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Three Phase Triangle Source Macro
Many power system simulations need a three phase voltage input source available. For a
three phase sine wave, it is a simple task to place three sine sources in a schematic and
set their phases at 0, 120, and 240 degrees. For other input waveforms, such as a three
phase triangle wave, it is a little more difficult since there is not a phase parameter that
is easily set. The figure below displays a three phase triangle source macro created in a standard
Y configuration.
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The macro has two parameters available for passing: Per and Mag. Per defines the period
of a single triangle wave, and Mag defines the magnitude of the triangle wave. The
macro circuit consists of three independent SPICE voltage sources. These sources are
located under the Analog Primitives/Waveform Sources section of the Component menu with
the name 'V'. The sources have their VALUE attributes defined using the PWL, piece-wise
linear, capability of the source as follows:
V1 (0 degrees):
PWL TIME_SCALE_FACTOR=per VALUE_SCALE_FACTOR=mag REPEAT FOREVER 0,0 .5,1 1,0 ENDREPEAT
V2 (120 degrees):
PWL TIME_SCALE_FACTOR=per VALUE_SCALE_FACTOR=mag REPEAT FOREVER 0,.6667 .3333,0 .8333,1 1,.6667 ENDREPEAT
V3 (240 degrees)
PWL TIME_SCALE_FACTOR=per VALUE_SCALE_FACTOR=mag REPEAT FOREVER 0,.6667 .1667,1 .6667,0 1,.6667 ENDREPEAT
Each of the sources have their time and voltage pairs defined in relation to one cycle
of the triangle wave. For example, the V1 source has its time/voltage pairs defined as:
0,0 .5,1 1,0
which will produce a voltage of 0 at time=0, a voltage of 1 at time=.5 and a voltage of
0 at time=1. The V2 and V3 sources have their time and voltage data adjusted to reflect
the phase shift that each one of them needs to produce in a three phase system. The
REPEAT FOREVER and ENDREPEAT keywords will repeat the data for the entire simulation
time so that the waveform is now periodic.
The TIME_SCALE_FACTOR uses the Per parameter to scale all of the defined time values.
The VALUE_SCALE_FACTOR uses the Mag parameter to scale all of the defined voltage values.
These two scale factors give the macro great flexibility in that the period or magnitude
of the waveforms can be easily scaled with the factor rather than having to edit each and
every data point within the PWL data. This is also the reason why the time and voltage
in the PWL definitions were based on a scale of 1 so that the factors can scale to the
appropriate period or magnitude using the parameter values passed into the macro.
The results of a 5ms transient analysis with the three phase triangle source is shown
below. In this case, the Per parameter was defined as 1m, and the Mag parameter was
defined as 5. Note that the period of the triangle waves is 1ms with a magnitude of
5V just as the parameters specified, and that the three sources have produced a nice
120 degree phase shift between each other.
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