Improve Power System Flexibility Research Articles

An Optimal Operation Strategy for Collaborative Flexibility Provision of a Carbon Capture and Utilization Process With Wind Energy

Improving power system flexibility by responsive demand is essential for integrating wind energy with a high level of variability in power systems. Carbon dioxide-based chemical processes as energy-intensive industrial loads may offer a vast potential of new forms of flexible operation due to their existing control infrastructure and storage capabilities. However, a collaborative decision model is needed for optimal energy sharing among the chemical plant and the grid under the variations and uncertainties of wind power. This study develops an optimal two-stage stochastic programming model for a novel flexible operation strategy of the chemical process coupled with wind turbines. In the proposed control scheme, a small-scale wind farm provides the power input of a chemical plant. Wind turbines are connected to the grid and actively participate in the day-ahead energy and reserve markets, considering the chemical plant as a source of flexibility. An equivalent scenario-based model of the proposed optimization problem is suggested using the Group Method of Data Handling (GMDH) for a data-driven prediction of stochastic variables. Simulation results demonstrate the effectiveness and significance of the proposed approach for an optimal and collaborative contribution in ancillary market of a carbon dioxide-based chemical plant supplied by wind energy.

Adjustable robust interval economic dispatch of integrated electricity and district heating systems under wind power uncertainty

With the increasing capacity of wind power in power systems, wind power volatility and uncertainty pose a great threat to the operation of the electricity system, especially for areas with high heating demand. Integrated electricity and district heating system (IEDHS) is a promising option to improve power system flexibility to accommodate more wind power. This paper excavates the potentiality of coordinated operation of IEDHS to alleviate the effects of wind power uncertainty with an adjustable robust interval approach. Firstly, the structure of IEDHS and operation models of district heating network are presented. An adjustable robust interval optimal dispatch model for IEDHS is established considering wind power uncertainty. The wind power mismatches in the worst-case scenarios are balanced by adjustable thermal units based on the time-varying participation factors. Then, the nonlinear mathematical formulation of the scheduling model is proposed and converted into a mixed-integer linear programming (MILP) problem utilizing a binary expansion method. By solving this model, the maximum allowable output intervals of wind power and optimal economic dispatch results of IEDHS can be obtained. Finally, case studies performed on two IEDHS are applied to verify the validity of the proposed model.

Planning of Flexible Generators and Energy Storages under High Penetration of Renewable Power in Taiwan Power System

The proportion of renewable power generation in the world has been increasing in recent years. However, the fluctuations and uncertainties of renewable power generation bring a considerable challenge to future unit scheduling. Therefore, the generation flexibility in power systems becomes more critical as a large amount of renewable generation is integrated into power systems. The use of flexible generators with energy storage systems is one of the most efficient methods of improving power system flexibility. The primary purpose of this study is to explore the effect of generation flexibility on the cost of unit scheduling. A flexibility index is used to evaluate the generation flexibility in the Taiwan power system, and a multi-scenario analysis for renewable power integration is considered. This study also considers various system constraints, such as the unit commitment of actual hydro and thermal units, the scheduling of flexible internal combustion engines (ICEs) and energy storage systems, and possible curtailments of renewable power generation. According to the seasonable characteristics of renewable power generation, this study provides a suitable capacity for flexible ICE units and energy storage systems. Furthermore, this study demonstrates that the cost of unit scheduling is effectively reduced by increasing flexible ICE units and energy storage systems. The results of this study can be used as a reference for power systems in preparing flexible generating units and energy storage systems under the integration of a large amount of renewable power generation in the future.

A new flexibility based probabilistic economic load dispatch solution incorporating wind power

Nowadays, by the growing in renewable energies in the power system, the uncertainty of power output related to these resources increases. This needs to improve power system flexibility to reduce the risk of load shedding or renewable curtailment due to the mentioned challenge. So, nowadays power system flexibility is an important characteristic especially in power system operation which should be evaluated continuously and maintained in the desired value. In operation horizon time such as operational planning or real time operation the system generation flexibility should be monitored, and sufficient system flexibility should be provided to avoid unacceptable generation/load unbalance cause unwanted renewable curtailment or load shedding.This paper presents a new flexibility based risk limiting dynamic economic load dispatch solution incorporating wind power. In the proposed method the generation system flexibility index, introduced by the authors is converted to economic value and included in the total operation cost function. Then by the suitable economic trade-off between system flexibility level and risk of load shedding and wind power curtailment, the best reduction in these two unwanted risks are obtained. Increasing the system generation flexibility comes from the generation rearrangement of thermal generation units imposes more cost to the generation cost but is balanced by reduction in unwanted renewable curtailment or load shedding.

Flexibility Optimal Dispatching for Power System Considering Demand Response

With the increasing penetration of renewable energy sources such as wind and solar power, higher requirements of flexible supply ability for power systems are put forward. In this context, an optimal dispatching method considering two types of demand response is proposed to improve power system flexibility. On the demand side, both the time-of-use (TOU) price and interruptible load are used to guide consumers to actively optimize the load curve, so as to relieve the pressure of the flexible supply of conventional units on the supply side. The demand response model consisting of TOU price and interruptible load is built. Then, taking the minimum cost as the objective function, the optimization model for power system dispatching is solved. Finally, the modified IEEE 30 bus system is taken as a case study. The results show that the consideration of two-type demand response in the optimal dispatching can improve the flexibility while ensuring economy, which verifies the effectiveness of the proposed method.

Optimization operation model of electricity market considering renewable energy accommodation and flexibility requirement

The renewable portfolio standard has been promoted in parallel with the reform of the electricity market, and the flexibility requirement of the power system has rapidly increased. To promote renewable energy consumption and improve power system flexibility, a bi-level optimal operation model of the electricity market is proposed. A probabilistic model of the flexibility requirement is established, considering the correlation between wind power, photovoltaic power, and load. A bi-level optimization model is established for the multi-markets; the upper and lower models represent the intra-provincial market and inter-provincial market models, respectively. To efficiently solve the model, it is transformed into a mixed-integer linear programming model using the Karush–Kuhn–Tucker condition and Lagrangian duality theory. The economy and flexibility of the model are verified using a provincial power grid as an example.

Operation optimization of electrical-heating integrated energy system based on concentrating solar power plant hybridized with combined heat and power plant

The integration of power and heating systems is a promising option to optimize unit operation and improve power system flexibility for reducing renewable energy sources curtailment. This study aims to excavate the potentiality of a concentrating solar power plant hybridized with a gas-fired combined heat and power plant to alleviate the effects of the uncertainty and variability of renewable energy sources. Firstly, in order to further utilize the scheduling ability of the concentrating solar power plant with a thermal energy storage (TES) system and improve the operational flexibility of the combined heat and power plant, a combined plant is proposed in this paper. Specifically, a concentrating solar power plant and a gas-fired combined heat and power unit are assembled together based on the temperature parameters of energy flow during operation. Secondly, taking the remaining state of charge (SOC) of TES in operating day into account, a three-stage multi-time scale stochastic unit commitment-economic dispatch model is formulated to optimize unit operation and reduce operating cost. Finally, in order to verify the operational flexibility and economic benefits of the proposed combined plant with multi-time scale stochastic unit commitment-economic dispatch model, several different energy supply modes are compared in the simulation. Results show that the proposed scheme has better economic benefits and development potential in the electrical-heating integrated energy system.

Power system transition in China under the coordinated development of power sources, network, demand response, and energy storage

AbstractChina is transiting its power system towards a more flexible status with a higher capability of integrating renewable energy generation. Demand response (DR) and energy storage increasingly play important roles to improve power system flexibility. The coordinated development of power sources, network, DR, and energy storage will become a trend. This paper examines the significance of source‐network‐demand‐storage coordinated development. Furthermore, an outlook of the power system transition in China is provided by virtue of source‐network‐demand‐storage coordinated planning. The paper also assesses the integration of multiple urban infrastructures in China and its impacts on source‐network‐demand‐storage coordination. Lastly, challenges for achieving the source‐network‐demand‐storage coordination and suggested measures are discussed.This article is categorized under: Energy Research & Innovation > Systems and Infrastructure Energy and Urban Design > Systems and Infrastructure

International Practice of Improving Power System Flexibility and Its Enlightenment to China

With the rapid increase in the proportion of renewable energy in the power system, the volatility of renewable energy output has greatly increased the risk of power system operation and brought about the need for power system flexibility. A reasonable market mechanism in the electricity market can stimulate flexibility resources and fully exploit the flexibility of the system, which plays an important role in the efficient and safe operation of the power system. This paper studies several countries or regions that have a high share of renewable energy and have established relatively mature power markets, and then analyzes and compares the power system flexibility needs of these regions and the market mechanisms used to increase flexibility. Finally, the enlightenment of international practice to China based on the current situation is summarized.

Fully Distributed Robust Reserve Scheduling for Coupled Transmission and Distribution Systems

To realize the potential of active distribution networks (ADNs) for improving power system flexibility and to cope with multiple uncertainties, a coordinated robust reserve scheduling (CRRS) model for the coupled transmission and distribution networks (CTD) is proposed in this paper. This model coordinates the generation resources both in the normal state and re-dispatch state to enhance the cost-effectiveness and reliability in a system perspective. A fully distributed framework based on the alternating direction method of multipliers (ADMM) is employed to solve this problem in a decentralized way. As the regional problem of the transmission system is non-convex, a two-layer iterative process (TIP) is presented to enhance the convergence property of standard ADMM. Since only the boundary information needs to be exchanged between the transmission and distribution systems, the communication burden is light and regional information is encrypted. Case studies on the T6D2 and T118D10 systems demonstrate the effectiveness of the proposed model and approach.

Multi-Technical Flexibility Retrofit Planning of Thermal Power Units Considering High Penetration Variable Renewable Energy: The Case of China

High penetration variable renewable energy introduces flexibility issues to the power system. For countries with coal as their main energy source, retrofitting existing thermal power units is one of the most realistic and feasible measures to improve power system flexibility. Multiple retrofit options will almost certainly be available for each individual power plant—all with distinct investment costs and performance implications. Therefore, this paper develops a multi-technical flexibility retrofit planning model to inform investment decisions of thermal power units in the short term. The model is formulated as a mix linear programming, with the goal of minimizing the systems overall investment and operational costs. In particular, a linear formulation is proposed to solve the coupling problem of retrofitting and operating, and take account of the changes in various units’ operational parameters after retrofit. The correctness and effectiveness of the proposed models are verified by a case study through a modified IEEE-30 bus system. The results demonstrate that it is necessary to consider the complementariness of multiple technologies between units. Besides, the proposed model could minimize the overall system investment and operational costs, and provide advice to planners and power generation companies.

Wind power development in the Belt and Road area of Xinjiang, China: Problems and solutions

Following the proposal of the “Belt and Road” strategy, Xinjiang has gradually become a critical wind power base and energy transmission channel in China. At present, however, much of Xinjiang's potential wind power is being curtailed. Owing to Xinjiang's strategic position, this issue may negatively impact wind power development in Xinjiang and China's overall energy strategy, and it is thus necessary to identify the causes of and solutions to wind power curtailment in Xinjiang. This study analyzes the problem of wind power development in Xinjiang, and proposes both technical and market policy measures. The research results show that establishing a regional power spot market and improving power system flexibility are the fundamental ways to solve the problem of wind power curtailment in Xinjiang.

Impact of Generation Flexibility on the Operating Costs of the Taiwan Power System Under a High Penetration of Renewable Power

The penetration of renewable energy is gradually increasing. Therefore, power system flexibility, which is required to maintain system security and to cope with renewable generation uncertainty, becomes more important. Various technologies, such as flexible generators, demand management, energy storage, network reconfiguration, and even efficient system operations, are capable of improving power system flexibility. Nevertheless, among them, flexible generation resources can provide a direct way to enhance the power system flexibility. This article first applies the fuzzy analytic hierarchy process to calculate the flexibility index of generation resources. Then, the process of unit scheduling is implemented under various operation scenarios to investigate the relationship between the generation flexibility and the cost of unit scheduling. Finally, the required flexibility and the corresponding capacity of flexible generators under a specified penetration of renewable power generation are investigated under different operation scenarios.

Dual Interval Optimization Based Trading Strategy for ESCO in Day-ahead Market with Bilateral Contracts

Being capable of aggregating multiple energy resources, the energy service company (ESCO) has been regarded as a promising alternative for improving power system flexibility and facilitating the consumption of renewable resources in the electricity market. Considering the uncertain variables in day-ahead (DA) market trading, an ESCO can hardly determine their accurate probability distribution functions. Traditional interval optimization methods are used to process these uncertain variables without specific probability distribution functions. However, the lower and upper bounds of the intervals may change due to extreme weather conditions and other emergent events. Hence, a dual interval optimization based trading strategy (DIOTS) for ESCO in a DA market with bilateral contracts (BCs) is proposed. First, we transfer the dual interval optimization model into a simple model consisting of several interval optimization models. Then, a pessimistic preference ordering method is applied to solve the derived model. Case studies illustrating an actual test system corroborate the validity and the robustness of the proposed model, and also reveal that ECSO is critical in improving power system flexibility and facilitating the ability of absorbing renewable resources.

Power load demand response potential of secondary sectors in China: The case of western Inner Mongolia

Existing literature shows that understanding demand response potential plays a key role to promote renewable energy consumption and improve power system flexibility. However, our knowledge is limited in the power shifting technical demand response potential covering all the secondary sectors and the achievable demand response potential of secondary sectors. To address this gap, this study aims to: (1) design a questionnaire to assess electricity load shifting technical demand response potential and achievable demand response potential; (2) conduct a case study of western Inner Mongolia. Covering all the secondary sectors; and (3) study demand response potential using the methods of qualitative analysis based on power load curves and face to face interviews with local enterprises, and quantitative statistics of questionnaire responses. The results show that, in secondary sectors, over half of the enterprises’ power load shifting technical demand response potential is less than 10%. Additionally, approximately three-quarters of enterprises in secondary sectors will use other energy sources to replace electricity when electricity sale price increases by 30%. These results can help power companies and government to identify adjusted power load potential and corresponding main consumers for demand response strategies to promote the utility grid safety and renewable energy consumption.

Privacy-Preserving Energy Scheduling for ESCOs Based on Energy Blockchain Network

Capable of aggregating multiple energy resources, the energy service company (ESCO) has been regarded as a promising alternative for improving power system flexibility and facilitate the consumption of renewable resources in the energy market. However, the issues have become significantly more serious related to the privacy and security of the data in consumption and trading. In this paper, we address the problem by proposing a privacy-preserving energy scheduling (PPES) model based on energy blockchain network. A Lagrangian relaxation method is applied to decompose the model into several individual optimal scheduling problems, and the individual scheduling problems are solved by consensus algorithm and smart contracts in energy blockchain network. The performance of the proposed model and method is evaluated with several case studies based on multiple energy nodes. Simulation results show the rationality and validity of the proposed method, and the model is conducive to the protection of environment and transparent scheduling of energy service companies (ESCOs). In addition, it can reflect the information of energy demand and supply to improve the privacy and security of data.

A Review of Power Electronic Converters for Variable Speed Pumped Storage Plants: Configurations, Operational Challenges, and Future Scopes

Pumped storage power plant has gained a high level of attention in recent years, mainly because of its ability to act as a large-scale energy storage option and to improve power system flexibility. Doubly fed asynchronous machine with the partially rated power electronic converter is adopted in pumped storage plants to provide variable speed operation and improve energy efficiency. This paper summarizes the power converter topologies in large rated variable speed pumped storage plant (VSPSP), also covers the suitability of each converter topology, modulation techniques, and parallel converter schemes. Also, it presents operational issues of the parallel converter system in VSPSP such as the shutdown of the plant due to insufficient converter redundancy and lack of fault-tolerant control schemes, a power outage due to the inadequacy of converter protection system, and unbalanced power sharing due to circulating current. Furthermore, the reliable mitigating/additional techniques are discussed for future research. It concludes that the refinement of these aforementioned issues will provide continuous operation of the plant.