Emergency Control Strategy Research Articles

Fast and optimal decision for emergency control of sudden water pollution accidents in long distance water diversion projects

Abstract Long distance water diversion projects transfer clean water to cities for industrial, agricultural and domestic use; there is a great risk of sudden water pollution accidents. Without a fast and optimal decision for emergency control in response to sudden water pollution accidents, dispatchers or decision-makers will not be prepared to respond to the accidents during the process of an emergency spill. To address this gap, a framework for fast and optimal decision support in emergency control is reported in this paper. The proposed fast and optimal decision system covers four stages. In this study, the analytical hierarchy process integrated with grey fixed weight clustering was used to determine the gate closing mode. The emergency control strategy in ice cover formation period is presented. A case study was examined in the demonstrative project conducted in the Middle Route of the South-to-North Water Diversion Project in China. The relative errors of the arrival time of the peak concentration and the peak concentration in monitoring points between the actual monitoring values and the formula calculation values are less than 18%.

Bi‐level optimised emergency load/generator shedding strategy for AC/DC hybrid system following DC blocking

This study presents a bi-level optimised emergency control strategy, including load and generators shedding following DC blocking. Due to different constraints for networks with different voltages, a bi-level optimised model spanning from the high voltages networks to the lower voltages is put forward. For the higher voltage level network, the overload area is identified and the seriousness of the overload is classified after DC blocking with the help of wide-area measurement systems. Then, the objective function is built with the minimum total amount of load shedding and generator tripping to be solved by improved particle swarm optimisation (IPSO), considering the constraints of frequency and voltage stability, respectively. For the low voltage level networks, the least cost as the objective function with the constraints of load shedding and generator tripping strategy based on the analytic hierarchy process-fuzzy comprehensive evaluation method. The modified 10-machine 39-bus system with HVDC lines is used as the test system. The simulation results demonstrated that the proposed strategy can give good control performance with consideration of different optimisation constraints following the DC line blocking.

Synchronized Measurement Technology Supported Online Generator Slow Coherency Identification and Adaptive Tracking

In an electric power system, slow coherency can be applied to identify groups of the generating units, the rotors of which are swinging together against each other at approximately the same oscillatory frequencies of inter-area modes. This serves as a prerequisite-step of several emergency control schemes to identify power system control areas and improve transient stability. In this paper, slow coherent generators are grouped based on the direction and the strength of electromechanical coupling between different generators. The proposed algorithm performs low-pass filtering of generator frequency measurements. It adaptively determines the minimal number of the measurements to be processed in an observation window, and performs data selectivity to prevent mixing of interfering coherency indices. Finally, it adaptively tracks grouping changes of slow coherent generators and determines a finite number of groups for an improved affinity propagation clustering. The proposed algorithm is implemented as an online MATLAB program and verified in real-time using RTDS power system simulator with the integration of actual synchronized measurement technology components as hardware-in-the-loop. The obtained results demonstrate the effectiveness of the proposed algorithm for robust and near real-time identification of grouping changes of slow coherent generators during the quasi-steady-state and electromechanical transient period following a disturbance.

Transient Frequency Stability Emergency Control for the Power System Interconnected With Offshore Wind Power Through VSC-HVDC

For the power system interconnected with the large-scale offshore wind power through VSC-HVDC, such as SZ power grid, it may be engaged with transient frequency stability and lack of related control due to the randomness, fluctuation and intermittence of the wind. This paper proposes a transient frequency control strategy for the power system interconnected with offshore wind power through VSC-HVDC based on sensitivity. Firstly, the structure of SZ power grid and the calculation method of transient frequency stability index are introduced, and the transient frequency problems existing in SZ power grid are explored. Secondly, the mathematical formulation for the transient frequency control is described, including the objective function and the constraints. Furthermore, a transient frequency emergency control strategy based on special sequence and the sensitivities is proposed, which includes thermal units regulation, wind power regulation, DC modulation and load shedding. Finally, the effectiveness of the proposed control strategy is verified by simulation in SZ power grid.

Emergency control strategy for renewable power systems considering utility-scale energy storage transient

Integration of renewable energy generators has greatly altered both static and dynamic characteristics of the system. Combined with the uncertainties it introduced, the risk of a system being transient instable is significantly alleviated. This paper proposes a multi-objective coordinated post-contingency control method. It aims to increase post-contingency system security with emergence control (EC) while minimizing the total control cost. Two ECs are adopted in this paper: energy storage systems (ESSs) and emergency load shedding (ELS). ESSs are immediately connected to the network after contingency occurrence to provide both active and reactive power support. ELS will be triggered when the support from ESSs is insufficient to stabilize the system to prevent further deterioration of system security. Performance of the proposed method was evaluated on a modified New England 39-bus benchmark system. The results indicate that the proposed method can find solutions to stabilize the system against credible contingencies and optimally balance between system stability and economy.

Ride-Through Control Method for the Continuous Commutation Failures of HVDC Systems Based on DC Emergency Power Control

Continuous commutation failures (CFs) are serious malfunctions in line-commutated converter high-voltage direct current (HVDC) systems that cause the continuous and rapid sag of transmitted power and may threaten the stability of AC systems. The conventional emergency control strategies of AC systems exhibit difficulty in responding quickly and accurately. After suffering from continuous CFs, the forced blocking of direct current (DC) converter to prevent AC system instability might also cause other adverse effects. This study proposes a ride-through control method to improve the endurance capability of AC systems against continuous CFs. An active power output model of inverter station under continuous CFs is built, while considering the process and mechanism of CFs. The impact of continuous DC power sag on the stability of sending-end system is analyzed through a four-area AC/DC equivalent model. A rolling calculation model for the power angle and acceleration area variations of the sending-end system during continuous CFs is established on the basis of model predictive control theory. A calculation method for the emergency power control reference is obtained by using the aforementioned models. Lastly, a ride-through control method for continuous CFs is developed by utilizing the emergency control of adjacent HVDC link. Simulation results show that the proposed control method can improve the endurance capability of an AC system to continuous CFs and reduce blocking risk in an HVDC link.

Synchrophasor-Based Emergency Generation Control for Area Balancing

In North America, balancing authority (BA) maintains the demand-supply balance and frequency stability within its responsible area. In case of an emergency, such as loss of supervisory control and data acquisition (SCADA), automatic generation control (AGC), state estimation and energy management system (EMS), system operators lose the automatic monitoring and control capability, as a result of which they have to manually dispatch units to maintain area balancing. This could be inefficient and at the risk of failure to comply with NERC’s balancing control performance standards. We propose an emergency control strategy to help BA balance the system cost-effectively based on the independent synchrophasor infrastructure in the event of SCADA/EMS failure. Depending on the availability of electronic dispatch network, the proposed emergency control decides if a synchrophasor-based AGC-like function should be performed every 4 s to regulate area control error. It also executes economic dispatch on a 5-min basis by solving the desired dispatch point of units with PMU installed through a linear programming problem to meet forecasted load change in 5 min. Closed-loop simulations demonstrate that the proposed scheme is able to successfully balance the system at a lower cost to fulfill the BA’s obligations under emergency operation conditions.

Multilevel Torque Hysteresis-Band Based Direct-Torque Control Strategy for a Three-Level Open-End Winding Induction Motor Drive for Electric Vehicle Applications

The number of levels present in the torque-hysteresis controller influence the performance of the direct torque controlled (DTC) induction motor drives. In this paper, the effects of the number of levels in the torque-hysteresis-band controllers (THBCs) on the performance of the conventional DTC-based three-level open-end winding induction motor drives are reported. A power-loss evaluation model was employed to investigate the influence of the number of levels present in THBC on the switching and conduction losses occurring in the dual-inverter system. The performance indices considered in this paper are: 1) the flux-ripple; 2) the torque ripple; and 3) the total power loss in the dual-inverter system. Furthermore, these performance indices are evaluated with a newly emerging control strategy, namely, the predictive torque control, and are compared with those obtained with the DTC. The simulation results are validated by showing the experimental results.

Adaptive Power System Emergency Control Using Deep Reinforcement Learning

Power system emergency control is generally regarded as the last safety net for grid security and resiliency. Existing emergency control schemes are usually designed off-line based on either the conceived "worst" case scenario or a few typical operation scenarios. These schemes are facing significant adaptiveness and robustness issues as increasing uncertainties and variations occur in modern electrical grids. To address these challenges, for the first time, this paper developed novel adaptive emergency control schemes using deep reinforcement learning (DRL), by leveraging the high-dimensional feature extraction and non-linear generalization capabilities of DRL for complex power systems. Furthermore, an open-source platform named RLGC has been designed for the first time to assist the development and benchmarking of DRL algorithms for power system control. Details of the platform and DRL-based emergency control schemes for generator dynamic braking and under-voltage load shedding are presented. Extensive case studies performed in both two-area four-machine system and IEEE 39-Bus system have demonstrated the excellent performance and robustness of the proposed schemes.

Fast emergency control strategy calculation based on dynamic equivalence and integral sensitivity

To simplify the transient stability analysis of a large-scale power system and realize real-time emergency control, a fast transient stability simulation algorithm based on real-time dynamic equivalence is proposed. Generator models are grouped and aggregated according to a fast numerical integration. A fast calculation method of the admittance matrix is then proposed to calculate the parameters of an equivalent system, and numerical integration is performed using the obtained equivalent system. Then, based on integral sensitivity, a new fast emergency control strategy is proposed for the equivalent system. The final emergency control strategy is obtained by mapping the control strategy for the equivalent system back to the original system. The results of a simulation on an East China Power System that includes 496 generators and 5075 buses show that the suggested algorithm can output an accurate transient stability simulation result and form an effective emergency control strategy. The proposed algorithm is much faster than the existing solutions and has the potential to be used for online pre-decision.

A measurement-simulation hybrid method for transient stability assessment and control based on the deviation energy

Nowadays, most power utilities design the emergency control schemes based on a large number of offline simulations, since the online measurement-based emergency control methods are far from mature and reliable at this moment. This paper proposes a novel measurement-simulation (M-S) hybrid method for transient stability assessment (TSA) and the emergency control scheme. Based on the deviation between offline simulation trajectory and the online trajectory equivalent to a single-machine-infinite-bus (SMIB) system, a new index named Deviation Energy (DE) is defined to fast assess the transient stability of the system online. This novel TSA method does not require trajectory prediction and can fully take into account local controls. Further, an additional control scheme is proposed to correspondingly stabilize the system, if the system is judged as unstable. The proposed method has been tested on the IEEE 39-bus system and an actual interconnected power grid model.

TDNetGen: An Open-Source, Parametrizable, Large-Scale, Transmission, and Distribution Test System

In this paper, an open-source MATLAB toolbox is presented that is able to generate synthetic, combined transmission and distribution network models. These can be used to analyse the interactions between transmission and multiple distribution systems, such as the provision of ancillary services by active distribution grids, the co-optimization of planning and operation, the development of emergency control and protection schemes spanning over different voltage levels, the analysis of combined market aspects, etc. The generated test-system models are highly customizable, providing the user with the flexibility to easily choose the desired characteristics, such as the level of renewable energy penetration, the size of the final system, etc.

Research on Emergency Control Strategy of Synchronous Condenser for Inhibiting HVDC Commutation Failure

As multi-infeed HVDC systems are integrated into power grid, the operation characteristics of power grid have changed significantly. The problems of the shortage of dynamic reactive power reserve and voltage support need the allocation of dynamic reactive compensation device such as synchronous condenser urgently. This paper researches the influence of installing synchronous condenser on system performance in multi-infeed HVDC power grid. Based on the analysis of the defects of synchronous condenser on HVDC commutation failure under existing conventional control mode, this paper presents the emergency control strategy and system architecture with synchronous condenser. In the end, the effectiveness of the proposed control strategy is verified based on the actual grid simulation.

Using inverter-based renewable generators to improve the grid power quality—A review

With the increasing penetration of renewable power in the grid, renewable generators are expected to play more important roles rather than merely working as active power sources. Considering the high controllability and considerable idle capacity of the inverter-based renewable generators, various auxiliary functions for them have been studied to benefit the grid. Among these auxiliary functions, the grid power quality improvement is very promising. This paper presents a review of the emerging control strategies for inverter-based renewable generators to improve grid power quality. The related papers are classified with different power quality issues and technical routes, and a comprehensive comparison is presented. The future trends of this research area are also discussed.

Additional reactive power control and emergency control of the ±1100 kV UHVDC system with a hierarchical connection mode

This paper proposes an additional reactive power control strategy and an emergency control strategy for ±1100 kV ultra-high voltage direct current (UHVDC) system with a hierarchical connection mode, in which the inverter station connect to two AC systems with different voltage levels. Firstly, the relationship between reactive power and DC voltage is analysed. Then, an additional reactive power control strategy is proposed to solve the voltage fluctuation caused by reactive power disturbance. Next, the reactive power emergency control strategy is proposed when a short-circuit fault occurs. Reactive power compensation devices will be inputted into the fault-free AC system to provide reactive power support through coupling relationship between two AC systems in the inverter side. Simulation results show that the additional reactive power control strategy can suppress reactive power disturbances without affecting the active power. Moreover, the reactive power emergency control strategy can reduce the probability of commutation failure in converters connected to the fault AC system while a short-circuit fault occurs.

Application of emergency control of central air conditioning in safe and stable operation of large power grid

Air conditioning is a load with thermal inertia, and short time control will not cause an obvious negative impact on user power consumption. Compared with the traditional mini-split-type air conditioner, it has the advantages of flexible control method, strong controllability, large power of the monomer, and so on. This paper studies the application potential of emergency control of central air conditioning in safe and stable operation of large power grid. Firstly, the working principle of central air conditioner and the model of central air conditioning are introduced. On this basis, the emergency control strategy of central air conditioning is put forward. Furthermore, the control strategy of central air conditioning response control signal of safety and stability control or frequency deviation signal is put forward. Finally, a practical engineering case is given to illustrate the feasibility of the proposed strategy and its application in a large power grid.

Emergency Control Scheme for Upstream Pools of Long‐Distance Canals

AbstractAn emergency control scheme is proposed for pools upstream of a canal experiencing flow obstruction incidents. In order to achieve a prompt and efficient transition process, operation strategies are set out. It is suggested to switch from a constant downstream depth operation method to a constant volume operation method under qualified conditions. Based on a balanced pool operation equation and a transitional time estimation equation, a two‐step gate operation method is designed, which is compatible with the operation method of constant downstream depth and the mixed pool operation method of constant downstream depth and constant volume. The emergency control scheme is tested by simulations on the 561 km long Middle Route Project (MPR) of the South‐to‐North Water Diversion Project in China consisting of 30 pools. The constant downstream depth and mixed pool operation methods are examined. Results indicate that the control scheme operates well under the emergency situation of a flow obstruction incident. Canal flow moves promptly and effectively to the new steady state by switching to the constant volume method. Back and forth volume variation is avoided and a significant improvement is obtained in terms of transition time, while the times of check gate operation remain roughly the same. © 2018 John Wiley & Sons, Ltd.

Voltage prevention and emergency coordinated control strategy for photovoltaic power plants considering reactive power allocation

This paper proposes a voltage prevention and emergency control strategy that consists of coordinately arranging multiple reactive power sources in order to handle the point of common coupling (PCC) voltage fluctuation and stability in large-scale PV power plants. When a disturbance occurs at the PCC, dynamic reactive power compensation devices are coordinated preferentially to support the PCC voltage. After the disturbance is cleared, the reactive power in dynamic and fast devices is transferred into static and slow devices so that the static VAR generation (SVG) can maintain a large power margin for coping with the next disturbance. Moreover, the reactive power output of the individual inverter in PV power plants is coordinately allocated using a model to optimize the in-station voltage distribution. Finally, the effectiveness of the proposed control strategy is verified by an example simulation of a practical large-scale PV power plant.

Control method of doubly fed wind turbine for wind speed variation based on dynamic constraints of reactive power

With the development of large wind farms, the voltage problem caused by the power changes of wind farms occurs continuously because of the wind speed variation. The problem cannot be resolved by extra reactive power compensation because of the limitations in cooperation and response speed. A doubly fed induction generator (DFIG) possesses the power decoupling control capability, which can be used to prevent the voltage change rapidly. However, the dynamic processes of the power demands of the grid and the power limits of the DFIG have not been considered. Therefore, a vector equivalent model of the DFIG considering the controllability of the rotor voltage is established. The feasible power ranges that are limited by the electromagnetic process and controller response are deduced. The dynamic requirement and limitation of the reactive power under the wind speed variation are investigated. The emergency control strategy of reactive power contributed by the DFIG is proposed on the basis of the requirement and limitation. The simulation shows that the rapid adjustment capability of the DFIG can be fully utilised by the proposed method.

Novel Detection Method for Consecutive DC Commutation Failure Based on Daubechies Wavelet with 2nd-Order Vanishing Moments

Accurate detection and effective control strategy of commutation failure (CF) of high voltage direct current (HVDC) are of great significance for keeping the safe and stable operations of the hybrid power grid. At first, a novel detection method for consecutive CF is proposed. Concretely, the 2nd and higher orders’ derivative values of direct current are summarized as the core to judge CF by analyzing the physical characteristics of the direct current waveform of the converter station in CF. Then, the Daubechies wavelet coefficient that can represent the 2nd and higher order derivative values of direct current is derived. Once the wavelet coefficients of the sampling points are detected to exceed the threshold, the occurrence of CF is confirmed. Furthermore, by instantly increasing advanced firing angle β in the inverter side, an additional emergency control strategy to prevent subsequent CF is proposed. Eventually, with simulations of the benchmark model, the effectiveness and superiorities of the proposed detection method and additional control strategy in accuracy and rapidity are verified.