Parallel Resonance Mechanism Analysis and Suppression of Inductance-Capacitance-Inductance Grid-Connected Inverters

Abstract

The resonance problem of multi-paralleled grid-connected inverters with inductance-capacitance-inductance (LCL) filters is a core matter which bothers the safety and stability operation of new energy distribution networks. Based on the impedance model of the paralleled system of two inverters, the influence of inverters on grid-connected current was analyzed through the superposition principle, and the grid-connected current was decomposed. The resonant mechanism generated by interactive current and the common current was studied, and the resonance frequency characteristics were compared and analyzed by a paralleled system using the same and differently rated power inverters. Based on the resonance frequency generated by interactive current, a digital notch filter was introduced into the traditional capacitance current active damping control scheme, which realized the non-static control of base wave signal and satisfied the standard of multi-paralleled grid-connected inverters with LCL filters. Finally, simulation results verified the correctness and validity of the proposed strategy.

Low-Loss Active Grid Impedance Cancellation in Grid-Connected Inverters with LCL Filter

“…The passive damping method acts on the LCL filter by inserting the impedance around the filter resonant frequencies at the expense of additional power loss and degradation of filtering attenuation [3][4][5]. The active damping (AD) approach is to integrate the damping function into the inverter control so that the inverter equivalent output impedance around the filter resonant frequencies or over the frequency range is increased [2,[6][7][8][9][10][11][12][13]. Among them, active damping methods are preferred because no additional power consuming resistor is required.…”