Showing papers by "Indrek Roasto published in 2018"

Multiport Interface Converter with an Energy Storage for Nanogrids

Abstract: Nanogrid is a small-scale microgrid that consists of loads, sources and storages interfaced with power electronic converters. Conventionally, the droop control provides power sharing. To establish autonomous operation with stable voltage and reliable power quality, an energy management system (EMS) in the form of a bidirectional multiport converter with energy storage at the PCC is used. Unlike typical approach, this paper proposes an EMS concept for nanogrids based on a single grid-forming voltage source. This allows using a simple voltage control algorithm instead of the droop control; in addition, it is compatible with all conventional power electronic interfaces. The EMS concept, its operation modes and control strategies are described. Some case studies are presented and analyzed by computer simulations.

Development of Experimental Load Management System for Nearly Zero-Energy Building

Abstract: Over two third of total electricity produced are consumed by residential and commercial buildings. According to this the nearly zero-energy building (NZEB) with local renewable power sources will play important role to reduce greenhouse gases. Local and intermittent renewable power generation is challenge for power quality and supply reliability of NZEB. It means higher demand for an Energy Management System (EMS) to provide power quality and balance between load and generation. This paper gives a brief overview of EMS for residential buildings. To test an EMS, the behavior of NZEB must be simulated in the laboratory. For this purpose, an experimental system was developed which includes variable load and its control as a part of EMS. Two load simulation methods for load management were studied and experimentally verified.

Bidirectional Operation of the Power Electronic Interface for Nearly-Zero Energy Buildings

Abstract: Nearly-zero energy buildings (NZEB) are buildings with extremely efficient energy usage and local energy generation capability. By the definition, the annual net energy consumption of NZEB should be zero, which can be achieved via a flexible energy management system (EMS). This paper proposes an EMS based on a bidirectional power electronic interface (PEI). The proposed PEI can have a variety of functions at the PCC, e.g., ancillary services, load DSM, on/off-grid operation mode, power quality control. As a result, the NZEB transforms into a hierarchically controlled nanogrid, which forms a small independent building block of the future microgrid. Synchronous and asynchronous operations of the NZEB were studied and the bidirectional energy flow control is demonstrated. The functionality and control strategies of the proposed PEI were verified by the computer simulations.

Control of Bidirectional Grid-Forming Inverter for Nearly Zero Energy Buildings

Abstract: A conventional nearly zero energy building (NZEB) is a grid connected system that cannot operate off-grid. By adding a special power electronic interface (PEI) to the point of common coupling, the conventional NZEB could be transformed into a hybrid nanogrid with a wider variety of functions, incl. off-grid operation and bidirectional energy flow control. However, most of the sources in the NZEB are grid followers and require a single grid-forming unit. Thus, typical decentralized control methods (e.g. droop control, virtual generator) cannot be implemented in such systems. This paper analyzes the bidirectional operation of the grid-forming inverter for the NZEB. The main focus is on the light or no load operation that corresponds to a mode when the PEI is naturally unable to control the voltage inside the building. Four control methods are proposed, analyzed and compared. The best method was determined and verified by the help of computer simulations.