Figure 3-1 Topology Of Perfect Harmony Vfd (3 Cells) - Siemens 6SR41 series Product User Manual

Theory
3.2 The Power Circuitry
Figure 3-1
Whenever the reference is greater than the first (unshifted) carrier, the signal L1 is high;
otherwise L1 is low. L1 is used to control the pair of transistors Q1 and Q2 in cell A1 (see the
left pair of transistors in Figure "Schematic of a Typical Power Cell"). Whenever the
reference is greater than the inverse of the first carrier, the signal R1 is low; otherwise R1 is
high. R1 is used to control the pair of transistors Q3 and Q4 in cell A1 (see the right pair of
transistors in Figure"Schematic of a Typical Power Cell").
The difference between L1 and R1 gives the output waveform of cell A1, shown in
Figure"Waveforms for Phase A"3 for Phase A as A1.
In a similar manner, the reference signal is compared with the second carrier (shifted 120
degrees) and its inverse to generate control signals L2 and R2 for the transistors in cell A2.
The output waveform of cell A2 is shown as A2.
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Topology of Perfect Harmony VFD (3 Cells)
Operating Instructions, Version AE 12/2009, A5E01454341C
Product User Manual