Current transformer saturation criterion based on virtual impedance model;

The output voltage wave, the output current wave and the output equivalent impedance (it is named virtual impedance Z) are important characteristics of CWG.

This paper proposes the concept of circulating impedance, and introduces it into current-sharing control strategy.

Based on the research and design on parallel-connected modularization UPS, several contents about inverter are studied in detail, such as the parallel model, circulating impedance and circulating current characteristics of the paralleling operation system based on instantaneous voltage PID feedback control,parallel sharing current technology based .

Based on the topologic of matrix converter(MC) virtual DC-link control strategy was applied,integrate with brushless DC motor(BLDC) three phases six state operation theory to implement MC feed BLDC commutation.

In this paper,control methods based on damping resistor and virtual resistor are presented.

To suppress reso- nance of LCL filter and improve stability of system,it is pre- sent that a voltage and current double loops control strategy based on virtual resistor concept.

In order to assure stable operation of system, in this paper a controlling strategy based on virtual resistor concept is presented to make controlling arithmetic replacing function of damping resistor.