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

This article proposes a high-voltage fault current limiter (HVFCL) for high-voltage dc power supplies (HVdcPSs) which limits the current of the power supply automatically in the short-circuit fault (SCF). The proposed HVFCL is based on the series-connected insulated gate bipolar transistors (IGBTs). The main achievements of this article are the balanced voltage sharing and a very low value of the short-circuit current near to the load nominal current for the series-connected IGBTs during the SCF. These achievements result in a longer maximum permissible short-circuit time. These achievements are obtained by a control strategy that puts the series-connected IGBTs in a specific operating point in the active region during the SCF. Based on the proposed master–slave control strategy, one of the IGBTs is current controlled and rolls as the master. The other IGBTs are voltage controlled and imitate the master IGBT voltage. Consequently, a balanced voltage sharing is guaranteed for the series-connected IGBTs in the SCF. PSPICE simulations and experimental results are provided to verify the proper performance of the proposed HVFCL.

A Voltage Balancing Method for Series-Connected IGBTs Operating as a Fault Current Limiter in High-Voltage DC Power Supplies

Clamp mode resistor capacitor diode (CMRCD) snubbers have a simple and easy implementing structure. They have been widely adopted in the pulsed power supplies to provide a safe operating condition for the series insulated gate bipolar transistors (IGBTs). The main problem of the CMRCD snubbers is their poor performance in the voltage balancing of the series IGBTs. They are essentially overvoltage protectors and clamp the voltage of the IGBTs in a probable potentially dangerous condition. This issue diminishes the expected lifetime of the series IGBTs, where a number of them face a higher level of the voltage than that of the others. The unbalanced voltage of the series IGBTs will result in a lower value of the expected lifetime of the series IGBTs. For improving the expected lifetime of the series IGBTs a CMRCD snubber with balanced voltage sharing for the series IGBTs is proposed. Adopting this proposal will lead to the balanced voltage sharing of the series IGBTs, even in the blocking voltage below the nominal designed value. Consequently, the highest value of the lifetime is estimated for the series IGBTs in the stack. The simulation and experimental results truly demonstrate the effectiveness of the proposed structure.

A Voltage Balancing Scheme for Series IGBTs to Increase Their Expected Lifetime in Pulsed Load Applications

Vacuum tubes such as gyrotrons and magnetrons require a specific range of high-voltage pulse rise time for their proper operation. Otherwise, unavoidable operation modes or even arcs may take place in the vacuum tubes. Hence, the capability of the adjustable output pulse rise time is very promising for pulsed power supplies when they are dedicated to vacuum tubes. This article proposes a high-voltage series stacked insulated gate bipolar transistor (IGBT) switch with rise time adjusting capability to evolve the pulsed power supply abilities. The rise time adjustment is carried out using a low-voltage ramped shape signal provided for all the IGBTs via a multi-winding transformer. In this way, the IGBTs are turned on as fast as possible with specific delays. The sequential turn on process of the IGBTs forms the output pulse rising edge. Unlike the extant strategies for controlling the turn on speed of the IGBTs, the dissipated power of the proposed method is negligible. The power associated with adjusting the output pulse rise time is recovered to the pulsed power supply using a simple and low-voltage dc/dc converter. The proper performance of the proposed structure is evaluated using simulations and experimental prototyping.

A High-Voltage Pulsed Power Supply With Online Rise Time Adjusting Capability for Vacuum Tubes

This article describes the development of an 18 kV, 30 kW power supply for a pulsed current load with the maximum current of 20 A and a di/dt equal to 100 A/μs. The achieved output ripple is less than 0.01%. In such a high level of precision, the most important issues are considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. Very low level of the voltage feedback and its sensitivity to the noise. The first issue necessitates a notable overdesign of the converter switches if the output voltage precision is dedicated to the converter. The second issue raises the problems relevant to observing the voltage ripple and providing it for the control loop. This article proposes, a fast and high current linear regulator developed based on the load current feedforwarding. Using this approach, the fast regulator compensates the voltage change caused by a high level of instantaneous power. The main converter maintains the average power. Thus, there is no need for converter overdesigning. Furthermore, the problems relevant to the high voltage feedback and providing it for the control loop are removed. The voltage feedback is solely served to correct the current loop probable error. Hence, the sensitivity of the control loop against the existing noise is minimized. Despite existing a 600 nF capacitor as the output capacitor, the output voltage drop is less than 0.01% in a wide range of the output current pulse up to 250 μs. The power supply is constructed and experimental results are provided to verify the mentioned specifications.

An Extremely Low Ripple High Voltage Power Supply for Pulsed Current Applications

High-voltage dc power supplies (HVDCPSs) have been widely adopted for the vacuum tubes. In this application field, the low ripple voltage cannot be easily achieved by increasing the size of the output capacitance of the HVDCPS due to the limited permissible level of the stored energy. To obtain a low level of the output ripple as well as the limited value of the stored energy, the previously published literature proposed switching frequency increment. This approach has several shortcomings such as switching power loss increment, a limited level of the achievable ripple, and low value of the insulators’ lifetime. To improve the mentioned deficiencies, this article hybridizes the series linear regulator and a high-frequency high-power dc interleaved converter. Using the proposed method, at the first stage, the level of the ripple decreases to a rational margin with increasing the ripple frequency. At the second stage, the level of the ripple reduces using the linear regulator to reach the expected precision. In order to validate the performance of the proposed structure, simulation and experimental results are provided for a 15-kV and 22.5-kW converter with the output voltage precision of 0.02%.

Mostafa Zarghani

Papers

A Voltage Balancing Method for Series-Connected IGBTs Operating as a Fault Current Limiter in High-Voltage DC Power Supplies

A Voltage Balancing Scheme for Series IGBTs to Increase Their Expected Lifetime in Pulsed Load Applications

A High-Voltage Pulsed Power Supply With Online Rise Time Adjusting Capability for Vacuum Tubes

An Extremely Low Ripple High Voltage Power Supply for Pulsed Current Applications

A Very Low-Ripple High-Voltage High-Power DC Power Supply Using an Interleaved Converter and a Linear Ripple Elimination Unit