Pulsating power mitigation in poly-source DC microgrids with single-phase inverters: A theoretical analysis

Abstract

This paper describes a method to reduce the DC bus power oscillation in a multi-home building AC–DC hybrid microgrid containing renewable resources, energy storage elements, and building loads. In general, the connection of several single-phase inverters to a DC bus to supply AC loads generates a double-frequency power oscillation in the DC link. Usually, each single-phase inverter has a random voltage phase angle reference and a different load power factor that strongly influences the DC bus power quality. To solve this problem, a method is proposed to ensure a minimum power oscillation. The adopted strategy considers a lead controller, which calculates the optimal voltage reference phase angle for each inverter, considering the load apparent power and power factor. A theoretical analysis is presented, and a method for minimizing unwanted components on the DC bus is proposed. The proposed method is based on the correct definition of the AC reference phase of each single-phase converter by implementing a gradient descent optimization algorithm. The paper shows a verification with real AC load profiles, performing the DC bus power low-frequency oscillation mitigation, reaching a 95% power oscillation reduction.

Keywords

• Microgrid
• DC bus power oscillation
• Double-frequency power oscillation
• Power converters
• DC–AC inverter
• Phase shift