How Is the High Voltage System and Powertrain Designed in Electric Trucks and Buses?
Introduction: Understanding High Voltage Systems in Electric Trucks and Buses
As a core enabler of sustainable transportation, electric vehicles rely heavily on high voltage architecture to deliver efficiency, safety, and reliability.c
In electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs), a high voltage system typically refers to any electrical system operating above the conventional safety threshold. This system is responsible for energy storage, power distribution, conversion, and utilization, making it a critical foundation of modern electric truck platforms and electric bus platforms.
This article aims to help OEMs, vehicle integrators, and engineering teams better understand the powertrain layout and high voltage system architecture used in commercial EVs. It also demonstrates Brogen’s capabilities in battery system integration, where we integrate proven standard battery packs with BMS, battery thermal management, and high-voltage systems to build reliable EV power systems—faster and with lower technical risk.
1. Why Powertrain Layout Matters in Commercial EVs
An electric vehicle powertrain refers to the system that converts electrical energy into mechanical motion. A typical EV powertrain consists of:
- Battery pack for energy storage
- Inverter to convert DC power into AC power
- Electric motor to generate mechanical torque
- Transmission or reduction system to deliver power to the wheels
In commercial electric vehicles, powertrain layout plays a decisive role in multiple aspects:
1.1 Performance and Efficiency
- Adapting to complex duty cycles
Commercial EVs often operate under demanding conditions such as frequent stop-and-go driving, heavy payloads, steep gradients, and long-distance cruising. Optimized layouts—such as multi-speed transmissions or dual-motor systems—help motors operate closer to their optimal efficiency zones across varying speeds and loads. - Improving energy utilization
By shortening power transmission paths and reducing mechanical losses, integrated solutions such as electric drive axles can significantly improve drivetrain efficiency and extend vehicle range.
1.2 Space Utilization and Vehicle Packaging
- Maximizing cargo and passenger space
Commercial vehicles must balance propulsion components with cargo or passenger capacity. Compact powertrain layouts free up valuable vehicle space. - Enabling flexible battery placement
Powertrain layout must be coordinated with battery system integration. A compact drivetrain allows greater flexibility in battery pack size, placement, and capacity.
1.3 Reliability and Durability
- Reducing failure risks
Rational layout design minimizes mechanical stress, vibration, and thermal interference between components. Modular and integrated designs improve serviceability and system reliability over long operating cycles.
1.4 Cost Control and Total Cost of Ownership (TCO)
- Lower manufacturing and assembly costs
Integrated solutions such as e-axles reduce part count, wiring complexity, and assembly steps. - Reduced operating costs
Higher drivetrain efficiency lowers energy consumption, while improved reliability reduces maintenance and downtime—both critical factors for fleet operators.
1.5 Intelligence and Future Scalability
- Supporting intelligent vehicle functions
Precise torque control and fast system response enabled by optimized layouts form the hardware foundation for advanced driver assistance and autonomous driving features. - Future-proofing vehicle platforms
Scalable powertrain architectures allow easier upgrades of battery technology, motors, or control strategies as EV technology evolves.
2. Typical EV Architecture Overview
In China’s EV industry, the three core propulsion systems—battery, drive motor, and motor controller—are commonly referred to as the “Big Three,” as they directly determine range, performance, and intelligence.
Supporting systems such as the Power Distribution Unit (PDU), On-Board Charger (OBC), and DC/DC converter are often called the “Small Three,” responsible for power distribution, conversion, and energy management.
Typical high voltage architecture in commercial EVs:
Battery Pack → PDU → Inverter → Motor
The PDU distributes high-voltage power from the battery to the inverter and auxiliary systems. The inverter drives the motor, while operational feedback is shared with the BMS and vehicle control systems to ensure safe and efficient operation.
3. Key Differences Between Electric Trucks and Electric Buses
While both belong to commercial EVs, electric truck platforms and electric bus platforms prioritize different design goals.
- Electric trucks focus on heavy payload capability, long range, and adaptability to complex operating conditions.
- Electric buses emphasize passenger comfort, urban operational efficiency, thermal stability, and intelligent service functions.
Typical Battery Placement and Capacity Ranges
| Vehicle Type | Battery Placement | Typical Capacity |
|---|---|---|
| Mini truck / Van | Under chassis | 10–50 kWh |
| Light / Medium truck | Center, side rails, behind cab | 18–160 kWh |
| Heavy truck | Behind cab, under cabin | 200–600 kWh |
| Bus / Coach | Roof, rear, or underfloor | 100–500 kWh |
Battery placement directly affects vehicle balance, cooling strategy, and high voltage routing, making early-stage layout planning essential.
4. Key Subsystems Explained
4.1 Powertrain Layout Options
Electric drive systems typically include a motor, motor controller, and reduction gear. The evolution of layouts includes:
- Central drive units replacing internal combustion engines but retaining driveshafts and axles
- Integrated electric drive axles (e-axles) combining motors with axles for higher efficiency
- Wheel-side drive systems eliminating driveshafts and differentials through electronic differential control
- In-wheel motors, offering the highest integration level and efficiency, with reduced mechanical losses and weight
Each architecture impacts battery placement, cooling design, and system complexity differently.
4.2 PDU and High Voltage System Design
Commercial EVs often operate at voltages exceeding 700V and currents up to 400A, posing significant challenges to high voltage system design.
The Power Distribution Unit (PDU) is a critical safety and control component responsible for:
- High-voltage power distribution
- Circuit control and protection
- Coordination between propulsion, charging, and auxiliary systems
Well-designed PDU and high voltage architecture incorporate multi-layer safety mechanisms to mitigate electrical, thermal, and operational risks.
4.3 Battery System and Thermal Management
Due to their size and power density, battery packs generate substantial heat during operation. Effective battery thermal management is essential to:
- Maintain optimal operating temperature (typically 20–40°C)
- Improve battery lifespan and energy efficiency
- Prevent safety risks such as thermal runaway
Modern systems may combine liquid cooling battery designs, air cooling, and heating functions to ensure temperature uniformity and safety across all operating conditions.y.
4.4 BMS and Vehicle Control Integration
The Battery Management System (BMS) acts as the “brain” of the battery pack, continuously monitoring voltage, temperature, current, and state of charge.
The Vehicle Control Unit (VCU) coordinates vehicle-level functions such as torque requests, energy recovery, and safety strategies. Seamless communication between BMS and VCU is fundamental to safe, efficient, and intelligent EV operation.
5. Common Design Challenges in Battery Systems
Battery system design faces three major challenges: space constraints, thermal control, and reliability.
5.1 Space Constraints
- Limited vehicle packaging space requires tight integration between battery packs and chassis
- Increasing energy density often competes with space needed for cooling channels, structural components, and safety features
5.2 Thermal Management Challenges
- High-rate charging and discharging generate significant heat
- Temperature non-uniformity accelerates aging and increases safety risks
- Extreme climates require both cooling and heating solutions
5.3 Reliability and Safety
- Battery packs must withstand vibration, shock, and fatigue over long service lives
- High-voltage electrical safety and thermal runaway prevention are critical design priorities
6. Why Standard Battery Packs Are a Practical Solution
Using standardized battery packs is an effective strategy to address these challenges:
- Modular dimensions and interfaces enable flexible integration across vehicle platforms
- Proven designs simplify battery thermal management and reduce development risk
- Validated structures improve reliability, safety, and serviceability
- Scalable configurations allow capacity adjustment without redesign
- Mass production lowers cost and shortens development cycles
Standard battery pack strategies are becoming a key pillar of modern battery system integration.
In a future article, we will further explore how standardized platforms accelerate commercial EV development and reduce total lifecycle cost. If you are evaluating battery pack solutions or need support with high voltage architecture design, feel free to contact our engineering team for a technical discussion or quotation.
