the control. Only one transistor gate drive circuit is needed for each switch cell. The
disadvantage is that the conduction losses are relatively high. During the conduction
stage, the three devices are conducted (two diodes and IGBT transistor). Moreover,
the direction of current through the switch cell cannot be controlled. The two most
commonly used configurations of switch cell are named the common emitter antiparalleled
IGBT configuration (Fig. 2.10b) and the common collector anti-paralleled
IGBT configuration (Fig. 2.10c). Each of these switch cells consist of two diodes and
two IGBT switches that are connected in an anti-parallel arrangement. The diodes are
included to provide reverse blocking capability, whereas, the IGBTs enable the independent
control of the current direction. Compared to the diode bridge switch cell
(Fig. 2.10a), here conduction losses are reduced, because only two devices are conducted
in each conduction path. Its disadvantage is the requirement of two gate drive
circuits for each IGBTs. For the arrangement shown in Fig. 2.10b, due to its common
emitter arrangement, one isolated power supply is required for each bi-directional
switch cell. Furthermore, by using common collector bi-directional switch cells
(Fig. 2.10c), the number of isolated power supplies required for the gate drive circuits
can be reduced to six. Finally, the switch cell is the anti-paralleled reverse blocking
IGBTs (RB-IGBT) [130], an arrangement shown in Fig. 2.10d [123, 149]. The main
feature of the RB-IGBT is its reverse voltage blocking capability, which eliminates
the use of diodes. For this reason there is a reduction in the number of discrete
devices and conduction losses. At any instant, there is only one device conducting
current in any direction. In this configuration, 18 gate drive circuits and six isolated
power supplies is required. Therefore, an anti-paralleled RB-IGBT configuration is
generally preferred for creating matrix converter bi-directional switch cells. The element
complexity of matrix converters with different switches cells is described in
Table 2.3 [21].
Furthermore, other switching devices, besides IGBT, could be used in MCs.
If the switching devices used for the bi-directional power switch have a reverse
voltage blocking capability, then it is possible to build bi-directional switches. For
example, MOS turn-off thyristor (MTOs), GTO thyristor and pure JFET may be an
applicable [93].
The first key problem is related to the practical realisation of bi-directional
switches. Currently, there are no small bi-directional power switches that are