Environmental Engineering Reference
In-Depth Information
14
Applications in Single-phase
to Three-phase Conversion
As an application of the neutral line provision, the conversion of a single-phase power supply
to independent three phases is discussed in this chapter so that balanced or unbalanced, linear
or non-linear, three-phase loads can be operated from a single-phase supply. It can be used in
places, e.g., rural areas, where only a single-phase power supply is available. The converter
consists of four legs: (i) one rectifier leg to generate a DC-link voltage; (ii) two phase legs
to generate two independent phases to form balanced three-phase voltages together with
the single-phase power supply; and (iii) one neutral leg to generate a neutral point, which is
common to the single-phase supply and the two phases generated. Decoupled control strategies
are developed to make sure that (i) the current drawn from the single-phase supply is sinusoidal
and in phase with the supply voltage; (ii) the generated phase voltages contain low voltage
harmonics even when the load is non-linear; and (iii) the neutral point is maintained as stable.
Simulation results are provided.
14.1 Introduction
In some remote areas, it is quite normal to only have a single-phase power supply even though
three-phase distribution systems are very common (Cipriano dos Santos
et al
. 2011). But some
electric appliances, e.g., air conditioners and motors above a certain power level, require three-
phase voltages. Hence, a device that converts a single-phase supply to balanced three-phase
voltages is often needed. This converter is expected to have the capability of powering single-
phase and/or three-phase, balanced or unbalanced, linear or non-linear loads and drawing a
clean current that is in phase with the supply voltage.
Normally, this conversion process involves an uncontrolled rectifier bridge cascaded with
a three-phase full-bridge inverter via a DC link as shown in Figure 14.1(a), which are widely
adopted in motor drives (Bose 2001). This topology causes high current harmonics and low
input power factor to the supply. Moreover, the power can only flow one way from the supply
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