VSG‐controlled parallel‐connected voltage‐source converters in low‐voltage microgrid with dominant resistive impedance

Abstract

This paper deals with the control and performance improvement of parallel‐operated voltage‐source inverters (VSIs) controlled as virtual synchronous generators (VSGs). In publications regarding the parallel‐operated VSGs, transmission lines are considered to be mainly inductive. However, less analytical works have been done regarding the control of paralleled VSGs in low‐voltage grids with dominant resistive impedances. Once VSIs are controlled as VSGs in a microgrid with more resistive transmission lines, swing equation and system representation for the power‐angle synchronization will change leading to a new control structure. Therefore, this paper deals with the control of parallel‐operated converter‐based VSGs in low‐voltage grids with dominant resistive line impedances. In this way, the VSG representation, comprising the swing equation and V‐P droop characteristic, for applications in highly resistive microgrids is presented, in which the swing equation and VSG frequency are related to reactive power. Then, the V‐P droop characteristic is modified and an enhanced P‐V droop characteristic for proper sharing of active power between the VSGs in highly resistive microgrids is proposed. Next, the VSG control is modified so that the R/X ratio at the VSG output increases and thus the decoupled control of active/reactive powers in relatively inductive cases is realized as well.