Predictive Control of Three Phase AC/DC Converters

Chapter 2
Voltage Source Converter
Main part of the Voltage Source Converter (VSC) is three phase IGBT module,
which consists of six transistors and parallel connected freewheeling diodes. To
design control system and simulation model, it is necessary to define mathematical
model. However, it is difficult to include all nonlinearities of IGBT module,
and therefore following assumptions have been taken into considerations:
• transistors are assumed to be ideal switches (“on” resistance is zero, “off ”
resistance is infinity),
• time delay between control signals and IGBT module is neglected,
• transistor switching off time delay is zero (no dead time),
• no switching loses.
Also, AC-side has been simplified as follows:
• symmetrical line voltages (three sinusoidal voltage supplies with equal amplitudes
and phase shift 120 ◦ ),
• internal resistance of voltage supplies and wires resistance is zero,
• negligible small supply inductance (related to VSC input choke inductance),
• ideal VSC input choke (without saturation effect and impedance coupling).
In this Chapter basic mathematical models of VSC in different coordinate systems
as well as its operation principals will be presented.
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