Experimental comparison of methods of employing IGBTs connected in series

Series connecting devices for high-voltage power conversion

“…Previously reported experimental investigations have shown that modern power-semiconductor devices, such as IGCTs, IGBTs and power MOSFETs, may be series connected and operated synchronously as single switches in high-voltage chopper, inverter and pulsedpower applications [1][2][3][4][5][6], and series-connected devices are now being used in IGCT and IGBT applications [8] What makes possible direct series operation is the use of an effective voltage balancing scheme, which ensures that the composite switch voltage drop is evenly distributed between the devices in a string during blocking (static voltage balancing) and during switching (dynamic voltage balancing). Without enforced voltage balancing, repeated device breakdown within strings would almost certainly occur because of the variability in off-state leakage current and switching characteristics which arise in practical circuits; not only due to production spread in device characteristics, but also due to imperfect synchronisation of isolated drive signals, imbalance in common-mode voltage effects, and imperfect matching of the electrical and thermal impedances of device packages and other related hardware [2,3].…”

“…In recent work on series device operation, a number of efficient innovative voltage-balancing schemes have been developed. Although, no single method outperforms all others in ease of implementation and minimising device switching-loss and -stress, there is some convergence towards using active voltage balancing with IGBTs [3][4][5][6] An important advantage of these schemes is their improved capability to provide voltage equalisation or clamping only when required, and to thus avoid the continuous power loss of conventional snubbers which are designed and operated as if worst-case conditions of device mismatch and high load-current are continually prevalent. Alternative voltage balancing schemes do, however, lack the ease of application and scalability of simple passive methods.…”

Integrated Solution for Driving Series-Connected IGBTs and Its Natural Intrinsic Balancing

“…Some IGBTs series connection techniques were introduced and discussed in [1][2][3][4], which summarized that the difficulties of this association were related to the following intrinsic characteristic differences in: Leakage currents (Ices); tail currents; output capacitances (Cce); gate threshold voltages (Vth); gate-emitter capacitances (Cge). As well as the following extrinsic characteristics, referring to the load and gate circuit differences in: Series parasitic inductances between devices; control circuits, due time delays between parallel firing channels; parasitic capacitances of each gate driver power supply.…”

“…The first one is the load-side balancing and uses simple circuits such as passive snubbers C, RC, RCD, PC [5,10] or more complex circuits such as active snubbers [15,16]; The other is the gate-side balancing, where the firing circuit is used to actively act on the current or voltage profile of the gate. Also, for practical elucidation, a turn-on transient example [4], is presented in Figure 2b where a voltage zoom shows clearly a poor dynamic voltage sharing when no-balancing method is applied. In [1], an active firing solution for series-connected IGBTs was described and an analogue feedback control circuit was used.…”

Parameters influencing the performance of an IGBT gate drive

“…1, where the collector-emitter voltage (V ce ) is intended to follow a predefined reference signal. V ce is fed back to the controller via a potential divider and compared with a reference voltage by means of a wide band current feedback operational amplifier [8]. The reference voltage is produced locally in the gate drive in response to raw on/off digital pulses.…”