The Vital Roles of EV Powertrain Components

At a Glance

In this comprehensive article, we shed light on the significance of individual EV powertrain components in driving the E-mobility revolution, especially power electronics. We begin by understanding the basics of power electronics and explore key EV powertrain components like the traction motor, traction battery pack, traction inverter, onboard charger, DC-DC converter, vehicle control unit, and power distribution unit. In the realm of EVs, understanding the significance of these power electronic components and how they interact is crucial. Exro's advancements in power electronics highlight the hidden power that drives the future of electric mobility.

As the world moves towards a cleaner, more sustainable future, electric vehicles (EVs) have taken center stage, experiencing a surge in popularity and adoption. While many enthusiasts and consumers are familiar with the more talked-about components of these vehicles – such as the electric traction motor or battery – there's a whole host of lesser-known but equally important parts working behind the scenes to drive the EV revolution. These unsung heroes are the power electronics, the technology which controls and manages the flow of electricity within the EV powertrain.

It is integral to understand the foundational EV powertrain components that work harmoniously within a vehicle, highlighting the importance and functionality of each. This includes the traction motor and battery along with the key power electronic components like the traction inverter, the onboard charger, the DC-DC converter, the battery management system, the vehicle control unit, and the power distribution unit. By understanding these EV power electronic components, we can better appreciate the intricate technology that propels the cars of the future, ensuring not only their performance but also their efficiency and safety.

Understanding EV Powertrain Components

Before diving into the specific components, let's grasp the basics of power electronics in EVs. Power electronics are the fundamental technology that controls and converts electrical power in various forms to ensure optimal performance of the EV system. These electrical circuits are critical to any EV’s overall performance, efficiency, and cost.

To fully appreciate the function and performance of an EV, it's crucial to gain a clear understanding of its powertrain components, an essential yet often overlooked area of technology. EV powertrain components act as the unsung conductors of the EV’s symphony, orchestrating the flow and transformation of electrical energy throughout the system. They play a critical role in all aspects of an EV's operation, from propulsion and performance to safety and energy management. EV powertrain components are essential to every process involved in making the vehicle operate smoothly, from charging to accelerating and decelerating.

Some typical EV powertrain components include:

Traction Motor

As we embark upon a journey into discovering the purpose of various EV powertrain components, we begin by exploring the EV traction motor. The traction motor is a type of electric motor in an EV powertrain system, serving as the primary propulsion system that drives the wheels. The electric traction motor is a key component that operates by converting electrical energy from the vehicle's traction battery into mechanical energy, providing the necessary torque and power to move the car.

An illustration labelling each parts of an EV traction motor including the rotor and stator.

An electric traction motor consists of two main parts: the stator and the rotor. The stator is the stationary part and is typically made up of copper coils wound around an iron core. These coils are connected to an electrical power source, such as the car's battery. The rotor is the rotating part and is usually equipped with permanent magnets or electromagnets.

When the driver activates the accelerator pedal, the vehicle control unit sends signals to the electric traction motor. The power electronics regulate the amount and frequency of the electrical current supplied from the battery to the motor, determining the motor's speed and torque output. As the electric current flows through the stator coils, it generates a rotating magnetic field, inducing motion in the rotor.

The interaction between the stator's magnetic field and the rotor's magnets causes the rotor to spin. This rotation generates mechanical energy, which is transferred to the wheels to propel the EV forward through a transmission or direct-drive system. This entire process occurs rapidly and without the need for fossil fuel combustion, making electric cars a clean and efficient mode of transportation. Unlike internal combustion engines, electric motors produce instant torque from the moment they start, offering quick acceleration and responsiveness.

EV traction motors fall into two main categories:

  1. Alternating Current (AC) motors: EVs commonly utilize AC motors, categorized into two main types: synchronous and asynchronous motors. Synchronous motors operate at a constant speed that aligns with the supply current frequency, providing higher efficiency and precise control but often coming with more complex and expensive designs. Asynchronous or induction motors, on the other hand, have a rotor speed that slightly lags the supply current frequency. This design lends itself to simplicity and cost-effectiveness, but it may result in lower efficiency at reduced speeds and less precise control over speed and positioning. In crafting the optimal EV driving experience, the choice between these motors depends on the specific application's needs. Synchronous motors are generally chosen for their precision and efficiency, while asynchronous motors are preferred for their simpler and more economical attributes. The careful balance between these characteristics allows engineers and designers to align the motor selection with the overall goals of performance, cost, and complexity.
  2. Direct Current (DC) motors: Most DC motors still fundamentally operate on AC, though utilize mechanical switching, such as a brush and commutator to change the current in the coils. Brushless DC motors, with higher efficiency and electronic commutation, are more commonly seen in EVs. Both brushed and brushless variations, offer simple control and high torque at low speeds. However, their larger size, lower efficiency, and maintenance needs make them less favored for EVs.

Within the two categories, various types of electric motor architectures can be seen in EVs, each with its own advantages and drawbacks. Examples of common EV traction motor types include:

  • DC Series Motor: Utilizes a wound field with both the armature and field windings in series, allowing the current to flow through both windings and creating a strong magnetic field. This design provides high starting torque and is known for its robustness and simple control. While offering high torque at low speeds, the DC Series Motor has drawbacks such as relatively larger size, and maintenance challenges related to brushes and collectors. Performance may also vary over different load and speed conditions.
  • Permanent Magnet Synchronous Motor (PMSM): Uses permanent magnets on the rotor to create a constant magnetic field that synchronizes with the rotating magnetic field in the stator. The synchronization results in efficient and precise torque delivery.
  • Brushless DC (BLDC) Motor: Although named a 'DC' motor, the BLDC is actually a type of three-phase permanent magnet synchronous machine, classifying it as an AC machine. Similar to PMSM, it employs permanent magnets, improving efficiency. BLDC motors are known for a wide constant power range, but high temperatures can negatively impact magnet performance. The lack of brushes in BLDC motors allows for more straightforward maintenance and longer life.
  • Three-Phase AC Induction Motor: Relies on a rotating magnetic field generated by three-phase alternating current (AC) in the stator to induce a current in the rotor, which in turn creates its own magnetic field and causes the rotor to rotate. Induction motors are commonly used in EVs for their simple construction, reliability, and cost-effectiveness, offering field-oriented vector control.
  • Switch Reluctance Motor (SRM): Employs the principle of magnetic reluctance, where the rotor moves to minimize the magnetic reluctance between rotor and stator. SRMs offer robustness, simple control, high efficiency, and wide constant power operation. They lack brushes, collectors, or magnets, making maintenance simple. SRMs are considered suitable for EVs due to their wide operating range.

The efficiency of an EV's motor influences battery weight, as lower efficiency requires more battery power. The motor's performance is determined by its torque-speed and power-speed characteristics, affecting factors like gradeability and maximum speed.

Traction Battery Pack

Continuing along the path of exploring the critical roles of EV powertrain components, we come across the traction battery pack. The traction battery pack is a crucial component of an EV. It is a large battery system that stores and provides the necessary electrical energy to power the electric motor and other various electrical systems in the vehicle.

An illustration of an EV traction battery pack, showcased within an EV structure.

Typical components of the traction battery pack include:

  • Battery Cells: The battery pack is made up of numerous individual battery cells. These cells are typically lithium-ion (Li-ion) or, in some cases, other advanced chemistries. Li-ion cells are preferred due to their high energy density and ability to store a large amount of energy in a compact form.
  • Battery Management System (BMS): The BMS is a sophisticated power electronics system that monitors and manages the battery pack. It ensures that each cell operates within safe limits, prevents overcharging or discharging, and monitors the battery's temperature. The BMS plays a critical role in maximizing the battery pack's performance, safety, and lifespan.
  • Cooling and Thermal Management: During the cold winter months, EVs can experience reduced range since they naturally produce less wasted heat than a traditional internal combustion engine (ICE) which would normally be converted into thermal comfort for the cabin. Instead EVs must utilize more power from the battery for all systems to function properly under extreme cold temperatures. The active cooling and thermal management system helps regulate the temperature of the battery pack at both extremes by cooling it in hot weather, often using liquid coolant that circulates through the battery pack and heating it in cold weather with electric heaters or heat pumps to ensure optimal operating temperatures for the battery.

One significant advantage of traction battery packs in EVs is their ability to support regenerative braking. When the driver decelerates or applies the brakes, the electric motor can act as generators, converting some of the kinetic energy back into electrical energy. This regenerative energy is then fed back into the battery pack through the traction inverter, effectively recharging it and increasing overall energy efficiency.

Boost your EV range or downsize battery packs without sacrificing range.
Boost your EV range or downsize battery packs without sacrificing range.

Traction Inverter

A visual of the Exro Coil Driver™ traction inverter connected to an electric traction motor.

One of the cornerstones of an EV’s power electronics is the traction inverter. At the most basic level, the traction inverter, as its name implies, is responsible for "inverting" the DC stored in the batteries to AC used by the motor to propel the vehicle.

However, the traction inverter’s job doesn't just stop at conversion. It also plays a pivotal role in controlling the speed and torque of the electric motor. It does this by adjusting the frequency and amplitude of the AC current supplied to the motor. The frequency determines the speed at which the motor runs, while the amplitude affects the motor's torque. By carefully controlling these factors, the traction inverter dictates the vehicle's speed and acceleration.

Exro Printed Circuit Board in foreground of Calgary Manufacturing Cleanroom.

Inside the robust casing of a traction inverter, we will find a complex array of Printed Circuit Boards (PCBs). These PCBs house numerous electronic components such as capacitors, resistors, and semiconductor devices like Insulated-Gate Bipolar Transistors (IGBTs) or Silicon Carbide (SiC) transistors. Each of these components plays a critical role in controlling and managing the flow of electricity.

The IGBTs or SiC transistors act as high-speed switches that turn on and off thousands of times per second. When these switches are off, the current doesn't flow, but when they're on, the current does flow, creating a 'pulse' of energy. By varying the width and frequency of these pulses (a technique known as pulse-width modulation), the inverter can create a waveform that closely mimics AC.

Considering the crucial role it plays, it's clear that the efficiency and reliability of the traction inverter can significantly impact an EV's performance. This is where Exro Technologies Inc. has made a game-changing contribution with its Coil Driver™ technology.

Exro's Coil Driver™ uses next-gen coil switching technology in its traction inverter to enhance EV performance. The coil switching technology makes it possible for electric motors to operate at optimal efficiency across a broader range of speeds and loads. In other words, it allows the motor to adapt to varying driving conditions in real-time, ensuring that the motor always operates at its highest efficiency. This results in increased energy efficiency, extended range, and overall improved performance of the vehicle.

For those interested in taking a deep dive into traction inverters, their evolution, and intricacies, we have compiled a detailed three-part article. You can read the article starting at part 1 of the series.

Onboard Charger

Within the complex network of power electronics in EVs, the onboard charger plays a vital role. However, its future relevance is uncertain, as its functions are increasingly being incorporated into either the traction inverter or the battery pack itself.

At its core, the onboard charger is tasked with a crucial responsibility: transforming the AC from an external power source, such as an AC charging station, into DC that can be stored in the vehicle's battery. While there are both AC and DC EV charging stations, the electric grid that sends electricity to power our homes and businesses operates using AC. AC is cost-effective but offers lower power levels, while DC is more expensive but offers faster charging. For a DC charger, no conversion or rectification is required within the vehicle as the rectifier is built into the external DC charger, however, with AC chargers, the current needs to be rectified to DC before it can be stored and managed in the battery pack, which is accomplished by the onboard charger inside the vehicle. The onboard charger intelligently collaborates with the vehicle control unit and charging station to determine the proper amperage and charging standard.

Safety features are intricately integrated into the onboard charger's design, including mechanisms that curtail power delivery if the load surpasses predefined limits and a well-engineered separation between external hardware and internal components. Recognizing the onboard charger's pivotal role as a conduit for data exchange between the EV and the grid, cybersecurity measures are of utmost importance.

The standard capacity for a single-phase onboard charger can range from 3.3kW; typically seen in Plug-in Hybrid Electric Vehicles (PHEVs) to ~7kW; most commonly seen in EVs. Meanwhile, to achieve maximum charging speeds with an 11kW power rating, a three-phase onboard charger is required. While 22kW onboard chargers exist, they are uncommon since most 22kW charging stations supply DC instead of AC, therefore an onboard charger is redundant.

A vehicle-to-everything (V2X) onboard charger carries grid-interconnection capabilities for vehicle-to-grid (V2G) chargers to supply electricity back to the grid, serving demand responses. Vehicle-to-home (V2H), or vehicle-to-load (V2L) solutions are also significant, essentially turning the vehicle into a mobile energy storage system that can be used as backup power during an outage to operate external electric systems using the vehicle’s battery power.

Image of an EV charger with graphic overlays highlighting EV charging functions

At Exro Technologies, a North American technology company, there have been major strides made in eliminating the onboard charger from the EV powertrain and integrating its functionality into the traction inverter. Unlike the onboard charger which is limited to 22 kW in a three-phase system, the Coil Driver™ traction inverter dual-functions as an onboard charger and is only limited by the power rating of the motor. For a commercial vehicle, this is ~300kW, competing with the highest power DC chargers with the potential upside of being much more cost-effective than a separate onboard charger.

This innovation is a testament to the seamless integration of power electronics components. Traditionally, the traction inverter and the onboard charger have been distinct entities within the EV's architecture. However, Exro has reimagined this paradigm. With the Coil Driver™, the traction inverter is empowered to double as an onboard charger, breaking down barriers between components and streamlining the charging process and overall vehicle architecture.

Imagine pulling up to a charging station and plugging in your EV. Behind the scenes, the Coil Driver™ traction inverter steps up to the challenge. It efficiently converts AC power from the charging station into the required DC power for battery storage, ensuring minimal energy loss during the transformation. Moreover, the dual functionality of the Coil Driver™ enables Level 2 charging, which offers faster charging times compared to standard Level 1 charging.

In the dynamic world of power electronics, the onboard charger stands as a testament to innovation's power to transform energy conversion and charging efficiency. And with Exro's groundbreaking Coil Driver™ technology leading the charge, the boundaries between components continue to blur, creating a more integrated and optimized EV ecosystem. Join us as we venture further into the intricacies of power electronics, shedding light on the components that fuel the electric vehicle revolution.

DC-DC Converter

As we continue our expedition through the components of an EV powertrain, we encounter a discreet yet necessary component: the DC-DC converter. While often overshadowed by its more prominent counterparts, the DC-DC converter plays a pivotal role in optimizing the functionality of various auxiliary systems within an EV.

To comprehend the DC-DC converter's significance, let's explore its primary purpose. In the intricate ecosystem of an EV, power sources can vary. While the main battery pack generates high-voltage direct current (DC) that propels the vehicle, other auxiliary systems within the EV—such as lighting, infotainment, and air conditioning—often require lower-voltage DC. This is where the DC-DC converter enters the scene.

The DC-DC converter serves as a bridge between these disparate voltage levels. It takes the high-voltage DC from the main battery and transforms it into the lower-voltage DC needed to power the ancillary systems. By facilitating this conversion, the DC-DC converter ensures that these systems receive a stable and appropriate power supply, to prevent system failures from excessive voltage delivery.  

Within the compact confines of the DC-DC converter lies a network of power electronics and circuitry. These components work in harmony to manage the transformation of voltage levels. Capacitors, inductors, and semiconductor devices, such as diodes and transistors, orchestrate the conversion process. The converter carefully controls the flow of electrical energy, maintaining a delicate balance between power input and output.

As we journey through the realm of power electronics in EVs, each component unveils its unique role in shaping the future of transportation. In our next segment, we'll illuminate the intricacies of the vehicle control unit, a powerhouse of intelligence that orchestrates the symphony of an electric vehicle's operations. Stay tuned as we delve deeper into the layers of technology propelling the EV revolution forward.

Vehicle Control Unit

Moving forward in our journey through the world of EV power electronics, we encounter the vehicle control unit. If we consider the traction inverter to be the 'heart' of an EV, converting and directing electrical power, then the vehicle control unit is the 'brain', controlling and coordinating all the vehicle's primary functions, offering complete control across the EV powertrain.

The Exro Vehicle Control Unit controls the primary functions of the EV powertrain

The vehicle control unit acts as the central communication hub for the vehicle, gathering and processing data from numerous sensors and controllers spread across the vehicle's systems. These could include components related to the electric motor, battery, and charging system, among others. After processing this data, the vehicle control unit determines the most efficient and effective response and sends out appropriate control signals.

For instance, when you press the accelerator, the vehicle control unit computes how much power is needed from the battery, communicates with the traction inverter to convert the right amount of energy, and ensures the motor receives it and delivers the torque to the wheels to provide the desired acceleration. Moreover, the vehicle control unit continuously optimizes vehicle performance, balancing power distribution, managing battery charging, and ensuring safety features function correctly.

Considering the vehicle control unit's integral role, it's evident that having a robust and reliable vehicle control unit is paramount. Not only must the hardware be capable of handling complex tasks and high data volumes, but the embedded software also must be dependable and highly efficient.

Exro Technologies Inc. understands the importance of the vehicle control unit in the EV ecosystem. Exro Vehicle Systems (EVS) provides comprehensive vehicle control unit solutions designed for reliable and efficient performance to ensure seamless communication and coordination between all the components within the EV powertrain, facilitating optimum vehicle performance and safety.

Power Distribution Unit

As our exploration of the intricate web of power electronics in EVs continues, we turn our focus to a key orchestrator behind the scenes: the power distribution unit. Often operating quietly and out of the spotlight, the power distribution unit plays a vital role in distributing and managing electrical energy within the EV's complex architecture.

The Exro Power Distribution Unit manages the distribution of electrical energy within the EV powertrain.

The power distribution unit is responsible for handling the distribution of high-voltage electricity from the battery to various EV powertrain components such as the traction inverter. Its primary task is to ensure that each system receives the right amount of power, at the right voltage, and at the right time. This orchestration is crucial for optimizing performance, enhancing efficiency, and maintaining the overall health of the EV powertrain.

At its core, the power distribution unit is composed of intricate circuitry and power electronics. Its components, which include relays, switches, fuses, and sometimes advanced semiconductor devices, form a sophisticated network that carefully directs electrical currents. By intelligently routing energy to where it's needed most, the power distribution unit helps prevent overloading of certain systems while enabling others to operate at peak efficiency.

In a rapidly evolving EV landscape, the role of the power distribution unit becomes even more pivotal. As new technologies emerge and the demand for energy-efficient features increases, the power distribution unit must adapt to accommodate higher power levels and more intricate energy management requirements. Furthermore, the power distribution unit's ability to handle different voltage levels becomes increasingly important as EVs transition from traditional 400-volt battery systems to more advanced 800-volt architectures.

In the dynamic interplay of power electronics, the Power distribution unit ensures that every subsystem receives its designated share of energy, contributing to a harmonious and efficient driving experience.

Join us in our ongoing exploration as we delve into the future landscape of power electronics and Exro’s role in shaping the e-mobility landscape.

The Future Landscape of EV Powertrain Components and Exro’s Involvement

Exro's power electronics ecosystem is comprised of the Coil Driver™ traction inverter, Cell Driver™ commercial and industrial energy storage system, and Exro Vehicle Systems; end-to-end EV engineering solutions.

In an era of accelerated global electrification, the landscape of EV technology is ever evolving. Exro stands at the forefront of this revolution, dedicated to delivering clean technology solutions that not only transform the power electronics industry but also redefine the way we approach electrification.

The centerpiece of Exro's innovative approach to power electronics is the Coil Driver™, a next-generation traction inverter that heralds a new era in EV technology. Unlike traditional inverters, the Coil Driver™ enables two operating modes within a single motor. Through its underlying coil switching technology, it ensures optimum efficiency and performance, perfectly sizing a machine to an application. For those seeking an in-depth exploration of the coil switching technology, Exro's white paper offers a comprehensive analysis.

Moreover, the Coil Driver™ serves a dual function as an on-board charger. By incorporating this feature, Exro streamlines the entire EV architecture, enhancing functionality while minimizing complexity. It's a breakthrough that not only simplifies the vehicle's powertrain system but opens new avenues for higher power AC charging, providing a cost-efficient alternative to DC Fast-Charging (DCFC).

Exro's commitment to innovation doesn't stop at mobile electric technology. We are also making significant strides in Battery Control Systems (BCS) and Energy Management Systems (EMS). Currently, these efforts are concentrated on stationary energy storage system (ESS) applications for commercial and industrial domains. By expanding our reach into these sectors, Exro ensures that our expertise in power electronics translates into sustainable solutions across a broader spectrum of energy needs and allows us to leverage our power electronics expertise across a wide technology ecosystem.

At Exro, we understand that the future of energy is not merely a transition to electric power, but a transformation towards smarter, more responsible, and more adaptable ecosystems. Our passion for technology, coupled with a commitment to environmental stewardship, positions us as a thought leader in the industry.

As we continue to chart new paths, break down barriers, and set new standards, we invite you to join us on this electrifying journey. Together, we can shape a world where power is not just about consumption, but about conscious creation and conservation, aligned with the highest principles of environmental responsibility and human ingenuity. Minimum energy – maximum results.

Learn how Exro is reshaping EV powertrain

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