Accuracy-Enhanced Miller Capacitor Modeling and Switching Performance Prediction for Efficient SiC Design in High-Frequency X-Ray High-Voltage Generators

High-voltage (HV) generators with a wide load range are widely adopted for X-ray beam excitation and density adjustment. A SiC-based LCC HV inverter at high switching frequency will benefit fast transient because of the more efficient utilization of an X-ray beam and its smaller size. A precise prediction of SiC switching characteristics provides important prerequisites for efficiency, thermal and power density, and reliability co-optimized design. Understanding the SiC switching loss at different switching conditions will help the resonant network design to achieve required gain and efficiency over wide operation ranges. SiC switching characteristics are strongly dependent on its parasitic capacitors. A Miller capacitor, existing across the gate-source loop and the drain-source loop, presents strong nonlinear characteristics. This article proposes an accuracy-enhanced Miller capacitor-modeling approach. An internal cascaded configuration of a fixed capacitor and a voltage-dependent capacitor with segmentations based on different doping concentrations is employed. The maximum mismatch between the proposed approach and the datasheet's C-V data is within 28%. Prediction accuracy improves two times compared with the device SPICE model. An enhanced double-pulse-test (DPT) circuit is used for comprehensive switching behavior verification. The proposed model has highest accuracy in switching loss prediction with up to 15× less mismatch compared with the state of the arts. The hard turn-on and turn-off losses are 157.7 and 48.1 μJ at 500 V/40 A. The ZVS turn on loss is 1.67 μJ at 40 A. The soft turn-off loss is reduced to 4.43 μJ with a 3.2-nF snubber capacitor. A SiC transistor with ZVS-ON and soft turn-off has the lowest overall switching loss of 6.1 μJ. Such a switching condition corresponds to the region of a switching frequency higher than the resonant frequency in an LCC inverter. Therefore, both high efficiency and high power density will be achieved under this optimal region.