1. Mechanical Construction
Power Device Characterization and Mechanical Construction of Cryogenically-Cooled Motor Drive for Aircraft Application
Jordan A. Jones1, Handong Gui2 , Leon Tolbert2
1 Tuskegee University 2 The University of Tennessee, Knoxville
Research Motivation
Cryogenically-cooled power electronics can be implemented in future aircraft applications where superconducting machines are used. Such power converter system requires special electrical and mechanical design. Double pulse test (DPT) is the main methodology to evaluate the dynamic characterization of power semiconductors, which determines the electrical performance of the converter. The coldplates, pipes and busbars need to be fabricated for the cryogenic cooling of the system.
Double Pulse Test
Mechanical Design
Silicon Carbide (SiC) MOSFET has been proven to be a more beneficial alternative to Si device due to its better dynamic performance and higher efficiency. Therefore, it can reduce the size and losses of a power converter. Usually, double pulse test (DPT) is used to characterize the switching performance of the SiC MOSFET.
Figure 1: DPT architecture and operation principle
Figure 2: Final schematic of inverter system
Testing Results
Mechanical Construction
A DPT platform is established. It mainly consists of device under test (SiC MOSFET, 1.2 kV, 30 A), gate drive PCB, DC link capacitor bank, load inductor, and measurement probes.
Fig. 4 shows the whole DPT process. Two pulses with different width are generated. The first pulse is to establish the required load current, and the second one is for analyzing the switching transient under certain load condition.
Coldplates are used to maintain the low temperature of power devices in inverter. The aluminum coldplates will be cooled using gas nitrogen transported in the aluminum tubes shown in Fig. 7 and Fig. 8. The coupled inductors are filters that act as a buffer between the inverters. These inductors are connected by aluminum tubes that are used to transport liquid nitrogen for cooling.
Figure 7: Coldplates and exhaust pipes
Figure 3: DPT platform
Figure 8: Coolant transfer pipes
Turn-off transient is characterized at the end of the first pulse Turn-on transient is captured at the beginning of the second pulse.
Fig 5 is the turn-on transient:
1: gate voltage increases
2: drain current increases to load current
3: drain-source voltage of lower switch decreases to zero
4: parasitic ring
Fig. 6 is the turn-off transient:
1: gate voltage decreases
2: drain-source voltage of lower switch increases to bus voltage
3: drain current decreases to zero
4: parasitic ringing
Figure 9: Coupled inductors
Figure 10: Coupled inductors
V GS : 2.5V/div
V GS : 2.5V/div
V GS : 2.5V/div
V DS_L : 75V/div
V DS_L : 75V/div
V DS_L : 75V/div
V DS_H : 90V/div
V DS_H : 90V/div
V DS_H : 90V/div
I D : 5A/div
I D : 5A/div
I D : 5A/div
Figure 4: Complete double pulse test
Figure 5: Turn-on waveform
Figure 6: Turn-off waveform
Conclusion
A DPT is conducted to analyze the switching characteristics of the SiC MOSFET. The results show that the device is functioning properly with the power loss during turn-on and off transients. The power loss can be further reduced in future advancements by keeping the parasitic inductance in the circuit low to reduce the ringing as well as increasing the switching time with better gate drive technology. Multiple pieces of mechanical parts have been fabricated for the cryogenic cooling system of the inverter. The fabricated parts will undergo tests at room temperature before testing at cryogenic temperatures.
Other US government and industrial sponsors of CURENT research are also gratefully acknowledged.
This work was supported primarily by the ERC Program of the National Science Foundation and DOE under NSF Award Number EEC