Environmental Engineering Reference
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more power was exchanged with the load. The generated phase voltages quickly settled down
with low THD (below 2.5%) and formed balanced three-phase voltages together with the
supply voltage. The three-phase loads worked properly and independently.
14.6 Summary
The independently-controlled neutral leg studied in Chapters 10-13 is applied to a four-leg
converter to provide an independent balanced three-phase power source from a single-phase
supply. The three-phase voltages generated contain low voltage harmonics and the current
drawn from the single-phase supply is clean and in phase with the supply voltage. A stable
neutral point that is close to the mid-point of the DC-link voltage is maintained and is shared by
the single-phase supply and the two phase voltages generated. The load of one phase is directly
fed by the single-phase supply and, hence, the converter only processes the power partially.
Because of the presence of a stable neutral point, the major functions of the converter can be
implemented independently. A synchronisation unit is designed to make sure that the current
drawn from the supply is in phase with the supply voltage and the generated two phase voltages
can form three-phase balanced voltages together with the supply. The generated voltages have
the same level as the supply voltage so no transformer is needed for loads that require the
same rated voltage as the supply voltage.
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