Modular open source solar photovoltaic-powered DC nanogrids with efficient energy management system

Abstract

Initially the concept of a DC nanogrid was focused on supplying power to individual homes. Techno-economic advances in photovoltaic (PV) technology have enabled solar PV stand-alone nanogrids to power individual devices using devicespecific architectures. To reduce costs and increase accessibility for a wider range of people, a modular open-source system is needed to cover all applications at once. This article introduces a modular PV-powered nanogrid system, consisting of a do it yourself (DIY) PV system with batteries to allow for off-grid power. The resultant open-source modular DC nanogrid can deliver DC power to loads of different voltage levels, which is possible because of the efficient and parametric energy management system (EMS) that selects modes of operation for the grid based on DC bus voltage and state of charge of batteries. Simulation results verify the coordination between the EMS and the PV-battery system under varying PV power generation and load conditions. This EMS has potential to enable easy personalization of a vast area of applications and expand appropriate technology for isolated communities. A thorough stability analysis has been conducted, leading to the development of an LQR (Linear Quadratic Regulator) controller as a replacement for the conventional PI (Proportional - Integral) controllers for better transient stability of the system.

NOMENCLATURE:
SoC    State of charge.
K_p      Proportional gain.
K_i       Integral gain.
Z_ocl    Closed loop output impedance.
Z_icl     closed loop input impedance.
Z_bus   Total bus impedance.J cost function.
Q       state weighting matrix.
R       control weighting matrix.
K       LQR gain matrix.
P       Unique positive definite solution of the
algebraic Riccati equation (ARE).