Existing models describing the dynamic behavior of a six-pulse rectifier during a short-circuit fault condition are derived from switch models using time-domain average value parametric functions. Unlike these models, novel non-parametric dynamic models have been developed using analytical average-value modeling approach in this work. In this modeling approach, depending upon the number of switches conducting during a switching cycle, the operating point of the rectifier is brought into one of three modes of operation of a six-pulse rectifier. The model for each mode is represented by a differential equation. During output current calculation for the rectifier the operating model is selected based on firing angle and overlap angle functions derived in this paper. They completely characterize the dynamic behavior of current flowing through the dc inductor for a wide range of operating conditions with the exception of harmonics and asymmetrical currents which are dominant for faults occurring at the terminals of the rectifier upstream of the smoothing inductor. The results from the average value model and few other simple models have been applied for Thevenin ac source and synchronous generator supplied rectifier models to determine the characteristics of short circuit current from the rectifier. / text

Hysteresis current control has been widely used in power electronics with the advantages of fast dynamic response under parameter, line and load variation and ensured stability. However, a main disadvantage of hysteresis current control is the uncertain and varying switching frequency which makes it difficult to form an average-value model. The changing switching frequency and unspecified switching duty cycle make conventional average-value models based on PWM control difficult to apply directly to converters that are controlled by hysteresis current control. In this work, a new method for average-value modeling of hysteresis current control in boost converters, three-phase inverters, and brushless dc motor drives is proposed. It incorporates a slew-rate limitation on the inductor current that occurs naturally in the circuit during large system transients. This new method is compared with existing methods in terms of simulation run time and rms error. The performance is evaluated based on a variety of scenarios, and the simulation results are compared with the results of detailed models. The simulation results show that the proposed model represents the detailed model well and is faster and more accurate than existing methods. The slew-rate limitation model of hysteresis current control accurately captures the salient detail of converter performance while maintaining the computational efficiency of average-value models. Validations in hardware are also presented.