DC Micro-grid with loads switching control in off-grid rural households

Abstract

A DC micro-grid with an autonomous load switching system is proposed in this paper to promote the pace of supplying electrical power in off-grid rural areas. The design includes a PV array as the primary renewable energy (RE) source and a battery energy storage system (BESS) for micro-grid reliability. The system operates in an islanding mode, in which the loads are supplied by the solar PV arrays and energy storage system only, with no utility grid connection. The batteries in a micro-grid are charged from the main DC bus line through the buck-boost converter. Both the PV array and the battery energy storage system are connected to the DC bus line through the voltage source converters (VSC). The AC loads are connected to a micro-grid through electromagnetic switches, which are controlled by a microcontroller chip to maintain the safety and stability of the micro-grid. The voltage and current sensors are used to sense a power line of a connected household, signals uploaded in a microcontroller, then switches are actuated to connect or disconnect the line based on the power consumption sensed. The controllers in the design, modify the duty cycle of the converters to adjust the output power of the micro-grid to the maximum point. An increment and conductance (IC) maximum power point tracking (MPPT) technique is used in a PV array to control the operation of the converter. The PI controller is used in the buck-boost converter of the energy storage system with a reference voltage of 375 VDC. The simulation result shows that regardless of PV system voltage fluctuation due to solar irradiation, the controller maintains constant DC bus line voltage. Suitable tuning of P and I values is applied in the PI controller of the DC/AC inverter to generate the proper AC voltage output for the loads.