An optimal under-frequency load shedding strategy considering distributed generators and load static characteristics

Summary Because of the high penetration of distributed generation, energy storage systems, and flexible loads, nodal power injections in active distribution networks (ADNs) would vary frequently and significantly. Thus, it becomes crucial to accurately and quickly assess the influence of power injection variations on key operation status of ADNs, such as nodal voltages, line losses, and branch power flows. Meanwhile, modern ADNs may include nonradial and DC network segments, which make power flow analysis more complicated. In this paper, power flow models of ADNs while considering nonradial topologies and hybrid AC/DC networks are analyzed to derive a suite of power sensitivity models with wide adaptability, including a quadratic sensitivity model of nodal power injections to line losses, a linear sensitivity model of nodal power injections to nodal voltages, and a quadratic and a simplified linear sensitivity models of nodal power injections to branch powers. Numerical results evaluate the accuracy and efficiency of the proposed sensitivity models.

Section: Introductionmentioning

confidence: 99%

Power sensitivity models with wide adaptability in active distribution networks considering loops and DC networks

Liu

Wang

et al. 2019

“…In a traditional multistage UFLS plan, a predefined amount of load is disconnected when the system frequency falls below a predetermined threshold after a certain time. To adjust the UFLS relays, three parameters should be optimally set as follows: Frequency threshold for every LS step. Time delay for every LS step. The amounts of load to be disconnected in every LS step. …”

Section: Introductionmentioning

confidence: 99%

Multiobjective optimal setting for UFLS relays considering voltage deviation

Alizadeh

Jafari‐Nokandi

Amraee

2018

Summary The postdisturbance power imbalance causes the power system frequency to drop. For preventing the frequency drop below the safe range, under frequency load shedding (UFLS) plan should be used by applying UFLS relays. In this paper, the conventional multistage UFLS plan is promoted via a linearized AC power flow model. A multiobjective mixed‐integer linear program is solved in order to minimize the load shedding amount and voltage deviation simultaneously. The proposed method simultaneously benefits from individual UFLS and under voltage LS (UVLS) features which may operate in the power system without coordination. The proposed method has been implemented in IEEE 39‐bus test system, and the results are presented under different scenarios. The results show that the proposed model for locating UFLS relays and their optimal setting can maintain both the system frequency and bus voltages in the secure operating limits.

“…When a sudden increase in demand or electrical shutdown happens, power systems will experience a frequency decline. Excessive frequency drop may cause damage to electric devices, outage of system equipment, and even system collapse …”

Section: Introductionmentioning

confidence: 99%

“…Wide area measurement system (WAMS) can provide state variables of power system with millisecond precision, which enables to predict the steady frequency more efficiently . Based on the WAMS measurements, the system frequency response model (SFR) derived in Anderson and Mirheydar is widely adopted in literatures . These methods calculate the steady frequency through the estimated amount of unbalanced active power but neglect the network parameters.…”

Section: Introductionmentioning

confidence: 99%

Steady frequency prediction algorithm for power system with governor deadband

Fan

Teng²,

Xie

et al. 2017

SummaryThe frequency stability of power system is usually jeopardized by the active power deficit for major disturbances. To deal with these events, adaptive load shedding schemes are effective, and the steady frequency prediction is considered as the prerequisite. However, none of previous predictive methods has taken into consideration the nonlinear segment that may distort system frequency response. This paper investigates the effect of speed governor deadband and presents a method to evaluate its effect on the steady frequency. Based on the wide area measurement system measurements, a predictive algorithm of steady frequency is studied. It utilizes the modified regulation coefficient to consider the governor deadband effect and employs instantaneous measurements of postdisturbance to calculate the steady frequency directly. Simulations on the IEEE-9 system and a practical system of China have solidified the effectiveness of the proposed algorithm.KEYWORDS frequency stability, governor deadband, steady frequency prediction, wide area measurement | INTRODUCTIONFrequency stability refers to the balance of active power in power systems. 1 When a sudden increase in demand or electrical shutdown happens, power systems will experience a frequency decline. Excessive frequency drop may cause damage to electric devices, outage of system equipment, and even system collapse. 2,3 After a disturbance, the balance of load and generation needs to be regained to maintain stable system frequency. Underfrequency load shedding and overfrequency generator tripping are effective emergency strategies against possible frequency collapse. It is of great importance to perform these control measures rapidly to avoid loss of synchronism 4 as well as unnecessary loss of load appropriately. 5 The mismatch between nominal and postdisturbance steady frequency indicates the amount of active power to be balanced. Therefore, fast and accurate prediction of steady frequency is one of key technologies in high-efficient control strategies.Wide area measurement system (WAMS) can provide state variables of power system with millisecond precision, which enables to predict the steady frequency more efficiently. 6,7 Based on the WAMS measurements, the system frequency response model (SFR) derived in Anderson and Mirheydar 8 is widely adopted in literatures. 2,9-11 These methods Nomenclature: b i , width of deadband in governor i (pu in 50 Hz); D, system damping (pu); A, maximum frequency deviation of inertia center (pu); H eq , equivalent inertia for disturbed power system (s); H i , inertia of generator i (s); ΔP d , deviation of perturbation power (pu in S B ); ΔP Gi , power output deviation of generator i (pu in S B ); R i , speed governor regulation coefficient (pu in S B ); R ′ i , modified regulation coefficient considering deadband (pu in S B ); S B , system base power (MVA); T i , time constant for governor system of generator i (s); ω, system frequency (Hz); Δω, frequency deviation (Hz); P mi , mechanical power of generator i (MW); P ei , el...