The OBC (On-Board Charger) is one of the interface components of an EV (Electric Vehicle). It must interact with the external environment through connections to the public power grid or dedicated electric vehicle supply equipment. These devices are interfaced with the AC power grid, and their ratings and requirements are beyond the control of the vehicle manufacturer. Therefore, any vehicle that incorporates a built-in charger must comply with certain regulations in order to be sold on the market.

For low-voltage equipment, the IEC 61000-3-2 standard shall be followed, where battery chargers are classified as Class A, covering all electrical equipment (single-phase and three-phase) with a rated current not exceeding 16A (Charging Mode 1) and connected to the low-voltage grid side. For higher current levels, the reference standard is IEC 61000-3-12, which applies to electrical equipment with a rated current greater than 16A and up to 75A, thereby covering the other two charging modes: Mode 2 and Mode 3. Voltage harmonics and flicker caused by the interconnection of the OBC charger are regulated in accordance with IEC 61000-3-3 and IEC 61000-3-11.

The aforementioned IEC power quality standards mainly focus on low-frequency harmonics up to the 40th order. However, advanced power electronic converters with high switching frequencies and low frequency distortion extend the frequency range from the typical 40th harmonic and above to 2kHz–150kHz, i.e., beyond the general harmonic range. Although this phenomenon is not mentioned in the current version of IEC 61851-1 (2019), it has attracted the attention of the industry, such as IEC 61000-2-2:2017.

Due to the evaluation of the battery pack system, strict size constraints are imposed on the OBC during vehicle charging. Additionally, OBCs designed with GaN high-frequency switching will generate superimposed high-frequency ripple currents on the battery pack system. Research has shown that batteries degrade more quickly under charging and discharging cycles with current ripple. Some scholars have studied the long-term impact of superimposed current ripple from 55 Hz to 20 kHz on battery aging using 18650-type batteries. The results indicate that, under the same number of cycles and the same ripple current magnitude, the temperature increase of the battery with the highest frequency ripple is higher than that of other samples. Moreover, the BMS (Battery Management System) protection range is between 10–1 mS, and it cannot activate voltage protection in time to prevent transient overcharge and overdischarge when the frequency is higher than 100 Hz–1 kHz. Although no literature has proposed specific requirements, some ways to properly improve the reliability of the battery pack system are listed in research reports: (a) Ripple current at frequencies above 1 kHz < 5%; (b) Independent AC/DC conversion to reduce ripple content during DC charging and discharging; (c) As shown in Figures 1a and b, the superposition of ripple currents in various CC/CV (Constant Current/Constant Voltage) charging/discharging modes for a battery stack composed of 96 cells. Since lithium-ion batteries (LIBs) are prone to "lithium plating," it is important to reduce charging current and ripple, especially at high states of charge (SoC).

Figure 1: Typical battery current and voltage waveforms: (a) G2V, (b) V2G

Due to the characteristics of switching power supplies, which involve high switching currents and voltages, electromagnetic radiation is generated during operation. This electromagnetic radiation propagates through conductors (conducted emission frequency range: 150 kHz - 30 MHz) or air (radiated emission frequency range: 30 MHz - 1 GHz) and may cause electromagnetic interference (EMI) with surrounding devices. The standard IEC 61851-21-1 defines the electromagnetic compatibility requirements for the conductive connection of electric vehicle on-board chargers to AC or DC power supplies. It adopts the standards of the International Special Committee on Radio Interference (CISPR), which are applicable to vehicles and electronic/electrical components used in vehicles.

IEC 61851-21-1 defines the measurement techniques and conducted emission limits on AC or DC power lines. These guidelines distinguish between Class A (residential) and Class B (light industrial) environments and set peak and quasi-peak limits for conducted emissions. As an automotive electronic product, the limits defined by CISPR 25 and IEC 61000-6-3 form the basis for the design application of OBCs (On-Board Chargers). Consistency testing for conducted emissions also relies on the test methods, test equipment, and correction factors described in CISPR 12, CISPR 16, and CISPR 36. Although conducted emissions can be minimized through modulation schemes and soft-switching techniques, EMI (Electromagnetic Interference) filter circuits are still necessary.

In addition to the basic definition requirements of CISPR 12, the development of CISPR 36 is based on the need to establish a vehicle radiated emission standard covering the frequency range of 150 kHz to 30 MHz (excluding mild hybrid vehicles). Electric vehicles often generate radiated emissions in the low-frequency bands not covered by CISPR 12 (CISPR 12 is also used to protect external receivers at a distance of 10 meters, but the frequency range is 30 MHz to 1000 MHz). To comply with the requirements for radiated interference, the layout of GaN-based OBC (On-Board Charger) designs needs to be optimized as much as possible to reduce radiated emissions caused by high dv/dt during switching instants.

Although bidirectional charging technology already exists, there are still relatively few standards involving bidirectional OBCs (On-Board Chargers). IEC 61851-1 describes the minimum safety requirements that charging equipment must meet for electric vehicle supply equipment with a rated supply voltage below 1 kV. These requirements include ingress protection (IP), leakage and clearance distances, temperature rise, electric shock protection, integrity of protective circuits, connection protocols, and protection against overload and short circuits. Among these, the requirements for contact current and residual current limits must also be strictly enforced by OBCs, with corresponding limits defined by IEC 61140. The limit for touch current passing between any AC interface and the vehicle chassis is 3.5 mA (rms) at 50 Hz. The limits specified by UL 2202 are stricter than those of IEC 61851, with IEC 61851 setting a leakage current limit of 0.75 mA (rms) for Class I electrical equipment. Finally, the literature also introduces non-isolated charger topologies. However, their implementation poses many issues, primarily the generation of leakage currents and the threats they pose to humans and surrounding equipment.

Figure 2: OBC topology

The IEC standards limit leakage current or residual current to 30 mA, which is monitored by the EV supply equipment. Inevitably, most advanced OBC designs adopt isolated converter topologies because they provide a less challenging way to meet the strict requirements of the standards and to mitigate nuisance tripping caused by common-mode currents.

In 2024, the International Organization for Standardization released the standard ISO 5474-2: Electrically propelled road vehicles - Functional and safety requirements for power transfer between vehicle and external electric circuit - Part 2: AC power transfer. This standard specifies the requirements for conductive power transfer using alternating current (AC) between electrically propelled road vehicles and external circuits, with voltages up to 1000 VAC. It also addresses conductive charging and reverse power transfer for Modes 2 and 3, in accordance with IEC 61851-1.

For protection requirements under single-fault conditions: If the vehicle is connected to a load for operation, at least one of the following protective provisions shall apply:

a) Separate residual current protection functions shall be provided, with individual leakage current protection for each on-board standard power socket or vehicle charging port. -- The requirement for leakage current detection is to meet a minimum of 30 mA/AC. If there is direct current in the system, DC leakage must also be detected.

b) An insulation resistance monitoring system shall be provided, which periodically or continuously monitors the insulation resistance of the vehicle's power circuit during vehicle operation.

The main concerns in the transformation of electric vehicles include user experience, range, safety, battery life, charging time, control robustness, and aging. Among these, the stress and lifespan of components are primarily assessed based on the automotive industry's standards set by the Automotive Electronics Council (AEC), specifically AEC-Q100 for Integrated Circuits (ICs) and AEC-Q200 for passive components. These standards include four levels that define environmental conditions, such as temperature and humidity, depending on the location of the device within the vehicle.

Figure 3: International standards related to the OBC applications

Writer：Bobby Guo