Black-start Units Research Articles

Hybrid Optimal Power System Recovery and Load Pick-Up With DGAllocation In Electrical Power System

The increasing demand for electricity, the expansion of complex power networks, and the operation of power systems near their capacity have heightened the risk of power outages. Consequently, control room operators must develop comprehensive restoration plans to minimize recovery time. Key steps in power system restoration include starting non-black-start units with black-start units and initiating load pick-up. This process requires identifying the shortest route between nodes to expedite repairs. This research presents an expert plan employing the Modified Cuckoo Search algorithm (MCSA) to determine optimal pathways. Additionally, it explores the optimal allocation of distributed generators (DG) to enhance the system's voltage profile and reduce power losses using particle swarm optimization (PSO). The results demonstrate that DG significantly reduces losses during recovery. The study prioritizes the restoration of DGs with strong black start capability, considering network and DG constraints. The effectiveness of the proposed restoration approach is validated through MATLAB simulations on theIEEE 39-bus system.

A MILP-based power system parallel restoration model with the support of mobile energy storage systems

During bulk power system restoration, black-start (BS) units are used to crank non-BS units in such a way that the over system generation capability is maximized. However, traditional power system restoration methods rely on stationary BS units, whose number is limited due to high investment and geographic conditions, impeding a fast system restoration. To enhance restoration efficiency, this paper proposes an integrated power system parallel restoration method considering the support of mobile energy storage systems (MESSs), which can provide cranking power to non-BS units and transform them into MESS-assisted BS units. MESSs are routed and scheduled via transportation network, along with restoration planning in power network by integrating them into a mixed integrated linear programming model. Specifically, to describe the interactive behavior between MESSs and the power system, a mobility model for MESSs is proposed, which indicates the travel path, travel time and connection nodes. Then, an integrated optimization model involving BS unit location, zone partitioning, network reconfiguration and generator start-up is formulated. The proposed method was simulated in the modified IEEE 30-bus transmission system coupled with 11-node transportation system. The results show that, in contrast with a decoupled restoration method, the proposed method increases system generation capability by 6.3%.

A Sequential Black-Start Restoration Model for Resilient Active Distribution Networks

This letter presents a novel sequential black-start restoration model to improve the system resilience after a natural disaster in an active distribution network. Two challenges have been addressed: First, a new set of radiality constraints is designed as the network topology is changing along the restoration paths; Second, a black-start restoration model is proposed where multiple backup black-start units in the system are coordinated to find the best restoration paths. Case studies on two IEEE test systems verify the effectiveness of the proposed model.

Optimal Generation Start-Up Methodology for Power System Restoration Considering Conventional and Non-Conventional Renewable Energy Sources

Power system restoration must be accomplished as soon as possible after a blackout. In this process, available black-start (BS) units are used to provide cranking power to non-black-start (NBS) units so as to maximize the overall power system generation capacity. This procedure is known as the generation start-up problem, which is intrinsically combinatorial with complex non-linear constraints. This paper presents a new mixed integer linear programming (MILP) formulation for the generation start-up problem that integrates non-conventional renewable energy sources (NCRES) and battery energy storage systems (BESS). The main objective consists of determining an initial starting sequence for both BS and NBS units that would maximize the generation capacity of the system while meeting the non-served demand of the network. The nature of the proposed model leads to global optimal solutions, clearly outperforming heuristic and enumerative approaches, since the latter may take higher computational time while the former do not guarantee global optimal solutions. Several tests were carried out on the IEEE 39-bus test system considering BESS as well as wind and solar generation. The results showed the positive impact of NCRES in the restoration processes and evidenced the effectiveness and applicability of the proposed approach. It was found that including NCRES and BESS in the restoration process allows a reduction of 24.4% of the objective function compared to the classical restoration without these technologies.

Power source–power grid coordinated typhoon defense strategy based on multiagent dynamic game theory

A power source–power grid coordinated typhoon defense strategy is proposed in this study to minimize the cost of power grid anti-typhoon reinforcement measures and improve defense efficiency. It is based on multiagent dynamic game theory. This strategy regards a typhoon as a rational gamer that always causes the greatest damage. Together with the grid planner and black start unit (BSU) planner, it forms a multiagent defense–attack–defense dynamic game model naturally. The model is adopted to determine the optimal reinforcements for the transmission lines, black start power capacity, and location. Typhoon Hato, which struck a partial coastal area in Guangdong province in China in 2017, was adopted to formulate a step-by-step model of a typhoon attacking coastal area power systems. The results were substituted into the multiagent defense–attack–defense dynamic game model to obtain the optimal transmission line reinforcement positions, as well as optimal BSU capacity and geographic positions. An effective typhoon defense strategy and minimum load shedding were achieved, demonstrating the feasibility and correctness of the proposed strategy. The related theories and methods of this study have positive significance for the prevention of uncertain large-scale natural disasters.

BESS Assisted Frequency Management for Black Start Process of Microgrid

This paper proposes a method for restoring the nominal frequency and improving the system recovery time using battery energy storage system (BESS) for an islanded microgrid (MG) which is operated by a black start unit (BSU). The frequency stability is controlled by varying the apparent power (MVA) rating of the BESS after simultaneously connecting with the BSU during the post fault scenarios. Simulations are performed on the IEEE Std. 399-1997 test MG using DIgSILENT PowerFactory. Results show that the nominal frequency of the system can be retained by connecting the BESS during the transient period and increasing the MVA rating up to a maximum value. Simulation results also show that with a higher distributed connection of the BESS units over the system, the frequency recovery time can be reduced.

Black-Start and Service Restoration in Resilient Distribution Systems With Dynamic Microgrids

The resilience of distribution systems has been challenged by power outages caused by natural disasters, which calls for novel solutions to system restoration. However, the existing black-start (BS) techniques are mainly developed at the transmission level. This problem can be resolved by adopting dynamic microgrids (MGs), i.e., MGs with dynamic and adjustable boundaries nested in the distribution systems. This article proposes a restoration procedure that adopts self-organizing inverters as BS units and achieves distribution system restoration in the context of dynamic MGs. The proposed restoration procedure is structured as a two-stage approach and designed to restore a complete blackout distribution system to the state where the system is ready for seamless main grid reconnection. A framework of dynamic MG operation is developed, which improves the self-healing capability of off-grid distribution systems with automatic sectionalization and flexible reconfiguration. A sequence of actions during restoration is defined, along with distributed controllers designed with considerations of practical operating challenges. The proposed restoration procedure is validated on a 34-bus system using real-time hardware-in-the-loop simulation.

Energization of windfarm infrastructure as part of microgrid based restoration

Studies on windfarms have focussed on their integration under normal and short duration weak grid conditions. With their increasing penetration at the same time that there is increasing disaster related blackouts, there is need to investigate their role during restorative conditions assuming a bottom-up approach in which local generation is used to re-energize the network. This is commonly referred to as microgrid based restoration. Wind Energy Conversion Systems (WECSs) are not blackstart units thus they require cranking from designated blackstart units in order to play a role in re-energizing the network. Prior to the WECSs being cranked up, the windfarm infrastructure, which includes underground cables, reactors (applicable to long HV cables), WECS transformers and yaw-pitch motor system, needs to be re-energized. This paper investigates the energization of different components within the windfarm considering availability of a single medium sized (5 MVA) blackstart synchronous source. Firstly, diesel based generation (DBG) will be used to study the different challenges associated with the energization of the different components considering different re-energization sequences after which thermal (TBG) and hydro (HBG) based generation will be used for comparison. High frequency modelling has been considered for static network components such as transformers, cables and reactors while dynamic models have been considered for rotating network components such as generators and motors. Excitation limiters have been included in the generation systems in order to obtain a near accurate response on energization of the different components. Discussion is provided on the different factors that influence the success of energization. Analysis is also provided on the effect of size of the excitation source and influence of the synchronous condenser which has been considered as part of the windfarm. Resonance, using a simple empirical formula, is briefly discussed as a factor in influencing and determining the energization sequence. A typical windfarm layout has been considered in this study with MATLAB/Simulink being used as the simulation platform due its flexibility in modelling.

Operational and control approach for PV power plants to provide inertial response and primary frequency control support to power system black-start

The renewable generation growth, which includes photovoltaic power plants, has posed challenges for the planning and operation of contemporary power systems. High penetration levels of generation based on fully rated converters makes the black-start of power systems more difficult due to the low equivalent inertia of the system, the performance deterioration of the primary frequency control, the reduced number of black-start units, and the energization of large loads. In the context of the planning and operational challenges imposed by renewable generation, this work proposes an operational and control approach for centralized photovoltaic generation to provide inertial response and primary frequency control support to the black-start of bulk power systems. The proposed control aims to provide inertial response and primary frequency control support only during the system restoration process. The work also proposes an analytical formulation to assess the impact of the operating point of photovoltaic modules on the dynamics of photovoltaic units. The obtained results have shown that photovoltaic power plants are capable of providing support to the black-start of power systems, improving the dynamic and steady-state performance of the system frequency response during the black-start. The performed dynamic analyses have shown that the operational region of the photovoltaic modules significantly affects the dynamics of the power balance in the photovoltaic unit and, consequently, the dynamics of the load pick-up of the photovoltaic modules. The proposed dynamic analysis is useful to support the formulation of control approaches for de-loaded operation of photovoltaic power plants.

An Interactive Partitioning Algorithm-Based Electrical Power Crisis Management for Service Restoration with Existing Black-Start Resources Considering Load Priority

This article explores a new clustering-based solution for power systems that would be restored by post-outage power supply. The suggested solution has divided the overall network into separate clusters in such a way that each cluster has at least one ‘black-start unit,’ which can restart its own generation. The proposed algorithm manages a variety of restrictions when creating clusters, such as black-start generation capability, supply–demand balancing, and load priority, and attempts to minimize the active and reactive power difference between black-start unit and cluster loads as well as minimize power losses. This paper focuses on the standby available sources in a network to act like ‘black-start units,’ while their neighboring high-priority loads as defined by the supply provider were called cluster participants. K-means neighbor clustering algorithm was used to form the clusters, and, before validating each cluster, the steady-state voltage stability of the clusters was tested using equivalent network L-index value analysis technique. Two separate case studies were performed on the modified distribution IEEE 33-bus system and New England electrical transmission system with 39 buses to demonstrate the efficacy of the proposed algorithm. The results of the simulation show that each cluster was consistently able to maintain reasonable voltage stability with minimum power imbalance between available BSU and loads.

A novel framework for restoration technique of an industrial microgrid using black start units

A novel framework for restoration technique of an industrial microgrid using black start units

An Offline Strategic Planning for Service Restoration Using Multi-Constraints Priority-Based Dijkstra’s Algorithm

Island action of a partitioning distribution network with the Black Start Unit (BSU) reflects an effective improvement in the reliability and security of power systems during restoration. Present article efforts to address the subject of island partitioning in the distribution network with the predefined size of BSU. A new algorithm for Service Restoration is used in the proposed solution by sectionalizing the entire power network into island parts so that each prior load and non-black-start generating station receives power from the BSU with the minimum number of switching operations. The priority-based multi-constraints Dijkstra’s algorithm was used to identify the best partitioning solution. The suggested partitioning solution is evaluated through a study with the IEEE 39 bus and IEEE 118 bus test model and validation also carried out using MI-Power and PSAT analytical toolbox. The result reveals that the suggested solution accomplishes well regarding assuring the consistent supply to prior loads with the acceptable voltage stability and the least amount of power losses.

Fast restoration of a critical remote load area using a gradual voltage build‐up procedure

This study validates an alternative restoration of a critical load area using remote black-start units. Using the conventional restoration, switching actions on a nominal system voltage create switching transients, especially when energising a transformer. The transients maybe close to the resonance frequencies of a weak island system, which may induce high voltages, delay the restoration and damage the equipment in the grid. This study proposes an alternative restoration procedure where, to avoid switching transients, hundreds of kilometres of transmission lines and several transformers are energised using a gradually increasing voltage, which is controlled by the synchronous generator exciter. This study presents detailed procedure flowcharts, a proof of concept for the proposed procedure using a Finnish and an Austrian field tests and theoretical analyses of the tests. The results show that with the gradually increased voltage, harmonic resonances and switching transients during the initial system energisation maybe avoided. In addition, the study shows that variations in the system frequency may cause voltage problems in a weak system during restoration since the system reactance is dependent on the system frequency. Thus, large frequency variations and the unstable operation regions of turbine governors should be avoided during the restoration.

A Parallel Sectionalized Restoration Scheme for Resilient Smart Grid Systems

A parallel automated resilience-based restoration methodology is presented in the power system to minimize impact due to emergency power outages. In this power restoration process, a black start unit is assigned to a small region (i.e., a section) on an as-needed basis. A mixed integer nonlinear programming model is developed in order to optimally sectionalize the region of interest all the while maximizing the resiliency in terms of load shedding, restoration time, and network connectivity. For solving this large scale optimization model, a bi-level programming approach is proposed. This approach consists of two optimization levels. The sectionalization problem (upper level) is a mixed integer programming model and finds the optimal section set. The restoration problem (lower level) is a linear model and determines the dc optimal power flow and restoration time for the optimal section set identified in the upper level. We use the pre-emptive method of goal programming to deal with multiple conflicting objectives in the model. Our proposed solution approach outperformed mathematical programming with equilibrium constraints and found near optimal solutions. Numerical results and sensitivity analysis from two case studies (6- and 118-bus IEEE test systems) are further discussed to demonstrate the efficiency of the solution approach.

Optimal Black Start Allocation for Power System Restoration

Equipment failures, operator errors, natural disasters and cyber-attacks can and have caused extended blackouts of the electric grid. Even though such events are rare, preparedness for them is critical because extended power outages endanger human lives, compromise national security, or result in economic losses of billions of dollars. Since most of the generating units cannot restart without connecting to an energized grid, the system operator relies on a few units with the ability to start autonomously, called Black Start (BS) units, to restore the power system. Allocating and maintaining these units is costly and can severely impact the restoration security and time. We formulate an optimization problem to optimally allocate BS units in the grid, while simultaneously optimizing over the restoration sequence. We extend existing optimal allocation models by including grid considerations such as active power nodal balance, transmission switching, nodal reactive power support and voltage limits. In order to aid the branch and bound tree that solves the resulting large scale mixed integer program, we propose a randomized heuristic that is executed multiple times in parallel on a high-performance computing environment to find feasible solutions. We proceed to solve the IEEE-39, the IEEE-118, and a simplified WECC system with 225 nodes and 136 generators to near optimality.

Power Grid Partition Method for Black Start Based On Complex Network Theory

The paper proposes one power grid partition method for black start based on complex network theory. The method is composed of splitting algorithm and agglomerative algorithm. The former algorithm divided grid to some temp zone according to the number of black-start unit, which determines the basic structure of the partition and reduces the number of iterations in agglomerative process. The latter algorithm redefines the line weight and weighted modularity based on flow distribution and network topology, then merges neighbouring temp zone to maximum weighted modularity. The method can reflect the close degree of the partition, accurately assess the partition quality and determine the optimal number of partitions. The simulation results on IEEE 39-bus test system illustrate the validity of this methodology.

An Optimal Source-Load Coordinated Restoration Method Considering Double Uncertainty

The security of power system restoration is severely affected by uncertain factors, especially the start-up time of generating unit and the amount of load pick-up. Solving the optimization restoration problem is challenging since it needs to determine different priorities in which units and loads are restored with the consideration of double uncertainty. Therefore, an optimal source-load coordinated restoration method that is based on information gap decision theory (IGDT) is proposed. Firstly, the time-domain restoration characteristics of black-start unit (BSU), non-black-start unit (NBSU), and load are described with analysis of double uncertainty. On this basis, a coupled multi-objective optimization model is built with double uncertainty, in which source-load coordinated restoration is realized. Then, IGDT is adopted to convert the uncertainty optimization model to a certain one with robustness, which tolerates the most uncertainty and still meets the desired requirement. Finally, the optimization model is solved by non-dominated genetic algorithm II (NSGA-II). The effectiveness and robustness of the proposed method is further illustrated through a case study based on the IEEE 39-bus system.

Advanced power system partitioning method for fast and reliable restoration: toward a self‐healing power grid

The recovery of power system after a large area blackout is a critical task. To speed up the recovery process in a power grid with multiple black-start units, it would be beneficial to partition the system into several islands and initiate the parallel self-healing process independently. This study presents an effective network partitioning algorithm based on the mixed-integer programming technique and considering the restoration process within each island. The proposed approach incorporates several criteria such as self-healing time, network observability, load pickup capability, and voltage stability limits. It can quickly provide multiple partitioning schemes for system operators to choose based on different requirements. Experimental results are provided to demonstrate the effectiveness of the proposed approach for IEEE 39-bus and IEEE 118-bus standard test systems. Also, the sensitivity of the partitioning solution with respect to the various parameters is presented and discussed. Ultimately, the advantage of the proposed method is demonstrated through the comparison with other references.

Fast network restoration by partitioning of parallel black start zones

The restoration of large electrical power systems after a blackout is often a challenging task. A typical restoration process includes the partitioning of the power systems into subsystems and the successive booting of large non-black start (NBS) units by black start (BS) units. A proper partitioning of the starting zone can reduce the restoration time significantly. This paper investigates a novel network partitioning algorithm to improve the restoration time and ratio of generation and load in each subsystem. The proposed algorithm consists of three stages. In the first stage, the number of subsystems is determined by the number of available BS units and their electrical distance. In the second stage, NBS units are assigned to each subsystem in the way that the rebooting time difference among subsystems is minimised. In the third stage, the substations are assigned to one of the subsystems to achieve the optimal ratio of generation and load in each subsystem. With the proposed algorithm, the switching transient and steady-state over-voltages at the receiving end of unload lines are kept within acceptable ranges and the self-excitation phenomenon does not occur in the subsystems. Furthermore, the start-up sequence of NBS units in each subsystem is determined simultaneously. The proposed algorithm is flexible and can be adjusted very easily according to the real status of the power system. The validity and performance of the proposed approach is demonstrated through simulations using a New England 39 Nodes network and a real network from south China.

A Novel Sectionalizing Method for Power System Parallel Restoration Based on Minimum Spanning Tree

Parallel restoration is a way to accelerate the black-start procedure of power systems following a blackout. An efficient sectionalizing scheme can reduce the restoration time of a system, taking into account the black-start ability, generation-load balance of subsystems, restoration time of branches, start-up time of generating units, and effects of dispatchable loads and faulted devices. Solving the sectionalizing problem is challenging since it needs to handle a large number of Boolean variables corresponding to the branches and nonlinear constraints associated with system topology. This paper investigates power system sectionalizing problem for parallel restoration to minimize the system restoration time (SRT). A novel sectionalizing method considering the restoration of generating units and network branches is proposed. Firstly, the minimum spanning tree (MST) algorithm is used to determine the skeleton network of a power system. Secondly, the number of subsystems is determined according to the number of black-start units. Based on the skeleton network, candidate boundary lines among subsystems are identified. Then, constraints are evaluated to identify feasible sectionalizing schemes. Except commonly used constraints on power balancing and black-start units, this paper also considers using dispatchable loads to meet the minimum output requirements of generating units. Finally, the sectionalizing scheme with the minimum SRT is selected as the final solution. The effectiveness of the proposed method is validated by the IEEE 39-bus and 118-bus test systems. The simulation results indicate that the proposed method can balance the restoration time of subsystems and minimize the SRT.