Inverter Three-phase

A relatively new innovation for use in electric motor compressor drives is the variable frequency power source. Fundamentally, the power source converts an existing three-phase source into DC then uses an inverter to convert back to a variable frequency supply. Thyristors or transistors are used to switch the output at the required frequency. 

Inverter output voltage regulation typically 480 volts plus or minus 2%, three-phase. 

The first report of an all-SiC, three-phase dc-ac inverter was presented by Seshadri et al. [17] in 1999. Although Seshadri s inverter used SiG GTOs and p-/-n diodes, it was operated at ambient temperature and at voltage and current levels so low that the authors were unable to ...determine typical switching characteristics of the individual SiG components. From the standpoint of technology development, there exists a need to evaluate SiC technology under relevant circuit stresses. 

In 2001, the authors of this chapter developed a 400-W, dc-to-ac inverter using SiC GTOs and p-/-n diodes for operation at case temperatures up to 150°C for driving three-phase, inductive loads up to 5 SOW. The inverter circuit was constructed to perform the first characterization of these SiC devices under significant electrical and thermal stresses, investigate the parametric operating space of the SiC devices, and uncover circuit-related failure modes. 

CL-DNA complexes form spontaneously when solutions of cationic liposomes (typically containing both a cationic lipid and a neutral helper lipid) are combined. We have discovered several distinct nanoscale structures of CL-DNA complexes by synchrotron X-ray diffraction, three of which are schematically shown in Fig. 1. These are the prevalent lamellar phase with DNA sandwiched between cationic membranes (Lo,c) [22], the inverted hexagonal phase with DNA encapsulated within inverse lipid tubes (Hnc) [23], and the more recently discovered Hj0 phase with hexagonally arranged rod-like micelles surrounded by DNA chains forming a continuous substructure with honeycomb symmetry [24]. Both the neutral lipid and the cationic lipid can drive the formation of specific structures of CL-DNA complexes. The inverse cone shape of DOPE favors formation of the... 

When the packing considerations are taken into account, this model practically predicts that amphiphiles with a single alkyl chain are will form micelles or bilayers, those with two alkyl chains bilayers, and those with three alkyl chains inverted hexagonal phases.[0]... 

Later, Yoshikawa and Matsubara [40] further studied a non-linear system and proposed a mechanism for the periodic behaviour that involved the formation of inverted micelles that suddenly moved to the oil phase after the concentration of adsorbed surfactants reached a critical value. They extended the experiment to a water/oil/water three-phase system in a U-shaped glass tube that gave spontaneous and stable oscillatory behaviour over a long period [41]. Since then, various characteristics of non-linear behaviour have been investigated and several mechaiusms for the non-linear behaviour have been proposed by many research groups including ours[2,5,10,42-48] however, the mechanism at a molecular level has not been clarified yet and no consensus has been achieved. The difficulty in the explanation seems to come from not only the complexity and diversity of the systems, but also limitations of the observation methods that enable us to monitor dynamic molecular behaviour at liquid/liquid interfaces with sufficient interfacial selectivity and time resolution. In this section, the TR-QELS method has been applied to the investigation of W/NB—sodium dodecyl sulfate (SDS) two-phase system [10]. 

AC electric drives require more sophisticated converters when they are supplied with DC sources, because electric machines requires periodic voltage and current waves with a variable frequency depending on the load requirements. In Fig. 5.8, the scheme of an example of three-phase induction motor driven by a pulse-width-modulated inverter is reported. In this scheme a three-phase bridge connection with six power modules is shown to form the so-called inverter. Each power module can be composed by a number of power switches connected in parallel to carry higher currents. Across each power switch (IGBT) a parallel diode is connected to provide a return path for the phase current when the power module is switched off. 

Fig. 5.8 Scheme of a three-phase induction motor driven by inverter... 

Thompson and Compton investigated, from a theoretical standpoint, the case of a spherical microparticle with an electroactive compound on its surface and attached to a solid electrode surface [33, 34]. The movement of charge was assumed to start exclusively from the contact point (or line) between the microparticle and electrode (i.e., at the three-phase boundary, if an electrolyte phase is considered) and to proceed over the particle surface only (see also Section 6.3.1). In Ref. [33], the idealized microparticle geometries of a full sphere, a hemisphere, and an inverted hemisphere have been considered (cf. Figure 6.8). 

A typical basic circuit is shown in Figure 14.3 which consists of two main parts, a three-phase bridge-connected thyristor rectifier and a three-phase bridge-connected thyristor inverter. 

The method described above can be modified to operate as a three-phase inverter. Single and three-phase inverters operating in this manner form the basis for many types of uninterruptible power supplies (UPSs), and variable speed drives for AC motors. 

High-power inverters were initially developed for the long-distance transmission of power from a three-phase source to a remote three-phase sink using a DC overhead transmission line or cable. Early DC power transmission used mercury arc thyratrons (gas-filled values or tubes), which functioned in a manner very similar to the early types of thyristors. The on state of the valves was controllable, but the off state was determined by natural commutation made available by the sinusoidal voltages of the sink power system, see Reference 13. A brief description of three-phase inverters follows. 

A 250 kW three-phase, fonr-pole, 50 Hz, 415 V, indnction motor is fed from a voltage source inverter. The motor has the following parameters for its star-wonnd windings. Find the cnrrents and air-gap voltage in the circnit. 

Clearly, a bond graph approach to FDI of systems modelled as a hybrid system is not limited to switched power electronic systems but may be applied to other engineering systems as well for which a hybrid model is appropriate. In the following, the case studies consider faults in a DC to DC boost-converter, in a three-phase DC to AC inverter and in a three-phase rectifier AC to DC. In some motor drives, a rectifier and an inverter are used back-to-back [8], Computations have been performed by means of the open source software program Scilab [21],... 

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