The electricity generation-transmission-utilization system was one of the first examples of a modern integrated energy system. The subsequent rapid growth of such systems is well-known. This approach was overly simplistic in that it promoted the conversion of almost all primary sources of energy into electricity and resulted in the spread of transmission lines and the use of electrical end-use appliances and equipment to meet energy needs. It is now recognized that such an approach suffers serious limitations. The principles of integrated systems based on a combination of energy sources which provide a variety of types of energy appropriate to different tasks are discussed. Mainly renewable, decentralized and locally-available sources are involved in such systems.

Integrated energy systems

With economic development in the world and growing energy demand, the concept of sustainable energy has received more attention from energy planners in different energy sectors. To achieve sustainable energy development (SED), appropriate utilization of all types of sustainable energy resources is vital. One further requirement for this is the integration of various energy systems in the framework of a multi-energy system where all energy system elements have the possibility of synergy with others for minimizing losses and maximizing the utilization of any availabilities. Further requirements for such a highly yet wisely integrated energy system (IES) have recently been specified in the context of smart energy systems (SESs). Smart energy hub (SEH) is introduced as a novel concept that provides a distinguished framework to model SESs. The main challenge for the modeling of SEH is finding the optimal design/sizing and operation strategy of the system components based on the uncertainty of renewable sources, demands, energy market spot prices, etc. Uncertainty modeling assists in reaching a realistic optimal approach in the decision-making process and thus is a promising line of future research in the modeling of SEH. The main aim of this work is to classify and evaluate the existing methods to employ uncertainty in the design, operation, and planning of SEH to reach a better understanding of future challenges in this way. 

A comprehensive review on optimization challenges of smart energy hubs under uncertainty factors

A microgrid scenario that consists of electric vehicle (EV) station, combined heat and power (CHP) co-generation, main power grid, and external natural gas station, as well as thermal energy storage water tank is considered in this paper. By jointly considering the uncertainty of real-time electricity price, electricity and heat demands and EVs’ behaviours, the EVs’ batteries are used as energy storage adjusters to reduce the time-averaged operation cost, which includes energy acquiring cost from main power grid, the natural gas cost for CHP generation and heat only generation. We propose a real-time energy management algorithm for EV based microgrid by adopting Lyapunov stochastic optimization technique which optimizes the microgrid average cost without knowing future price, demands and other system information. Furthermore, our approach can accommodate a wide spectrum of characteristics of EVs, including the independent charging/discharging action, dynamic charging energy limits, and lifetime-guaranteed battery. Lastly, extensive simulations are provided to demonstrate that our proposed algorithm can outperform the other three alternatives.

Real-Time Energy Management for Microgrid With EV Station and CHP Generation

The demographic growth and the irreversible decline of fossil fuel deposits argue for alternative resources to meet energy demand. The main challenge is to make renewable energy sources (RES) and hydrogen carriers work synergistically to minimise waste and increase sustainability. Hybrid renewable energy systems (HRES) tackle this task by integrating RES and other resources to provide energy. Recently, Power-to-X (P2X) has been gaining attention for its versatility in converting hydrogen into different energy carriers. This review provides a comprehensive overview of the HRES literature and the current state of the art, highlighting key features, analysis, and methods. Future research trends are discussed, emphasising the need to integrate other energy carriers, including hydrogen. A survey of the Power-to-X possible uses in HRESs is carried out, describing which Power-to-X technologies belong to HRES state-of-the-art. Power-to-X paths not yet explored are discussed, remarking the benefit and potential uses as a means to increase the reliability of the energy system of each HRES Power-to-X technology integration, highlighting the unexplored paths. In addition, future developments and gaps in the current state of the art according to HRES with Power-to-X are highlighted. Finally, recommendations on hybrid renewable energy systems, including Power-to-X, are highlighted by outlining future research areas. • HRESs scientific literature and current state-of-the-art. • HRES future research trends. • HRES with P2X state-of-the-art. • Current gaps and trends on P2X in HRES integration. 

The role of power-to-X in hybrid renewable energy systems: A comprehensive review

As the types of loads have been diversified and demand has increased, conventional distribution transformers are difficult to maintain the constant voltage against voltage drop along with distance, grid voltage swell/sag, and various loads. Also, it is hard to control the power flow when connecting renewable energy sources. Active hybrid solid state transformer (AHSST) is application to keep the voltage and power quality. AHSST is a system that combines conventional distribution transformer and converter. Accordingly, it can be applied directly to distribution infrastructure and it has both the advantages of solid state transformer (SST) and conventional transformer. AHSST is capable of active voltage and current control and power factor control. It has a simpler structure than SST and it can perform the same performance with the lower rating converter. This paper presents two stage AHSST system based on multi-level converter. The converter is composed of the back-to-back converter using silicon carbide (SiC) metal-oxide semiconductor field effect transistor (MOSFET). Proposed system has a wider voltage and power flow control range, lower filter size, and simpler control sequence than existing AHSST systems. The performance of the proposed system was verified by prototype system experiments.

https://www.mdpi.com/1996-1073/12/1/66/pdf

Active Hybrid Solid State Transformer Based on Multi-Level Converter Using SiC MOSFET

The energy crisis and increasing concerns about the environment in modern society have fostered the development of the integrated energy system (IES) in smart grid. The energy hub (EH) is a minimum construction of the IES. The chief purpose of this paper is to propose a Lyapunov optimization-based energy management strategy for the energy hub with an energy router. First, this paper describes a configuration of the EH with an energy router and sets the basic operating principles of the energy router. Second, a method is proposed to analyze the energy balance equations of the EH. Furthermore, the problem of energy management is formulated considering the constraints of energy balance equations, energy storage, flexible loads, and other constraints of operation. Finally, energy storage and flexible electric loads are modeled as stochastic processes, and three virtual queues are constructed to relax these constraints. The Lyapunov drift-plus-penalty function is applied to formulate a relaxed form of the energy management problem. Case studies of a single EH and two-connected EHs are performed to test the effectiveness of the proposed strategy, and the results are compared with a greedy algorithm.

A Lyapunov Optimization-Based Energy Management Strategy for Energy Hub With Energy Router

Solid State Power electronic transformer (PET) is an emerging new type of power converter in recent years. It has not only the basic functions of power transformation and isolation, but also the extra functions of power quality control. This paper presents the key control strategies of solid state PET for electrical distribution system application, especially under voltage disturbance conditions. Several critical grid voltage disturbances are generated by a disturbance voltage source based on a three phase PWM inverter. And the solid state PET prototype is tested and passed voltage disturbance ride through function. The experimental results verify the PET power quality control abilities.

Control strategy of solid state power electronic transformer under voltage disturbance conditions

Power electronic transformer (PET) is an emerging new type of power converter in recent years. It has not only the basic functions of power transformation and isolation, but also the extra functions of power quality control. A novel power electronics transformer for distribution system named flexible power distribution unit is proposed in this paper, and the energy exchange mechanism between the network and load is revealed. Finally, a 100kW 600Vac/220Vac/110Vdc medium frequency isolated prototype is developed and demonstrated in laboratory. The experimental results show that the proposed structure and control strategy are feasible.

Flexible power distribution unit — A novel power electronic transformer development and demonstration for distribution system

With the continuous development of power electronic technology, the distributed renewable energy generation connected to the distribution network is increasing, and the flexible load such as electric vehicles is also increasing. As a multi-port power electronic equipment, power router (PR) can accept power electronic power supply and load, and be used to build a flexible power distribution system with high power electronic source and load penetration. First, based on VSC power flow calculation steady-state model, this paper proposes a steady-state model of PR; Second, according to the type of bus at both ends of the line and the type of line, the line structure in the AC/DC hybrid power distribution system based on PRs is divided into 8 categories. Power balance equations, supplementary nodes and equations at node i under various structures are analyzed, and based on the classification of the line structure, the node equations of PR nodes and non-PR nodes are analyzed. Finally, the operating constraints of PR and VSC are introduced, with the goal of minimizing the total power generation cost of the system, and the optimal power flow calculation model for the AC-DC hybrid distribution network based on PRs is constructed. Some nodes are replaced with PR of IEEE14 system as a test system for test verification.

Optimal Power Flow Calculation Method for AC/DC Hybrid Distribution Network Based on Power Router

The paper proposes a Fully Flexible Power Transmission & Distribution System (FPTDS) for the next generation power grid, the FPTDS structure used the brand new flexible electric equipment: Energy-Router, Energy-Switcher and Energy-Hub. And then from the Cyber Physical Systems(CPS), the paper gives a Power-CPS (P-CPS) interconnect reference model, and thereby, focuses on designing the fully flexible next generation equipment for Fully Flexible Power Distribution System (FPDS): Energy-Switcher architecture in detail, and researches the next generation distribution grid patterns with Energy-Switchers, presents the grid patterns for all kinds of practical application scenes, finally simulates the Energy-Switcher AC & DC power supply pattern under computer condition, the simulation results demonstrate the systems are feasible and valid.

Qing Duan

Papers

A Lyapunov Optimization-Based Energy Management Strategy for Energy Hub With Energy Router

Control strategy of solid state power electronic transformer under voltage disturbance conditions

Flexible power distribution unit — A novel power electronic transformer development and demonstration for distribution system

Optimal Power Flow Calculation Method for AC/DC Hybrid Distribution Network Based on Power Router

Fully Flexible Power Distribution System for the next generation distribution grid