As the advanced air mobility (AAM) market evolves towards higher payload, longer inter-city range, and stringent safety standards, the internal electric propulsion and power management systems of eVTOL aircraft are not merely energy converters. They are the core determinants of flight performance, operational economy, and ultimate certification. A meticulously designed power chain is the physical foundation for these aircraft to achieve robust vertical lift, efficient cruise, and fault-tolerant durability under demanding aerodynamic and environmental conditions.
However, building such a chain presents extreme challenges: How to maximize power-to-weight ratio while ensuring thermal stability in a confined airframe? How to guarantee the absolute long-term reliability of power devices against high-altitude temperature cycles, intense vibration, and potential thermal runaway? How to seamlessly integrate high-voltage safety, distributed thermal management, and redundant power distribution? The answers lie within every engineering detail, from the selection of key components to system-level integration.
I. Three Dimensions for Core Power Component Selection: Coordinated Consideration of Voltage, Frequency, and Power Density
1. Main Propulsion Inverter MOSFET: The Core of Thrust and Cruise Efficiency
The key device selected is the VBP15R25S (500V/25A/TO-247, Super-Junction Multi-EPI), whose selection requires deep technical analysis for aviation.
Voltage Stress and Frequency Analysis: Considering next-generation eVTOL high-voltage platforms targeting 800VDC or higher, the 500V rating of this device is optimal for phase-leg configurations or for use in 400V bus architectures with ample margin. Its Super-Junction (SJ) Multi-EPI technology enables significantly higher switching frequencies (50-100kHz range) compared to IGBTs, which is critical for reducing motor iron losses and minimizing the size/weight of output filters and motor magnetics—a paramount concern for aircraft weight.
Dynamic Characteristics and Loss Optimization: The low specific on-resistance (RDS(on)@10V: 127mΩ) directly impacts conduction loss during high-thrust phases (takeoff/hover). The fast switching capability of SJ MOSFETs reduces switching losses at high frequency, contributing to overall inverter efficiency exceeding 99%. The absence of a tail current (vs. IGBTs) is crucial for precise control and efficiency.
Thermal and Power Density Relevance: The TO-247 package, when mounted on a direct bonded copper (DBC) substrate integrated into a liquid-cooled cold plate, achieves minimal thermal resistance. The high frequency operation allows for a drastic reduction in passive component size, directly boosting the power density (kW/kg) of the entire electric propulsion unit (EPU).
2. High-Voltage to Low-Voltage DC-DC Converter MOSFET: The Backbone of Avionics Power
The key device selected is the VBMB18R06SE (800V/6A/TO-220F, SJ Deep-Trench), whose system-level impact is critical for safety and weight.
Efficiency, Voltage Rating, and Isolation: The 800V drain-source voltage rating allows this MOSFET to connect directly to the high-voltage traction battery (e.g., 650-750VDC) without requiring additional pre-regulation, simplifying topology and enhancing reliability. The SJ Deep-Trench technology ensures low switching losses even at the high input voltage. This is essential for an isolated DC-DC converter (e.g., 800V to 28V) that powers all critical avionics, flight control computers, and sensors. High efficiency (target >96%) minimizes heat dumped into the pressurized cabin or equipment bay.
Aircraft Environment Adaptability: The TO-220F (fully isolated) package simplifies mounting to heatsinks without insulation kits, improving thermal performance and reliability. Its high VGS rating (±30V) offers robust noise immunity in the electrically noisy environment of an inverter and motor.
Design for Redundancy: Critical DC-DC converters will be implemented in a redundant N+1 architecture. The relatively low current rating (6A) of this device is perfectly suited for parallel operation in multi-phase interleaved converter designs, which also reduces input/output current ripple and improves transient response.
3. Critical Load Management & Auxiliary System MOSFET: The Execution Unit for Redundant Power Distribution
The key device is the VBA3316SD (30V/10A/SOP8, Half-Bridge N+N), enabling highly integrated and reliable load switching.
Typical Load Management Logic in eVTOL: Manages power distribution to mission-critical and non-essential loads with possible priority shedding during low-power scenarios. Controls actuators for flight surfaces (if applicable), landing gear, cabin environmental control system (ECS) blowers, and lighting. The integrated half-bridge configuration allows it to be used as a compact, high-reliability driver for small brushless DC motors or as a bidirectional load switch in redundant power buses.
PCB Layout, Reliability, and Weight Saving: The dual MOSFET half-bridge in a tiny SOP8 package is ideal for distributed power distribution units (PDUs) located near loads, saving precious weight in wiring harnesses. The very low RDS(on) (18mΩ @10V) ensures minimal voltage drop and power loss. Its operation within the 28V low-voltage system avionics standard is perfect. Design must include adequate PCB copper pour and thermal vias to manage heat, as the small package has limited thermal mass.
II. System Integration Engineering Implementation for Aviation
1. Lightweight & Hierarchical Thermal Management Architecture
A multi-level cooling system is essential for weight and efficiency.
Level 1: Liquid Cooling Loop: Targets the VBP15R25S MOSFETs in the main propulsion inverters and possibly the VBMB18R06SE in high-power DC-DC converters. Uses a lightweight, high-performance glycol-water coolant loop with cold plates designed for minimal pressure drop. The cooling system must be redundant or fault-tolerant.
Level 2: Forced Air Cooling (Ram Air / Dedicated Fans): Cools avionics bays containing multiple VBA3316SD-based PDUs and other equipment. Uses aircraft speed-induced ram air during cruise and electric fans during hover/low speed. Ducting design is critical.
Level 3: Conduction Cooling to Airframe: For non-critical, low-power components, heat is conducted via PCB and mounting structures to the aircraft skin or internal structure, which acts as a heat sink.
2. Electromagnetic Compatibility (EMC) and High-Voltage Safety Design (DO-160 / MIL-STD Compliance)
Conducted & Radiated EMI Suppression: Inverters using VBP15R25S must implement strict shielding. Motor phase cables will be shielded. Laminated busbars within the inverter are mandatory. The entire EPU and PDU enclosures must be conductive and properly bonded to the airframe. Ferrite cores on all cable penetrations.
High-Voltage Safety and Reliability Design: Must comply with aviation standards and functional safety guidelines akin to ASIL D. Isolation monitoring between the high-voltage system (featuring VBMB18R06SE) and the airframe is mandatory. Redundant, dissimilar over-current and short-circuit protection with arc-fault detection is required for all high-power circuits.
3. Reliability & Redundancy Enhancement Design
Electrical Stress Protection: Snubber networks across VBP15R25S are crucial to clamp voltage spikes at high di/dt. Gate drive circuits for all key MOSFETs must be robust with TVS protection.
Fault Diagnosis and Predictive Health Management (PHM): Implement real-time monitoring of MOSFET RDS(on) increase for VBP15R25S and VBMB18R06SE as a precursor to failure. Monitor thermal cycles and vibration levels. Data can be uplinked for ground-based fleet PHM analytics.
III. Performance Verification and Testing Protocol (Airworthiness Focus)
1. Key Test Items and Standards
Testing must be more stringent than automotive, targeting RTCA DO-160G or similar.
Altitude-Temperature Cycle Test: From ground-level high temperature to cold soak at high altitude equivalent (e.g., -40°C to +55°C at 15,000 ft pressure).
Vibration and Shock Test: Apply random and sine vibration profiles representative of rotor-induced vibrations and hard landing shocks.
EMC Test: Must meet DO-160 Section 21 for conducted susceptibility and Section 22 for lightning induced transient susceptibility.
Endurance and Life Test: Execute accelerated life testing equivalent to tens of thousands of flight hours, focusing on thermal cycling of power modules.
2. Design Verification Example
Test data from a 250kW eVTOL propulsion inverter (Bus voltage: 800VDC, Switching freq: 50kHz):
Inverter system efficiency > 99% at cruise power, > 98.5% at peak take-off power.
Critical PDU channel (VBA3316SD based) voltage drop < 50mV at full 10A load.
After simulated high-power climb, estimated VBP15R25S junction temperature stabilized at 115°C with liquid cooling.
System passed DO-160 vibration profiles without performance degradation or mechanical failure.
IV. Solution Scalability & Technology Roadmap
1. Adjustments for Different eVTOL Configurations
Lift+Cruise (Multiple Propellers): The VBP15R25S solution scales well for parallel inverters per motor. The VBA3316SD is ideal for distributed PDUs in each nacelle or wing.
Ducted Fan/Vectored Thrust: May require even higher switching frequencies for acoustic signature management—benefiting further from the SJ MOSFET technology.
2. Integration of Cutting-Edge Technologies
Silicon Carbide (SiC) Technology Roadmap:
Phase 1 (Certification Basis): The selected SJ MOSFET (VBP15R25S) and SJ Deep-Trench MOSFET (VBMB18R06SE) provide a reliable, high-performance baseline for first-generation certified eVTOLs.
Phase 2 (Next-Generation Performance): Transition main propulsion inverters to 1200V SiC MOSFETs (e.g., a future variant of VBL15R18S technology). This enables direct 800V+ bus operation, higher switching frequencies (>100kHz), and potentially 1-2% system efficiency gain, directly extending range.
Phase 3 (Full Optimisation): Adopt SiC for both propulsion and high-power DC-DC conversion, maximizing power density and enabling higher operating temperatures, potentially simplifying thermal management.
Domain-Centralized Vehicle Energy Management: Integrates propulsion, battery management, and thermal management control. Dynamically allocates power and cooling resources based on flight phase (hover vs. cruise) and system health, optimizing total aircraft energy consumption.
Conclusion
The power chain design for high-end inter-city eVTOL aircraft is a pinnacle of multi-disciplinary systems engineering, balancing extreme power density, unparalleled efficiency, rigorous environmental adaptability, and fault-tolerant safety. The tiered optimization scheme proposed—prioritizing high-frequency, high-efficiency SJ MOSFETs at the main propulsion level, selecting high-voltage-rated devices for direct avionics power conversion, and employing highly integrated load switches for intelligent, redundant distribution—provides a clear and certifiable implementation path.
As AAM matures, aircraft power management will evolve towards greater integration and health-aware operation. Engineers must adhere to stringent aviation design standards and testing protocols while using this framework, preparing for the inevitable transition to wide-bandgap semiconductors. Ultimately, excellence in aerial vehicle power design is measured in silent reliability, extended range, and the unwavering confidence of passengers and operators—the true metrics of success in the third dimension of transportation.

Detailed Topology Diagrams