Abstract

With the acceleration of urbanization, building an efficient, green, and intelligent transportation system has become a core issue. As the cornerstone of modern power electronics, switching power supply technology—characterized by high efficiency, high power density, and excellent controllability—has deeply penetrated all aspects of urban transportation. This paper systematically elaborates on the full-spectrum applications of switching power supplies, spanning from ground-based charging infrastructure and vehicle powertrains to station support systems and intelligent transportation management. It also analyzes the technical challenges faced by the technology and outlines future development trends.

1. Introduction: The Core Enabling Technology for Urban Transportation Electrification

The urban transportation system is a complex megasystem, and its electrification and intelligent transformation rely heavily on efficient electrical energy conversion and management. Through the switching operations of high-frequency power semiconductor devices, switching power supply technology enables precise conversion, distribution, and control of electrical energy. Its performance directly determines the energy efficiency, reliability, and cost of the entire transportation system.

2. Analysis of Core Application Fields

2.1 Ground-Based Charging Infrastructure

As the "energy supply stations" for urban transportation electrification, ground-based charging facilities rely on switching power supply technology as their core.

On-Board Charger (OBC)

Function: Fixed inside electric vehicles (EVs), it converts AC grid power (AC 220V/380V) into high-voltage DC power to charge the traction battery.

Technical Key Points: Adopts high-efficiency topologies such as Power Factor Correction (PFC) circuits and LLC resonant converters. It prioritizes high power density to fit the limited space inside vehicles, with a typical charging efficiency of > 95%.

DC Charging Piles/Stations

Function: Bypasses the on-board charger to directly supply high-voltage DC power to the battery, enabling fast energy replenishment.

Technical Key Points: Essentially a high-power switching power supply system. It uses three-phase PFC rectifiers and multiple parallel DC/DC modules, with power ratings ranging from several tens of kW to 480 kW or higher. Key challenges include thermal management, efficiency optimization (peak efficiency > 96%), and real-time communication with the Battery Management System (BMS).

Ground Power Supply for Rail Transit

Function: Rapidly charges supercapacitors or battery energy storage units in catenary-free lines (e.g., certain trams or APM systems).

Technical Key Points: Utilizes high-power, bidirectional DC/DC converters that can complete energy injection within tens of seconds during station stops and support regenerative braking energy recovery.

2.2 Vehicle Powertrain and Auxiliary Systems

Switching power supplies serve as the "heart" and "blood vessels" of various electric transportation vehicles.

Electric Buses/Passenger Cars

Main Drive Inverter: Converts DC power from the battery into three-phase AC power to drive the motor, acting as the core powertrain switching power supply. SiC MOSFETs are widely adopted to increase switching frequency, improve system efficiency, and reduce size and weight.

DC/DC Converters:

High-Voltage to Low-Voltage Conversion: Converts high voltage from the traction battery (e.g., 400V/800V) to low voltage (12V/24V) to power vehicle controllers, lights, audio systems, etc.

Bidirectional DC/DC: Enables bidirectional energy flow between the battery and low-voltage systems in hybrid vehicles or specific architectures.

Rail Transit Vehicles

Traction Converter: A megawatt-level high-power switching power supply system. It adopts four-quadrant converters (for AC power supply) and multi-level inverter topologies to realize traction, braking, and energy feedback.

Auxiliary Power System (APS): Converts high voltage from the catenary (DC 1500V/AC 25kV) into multiple isolated power supplies (e.g., AC 380V, DC 110V) required inside the vehicle, powering systems such as air conditioning, lighting, and control. It demands extremely high reliability and electromagnetic compatibility (EMC).

2.3 Station Support and Intelligent Transportation Systems

These systems act as the "neural network" and "logistics base" to ensure stable operation of the overall transportation system.

Traffic Signal Control and Command Centers

Application: Provides uninterrupted power supply for intersection traffic signals, electronic police devices, and central servers.

Technical Key Points: Adopts modular Uninterruptible Power Supply (UPS) systems with N+X redundancy and hot-swappable functions to ensure 24/7 uninterrupted operation. Strict EMC design is implemented to prevent interference with sensitive electronic equipment.

Station Auxiliary Facilities

Application: Powers ventilation, lighting, elevators, and security inspection equipment in subway stations and bus hubs.

Technical Key Points: Uses standardized switching power supply modules, prioritizing high efficiency and long service life to reduce operational energy consumption and maintenance costs.

Intelligent Transportation Equipment

Application: Powers built-in systems of Roadside Units (RSUs), variable message signs, and smart streetlights.

Technical Key Points: Features miniaturization and high environmental adaptability (wide temperature range, moisture resistance, lightning protection). It is also beginning to integrate intelligent control functions, supporting remote monitoring and management.

3. Key Technical Challenges and Solutions

Challenge 1: Improving Efficiency and Power Density

Issue: Limited space in charging facilities and vehicles creates a trade-off between high power density and high efficiency.

Solutions:

Adopt wide-bandgap semiconductors (SiC, GaN) to increase switching frequency and reduce switching losses;

Apply soft-switching technologies (e.g., LLC, phase-shifted full-bridge);

Use integrated magnetic components and advanced thermal management technologies (e.g., liquid cooling, phase-change materials).

Challenge 2: Electromagnetic Compatibility (EMC) and Power Quality

Issue: High-power switching operations generate electromagnetic interference (EMI), which pollutes the power grid and affects surrounding equipment.

Solutions:

Design multi-stage EMI filters;

Optimize PCB layout and shielding;

Adopt active PFC technology to ensure sinusoidal grid-side current, complying with standards such as EN 55032 and CISPR 25.

Challenge 3: Reliability and Environmental Adaptability

Issue: Transportation equipment operates in harsh environments (e.g., vibration, extreme temperature changes, dust, salt spray).

Solutions:

Implement enhanced mechanical design and triple-proof (moisture, dust, corrosion) treatment;

Use long-life components (e.g., solid-state capacitors);

Conduct HALT/HASS (Highly Accelerated Life Test/Highly Accelerated Stress Screen) reliability testing;

Design products to meet IP65 or higher protection ratings.

Challenge 4: Intelligent and Networked Management

Issue: Massive and scattered power supply devices make efficient operation, maintenance, and coordination difficult.

Solutions:

Integrate digital control and communication interfaces (e.g., CAN, Ethernet);

Build cloud-based management platforms to enable status monitoring, fault early warning, energy efficiency analysis, and remote firmware updates.

4. Technology Development Trends

Full-Spectrum Wide-Bandgap Semiconductor Adoption

SiC and GaN devices will expand from high-end vehicles and ultra-fast charging piles to all application fields, driving system efficiency to exceed 98.5% while significantly reducing size and weight.

Ultra-Fast Charging and Wireless Charging Technologies

High-power ultra-fast charging technology based on liquid cooling (800V platform) will become mainstream; magnetically coupled resonant wireless charging technology for low-to-medium speed scenarios will gradually be commercialized.

High Integration and Standardization

Integrated powertrain and power supply modules—such as "2-in-1" (PFC + LLC) and "3-in-1" (MCU + DC/DC + OBC)—are emerging as trends, reducing costs and improving reliability.

AI-Enabled Intelligent Power Management

Artificial intelligence algorithms will be applied for load prediction, efficiency optimization, and predictive maintenance, transforming power supply systems from "energy guarantee" to "optimal energy utilization."

Deep Integration with the Energy Internet

Charging piles will serve as distributed energy nodes to participate in grid peak shaving and valley filling (Vehicle-to-Grid, V2G), and switching power supply technology is the key to enabling this bidirectional interaction function.

5. Conclusion

Switching power supply technology has been deeply integrated into the "bloodstream" of urban transportation and serves as an indispensable foundation for driving its electrification and intelligent transformation. From ground-based charging and vehicle propulsion to station management and intelligent control, the evolution of this technology directly determines the energy efficiency, operational costs, and user experience of urban transportation systems. In the future, with continuous breakthroughs in materials science, semiconductor technology, and digital intelligence, switching power supplies will continue to provide core impetus for building a greener, more efficient, and resilient future urban transportation network—with higher efficiency, stronger intelligence, and tighter system integration.