The necessity of RonRoff modeling for high switching frequency applications

RonRoff modeling means that the closed switch is modeled as a small resistance, the open switch is modeled as a large resistor. It is a classic switch modeling method used in offline electromagnetic transient simulation software. With RonRoff modeling, the corresponding resistor values are switched when the switch state changes, so that when the switches in the power electronic converter bridge are frequently turned on and off, the admittance matrix of the system is constantly changing; this is very challenging for simulation based on FPGA.

The classical switching LC modeling approach has a very good advantage that no matter how the switch state changes, only the injection current calculation changes while the system admittance matrix remains unchanged. However, the limitation is that since the switch is modelled with an energy storage element (inductor or capacitor), the energy stored in the inductor or capacitor is easily lost when the switch state is changed, resulting in spurious power loss. When the switching frequency is less than 20 kHz, in general, the switching loss can be reduced with a proper setting of Gs and the switch-off initial voltage (Vs_off_init), and a better simulation result can be achieved. However, when PWM frequencies are higher than 20 kHz, it is often difficult to achieve good results with LC modeling.

For this reason, ModelingTech has introduced a hybrid simulation method of RonRoff and LC modeling. For low switching frequency topologies, users can use LC modeling, for high switching frequency topologies, users can choose the RonRoff modeling method to achieve better simulation results.

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