Two-Stage Bidirectional Inverter Equivalent Circuit Model for Distribution Grid Steady-State Analysis and Optimization

TL;DR

This paper introduces a physics-based, two-stage bidirectional inverter model that accurately captures losses, supports multiple control modes, and scales efficiently for large distribution network analyses and optimizations.

Contribution

It presents a novel, circuit-level inverter model that explicitly accounts for losses, enables seamless control mode integration, and is scalable for large distribution grid studies.

Findings

More accurate inverter modeling of losses.

Seamless integration of control modes.

Scalable to large distribution networks.

Abstract

This paper presents a \textit{physics-based} steady-state equivalent circuit model of a two-stage bidirectional inverter. These inverters connect distributed energy resources (DERs), such as photovoltaic (PV) and battery systems, to distribution grids. Existing inverter models have technical gaps on three fronts: i) inadequate modeling of inverter losses; ii) use of mathematical abstractions for bidirectional flow of power; and iii) inability to integrate different control modes into nonlinear solvers without loss of generality. We propose a physics-first model that explicitly captures losses in passive circuit components based on circuit-level principles. We enable bidirectional power flow without binary or complementarity constraints by formulating loss terms as smooth, sign-aware expressions of current. We introduce and parameterize controlled current sources with twice-differentiable continuous functions to enable inverter control modes without loss of generality. We integrate DERs with the proposed inverter model at the load buses of distribution networks to perform power flow and optimization studies on real-world distribution networks with over 20,000 nodes. We demonstrate that the proposed model is more accurate, integrates seamlessly with various control modes without loss of generality, and scales robustly to large optimization problems. Index Terms: bidirectional inverter model, circuit-based modeling, DERs, inverter efficiency, power control, steady-state analysis.