With the global emphasis on sustainable urban transportation, tram energy storage systems have become a core technology for achieving efficient energy recovery, peak shaving, and operational stability. The bidirectional DC-DC converter, serving as the "heart" of the entire system, needs to provide high-efficiency, high-power-density energy conversion between the traction network and supercapacitor/battery packs. The selection of power MOSFETs directly determines the system's conversion efficiency, power density, thermal performance, and operational reliability under demanding conditions. Addressing the stringent requirements of tram systems for high voltage, high current, ruggedness, and long lifespan, this article centers on scenario-based adaptation to reconstruct the power MOSFET selection logic, providing an optimized solution ready for direct implementation.
I. Core Selection Principles and Scenario Adaptation Logic
Core Selection Principles
High Voltage & Sufficient Margin: For traction network voltages (e.g., 600V, 750V DC), the MOSFET voltage rating must withstand significant switching voltage spikes and line transients with a safety margin ≥20-30%.
Ultra-Low Loss Priority: Prioritize devices with extremely low on-state resistance (Rds(on)) and optimized gate charge (Qg) to minimize conduction and switching losses, which are critical for efficiency and heat management in high-power applications.
Package & Thermal Performance: Select robust packages like TO-220, TO-263, TOLL capable of handling high currents and facilitating efficient thermal interface with heatsinks, considering vibration and shock resistance.
Ruggedness & Reliability: Devices must meet requirements for high ambient temperature, continuous charge-discharge cycling, and possess high avalanche energy capability and strong anti-interference characteristics.
Scenario Adaptation Logic
Based on the core functions within the tram energy storage system, MOSFET applications are divided into three main scenarios: Main Bidirectional DC-DC Power Stage (High-Power Core), High-Current Path & Synchronous Rectification (High-Density Unit), and Safety & Pre-charge Control (Auxiliary Critical). Device parameters and characteristics are matched accordingly.
II. MOSFET Selection Solutions by Scenario
Scenario 1: Main Bidirectional DC-DC Power Stage (650V-750V Class) – High-Power Core Device
Recommended Model: VBM165R11SE (Single N-MOS, 650V, 11A, TO220)
Key Parameter Advantages: Utilizes SJ_Deep-Trench technology, achieving a low Rds(on) of 290mΩ at 10V Vgs. A 650V rating is suitable for 600V-class systems with margin. The 11A continuous current rating supports substantial power levels.
Scenario Adaptation Value: The TO220 package is ideal for robust heatsinking. The Super-Junction structure provides an excellent balance of low conduction loss and fast switching, essential for the high-efficiency primary switches in a bidirectional converter. It enables high-frequency operation, reducing passive component size.
Applicable Scenarios: Primary high-side and low-side switches in non-isolated or isolated bidirectional DC-DC converters for energy storage systems.
Scenario 2: High-Current Path & Synchronous Rectification – High-Density Unit Device
Recommended Model: VBGL71203 (Single N-MOS, 120V, 190A, TO263-7L)
Key Parameter Advantages: Features SGT technology delivering an ultra-low Rds(on) of 2.8mΩ at 10V Vgs with a massive 190A current capability. The TO263-7L (D²PAK-7L) package offers very low parasitic inductance and excellent thermal performance from exposed pad.
Scenario Adaptation Value: The extremely low Rds(on) minimizes conduction losses in high-current paths, such as the low-voltage side of the DC-DC converter connected to supercapacitors or battery strings. This is crucial for maximizing system efficiency and energy recovery during regenerative braking. The high current rating ensures reliability under peak power demands.
Applicable Scenarios: Synchronous rectification MOSFETs, high-current bus switches, and low-side switches in high-power density converter modules.
Scenario 3: Safety & Pre-charge Control – Auxiliary Critical Device
Recommended Model: VBMB2255M (Single P-MOS, -250V, -10A, TO220F)
Key Parameter Advantages: A -250V P-Channel MOSFET with Rds(on) of 500mΩ at 10V Vgs and -10A current rating. The TO220F (Fully Isolated) package provides easy mounting and electrical isolation.
Scenario Adaptation Value: P-MOSFETs simplify high-side switching circuits. This device is ideal for implementing pre-charge circuits to limit inrush current to the DC-link capacitors, and for safety isolation contactors or auxiliary load control on the high-voltage bus. The isolated package enhances system safety and simplifies thermal management.
Applicable Scenarios: Pre-charge circuit switch, high-side safety disconnect switch for auxiliary loads, and control of high-voltage contactor coils.
III. System-Level Design Implementation Points
Drive Circuit Design
VBM165R11SE: Requires a dedicated high-voltage gate driver IC with sufficient current capability and isolation. Careful attention to minimizing gate loop inductance is critical.
VBGL71203: Needs a powerful low-voltage gate driver capable of sourcing/sinking high peak currents to quickly charge/discharge its large gate capacitance. Use Kelvin source connection if available.
VBMB2255M: Can be driven by a level-shifted signal from a controller. Ensure the gate drive circuit can pull the gate sufficiently below the source for full enhancement.
Thermal Management Design
Graded Heatsinking Strategy: VBM165R11SE and VBMB2255M require dedicated heatsinks sized for the worst-case power dissipation. VBGL71203 requires a large PCB copper area or connection to a baseplate/heat sink via its exposed pad.
Derating & Monitoring: Implement significant current and junction temperature derating (e.g., 50-70% of rated current at max ambient). Consider integrating temperature sensors near high-power devices.
EMC and Reliability Assurance
Snubber & Filtering: Implement RC snubbers across the drain-source of high-voltage switches (VBM165R11SE) to dampen voltage ringing. Use input and output EMI filters on the DC-DC converter.
Protection Measures: Incorporate comprehensive overcurrent, overvoltage, and overtemperature protection at the system level. Use TVS diodes on gate drivers and bus bars for surge protection. Ensure PCB creepage and clearance distances meet traction voltage standards (e.g., EN 50155).
IV. Core Value of the Solution and Optimization Suggestions
The power MOSFET selection solution for tram energy storage systems, based on scenario adaptation logic, achieves precise matching from the high-voltage power stage to safety-critical auxiliary functions. Its core value is mainly reflected in the following three aspects:
Maximized System Efficiency & Energy Recovery: By selecting the ultra-low-loss VBGL71203 for high-current paths and the efficient SJ MOSFET VBM165R11SE for the primary switches, conduction losses are minimized across the power chain. This directly translates to higher round-trip efficiency for the energy storage system, capturing more regenerative braking energy and reducing net energy consumption.
High Power Density with Functional Safety: The use of compact, high-performance packages (TO263-7L, TO220F) alongside the high-current and high-voltage capabilities enables a power-dense converter design. The inclusion of the P-MOSFET (VBMB2255M) simplifies and enhances the reliability of critical safety functions like pre-charge and isolation, which are paramount in railway applications.
Optimal Balance of Ruggedness and Lifetime Cost: The selected devices offer robust electrical characteristics and package options proven in demanding environments. Compared to using only the latest wide-bandgap devices, this combination of mature, high-performance Si MOSFETs provides a highly reliable and cost-effective solution, ensuring long-term operational stability and favorable total cost of ownership for fleet-wide deployment.
In the design of tram energy storage systems, power MOSFET selection is a cornerstone for achieving high efficiency, high reliability, and safety compliance. The scenario-based selection solution proposed in this article, by accurately matching the distinct requirements of the main power converter, high-current paths, and safety circuits, and combining it with robust system-level design practices, provides a comprehensive, actionable technical roadmap. As energy storage systems evolve towards higher voltages, greater power densities, and increased intelligence, future exploration could focus on the application of SiC MOSFETs for the main switches and the integration of current/temperature sensing within power modules, laying a solid hardware foundation for the next generation of high-performance, ultra-efficient tram propulsion and energy management systems. In the era of green urban transit, optimized power electronics hardware is key to unlocking the full potential of energy storage technology.

Detailed Topology Diagrams