Inverter diode-load

Fig. 13.11. Schematic of a diode load inverter (a) and of a diode load inverter with level shifter (b).

Fig. 13.12. Transfer characteristics of a typical diode load inverter (a) [Vtrip = —10.8 V,...

Amax = 2.1, NM = 0.5 V] and of a typical diode load inverter with level shifter for different... 

Section 8.2.3 also considers the effect of an abrupt parametric fault in one phase of the inverter s load. In this case study, the load of the three-phase inverter is an RL-network in delta configuration often used in studies of three-phase PWM voltage source inverters. The study may be extended by replacing the RL-network by a sophisticated BG-model of an induction motor (see for instance [31, Chap. 8]). Studies of the three-phase diode bridge rectifier typically assume a resistive load in parallel to a filter capacitor. 

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. 

In this section, we have described a demonstration of an all-SiC dc-ac inverter (using SiC power switches and SiC diodes) operated in excess of 400W and at case temperatures of approximately 150°C. Two factors related to the system s implementation limited the operational power levels of this circuit. First, load instability caused excessive current spikes and GTO failures and was corrected using a closed-... 

Accurate predictions of the effect of AVt on TFT-based circuit operation can only be made by computer simulation. In general, a AVt in the gate-on direction leads to an increase of the on-state resistance of the transistor. For example, if the TFT is a switch in a display backplane, the increased resistance determines an increase in pixel charging time. In a diode-connected inverter, a negative AVt of the load transistor with respect to the Vr of the drive reduces the output swing of the inverter. On the other hand, a negative AVt of the drive transistor relative to the load shifts the trip voltage of the inverter. 

For instance, if there are high amp draws from motor start ups, etc., put a supercapacitor in parallel connection with a 12 volt rechargeable battery, and use this to supply those intermittent load needs adequately. To use a rechargeable battery alone, as mentioned, simply connect the output from the fuel cells to the battery and draw power from the battery. To use a supercapacitor and rechargeable battery, connect the battery and supercapacitor in parallel, connect the fuel cell output to these, and draw your power from the supercapacitor and battery connected leads. With these system additions you will need a diode so that reverse flow does not occur to the fuel cell stack, and fuse the circuit on both sides in case of shorts. A switch, either remote or direct, should be used to connect the power supply with any lines or equipment being powered. If you have AC power requirements you will need an inverter to convert DC to AC electricity. 

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. 

Semiconductor switches in power electronic inverters are commonly made up of a transistor together with a diode in anti-paraUel connection as depicted in Fig. 2.13a for a bipolar transistor to provide a path for an inductive load current when conducting switches are turned off and thus to avoid damage of the transistors in an inverter. MOSFET transistors have a built-in diode. Figure2.13b shows a bond graph model of such a transistor-diode pair. 

With the capacitor disconnected again, the scope will show the "full wave" pattern in the figure, when the second diode is connected via the dashed line wires. This "inverts" negative half-waves and then inserts them as positive halves, fitted into the otherwise-empty time slots between the first half-waves. With the capacitor attached again, there is less ripple, even with a IK resistor load. Also, twice as much power can be taken from this "dc power supply" circuit, without draining the capacitor to the point where the output voltage is much lower than desired. Therefore a full wave rectifier yields higher power with less ripple. 

The arrangement of the key components of a single-phase inverter is shown in Figure 10.9. There are four electronic switches, labelled A, B, C, and D, connected in what is called an H-bridge. Across each switch is a diode, whose purpose will become clear later. A resistor and an inductor represent the load through which the AC is to be driven. 

The basic operation of the inverter is quite simple. First switches A and D are turned on and a current flows to the right through the load. These two switches are then turned off at this point we see the need for the diodes. The load will probably have some inductance, and so the current will not be able to stop immediately, but will continue to flow in the same direction, through the diodes across switches B and C, back into the supply. The switches B and C are then turned on, and a current flows in the opposite direction, to the left. When these switches turn off, the current free wheels on through the diodes in parallel with switches A and D. 

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