Black Start Research Articles

Analysis of Black Start of a Microgrid with PV, DG, and BESS

Different combinations of operating scenarios for a microgrid with distributed energy resources and energy storage system is considered to understand the operation of a microgrid. An operational strategy analysis of a microgrid system consisting of photovoltaics, diesel generator, and battery energy storage system during a black start in islanded mode is considered in this paper. BESS under study consists of a bidirectional converter and a battery system. BESS is assumed to be active as a solution provided in all the scenarios. The various capabilities of BESS in a microgrid system is also discussed. Microgrid system provides reliable power supply and hence black start capability for such a system is essential in keeping intact the advantages of a microgrid. Performing a black start requires a sequential process to be followed to avoid fluctuations in bus voltage, frequency, and protecting the fuses/ contactors from blowing. To black start the system under study, the DC breaker connecting the battery and the bidirectional converter needs to be closed. Closing the DC breaker results in high inrush current from batteries at the DC output of the bidirectional converter. A DC arrangement is envisaged in the battery energy storage system to avoid arcing due to high inrush current.

Two‐stage restoration strategies for power systems considering coordinated dispatch between plug‐in electric vehicles and wind power units

With increased penetration of wind power units and plug-in electric vehicles (PEVs), their control flexibility and quick response potentially provide an alternative way to fulfil the need for rapid restoration. A two-stage restoration strategy optimisation approach is presented with the coordination of PEVs and wind power units considered. The optimisation model is to maximise the restored generation capability and minimise the fluctuation of cranking power. In the first stage, the aim is to provide reliable cranking power remotely for black start generators through coordinated dispatch of PEVs and wind power units and quadratic programming (QP) models for dispatching electric vehicle aggregators (EVAs) subject to wind power fluctuations, and for dispatching numerous PEVs within each EVA are developed. To ensure close coordination between these two dispatching procedures, bi-level programming-based hierarchical decomposition approach is used to solve the QP models in an iterative way. In the second stage, an integer linear programming model is proposed to optimise the restoration schedules through an effective transformation of the original non-linear formulation, so as to reduce the computing time and effort significantly. Finally, a case study is presented to demonstrate the effectiveness and essential features of the developed models and methods.

Hierarchical model predictive control of wind farm with energy storage system for frequency regulation during black-start

In high wind power penetration power system, using wind farm equipped with energy storage system (WF-ESS) as black-start (BS) source needs to maintain system frequency stability when starting up ancillary machine or picking up load. A hierarchical model predictive control (HMPC) method of WF-ESS for frequency regulation during BS is proposed in this paper, which consists of two control modes: frequency regulation mode and reserve recovery mode. For the first control mode, a PI controller is used to generate reference power for WF-ESS and to recover system frequency to 50 Hz. The proposed HMPC is divided into WF level and wind turbine (WT) level to accurately track the reference power and guarantee secure operation of each WT. Considering WTs’ different operation conditions, WF level MPC distributes reference power to WTs according to the proportion of single WT reserve to total WF reserve. The ESS power is utilized as supplementary when WF output power is insufficient. The rotor speed and pitch angle constraints are included in the WT level MPC while providing frequency response. After frequency deviation is eliminated, WF and ESS are coordinated by the second control mode to avoid a second frequency drop meanwhile reserve a certain proportion of WF available power for managing potential frequency disturbances in the future. A case study is conducted to show the effectiveness of the proposed control method under both low and high wind conditions.

An Integrated Transmission Expansion and Sectionalizing-Based Black Start Allocation of BESS Planning Strategy for Enhanced Power Grid Resilience

This paper proposes a new comprehensive integrated planning strategy for the resilience enhancement of power system, including determining the transmission expansion and sectionalizing-based optimal black start (BS) resources allocation of battery energy storage system (BESS) during extreme events. The planning model comprises of two stages, namely the normal stage and resilience stage. The first stage is to make the collaborative planning decisions, i.e., constructing transmission lines and installation of BESS as BS sources. The second stage minimizes the power system generation cost and load shedding cost under disaster conditions. The planning algorithm is developed to describe the uncertainty of transmission lines outage status, which can be affected by the normal stage expansion states. In algorithm ways, the model was solved with a duality-based column and constraint generation (D-CCG) method. Taking IEEE 30-bus and 39-bus system for examples and GUROBI/CPLEX was utilized to solve proposed model. Numerical cases show the effectiveness of the model and the superiority of the solution strategy.

Distributed Control Strategies for Microgrids: An Overview

There is an increasing interest and research effort focused on the analysis, design and implementation of distributed control systems for AC, DC and hybrid AC / DC microgrids. It is claimed that distributed controllers have several advantages over centralised control schemes, e.g., improved reliability, flexibility, controllability, black start operation, robustness to failure in the communication links, etc. In this work, an overview of the state-of-the-art of distributed cooperative control systems for isolated microgrids is presented. Protocols for cooperative control such as linear consensus, heterogeneous consensus and finite-time consensus are discussed and reviewed in this paper. Distributed cooperative algorithms for primary and secondary control systems, including (among others issues) virtual impedance, synthetic inertia, droop-free control, stability analysis, imbalance sharing, total harmonic distortion regulation, are also reviewed and discussed in this survey. Tertiary control systems, e.g., for economic dispatch of electric energy, based on cooperative control approaches, are also addressed in this work. This review also highlights existing issues, research challenges and future trends in distributed cooperative control of microgrids and their future applications.

On Integration of Wind Power into Existing Grids via Modular Multilevel Converter based HVDC Systems

Due to the advent of advanced solid-state power devices and converters, it is now promising to transmit huge quantities of renewable energies to the main electrical grids. One of the major renewable energy resources is the wind power plant, which has the benefits of very low generation cost, simple infrastructure, lesser operating staff, lesser erection times, and negligible environmental pollution. Various far located power stations, including offshore and mainland wind power plants, as well as big industrial loads can be joined together with the existing AC grids by implementing multiterminal HVDC transmission systems. This recently established strong feature of HVDC systems is making them more feasible for future grids. The current source converter (CSC) is an established topology used in HVDC systems, worldwide. Rigorous research is being carried out on the voltage source converters (VSCs), especially on Modular Multilevel Converters (MMCs) based HVDC systems that are distinguished by their benefits of lower harmonics, lower maintenance, almost absence of bulky DC link capacitors and AC filters, black start capability, smooth control of powers, and addition of renewable energy using DC cables with the prevailing AC grids. In this paper, technical features associated with wind power plants and the interconnection of such plants via new MMC based HVDC systems with the present AC grids are discussed in detail. Mathematical modeling and performance analysis of advanced MMC technology is carried out by performing simulations in Matlab/Simulink ® . The deduced technical outcomes remarkably show the effective use of this converter in the near future grids.

Contribution of Energy Storage Technologies in Load Frequency Control - A Review

Due to increase population and the continuous efforts through the global residents to lessen the impact of environment change have caused the prompt usage of renewable based energy plants such as wind power plant and solar centered different power generation units. The usage of such power generating unit is purely dependent upon nature. Additionally, integration of renewable unit to power system causes instability. The frequency stability is one of the important aspects and depends on balance between generation and demand. To restore the frequency deviation back to its normal condition, an effective control strategy called Load Frequency Control (LFC) is adopted. To improve the performance of the control scheme different energy storage technologies can be considered. The storage technology not only has distinctive features of fast response and high energy density but also helps in load leveling, peak shaving, black start support etc. In this paper, comprehensive survey of diverse energy storage technology, its current market scenario and utilization in LFC services are presented by collecting, reviewing and interrupting numerous research articles. From the litertures survey, it is observed that, the existing strategies can be categorized in to two categories that is Grid scale System and Load Scale system. Further, load scale system is sub-categorized into coordinated aggregate system and non-coordinated individual system. In this paper, each control scheme is discussed theatrically also the pros and cons of each is addressed from technical point of view.

Assessing the viability and requirements of black start from DER

Assessing the viability and requirements of black start from DER

Temporary emergency power supply using medium-voltage islanded microgrids – a modular concept for distribution system operators

Due to the continuous increase of distributed generation (DG) units at the distribution grid level, temporarily islanded microgrid (TIM) operation in case of a blackout becomes energetically feasible. DG units with black start capability and additional MVA-scale generation units in TIMs are a strong option for a fast intermediate supply. They create possibilities for a longer-term emergency supply for a large number of customers until the overall grid restoration (GR) is completed. To develop generalised concepts that are applicable for more than one individual medium-voltage grid, general requirements and conditions have to be analysed thoroughly and defined as generic as possible. Therefore, a modular concept is developed comprising individual modules for GR, energy management (EM), control, protection, communication and operation. The focus of this study is to present the developed modular concept with a special focus on EM and control approaches for TIMs. As a result, the exemplary application of the modular concept is successfully conducted. Finally, the modular concept provides recommendations for project planning and engineering for distribution system operators, which can easily be extended. Special requirements of the distribution grid operation can be defined and considered by this approach.

Fault ride-through control strategy of H-bridge cascaded energy storage system

The cascaded energy storage system has received extensive attention in areas such as new energy consumption, maintaining stable operation of the power grid, and supporting black start due to its advantages such as high access voltage level, large single unit capacity, and fast dynamic response rate. This paper aimed to improve the fault ride-through capability of the cascaded energy storage system, and proposed a fault ride-through control method. Firstly, the mathematical model of the cascaded energy storage system was established, and then the rapid detection method of the abnormal state of the power grid and the fault ride-through method were analyzed, and finally the simulation analysis was performed. The feasibility and correctness of the control method can be seen from the experiments.

On the Secondary Control Architectures of AC Microgrids: An Overview

Communication infrastructure (CI) in microgrids (MGs) allows for the application of different control architectures for the secondary control (SC) layer. The use of new SC architectures involving CI is motivated by the need to increase MG resilience and handle the intermittent nature of distributed generation units. The structure of SC is classified into three main categories, including centralized SC (CSC) with a CI, distributed SC (DISC) generally with a low-data-rate CI, and decentralized SC (DESC) with communication-free infrastructure. To meet the MGs' operational constraints and optimize performance, control and communication must be utilized simultaneously in different control layers. In this survey, we review and classify all types of SC policies from CI-based methods to communication-free policies, including CSC, averaging-based DISC, consensus-based DISC methods, containment pinning consensus, event-triggered DISC, washout-filter-based DESC, and state-estimation-based DESC. Each structure is scrutinized from the viewpoint of the relevant literature. Challenges such as clock drifts, cyber-security threats, and the advantage of event-triggered approaches are presented. Fully decentralized approaches based on state-estimation and observation methods are also addressed. Although these approaches eliminate the need of any CI for the voltage and frequency restoration, during black start process or other functionalities related to the tertiary layer, a CI is required. Power hardware-in-the-loop experimental tests are carried out to compare the merits and applicability of different SC structures.

Strong Mixed-Integer Formulations for Power System Islanding and Restoration

Intentional controlled islanding (ICI) and black start allocation (BSA) are two examples of problems in the power systems literature that have been formulated as mixed integer programs (MIPs) and allow reconfiguration of the power system topology. A key consideration in both of these problems is that each island that appears after a reconfiguration must have at least one energized generator. In this paper, we examine three alternative MIP formulations for this restriction, show their equivalence, and prove that two of them are stronger in terms of their linear programming relaxation than the formulation most commonly used in the power systems literature. Since the time to solve MIPs can vary significantly between equivalent formulations, we also present computational experiments on the IEEE test systems for the ICI and BSA problems. We observe that a polynomially separable, exponential in size, strong formulation yields the best performance for the BSA problem and exhibits a comparable performance to a linear in size, weak formulation for the ICI problem.

Frequency Regulation Strategy for AC–DC System During Black Start

High-voltage direct current (HVDC) can speed up the recovery of a power system. However, both rectifier and inverter sides of HVDC are weak systems during a black start. To coordinate frequency characteristics of both sides within the frequency deviation constrain, a frequency regulation strategy for AC–DC system during a black start is proposed. First, the mathematical models of asynchronous interconnected AC–DC system are established, and the optimal HVDC transmission power leading to minimum frequency deviation of both sides is obtained based on the linear quadratic optimal control method. To adapt to the continuously changing parameters and configurations of the AC power system during a black start, a Narendra adaptive tracking control method is developed to obtain the control law of the target value of governor, which allows the actual system frequency follow the reference system frequency under the optimal HVDC transmission power. Finally, the simulation model is established using PSCAD/EMTDC software to verify the proposed strategy.

A Tunable Power Sharing Control Scheme for the Output-Series DAB DC–DC System With Independent or Common Input Terminals

To connect the low voltage energy storage source equipment and the medium voltage dc (MVdc) bus, the output-series dual-active-bridge (OS-DAB) dc–dc converter system with independent or common input terminals becomes a promising option. For the OS-DAB dc–dc converter system, this letter proposes a simple tunable power sharing control (TPSC) strategy to maintain the voltage of MVdc bus, manage power sharing ratio for each energy storage system. The proposed strategy allows energy storage equipment hot swap as well as converter system black start. Experimental results verify the analysis in this letter and the excellent performance of proposed TPSC strategy.

Security margin analysis of wind power participating in black start

The increasing wind power penetration makes it necessary for wind power to participate in system restoration, while the maturing wind power control technology makes it possible. To characterise the security level of the system accommodating a certain amount of wind power during black start, the security margin evaluation indexes of wind power particpating in black start were put forward, based on the influence of wind power on the system recovery. Then, the law of wind speed prediction error was analysed, the representative sample set of future wind conditions was generated by historical simulation method, the worst future wind conditions were obtained at a certain level of confidence, and the solution method of the security margin based on time-domain simulation was given. Additionally, with a specific black-start scheme, general steps to solve the security margin were demonstrated, the ‘wind power integration capacity – security margin’ curves were obtained, and the influence of wind power on system restoration security was analysed from multi-views. At last, the impact of wind speed prediction accuracy on system security margin was explored, and other applications of the presented method were given.

PMSG-Based Black-Start Technology and Its Field Tests

It is of great importance for power grids to have black-start capability for rapid recovery, and there is great theoretical significance and practical application value in studying how to use wind farms as the black-start power supply source for power grids with large-scale renewable energy generation. In this paper, a black-start scheme using a permanent-magnet synchronous generator (PMSG)-based wind farm as black-start power supply source is formulated. First, a diesel generator is used as an external supporting power supply for the self-start of a wind power unit (WPU). Then, after all the planned WPUs operate normally, the wind farm with the diesel generator and static var generator (SVG) is used to black start the simulated auxiliary load of a thermal power plant. A field test of the proposed black-start scheme is carried out on an actual wind farm in Jiangsu Province (China). The results of the field test show that wind farms can act as a black-start power supply source for the grid after appropriate technological transformation.

Enabling wind farm to be black‐start source by energy storage

An energy storage system (ESS) sizing method is proposed to enable wind farm (WF) to be a black-start (BS) source. This method handles three challenges: firstly, ESS has enough power to help WF start up. Secondly, the WF together with ESS is modelled as a virtual synchronous generator (VSG), and its frequency regulation capability is considered when sizing ESS. Thirdly, the power and capacity of ESS are determined so that VSG can deliver the required power during black-start. Instead of using wind speed probability distribution, kernel density estimation is used in this paper to directly estimate the probability distribution characteristics of ESS sizing. Simulation results show that with minimum investment cost on ESS, WF is able to be BS source.

Energy storage sizing by copula modelling joint distribution for wind farm to be black‐start source

To achieve fast power system restoration with high penetration of wind power, using wind farm (WF) as black-start (BS) source is a promising choice. An energy storage system (ESS) sizing method with the minimum investment cost is proposed to enable WF to be a reliable BS source. The proposed method covers three aspects: (i) providing WF self-starting power, (ii) dealing with frequency deviation when starting up ancillary machines and (iii) smoothing WF output power while starting up generator unit. During BS progress, ESS power sizing and capacity sizing are both considered as random variables and their marginal distributions are estimated by kernel density estimation to avoid the distribution model mismatch. The correlation between these two random variables is discussed, which shows that these two variables are not independent. To model the dependence structure between ESS power sizing and capacity sizing, copula theory is applied to build the joint probability distribution. A tail dependence analysis and goodness-of-fit test included copula selection procedure is conducted to choose the most suitable copula function. A case study with real WF data demonstrates that a better-fitted copula has lower ESS sizing cost.

Optimal black start strategy for microgrids considering the uncertainty using a data‐driven chance constrained approach

Microgrids may suffer from full blackouts when confronted with unexpected disruptions due to man-made faults or natural disasters. How to quickly restore the power supply of microgrids by making use of local distributed energy resources (DERs) is therefore a practical issue to help microgrids ride through full blackouts. Accordingly, this study proposes a novel black start strategy for microgrids to determine the restoration sequence and optimally allocate the DERs after full blackouts. In particular, the uncertainty of power output of renewable energy sources is considered using a data-driven chance-constrained approach when renewable energy sources are integrated. The proposed approach only utilises historical data and does not need any prior knowledge about the true probability distribution of the uncertainty. In addition, affine-based techniques and sample-dependent band functions are developed to convert the chance-constrained problem into a tractable mixed-integer linear programming problem. Finally, numerical experiments based on two microgrid test systems are performed to validate the effectiveness of the proposed model.

Control of Energy Storage System Integrating Electrochemical Batteries and Supercapacitors for Grid-Connected Applications

The implementation of ancillary services in renewable energy based generation systems requires controlling bidirectional power flow. For such applications, integrated energy storage systems (ESSs) in such generation platforms have emerged as a promising solution. However, a large variety of ESS solutions are available in the market, and even hybrid systems are proposed to optimize the overall performance. In this regard, the integration of supercapacitors (SCs) and electrochemical batteries is an attractive and feasible solution, as it takes the most of the combination of the large storage capacity of batteries with the high dynamic performance of SCs. This combination enables the implementation of energy and power services, such as inertia emulation, black start, or power oscillation damping among others. This solution avoids oversizing ESS and enlarges the battery lifetime, since the SCs absorve the high dynamic response meanwhile the battery feeds an attenuated power profile. This paper presents a strategy to manage mixed energy storage technologies, composed by a direct connection of a battery and an SC bank interfaced through a dc–dc converter. A power control loop distributes the power flow through each element in order to achieve an optimized performance, meanwhile, it permits to provide grid-frequency support and minimizes the number of cycles applied to the battery. The analysis made and the initial sections are endorsed by simulation and experimental results collected in a 50-kW test-bench.