Adaptive Load Shedding Research Articles

An adaptive load shedding methodology for renewable integrated power systems

System stability issues regarding frequency and voltage in modern power systems are growing in importance as they incorporate more and more complex components. To ensure a sustainable, pollution-free power generation, modern power systems are designed to incorporate more renewable generation sources than traditional ones. Therefore, in the event of a large-scale disruption event, conventional load-shedding strategies are unable to keep the voltage and frequency limit below the threshold value. The suggested approach takes into account this issue by rating load buses in relation to relevant frequency changes, their voltage stability, system load damping coefficients, and the introduction of green energy sources in place of fossil fuel-based ones. Battery Energy Storage Systems (BESS) are used in the proposed method to minimize load shedding amount required for conventional schemes. After determining the amount, the scheme dynamically chooses feeders as per relative weightage of the stability components (voltage, frequency) to ensure that the overall load shed amount is near to the calculated value. To verify this, the scheme is tested on IEEE 39 bus with python scripted simulation. There are four scenarios considering 250 MW, 500 MW and 1500 MW injection of PV based power generation sources with conventional generation loss of 800 MW and 1000 MW. The threshold frequency is considered 49.10 Hz. The total amount of BESS is 300 MW. For every scenario, it has been found that the methodology successfully maintains the system frequency above 49.10 Hz with a minimal amount of load shedding. Hence, the proposed methodology is able to maintain frequency stability for a modern power system with large-scale PV generation through adaptive feeder selection for load shedding.

Adaptive Load Shedding as Part of Primary Frequency Response To Support Networked Microgrid Operations

Global changes in the deployment of distributed energy resources, control and communications technologies, business models, and regulatory policy are increasing the operational options for future distribution systems. One such option is the coordinated operation of distributed resources to form microgrids and networks of microgrids to support traditional bulk power systems during normal operations and critical end-use loads during outages. While individual standalone microgrids have been extensively studied and deployed, the coordinated operation of networked microgrids is operationally more challenging due to the dynamic boundaries and changing mix of generation resources. This paper presents a method of using a distributed control architecture to support primary frequency response in networked microgrids operations. The support of primary frequency response is accomplished using the Open Field Message Bus reference architecture and Grid Friendly Appliance controllers.

A Prioritised Automatic Switching Algorithm for Load Shedding Using Labview

Load shedding is employed at the Ghana Grid Company (GRIDCo) Tarkwa power substation to ensure a balance between power demand and available power. This involves taking off loads from the power transmission network when demand exceeds available power. Such loads are later reintroduced when available power is adequate to supply applied loads. The traditional technique of load shedding employed at the GRIDCo power substation in Tarkwa requires dropping electrical loads based on frequency variations. This may lead to dropping load of entire sections without consideration of essential loads. Research into prioritised load shedding algorithm using semi adaptive load shedding approach can continuously monitor and switch loads at the study area which is a transmission substation located in the Western Region of Ghana. Electrical Transient Analysis Program (ETAP) software version 2019 was used to simulate the single line system of the GRIDCo substation to determine the rate of change of frequency against varying loads. The implementation of the proposed technique was achieved with Laboratory Virtual Instrument Engineering Workbench (LabVIEW) software version 2019. Using typical load shedding data from the GRIDCo Tarkwa power substation, the proposed design was tested and found to be effective in carrying out load shedding.

Reinforcement Learning Based Adaptive Load Shedding by CANFIS Controllers for Frequency Recovery Criterion-Oriented Control

Reinforcement Learning Based Adaptive Load Shedding by CANFIS Controllers for Frequency Recovery Criterion-Oriented Control

Innovative Load Shedding Scheme to Restore Synchronous Generator-Based Microgrids During FIDVR

Fault induced voltage recovery (FIDVR) phenomenon may occur in microgrids ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Gs) and distribution systems due to the induction motors (IMs) behavior after system voltage sags especially short circuit faults. For the case that motors reaccelerate, system voltage may recover to its nominal value after few seconds. However, it may remain low during motor stalling condition, which result in unstable (non-recoverable) FIDVR. In this paper, an adaptive load shedding scheme is proposed to mitigate unstable FIDVR in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Gs containing synchronous dispersed generators (SDGs) to enhance system dynamic behavior. Derivative of the imaginary part of equivalent admittance seen from the distribution feeders with respect to time is utilized to discriminate stable FIDVR from unstable ones. In addition, a new criterion is proposed to determine SDG stability margin during the FIDVR phenomenon. Then, a new load shedding scheme is presented based on the proposed SDG stability margin and IM reacceleration index. Moreover, the load shedding time delay is adaptively calculated based on motor reacceleration time. Performance of the proposed method is evaluated by comprehensive simulation studies on two realistic networks. These investigations fairly reveal security and reliability of the proposed method in various conditions.

Toward Adaptive Load Shedding Remedial Action Schemes in Modern Electrical Power Systems

Toward Adaptive Load Shedding Remedial Action Schemes in Modern Electrical Power Systems

A Hybrid Adaptive Algorithm for Power System Frequency Restoration Based on Proposed Emergency Demand Side Management

The power system blackouts have occurred in recent years all across the world. Therefore, it is necessary to develop more effective methods for preventing such events. In this paper, a novel effective method is proposed to restore the frequency of power system and make the system stable for major disturbances. To do this, for the first time, the adaptive load shedding and emergency demand response algorithms are combined to improve the power quality in addition to system stability. To evaluate the proposed method, the New England 39-bus standard grid is selected and simulated using DIgSILENT software package and its performance is studied for moderate and large power deficit scenarios. The obtained results prove the superiority of the new method in comparison with the pervious methods from points of view lower power interruption and reducing the probability of power system collapse by decreasing the convergence time and minimizing the frequency drop.

An Adaptive Underfrequency Load Shedding Scheme in the Presence of Solar Photovoltaic Plants

Load shedding is performed, as last option, for emergency measure when system frequency drifts below the allowed limit. Utilities use underfrequency load shedding schemes to bring back frequency within limit. In this article, an adaptive underfrequency load shedding scheme is proposed for the power system in the presence of solar photovoltaic plants using wide-area measurements. Stepwise load shedding is performed at selected buses with consideration of any change in photovoltaic power output and load/generation at each step. Share of load to be shed at a bus is based on the voltage stability index of the buses at that instant considering predefined load priority. The voltage stability index at a bus is obtained using the Thevenin equivalent of the system. For a solar photovoltaic plant integrated system, the Thevenin equivalent changes with solar power variation, where available methods become inaccurate. A Thevenin equivalent calculation approach is proposed in this article using an equivalent model of synchronous generators and photovoltaic plants. The proposed load shedding method is tested on the New England 39-bus system and the 233-bus North Eastern Indian grid with integrated photovoltaic plants. It is compared with available methods and found to be a better technique in bringing system frequency to normalcy with adaptive load shedding.

A New Adaptive Load-Shedding and Restoration Strategy for Autonomous Operation of Microgrids: A Real-Time Study

Islanding operation is one of the main features of a MicroGrid (MG), which is realized regarding the presence of distributed energy resources (DERs). However, in order to deal with the control challenges, which an MG faces during island operation, particularly when the transition is associated with certain excessive load, an efficient control strategy is required. This paper introduces a Central Management Agent (CMA) which maintains the stability of the MG, once it is islanded, by controlling an Energy Storage System (ESS) and a Central Synchronous Generator (CSG). Further, this paper proposes a new adaptive load-shedding/restoration schemes that calculates the amount of power imbalance based on frequency measurements combined with the mean value of the frequency gradient. The primacy of the proposed scheme over existing schemes, like instantaneous frequency gradient-based load shedding scheme, is its robustness against frequency oscillations. Moreover, the proposed method acts compatible with the control routine of DERs and the intermittent nature of the PV plant. As another salient feature of this paper, a Hardware In the Loop (HIL) testbed for real-time simulation is developed under which the proposed scheme and related communication with CMA along with other components are evaluated. The obtained results show that the control strategy can confidently conserve the stability of the MG in islanded mode and meet smooth reconnection to the grid-connected mode.

A hybrid scheme of load shedding using globalized frequency and localized voltage (GFLV) controller

Load shedding is a control action to maintain the stability of power system by disconnecting the load in case of electricity shortfall. For the safe operation of electrical power system, it is necessary that frequency and voltage should be within the specific range. In this paper, a novel load shedding technique is proposed based on globalized frequency and localized voltage (GBLV). The proposed strategy is implemented through simulation on PSCAD/EMTDC. Simulations results reveal that the proposed schemes are successfully catering the decline in frequency and voltage by performing adaptive load shedding to sustain the stability of power system.

Adaptive Voltage-Based Load Shedding Scheme for the DC Microgrid

The direct current (DC) microgrid requires a fast load shedding scheme that prevents instability and voltage collapse when the distributed energy resources are unable to meet the power demand. The load shedding scheme is also expected to prevent unnecessary service interruptions caused by over-shedding of loads. This paper proposes an adaptive voltage-based load shedding scheme utilizing voltage thresholds that are automatically adjusted depending on the rate of change of locally measured bus voltages. The performance of the proposed load shedding scheme is investigated and compared with that of the conventional voltage-based load shedding scheme, using a realistic and detailed study system, under various disturbances. The comprehensive simulation studies that are conducted using the PSCAD software indicate that the adaptive load shedding scheme (i) effectively maintains the DC microgrid power balance through fast and coordinated load shedding, (ii) prevents the DC bus voltages from falling below acceptable levels, (iii) ensures that the critical loads do not experience excessive steady-state voltage deviations, (iv) minimizes the durations and magnitudes of the temporary voltage drop caused by sudden disturbances, and (v) improves power supply reliability.

Decentralized Adaptive Under Frequency Load Shedding Scheme Based on Load Information

The inertia of the power system changes when the generators in the system are disturbed or tripped. However, in some systems, there is no control center or communication device falling behind. It makes real-time inertia difficult to obtain and affects the adaptive under frequency load shedding (UFLS) scheme. This paper proposes an adaptive decentralized UFLS scheme based on load information to overcome this problem. First, a calculation method is derived according to the load information after the disturbance to identify the real-time of load equivalent virtual inertia. Then, the power deficit of load is estimated and the optimal adaptive load shedding scheme is obtained. Finally, compared with conventional UFLS schemes, the proposed scheme can be performed merely by load information. Hence, the requirement of communication conditions and the dependence on the control center are reduced. The simulation is carried out on the island utilizing the IEEE39-bus system. Furthermore, the accuracy of real-time identification of load equivalent virtual inertia and the validity of the load shedding scheme are verified.

An improved adaptive wide-area load shedding scheme for voltage and frequency stability of power systems

Conventional under-frequency and under-voltage load shedding schemes are known as effective approaches for load shedding purposes. Generally, these two schemes are deployed independently within which the combinatorial disturbances are overlooked. Contributing to this context, the ongoing study raises a high concern on developing a generalized wide-area adaptive load shedding scheme. In order to preserve the voltage and frequency stabilities, the established approach deploys the variations of voltage, frequency, active, and reactive power in all buses, simultaneously. More specifically, the reactive power variation on voltage stability is incorporated in the proposed load shedding index. This idea improves the performance of the proposed scheme, significantly. Infield phasor measurement units are establishing a wide-area basis, enabling the proposed approach in modern control centers. Extensive numerical studies are devised to assess the performance of the proposed approach encountering various disturbances. The obtained results are discussed in depth.

An Adaptive Wide-Area Load Shedding Scheme Incorporating Power System Real-Time Limitations

Under frequency load shedding (ULFS) schemes are devised to help power system maintain the load-generation balance by shedding adequate loads to match the generation. In this paper, a new centralized adaptive load shedding scheme is proposed in three stages. The first stage determines the requirements needed for implementation of the proposed scheme. The optimal amount and location of load drops and post load shedding strategies are specified in the second stage. In addition to consideration of operational limitations and voltage stability criteria, this stage takes the interruption cost of dropped loads into account. In the third stage, the event type is determined in real time and the pre-specified optimal load shedding scheme and post load shedding strategies associated with the event are implemented. The proposed methodology is successfully testified in the IEEE 39-bus system through several case studies.

Improved UFLS with consideration of power deficit during shedding process and flexible load selection

This study presents an improved under-frequency load shedding (UFLS) scheme that can detect power deficit during the shedding process and accordingly adjust the amount of load shedding. This is achieved by continuous monitoring of the overshooting signal of the second frequency derivative of the centre of inertia. Once detected, an equivalent system inertia constant is estimated in order to quantify the new power deficit. The scheme is also equipped with an optimisation algorithm to determine the best combination of loads that is close to the amount of power deficit, which minimises frequency overshoot/undershoot. The optimisation technique selected for this work is based on particle swarm optimisation. The performance of the proposed UFLS scheme was validated using a modified IEEE 33 bus with two mini-hydro generators and one full converter wind turbine. The system and the proposed UFLS was modelled and simulated in PSCAD/EMTDC software. The results confirmed that the proposed scheme is capable of shedding loads with minimum undershoot/overshoot, and detect and estimate a new power deficit during load shedding. The results reported by the proposed scheme proved to be significantly better than those reported by conventional and adaptive load shedding schemes.

A Plug-and-Play Selective Load Shedding Scheme for Power Systems

In contemporary power systems, conventional load shedding schemes are typically used. These load shedding schemes employ a preset step-level structure that identifies the amount of load to be shed. There are predefined candidate circuit breakers to be opened, based on the importance of loads, historical data for the load demand at each substation, and the operator's experience. Clearly, real conditions at the time of fault differ, resulting in the shedding of a larger or smaller amount of load and to a nonoptimal operation of the load shedding scheme. A second point to note is that adaptive load shedding schemes are usually only theoretically functional due to the large amount of real-time monitoring data required to perform satisfactorily. These data cannot be obtained on a large scale and in a cost effective manner. Last but not least, adaptive load shedding schemes do not always respond adequately against newly emerging or combinational events. In this paper, an adaptive load shedding scheme is proposed, based on a single measurement of the electric frequency of the power system. It approximates online the certain structure of the nonlinearities of the swing equation of the power system and adaptively bounds the load disturbances and the functional approximation errors of the nonlinearities. This way, a control law is extracted that “cancels” the nonlinearities and responds adequately to the load disturbances, achieving the frequency stability of the system effectively.

Adaptive Under-Frequency Load Shedding Scheme in System Integrated with High Wind Power Penetration: Impacts and Improvements

As the requirements of economical operation and reliability on power grid are enhanced gradually nowadays, the existing under frequency load shedding (UFLS) scheme is not quite fit for the modern power system that integrates high wind power. In this paper, the impacts of high wind power penetration on the UFLS are discussed thoroughly. A novel adaptive load shedding (LS) scheme is presented taking the high wind power penetration into account. In the proposed scheme, the equivalent inertia constant (EIC) is calculated accurately to improve the power deficit accuracy so as to reduce the error of LS. The dynamic correction of power deficit is able to solve the negative effects of the wind power output random reduction/the wind generator tripping. Besides, the locking criterion is capable of avoiding the influences of the wind power output random increase on the LS, thus cutting down the LS costs and even preventing the frequency overshoot. Moreover, in terms of the LS parameters setting, the coordination of the low frequency protection of the wind generator and the frequency threshold is addressed. The location and capacity model of LS, which is based on the load characteristics, can ameliorate the frequency recovery process. Finally, the validity and robustness of the proposed scheme are verified in the simulations on the IEEE-39 bus system with high wind power penetration.

An Analytical Adaptive Load Shedding Scheme Against Severe Combinational Disturbances

To diminish damaging consequences of power system major disturbances, under frequency load shedding (UFLS) plans are devised so as to prevent power networks from collapse. Since load shedding scenarios in conventional UFLS plans are specified regardless to voltage stability criteria, they cannot bring desired outcomes at the event of severe and combinational contingencies. In these circumstances, the location of load drops, in addition to their amounts, should be determined as well. This paper presents a two-unit wide-area adaptive load shedding scheme based on synchrophasors. In the first unit, an adaptive precise system frequency response (SFR) model is developed, by the help of which, the appropriate amount of load rejections is determined such that the dynamic and steady state frequency limitations are fulfilled. Incorporation of both static and dynamic loads into the adaptive SFR model results in a negligible error in calculations. Specifying the best location of load drops based on suitable voltage stability criteria is the main task of the second unit. These two units are executed in a parallel way; the computational burden of the proposed approach is thus tractable for real world applications. The new method is successfully testified in the IEEE 39-bus system and Khorasan network.

Adaptive load shedding scheme for frequency stability enhancement in microgrids

The imbalance between the generated power and the load demand is the major factor that is usually responsible for frequency instability in power systems, most especially islanded microgrids. To determine the size of the loads that should be shed and their appropriate locations in the power system, to maintain the system frequency within the permissible limits, this paper presents an effective adaptive control scheme. In the proposed controller, a stepwise load-shedding approach is designed in the islanded MGs to regulate the grid frequency while providing the amount of power shortage. To this achieve, it locally measures the system parameters most especially voltage and frequency signals. Thereafter, a stepwise load-shedding will take place in locations where the highest voltage drop and frequency variation are experienced. The load-shedding step changes according to certain factors such as shedding speed, location and value, and the rate of frequency change. The proposed approach eliminates the adjustable loads to return the frequency back to the desired value. Simulation results of the proposed method under different practical scenarios, when compared with the conventional PID controller, provide considerable enhancement in the power system frequency stability.

Venus: Scalable Real-Time Spatial Queries on Microblogs with Adaptive Load Shedding

Microblogging services have become among the most popular services on the web in the last few years. This led to significant increase in data size, speed, and applications. This paper presents Venus ; a system that supports real-time spatial queries on microblogs. Venus supports its queries on a spatial boundary $R$ and a temporal boundary $T$ , from which only the top- $k$ microblogs are returned in the query answer based on a spatio-temporal ranking function. Supporting such queries requires Venus to digest hundreds of millions of real-time microblogs in main-memory with high rates, yet, it provides low query responses and efficient memory utilization. To this end, Venus employs: (1) an efficient in-memory spatio-temporal index that digests high rates of incoming microblogs in real time, (2) a scalable query processor that prune the search space, $R$ and $T$ , effectively to provide low query latency on millions of items in real time, and (3) a group of memory optimization techniques that provide system administrators with different options to save significant memory resources while keeping the query accuracy almost perfect. Venus memory optimization techniques make use of the local arrival rates of microblogs to smartly shed microblogs that are old enough not to contribute to any query answer. In addition, Venus can adaptively, in real time, adjust its load shedding based on both the spatial distribution and the parameters of incoming query loads. All Venus components can accommodate different spatial and temporal ranking functions that are able to capture the importance of each dimension differently depending on the applications requirements. Extensive experimental results based on real Twitter data and actual locations of Bing search queries show that Venus supports high arrival rates of up to 64 K microblogs/second and average query latency of 4 msec.