The limited value of the insolated-gate bipolar transistors (IGBTs) blocking voltage is an important issue for applying these devices to the high-voltage power converters. An effective solution is to use a series configuration of these devices in order to achieve higher voltage ratings in addition to save the interesting features such as fast rising time. To reach this goal, acceptable equal voltage sharing for the IGBTs are provided by the series stacking schemes in the normal operation. However, a considerable difference in their voltage level will be occurred in the short-circuit condition. Although the IGBT can withstand the short-circuit current in a defined time, the occurred high voltage stress for the IGBT is fatal in such condition. To solve the mentioned problem, this paper proposes a short-circuit protection system suitable for the series stacked IGBTs. Using this proposal, the safe voltage level for IGBTs as well as the adequate time for the performance of the detection and elimination of the short-circuit fault will be provided. Each IGBT can have a different short-circuit current in the active region since the proposed scheme makes the IGBTs independent in terms of the current in the series structure. An external resistor added to the IGBTs emitter improves the equality of the IGBTs short-circuit currents and consequently their voltage sharing. This resistor controls the system short-circuit current by changing the operating point of IGBTs in active region in the short-circuit fault. The experimental and simulation results show that the safe condition is provided for the IGBTs under the short-circuit fault.

A Series Stacked IGBT Switch With Robustness Against Short-Circuit Fault for Pulsed Power Applications

Limited by low availability, high price, and poor switching performance of high-voltage power devices, connecting low-voltage devices in series to block much higher voltages is always an option. However, severe voltage unbalance during turn-off transient remains to be solved. Most of the existing methods designed for low-speed silicon (Si) insulated gate bipolar transistor (IGBT) cannot be directly transplanted to the series-connected silicon carbide (SiC) MOSFETs with high switching speed. To maximum the switching performance of SiC MOSFETs, an elegant implementation of adjusting driving signal time delay method is proposed. In addition, a simplified model during drain–source voltage rising transient is discussed to basically reveal features and problems of the series-connected SiC MOSFETs. The factors affecting the appropriate time delay are discussed as well, especially the influence of the load current. The simplified model and the implementation are both verified by experiments. Indeed, the proposed active voltage balancing control works well and has no penalty of sacrificing switching performance of SiC MOSFETs.

An Active Voltage Balancing Control Based on Adjusting Driving Signal Time Delay for Series-Connected SiC MOSFETs

Pulsed electric field (PEF) technology is a promising nonthermal processing techniques that can be utilized to inactivate microorganisms in liquid food with high-voltage PEF. Herein, a high-voltage solid-state switch consisting of 64 insulated gate bipolar transistors (IGBTs) connected in series was designed and developed for the PEF treatment. Regarding the unbalanced sharing of voltage in series-connected IGBTs, the resistor–capacitor–diode snubber circuit was specifically used and investigated in terms of model of parameters. Furthermore, using gate drivers and optic fiber, the driving circuit and protection circuit were designed and validated. A 50-kV isolation level power supply was built in order to provide 16 independent IGBT stacks with 24 V of power each. The results show that the developed switch works adequately a delay time of 380 ns with 35.8-kV voltage and 44.8-A current capacity. Moreover, the response time of the short-circuit protection is acceptable as well with a reaction time of under $7~\mu \text{s}$ . In conclusion, the switch designed for PEF treatment of liquid food performs within set parameters and is ready for pilot-scale processing capability.

A High-Voltage Solid-State Switch Based on Series Connection of IGBTs for PEF Applications

Growth in high-voltage power-conversion applications in recent years shows the importance and requirement of high-voltage/high-power converters in power electronic applications. The major limitation in this industry is the maximum voltage blocking capability of semiconductor switches. To overcome this restriction, the power switches are connected in series to build a high-voltage compact switch. This paper proposes a modified circuit based on quasi-active gate control, which provides the capability of connecting a desired number of insulated gate bipolar transistors (IGBTs) in series. In addition, overcoming the limitation of balancing capacitors’ sizing, alleviation of low-frequency oscillations, and better turn-OFF characteristics are some improvements obtained by the proposed circuit. Simulation results show an excellent voltage balancing between four and eight series-connected IGBTs. Also, experimental results are presented to verify the performance of the proposed circuit.

A Gate Driver Circuit for Series-Connected IGBTs Based on Quasi-Active Gate Control

Clamp mode snubbers are very well suited for the series structure of the insulated-gate bipolar transistors (IGBTs) in pulsed power applications. They properly meet the necessities expected from them such as the fast operating of the series IGBTs since they have no effect on the gate side. In addition, they can provide safe voltage condition for the IGBTs in short circuit faults, which are very probable in pulsed applications. The clamp mode snubber can perform its voltage balancing task whenever the power capacity of the snubber can support the injected powers due to the voltage unbalancing factors. This paper initially introduces the main factors injecting power to the snubbers. Then, it will be illustrated that the exact injected power to each predetermined snubber cannot be determined due to the uncertainties about the effect of the voltage unbalancing factors. Although it is impossible to determine the exact value of the power injected to each snubber, the total injected powers to the snubbers can be calculated. Therefore, as an effective remedy, this paper proposes a concentrated snubber. Using the proposal, all the injected powers are conducted to a centralized circuit and can be easily managed. In addition, analytical expressions are provided for proper dimensioning of the proposed concentrated snubber elements. Furthermore, the performance of the proposed concentrated snubber is evaluated using simulations and experimental prototyping.

A Series Stacked IGBT Switch Based on a Concentrated Clamp Mode Snubber for Pulsed Power Applications

The series configuration of fast semiconductor switches seems to be the key component in the high-voltage and fast rising time pulse generation In this approach, two important issues must be considered The first is to provide a safe operating condition for the switches in transient intervals The second is to design a gate drive system with the capability of driving a large number of discrete devices simultaneously The aim of this paper is to obviate these two requirements First, different factors affecting the unbalanced voltage sharing between the series switches are discussed In this investigation, the switch-to-ground parasitic capacitance effect has been recognized as the major effect on the unbalanced voltage sharing in the transient interval Two schemes for abating this effect are proposed To solve the unbalanced voltage distribution, the structure with a snubber circuit in the clamp mode operation is suggested This scheme can be used for any number of switches without destructively affecting their behavior In addition, the output pulse with a fast rising time could be obtained by the proposed gate drive system In order to evaluate the operation of the proposed structure, a stacked switch with the voltage capability of 36 kV is tested experimentally The characteristics of the obtained pulse are the fast rising time (695 ns) with the dV/dt of 460 kv/ $\mu \text{s}$ and the wide range of the pulsewidth adjusting to 05–15 $\mu \text{s}$  In addition, the voltage variance of the switches level in the series structure is about 10%

A Fast and Series-Stacked IGBT Switch With Balanced Voltage Sharing for Pulsed Power Applications

The safe operating condition for the vacuum tubes is very important and critical since they are very expensive and delicate. Providing limited short circuit energy for the vacuum tube and fast transferring from the short circuit to the nominal operation state are absolutely necessary. Extant protection strategies threat the availability of the vacuum tubes. In addition, they cannot completely protect the tube due to the delay of the fault detection system. This article proposes a high voltage (HV) short circuit fault current limiter which can limit the short circuit energy of the system inherently. The proposed structure activates automatically when the current exceeds the predetermined value. Hence, the need for the fault detection unit is minimized. The proposed short circuit fault current limiter is based on the series insulated gate bipolar transistors (IGBTs). Due to the interesting current limiting feature of the IGBTs, the short circuit current is limited for a definite time. During this time interval, the vacuum arc interrupts and the tube can operate instantaneously. In order to provide a safe operating condition of the series-connected IGBTs in the short circuit fault, several external circuits are suggested. The proper operation of the proposed short circuit fault current limiter is evaluated using simulations and experimental prototyping.

A Series Stacked IGBT Switch to Be Used as a Fault Current Limiter in HV High-Power Supplies

Applying series configuration of the insulated gate bipolar transistors (IGBTs) to the pulsed power supplies offers unique features such as compactness and long life time. In the high-voltage pulsed power supplies, a large number of the IGBTs are required to be serially connected. Hence, the safe operating condition provision for the series IGBTs is an important and crucial issue. The effect of the voltage unbalancing factors becomes remarkable when the number of switches in the series structure increases. There are passive and active methods to balance the voltage of the series IGBTs. In both of these methods, an amount of power must be dissipated to remove the effect of the voltage unbalancing factors. Consequently, the power loss is considerable when a large number of series devices are necessary. This paper proposes an effective power recovery system that recovers the power associated with the series stacking of the IGBTs. Using this proposal, the efficiency of the resulted series switch enhances considerably. The power recovery system can be implemented easily for any number of series IGBTs. It consists of a simple dc–dc converter and several interconnection diodes for power recovery procedure. Proper performance of the proposed structure is evaluated by the aid of simulations and experiments.

Mostafa Zarghani

Papers

A Fast and Series-Stacked IGBT Switch With Balanced Voltage Sharing for Pulsed Power Applications

A Series Stacked IGBT Switch Based on a Concentrated Clamp Mode Snubber for Pulsed Power Applications

A Series Stacked IGBT Switch to Be Used as a Fault Current Limiter in HV High-Power Supplies

A High-Voltage Series-Stacked IGBT Switch With Active Energy Recovery Feature for Pulsed Power Applications

RCD snubber design based on reliability consideration: A case study for thermal balancing in power electronic converters