June/July 2021

www.apec-conf.org APEC 2021 27 www.power-mag.com Issue 3 2021 Power Electronics Europe Circuit protection is a key enabler for future medium-voltage direct-current (MVDC) distribution systems. Hybrid dc circuit breaker (HCB) offers low conduction losses and reasonably fast response times, but suffers from large size. In this awarded paper (Best Presentation), a high power density power electronic interrupter design is introduced for the HCB. The device selection and trade-off analysis of voltage clamping circuit are investigated. A small sized module with two parallel 1.7 kV discrete IGBTs are selected as main switches. The RC snubber and MOV are carefully designed to guarantee no tail current bump and sufficient turn-off voltage margin. Experimental results at 12 kV and 1 kA are provided to verify the operation of the prototype. J ian Liu, Center for Power Electronics Systems, Virginia Tech (jianl@vt.edu ) Although medium-voltage DC (MVDC) system is very attractive, protection equipment of DC circuit breaker (DCCB) against short circuit fault represents a major technical barrier in development of MVDC networks. Because the lack of natural zero crossing point and the faster rise of DC fault currents due to lower system inductance, bring several challenges to DCCB. DCCB can be categorized into three main types, mechanical circuit breaker (MCB), solid- state circuit breaker (SSCB) and hybrid circuit breaker (HCB). Compared to the switches. Figure 1 shows a PCB with three series modules, and three stacked boards are connected in series to obtain 12 kV clamping voltage. It can be seen the total size is similar to two 4.5kV/500A IGBT modules from Infineon (single one is 14 cm 13 cm 5 cm). But it should be noted that six IGBT modules are required to build a 12 kV bidirectional PEI. Simultaneous experimental results at 12 kV and 1 kA are shown in Hybrid DC Circuit Breaker Figure 1: (a) Single board with three series modules, (b) three stacked boards as 12 kV PEI prototype Figure 2: Breaking waveform showing 12 kV and 1 kA peak PEI voltage and current, (a) simultaneous turn-off, and (b) staged turn-off other two type circuit breakers, HCB combines the low loss advantages of mechanical switches with the fast response times offered by solid-state switch. Therefore, it is regarded as one of the most promising solutions. Considering the state of art bulky HCB system, this paper tries to increase the power density of current HCB, especially focusing on the power electronic interrupter (PEI) part. PEI prototype Two parallel 1.7 kV/ 170A discrete IGBTs are selected as the main Figure 2(a). It can be seen the fault current is interrupted successfully, the voltage ripple after current at zero is caused by the oscillation between snubber capacitor, DC bus capacitor bank and line inductor. An improved staged turn-off strategy test results is shown in 2(b), nine IGBTs are turned off one by one to make sure the clamping is always smaller than the dielectric strength between vacuum switch contactors. In this way, the peak voltage, current, MOV energy and interruption time could be reduced. Literature High Power Density Design of Power Electronic Interrupter in Hybrid DC Circuit Breaker, APEC 2021 Procedings, pages 33-38 www.power-mag.com