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Piecewise Average-Value Model of PWM Converters With Applications to Large-Signal Transient Simulations

State-space average-value models (AVMs) of pulse width modulation converters are widely used in both small-signal frequency-domain analysis and large-signal time-domain transient simulations. This paper is focused on the latter category. The limitations of the traditional state-space AVM (T-AVM) are discussed. A piecewise state-space AVM, P-AVM, is proposed, which uses the actual duty ratio as the control input instead of the continuous duty ratio used by the T-AVM. In order to consider the effect of switching ripples, an approximate ripple function is obtained. An iterative algorithm is proposed for utilization of P-AVM and ripple function for large-signal time-domain transient simulations. A boost converter and a two-level three-phase ac-dc converter are used to validate the performance of the P-AVM in comparison with the T-AVM under large ripple and large disturbance conditions. The detailed models developed in PSCAD/EMTDC are used as benchmarks. Improvement in accuracy is demonstrated. The efficiency of the iterative algorithm is discussed. Experiments on a 50-kVA three-phase ac-dc converter are conducted to validate the proposed method.