D. Morton

Challenges in integrating distributed Energy storage systems into future smart grid

Distributed energy storage systems in combination with advanced power electronics have a great technical role to play and will have a huge impact on future electrical supply systems and lead to many financial benefits. So far, when Energy storage systems (ESSs) are integrated into conventional electric grids, special designed topologies and/or control for almost each particular case is required. This means costly design and debugging time of each individual component/control system every time the utility decides to add an energy storage system. However, our present and future power network situation requires extra flexibility in the integration more than ever. Mainly for small and medium storage systems in both (customers and suppliers) side as the storage moves from central generation to distributed one (including intelligent control and advanced power electronics conversion systems). Nevertheless, storage devices, standardized architectures and techniques for distributed intelligence and smart power systems as well as planning tools and models to aid the integration of energy storage systems are still lagging behind.

Control Strategy for Three-/Four-Wire-Inverter-Based Distributed Generation

Future power distribution requires advanced expandability and flexibility in the integration of distributed energy resources which normally require interfacing units to provide the necessary crossing point to the grid. The core of these interfacing units is power-electronics grid front end, namely, inverters. The inverter is the primary interface that provides not only their principal interfacing control function but also various utility functions. This paper presents the flexible control methodology of inverters as grid front end using an isochronous control function which is used by synchronous generators in conventional power systems to provide load sharing and control.

An Online Control Strategy for DC Coupled Hybrid Power Systems

This paper describes how different power sources of a hybrid power system may be connected together through a DC bus and then to a grid through a main inverter in such a way that a decoupling between the state variables of the power sources and the state variables of the grid is achieved. A layout showing such a structure will be presented, and an online control strategy for such a layout will be developed to show that it is modular, expandable, and easily controllable. The transmission behaviour of such a structure under different load and meteorological conditions will be investigated by applying the developed control strategy to a developed simulation model of the structure. Afterwards the results of a simulation case study will be introduced and discussed.

Supervisory control and energy management of an inverter-based modular smart grid

A key element at the grid side of future smart power systems is the inverter. This paper introduces a robust hierarchical control strategy for realistic distributed power system with power electronics inverters as front-end. The proposed control architecture maintains the three phase voltages and frequency in the grid within limits and provides power sharing between the units according to their rating and user settings. The proposed system philosophy is totally flexible in that the developed control and management functions do not depend on the types, sizes, or numbers of the used energy conversion systems. The proposed system philosophy is also compatible with conventional grids. Therefore, the potential application areas of the proposed philosophy cover not only remote and rural electrification where stand-alone systems are required, but also distributed generation where interconnection to conventional grids is preferred.

A general architecture for modular smart inverters

At present, power supply systems all over the world are facing challenging situations where they have to be extremely flexible, reliable and expandable. Existing grids have to be modified due to the growing proportion of distributed and renewable energy sources. Power electronic inverters are the key components to couple different energy conversion systems and to manage their operation. To fulfill the changing demands of the growing smart grids, new concepts for inverter design are needed. In this paper an innovative concept for future oriented power systems - the modular inverter design - is detailed. The introduced concept offers the required flexibility and adaptability for modern power supply systems. Modularity supports faster customization while all inverter components still can be manufactured in mass production. Using up-to-date technologies and the introduced advanced inverter concept, modular, flexible, reliable and cost-effective power supply structures can be built up with less effort in design and maintenance. Furthermore, existing systems can be changed, rescaled and expanded.

Multi-level hierarchical control strategy for smart grid using clustering concept

Recently, the distributed generation (DG) based on renewable energy sources (RESs) is quickly penetrating and integrating into the power systems. Moreover, a large number of intelligent infrastructures are installed into the power systems in order to establish a future power system, called smart grid. However, the increased grid integration of these sources leads to significant structural changes for grid automation and control. Nevertheless, there are still no sufficient available strategies for active grid integration of the distributed generation units and their participation in grid control. A new flexible cluster control concept of the power system is required to ensure stable and secure operation. This paper introduces a multi-level hierarchical control strategy for efficient grid control for the distributed generation units. This proposed control strategy provides availability and reliability for future power systems.

Grid-Forming Three-Phase Inverters for Unbalanced Loads in Hybrid Power Systems

A key component at the grid side of a PV/hybrid power system (HPS) is the inverter. One of the desirable characteristics of inverters in three-phase systems is the ability to feed unbalanced loads with voltage and frequency nominal values. This paper introduces innovative three-phase inverter topologies in combination with an advanced control function able to feed isolated grids with unbalanced loads. Therefore, standardized advanced control functions based on symmetrical components will be used. In this paper a four leg power electronics topology in combination with the developed control algorithm is used to perform a three-phase symmetrical voltage source with a controlled neutral point. The advantages of the developed control function will be introduced and discussed by a simulation study

Recycling conventional control strategy and hierarchy for future DG control

The penetration of distributed generation is increasing to assist main power plants worldwide. An efficient strategy of grid control integration, to interconnect the DG systems to conventional power systems, is required to improve the power quality and reliability (PQR). The main task of the interconnected system is to control and maintain frequency and voltage of the power system in an acceptable range. This task has been currently operated using synchronous generators in many interconnected power systems. The power dispatch, frequency control and voltage control, power exchange and power optimization are managed in conventional power supply systems. Therefore, the control strategy of the conventional power systems can be adapted to DG technologies through their interface unit to the grid, namely the inverter. The inverter is the primary interface unit between the energy source and the grid. This paper proposes an adaptable and flexible control strategy for future DG systems in interconnected grids based on inverters as front-end. The proposed control strategy can be a basic strategy to implement the DG system into existing conventional power systems.

A novel space vector modulation control strategy for three-leg four-wire voltage source inverters

One of the desirable characteristics of inverters in three-phase systems is the ability to feed unbalanced loads with voltage and frequency nominal values. This paper introduces an innovative control method in combination with a three dimensional space vector modulation (3D-SVM) control strategy. It is able to feed grids with unbalanced loads while reducing the switching frequency losses. The results from this study show that the developed control scheme in combination with three-leg four-wire inverters can carry out the grid feeding requirements under extreme unbalanced load conditions efficiently.

Cluster fractal model — A flexible network model for future power systems

A grid integration ratio of decentralized energy conversion systems (ECSs) in combination with renewable energy sources (RESs) has been recently increased in order to build up sustainable electrical power supply systems. Due to those changes, it can be predicted that the decentralized systems will change the conventional top-down power flow process to be the bidirectional process. Then the power flow can be reversed from distribution level to transmission level. To handle those significant changes, the cluster power systems approach has been developed and proposed to be the future of power systems. The strategy is to cluster the power systems in several areas, called cluster area. And the smart grid cluster controller (SGCC) unit is announced as a smart controller to operate the cluster based on each area. Presently, SGCC control functions have been published and proved that the SGCC can give an opportunity to establish control function down to local level. On the other hand, the cluster systems structure must be thoroughly considered to complete the clustering approach. Therefore, the cluster fractal model is proposed in this paper as a flexible and an adaptive model to organize the cluster network structure. According to fractal model, the internal structure of each cluster can be described by using the same network model. And the linkage to another cluster is allocated by the hierarchical system; superordinate, ordinate and sub-ordinate level. To this point of view, the fractal model has the flexibility to model the network of clustering power systems and ensures the bottom-up approach strategy. With the fractal model of cluster network structure and the SGCC, the cluster power systems philosophy will finally simplify the way for future smart gird.