Analysis of DC-DC Converter Circuit in OBC System

Hello everyone, today we will discuss a crucial component in the OBC (On-board Charger) system - the DC-DC converter .

The DC-DC converter plays a key role in converting AC power into DC power in the electric vehicle charging system. Different models and power levels have different DC-DC circuit designs and topologies. We will take Tesla Model Y and BYD Haibao as examples to analyze their DC-DC converter circuit design features in detail to help you better understand this core technology.

OBC system composition and the core role of DC-DC converter

The main components of the OBC system include:

AC input interface: Receives external AC power, usually through a household power grid or a charging station.

EMC filter: eliminates electromagnetic interference and ensures stable input current.

PFC (Power Factor Correction) circuit: Corrects the power factor and reduces energy waste.

DC-DC converter: Converts AC power into DC power suitable for battery charging.

Control circuit: monitors the charging process to ensure safety and efficiency.

Among them, the role of the DC-DC converter is crucial, because electric vehicle batteries can only be charged using direct current, and the external power supply received by the OBC is usually alternating current. Therefore, the DC-DC converter is responsible for efficiently converting these alternating currents into direct current.

Analysis of DC-DC Converter Circuit of Tesla Model Y

Power specifications: Tesla Model Y's OBC system supports 11 kW (three-phase) or 7.2 kW (single-phase) AC charging. In order to handle such high-power charging, Model Y's DC-DC converter uses high-efficiency soft switching technology and combines a complex topology to ensure the efficiency of power conversion.

DC-DC topology: The DC-DC converter of Tesla Model Y adopts a full-bridge topology , which is a common design in high-power DC-DC conversion circuits. The full-bridge topology has the following advantages:

High efficiency: The full-bridge circuit controls the current direction through four power switching devices (such as MOSFETs), which can achieve higher efficiency.

High power handling capability: The full-bridge topology is suitable for high-power application scenarios. The 11 kW charging power of Model Y requires processing a large amount of electrical energy in a short period of time to ensure efficient energy conversion.

Soft switching technology: Model Y's DC-DC converter also uses soft switching technology . Compared with traditional hard switching, soft switching reduces switching losses by reducing the transient current and voltage changes generated by the switching device during the switching process. This is particularly critical in high-power applications because switching losses will generate a lot of heat under high-power conditions of 11 kW. Soft switching technology not only improves conversion efficiency by reducing high-frequency losses in the circuit, but also reduces system heat and extends the service life of the equipment.

Working process: AC power enters the OBC system through the input interface. After the EMC filter eliminates electromagnetic interference, the current enters the PFC circuit for power factor correction. The current after PFC correction enters the full-bridge DC-DC converter. The four power switching devices alternately control the current direction and convert AC power into DC power through a high-frequency transformer. Finally, the control circuit monitors and adjusts the voltage and current in real time to ensure safe and efficient charging of the battery.

Circuit features of Tesla Model Y: High-efficiency full-bridge topology : Able to maintain high conversion efficiency in high-power applications, suitable for fast charging scenarios.

Soft switching technology: reduces switching losses and improves conversion efficiency, especially under 11 kW high-power charging conditions.

Highly integrated control system: Tesla uses an advanced software system to manage the operating status of the DC-DC converter in real time to ensure charging safety and system stability.

Analysis of BYD Seal's DC-DC Converter Circuit

Power specifications: BYD Haibao's OBC system also supports 11 kW high-power charging and is compatible with single-phase and three-phase power grids. In order to maintain efficient power conversion in these different charging environments, BYD Haibao also adopts a full-bridge topology and is equipped with a soft-switching DC-DC converter.

DC-DC topology: BYD Haibao's DC-DC converter is similar to Tesla Model Y, and also uses a full-bridge inverter topology . The advantage of this topology is that it can handle higher currents and maintain high conversion efficiency under high power conditions. The full-bridge topology designed by BYD Haibao is mainly aimed at fast charging needs, especially when using three-phase power supply in public charging piles, which can ensure that the vehicle can be charged in a shorter time.

Soft switching technology and features: BYD Haibao's DC-DC converter also uses soft switching technology. This design enables the system to reduce electromagnetic interference and heat loss generated during the switching process. When charging at high power, soft switching not only improves overall efficiency, but also reduces the demand for cooling systems and reduces additional energy losses.

Workflow: When the vehicle is connected to the charging station, external AC power enters through the input of the OBC system. After the EMC filter ensures that the current is stable, the current passes through the PFC circuit for power factor correction. In the DC-DC conversion stage, the current is efficiently converted through the full-bridge topology structure, and the switching loss of the current is reduced through soft switching technology. Finally, the converted DC power is sent to the battery.

Circuit features of BYD Haibao: Combination of full-bridge topology and soft switching : The full-bridge topology is suitable for handling high-power currents, and the soft switching technology ensures efficient operation of the system and reduces switching losses, especially in the 11 kW charging scenario, which can ensure continuous and efficient energy conversion.

Adapt to various charging environments: BYD Haiba's DC-DC converter design not only supports high-power three-phase charging, but is also compatible with single-phase household charging, ensuring the flexibility and efficiency of the system.

Comparison between Tesla Model Y and BYD HiSeal DC-DC converter

The OBC systems of Model Y and BYD SEAL both support 11 kW high-power charging. Both DC-DC converters use a full-bridge topology, which can handle high-power currents and ensure efficient power conversion.

Soft switching technology: The DC-DC converters of both models use soft switching technology. Soft switching is particularly important in high-power applications because it can reduce the loss of switching devices, improve overall efficiency, and reduce heat generation in the circuit. The application of this technology in Model Y and BYD Haibao enables them to maintain high energy conversion efficiency during long-term high-power charging.

The control circuit of Tesla Model Y is highly integrated with its on-board operating system and has dynamic adjustment capabilities, which can optimize the charging process in real time according to the battery status and charging needs. BYD Haibao also has intelligent control functions, but its control logic focuses more on multi-scenario adaptation, including flexible conversion between home charging and public fast charging.

Through the analysis of the DC-DC converter circuits of Tesla Model Y and BYD HiSeal, we can see that in high-power OBC systems, full-bridge topology and soft switching technology have become key designs for improving power conversion efficiency. Both Tesla and BYD use similar technologies, but they are slightly different in control logic and application scenarios.

Tesla Model Y: Through a highly integrated full-bridge topology and intelligent control system, Model Y performs well in high-power fast charging scenarios, especially when used at public charging stations, enabling efficient power conversion and intelligent management.

BYD Seal: BYD's OBC design emphasizes flexibility. It is not only suitable for high-power three-phase charging, but also can take into account single-phase household charging.

The application of full-bridge topology and soft switching technology ensures efficient charging and can maintain stable conversion efficiency under different charging environments.

I hope that through today's explanation, everyone has a deeper understanding of the DC-DC converter circuit of electric vehicles. If you have more questions, please feel free to ask. Thank you!