Power Balance Of System Research Articles

Substitute energy price market mechanism for renewable energy power system with generalized energy storage

Incompatibility of current electricity market mechanisms based on locational marginal price (LMP) become prominent in power systems with increasing renewable energy (RE) and generalized energy storage (GES), resulting in soaring electricity prices, high costs of balancing RE, etc. To fundamentally solve this problem, we propose a novel substitute energy price (SEP) market mechanism, compatible with objective market value, new supply–demand relationship and nature of continuous power balance of RE power systems. SEP, reflecting market value of per-unit substitute energy, is discovered for the first time, and thus energy curves can be traded as substitutes at vector level. Based on designed regulation responsibility mechanism, any entity, especially RE generator, can transform its energy curve with regulation demands into substitute by indirect payment. To supply these regulation demands generated by REs and loads, regulation energy is proposed as independent tradable commodities with quantitative market value to adapt to GESs and dispatchable generators. Numerous experiments indicate SEP mechanism overcomes major deficiencies of existing LMP mechanism, provides a level playing field for all energy and regulation resources, promotes construction of GESs and helps improve global social welfare and relieve duck-curve problem. This work will be instrumental in the transformation of current power systems to carbon–neutral RE power systems.

Event-Triggered Consensus Control of Large-Scale Inverter Air Conditioners for Demand Response

The boom of fluctuating renewable energies puts forward higher requirements on reserve capacity for maintaining the power system balance. To address this issue, this letter investigates a novel distributed event-triggered consensus control (ETCC) method of large-scale inverter air conditioners (IACs) for demand response, which can achieve the same regulation objective and response speed while significantly relieving the communication burden compared with traditional time-scheduled consensus control methods. Based on Lyapunov stability theorem, we also prove the convergence of the ETCC with nonlinear protocol for massive IACs. Finally, the above models and methods are verified by numerical studies.

Optimization dispatching of isolated island microgrid based on improved particle swarm optimization algorithm

Aiming at the microgrid system including wind turbine, microgas turbine, diesel generator, fuel cell and battery under the isolated island mode, the optimization dispatching model was established by taking the comprehensive cost considering economy and environmental protection as the objective function and combining with the constraints of system power balance and output limit of each unit. In view of the prematurity and convergence problems of the standard particle swarm optimization algorithm, an improved PSO algorithm with adaptive inertia weight and contraction factor is proposed to enhance the global and local search capability of the algorithm. Finally, the simulation analysis is carried out based on the operation data of typical daily island microgrid. The results show that the improved PSO algorithm adopted in this paper effectively reduces the comprehensive target cost and achieves good optimization effect.

Energy arbitrage optimization of lithium-ion battery considering short-term revenue and long-term battery life loss

To achieve the ambitious goal of net-zero by 2050, the power sector in many countries has been increasingly using renewable energy sources (RES). The power system balance will be significantly challenged due to the intermittency of RES. Lithium-ion battery energy storage systems (BESS) can effectively address the challenge by providing flexibility to fill the mismatch between the intermittent supply and the varying demand, generating revenues for BESS to payback the initial investment. However, every grid participation also results in an inevitable lifetime loss. From the asset owner’s perspective, therefore, it is important to balance the short-term revenue from the fluctuating electrical market with the long-term battery life loss. To achieve this in this study, first, a novel online-applied battery life model is established, which is computationally efficient to comprehensively consider the battery’s historical aging, state of charge (SOC), charge–discharge rate (Crate). Then, an online-applied sliding-window dynamic programming (SWDP) strategy is proposed to optimize short-term grid service revenues and long-term battery life losses. The SWDP is also compared with an offline-applied dynamic programming (DP) strategy. The simulation results show that the cost due to battery life decay is significant, which indicates the importance of tracking the battery life loss in the battery asset management. Additionally, the prediction accuracy of electricity price significantly influences the performance of SWDP strategy. The BESS’s total profit can reduce by half in the considered case study if the electricity prediction error is 12.5%.

Research on power and energy balance of new power system under low carbon emission path

Combined with the requirements of low-carbon transformation of power system, this paper points out the existing problems in power and energy balance of new power system under the dual carbon target. The technical solutions for electric power balance are summarized from the perspectives of planning and operation. The concept of “carbon correlation” is proposed to quantitatively represent the matching degree between equipment characteristics and dual carbon paths, which can provide alternative reference for planning. Secondly, considering the uncertainty and uncontrollability of new energy, the operation level is divided into normal state and emergency state, so as to improve the resilience of the power system. Finally, seasonal energy storage planning is taken as an example1 to clarify its role in medium - and long-term power balance, and the results show that although seasonal storage increases the configuration cost of energy storage, it can reduce the operating cost and improve the economy of the system as a whole. The multi-stage low-carbon planning of multi-energy complementary comprehensive energy park is taken as example 2 to clarify the steps of carbon-energy collaborative planning. The results show that the multi-stage planning method can avoid the waste caused by the equipment in the early stage and make the time sequence of capacity expansion and load increase consistent. At the same time, the demand response method can be used to be more flexible and reasonable, and can further improve the economy of the system.

Multi-Flexibility Resources Planning for Power System Considering Carbon Trading

Clean and low-carbon energy represented by wind power and photovoltaic power will develop rapidly and will form a new power system with a high proportion of renewable energy. In the context of a low-carbon economy, how to make reasonable planning for power system flexibility resources is crucial for the development of new power systems. In this paper, we establish a multi-flexibility resource planning model for a power system based on a low carbon economy by considering the planning of multi-flexibility resources of “source–load–storage”. First, a ladder-type carbon trading cost accounting model is proposed, and a set of power system flexibility evaluation indexes are proposed. Then, with the objective of minimizing the sum of low carbon operation cost, investment cost, and operation cost of the system, the planning model of multi-flexibility resources is established by considering constraints such as system power balance constraint, investment constraint, and wind power consumption constraint. Finally, the model proposed in this paper is validated by the IEEE-RTS96 system; the results show that: (1) collaborative planning of source–load–storage multi-flexible resources can obtain the best overall system economics, although the investment cost increases by USD 12.6M, the total system cost is reduced by 11.22% due to the reduction in coal generation consumption cost, carbon trading cost, and wind curtailment penalty cost; (2) as the penetration of wind power grows, the demand for energy storage in the power system is gradually increasing; when the installed capacity of wind power grew from 800 MW to 1600 MW, the demand for new thermal power decreased by 53.5% and the demand for new energy storage increased by 200%; (3) the total cost of the planning model considering ladder-type carbon trading decreases by 1.35% compared to the model without carbon trading, and increases by 2.5% compared to the model considering traditional carbon trading, but its carbon emissions decrease by 5.5%.

Research on a cross-regional robust trading strategy based on multiple market mechanisms

With the increase in the variety of market players in cross-regional trading, the interaction of interests among multiple participants is complicated, resulting in unbalanced interests in the cross-regional trading market. Therefore, a robust trading model with joint multi-market mechanisms is proposed in this paper to cope with the intricate interactions among market players. The proposed model builds a joint trading market framework of carbon emission rights and green certificates to incentivize more market players to participate in cross-region trading. To better balance the interests among the market players, a multi-market player alliance based on the cooperative game theory is established, and a profit distribution method based on the contribution degree of system power balance is proposed. To ensure the balance of energy supply and demand for cross-regional trading, the distributed robust optimization method based on the Wasserstein metric is proposed considering the uncertainty of renewable energy generation. Finally, the feasibility of the proposed dispatching model is demonstrated with the modified IEEE 39 bus system and the Hami power grid as an example. The results show that the proposed model can obtain a conservative and economical operating scheme with fast operation time, and the joint trading mechanism can further save the operating cost.

An improved energy management control strategy for a standalone solar photovoltaic/battery system

This <span>paper proposes efficient energy management in hybrid microgrid-comprising of photovoltaic (PV) and battery storage systems. The proposed technique. The hybrid system's power balance is based on smart control to meet the demands of isolated off-grid direct current (DC) loads as well as to stabilize the voltage to DC Bus. The Perturb and Observe technique (P&O) is used to achieve maximum power point tracking by adjusting the duty cycle of the Bidirectional converter, which links the Li-ion battery to the DC Bus of stand-alone power systems (SPS). The proposed controller regulates the power flow of the battery for efficiency voltage control in a microgrid. The energy management system proposed has been approved using MATLAB/Simulink under variable solar irradiation conditions. The simulation results show that the technique used increases the battery cycle-life and better energy management and voltage control performance compared with previous examples</span>.

Multistage Economic Scheduling Model of Micro-Energy Grids Considering Flexible Capacity Allocation

Micro-energy grids integrating multiple energy sources can realize the efficient use of renewable energy and accelerate the process of energy transition. However, due to the uncertainty of renewable energy, the stability and security of system operations should be taken into account with respect to multi-energy coupling economic operations. Thus, it is essential to make flexible capacity allocations in advance of the actual scheduling of production in the micro-energy grid. With this motivation, this paper constructs a three-stage scheduling model corresponding to the running stage of the spot market. Specifically, the capacity of flexible, active devices is configured in the day-ahead stage; then, the intraday economic operation dispatching scheme is provided according to the capacity configuration. Based on the day-ahead and intraday optimization results, the system power balance is realized through the dispatching process using the reserve capacity of flexible active devices for deviations generated in the real-time stage of renewable energy. For the uncertainty of renewable energy output, the clustering method is applied to realize the clustering analysis of renewable energy output scenarios. In addition, the conditional value at risk (CVaR) theory is introduced to modify the three-stage stochastic optimization model, and the risk values caused by uncertainty are quantitatively evaluated. Finally, we simulate a practical case to verify the effectiveness of the proposed model. The results show that day-ahead flexible capacity allocation enhances the autonomy of the micro-energy grid system, ensures a certain degree of system operational security, and reduces balancing costs in the real-time stage. The higher the risk aversion factor, the more operational costs the system operator pays to avoid the risk. In addition, if the carbon penalty coefficient is higher, the overall carbon emission level of the micro-energy grid will decrease, but it will gradually converge to a minimal level. This paper guides the development of micro-energy grids and has important constructional significance for the construction of multi-energy collaborative mechanisms.

Introducing explainability in sequence-to-sequence learning for short-term load forecasting

Methods to forecast electric loads and generation timeseries are widely applied in power system operation and balancing. For this purpose, most sophisticated forecasting methods are complex, since the net electricity consumption is not dependent on and explainable by a single cause. The increasing complexity furthers a trend towards machine-learning methods that achieve more accurate load forecasts with exogenous features. However, a well-known downside of machine learning is that forecast users will face non-transparent, and inexplicable models that are difficult to relate to. In this paper, we propose a graphical representation of the most salient exogenous features as functions of time for day-ahead residual load forecasting. The presented work extends a sequence-to-sequence recurrent neural network model to visually accommodate the explanation of the produced forecast. The resulting saliency maps reduce the high complexity of the input–output relationships to the two-dimensional plane of features over time steps.

Modeling and performance analysis of renewable hydrogen energy hub connected to an ac/dc hybrid microgrid

This paper proposes a system modeling and performance analysis of a renewable hydrogen energy hub (RHEH) connected to an ac/dc hybrid microgrid (MG). The proposed RHEH comprises a photovoltaic (PV)-based renewable energy source (RES) as the primary source, a proton exchange membrane fuel cell (PEMFC) as the secondary power source, and a proton exchange membrane electrolyzer (PEMELZ) that can generate and store hydrogen in a hydrogen tank. All these resources are directly connected at the dc bus of the ac/dc microgrids. The PEMFC operates and utilizes the hydrogen from the hydrogen tank when the energy generated by RES cannot meet the load demand. A coordinated power flow control approach has been developed for the RHEH to mitigate the mismatch between generation and demand in the ac/dc microgrid and produce renewable hydrogen when renewable power is in excess. The paper also proposes a modified hybrid Perturb & Observe-Particle Swarm Optimization (Hybrid PO-PSO) algorithm to ensure the maximum power point tracking (MPPT) operation of the PV and the PEMFC. The operation of the proposed RHEH is validated through simulations under various critical conditions. The results show that the proposed RHEH is effective to maintain the system power balance and can provide power-to-hydrogen and hydrogen-to-power when required.

Types, applications and future developments of gravity energy storage

In recent years, the clean and environmentally-friendly renewable energy technologies have developed rapidly. How to ensure balance and flexible output of power system has become a new challenge after all kinds of volatile power sources are connected to the power system. Among different forms of stored energy, gravity energy storage, as a kind of physical energy storage with competitive environmental protection and economy, has received wide attention for its advantages such as high safety, high cost-performance, great environmental-friendliness and strong environmentally adaptation. This paper firstly introduces the basic principles of gravity energy storage, classifies and summarizes dry-gravity and wet-gravity energy storage while analyzing the technical routes of different types of gravity energy storage. Separated into groups of dry and wet gravity energy storage, these storage shows similar features and promising advantages in both environmental and economical way. Among them, LEM-GES shows a new concept of storage and will be the target for future study. Then follows an analysis of the practical applications of gravity energy storage in real scenarios such as mountains, wind farms, oceans, energy depots and abandoned mines, and finally an outlook on the future development trends of gravity energy storage technology.

Multi-objective energy management for modern distribution power systems considering industrial flexibility mechanisms

Increasing energy generation from variable and uncertain renewable resources leads to high demand for flexibility procurement from different energy sectors to maintain supply/demand balance in distribution power systems. Industrial energy systems are rapidly emerging as the primary contributor in providing the bulk of said flexibility to the electrical power systems due to their energy capacity, reliable infrastructure, and potential financial benefits. However, there is a lack of available energy management models that help integrate industrial flexibility into the fold and can solve for an optimal operation of the distribution power system. This paper proposes an efficient energy management model that solves a distributed multi-objective optimal power flow for a modern distribution grid, including industrial prosumers and distributed generation resources. We generate two distinct kinds of flexible industrial load profiles: one uses optimal peak shaving with an energy storage system, and the other employs process optimization in the industrial grid. The obtained results show that the proposed energy management model can solve for optimal operation of all involved participants while maintaining data privacy between them. Industrial prosumers save up to 4.85% in financial expenses and 18.6% in energy exchange with the grid. Further, the grid operator can reduce its CO2 emissions by 4.6%.

Joint coordination of optimal power management and energy storage system sizing for a full-scale marine current turbine considering microgrid integration constraint

The issues of variability and uncertainty of tidal speed result in severe challenges for standalone microgrid (as island grids for examples) operators. Indeed, to maintain the system power balance, existing classical generators which are associated with tidal power units must be able to frequently change their operating point, either up or down, to respond to the fast fluctuations of tidal power and consumption and sometimes exceed their maximal ramp capability. This in turn accelerates aging process and results in serious damage. The switching to a safer and more reliable system seems to be a promising and long-term solution. This paper proposes to associate a supercapacitor-based Energy Storage System (SC-ESS) to a tidal turbine to smooth the fast power production fluctuations. The association of this SC-ESS with the tidal turbine unit aims to meet requirements on the variation of injected tidal power in an islanded microgrid. An original smart power management strategy is proposed for the use of the ESS. Taking into account this strategy, an optimal design methodology based on simulations on the more severe encountered day cases is proposed. This methodology allows to determine a minimal sizing of the ESS to fulfil the grid requirements. The paper also proposes a complete modeling of the whole system behavior. The Energetic Macroscopic Representation (EMR) tool is used to realize the system model where the inversion-based control principle is then used to deduce the control schemes. This global methodology is applied to a test tidal turbine which is based on a real 1 MW prototype setup to the islanded grid of Ushant in France. Using real measured data, it is shown that a relatively small and low cost SCs pack is sufficient to accommodate the high tidal power fluctuations. A comparison is performed between the existing configuration where a resistor bank is used to shave the excessive power variation and the considered case where SCs pack is used. For one tidal cycle, it is shown that a reduction in energy loss of 18.2% is achieved, which presents a non-negligible gain for Ushant's Island microgrid.

Real-Time Three-Phase Dynamic Full ACPF Distribution System Model

Power flow is the backbone for power system operation and control. Power system balancing, where supply of energy has to equal demand all time, is a very important operation constraint for electric power systems. In recent years, penetration of Distributed Energy Resources (DERs) especially Renewable Energy Sources (RESs) into the distribution system has increased. RESs are known by their intermittent behavior in nature. Hence, as the number of these RESs increases, the sudden frequent change in power flow increases. Therefore, new obstacles to the operation and control of power systems arise. Power distribution system is also sparse and large system. Moreover, most traditional power flow solutions are based on iterative techniques which obviously take time. Therefore, computation time is a real problem when finding power flow solutions at distribution system especially with the unpredictability of RESs. To overcome these problems, a real-time linearized three-phase AC Power Flow (ACPF) model at distribution system is proposed. In this paper the linearized ACPF at distribution system is molded as follows. First Quasi linearized ACPF equations are developed for short period of time based on Newton’s Raphson (NR) method. Second sparse reordering algorithm techniques are used to reorder the node numbering of the power distribution system to reduce computational time. Then, simulation on IEEE 4 bus power system and IEEE 37 bus power distribution system are presented to validate the proposed model. Furthermore, Monte Carlo simulation is used to test the robustness of the proposed model.

Market-based TSO-DSO coordination for enhanced flexibility services provision

This paper proposes a framework for DSO-TSO market-based coordination in a feasible and transparent way, compatible with the European-type electricity market. The DSO participates in the balancing market as a Balance Responsible Party, by submitting price-taking offers that represent the net outcome of DSO scheduled actions at the distribution level. With this approach, the balancing market clearing results reflect the impact of scheduled actions at distribution level on system power balance. In addition, specific design aspects of the DSO market are highlighted that could align DSO and TSO market, increasing the market coordination efficiency and promoting the wider participation of distributed energy resources in both markets. The advantages of the proposed method are: (a) more accurate balancing market pricing signals while congestion management services and balancing services remain decoupled, (b) low data exchange requirements between the two Operators, (c) distributed energy resources opportunity to participate efficiently either in one or both markets, and finally (d) easy pan-European market-based coordination of TSOs-DSOs based on current balancing market development action plans.

Modeling Integrated Power and Transportation Systems: Impacts of Power-to-Gas on the Deep Decarbonization

The deployment of renewable energy sources, power-to-gas (P2G) systems, and zero-emission vehicles provide a synergistic opportunity to accelerate the decarbonization of both power and transportation system. This article investigates the prospects of implementing hydrogen P2G technology in coupling the power system and the transportation system. A novel coordinated long-term planning model of integrated power and transportation system (IPTS) at the regional scale is proposed to simulate the power system balance and travel demand balance simultaneously, while subject to a series of constraints, such as CO2 emission constraints. IPTS of Texas was investigated considering various CO2 emission cap scenarios. Results show unique decarbonization trajectories of the proposed coordinated planning model, in which IPTS prefers to decarbonizing the power sector firstly. When the power system reaches ultralow carbon intensity, the IPTS then focuses on the road transportation system decarbonization. The results show that with the P2G system, IPTS of Texas could achieve 100% CO2 emission reductions (relative 2018 emissions level) by adding a combination of approximately 143.5 GW of wind, 50 GW of solar PV, and 40 GW of P2G systems with 2.5% renewables curtailment. The integration of the P2G system can produce hydrogen by use of surplus RES generation to meet hydrogen demand of Fuel cell electric vehicles (FCEVs) and to meet multiday electricity supply imbalances.

Quantitative Assessment of Flexibility at the TSO/DSO Interface Subject to the Distribution Grid Limitations

In the last years, renewable energy sources have been changing the power system by making it more challenging to balance the generation and demand at every single point in time. The increasing penetration of distributed generation represents another trend at the distribution level that impacts the exploitation of existing distribution assets. In this context, the flexibility of distributed energy resources connected to the distribution systems may play an important role. The flexibility products are represented by variations in the scheduled/expected active and reactive power setpoints. Recently, regulatory bodies suggested many proposals and undertook actions for enabling new players, such as the distributed energy resources connected to the distribution systems, to provide both system and local services. However, currently, there are still barriers that might limit their effective involvement. Market schemes have been proposed for opening the participation of distributed energy resources in the service markets. This paper proposes an analytical quantification of how much the use of flexibility by the transmission system operator can influence the distribution system operator activities and the expected costs. The final goal is quantifying the flexibility that the transmission system operator can procure from the distribution system without a harmful impact on the distribution network operation. The paper investigates the expected interactions between the use of flexibility for power system balancing and security and the operation of distribution systems. The application of the methodology to a significant Case Study showed that even though the fit and forget approach causes a hypertrophic development of distribution systems to host distributed generation, the transmission system operator cannot obtain the required flexibility services or has to pay extra costs for bottlenecks caused by distribution system operational issues.

THE BALKANS IN A MULTIPOLAR WORLD - PERSPECTIVES AND CHALLENGES

The international relations of the 20th century were largely characterized by the balance of power, and it could be said, a balance of fear, of two opposing alliances. Precisely these two centers of power ,the USA and the USSR led to division within the system of the entire international community. However, the breakup of the USSR, the emergence of new states, the end of the Cold War also led to the end of bipolarity and the emergence of unipolar world. The only remaining hegemon the USA ,using all its available resources as well as the resources of their “followers” disrupted the system of power balance in their favor. That disruption of the power balance system was most bloodily manifested in the Balkans as part of the European continent and a kind of connection between worlds. Regardless of the large resources available, both the “ hard” and the “soft” powers, the USA could not completely bring the Balkans under their control. Changes in the international relations we live in, question the current order based on globalization and one hegemon. However, this very hegemon, using all resources selflessly, is trying to preserve its order by enabling itself and its followers to play the role of “ the master of the world” and assigning itself eternal world policeman role. Throughout the globe, questions are being raised about the value of global order and the USA’s power as the sole global power. By shifting the economic flows to the East, e.i. to the Asia-Pacific part of the world, Western hegemons are slowly becoming naked in their imperialistic interests. Re-questioning the power of the “world policeman” is reflected on those parts of the world that are at the junction of “different worlds”. One such part of the world is certainly the Balkans. Therefore, the theme and the aim of this paper is to point out the importance of the Balkans in terms of power projection of key global and regional factors of international relations at the begin- ning of the new millennium. By analyzing influences of global and regional factors of international relations, it can be stated that peoples on the Balkans already live in a multipolar world, which is characterized by great instability due to undefined zones of influence of global and regional players. Defining those areas of interest becomes an imperative for the human civilization survival.

Multi-Objective Approach for Managing Uncertain Delivery from Renewable Energy Sources within a Peer-to-Peer Energy Balancing Architecture

On the energy markets, conscious customers may exist who are not only interested in minimising the cost of energy purchase, but, simultaneously, in optimising some other quality criteria (arising from ecological concerns, or social responsibility of the energy producers). In this paper, we develop both a mathematical optimisation problem and a market framework for balancing a power system in a peer-to-peer market setup, where product differentiation can be considered directly on the market. Thus, origins of energy may be clearly identified, and product quality characteristics can be understood by various actors (including households). We derive a multi-objective (mixed-integer) linear programming optimisation problem for balancing the energy system in a peer-to-peer energy trading environment, where not only the cost but also other additional quality criteria are considered. We have identified many possible actors to be present within the proposed market setup. They include consumers, producers, brokers and flexible prosumers with storage. The approach was tested on the IEEE 30-bus standard test system, over three different scenarios, by analysing the impact of various actors/peers activities and different extensions. It has been shown that a multi-objective energy balancing scheme may be developed through crafted optimisation problem and that each type of studied peers may bring some added value to the power system balancing.