Feasibility study, dynamic modeling, optimization, and implementation of low-cost communication systems for remote DC microgrids in Nigeria

Ndukwe, Cherechi Izuchukwu (2022) Feasibility study, dynamic modeling, optimization, and implementation of low-cost communication systems for remote DC microgrids in Nigeria. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Renewable energy-based microgrids are important contributors toward meeting the growing global energy needs in remote communities. In designing such microgrids, Supervisory Control and Data Acquisition (SCADA) systems and their communication methods are very crucial towards achieving reliable parameter control for optimal performance. A hierarchical microgrid is, in general, divided into three control levels: primary, secondary, and tertiary. Research over the years showed that control of the primary control level could be achieved without communication systems using control schemes such as droop control and other modified communication-less control schemes. On the other hand, the secondary and tertiary control levels are mostly achieved using communication systems for data transfer between the controllers. This, therefore, entails that a reliable and robust communication system that meets the requirements of each control level supported by a SCADA system is essential in achieving the optimum performance of a remote microgrid. The first part of this thesis presents a techno-economic sizing of AC and DC microgrids for a remote rural community in West Africa. In the first research, an AC microgrid was sized in Homer to meet the energy requirements of the community. Being that the community was a peasant community, it had low amount of electrical equipment and as such had lower energy needs. Further, due to the low energy requirement, a DC microgrid was sized for the same community after analysing the community. The sized DC microgrid also met the energy needs at a low financial cost. The result of the sizing showed that when the traditional AC equipment was switched to DC, the community energy needs were reduced and well met with a DC microgrid. Finally in this part of the research the sized DC microgrid was simulated in MATLAB and the control schemes were employed to observed the dynamic performance of the DC microgrid. The second part proposes a LoRa-based wireless communication system for data transfer in DC microgrids at the secondary control level. The proposed method allows the connection of multiple sensors to the LoRa transceivers and enables the data collection from various units within a microgrid. Chapter 4 and Chapter 6 focused on communications at the secondary communication level of the microgrid between local controllers of each distributed generation (DG) unit and the microgrid central controller due to the possibility of using low-bandwidth communication systems. The data transfer process and management scheme for priority data transfer in a microgrid are analyzed. Furthermore, the data transmisson time, and control action transmission between the central microgrid and the local microgrids are assessed. The third part presents an open-source, low-cost Internet of Things (IoT) based SCADA system that uses the Chirpstack IoT platform to achieve SCADA functions. The proposed system is an improvement to the existing IoT solutions by eliminating cloud-based IoT platforms and introducing an all in one system where the IoT gateway and platform are installed on one machine. This solution increases systems reliability by reducing the number of components and at the same time, reducing the costs involved. This solution eliminates the requirement for the internet for data transfer. The proposed system prototype consists of voltage and current sensors, Arduino Uno microcontroller, and Raspberry Pi. The sensors acquire data from the monitored unit. The Arduino Uno receives and processes the data for transmission to the Raspberry Pi using LoRa communication. At the Raspberry Pi, the local Chirpstack platform processes and displays the measured data using the Grafana dashboard for real-time data monitoring. The information is stored in an InfluxDB database. For system validation purposes, the prototype is designed, developed, and set up to monitor a set of solar photovoltaic (PV) panel voltages, currents, and battery voltages. The results obtained from the test setup are compared with the physical point measurements. The proposed system is featured as a low-cost, open-source, scalable, and interoperable system. This, therefore, makes the proposed SCADA system an alternative for commercial SCADA systems, especially for remote renewable energy-based microgrid applications. The system proposed in this research can be deployed for large industrial systems with appropriate upgrades and customization.

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