Design of a Microgrid for a Desalination Plant in Pozo Colorado, Paraguay

Abstract

The village of Pozo Colorado in Paraguay suffers lackluster access to potable water. A desalination plant using a process known as reverse osmosis, the groundwater can be converted into freshwater, and thus solve the problem.The plant is planned in three stages. The first stage will consist of a single production line, a well pump to extract the groundwater from the ground, and a couple of solar panels. In each stage an additional production line, well pump and more solar panels will be added. Each production line consist of a smaller feed pump, and two equal main pumps, connected in series. The plant will also include a battery bank, distribution pump, pumping the potable water up to an elevated tank.In this thesis a microgrid is designed to ensure a reliable supply to the plant. The system is divided into a DC-bus and an AC-bus. The majority of the load is directly connected to the latter. AC-bus voltage is 380 volt phase-to-phase, and connected to the local 23 kV grid trough a transformer. A simple model of a back-up diesel generator is also added to this bus.The PV-array and the battery bank is connected to the DC-bus trough DC-DC converters. Voltage on the PV-array is controlled by a MPPT algorithm, ensuring optimal solar power output. The last motor on each production line, and the distribution motor, are connected to the DC-bus trough VFD inverters controlled by DTC regulators. the DC-bus voltage is set to 700 volts. The two bus are connected with a 15 kVA VSI.The system is modelled in Matlab Simulink, and tested in a series of simulations. These simulations show that system performs well. Though a couple of aspects needs further work, as an improved back-up generator model and further development of overall system operation and control.