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Stability Analysis of Three-Phase PWM Converter with LCL Filter by Means of Nonlinear Model

In this paper the stability problem of the three phase PWM converters with LCL filter without additional passive or active damping is analyzed. The system with the converter current feedback is considered where the stability problem is more acute. The analysis is performed using two theoretical methods, the discrete z-domain root locus technique and the nonlinear model simulation. The system with two different LCL filters is considered, one with the iron core inductors and the other with the air core inductors. In that way the influence of the iron losses on the system stability is investigated. It is shown that the stability margins obtained by means of the nonlinear model simulation are somewhat wider than the ones obtained by the root locus technique. The theoretical results are validated by the measurements performed on a 40 kW laboratory setup.

PWM converter; LCL filter; Stability; Root locus; Nonlinear model; Iron losses

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