Kyungmin Sung

3-Level power converter with high-voltage SiC-PiN diode and hard-gate-driving of IEGT for future high-voltage power conversion systems

Reductions in the size and weight of medium-voltage power converters are essential for saving space of power conversion systems and cutting their cost. Volumes of magnetic components such as transformers and LC filters are significant in medium-voltage power converters. High-switching-frequency operation is essential for reducing the volume of magnetic components. In this work, hybrid pairs of 6 kV SiC-PiN diodes and 4.5 kV Si-IEGTs have been applied to realize the high-switching-frequency operation of medium-voltage power converters. For low switching losses and series operation of power devices, a gate-driving technique with an extremely low gate resistance called hard gate driving is employed. Switching characteristics of the hybrid pair are measured experimentally. It has been demonstrated that the total switching loss can be reduced up to 50% with the hybrid pair. In order to demonstrate a 2 kHz switching frequency operation of the hybrid pair, which is about 4 times higher than that of conventional medium-voltage power converters, a 378 kVA prototype 3-level inverter has been designed and constructed.

Switching characteristic of Si-IEGTs and SiC-PiN diodes pair connected in series

In this paper, in order to realize high voltage static switches of voltage source inverters in high power applications, two series connected 4.5kV rate Si-IEGT with SiC-PiN diode pairs (hybrid combination) are considered with hard switching method. The switching test of power module that is hybrid combination is carried out under 5kV DC bias voltage. The gate driver circuit is designed by high output power capacity for high speed hard switching. Small reverse recovery charge of SiC-PiN diode and the hard switching method are adopted for the purpose of not only high switching frequency but also high power density in the high power converter system. Experimental results show good switching characteristic of voltage balancing with small size capacitor and balance resistors at the switching period.

Optimum Combination of SiC-diodes and Si-switching Devices in High Power Application

In this paper, several combinations of silicon carbide diodes and silicon switching devices are evaluated using device simulation. The 1.2kV and 3.3kV SiC-PiN diode, SiC-SBD, Si-PiN diode, Si-IGBT and Si-IEGT are used. The devices structures in device simulation are determined by comparing static and switching characteristics to those in the experiment. Moreover it is confirmed that the total devices switching loss in device simulation is appropriate by comparing it with experimental results. In device simulation, six combinations are evaluated under 1200 DC voltage and two temperature conditions. As the simulation results, we present optimum combination of silicon carbide diodes and silicon switching devices from the viewpoint of devices loss in the switching frequency of several kHz.

A study on switching frequency limitation of high voltage power converters in combination of Si-IEGT and SiC-PiN diode

In this paper, we present a comparison between 2.5kV silicon carbide (SiC-) PiN diode and commercial 3.3kV silicon (Si-) PiN diode with 3.3kV silicon injection enhancement gate transistor (Si-IEGT) in the inductively loaded chopper circuit. The experimental switching characteristics of SiC-PiN diode are presented under 1200-V DC bias voltage and 40-A cutoff current and compared to commercially available a Si-PiN diode. Experimental results show that the reverse recovery time and Si-IEGT turn-on loss are significantly reduced in the combination of SiC-PiN diode and Si-IEGT. Also, we propose a design concept of Si-IEGT combined with SiC-PiN diode to reduce switching losses and investigate the limitation of switching frequency in the high power converters. The proposed design concept is evaluated based on device simulation. The internal parameters of the Si-IEGT are adjusted to find the minimum value of total devices loss. In the device simulation result, the possible switching frequency by comprehensive total devices loss in the test circuit is discussed

Experimental investigation of normally-on type bidirectional switch for indirect Matrix Converters

In this paper, the novel normally-on type bidirectional switch, in which is comprised of SiC-JFET, SiC-SBD, and Si-IGBT is proposed for one of a protection method of the Matrix Converter (MC). When the MC becomes gate block situation, a diode clamp circuit or auxiliary circuits keeps inductive load current loop in a conventional MC utilized a bidirectional switch. We focus that the normally-on type SiC-JFET becomes turn-on state, when zero gate bias voltage and a SiC-devices have a good tolerance capability for short current than silicon devices. These characteristic of normally-on type SiC-JFET is used to replace diode clamp circuit in MC driver system. The experimentation based on indirect MC induction motor driver system was carried out. The experimental result of IM driver shows that the proposed bidirectional switch can overcome a generated inductive load current by IM. Finally, in order to design heat sink, the power loss of each devices of proposed switch was estimated by experimental results.

Quantitative study on operation frequency limitation of multi-level high voltage power converter equipped with Si-IEGT and SiC-PiN diode

This paper has quantitatively investigated the operation frequency limitation of high voltage NPC 3-level converter with 4.5 kV Si-IEGT and 5 kV SiC-PiN diode hybrid pair. In order to investigate the limitation, the high speed switching capability of the hybrid pair under a hard drive condition is evaluated, and an exact power loss estimation method is proposed to estimate the power losses of NPC 3-level converter with high voltage bipolar power devices. The possibility of high frequency operation in NPC 3-level converter with the hybrid pair under the hard drive condition is revealed by using the power loss estimation method.

High-frequency switching high-power converter with SiC-PiN diodes and Si-IEGTs

High-frequency switching operations are required in medium-voltage power converters to realize compact power converter systems. High-voltage hybrid pair modules using SiC-PiN diodes and Si-IEGT are expected to increase the switching frequency. In this work, 4.5 kV–400 A SiC-PiN diode and Si-IEGT hybrid pair modules have been developed. Hard driving is applied to the hybrid pair module for low switching losses and stable series voltage balance between two series-connected modules. Operation tests of developed hybrid pair modules with the switching frequency of more than 2 kHz have been carried out in a 1 MVA class prototype power converter.

High-power converters with high switching frequency operation using SiC-PiN diodes and Si-IEGTs

High-frequency switching operations are required in medium-voltage power converters to realize compact power converter systems. High-voltage hybrid pair modules using SiC-PiN diodes and Si-IEGT are expected to increase the switching frequency. In this work, 4.5 kV–400 A SiC-PiN diode and Si-IEGT hybrid pair modules have been developed. Hard driving is applied to the hybrid pair module for low switching losses and stable series voltage balance between two series-connected modules. Operation tests of developed hybrid pair modules with the switching frequency of 4 kHz have been carried out in a 1 MVA class prototype power converter.

2.5kV, 200kW bi-directional isolated DC/DC converter for medium-voltage applications

A bi-directional isolated DC/DC converter for medium-voltage applications have been discussed for the next-generation electrical grid, such as smart girds. To realize the DC/DC converter for installing on a power distribution system, it should be achieved higher-efficiency and lower-volume. Higher switching frequency enables to reduce the volume of the transformer. However, it is difficult to realize the both higher-efficiency and lower-volume of the DC/DC converter, because it could not operate higher frequency with high power devices such as medium-voltage IGBTs. This paper discusses switching losses and operation limitations for the actual medium-voltage isolated DC/DC converter, in the case of using Si-IGBT. In addition, the experimental system rated at 2.5 kV, 200 kW, and 5kH of the DC/DC converter with a medium-frequency transformer is designed, and the experimental results are shown.

Maximum switching frequency characterization of 4.5kV–400A SiC-PiN diode and Si-IEGT hybrid pair power module

The maximum switching frequency of a 4.5 kV-400 A SiC-PiN diode and Si-IEGT hybrid pair module has been analyzed from the viewpoints of cooling capacity of the hybrid pair module and the minimum pulse width of the PWM signal. In the developed hybrid pair module, a direct water cooling type heat sink is employed to enhance the cooling capacity. It found that the developed 4.5 kV-400 A hybrid pair module could be operate at 10 kHz PWM switching frequency with the peak current of 110 A and the dc voltage of 2.5 kV. In this operating condition, the power losses of the Si-IEGT and SiC-PiN diode in the hybrid pair module are 2380W and 100 W, respectively.