Optimized Models for Maximum Speed and Accuracy
Ideal Switch Models
In PLECS, models of power semiconductors, circuit breakers, etc. are based on ideal switches. In the closed position they represent a true short circuit (Ron = 0) and in the open position an ideal open circuit (Roff = ∞). They toggle instantaneously between these two positions. The use of ideal switches in modeling offers three major advantages: ease of use, robustness and speed.
Simple to use
In most cases, using ideal switches for simulations of power electronic systems is perfectly sufficient to investigate all aspects of controls and thermal management. Ideal switches eliminate the burden of obtaining detailed physical parameters for a given semiconductor and facilitate a top-down design approach. If better fidelity is desired, PLECS' behavioral models can be extended as more detailed information about parasitics becomes available.
Behavioral models based on ideal switches do not have the numerical stability issues typical for SPICE-type physical models. The PLECS semiconductors do not require a non-physical snubber or the use of a fixed time step solver to suppress numerical instabilities. The variable-step solvers available in PLECS allow the exact determination of switching events. The user has a choice of higher-order solvers to accurately simulate non-stiff and stiff circuits.
In conventional circuit simulation programs, switching transients are computationally expensive. The finite slopes force the program to take small time steps. In PLECS, this problem is avoided by instantaneous operation of the ideal switches. Only two steps are needed for each switching event, as illustrated below. This speeds up the simulation considerably. PLECS Standalone users will experience lightning fast simulation runs due to the highly optimized PLECS solvers.
In addition to the ideal switch models, PLECS offers behavioral models for simulating dynamic parasitic effects in power semiconductors, such as diode reverse recovery or limited di/dt during IGBT turn-on and turn-off. These models are intended to detect critical overvoltages that may occur across stray inductors and can be further enhanced by the user.