INVERTER I TECHNOLOGY
IGBT by creating a high carrier concentration similar to that of a thyristor, allowing the saturation voltage to be much lower than a conventional IGBT and comparable to the forward voltage of the thyristor. The blocking voltage is also higher than that of an IGBT, and similar to that of a thyristor.
Figure 1. Latest hybrid silicon-IEGT/SiC-SBD half-bridge module.
main switching element. Both device types have strengths and weaknesses, which force designers to make a selection that will deliver the best compromise in relation to a given application.
Power switch performance Generally, thyristors have a low forward voltage, resulting in low conduction losses, but can require more complicated commutation circuitry to turn the device off. The Gate Turn Off (GTO) thyristor overcomes this reliance on commutation circuitry, although switching effi ciency remains lower than that of an IGBT.
The IGBT combines the advantage of a voltage-controlled Metal- Oxide Semiconductor (MOS) gate, which allows relatively simple gate-drive circuitry, with the low saturation voltage of a bipolar transistor. Its ability to support high switching frequencies allows the use of smaller capacitive and inductive components. The IGBT also has a large Safe Operating Area (SOA), which helps enhance safety and reliability. The one drawback of the IGBT is its relatively high saturation voltage, compared to the thyristor’s low forward voltage, resulting in higher conduction losses which can impair overall energy effi ciency.
Injection enhancement gate transistors In recent years we have seen the development of the Injection Enhancement Gate Transistor (IEGT). These combine the ease of use, support for high switching speeds, and large SOA of the IGBT with high conduction effi ciency normally associated with a thyristor–based design.
The IEGT is a high-power trench MOS gate device that behaves in the same way as an IGBT, yet has a low saturation voltage comparable to the forward voltage of a thyristor. The thyristor’s low forward voltage is the product of high carrier concentration resulting from the injection of electrons at both the anode and the cathode. In contrast, the conduction performance of a conventional IGBT is governed by the movement of holes from the collector to the emitter resulting in a relatively low carrier concentration at the emitter side.
The IEGT process, combined with an optimised gate structure and distance between electrodes, overcomes this limitation of the
Figure 2b. Comparison of module reverse-recovery losses with silicon and silicon-carbide diodes.
Issue IV 2014 I
www.solar-international.net 19
Diode reverse recovery In power-conversion applications where anti-parallel diodes are connected to conduct freewheel currents, the reverse- recovery characteristic of the diode has an important effect on the operating effi ciency of the circuit. When conducting freewheeling current, the diode stores charge as minority carriers that contribute to minimising the diode forward voltage. When the diode is commutated, this stored charge must be neutralised by recombination and reverse-current fl ow before the diode can behave as if turned off. This process of reverse recovery contributes a proportion of system energy losses.
To minimise these losses, equipment designers have typically used ultrafast or hyperfast silicon Fast-Recovery Diodes (FRDs)
Figure 2a. Module turn-on energy and reverse-recovery current with FRD and SiC SBD.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96