Fast Reactive Power Sharing, Circulating Current and Resonance Suppression for Parallel Inverters Using Resistive-Capacitive Output Impedance

Abstract

In this paper, an inverter using resistivecapacitive output impedance (RC-type inverter) is proposed not only to provide fast reactive power sharing to support microgrid voltage, and but also to reduce circulating currents and damp high-frequency resonances among inverters. Introducing the RC virtual impedance loop, the inverter provides fast transient response. Based on the RC-type inverter modeling, the comparative frequency-domain analysis of equivalent output impedances are discussed, and the impact of the virtual complex impedance over the circulating currents and high-frequency resonances among parallel inverters are quantitatively analyzed. The control parameters are systematically selected, and effect of virtual complex impedance on the inverter output voltage is depicted. The RC-type inverter can reduce circulating currents and damp resonances due to different equivalent output impedances of inverter, and line impedances. Simulation and experimental results verify the effectiveness of proposed method.

Overview of power quality analysis and control technology for the smart grid

“…The resistive (R-type) inverter, inductive (L-type) inverter, resistive-inductive (RL-type) inverter, and resistive-capacitive (RCtype) inverter can be easily designed by using the virtual impedance technology to meet the different operating requirements of the microgrid [66][67][68][69]. In general, the output impedance of the inverters in the middle-voltagelevel microgrid is designed to be inductive; on the contrary, the output impedance is often designed to be resistive-inductive in the low-voltage-level microgrid.…”

Simultaneous reactive power sharing and voltage regulation in an autonomous networked microgrid

“…The strategy for the reactive power sharing is to make the converters' contributions in supporting the reactive power according to their capacity to prevent them from overcurrent condition. It is executed by assigning the V-Q droop gains at each generation bus so that the equilibrium point given in (8) is established [16]. 11 1:…”

“…The strategy in bulk power systems for voltage regulation is to keep the voltage magnitude at a constant value at generation buses via automatic voltage regulator (AVR) and the same strategy exists at load buses using flexible compensators. In MGs, however, because of the small value of the feeder impedance as well as feeders' impedance mismatch, a small error in the voltage magnitude poses the circulating current among converters, which in turn imposes extra power losses and also limits converters' and network's capacities [16]. To address this issue reactive power sharing is adopted as a means of voltage regulation to avoid circulating current.…”

Multimode Operation for On-Line Uninterruptible Power Supply System

“…stability. As the output impedance shows a resistive nature by adding the virtual resistance, ~ and ~ droop control strategy is implemented in the control loop [39] and expressed as :…”