Provision Of Frequency Regulation Research Articles

Revenue assessment of damage aware wind farm control for secondary frequency regulation provision

Abstract In this paper, a case study of a wind power plant participating in the balancing market is presented and any potential revenue benefits are estimated. To make a representative performance assessment, an existing case for the frequency regulation market is selected, based on the pay-for-performance scheme of the US regional transmission operator Pennsylvania-New Jersey-Maryland (PJM). In this implementation, the wind power plant is being rewarded or penalized based on its signal-tracking capabilities, which are quantified by proper performance metrics. The fast response characteristics of the wind turbines allow for tracking even the faster automatic regulation signal (RegD from PJM). However, one of the significant challenges associated with providing such type of active power reference tracking on the wind farm scale is that different turbines have different responses and structural damage accumulation due to the local environmental conditions and the coupling due to wakes. The in-house developed, numerically efficient, wind farm simulation model “regfarm” is employed, allowing for a thorough analysis and revenue assessment under various operating regimes and weather conditions. Numerous time-domain simulations and historical pricing time series are used to quantify the expected revenue from market participation. Under the regulation market pay-for-performance compensation scheme, the simulated wind farm earned a lower revenue when compared to maximizing energy production. Depending on the configuration, the wind farm experiences between a 2.14% and a 2.38% decrease in revenue when providing 10% of the estimated available power to the regulation market. The wind farm is operated as both damage-ignorant and damage-aware, with no significant comparative loss in revenue when the damage distribution is considered.

Stacked revenues for energy storage participating in energy and reserve markets with an optimal frequency regulation modeling

This paper investigates the opportunity for a Battery Energy Storage System (BESS) to participate in multiple energy markets. The study proposes an offline assessment to calculate the maximum annual revenues to reach the optimum stack of services through deterministic simulations. The markets include wholesale energy markets (day-ahead and intraday), ancillary services (frequency regulation and reserve), and the capacity mechanism. The study case performed on the French markets shows that frequency services overperform the other markets, where the long-term capacity market has the least potential. Moreover, providing multiple services maximizes the battery's revenues, for example, participating in joint energy and reserve markets showed a 76% increase in annual profits. Furthermore, a novel operation approach was proposed to enhance the performance of these joint markets, by indirectly utilizing energy products as frequency reserves. The results demonstrate that the proposed formulation allows a revenue increase of ∼23% compared to the conventional framework for the provision of frequency regulation with BESSs. Additionally, the joint markets have been shown to be economically viable with 6.2 years payback period after considering battery degradation and depreciation cost.

PowerMorph: QoS-Aware Server Power Reshaping for Data Center Regulation Service

Adoption of renewable energy in power grids introduces stability challenges in regulating the operation frequency of the electricity grid. Thus, electrical grid operators call for provisioning of frequency regulation services from end-user customers, such as data centers, to help balance the power grid’s stability by dynamically adjusting their energy consumption based on the power grid’s need. As renewable energy adoption grows, the average reward price of frequency regulation services has become much higher than that of the electricity cost. Therefore, there is a great cost incentive for data centers to provide frequency regulation service. Many existing techniques modulating data center power result in significant performance slowdown or provide a low amount of frequency regulation provision. We present PowerMorph , a tight QoS-aware data center power-reshaping framework, which enables commodity servers to provide practical frequency regulation service. The key behind PowerMorph is using “complementary workload” as an additional knob to modulate server power, which provides high provision capacity while satisfying tight QoS constraints of latency-critical workloads. We achieve up to 58% improvement to TCO under common conditions, and in certain cases can even completely eliminate the data center electricity bill and provide a net profit.

Using PV systems and parking lots to provide virtual inertia and frequency regulation provision in low inertia grids

In this research, a novel formulation for smart frequency control and virtual inertia support in a low inertia grid is proposed. The approach takes advantage of EV parking lots and PV distributed resources abilities for this purpose directly or through aggregators. The model also considers governor control of the conventional plants in addition to the controllable loads, namely under-frequency load shedding devices. The model seeks to minimize the total amount of disconnected load in case of severe contingencies. Furthermore, the rate of change of frequency (ROCOF) is formulated and employed as another objective function. The control parameters are optimally tuned by Mixed Integer Linear Programming (MILP) model to minimize the amount of load shedding while satisfying the specified frequency constraints. Linearity of the model assures achieving the global optima and is suitable for large-scale real-life systems without convergence concerns. The proposed smart control scheme is implemented on the IEEE 39-bus system, where the simulation results demonstrate a dramatic decrease of load shedding from 0.1676 p.u to 0.1235 p.u for one of the cases by the incorporation of converter based frequency providers. The system ROCOF, moreover, is reduced from -2.94 Hz/s to -1.93 Hz/s which indicates the efficiency of the methodology.

Optimal intra-day operations of behind-the-meter battery storage for primary frequency regulation provision: A hybrid lookahead method

Battery energy storage systems (BESSs) are being widely installed behind-the-meter to reduce electricity bill. By providing grid ancillary services, behind-the-meter BESSs can increase potential revenue streams. This study targets the simultaneous electricity bill reduction and primary frequency regulation (PFR) provision. With the expansion of the application spectrum, the intra-day operations become more and more complicated. In this paper, a hybrid lookahead method with value function approximation strategy is proposed for intra-day operations, wherein the concept of “offline calculation—online application” is devised and implemented. The approximate value function is trained offline to represent the expected long-term benefit. A two-stage robust approximate dynamic programming (ADP) model is formulated for one day operation which is optimized to adjust the power baseline with a forward rolling horizon. Furthermore, multi-dimensional indicators are introduced to evaluate the proposed strategy. Simulations and benchmarking comparisons are performed for a 0.5 MW/1.0 MWh BESS to verify the superior performance of the proposed strategy. The results show that the approximate value function can be obtained offline with 99.07% convergence precision. Moreover, the proposed strategy can ensure the economic benefit and PFR provision within a short online computing time. The resulting intra-day economic benefit can reach 95.55% of the theoretical optimum, and the online optimization consumes only 4.65s for a prediction horizon of 5 min, which ensures the feasibility of real-time predictive optimization.

On the Participation of Power-To-Heat Assets in Frequency Regulation Markets—A Danish Case Study

Due to the new green energy policies, district heating companies are being increasingly encouraged to exploit power-to-heat assets, e.g., heat pumps and electric boilers, in their distribution networks besides the traditional central combined heat and power units. The increased utilization of these assets will generate a more complex interaction between power distribution grids and district heating networks including markets for provision of ancillary services. Enabling the participation of power-to-heat units in the ancillary service markets, e.g., frequency reserves, may increase the revenue streams for assets’ owners. However, some technical challenges must first be addressed, including optimization of portfolios of assets that accounts for ancillary service markets, new coordination and operational schemes for portfolio of assets, increase data exchange and interactions with transmission system operators, and new local control schemes for units. This paper proposes a systematic model based design approach for assessment of provision of frequency regulation by power-to-heat assets using the smart grid architecture model. The proposed approach is demonstrated in a Real-Time Control Hardware-in-the-Loop laboratory environment.

Assessments of data centers for provision of frequency regulation

There are numerous opportunities for data centers to participate in demand response programs considering their large energy capacities, flexible working environments and workloads, redundant design and operation, etc. As a type of demand response, frequency regulation requires fast response, and its potential is not fully explored by data centers yet. This paper proposes a synergistic control strategy for data center frequency regulation which uses both IT and cooling systems. It combines power management techniques at the server level with control of the chilled water supply temperature to track the regulation signal from the electrical market. A frequency regulation flexibility factor is also proposed to increase the IT capacity for frequency regulation. The performance of the control strategy is studied through numerical simulations using an equation-based object-oriented Modelica platform designed for data centers. Simulation results show that with well-tuned control parameters, data centers can provide frequency regulation service in both regulation up and down. The performance of data centers in providing frequency regulation service is largely influenced by the regulation capacity bid, frequency regulation flexibility factor, workload condition, and cooling mode of the cooling system, and not significantly influenced by the time constant of chillers. In addition, compared with a server-only control strategy, the proposed synergistic control strategy can provide an extra regulation capacity of 3% of the design power when chillers are activated. When chillers are deactivated, both strategies have a similar regulation capacity.

Profitability of Frequency Regulation by Electric Vehicles in Denmark and Japan Considering Battery Degradation Costs

This paper determines the profitability of the primary frequency regulation (FR) service considering the wear of the electric vehicle (EV) battery as a cost. To evaluate the profitability of the FR service, the cost of degradation from FR provision is separated from the degradation caused by driving usage. During FR, the power response is proportional to the frequency deviation with full activation power of 9.2 kW, when deviations are larger than 100 mHz. The degradation due to FR is found to be an additional 1–2% to the 7–12% capacity reduction of a 40 kWh Lithium-ion NMC battery pack over 5 years. The overall economic framework is applied in Denmark, both DK1 and DK2, and Japan, by considering historical frequencies. The DK2 FR market framework is taken as reference also for the Japanese and the DK1 cases. Electricity prices and charger efficiency are the two main parameters that affect the profitability of the service. Indeed, with domestic prices there is no profitability, whereas with industrial prices, despite differences between the frequencies, the service is similarly profitable with approx. 3500€ for a five-year period.

Modeling a Large-Scale Battery Energy Storage System for Power Grid Application Analysis

The interest in modeling the operation of large-scale battery energy storage systems (BESS) for analyzing power grid applications is rising. This is due to the increasing storage capacity installed in power systems for providing ancillary services and supporting nonprogrammable renewable energy sources (RES). BESS numerical models suitable for grid-connected applications must offer a trade-off, keeping a high accuracy even with limited computational effort. Moreover, they are asked to be viable in modeling for real-life equipment, and not just accurate in the simulation of the electrochemical section. The aim of this study is to develop a numerical model for the analysis of the grid-connected BESS operation; the main goal of the proposal is to have a test protocol based on standard equipment and just based on charge/discharge tests, i.e., a procedure viable for a BESS owner without theoretical skills in electrochemistry or lab procedures, and not requiring the ability to disassemble the BESS in order to test each individual component. The BESS model developed is characterized by an experimental campaign. The test procedure itself is framed in the context of this study and adopted for the experimental campaign on a commercial large-scale BESS. Once the model is characterized by the experimental parameters, it undergoes the verification and validation process by testing its accuracy in simulating the provision of frequency regulation. A case study is presented for the sake of presenting a potential application of the model. The procedure developed and validated is replicable in any other facility, due to the low complexity of the proposed experimental set. This could help stakeholders to accurately simulate several layouts of network services.

Frequency regulation service provision in data center with computational flexibility

The rapid adoption of cloud storage and computing services led to unprecedented growth of data centers in the world. As bulk energy consumers, large-scale data centers in the U.S. rack up billions in electricity costs annually. Fortunately, the operational flexibility of data centers can be leveraged to provide valuable frequency regulation services in smart grids to mitigate the indeterminacy of the renewable generation resources. Specifically, this paper aims to leverage computational flexibility provided by servers, such as dynamic voltage frequency scaling and dummy loads. This paper develops a comprehensive framework for data center’s frequency regulation service provision in both hour-ahead market and real-time operations. A risk constrained hour-ahead bidding strategy along with a real-time data center power consumption control algorithm are developed to minimize electricity bills and the total response time of the requests. The introduction of dummy load, realistic bi-linear server power consumption model, and probabilistic forecast of electricity and frequency regulation service prices enable the data center to accurately follow frequency regulation signals, while reducing the financial risks associated with electricity market participation. The simulation results show that the proposed frequency regulation provision framework results not only in significant cost reduction for data centers, but also limits degradation in quality of service. Meanwhile, the stability and reliability of a power grid will be improved by the frequency regulation service provision.

A stochastic operational model for controlling electric vehicle charging to provide frequency regulation

The charging of battery electric vehicles (BEVs) is a potential source of flexibility and ancillary services to power systems. This paper proposes a two-stage stochastic problem that can be used to optimize the charging of BEVs in a public charging station to provide frequency regulation and energy arbitrage. The model also co-optimizes the use of distributed energy resources, including battery energy storage and photovoltaic solar panels. We demonstrate the performance of the proposed model using a case study based on the Central-Ohio region. The case study shows that proper management of flexibility in BEV charging can provide high-quality frequency regulation services, which is also of significant financial value to the station operator. As such, the modeling methodology that we propose here can further accelerate the adoption of BEVs. This is because the value streams generated by the provision of frequency regulation can reduce the cost of BEV ownership and the net cost of owning and operating a public BEV-charging station.

Receding Horizon Control of Wind Power to Provide Frequency Regulation

With the increased penetration of wind generation in power systems, there is a rising interest in the provision of frequency regulation by wind turbines in order to relieve the burden on remaining conventional generation units. As a first step, the possible contribution of wind power to frequency regulation by optimally anticipating load imbalances in the power system is investigated. This ability is studied by implementing a receding horizon control which takes future load and wind variations into account. In this way, the available energy reserves of the wind turbine over a certain time horizon are optimally exploited to damp frequency oscillations while keeping the energy losses within defined limits. Results indicate that the receding horizon controller will mainly damp overfrequencies as its upward regulation capability is restricted to the available kinetic energy in the turbines. Moreover, it is shown that load forecast errors only slightly influence the results as the controller iteratively determines the optimal trajectory. Even if no load forecast is available, the proposed controller is still capable of damping frequency variations resulting from the simulated load profile by 25%, while keeping the energy yield above 97% compared to optimal power point tracking.

On the Provision of Frequency Regulation in Low Inertia AC Grids Using HVDC Systems

This paper proposes an improved model of a high voltage dc (HVDC) link capable of providing frequency support to networks with no inertia or near-zero inertia; for instance, ac grids with small synchronous generators. The model is useful to carry out steady-state and dynamic simulations of ac grids described by their positive-sequence representation using phasorial information. The core of the frequency control scheme put forward in this paper uses the angular aperture that exists between the internal phase-shifting angle of the voltage source converter (VSC)-HVDC rectifier and the voltage angle at its ac terminal. This is amenable to power flow regulation in the dc link and, hence, to frequency control in the low-inertia grid. A feature of this model is that the developed VSC-HVDC link model may also be used to feed an island system; for instance, a system with dead load, where the inverter station provides the electrical angular reference. Hence, the inverter acts as a virtual synchronous generator with frequency regulation capabilities as seen from the low-inertia ac grid. The dynamic control scheme that enables the VSC-HVDC to provide frequency control in such operating environments has been comprehensively investigated under a wide range of credible scenarios. Overall, the dynamic system of equations describing the VSC-HVDC and the synchronous generators are discretized using the trapezoidal rule, and the ensuing equations are combined together with the algebraic equations of the ac and dc grids in a linearized reference frame amenable to iterative solutions using the Newton-Raphson method.

DC Switch Driven Active Power Output Control of Photovoltaic Inverters for the Provision of Frequency Regulation

In this paper, a control strategy for the participation of photovoltaic (PV) systems in frequency regulation is suggested. A number of strings from every inverter of a PV system are kept as reserve by disconnecting them through dc-relays. Hence, as the control algorithm monitors the grid frequency, it reconnects or disconnects strings, according to the occurring frequency deviations (negative and positive, respectively). Contrary to previous approaches, the suggested methodology here avoids the use of storage devices, which implies additional investment costs, and/or the manipulation of the maximum power point tracking (MPPT) algorithm of the inverter, which represents higher control complexity and special considerations depending on each algorithm. Simulation results from frequency phenomena and solar irradiation changes on a two-bus system in MATLAB Simulink are presented to show the favorable behavior and effective performance of the proposed control strategy. The design concept is also experimentally tested under various operating conditions and on different devices; the results also confirm the feasibility and simplicity of the method.