Demand and Storage Management in a Prosumer Nanogrid Based on Energy Forecasting

Energy efficiency and consumers' role in the energy system are among the strategic research topics in power systems these days. Smart grids (SG) and, specifically, microgrids, are key tools for these purposes. This paper presents a three-stage strategy for energy management in a prosumer nanogrid. Firstly, energy monitoring is performed and time-space compression is applied as a tool for forecasting energy resources and power quality (PQ) indices; secondly, demand is managed, taking advantage of smart appliances (SA) to reduce the electricity bill; finally, energy storage systems (ESS) are also managed to better match the forecasted generation of each prosumer. Results show how these strategies can be coordinated to contribute to energy management in the prosumer nanogrid. A simulation test is included, which proves how effectively the prosumers' power converters track the power setpoints obtained from the proposed strategy.Spanish Agencia Estatal de Investigacion ; Fondo Europeo de Desarrollo Regional

Control and Stability of Residential Microgrid with Grid-Forming Prosumers

The rise of the prosumers (producers-consumers), residential customers equipped with behind-the-meter distributed energy resources (DER), such as battery storage and rooftop solar PV, offers an opportunity to use prosumer-owned DER innovatively. The thesis rests on the premise that prosumers equipped with grid-forming inverters can not only provide inertia to improve the frequency performance of the bulk grid but also support islanded operation of residential microgrids (low-voltage distribution feeder operated in an islanded mode), which can improve distribution grids’ resilience and reliability without purposely designing low-voltage (LV) distribution feeders as microgrids. Today, grid-following control is predominantly used to control prosumer DER, by which the prosumers behave as controlled current sources. These grid-following prosumers deliver active and reactive power by staying synchronized with the existing grid. However, they cannot operate if disconnected from the main grid due to the lack of voltage reference. This gives rise to the increasing interest in the use of grid-forming power converters, by which the prosumers behave as voltage sources. Grid-forming converters regulate their output voltage according to the reference of their own and exhibit load sharing with other prosumers even in islanded operation. Making use of grid-forming prosumers opens up opportunities to improve distribution grids’ resilience and enhance the genuine inertia of highly renewable-penetrated power systems. Firstly, electricity networks in many regional communities are prone to frequent power outages. Instead of purposely designing the community as a microgrid with dedicated grid-forming equipment, the LV feeder can be turned into a residential microgrid with multiple paralleled grid-forming prosumers. In this case, the LV feeder can operate in both grid-connected and islanded modes. Secondly, gridforming prosumers in the residential microgrid behave as voltage sources that respond naturally to the varying loads in the system. This is much like synchronous machines extracting kinetic energy from rotating masses. “Genuine” system inertia is thus enhanced, which is fundamentally different from the “emulated” inertia by fast frequency response (FFR) from grid-following converters. Against this backdrop, this thesis mainly focuses on two aspects. The first is the small-signal stability of such residential microgrids. In particular, the impact of the increasing number of grid-forming prosumers is studied based on the linearised model. The impact of the various dynamic response of primary sources is also investigated. The second is the control of the grid-forming prosumers aiming to provide sufficient inertia for the system. The control is focused on both the inverters and the DC-stage converters. Specifically, the thesis proposes an advanced controller for the DC-stage converters based on active disturbance rejection control (ADRC), which observes and rejects the “total disturbance” of the system, thereby enhancing the inertial response provided by prosumer DER. In addition, to make better use of the energy from prosumer-owned DER, an adaptive droop controller based on a piecewise power function is proposed, which ensures that residential ESS provide little power in the steady state while supplying sufficient power to cater for the demand variation during the transient state. Proposed strategies are verified by time-domain simulations

Analysis of the economic feasibility and reduction of a building’s energy consumption and emissions when integrating hybrid solar thermal/PV/micro-CHP systems

The aim of this paper is to assess the performance of several designs of hybrid systems composed of solar thermal collectors, photovoltaic panels and natural gas internal combustion engines. The software TRNSYS 17 has been used to perform all the calculations and data processing, as well as an optimisation of the tank volumes through an add-in coupled with the GENOPT® software. The study is carried out by analysing the behaviour of the designed systems and the conventional case in five different locations of Spain with diverse climatic characteristics, evaluating the same building in all cases. Regulators, manufacturers and energy service engineers are the most interested in these results. Two major contributions in this paper are the calculations of primary energy consumption and emissions and the inclusion of a Life Cycle Cost analysis. A table which shows the order of preference regarding those criteria for each considered case study is also included. This was fulfilled in the interest of comparing between the different configurations and climatic zones so as to obtain conclusions on each of them. The study also illustrates a sensibility analysis regarding energy prices. Finally, the exhaustive literature review, the novel electricity consumption profile of the building and the illustration of the influence of the cogeneration engine working hours are also valuable outputs of this paper, developed in order to address the knowledge gap and the ongoing challenges in the field of distributed generation

Modeling a Grid-Connected PV/Battery Microgrid System with MPPT Controller

This paper focuses on performance analyzing and dynamic modeling of the current grid-tied fixed array 6.84kW solar photovoltaic system located at Florida Atlantic University (FAU). A battery energy storage system is designed and applied to improve the systems stability and reliability. An overview of the entire system and its PV module are presented. In sequel, the corresponding I-V and P-V curves are obtained using MATLAB-Simulink package. Actual data was collected and utilized for the modeling and simulation of the system. In addition, a grid- connected PV/Battery system with Maximum Power Point Tracking (MPPT) controller is modeled to analyze the system performance that has been evaluated under two different test conditions: (1) PV power production is higher than the load demand (2) PV generated power is less than required load. A battery system has also been sized to provide smoothing services to this array. The simulation results show the effective of the proposed method. This system can be implemented in developing countries with similar weather conditions to Florida.Comment: 6 pages, 14 figures, PVSC 201

Photovoltaic Sub-module Integrated Converter Analysis

abstract: With the rapid expansion of the photovoltaic industry over the last decade, there has been a huge demand in the PV installations in the residential sector. This thesis focuses on the analysis and implementation of a dc-dc boost converter at photovoltaic sub-module level. The thesis also analyses the various topologies like switched capacitors and extended duty ratio which can be practically implemented in the photovoltaic panels. The results obtained in this work have concentrated on the use of novel strategies to substitute the use of central dc-dc converter used in PV module string connection. The implementation of distributed MPPT at the PV sub-module level is also an integral part of this thesis. Using extensive PLECS simulations, this thesis came to the conclusion that with the design of a proper compensation at the dc interconnection of a series or parallel PV Module Integrated Converter string, the central dc-dc converter can be substituted. The dc-ac interconnection voltage remains regulated at all irradiance level even without a dc-dc central converter at the string end. The foundation work for the hardware implementation has also been carried out. Design of parameters for future hardware implementation has also been presented in detail in this thesis.Dissertation/ThesisM.S. Electrical Engineering 201

Application of heat pumps and thermal storage systems for improved control and performance of microgrids

The high penetration of renewable energy sources (RES), in particular, the rooftop photovoltaic (PV) systems in power systems, causes rapid ramps in power generation to supply load during peak-load periods. Residential and commercial buildings have considerable potential for providing load exibility by exploiting energy-e_cient devices like ground source heat pump (GSHP). The proper integration of PV systems with the GSHP could reduce power demand from demand-side. This research provides a practical attempt to integrate PV systems and GSHPs e_ectively into buildings and the grid. The multi-directional approach in this work requires an optimal control strategy to reduce energy cost and provide an opportunity for power trade-o_ or feed-in in the electricity market. In this study, some optimal control models are developed to overcome both the operational and technical constraints of demand-side management (DSM) and for optimum integration of RES. This research focuses on the development of an optimal real-time thermal energy management system for smart homes to respond to DR for peak-load shifting. The intention is to manage the operation of a GSHP to produce the desired amount of thermal energy by controlling the volume and temperature of the stored water in the thermal energy storage (TES) while optimising the operation of the heat distributors to control indoor temperature. This thesis proposes a new framework for optimal sizing design and real-time operation of energy storage systems in a residential building equipped with a PV system, heat pump (HP), and thermal and electrical energy storage systems. The results of this research demonstrate to rooftop PV system owners that investment in combined TSS and battery can be more profitable as this system can minimise life cycle costs. This thesis also presents an analysis of the potential impact of residential HP systems into reserve capacity market. This research presents a business aggregate model for controlling residential HPs (RHPs) of a group of houses that energy aggregators can utilise to earn capacity credits. A control strategy is proposed based on a dynamic aggregate RHPs coupled with TES model and predicting trading intervals capacity requirements through forecasting demand and non-scheduled generation. RHPs coupled with TES are optimised to provide DSM reserve capacity. A rebound effect reduction method is proposed that reduces the peak rebound RHPs power

Hybrid model predictive control of a residential HVAC system with PVT energy generation and PCM thermal storage

This paper describes an experimental investigation into the performance of a Hybrid Model Predictive Control (HMPC) system implemented to control a novel solar-assisted HVAC system servicing the Team UOW Solar Decathlon house, the overall winner of the Solar Decathlon China 2013 competition. This HVAC system consists of an air-based photovoltaic thermal (PVT) collector and a phase change material (PCM) thermal store integrated with a conventional ducted reverse-cycle heat pump system. The system was designed for operation during both winter and summer, using daytime solar radiation and night sky radiative cooling to increase the energy efficiency of the air-conditioning system. The PVT collector can exchange heat with the PCM thermal storage unit, and the stored heat can be used to condition the space or precondition the air entering the air handling unit (AHU). The HMPC controller includes two levels of control, where the high-level controller has a 24-hour prediction horizon and a 1-hour control step is used to select the operating mode of the HVAC system. Low-level controllers for each HVAC operational mode have a 1-hour prediction horizon and a 5-minute control step, and are used to track the trajectory defined by the high-level controller and to optimize the operating mode selected. The results from this preliminary experimental work have demonstrated the value of the HMPC approach in optimally controlling the solar-assisted HVAC system in the Solar Decathlon house. Results show that the HMPC controller successfully selected the appropriate operating mode to achieve multiple objectives, including: maintenance of indoor comfort conditions within a defined, and potentially variable, thermal comfort band; and optimization of the overall energy efficiency of the system using all available on-site energy resources