PDU (Power Distribution Unit) is responsible for the power distribution and management in the high-voltage system of new energy vehicles, providing charging and discharging control, high-voltage component power-on control, circuit overload and short-circuit protection, high-voltage sampling, low-voltage control and other functions for the whole vehicle, protecting and monitoring the operation of the high-voltage system.
PDU can also integrate BMS master control, charging module, DC module, PTC control module and other functions.

BDU (Battery Disconnect Unit) is a type of power distribution box designed for the inside of a battery pack. Currently, BDUs are customized based on the needs of car manufacturers, so it is important to collect customer needs and the electrical performance of the customer’s vehicle. According to the location of the BDU in the battery pack, it can be divided into the type installed inside the battery box and the type installed outside the box (also called battery junction box).

Both the BDU and PDU serve different yet essential roles in managing power in Electric Vehicles and Energy Storage Systems. Understanding their differences is crucial for optimizing system efficiency and safety.

The BDU disconnects the battery in emergencies, while the PDU distributes power to various vehicle or system subsystems.

While both components are involved in managing electrical power, their functions are distinct. The BDU is primarily concerned with disconnecting the battery when necessary, ensuring safety and preventing damage. It monitors the battery’s health and isolates it in case of emergencies or faults. The PDU, on the other hand, ensures that power is evenly distributed across the system, from the battery to individual components like motors and sensors. It helps prevent overloads and ensures the system operates efficiently.

PDU and BDU are typical integrated design products. Therefore, they need to integrate relatively more functions and components. Here are the main ones introduced.

High voltage DC contactor (relay)

According to the conventional circuit, high voltage dc contactor can be divided into high-voltage main positive/main negative contactors (relays), pre-charge contactors, fast charge contactors (relays), PTC heating contactors, air conditioning contactors,etc. Mainstream dc contactor manufacturers can provide models ranging from 10A to 400A.

Fuse

The fuse of the battery pack generally has a main circuit fuse, which is used to protect the battery pack and usually has the largest current; there are other auxiliary circuit fuses. The fuse is generally composed of a tube body, a melt and an end cover. The melt is the most important component, which is composed of a sheet of pure silver strip, and some are made of copper-silver composite strips. The melt is welded on the contact blade and is inside the tube body with the quartz sand. The tube body and the two end covers form a closed space arc extinguishing, and different tube bodies correspond to different voltage levels.

The fuse is connected in series in the circuit to protect the circuit. When overcurrent occurs, the metal component with a smaller cross-sectional area will reach the melting point and have the characteristic of being fusible. The circuit can be cut off (protected) by fusing.

Connectors and MSD

The high-voltage connectors used in electric vehicles are divided into male and female ends. The male end is often in the form of a wire end, and the female end generally has three types of wire outlets: copper busbars, bolts, and cable crimping. In terms of performance, there are also higher requirements than traditional connectors, such as high-voltage interlocking HVIL, IP67/68, IP6K9K protection, flame retardant grade V0, electromagnetic protection, etc.

Current acquisition

There are two common types of components for current acquisition: current sensors and shunts. These components are used in battery detection and require high precision and extremely low offset requirements. The actual current range (for a long time) is recommended not to exceed the rated current. During operation, heat generation requires extra attention. After the temperature rise changes tend to stabilize, the corresponding temperature requirements should be met under different rated currents. If the temperature is exceeded, an alarm should be issued to avoid the sensor temperature being too high, which will reduce the detection accuracy.

Pre-charge resistance

The pre-charge resistor is located in the pre-charge circuit, mainly to protect the battery system from transient shocks when powered on.

Copper busbar

Copper busbars are made of copper material and can be divided into two categories: soft copper busbars and hard copper busbars according to the processing technology.

The current carrying capacity is calculated based on the relationship between the cable’s current carrying capacity and cross-sectional area. The copper busbar cross-sectional area and current temperature rise curve are referenced, and the corresponding copper busbar cross-sectional area is selected based on experience. There will be design redundancy in the early copper busbar design and selection. When a large overload current passes through, it will cause a high temperature rise. It can still withstand the impact of 10 times the rated current within a few seconds.

Box structure appearance and materials

Fixing method

For PDU and BDU installed outside the battery box, in order to meet the IP67 protection level, it is usually necessary to add a waterproof ring seal to the structural design to meet the watertight requirements.

The electrical safety of PDU and BDU requires attention to grounding and creepage distance. Usually, the working voltage of the distribution box for electric vehicles is between 301 ~ 660V. The minimum electrical clearance and creepage distance refer to the standard UL2580 Table 5.1 to determine the minimum electrical clearance.

Other common safety measures include setting up anti-touch finger structures on copper busbars, adding plastic protective caps when the distance between high voltage and low voltage is insufficient, separating high voltage components and low voltage wiring harnesses inside the box to prevent creepage, and adding glass fiber tubes and textile tubes to cables to prevent leakage.

Thermal design is another key technology for PDU and BDU. It is necessary to pay attention to whether there is an on-board charger and DCDC power supply (to confirm the appropriate cooling method with the customer based on the heat generated by the charger and DCDC). At the same time, according to Hotson’s experience, relays can add heat dissipation cold plates, aluminum alloy boxes can add heat dissipation plate structures, and plastic boxes can add heat dissipation ventilation holes, etc. These are all effective solutions.

As the vehicle development cycle continues to shorten, the quality of product development has not decreased. In this case, simulation has become an indispensable technical means. For PDU and BDU companies, simulation analysis is particularly important. Companies need to provide corresponding simulation materials to vehicle or battery system companies in a timely manner so that overall simulation can be carried out.

To facilitate customized BDU/PDU design, customers should provide as much detailed information as possible before project initiation. This information directly impacts the development of design plans and product performance optimization.

Application Scenarios
Describe the practical application scenarios of the device, such as EV power systems, energy storage systems, or industrial power systems.
Rated Parameters
Include rated voltage, rated current, and peak current parameters.
Load Characteristics
Explain the type, quantity, and power requirements of connected loads.
Environmental Requirements
Temperature Range: Operating and storage temperature range.
Protection Levels: Dustproof, waterproof, and shockproof ratings (e.g., IP67).
Special Environments: Indicate if there are extreme conditions like high humidity, salt spray, or high vibration.
Functional Requirements
Protection Features: Indicate if additional protection features like overvoltage or reverse current protection are needed.
Custom Modules: Specify additional functionality, such as remote control or auxiliary power interfaces.
Certifications and Compliance
Provide relevant certification or standard requirements based on the target market or industry, such as:
International Standards: ISO 26262 functional safety certification, UN R100 regulations.
Regional Certifications: UL certification for North America, CE certification for Europe.
Customer-Specific Standards: Internal enterprise requirements or testing standards.
Project Schedule

To ensure timely delivery, customers should clarify project timelines:
Sample Delivery: Expected timeline for sample delivery.
Mass Production Plans: Estimated timeline for mass production and initial demand.
Project Phase: Current project stage (concept design, engineering validation, mass production readiness (EVT, DVT, PVT, MP), etc.).

Customizing PDU and BDU is a complex and critical process that requires a professional technical team and rich industry experience. By defining requirements, providing detailed information, and maintaining effective communication with suppliers, customers can obtain electrical solutions that suit their system needs.
Hotson is committed to providing efficient, safe, customized high-voltage DC contactors for PDU and BDU solutions. For consultation or more information, please visit our website or contact our sales team directly. We look forward to working with you to promote industry development together!