Viability and analysis of implementing only voltage-power droop for parallel inverter systems

Srinivasa Salapaka, Brian Johnson, Blake Lundstrom, Sangsun Kim, Scott Collyer, Murti Salapaka

Research output: Contribution to journalConference article

Abstract

In microgrids that are predominantly resistive, real and reactive power can be controlled by implementation of voltage and frequency droop laws respectively. However, the variable frequency displayed by such a system complicates analysis such that design approaches rely on approximations and linearized models. In this work, we present a modified form of droop control where only the voltage versus real power relationship is upheld and the frequency is held constant. Since the frequency is not explicitly controlled and the reactive power is not measured, the controller can be simplified. In such a setting, the only assumption we make is that all inverters have access to a common time-reference. Because fixed frequency operation is enforced by design, a variety of analytical tools can be leveraged to formulate a comprehensive analytical framework which facilitates a precise design methodology. In particular, closed-form expressions on the output current phase differences are obtained which yield practical selection guidelines on the voltage-power droop gains such that reactive flows between inverters are kept small. As a corollary, it is demonstrated that there are no reactive power flows in the presence of purely resistive loads. For the particular case of a single inverter, an almost exact solution describing the nonlinear dynamics of the inverter output voltage, current, and power are derived. Accompanying simulation results validate the analytical results and demonstrate the feasibility of the proposed control approach.

Original languageEnglish (US)
Article number7039891
Pages (from-to)3246-3251
Number of pages6
JournalProceedings of the IEEE Conference on Decision and Control
Volume2015-February
Issue numberFebruary
DOIs
StatePublished - 2014
Event2014 53rd IEEE Annual Conference on Decision and Control, CDC 2014 - Los Angeles, United States
Duration: Dec 15 2014Dec 17 2014

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Modeling and Simulation
  • Control and Optimization

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