Control of Power Inverters in Renewable Energy and Smart Grid Integration电力—ch14.pdfVIP

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 adopt