Abstract
Switching models possess discontinuous and nonlinear behavior, rendering difficulties in simulations in terms of time consumption and computational complexity, leading to mathematical instability and an increase in its vulnerability to errors. This issue can be countered by averaging detailed models over the entire switching period. An attempt is made for deriving improved dynamic average models of three phase (six-pulse) and nine phase (18-pulse) diode rectifiers by approximating load current through first order Taylor series. Small signal AC/DC impedances transfer functions of the average models are obtained using a small signal current injection technique in Simulink, while transfer functions are obtained through identification of the frequency response into the second order system. For the switch models in Simulink and the experimental setup, a small signal line to line shunt current injection technique is used and the obtained frequency response is then identified into second order systems. Sufficient matching among these results proves the validity of the modelling procedure. Exact impedances of the integral parts, in interconnected AC/DC/AC systems, are required for determining the stability through input-output impedances.
Highlights
The demand for power electronic converters has increased with the dependence on electronic appliances, digital products and computer systems in both industrial and household applications [1].Power converters are required almost in every field that deals with electronics such as aircrafts, sea ships, communication systems, renewable energy generations, such as wind generation systems, photovoltaic systems and fuel cells etc. [2,3]
Converters are found to be one of the best solutions for providing loads with output voltages and currents having less ripples, reliable as well as rarely polluting the ac supply sources. These converters help in keeping lower total harmonic distortion (THD) at the ac side and less power consumption for the rated devices
This paper proposes an improvement in the static models derived in [44,45], where load current is treated as a constant dc value
Summary
The demand for power electronic converters has increased with the dependence on electronic appliances, digital products and computer systems in both industrial and household applications [1]. ABC model (three-axes coordinate system) is converted into DQ synchronous reference frame (two-axes coordinate system) and linearized AVM of the specified system is utilized to obtain the small signal transfer functions for the input/output impedances, required for stability measurements These transfer functions can be validated by comparing with those of prototypes or detailed models by applying impedance extraction techniques discussed in [43]. Using this concept, improved dynamic average value models have been developed for 3-phase and 9-phase diode rectifiers using first order Taylor series expansion of the load current (Idc ) so that to capture the dynamics of the system as well These AVMs are linearized to obtain small signal transfer functions of the input/output.
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