Power Loss Minimization of Off-Grid Solar DC Nano-Grids—Part I: Centralized Control Algorithm

Abstract

Peer-to-peer interconnection of households having on-site batteries, multi-port converters and solar panels to form a multi-port converter-enabled solar DC nano-grid is an emerging approach for providing affordable energy access in rural areas. Battery charge and discharge losses, distribution losses and converter losses are significant problem when operating such nano-grids. This paper presents a centralized control algorithm that can help address the power loss problem. The proposed algorithm uses a new problem formulation where the power loss problem is formulated as a two-stage convex optimization problem. The first stage of the optimization problem is an optimal battery dispatch problem for determining optimal battery charge and discharge currents. The second stage is an optimal current flow problem for determining optimal distribution voltages which corresponds to the optimal battery currents. Simulation results of the nano-grid show that the proposed algorithm can minimize the nano-grid power losses while facilitating the power exchange between the households. The proposed algorithm is suitable for small nano-grids where privacy of households is not a concern. In Part II of this paper we propose a distributed control algorithm that preserves the privacy of the households especially where the size of the nano-grid is large.

Power Loss Minimisation of Off-Grid Solar DC Nano-Grids—Part II: A Quasi-Consensus-Based Distributed Control Algorithm

“…The key physical phenomenon of the FPC is the power loss which occurs as currents and voltages are converted from one form to another. The FPC loss p c loss,i can be expressed as a quadratic function of load power, P L,i as follows [25] p c loss,i = 17.765 + 0.00175P L,i + 0.000791P 2…”

“…To minimize the power losses, the batteries must be optimally dispatched. To achieve this, we adopt a two-step optimization problem formulation approach proposed in our earlier work in [25]. The approach consists of two sub-problems, the optimal battery dispatch problem (OBDP) and the optimal current flow problem (OCFP).…”

“…As detailed in Part I of this paper [25], the solution to OBDP (without inequality constraints) can be achieved when the incremental loss λ i = ∂J/∂I b,i for every i-th battery in the nano-grid is equal to the global incremental loss λ given by…”

“…The proposed algorithm addresses the power loss problem in a distributed manner by finding optimal distribution voltage control signals. It should be noted that this paper is a continuation of our work presented in Part I [25] where the same power loss problem was addressed in a centralized manner. Thus, we adopt the power loss optimization problem formulation described in Part I.…”

Towards Resiliency Enhancement of Network of Grid-Forming and Grid-Following Inverters

“…Various control approaches for network of GFM and GFL inverters in PEDG have been proposed in literature and are mainly classified as: centralized and distributed control schemes [3,9,10]; that can mitigate disturbance impacts to some extent. In centralized control approach, the satisfactory operation of the PEDG clusters heavily relies on a central SC which provides adequate power references to inverters along with vital protection features in the grid-connected and islanded modes [11,12]. Various primary controllers for GFM and GFL inverters such as droop-based, virtual synchronous generator (VSG)-based, and virtual oscillator control (VOC)-based schemes are deployed in centralized control architecture where the SC provides the active-reactive power setpoints to these inverter's primary controllers to maintain system stability.…”