Frequency-Domain Model of Voltage-Source Inverters with Closed-Loop Current Control

The goal of this paper is to derive a modeling approach in the frequency domain for pulse-width modulated voltage-source inverters with closed-loop control. The feedback loop of a closed-loop control introduces a harmonic content into the input signal of the modulator. Based on models for pulsewidth modulation with multiple-frequency input signals presented in previous publications, the incorporation of the feedback loop became feasible. However, the pulse-width modulator models are unidirectional and do not cover the reaction of the plant through the feedback control loop. This paper develops an analytical nonlinear model for voltage-source inverters with closed-loop control for steady-state operation, based on Fourier coefficients. The model of a digital control system including the feedback of the dc-link voltage and the feedback of the ac-side current is created, incorporating the influence of the analog-to-digital conversion and the discrete-time control. The nonlinear equation system is numerically and simultaneously solved and validated with time-domain simulations and measurements on a converter prototype.