Low-frequency Load Shedding Research Articles

Energy Storage Capacity Configuration Planning Considering Dual Scenarios of Peak Shaving and Emergency Frequency Regulation

New energy storage methods based on electrochemistry can not only participate in peak shaving of the power grid but also provide inertia and emergency power support. It is necessary to analyze the planning problem of energy storage from multiple application scenarios, such as peak shaving and emergency frequency regulation. This article proposes an energy storage capacity configuration planning method that considers both peak shaving and emergency frequency regulation scenarios. A frequency response model based on emergency frequency regulation combined with low-frequency load shedding is established, taking into account the frequency safety constraints of the system and the principle of idle time reuse, to establish a bi-level programming model. In the upper-level model, the optimization objective is to minimize the annual operating cost of the system during the planning period, combined with the constraints of power grid operation to plan the energy storage capacity. The lower-level model embeds frequency safety constraints with the optimization objective of minimizing the cost of fault losses. To solve the bi-level optimization problem, the Karush–Kuhn–Tucher (KKT) condition and Big-M method were used to transform the bi-level model into a single-layer linear model. Finally, an improved IEEE RTS-24 system was used for numerical verification. The results show that the method proposed in this article can reasonably plan the capacity of energy storage, improve frequency safety during system operation, and reduce the operating cost of the power grid.

A Two-Stage Power Distribution Scheme of Multiple Wind Farms Participating in Primary Frequency Regulation

With the increasing penetration rate of renewable energy power generation (RPG) in power system, improving the frequency regulation ability of RPG has become a general trend. The premise of effective participation of RPG in primary frequency regulation (PFR) is to reasonably design the power distribution scheme for RPG devices. In order to effectively evaluate the frequency support capability of wind power generation system, the system frequency response (SFR) model under the joint action of synchronous generators, wind farms (WF) and low frequency load shedding device is established in this paper. According to the time-domain solution of this mathematical model, the influence of the output power of the WF on SFR is mathematically explained. At the same time, the influence of time delay on SFR is further demonstrated. In order to maximize the release of the rotor kinetic energy of the wind turbine and ensure the safe operation of the wind turbine when designing the power distribution scheme, an accurate prediction method of wind turbine rotor speed based on piecewise fitting and Bernoulli equation is proposed. Based on the established SFR model and rotor speed prediction method, a two-stage power distribution scheme for multiple WFs during PFR is proposed, which comprehensively considers the SFR requirements and different power output capabilities of multiple WFs. The effectiveness and superiority of the proposed power distribution scheme are validated with revised IEEE 39-bus test system and revised PG&E 69-bus test system.

Low-Frequency Defense Strategy for Wind Turbine Participating in Power Grid Frequency Adjustment

With the continuous increase of wind power permeability, the dynamic behavior of the power system also changes, which also has a great impact on the setting of the low-frequency load-shedding scheme. The original low-frequency load-shedding scheme has no good adaptability to the system of high-permeability wind power. So, this article analyzes the principles of wind turbines in power grid frequency control. This paper expounds on the principle of low-frequency load-shedding strategy in the power system configuration. Connecting with the actual operation of the grid simulation, simulation results show that wind turbines in power grid frequency modulation can significantly reduce the low-frequency load shedding process of loads and wind power in frequency modulation of low-frequency with a positive impact.

Modelling and control of central air‐conditioning loads for power system emergency frequency control

The physical model as well as the corresponding parameter identification method of central air conditioning load is proposed in this paper, based on which emergency control strategy of central air conditioning is designed to participate in emergency frequency control after the sudden large power loss in receiving end grid such as high voltage direct current (HVDC) blocking fault. Firstly, the basic principle of the central air conditioner is introduced. On this basis, the physical model of the central air conditioner which includes central air conditioning unit, temperature change of refrigerated inflow and outflow water, heat exchange between the cooling water of the fan coil and the room, indoor average temperature change as well as the proportion of the room in the open state are established. Moreover, combined with the central air-conditioning model, a parameter identification method of the model is proposed. Then, the emergency control and flexible recovery strategy of central air-conditioning are proposed. The application prospect of emergency control of central air conditioning in response stability control and low frequency load shedding (UFLS) after HVDC blocking faults of receiving power grid is discussed, respectively. The experimental platform is set up to verify the accuracy of the model and parameter identification method and the feasibility of emergency control.

Improved Method of Local Feeder Automation Considering Small Hydro-power Connection

With the access of small hydro-power stations (SHS), the distribution system presents a multiple power supply pattern, which has a negative impact on the original local feeder automation (LFA) which is suitable for single side power supply system. In view of this effect, the phase to phase short-circuit fault (PPF) and single-phase grounding fault (SPGF) are treated differently, and an improved LFA method (IMLFA) considering SHS’s access based on low-frequency load shedding (LFLS) and high-frequency generator tripping (HFGT) is proposed. In case of SPGF, the section switch (SSW) and the outgoing circuit breaker of the substation shall be opened in sequence, and the isolated network (IN) generated in the process can be operated stably by cooperating with LFLS or HFGT while the fault is preliminary isolated. The SSW and the breaker are added with the function of no-voltage detection and synchronization detection. In case of instantaneous fault, the power supply in the fault area can be restored after a series of operations, and the IN can be connected to the grid. If it is a permanent fault, the section switches (SSWs) around the fault area will be locked to close in order to isolate the fault effectively, and the IN, not separated by the fault area from the grid, can be connected to the grid. Analysis and simulation show that the method is correct and feasible.

Analysis of the Influence of Renewable Generator Frequency Endurance Capability on Low-Frequency Load Shedding: A Hunan Case Study

With the rapid development of renewable generators such as distributed photovoltaic and profound changes of the power structure, this paper analyzes the frequency characteristics of the power system with high penetration of renewable generations in the process of low-frequency load shedding and discusses the influence of the distributed renewable generator frequency endurance capabilities on the implementation effect of low-frequency load shedding in detail. Finally, the influences of the distributed renewable generator frequency endurance capability and the capacities of the distributed renewable generator on frequency response characteristics of an actual Hunan power grid are simulated. The simulation results show that more distributed photovoltaic capacity without frequency endurance capability leads to deeper frequency drops after the disturbance and requires more basic rounds of load shedding. When the penetration rate of distributed photovoltaic is too high, it may cause load shedding, resulting in power grid load losses and, at the same time, leading to an overshoot phenomenon in the process of frequency recovery. Therefore, the influence of distributed photovoltaic on the control of low-frequency load shedding should be considered when designing low-frequency load shedding schemes for the power grid with high penetration of distributed photovoltaic.

Research on the Hydropower Frequency Control Strategy for Power Delivery Grid Splitting

After power delivery grid splitting off from the main power grid, there is the risk of over frequency generator tripping leading to low frequency load shedding action. Regulation characteristic of hydro-turbine speed control system for regional power grid is analyzed by using the measured parameters of hydropower. The turbine speed control effect is analyzed without lower limit of primary frequency regulation. Frequency control improvement program of hydropower generating units in isolated power system is proposed based on wide area measurement system. The scheme uses WAMS to collect power information as governor PID output lead, and to calculate power target into the speed control system.

The Analysis of Strategies for Large Thermal Power Unit Frequency Control after the Breakdown of Isolated Network in Sending-End Network

As for the hidden dangers of low-frequency load shedding caused by high frequency generator tripping in isolated power grid because of the failure connection between outward transmission district grid and leadership grid, we gave an analysis to problems with high-frequency in sending network and isolated power grid, and reasons causing the unmatching between OPC and governors. Then, we adopted the measured parameters of thermal power units for the analysis of its regulating system under the isolated power grid, and discussed the regulating effect when the lower amplitude of the primary frequency was-30% and full liberalization. As for the high rate of load shedding in the sending network, this paper has put forward an optimization strategy for thermal power unit frequency control in isolated network. Release primary frequency amplitude to-30% in isolated network, measure the acceleration of rotation speed when OPC acts at the first time, calculate the tragic power of the unit and send it to AGC system. The unit quickly adjusts the power of the unit according to new AGC instruction, and stabilizes the frequency in isolated network. This strategy can help to realize the coordination between OPC and speed governor, and improve the margin of high-frequency in isolated network.

The Study on Isolated Power Control System Based on Coordinated Control

This paper analysis the formation conditions of isolated power system, its influencing factors, revealing the operation mode, automatic safety device, generator protection regulation characteristics and these factors to stable operation of isolated power system. The dynamic models for isolated power system with generating unit of medium and small capacity are proposed in the paper to meet the need of the applicable ones to study their dynamic characteristics. The differences between isolated and the interconnected power system in the frequency characteristics are proposed and consider into low-frequency load shedding scheme and optimization methods that can meet both isolated and the interconnected power system frequency stability requirements. Not only more proper control strategy of units but their evaluation indexes are suggested to improve performance and achieve stability in islanded power system.

A Spinning Reserve, Load Shedding, and Economic Dispatch Solution by Bender's Decomposition

Spinning reserve in a thermal power system is a type of relevant economic issue in a deregulated environment. As system security is dependent on the dynamic response, the influence of system fast spinning reserve and amount of low-frequency load shedding are elements of economic cost. This work deals with the composed problem of optimizing economic dispatch, fast spinning reserve and load shedding in order to withstand major sudden generation losses without collapsing by cascading effects. The proposed method uses Bender's decomposition in order to solve the problem by stages and is applicable to any power system. Application to Chilean Northern System is included to test the proposed method. Results show good convergence and easiness to obtain an optimum despite the wide range of feasible solutions for the problem. The composed cost of reserve and load shedding represents an important percentage of this system operating costs.