Papers by Mostafa Zarghani
A Distributed Turn-off Delay Compensator Scheme for Voltage Balancing of Series-connected IGBTs
IEEE journal of emerging and selected topics in power electronics, 2024
IEEE Transactions on Power Electronics, 2021
This paper proposes a scheme for balancing the voltage of series-connected Insulated Gate Bipolar... more This paper proposes a scheme for balancing the voltage of series-connected Insulated Gate Bipolar Transistors (IGBTs), which is also very effective under short-circuit conditions. An optimized clamp-mode snubber is proposed, including an active-driver to balance the currents of the IGBTs during short-circuit, which in turn allows a considerable reduction of the snubber capacitance. The approach is proven to be effective under short-circuit conditions by a maximum 10% voltage imbalance and a negligible difference in the current values. The effectiveness of the proposed approach is demonstrated through simulations in PSPICE software and experimental tests performed at 2000 V.
A High-Voltage Pulsed Power Supply With Online Rise Time Adjusting Capability for Vacuum Tubes
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021
Vacuum tubes such as gyrotrons and magnetrons require a specific range of high-voltage pulse rise... more 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.
2021 IEEE Energy Conversion Congress and Exposition (ECCE), 2021
This paper presents an energy recovery scheme for traditional Resistor-Capacitor-Diode (RCD) snub... more This paper presents an energy recovery scheme for traditional Resistor-Capacitor-Diode (RCD) snubber in the series-connected configuration of IGBTs. In the series configuration of IGBTs, an RCD snubber is used in parallel to each IGBT to provide a safe operating condition for the IGBTs. In the proposed scheme, by using interconnection diodes, the capacitors of the snubbers are parallelized in the on-state of the IGBTs. Thus, the stored energies in the snubber capacitors are lumped together and transferred to the DC link by using a transformer and a resonant circuit. By using of the proposed method, the capacitor of the snubber can have a higher value. Higher value of the snubber capacitance improve voltage sharing of the IGBTs and reduce the turn-off switching power losses of the IGBTs. The proposed scheme is simulated for a case study using PSPICE software and tested through an experimental setup. Simulation and experimental results imply the proper performance of the proposed scheme.
A Series Stacked IGBT Switch to Be Used as a Fault Current Limiter in HV High-Power Supplies
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021
The safe operating condition for the vacuum tubes is very important and critical since they are v... more 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 Voltage Balancing Scheme for Series IGBTs to Increase Their Expected Lifetime in Pulsed Load Applications
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021
Clamp mode resistor capacitor diode (CMRCD) snubbers have a simple and easy implementing structur... more 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 Method for Series-Connected IGBTs Operating as a Fault Current Limiter in High-Voltage DC Power Supplies
IEEE Transactions on Industrial Electronics, 2020
This article proposes a high-voltage fault current limiter (HVFCL) for high-voltage dc power supp... more 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.
IEEE Transactions on Power Electronics, 2020
This paper describes the development of an 18 kV, 30 kW power supply for a pulsed current load wi... more This paper 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: 1) A considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. 2) 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 paper 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 not any need for the 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 600nF 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.
IEEE Transactions on Industrial Electronics, 2019
Applying series configuration of the insulated gate bipolar transistors (IGBTs) to the pulsed pow... more 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 switches number 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.
IEEE Transactions on Power Electronics, 2019
Microelectronics Reliability, 2018
In a turn-off RCD snubber, the capacitor value is usually optimized in order to minimize the powe... more In a turn-off RCD snubber, the capacitor value is usually optimized in order to minimize the power dissipated in the switch and snubber circuit. However, it may not be the best value of the snubber capacitor from the reliability point of view. In this paper, the capacitor value is optimized based on reliability considerations. Proposed method presents a new design to achieve the maximum reliability for the set of switch and its snubber. Mathematical analysis of the proposed method is conducted in MATLAB environment. Also, the experimental results are presented for validity of the theoretical analysis.
Fault-Tolerant DC Power Distribution Unit Based on Nonexclusive Redundant Modules
IEEE Transactions on Industrial Electronics, 2016
Reliability of the power distribution unit (PDU) is very important in electrical systems. Since a... more Reliability of the power distribution unit (PDU) is very important in electrical systems. Since any failure in this unit leads to system failure. A commonly used method for increasing the reliability of a dc PDU is using the redundant modules. If a fault occurs in a voltage regulator of PDU, it is replaced by its redundant module. In conventional redundancy, each dc voltage regulator has its exclusive redundant modules. Therefore, if both a regulator and its redundant modules fail, the system is stopped. It is an important drawback since the exclusive redundant modules of other voltage regulators may not be used, but, the PDU cannot use them instead of faulty regulators. In this paper, the application of the nonexclusive redundant regulators is presented for solving this problem. In the proposed method, dc power distribution unit consists of a number of redundant modules, which can be adjusted to a desired voltage and can be used instead of faulty regulators. An analysis based on Markov model is presented to compare reliability of the proposed structure with the conventional structure presuming a variable failure probability. Theoretical study indicates more reliable operation of the proposed PDU structure than the conventional structure. Experimental results are presented to show practical considerations of the proposed structure and its proper performance.
IEEE Transactions on Plasma Science, 2016
The series configuration of fast semiconductor switches seems to be the key component in the high... more 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 (69.5 ns) with the dV/dt of 460 kv/µs and the wide range of the pulsewidth adjusting to 0.5-15 µs. In addition, the voltage variance of the switches level in the series structure is about 10%.
A Very Low-Ripple High-Voltage High-Power DC Power Supply Using an Interleaved Converter and a Linear Ripple Elimination Unit
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021
High-voltage dc power supplies (HVDCPSs) have been widely adopted for the vacuum tubes. In this a... more 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%.
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Papers by Mostafa Zarghani