SIMPLORER User Manual V6.0 - FER-a

Basic Rules for the Proper Choice of Time Step
SIMPLORER 6.0 — Manual 399
Circuit Simulator Parameters
SECM.SOLVER Used integration method. 0=Euler, 1=Trapez
Trapez
Used for oscillating LC systems or analog oscillators, especially useful
for investigating energy problems
Euler Integration
Used for all other simulation problems. Damping effects may cause
false results for energy relationships.
SECM.LDF Local discretization error [%]. Defines the time step dependent on the
(0.1…10)
dynamic of the circuit. A small error increases the precision but also
the calculation time. This number itself gives no clue as to the precision
of the overall result.
SECM.ITERATMAX Maximum number of iterations for one simulation step. If convergence
(5…30)
problems occur, the calculation for the active simulation step will be
stopped when the maximum value is reached without consideration of
other error limits.
SECM.IEMAX Maximum current sum error. A very small value lead to accurate re-
1µ…100µ
sults, but convergence problems might be possible in the Newton integration
method.
SECM.VEMAX Maximum voltage error. A very small value leads to accurate results,
1m…1
but convergence problems may occur using the Newton integration
method.
Correct simulation processing and results depend on the proper choice of minimum and maximum
values for the integration step size. The smaller the maximum integration step size, the
more correct the results, but the longer the processing time.
This means that, when specifying these minimum and maximum time step values, you need
to compromise between accuracy and time. The basic rule of measurement “Not as precise as
possible, but as precise as required” is also valid for a simulation. The following guidelines
should help you prevent elementary mistakes in choosing the proper integration step width:
Model properties Recommended
What is the smallest time constant (τ min ) of the electric circuit (R*C or
L/R) or of the block diagram (PTn-elements)
What is the largest time constant (τ max ) of the electric circuit (R*C or
L/R) or of the block diagram (PTn-elements)
Which is the smallest cycle (T min ) of oscillations that can be expected
(natural frequencies of the system or oscillating time functions)
Which is the largest cycle (T max) of oscillations that can be expected
(natural frequencies of the system or oscillating time functions)
τmin Hmin < ----------
10
τmax Hmax < ----------
10
Hmin Tmin < -----------
20
Hmax Tmax <
-----------
20