Si/SiC Hybrid 5-level Active NPC Inverter for Electric Aircraft Propulsion Drive Applications

ABSTRACT:

 Medium voltage DC(MVDC) system is considered as a promising technology to improve the efficiency and power density of electric aircraft propulsion(EAP) drives. To adapt to the MVDC voltage level and achieve high drive performance, a five-levelactive neutral point clamped(5L-ANPC) inverter consisting of three-level ANPC and flying capacitor circuits is investigated, which possesses higher voltage capability, lower output harmonics, as well as mitigated dv/dt and common-mode voltage. To fulfill the requirements of high-speed operation and pursue further enhanced efficiency and power density of the inverter for the next-generation EAP drives, Silicon Carbide(SiC) semiconductor devices are considered for implementing the 5L-ANPC inverter. However, the large commutation loops associated with certain switching states of the inverter lessen the benefits of configuring all the switches as SiC devices. As a result, a hybrid Si/SiC 5L-ANPC inverter is developed with a synchronous optimal pulse(SOP) width modulation strategy for controlling the switches in cell 2 and finite-control-set model predictive controller(FCS-MPC) for those in cell 3 of the inverter. Consequently, in the proposed topology, the SiC devices are merely used for the high-frequency switches in cell 3 and the rest of the low-frequency switches are configured with Si IGBTs. This Si/SiC hybrid ANPC inverter concurrently provides high efficiency and low implementation cost at high-speed operation mode. Simulation and experimental results are provided to verify the effectiveness of the proposed hybrid inverter.

 KEYWORDS:

1.      Five-level ANPC

2.      Flying capacitor

3.      SOP

4.      FCS-MPC

5.      Carrier-based modulation

6.      High efficiency

7.      MVDC

8.      Electric aircraft propulsion

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig. 1 High frequency commutation loops of a conventional 5L-ANPC between: S7-S8 (dash-dotted line), and S5 S6 (positive and negative half-cycles in dashed lines)

 EXPECTED SIMULATION RESULTS:

 Fig. 2 Simulation results using hybrid FCS-MPC with λ1=2.5 and λ2=0; From top to bottom: load current, line-line voltage, line-neutral voltage, DC-link capacitors voltage, FCs voltage, and CMV

 

Fig. 3 Simulation results using hybrid FCS-MPC with λ1=4 and λ2=0.08; From top to bottom: load current, line-line voltage, line-neutral voltage, DC-link capacitors voltage, FCs voltage, and CMV

 

CONCLUSION:

A three-phase Si/SiC hybrid 5L-ANPC inverter for electric aircraft propulsion drive applications has been presented in this paper. To simultaneously attain higher efficiency and low implementation cost, only the cell 3 of the inverter has been configured with SiC devices, while the rest of the switches are designed with Si IGBTs switching at lower frequencies. Furthermore, to overcome the issue of large commutation loops with the switches in cell 2 and also pursue further loss reduction, synchronous optimal PWM has been applied as a low frequency modulation method. Both thermal and electrical simulation results have been provided to demonstrate the effectiveness of the proposed inverter and the related PWM strategy. Experimental Results have been presented to demonstrate the efficacy of the hybrid “SOP+MPC” modulation method. Test results have verified the performance of the proposed method and the fact that this hybrid inverter topology provides high efficiency and low output harmonic distortions at low cost.

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