Series-connected Insulated Gate Bipolar Transistors Research Articles

An Online Condition Monitoring Method for Series-Connected IGBTs to Avoid Cascading Failure

The series-connected insulated gate bipolar transistors (IGBTs) have numerous applications in industry and research fields. One of the risks of the resultant series high-voltage switch (RSHVS) is the IGBTs short circuit failure. The number of the IGBTs in a RSHVS is usually designed with an appropriate voltage de-rating factor to make it resilient against a limited number of the IGBTs short circuit failures. However, by the increased number of failures, the withstand voltage of the healthy IGBTs finally violates the IGBTs' tolerable voltage in the off-state. In such conditions, a cascading failure occurs and breaks all remaining healthy IGBTs. This paper proposes a condition monitoring (CM) method to avoid cascading failure in RSHVSs. The proposed method works based on the change of the rising edge of the load current in the RSHVS turning-on time. It will be shown when some of the IGBTs in the series structure fail short, the turning-on time of the RSHVS increases. Thus, the rising edge of the current also increases which leads to the decrement of high-order harmonics magnitude. The proposed CM analyzes such harmonics and provides a constant voltage as the CM output. The performance of the proposed CM is evaluated using simulations and experiments for a RSHVS consisting of eight IGBTs.

Overvoltage Suppression Scheme for Minimized Snubber Requirements in MVDC Solid-State Breakers With Series-Connected IGBTs

Solid-state dc breakers are the ultimate technology for protecting medium-voltage dc grids having equipment vulnerable to excessive fault-current stress, due to the very short fault-clearing times. A typical implementation of such breakers is based on insulated gate bipolar transistors (IGBTs). However, as the rated voltage of the grid increases, series connection of IGBTs is inevitable and impose challenges on transient and steady-state blocking voltage distribution. This article presents a novel voltage-balancing scheme that combines passive resistive-capacitive-diode (RCD) snubber circuits and a gate driver containing a gate-current balancing magnetic-core. The proposed concept aims at minimizing the required snubber capacitances, which may be high. The impact of the proposed configuration on the breaker design and its performance are studied under different fault scenarios. Using the proposed breaker configuration, the snubber capacitance has been reduced by up to 60%. Besides, both simulations and experimental results reveal the mitigation of high peak voltage stress across the early turned-off IGBTs under gate signal propagation delays.

Voltage Balancing of Series IGBTs in Short-Circuit Conditions

This article 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 for a considerable reduction of the snubber capacitance. The approach is proven to be effective under short-circuit conditions by a maximum of 55 V voltage increment 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 2 kV.

Design new voltage balancing control series connected for HV-IGBT`s

<span>The insulated gate bipolar transistors (IGBTs) are widely used in various applications as they require low gate drive power and gate voltage. This paper proposes an active gain circuit to maintain voltage stability of series-connected IGBTs for high voltage applications. The novel gate driver circuit with closed-loops control amplifies the gate signal while restricting the IGBT emitter voltage below a predetermined level. With the proposed circuit, serial-connected IGBTs can replace high-voltage IGBTs (HV-IGBTs) for high-voltage applications through the active control of the gate signal time delay. Closed-loop controls function is to charged current to the gate to restrict the IGBT emitter voltage to a predetermined level. This paper also presents the experiment on the gate driver capability based on a series-connected IGBTs with three IGBTs and a snubber circuit. The experimental results show a voltage offset with active control with a wide variation in load and imbalance conditions. Lastly, the experimental results are validated with the simulation results, where the simulation results agree with the experimental results.</span>

An Active Voltage Balance Method Based on Adjusting Driving Signals Time Delay for Series-Connected IGBTs

Connecting low-voltage insulated gate bipolar transistor (IGBT) in series to withstand much higher dc -link voltages has some advantages over using a single high-voltage IGBT or the multilevel topologies. However, severe voltage imbalance during turn-off transient remains to be solved. In all existing methods, adjusting driving signal time delay (ADSTD) is attractive and has no penalty of sacrificing the switching performance of IGBT. Moreover, instead of using a snubber, the voltage imbalance caused by the difference in tail currents can be mitigated by using ADSTD as well. An active voltage balance method based on ADSTD is proposed and verified by experiments in this article. Besides, a more accurate equivalent capacitance for IGBT considering the stored carriers in the n-drift region is discussed. The factors affecting a proper driving signal time delay are also discussed in detail. These contents are well supported by experimental results as well.

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

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 Module-Based Self-Balancing Series Connection for IGBTs

This article presents a self-balancing technique for voltage sharing of series-connected insulated gate bipolar transistors (IGBTs). Each series IGBT is augmented with an auxiliary switch, which operates in complementary to the main one, and a capacitor in series. When gate signal delays, based on the capacitor voltage feedbacks, are applied to the series modules, the voltage sharing can be balanced. The delays are generated with local controllers without DSP/field-programmable gate array, regardless of the parasitic element distribution, thermal characteristics of the devices, or current amplitudes. Since there is no resistive element in the auxiliary branch, the balancing circuit is low loss. The circuit and the operation modes are provided in detail and illustrated with simulation models. Experimental results with ten series modules at different voltage levels are presented to demonstrate the principle of control, and the performance of the proposed technique.

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

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.

Repeater coil‐based wireless power transfer system powering multiple gate drivers of series‐connected IGBTs

It is challenging to power a large number of gate drivers of the series-connected insulated gate bipolar transistors (IGBTs) in a high-voltage application because multiple isolated power supplies are needed. In this study, a novel wireless power transfer (WPT) system using repeater coils is designed to solve this problem. Every two repeater coils form a repeater unit, which transfers power to one load. With multiple repeater units in the system, multiple loads can obtain power simultaneously. To eliminate undesirable magnetic couplings between these coils, bipolar coils are used and the two bipolar coils in the same repeater unit are placed perpendicularly. It is derived that constant voltage can be obtained for all the loads, which is especially suitable for powering the IGBT's gate driver. Moreover, the variation of one load power will not affect others. The receiving circuit is designed to transform the received power to the DC voltage compatible with the driving circuits. An experimental setup with six loads has been constructed to validate the proposed WPT system.

A Monopolar Symmetrical Hybrid Cascaded DC/DC Converter for HVDC Interconnections

With the rapid development of voltage source converter-based high-voltage direct current (HVdc) transmission, it is an irresistible trend that HVdc grid will come into being. High-voltage and high-power dc/dc converters will serve as dc transformers in HVdc grid to interconnect dc lines with different voltage ratings. This article proposes a monopolar symmetrical dc/dc converter which is composed of cascaded half-bridge submodules and series-connected insulated-gate bipolar transistors. This hybrid topology features low capital costs, high efficiency, small footprint, and bidirectional power transfer capability. Operation principle, parameter design, and the control strategies of this topology are introduced. A 480-MW, ±500 kV/±160 kV monopolar symmetrical dc/dc converter is simulated to verify its performance and evaluate the efficiency. In addition, a downscaled prototype rated at 2.4 kW, ±300 V/±100 V has been built and tested. Experimental results further validate the effectiveness of the proposed dc/dc converter.

Impact of snubber parameters on voltage sharing in series-connected insulated gate bipolar transistors

This paper shows the relationship between the circuit parameters and the voltage sharing performance in series-connected insulated gated bipolar transistors (IGBTs). A simple analytic model is proposed to examine voltage balancing in series-connected IGBTs. By the proposed model, the reason for voltage imbalance is easily analyzed. In addition, the impact of the time constant of the snubber, which is affected by the snubber components, is detailed. From this analysis, it has been demonstrated that the snubber capacitance should be at least double the output capacitance of the switching device to stabilize voltage sharing. To verify the usefulness of the proposed technique, a multiple pulse tester has been implemented and tested. Experimental results reveal that the error between the proposed model and the practical system is only 1.7%. In addition, the accuracy of the proposed model is high enough to be utilized for the analysis of the series-connected IGBTs.

Turn-Off Delay Compensation of Series-Connected IGBTs for HVDC Applications

This letter shows a computationally inexpensive delay compensation algorithm for series-connected insulated-gate bipolar transistors (IGBTs). The algorithm adjusts the relative turn-off delays among series-connected IGBTs based on the measured clamp capacitor voltages. Experimental results show that the capacitor voltage differences are compensated in a few iterations, making it suitable for delay compensation of industrial series-connected IGBTs.

A Power Relay System With Multiple Loads Using Asymmetrical Coil Design

In this article, we propose a power relay system to power multiple loads wirelessly via magnetic coupling. Multiple power relays are placed in a line and the power can be transferred between these relays. Each power relay consists of two relay coils, which function as the receiver and transmitter, respectively. In order to suppress the magnetic coupling between the two relay coils in the same power relay, bipolar coils are adopted and placed perpendicularly. A compensation capacitor is connected in series with each transmitting coil, while another one is connected in parallel with each receiving coil. It is derived that the constant voltage characteristics can be obtained for each load, which means the load power is decoupled from each other. The two coils in the same power relay have different inductance values, which form an asymmetrical structure to achieve equal load voltage distribution. Moreover, zero phase angle can be obtained for the input impedance. The proposed system is suitable to power the gate drivers of series-connected insulated gate bipolar transistors, where multiple isolated power supplies are needed. An experimental prototype with six loads has been constructed to validate the proposed system. The maximum efficiency can reach 94.0% at a power level of 12.6 W.

Modular Directed Series Multilevel Converter for HVDC Applications

Modular multilevel converter is the most prominent topology for high-voltage dc (HVDC) applications. However, it requires a large number and size of its submodule (SM) capacitors, proportionally large number of semiconductor switches and has high losses. To address some of these issues, the modular directed series multilevel converter (MDSMC) is proposed in this article. It requires significantly reduced size of SM capacitors and lower number of semiconductor switches and capacitors for the same power output. It is a hybrid topology having two main circuit components, namely, the chain-links consisting of a number of series-connected SMs and the director switches realized using a number of series-connected insulated-gate bipolar transistors (IGBTs). A detailed analysis and operating principles of MDSMC are presented to highlight its important features. The control and modulation schemes of MDSMC are presented that enable this converter to be utilized most effectively. The SMs capacitor size calculation is performed and compared with the major HVDC converters to validate its lowest capacitive energy storage requirement. The performance of MDSMC is evaluated using PSCAD/EMTDC for both standalone and HVDC systems under varying system conditions. Its ability to provide wide operating range and four-quadrant operation for HVDC application are also verified. Loss computation validates the ability of MDSMC to provide higher efficiency. A detailed comparison between MDSMC and other major HVDC converters is performed on the basis of their various structural parameters. Furthermore, a three-phase 13-level MDSMC experiment prototype is developed to validate its feasibility, operating principles, and control logic.

Plug-in gate-loop compensators for series-connected IGBT drivers in solid-state fault current limiter

Solid-state fault current limiter (SSFCL) is the key protective equipment in direct current distribution network. To meet the high voltage requirement meanwhile reduce the cost, implementing a SSFCL based on series-connected insulated gate bipolar transistors (IGBTs) is a promising way. However, voltage unbalancing of IGBTs would be introduced if the gate-loops of the IGBTs are non-identical. In this paper, a plug-in gate-loop compensator with discrete gate voltage feedback and pulsewidth current compensation is proposed. The main merits are 1) with the plug-in structure, the extra current sources only provide small power to fine-tune the gate-loop without affecting the functions provided by the commercial IGBT gate driver; 2) the gate-emitter voltages of IGBTs are compared with the preset thresholds to obtain control criterions, and the pulsewidths of the current sources are controlled for gate-loop compensation, thus both analog-digital and digital-analog converters are avoided; 3) the control law is easy to be implemented in FPGA, and is robust to voltage variation of power-loop. With the proposed compensator, the voltage unbalancing is alleviated immediately at the present switching cycle, and further eliminated cycle-by-cycle during current limitation process. Experimental results verify the feasibility of proposed compensator.

A Physics-Based Transient Electrothermal Model of High-Voltage Press-Pack IGBTs Under HVdc Interruption

The wide use of press-pack insulated-gate bipolar transistors (IGBTs) in high-voltage dc (HVdc) applications makes the accurate modeling of high-voltage press-pack IGBTs more urgent. Based on the mechanism of the switching transient, a physics-based electrothermal transient model of the high-voltage press-pack IGBT is proposed. Considering the wider base width of high-voltage IGBTs (HVIGBTs), a transient model of the HVIGBT with buffer layer is presented taking into account the carrier recombination in the base region and the injection level in the buffer layer. Besides, a modified thermal network of press-pack IGBTs is implemented considering the double-sided heat transfer structure. An electrothermal coupling model of high-voltage press-pack IGBTs is then obtained combining the proposed electro and thermal models. Finally, simulations of key dynamic performances of the proposed HVIGBT model match well with the testing results. Furthermore, the HVdc interruption process of a solid breaker with different number of series-connected IGBTs is simulated using the proposed IGBT model and tested. The testing results show good consistency between the simulated and measured voltage and current of the series-connected press-pack IGBTs, which brings strong support to the accurate design of solid breakers in the HVdc transmissions.

Balancing Algorithm for a Self-Powered High-Voltage Switch Using Series-Connected IGBTs for HVDC Applications

This paper presents a balancing algorithm for the so-called Director Switch, a controlled, reverse conducting, self-powered, high-voltage switch, using series-connected insulated gate bipolar transistors (IGBTs). This is a key component on two new voltage-source, high-voltage direct current (HVDC) converter topologies. These, which promise efficiency, cost, and size reductions, are an alternate arm converter and a series bridge converter. One of the main design challenges of the director switch is how to supply the IGBT gate drivers, and other auxiliary electronics while overcoming the high-voltage insulation barrier to ground level. In this paper, this is achieved by using the energy stored in a capacitive clamp snubber circuit, which also helps with the overvoltage mitigation during rare hard-switching events. However, the clamp capacitor and by proxy the IGBT voltages become highly unbalanced during operation, compromising the integrity of the switch. This paper presents a balancing strategy that consists in applying a controlled delay in the switching of the IGBT levels, in a way that forces a voltage balance on all the switch levels. The paper explains the unbalance. Then, the balancing strategy is explained and validated on simulation and on a high-voltage experimental rig, on switches comprising two and three series-connected IGBTs, respectively.

A Multiport Circuit Breaker-Based Multiterminal DC System Fault Protection

Although hybrid circuit breaker (HCB) uses a combination of mechanical switch and insulated-gate bipolar transistors (IGBTs) to accommodate HVDC application, it still has a large number of series-connected IGBTs in its main breaker. Besides, in multiterminal HVDC system, three or more HCBs appear in cluster at one node, which worsens the HCBs’ disadvantage in volume. To simplify the breaker cluster’s topology structure and control system as well as increase the compactness, a multiport circuit breaker (MPCB) is proposed in this paper with its control procedure presented. By assembling the HCBs at one node, it can not only cut down the component count for fault interruption remarkably but also reduces the number of control signals. Apart from this, due to a more compact structure, the proposed circuit breaker avoided the use of a dc bus and, hence, dc bus fault which will result in disconnecting the node completely from the system. Hence, regardless of faults and their fault locations, it is always able to connect the remaining healthy ports together. Finally, the effectiveness of the proposed MPCB in different fault scenarios is verified by RTlab.

A Non-Isolated Hybrid-Modular DC-DC Converter for DC Grids: Small-Signal Modeling and Control

This paper presents small-signal modeling, stability analysis, and controller design of a non-isolated bidirectional hybrid-modular DC-DC Converter for DC grid applications. The DC-DC converter can be used to interconnect two different DC voltage levels in a medium-/high-voltage DC grid. Half-bridge Sub-Modules (SMs) and a high-voltage valve are the main components of the converter. The high-voltage valve can be implemented via employing series-connected Insulated-Gate Bipolar Transistors (IGBTs). Operation with zero voltage switching of the involved high-voltage valve is feasible, i.e., there is no concern pertinent to dynamic voltage sharing among the series-connected IGBTs. The power is transferred from one side to another through the involved SMs, where their capacitors are connected in series across the high-voltage side, while they are connected sequentially across the low-voltage side. In this paper, the state-space averaging technique is employed to derive the small-signal model of the presented converter for controller design. Closed-form expression of the duty cycle-to-inductor current transfer function is extracted. Comparison between simulation results of the small-signal model and the detailed circuit model is presented to authenticate the accuracy of the derived small-signal model. Finally, a scaled-down prototype is used to verify the accuracy of the small-signal model.

Conceptual Design of Switch Network Unit for CFETR Coil Power Supply Systems

The China Fusion Engineering Test Reactor (CFETR) device is a milestone in the roadmap for the utilizing of fusion energy in China, whose final goal of plasma current is up to 10.02 MA. As the key system to generate a high enough voltage (20 kV) required for gas breakdown and plasma initiation, the Switch Network Unit (SNU) should have the ability to transfer 80 kA direct current by inserting resistor ( $0.25~\Omega $ ) to the superconducting coil circuit in 12 milliseconds. SNU topologies applied in other fusion devices are mostly based on the utilization of oscillation zero-point circuit, or combination of mechanical switch and semiconductor switch and so on, which bring stricter requirements for the components in the circuit and raise the cost due to the series and parallel connection of multiple devices if used in 80 kA/ 20 kV application. Based on the combination of solid-state switch (SSS) and auxiliary capacitor, this paper proposes a novel hybrid switch scheme. The SSS consists of insulated gate bipolar transistors (IGBT) group and thyristors group connected in series. The combination of added auxiliary capacitor and SSS can significantly reduce the number of series-connected IGBTs. This paper introduces the operation principle, design methods and simulation analysis of proposed scheme in detail. Coinciding with the analysis, the simulation results of SNU demonstrates the feasibility and reliability of the proposed scheme, which suggests its promising applications in fast switches with tens of kilovolts and hundreds of kilo-amperes.