The first is Main Harbor Charging, primarily used at home or in the office. This method requires a long charging time of more than three hours and is essential for charging battery electric vehicles (BEVs) and plug-in hybrid vehicles (PHEVs). OBCs are the most common charging method.

The second is destination charging. This is primarily used for short-term charging while parked at locations like movie theaters or restaurants. Its frequency is relatively short, around once a week, and charging times are short, typically under three hours. While not essential, it's advantageous for BEVs and PHEVs.

The final option is Range Extension Charging. This can be understood as a method of refueling electric vehicles. It's used for long-distance driving, such as at highway rest stops. The charging time is less than 30 minutes, which is much shorter than the previous two methods.

OBC types are divided into insulated and non-insulated types.

▲Features of insulated and non-insulated OBC types (Image source: e4ds webinar capture)

The isolated type consists of a PFC stage and a DC-DC stage, and uses a transformer at the DC-DC stage to achieve isolation. The presence of the DC-DC stage in isolated types requires more power semiconductor components. These additional components increase size and weight, reduce power density, and increase price. However, the advantage is that it provides isolation between the AC input and the HV battery, which improves stability and eliminates the need for additional isolation-related monitoring.

Non-isolated types lack a DC-DC stage and provide no isolation between the AC grid and the battery. While regular monitoring is required to ensure proper isolation, this is difficult to implement and prove. The advantage is that the absence of a DC-DC stage allows for a reduction in power switches and other semiconductor components, reducing weight, size, and cost, while also increasing power density.

The vast majority of OBCs in use today are insulated. This is because non-insulated types cannot meet the safety requirements stipulated by international standards such as VDE, ISO, and EN. Currently, many companies are continuously conducting research and development, emphasizing the advantages of non-insulated types.

The power classes of OBCs range from 3.6 to 22 kW.

The 3.6kW OBC, with single-phase input, is used globally and is applied to PHEVs and compact BEVs. The 6.6kW and 7.2kW OBCs, with single input in Asia and North America and dual input in the EU, are the most widely used power classes. The 11kW OBC, with single input in North America and three-phase input in the EU and China, is widely used in mid-range and higher-end electric vehicles. The 22kW OBC, with three-phase input, is actively being developed in Europe and China. Due to cost considerations, the 22kW OBC is expected to be applied to luxury vehicles.

While BEVs and PHEVs utilize various power classes depending on their intended use, the trend is toward higher-power OBCs. As of 2017, approximately 80% of PHEVs were equipped with a 3.6kW OBC, but by 2026, over 90% are expected to be equipped with a 7.2kW OBC. BEVs were also dominated by 3.6kW in 2017, but are expected to move to 7.2kW and 11kW by 2026, with 22kW also expected to account for a portion.

The vice president said that the reason why the OBC power is increasing in BEVs is because as the vehicle driving distance increases, the battery capacity is also increasing, which requires faster charging, so the power of the OBC is also increasing accordingly.

He then divided the OBC trend into four categories and explained them.

▲OBC's Four Trends (Image Source: e4ds Webinar Capture)

The first is the bidirectional OBC. While its development was initially intended to implement a smart grid, today its primary purpose is to satisfy consumer convenience. While bidirectional OBCs accounted for less than 20% of vehicles in 2017, they are expected to be installed in nearly all vehicles by 2030.

As the driving range of electric vehicles increases, so does their battery capacity. The OBC power class is increasing to enable faster charging of larger batteries, according to the report.

High battery voltage is also associated with increased driving range. To increase driving range, one can either increase the efficiency of the inverter or improve the efficiency of the vehicle itself. At this time, the system efficiency can be further increased by increasing it to 800V rather than 400V, and the charging time can be reduced by performing fast charging with DC, so the trend is changing, and the output of the OBC is also being developed to be adjusted to 800V.

The final factor is power density. This is being continuously developed to improve vehicle space utilization. While electric vehicles have simple powertrains, increasing the power density of the OBC allows for smaller components, including the inverter, to be made smaller, reducing weight. A lighter weight also translates to improved fuel efficiency, and this is why continuous development is underway.