A UNIFIED "SCALAR" DISCRETE-TIME MODEL FOR ENHANCING BIFURCATION PREDICTION IN DIGITALLY CONTROLLED H-BRIDGE GRID-CONNECTED INVERTER

In this paper, a unified "scalar" discrete-time model is proposed for enhanced bifurcation prediction in digitally controlled H-bridge grid-connected inverter system. The model is established by analytically expressing the elements of the matrix exponential involved in the exact discrete-time model. In high-order system, different from the discrete-time model using the state-transition matrix directly, obtaining the discrete-time model of the state-variable vector only, in this system, the discrete-time model of each state variable can be obtained directly and separately. In addition, the stability boundary of Hopf bifurcation, period-doubling bifurcation and saddle-node bifurcation can be obtained by analytical expressions. The modeling method is validated by an LCL-filter system as an example using practical circuit parameters. The results of the analysis can simplify the modeling process and enhance the bifurcation prediction of the digitally controlled inverter system.