Improve Frequency Stability Research Articles

Magnetic permeability stability of composite material with nominal composition Ni0.6Fe2.4O4

A composite material with a nominal composition of Ni0.6Fe2.4O4 was prepared by the solid-phase reaction method. X-ray diffraction analysis shows that the product is composed of α-Fe2O3 and a solid solution of Fe3O4 and NiFe2O4. Although α-Fe2O3 non-magnetic phase reduces the saturation magnetization, it greatly improves the temperature and frequency stability of magnetic permeability. Based on the measurement results of the amplitude permeability in the range of −60 °C to 100 °C, the temperature coefficient αμ and specific temperature coefficient β were calculated. αμ and β of the composite material are 7.15 ×10-5/°C and 8.6 ×10-6/°C, respectively, which are much smaller than αμ (1.26×10-3/°C) and β (9.5×10-5/°C) of NiFe2O4. At the same time, the magnetic spectrum curves show that the real part of the complex permeability μ' basically remains unchanged within the measurement frequency range (f < 106 Hz). This improvement in temperature and frequency stability is attributed to the effect of the α-Fe2O3 phase.

The impact of additional injected signals on the stability and bandwidth of the quantum cascade lasers with external cavities

- In recent years, special attention has been paid to the injection lock of quantum cascade lasers, which leads to the improvement of their small signal properties and output power. In this paper, the operation of an injection-locked quantum cascade laser including the output characteristics and modulation response has been investigated. By using one external cavity for optical lock, the resulted structure has complexities may cause instability of a laser that limit the use of this system. In this paper, for the first time, to solve this problem, an optical self-locking system was proposed and the properties of laser under these conditions were investigated. By adding a second external cavity to a single external cavity laser, output power will reach a constant value. The output power of the single cavity laser in free-running mode was about 400 mw while the output power of the laser with two external cavities has been increased to 700 mw. In addition to stabilizing the output power, we also see an increase in bandwidth. We found that for different lengths and reflectivity, the output power of the proposed one external cavity laser in free-running mode does not reach a fixed value and even in some cases, it becomes unstable. But by adding a second cavity to the laser in the free-running mode, it will be able to produce a stable laser with constant output power. Adding external cavities can be used as an effective tool to improve frequency stability or increase bandwidth.

Automatic Generation Control of a Future Multisource Power System Considering High Renewables Penetration and Electric Vehicles: Egyptian Power System in 2035

Egypt aims to diversify electricity generation sources and targets 42% of its power capacity through different renewable energy sources (RESs) by 2035. Such an increased share of RESs will make grid operation and control more tedious and may have a negative impact on power system frequency stability. Therefore, this paper is the first study that studies the automatic generation control of future multi-source power systems (e.g., Egyptian Power System (EPS) in a future 2035 scenario) considering high RESs penetrations and electric vehicles (EVs). The RESs in this future scenario include photovoltaic plants, wind generation plants, concentrated solar power plants, and hydropower plants. The EPS also contains other traditional power plants based on fossil fuels (i.e., coal, oil, and natural gas) and nuclear power plants. Moreover, this study investigates the effect of participation of EVs in enhancing the frequency stability of the future-scenario EPS. Furthermore, this study proposes a fractional-order proportional integral derivative (FOPID) controller for load frequency control (LFC), and its parameters are tuned using RUNge Kutta optimizer (RUN), which is a new optimization algorithm. To assess the FOPID controller performance, it was compared with a proportional-integral-derivative controller, proportional-integral controller, and integral controller. The results showed the positive effect of EVs’ participation in frequency regulation of the future-scenario EPS, the effectiveness of RUN optimizer in LFC application, and the superior performance of the FOPID controller over its peers of controllers used in the literature in improving frequency stability through reducing frequency deviations caused by different disturbances and under various power system conditions.

Dynamic Electrical Equivalent Circuit Modeling of the Grid-Scale Proton Exchange Membrane Electrolyzer for Ancillary Services

As the percentage of renewable energy sources grows, excess electrical power from renewables can be converted using electrolyzers to produce hydrogen, which can be stored, and later utilized by industries, homes, or the transportation system. Further, electrolyzers can also be utilized for frequency and voltage control to improve the stability of the power system. In this paper, a novel electrical circuit model for a 400W PEM electrolyzer is designed and validated using the experimental data from a reported paper&#x00A0;for a 400W electrolyzer. To demonstrate its adaptive feature, the proposed 400W model is then scaled up to a 1 MW array by series and parallel connections, and the resulting system is validated by comparing it to another reported experimental results of a 1 MW stack. These results reveal that the developed model can reproduce very similar step responses to those obtained from experimental results from the reported 400W electrolyzer and the 1 MW stack. Finally, using the proposed electric circuit model, the step response of the equivalent circuit model to the step-change in the grid frequency has been investigated and the results show that the electrolyzers can respond to frequency step change faster than traditional generators demonstrating that employing electrolyzers can have a great potential to improve frequency stability.

Dynamic Adjustment of a VSC's Reactive Current Limit to Improve Frequency Stability

Future renewable energy sources will need to provide all ancillary network services, previously provided by the synchronous generators that are being decommissioned. The voltage sourced converter (VSC), with its ability to control active and reactive power independently, can be adapted to provide voltage support. The ability to provide voltage support can require the sacrifice of active power, which can be detrimental to the frequency stability. This paper presents three methods to limit the quantity of reactive power injection that can occur if the frequency has been perturbed. The aim is to provide support to the system frequency by limiting the quantity of active power reduction from the VSC. The three options presented use frequency deviation, rate of change of frequency, or a combination of both, to reduce the maximum reactive current limit. In this work it is shown that using the rate of change of frequency to reduce the maximum reactive current limit, provides the greatest benefit to the frequency stability. All options presented, allow the VSC to provide continually operating voltage support without having to prioritize one form of ancillary service over another.

OPTIMIZING LOAD STEP PRE-ANNOUNCEMENT AND BANG-BANG CONTROLLER FOR ENHANCED ISLANDED MICROGRID FREQUENCY STABILITY

A novel control method that can assist conventional frequency control to improve frequency stability of islanded microgrids is presented. As two time parameters strongly affect the performance of the proposed method, definition and influential factors of optimal time parameters are studied, focusing on the dependency on non-controlled generation and load variation. A test islanded microgrid is simulated. Using three optimization criteria, correlations between influential factors and optimal system time parameters are investigated. The effectiveness of the control method is presented in terms of dynamic simulation results.

Post-Manufacturing Process and Temperature Calibration of a 2-MHz On-Chip Relaxation Oscillator

In this work, the design methodology of the relaxation oscillator with the post-processing trimming option for frequency and temperature coefficient is presented. A novel oscillator core is introduced, which ensures good control linearity and insensitivity to CMOS variations of the output frequency as a prerequisite for frequency and temperature calibration. The proposed oscillator operates at 2 MHz and consumes typically about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{DD}=97.8\,\,\mu \text{A}$ </tex-math></inline-formula> at the nominal temperature of 42.5°C and nominal supply voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{DD}=1.8$ </tex-math></inline-formula> V. The oscillator is verified experimentally with 10 samples manufactured in 180 nm CMOS process, each covering an area of 0.075 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The frequency and temperature calibration was performed based on the two-point temperature measurements, resulting in a significant improvement in frequency stability. The temperature calibrated oscillator has a temperature variation ±0.30% in the temperature range from −40°C to 125°C, and the variation with the power supply ±0.07% in the supply range from 1.62 V to 1.98 V.

신재생에너지 확대에 따른 계통관성 영향성 평가 및 안정도 향상 방안에 관한 연구

As the environmental pollution problem becomes serious, interest in renewable energy is increasing around the world, and overseas power companies and domestic companies are also planning to expand renewable energy. With the expansion of renewable energy, the system inertia is decreasing due to the decrease of existing synchronous generators and the increase of inverter-based generators. In this paper, the effect of frequency response due to expansion of renewable energy was evaluated and a method for improving frequency stability was simulated. Based on the 9th power supply and demand plan, a scenario was constructed according to the amount of renewable generation, and the effect for changing and installing the synchronous inertia, frequency reserve, governor droop and ESS was analyzed through frequency response simulation in case of simultaneous generator accidents. The frequency response characteristics are analyzed through those methods to confirm that four methods can be applied as stability improvement measures.

A cogeneration scheme with biogas and improvement of frequency stability using inertia based control in AC microgrid

Abstract Currently, penetration of the renewable energy sources (RES) like solar photovoltaic (PV) panels, wind turbine-based plants is increasing in the conventional power grid to combat pollution, global warming, and to enhance energy sustainability. Fast power electronic converters are necessary to extract power from these sources which do not have any inertia. When more renewable sources are connected to the power grid, it reduces the effective system inertia which results in unacceptable grid frequency changes for any transient. This leads to frequent tripping, cascading fault, and instability of the overall system which can create large-scale blackouts. This work is related to the generation of physical inertia through the biogas plant and emulates inertia from the dc-link capacitor to control the rate of change of frequency (RoCoF) under abrupt load change. The stored energy in a biogas plant and dc-link capacitor in an AC microgrid (MG) can support momentary power requirement which improves the transient performance of grid frequency under unavailability of PV power. A storage system can help to compensate for abrupt frequency change during transient but due to its higher cost and relatively lesser lifetime, these systems can’t be relied upon in the long run. The proposed scheme of cogeneration and frequency control can provide better performance which is simulated in MATLAB 2013 (b). The control system is implemented in hardware using NI-cRiO 9082 in 500 W AC MG which shows 53.57% improvement in RoCoF which complies with the requirement of IEEE/IEC 60255-118-1.

Contribution of Voltage Support Function to Virtual Inertia Control Performance of Inverter-Based Resource in Frequency Stability

Inertia reduction due to inverter-based resource (IBR) penetration deteriorates power system stability, which can be addressed using virtual inertia (VI) control. There are two types of implementation methods for VI control: grid-following (GFL) and grid-forming (GFM). There is an apparent difference among them for the voltage regulation capability, because the GFM controls IBR to act as a voltage source and GFL controls it to act as a current source. The difference affects the performance of the VI control function, because stable voltage conditions help the inertial response to contribute to system stability. However, GFL can provide the voltage control function with reactive power controllability, and it can be activated simultaneously with the VI control function. This study analyzes the performance of GFL-type VI control with a voltage control function for frequency stability improvement. The results show that the voltage control function decreases the voltage variation caused by the fault, improving the responsivity of the VI function. In addition, it is found that the voltage control is effective in suppressing the power swing among synchronous generators. The clarification of the contribution of the voltage control function to the performance of the VI control is novelty of this paper.

Rule-based adaptive control strategy for grid-forming inverters in islanded power systems for improving frequency stability

Operating isolated power systems with increasing shares of renewable energy sources requires the integration of battery energy storage systems in order to assure enhanced frequency regulation capabilities. The control mode of power converters interfacing battery energy storage systems to the grid can be based on grid-forming type structures given its superior performance with respect to the mitigation of network frequency disturbances. Nevertheless, in case of network faults, the interactions between existing synchronous units and the grid-forming type converters may adversely affect the global system behavior. Therefore, this paper addresses the study-case of a MW-scale isolated power system with large shares of converter-interfaced renewable generation, operating with both synchronous machines and a grid-forming type power converter. An optimal grid-forming control parameter tuning procedure considering different disturbances is presented, aiming to reduce the associated battery energy storage system power regulating effort following the disturbances. Moreover, it is proposed and discussed the need of a novel rule-based adaptive control solution to switch between different sets of control parameters used in grid-forming type converters depending on the network status following a fault-type disturbance. Extensive numerical simulations performed over different operating scenarios illustrate the performance of the proposed solution.

Coordinated Control Strategy and Validation of Vehicle-to-Grid for Frequency Control

The increased penetration of renewable energy sources (RES) and electric vehicles (EVs) is resulting in significant challenges to the stability, reliability, and resiliency of the electrical grid due to the intermittency nature of RES and uncertainty of charging demands of EVs. There is a potential for significant economic returns to use vehicle-to-grid (V2G) technology for peak load reduction and frequency control. To verify the effectiveness of the V2G-based frequency control in a microgrid, modeling and simulations of single- and multi-vehicle-based primary and secondary frequency controls were conducted to utilize the integrated components at the Canadian Centre for Housing Technology (CCHT)-V2G testing facility by using MATLAB/Simulink. A single-vehicle-based model was validated by comparing empirical testing and simulations of primary and secondary frequency controls. The validated conceptual model was then applied for dynamic phasor simulations of multi-vehicle-based frequency control with a proposed coordinated control algorithm for improving frequency stability and facilitating renewables integration with V2G-capable EVs in a microgrid. This proposed model includes a decentralized coordinated control of the state of charge (SOC) and charging schedule for five aggregated EVs with different departure times and SOC management profiles preferred by EV drivers. The simulation results showed that the fleet of 5 EVs in V2B/V2G could effectively reduce frequency deviation in a microgrid.

A New Adaptive Underfrequency Load Shedding Scheme to Improve Frequency Stability in Electric Power System

This paper proposes a new adaptive underfrequency load shedding scheme (UFLS) to avoid frequency instability in electrical power system during abnormal wide area disturbances. The developed scheme is based on online monitoring of the distance relay zone 3 decisions of some tie lines using (WAMS) and SCADA/EMS systems, to check rapidly and reliably the uncontrolled islanding conditions and, permit an automatic load shedding action to maintain frequency stability of power system. Simulation results on 400 kV Turkish transmission systems demonstrated the effectiveness of the proposed scheme compared to current frequency load shedding schemes which they cannot consider all possible circumstances because of their limited access to the power network data. Simulation results clearly indicate that large disturbances in power systems can be avoided and their propagation can also be stopped using the proposed scheme.

Frequency Stability Improvement of Power System using ABC Algorithm

Frequency Stability Improvement of Power System using ABC Algorithm

A new synthetic inertia system based on electric vehicles to support the frequency stability of low-inertia modern power grids

The increasing share of renewables into modern power systems has resulted in lower levels of existing rotational inertia accompanied by conventional generation units. This issue results in an increase in system frequency fluctuations, which leads to system deterioration and instability. To overcome the ever-decreasing issue of inertia, several endeavors in inertia emulation have been provided based on external sources of energy (e.g., energy storage systems (ESSs)). However, the high capital and running costs associated with the adoption of these sources for inertia enhancement significantly deter their wide applications. Hence, to tackle these issues, this study proposes a new synthetic inertia control (SIC) system that relies on electric vehicles (EVs) as a pre-existing energy source in low-inertia modern power grids to expand inertial emulation capability and support frequency stability. In this way, the power system inertia can be imitated by exploiting the surplus stored energy in already existing system resources (e.g., EVs) without changing system hardware, thus decreasing the ESS’s required capacity. The proposed SIC is constructed based on the derivative control technique, where it is utilized to estimate the rate of change of frequency (RoCoF) to add adequate inertia power to the power grid set-point during contingencies, thereby improving frequency stability of low-inertia systems. The usability and superiority of the suggested SIC system based on EVs are validated by comparison with the traditional frequency control system against variant load/renewables disruptions, uncertainties, and physical constraints. The simulation results verified that the suggested SIC system exhibits ameliorated system performance and reliability, which could greatly support low-inertia modern power grids against contingencies.

Enhancing Power System Frequency with a Novel Load Shedding Method Including Monitoring of Synchronous Condensers’ Power Injections

Under-frequency load shedding (UFLS) is a classic and a commonly accepted measure used to mitigate the frequency disturbances in case of loss-of-generation incidents in AC power grids. Triggering of UFLS is classically done at frequency thresholds when system frequency collapse is already close to happening. The renewed interest for synchronous condensers due to the global trends on massive commissioning of non-synchronous renewable power generation leading to reduction of system inertia gives an opportunity to rethink the approach used to trigger load-shedding activation. This question is especially relevant for the Baltic states facing a desynchronization from Russian power grid and a necessity to operate in an isolated island mode. The main goal of this paper is to introduce a predictive load shedding (LS) method without usage of either frequency or ROCOF measurements based on the monitoring of active power injections of synchronous condensers and to prove the efficiency of the concept through several sets of case study simulations. The paper shows that the proposed approach can provide a greatly improved frequency stability of the power system. The results are analyzed and discussed, the way forward for the practical implementation of the concept is sketched.

A Novel Adaptive Virtual Inertia Control-Based Adaptive Neuro-Fuzzy to Enhance Frequency Stability of a Microgrid with Seamless Transition

A frequency stability improvement of a microgrid with low-inertia constant during severe disturbances remains a challenge using a virtual inertia control to compensate the inertia power to the microgrid, using a battery energy storage system. However, the fixed virtual inertia constant and the low-order model of the battery energy storage system utilized in virtual inertia control can affect the stability behaviors of microgrid and virtual inertia control design. Hence, for solving these issues, this paper proposes a novel adaptive virtual inertia control utilizing an adaptive neuro-fuzzy inference system based on a training data design in order to adjust the controller gain that applies for the direct and the quadrature axis model of the battery energy storage system. In order to investigate the proposed method and to verify the performance, the various case studies are carried out under the high, the low levels existing of renewable energy, and the parameter uncertainties in a microgrid. The simulated results with the proposed scheme are compared with the virtual inertia based-linear quadratic Gaussian synthesis and without the virtual inertia control. The comparative results reveal that the proposed method enhances the frequency stability during the disturbances, reduces the switching transition time from the islanded to the grid-connected mode of the microgrid, seamlessly, with superior performance in comparison with the other methods, satisfying a frequency grid code in Thailand.

Frequency Trajectory Planning Based Strategy for Improving Frequency Stability of Droop-Controlled Inverter Based Standalone Power Systems

Inverter-based standalone power systems (ISPSs), with limited inertia/damping, are prone to significant changes in frequency indicators encompassing frequency deviation and rate of change of frequency (RoCoF), which can easily exceed the pertinent relay thresholds and cause power outages. Limited by estimating the disturbance and system inertia/damping deficiency, existing controls cannot ensure system frequency stability. To overcome this issue, a frequency trajectory planning (FTP) based strategy is developed in this article to improve frequency stability of droop-controlled ISPS. This frequency-indicator-oriented control relates system frequency with several pre-defined planning parameters, decoupling from system’s disturbances and inertia/damping deficiency that are difficult to evaluate. During normal operation or when the disturbance level is insignificant, the inverter operates in standard droop mode since the system intrinsic inertia/damping features suffice to regulate the frequency. In the event of a large disturbance, an FTP block is triggered by detected frequency indicators, and a marginally safe frequency trajectory is planned according to the requirement of the grid code. In this case, by tracking the planned frequency trajectory, the inverter provides suitable inertia/damping support needed by the system, thereby guaranteeing frequency stability of the ISPS. Finally, simulation and experimental results proved the effectiveness and advancement of the FTP based strategy.

Analysis of Control Strategies Based on Virtual Inertia for the Improvement of Frequency Stability in an Islanded Grid with Wind Generators and Battery Energy Storage Systems

Rising levels of non-synchronous generation in power systems are leading to increasing difficulties in primary frequency control. In response, there has been much research effort aimed at providing individual electronic interfaced generators with different frequency response capabilities. There is now a growing research interest in analyzing the interactions among different power system elements that include these features. This paper explores how the implementation of control strategies based on the concept of virtual inertia can help to improve frequency stability. More specifically, the work is focused on islanded systems with high share of wind generation interacting with battery energy storage systems. The paper presents a methodology for modeling a power system with virtual primary frequency control, as an aid to power system planning and operation. The methodology and its implementation are illustrated with a real case study.

A robust PID controller based on linear quadratic gaussian approach for improving frequency stability of power systems considering renewables

This paper proposes a novel robust controller for frequency stabilization of electrical systems taken into consideration a high renewable energy sources (RESs) penetration. The suggested controller, robust PID (RPID) controller, is combination of a proportional–integral–derivative (PID) controller and a linear quadratic gaussian (LQG) controller. Furthermore, the Improved lightning attachment procedure optimization (ILAPO) technique is applied for determining the optimal setting of the parameters of the introduced RPID controller. A studied power system with RESs is used as a test system to justify the performance of the RPID controller. The superiority of the introduced robust controller is verified through a comparison of its performance under system uncertainties with those of other robust controllers presented in the literature. The results elucidate that the RPID controller can effectually enhance frequency stability and guarantee reliable performance for power grids supplied with high share of renewable energy for all studied scenarios. Consequently, the proposed RPID controller purveys creditable for modern power systems considering RESs.