Abstract

With the large-scale development of the electric vehicle (EV) industry, the technical performance of charging infrastructure has become a key factor affecting user experience and power grid stability. This paper systematically analyzes the system architecture, core technical challenges, and development trends of switching power supply technology in the field of EV charging, with a focus on exploring the power topology, energy efficiency optimization methods, and system integration solutions of on-board chargers (OBCs) and DC charging piles.

1. Introduction

An EV charging system is essentially a high-power energy conversion device that enables efficient, reliable, and safe transmission of electrical energy from the power grid to the vehicle’s traction battery. As the core of this system, the performance indicators of switching power supply technology directly determine the conversion efficiency, power density, system cost, and grid interaction capability of charging equipment. From a technical implementation perspective, EV charging equipment can be divided into two categories: on-board chargers (OBCs) and off-board DC charging piles, each corresponding to different technical paths and engineering challenges.

2. On-Board Charger (OBC): A Bidirectional Energy Conversion System

2.1 Evolution of System Architecture

Traditional OBCs adopt a unidirectional two-stage architecture: the front stage is a power factor correction (PFC) unit, and the rear stage is an isolated DC-DC conversion unit. With the development of vehicle-to-grid (V2G) technology, bidirectional OBCs are gradually becoming the mainstream. Their typical architecture includes:

Bidirectional PFC Stage: The totem-pole bridgeless PFC topology is widely used. Combined with the high-frequency characteristics of GaN HEMTs or SiC MOSFETs, the conversion efficiency can reach over 99% under conditions of 230V AC input and above half-load.

Bidirectional Isolated DC-DC Stage: Mainly adopts dual-active bridge (DAB) or improved LLC resonant converters, which realize bidirectional energy flow through precise phase-shift control or frequency conversion strategies.

2.2 Key Technical Challenges and Engineering Solutions

Power Density Optimization: Through precise optimization of switching frequency (150-400 kHz), 3D packaging technology, and hybrid cooling solutions, the power density is increased from the traditional 2 kW/L to over 4 kW/L.

Electromagnetic Compatibility (EMC) Design: Adopts active common-mode noise cancellation technology, optimizes the interlayer distributed capacitance of transformers, and uses multi-level shielding structures to meet the requirements of the CISPR 32 Class B standard.

Thermal Management Strategy: Combines conductive cooling and forced liquid cooling technologies to ensure that the junction temperature of key power devices (such as SiC MOSFETs) remains below the rated value of 150°C.

3. DC Charging Pile: A High-Power Modular Architecture

3.1 System Architecture Analysis

DC charging piles adopt a distributed modular architecture. The rated power of a single power module is usually 20-40 kW, and the total system power of 150-600 kW is achieved through parallel connection.

Its typical energy flow path is:

[Three-Phase AC Grid] → [Three-Phase PFC Module] → [600-800V DC Bus] → [Isolated DC-DC Module] → [Output Contactor System] → [Vehicle Traction Battery]

3.2 Key Power Supply Technologies

Front-Stage PFC Module: Adopts a three-phase VIENNA rectifier or T-type three-level rectifier topology, achieving a power factor of >0.99 and a total current harmonic distortion (THD) of <5% under rated conditions.

Isolated DC-DC Stage: Prefers LLC resonant converters or active-clamp phase-shifted full bridges. Soft-switching technology is used to increase the peak efficiency to 97%-98.5%.

Parallel Current Sharing Technology: Realizes precise current distribution among multiple modules through a CAN bus or a dedicated current-sharing controller, with the static current-sharing imbalance controlled within ±3%.

3.3 Thermal Management and Reliability Engineering

Advanced Cooling System: Liquid cooling solutions are widely used for power modules of 30 kW and above to ensure continuous full-power operation at an ambient temperature of 45°C.

System Fault-Tolerant Design: Adopts an N+X redundancy configuration. When a single module fails, the system automatically redistributes power to avoid interruption of the charging process.

4. Core Technical Challenges and Development Paths

4.1 Energy Efficiency Optimization Technologies

Application of Wide-Bandgap Devices: Under the condition of 1200V/40A, SiC MOSFETs reduce switching losses by 65%-70% compared with silicon IGBTs.

Topology Innovation: New topologies such as three-level ANPC and AIBT significantly improve efficiency characteristics in 800V bus systems.

Intelligent Control Strategy: Dynamic optimization algorithms based on model predictive control (MPC) achieve an efficiency of >96% in the load range of 10%-100%.

4.2 Grid Interaction and Intelligent Management

V2G Technology Implementation: Supports frequency and peak regulation services of the power grid through bidirectional OBCs and intelligent charging piles.

Dynamic Power Control: Adjusts the output power in real time according to power grid dispatching instructions, supporting communication protocols such as IEEE 2030.5.

Predictive Maintenance System: Realizes device-level life prediction by monitoring key parameters such as the equivalent series resistance (ESR) of capacitors and the thermal resistance of heat sinks.

5. Standard Compliance and Test Verification

Safety Specifications: Fully complies with the electrical safety and functional safety requirements of standards such as IEC 61851-1 and GB/T 18487.1.

Energy Efficiency Certification: Meets the 80Plus Platinum level or China’s CQC 1105-2014 energy efficiency standard.

Electromagnetic Compatibility: Passes the CISPR 11 Class A radiated emission test and the IEC 61000-4-4 electrical fast transient (EFT) burst immunity test.

6. Conclusion and Outlook

Switching power supply technology in the field of EV charging is developing in a coordinated manner along three dimensions: high efficiency, high power density, and intelligence. Future technological evolution will focus on the following aspects:

Ultra-High-Frequency Power Conversion: GaN-based MHz-level switching technology will drive power density to exceed 6 kW/L.

System-Level Integration: Through magnetoelectric hybrid integration technology, the system volume will be reduced by more than 35%.

Grid Adaptability: In-depth support for microgrid operation and demand response functions.

New Material Systems: Engineering application of new materials such as gallium nitride-on-diamond (GaN-on-Diamond) and ultra-low-loss magnetic materials.

The continuous innovation of switching power supply technology is the core driving force for promoting the maturity of the EV industry and the upgrading of energy infrastructure. Its technical level directly determines the performance limits, reliability, and whole-life-cycle cost of charging equipment.