Danny Morton

As the amount of decentralized generation is continuously increasing the controlling and maintaining of grid stability becomes more complex. This is caused by a change of production capacities from the high voltage area into the distribution network. In order to ensure stability of future smart grids a new 3-Level 4-Leg inverter as a part of a power electronic regulator is introduced. This topology is compared to a 3-Leg 4-Wire (3L4W) operation mode with focus on harmonic injection method. The difference between THD and efficiency is evaluated. As a result the 4L4W operation with harmonic injection can increase efficiency in most operation points. The THD is reduced in all test cases compared to the 3L4W operation. Additionally the overall flexibility is increased by an increased DC-Link voltage operation range.

The share of decentralized power generation is increasing, which causes general changes and challenges for the conventional power system. Hence, distribution system operators (DSO) need new technologies to ensure the stability of the entire electrical power system. As a feasible solution for structuring power networks, the Clustering Power System Approach (CPSA) has been introduced, providing an innovative and reasonable way of decentralisation for future-oriented power systems. With this approach, based on the Cluster Fractal Model, the stabilization of the power systems can be realized in a bottom-up direction from decentralized generation units in distribution grids to the upstream transmission grids. However, to accomplish smart operations in such decentralized and intelligent electricity networks an appropriate strategy for the interoperation between cluster areas is needed. To realize this concept this paper proposes a real-time orchestration system as a core functionality of Smart Grid Cluster Controllers (SGCC) to run the distribution control and management functions. Hereby, the characteristic needs of such functions inside or between clusters can be taken into account. Structural or hierarchical dependencies of the functions can also be considered. Lastly, the SGCC is implemented on different hardware platforms.

Due to the trend of decentralized generation (DG) residing in low voltage distribution network, more inverters are connected to the grid in three-phase four-wire systems under asymmetrical condition. This paper presents an algorithm to balance DC-link capacitor voltages and minimize switching loss of three-level four-leg inverters which is suitable for asymmetrical condition. The algorithm is based on three-dimension space vector modulation (3D-SVM) in natural coordinates. The algorithm balances DC-link capacitor voltages by the selection of redundant standard vectors. Switching sequences are selected to minimize switching loss. Simulation results show that the method is able to balance DC-link capacitor voltages and reduce middle point voltage ripple.

The ongoing trend to sustainable energy supply based on renewable energies is coming along with new challenges in network control. Especially in the low voltage distribution networks, new control structures are required, since they have been considered as a passive system in regards of network control. As a feasible solution for structuring power networks the Clustering Power System Approach (CPSA) has been introduced, in order to allow adequate control architecture. This paper focuses on a new network control application for clustered power systems, being suitable for directed manipulation of power flows in low voltage networks. The core component is a smart inverter system in combination with a battery storage, which will be placed into the connection lines between interacting clusters. The network control application is introduced in this paper and initial results of the capabilities of the smart inverter system, especially at asymmetrical grid conditions, are presented.

The power generation in power systems nowadays changes from the traditional centralized to contemporary decentralized structure that disperses widely in distribution grids. It results in power generation from the bottom level, i.e. in local area, which is contrary to the traditional centralized power generation that provides power flow in top-to-down direction. A way to handle the impact of power generation in the local area is introduced by using clustering power systems approach (CPSA). The concept of this approach is to enable stabilization of power systems in bottom-up direction from generation units in the distribution grids to the upstream transmission grids. To realize this concept and make it consistent with the emerging smart grid technology, a massive data must be taken into account. Hence, the data management infrastructure for the CPSA is proposed. It is based on the database system and designed for online data management. In addition, the web-based user interface is developed to manipulate data efficiently and achieve concurrently the flexibility in power systems control. Eventually, this paper demonstrates an experiment, a pragmatic real-time simulation of the integration of the CPSA and the proposed data management infrastructure. The focus of the experiment is to prove the application of the data management, and the realization of the cluster concept.

With the rapid development of information technologies, knowledge management systems are facing the problem of how to manage the massive volume of data and make an efficient usage for the data. In this paper, we analyzed the current challenge of knowledge management system and proposed a multi-indexed graph based knowledge storage system to avoid the data duplication and optimized for parallel processing.

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.

Distributed generators (DGs) in Smart Grids should actively participate in the grid control of active power (P), reactive power (Q), frequency (f), and voltage (U) through their grid interfaces, namely inverters. As these DGs are joining the existing conventional power systems and for smooth transition towards Smart Grids, these DGs must follow the existing grid control, which is used by the UCTE. However, standard communication between utilities controllers and inverters is needed for the grid control and for the exchange of power. Therefore, a strategy is proposed depending on the UCTE grid control by clustering the secondary control using international communication standards. De facto, proprietary and standard protocols are investigated for this purpose. Then, logical nodes needed for primary and secondary grid control are adopted from the IEC 61850 that ensures interoperability. For communication, standard legacy SCADA protocols IEEE P1815 (DNP3) and IEC 60870-5-104 are proposed, which introduce standard communication mechanism.

Distributed Energy Resources (DERs) are rapidly penetrating in power systems including their accompanying software and hardware (SW/HW) systems that are also distributed and related to different manufacturers and owners. Information integration and interoperability are two problems in distributed systems. This paper presents a comparison between the available integration middleware and standards for inter-application interoperability of distributed SW/HW systems accompanying DERs such as Common Object Request Broker Architecture (CORBA), Web Services, multiagent systems (MASs), and recently IEC 61850. In addition, the paper shows the possibility of mapping the information objects of IEC 61850 to the data objects of legacy SCADA protocols for physical control and integration of DERs interfaces, namely inverters, into the future Smart Grid over IP-based networks, to achieve inter-device and device-to-application interoperability. Moreover, billing functionality can be added to the inverter to count for injected power into the Smart Grid, and hence the inverter has business-related functions.

Distributed energy resources such as photovoltaic, fuel cells and micro turbines are emerging into power supply systems. Strategies of grid control integration, to emerge these sources are still lagging behind. These sources require interfacing units to provide the necessary crossing point to the grid. The cores of these interfacing units are power electronics technologies such as inverters (multifunctional grid front-ends) since they can provide not only their principle interfacing function, but also various utility functions. This paper presents the possibility of adapting the isochronous control methodology, used by synchronous generators in conventional power systems, to provide load sharing and control for inverters as front-end.