical challenges may emerge in weak grids where low system strength could cause voltage instability, eventually potentially hindering provision of FFR too. This paper provides a systematic and comprehensive analysis of the challenges, and proposes relevant solutions, for BESS in providing FFR and general dynamic active and reactive responses under low system strength conditions. In particular, first we propose a constraint to describe the negative impact of low system strength on BESS phase-locked loop (PLL) stability and possible mitigation solutions. We then investigate the negative impact of large contingencies on BESS DC-link stability and active power control by introducing d-q current-power sensitivity factors and propose a solution based on reactive power prioritization that prevents converter-level instabilities while providing simultaneous active and reactive dynamic responses. Possible negative active/reactive power interactions due to BESS converter capacity constraints and the impact of the BESS operating point are also addressed. All these issues are investigated, and the proposed solutions tested, through explicit mathematical modelling as well as dynamic simulations of the South Australia's Eyre Peninsula weak grid.

Grid Services and Stress Reduction with a Flywheel in the Rotor of a Wind Turbine

Wind power penetration increases in most grids and the sizes of wind turbines increase. This leads to increasingly tough requirements, which are imposed on wind turbines, both from the grid as well as from economics. Some of these partially contradictory requirements can only be satisfied with additional control mechanisms in the wind turbines. In this paper, such a mechanism, i.e., a hydraulic–pneumatic flywheel system in the rotor of a wind turbine, is discussed. This flywheel system supports a wind turbine in providing grid services such as steadying the power infeed, fast frequency response, continuous inertia provision, power system stabilization, and low voltage ride-through. In addition, it can help mitigate the stress on the mechanical structure of a wind turbine, which results from varying operating points, imbalances in the rotor, gravitation that acts on the blades, in-plane vibrations, and emergency braking. The study presented in this paper is based on simulations of a publicly available reference wind turbine. Both the rotor blade design as well as the design of the flywheel system are as previously published. It is discussed how the aforementioned grid services and the stress reduction mechanisms can be combined. Finally, it is concluded that such a flywheel system broadens the range of control mechanisms of a wind turbine substantially, which is beneficial for the grid as well as for the wind turbine itself.

Novel Coordinated Control Strategy of BESS and PMSG-WTG for Fast Frequency Response

An increase in inverter-based resources (IBRs) can lower the inertia of a power system, which may adversely affect the power system by causing changes such as a frequency nadir reduction or an increased initial rate of change of frequency (RoCoF). To prevent this, an ancillary service called fast frequency response (FFR) helps the inertia response by using IBRs. The main resources used in FFR are variable-speed wind turbine generators (VSWTGs) or energy storage systems (ESSs), which can respond quickly through converter control. The control is applied to the frequency regulation service faster than the primary frequency response, so the second frequency nadir may fall below the first frequency nadir. This study proposed a novel coordinated control strategy to efficiently utilize energy to improve the frequency nadir through coordinated control of wind turbines based on permanent magnetic synchronous generators (PMSGs) and battery energy storage systems (BESSs). The simulation results confirmed that the two-bus test system was composed of PSCAD/EMTDC, and the frequency nadir increased by utilizing the same amount of energy as in traditional control systems.

LQR-Based Adaptive Virtual Inertia for Grid Integration of Wind Energy Conversion System Based on Synchronverter Model

This paper proposes adaptive virtual inertia for the synchronverter model implemented in a wind turbine generator system integrated into the grid through a back-to-back converter. A linear dynamic system is developed for the proposed adaptive virtual inertia, which employs the frequency deviation and the rotor angle deviation of the synchronverter model as the state variables and the virtual inertia and frequency droop gain as the control variables. In addition, the proposed adaptive virtual inertia uses a linear quadratic regulator to ensure the optimal balance between fast frequency response and wind turbine generator system stress during disturbances. Hence, it minimizes frequency deviations with minimum effort. Several case simulations are proposed and carried out in MATLAB/Simulink software, and the results demonstrate the effectiveness and feasibility of the proposed adaptive virtual inertia synchronverter based on a linear quadratic regulator. The maximum and minimum frequency, the rate change of the frequency, and the integral of time-weighted absolute error are computed to quantify the performance of the proposed adaptive virtual inertia. These indexes are reduced by 46.61%, 52.67%, 79.41%, and 34.66%, in the worst case, when the proposed adaptive model is compared to the conventional synchronverter model.

Impact of Circular Layout on Characteristics in LSAMBM APD Based on SOI Film

Lateral separate absorption multi-buffer multiplication avalanche photodiode (LSAMBM APD) with rectangular layout based on SOI film had been investigated as a promising candidate in the high-speed weak-light detection application. In this article, the layout-dependent characteristics of LSAMBM APD were investigated furthermore. Comparing to rectangular layout, the circular layout could shorten the length and improve electric field intensity of absorption region under the same sensitive area. In this way, carriers’ drift velocity could be accelerated, and the photon-generated carriers would be more effectively separated to achieve high responsivity and fast frequency response in LSAMBM APD with circular layout. When the illumination wavelength was 400 nm and input optical power was 0.001 W/cm2, the circular layout could enhance LSAMBM APD to achieve high responsivity and fast frequency response under the reverse bias voltage of 8.11 V and 9.2 V, and reach to 1236.9A/W and 3.2GHz, respectively. All results revealed that the LSAMBM APD with circular layout was more appropriate to high-speed single photon detection systems.

Fast Frequency Response From Utility-Scale Hydrogen Electrolyzers

This paper introduces the modelling foundations to study the fast frequency response (FFR) from utility-scale hydrogen electrolyzers (HEs). Specifically, we propose a dynamic model of the HE electrolysis stack, power-electronics interface, and downstream hydrogen process operational constraints, which is suitable for system-level frequency dynamics studies. We then model and study HE FFR dependency on pre-contingency operating point, size, converter's overloading capability, network location, and active power-frequency controller. Different case studies are run on the Australian multi-area test system via dynamic simulations of a 2030 scenario with 50% renewables and in the context of the August 2018 separation event. Our modelling and results illustrate how grid-scale HEs could support a more secure and resilient operation of low-carbon systems for both credible and extreme outages and the role of different design setups and operating conditions and constraints.

Co-Optimizing Virtual Power Plant Services Under Uncertainty: A Robust Scheduling and Receding Horizon Dispatch Approach

Market and network integration of distributed energy resources can be facilitated by their coordination within a virtual power plant (VPP). However, VPP operation subject to network limits and different market and physical uncertainties is a challenging task. This paper introduces a framework that co-optimizes the VPP provision of multiple market (e.g., energy, reserve), system (e.g., fast frequency response, inertia, upstream reactive power), and local network (e.g., voltage support) services with the aim of maximizing its revenue. To ensure problem tractability, while accommodating the uncertain nature of market prices, local demand, and renewable output and while operating within local network constraints, the framework is broken down into three sequentially coordinated optimization problems. Specifically, a scenario-based robust optimization for day-ahead resource scheduling, with linearized power flows, and two receding horizon optimizations for close-to-real-time dispatch, with a more accurate second-order cone relaxation of the power flows. The results from a real Australian case study demonstrate how the framework enables effective deployment of VPP flexibility to maximize its multi-service value stack, within an uncertain operating environment, and within technical limits.