Page 126 - Rashid, Power Electronics Handbook

7 Insulated Gate Bipolar Transistor 113

(C ) is implicitly de®ned by the emitter-base voltage as a GATE
eb
function of base charge; I ceb is the emitter-base capacitor
current that de®nes the rate of change of the base charge. CATHODE
The current through the collector-emitter redistribution capa- g
citance (I ccer ) is part of the collector current, which in contrast xa
to I css depends on the rate of change of the base-emitter
voltage; I bss is part of the base current that does not ¯ow C C
through C eb and does not depend on the rate of change of gs gd
base-collector voltage.
Impact ionization causes carrier multiplication in the high c s
electric ®eld of the base-collector depletion region. This carrier I mos d
C
multiplication generates an additional base-collector current dsj
component (I ), which is proportional to I , I , and the
mult c mos
multiplication factor. The resulting Saber IGBT model should
be able to describe accurately the experimental results for the I
c I
range of static and dynamic conditions where IGBT operates. mult
Therefore, the model can be used to describe the steady-state I b I
ccer ceb
and dynamic characteristics under various circuit conditions.
I I
The currently available models have different levels of css bss
C cer C eb
accuracy at the expense of speed. Circuit issues such as
switching losses and reliability are strongly dependent on the
device and require accurate device models. However, simpler
models are adequate for system-oriented issues such as the
behavior of an electric motor driven by a PWM converter. e
Finite-element models have high accuracy, but are slow and
require internal device structure details. Macromodels are fast R b
but have low accuracy, which depends on the operating point.
a
Commercial circuit simulators have introduced 1D physics-
ANODE
based models, which offer a compromise between the ®nite-
element models and macromodels. FIGURE 7.17 IGBT circuit model.

power module (IPM) is an attractive power device integrated
7.8 Applications with circuits to protect against overcurrent, overvoltage, and
overheating. The main application of IGBT is for use as a
switching component in inverter circuits, which are used in
Power electronics evolution is a result of the evolution of both power supply and motor drive applications. The advan-
power semiconductor devices. Applications of power electro- tages of using IGBT in these converters are simplicity and
nics are still expanding in industrial and utility systems. A modularity of the converter, simple gate drive, elimination of
major challenge in designing power electronic systems is snubber circuits due to the square SOA, lower switching loss,
simultaneous operation at high power and high switching improved protection characteristics in case of overcurrent and
frequency. The advent of IGBTs has revolutionized power short-circuit fault, galvanic isolation of the modules, and
electronics by extending the power and frequency boundary. simpler mechanical construction of the power converter.
During the last decade the conduction and switching losses of These advantages have made the IGBT the preferred switching
IGBTs have been reduced in the process of transition from the device in the power range below 1 MW.
®rst- to the third-generation IGBTs. The improved character- Power supply applications of IGBTs include uninterruptible
istics of the IGBTs have resulted in higher switching speed and power supplies (UPS) as is shown in Fig. 7.18, constant-
lower energy losses. High-voltage IGBTs are expected to take voltage constant-frequency power supplies, induction heating
the place of high-voltage GTO thyristor converters in the near systems, switch mode power supplies, welders (Fig. 7.19),
future. To advance the performance beyond the third-genera- cutters, traction power supplies, and medical equipment
tion IGBTs, the fourth-generation devices will require exploit- (CT, X-ray). Low-noise operation, small size, low cost and
ing ®ne-line lithographic technology and employing the high accuracy are characteristics of the IGBT converters in
trench technology used to produce power MOSFETs with these applications. Examples of motor drive applications
very low on-state resistance. Intelligent IGBT or intelligent include the variable-voltage variable-frequency inverter as is