Power Electronic Converters for Electric Vehicles – Trends & Challenges

Power Electronic Converters for Electric Vehicles – Trends & Challenges

In the past decade, the demand for sustainable mobility has surged, driven by environmental concerns, accelerated climate change, fossil fuel depletion, and increased energy consumption. Electric vehicles (EVs) have emerged as a promising alternative to traditional internal combustion engine (ICE) vehicles, boasting user-friendly features and cost-effectiveness.

The building blocks for electric vehicles are efficient electric motor drives, high-voltage storage systems, electrified powertrains, and various types of Power Electronic Converters (PECs).  Electric motor drives and Power Electronic Converters (PECs) regulate the flow of electrical energy in and out of vehicles, managing interactions with charging stations and the grid.

PECs are essential for the efficient and rapid control and conversion of electricity, forming the technological foundation for widespread electric vehicle (EV) adoption. This article explores the role of PECs in all-electric vehicles, current trends, and the opportunities and challenges shaping the EV landscape.

Get ready for an insightful journey into electric vehicle technology!

Role of Power Electronic Converters in Electric Vehicles

PECs are typically used in three main systems of an electric vehicle: battery charging, powertrain, and regenerative braking. They are primarily needed for electrical power regulation in these systems.

Additionally, PECs facilitate the operation of various voltage ratings for various electrical loads, including low voltage electronic loads like sensors, tacho meters, and communication systems, as well as high voltage electrical loads like power windows, air conditioning, car interior lighting, electric power steering, and auto start/stop.

The block diagram of a typical electric vehicle with power supply system is shown below:

Power Electronics and Battery Charging System

The Battery charging system plays a major role in design and operation of electric vehicles. During the charging and discharging process, control, conversion, and management of electrical energy come from the power electronics. Two types of charging are possible in electric vehicles – On-board charging and off-board charging.

In Onboard charging, AC-DC converter (Rectifier) which is a type of PEC is used to convert the AC voltage from the three phase AC grid to a DC voltage suitable for charging the vehicle’s batteries, whereas in Off-board charging, DC fast-charging is included.

The PECs in these systems convert the AC supply from three phase AC grid into a high-voltage DC output, which can directly charge the vehicle’s batteries bypassing the . Apart from conversion, PECs regulate the charging rate of battery with the help of advanced control strategies.

While offboard chargers or DC fast charging stations are located outside electric vehicles at locations like parking garages, retail centres, hospitals, and charging stations, onboard chargers and battery storage systems are installed inside these vehicles.

PECs are also essential components of Battery Management Systems (BMS). These systems monitor the health, safety, and optimal operation of the battery pack, ensuring its extended life and effective energy use. EV batteries can be charged quickly and effectively while remaining within their safe operating limits due to advanced charging systems controlled by power electronics.

Power Electronics and Powertrain

For bidirectional power flow between a grid and a vehicle, a Bidirectional DC-DC converter with boost and buck modes are utilized in the powertrain. Both boost and buck modes can be used with a bidirectional DC-DC converter by choosing the appropriate switching patterns.

When in boost mode, it boosts the voltage from battery to a high voltage required for DC bus. This high-voltage DC bus has a voltage level of between 400 and 750 V. The vehicle’s batteries can be recharged when the electric motor’s generated voltage is bucked (stepped down) through a bidirectional DC-DC converter during regenerative braking.

The process of converting the vehicle’s kinetic energy—which is typically lost as heat when braking—into electrical energy that can be stored in the battery for later use is known as regenerative braking. It is a productive method of increasing an electric vehicle’s driving range and lessening the strain on its mechanical brakes.

Power Electronics and Traction Motors

Another type of power electronic converter is the Inverter, used to invert high DC voltage, resulting in a variable AC voltage and frequency supply that can be used to feed and power an electric traction motor. Inverter also determines the driving behaviour and electric motor control.

The inverter always operates in the same way, whether the motor is brushless DC, synchronous, or asynchronous. To improve the range, efficiency and performance of the electric motor, modern inverters also include intelligent control algorithms that enable variable frequency drive.

During regenerative braking, the traction motor functions as a generator. The generated AC power must be converted back to DC power for battery charging.

Innovations in the Field of Power Electronics for Electric Vehicles

Manufacturers of electric vehicles are searching for the newest technological advancements to satisfy the expanding market demands. In this section, we explore innovations and trends in the field of power electronics for electric vehicles.

1. Wide Bandgap (WBG) semiconductor devices

The converter’s core relies on power semiconductors. Wide Bandgap Semiconductors (WBGSs) such as Gallium Nitride (GaN) and Silicon Carbide (SiC) based devices are new types of semiconductor devices on which a lot of research is going on. SiC based converters are used for high voltage and power applications whereas GaN based converters are used for lower-voltage and power.

Si-based power semiconductor technology, which was extensively employed in the electronics industry in previous decades, is no longer adequate for meeting today’s advanced needs. This is primarily due to their limitations in maximum switching frequency and device thermal dissipation.

These drawbacks of Si-based power converters can be addressed by using WBGS-based power converters. In contrast to conventional silicon devices, SiC devices present advantages such as reduced losses, enhanced thermal conductivity, and the capability to function at elevated frequencies. These attributes contribute to the creation of more compact, lighter, and more effective systems, playing a crucial role in extending the mileage of electric vehicles (EVs).

The price of WBGS-based devices is their only limitation. GaN devices are currently much more expensive than Si-based devices, which can be made more affordable by mass producing and shrinking the size of passive parts like capacitors and inductors.

2. Wireless charging technology

Although there are many advantages to using electric vehicles over traditional internal combustion engines (ICE) vehicles, there are still certain drawbacks, such as lengthy charging times, long lines at charging stations, and range anxiety.  These issues are all connected to the state of battery technology today and problems with energy density, cost, and capacity. The primary obstacle remains the absence of effective infrastructure for charging, in contrast to ICE vehicle refuelling stations.

The limitation of the infrastructure for charging can be overcome by using new technologies, such as wireless power transfer, to charge the car while it is moving or stationary. Even though wireless charging technology is still in its early stages of development, a lot of research is being done on it.

Wireless charging allows a vehicle to be charged without a charging cable by simply parking in a designated spot. Electromagnetism of the wire coils can be used to create wireless or inductive chargers. Wireless charging infrastructure still needs to address concerns like cost, performance, safety, and efficient power transfer even though it is a convenient method.

3. Powertrain design with Integrated Power Modules

Integrated Power Modules (IPMs) combine various power electronics components into a single module and offers higher power density, better thermal management, and reduced electromagnetic interference (EMI) than traditional discrete components. Power semiconductor devices lose a substantial amount of power because of reduced chip size, high power density, and increased power demand from electrical loads.

There have been several high-power density power electronics packaging architectures proposed to address the shortcomings of the commercial power modules.  SiC MOSFETs can raise the operating device temperature in traction drive systems without affecting system performance, thus lowering the need for cooling.

4. Aluminium Nitride

Aluminium Nitride (AlN) is an emerging semiconductor in power electronics. It can act as a semiconductor, insulator, and semiconductor based on different temperatures and conditions. AlN exhibits extremely low power loss and efficient power dissipation due to its superior thermal conductivity.

AlN has remarkable mechanical, electrical, and chemical characteristics that could make it one of the best Ultra WBG semiconductors available for the power electronics market. However, the availability and cost of manufacturing AlN compared to SiC and GaN is a challenging process for the coming years.

5. Advanced battery management system

Battery management is another area where PECs are used. Lithium-ion batteries, which are commonly used in EVs, require Battery Management System (BMS) to ensure their safe and efficient operation. BMS helps in regulation of charging and discharging of batteries and thermal management.

In recent times, research work is going on using artificial intelligence (AI) algorithms for forecasting battery health and enhancing charging patterns. Features like state-of-charge estimation, overvoltage protection, and cell balancing are also included in advanced BMS systems.

Analyzing Trends in the Power Electronics Market for Electric Vehicles

The landscape of power electronic converters in electric vehicles is witnessing dynamic shifts, reflecting robust growth in the market. Here are some stats and figures showing how the numbers have been on a roll –

• According to research by Prwireindia and Allied Market Research, in 2018, the market size of power electronics for electric vehicles globally reached $2.59 billion, and it is anticipated to achieve a substantial growth, reaching $30.01 billion by 2026, exhibiting a remarkable CAGR of 35.5% by 2026.
• As per a study conducted by Future Market Insights, anticipated to grow at a 5% CAGR, the demand for power electronics is poised to reach a valuation of US$ 44 Billion by 2032. The market, which is expected to be valued at US$ 28 Billion in 2022, is driven by the expansion of power generation industries and heightened consumption in developing regions.
• Certain reports show that the global market size for electric vehicle power electronics stood at US$ 1.8 billion in 2022 and is forecasted to experience significant growth, with an estimated CAGR of 24.1% from 2023 to 2031. By the end of 2031, it is projected to reach a valuation of US$ 12.8 billion.

Challenges to be Addressed for Power Electronic Converters in Electric Vehicles

1. Recharge electric vehicles with fast charging

Factors like long charging time, queuing time at charging stations, and range anxiety all are related to current battery technology and inefficient charging infrastructure. Fast charging stations that don’t compromise battery health are essential to ensure faster charging of electric vehicles.

New technological solutions are required in the field of power electronics and battery charging system to ensure that chargers can deliver electricity at the highest currents and voltages without getting overcharged or overheated. Off-board charging through fast charging stations where peak demand is planned and managed, can be the key to reducing the impact of electric vehicles on the electricity grid.

2. Efficient thermal management

In countries like India, where climatic conditions get extreme with high temperatures and humidity, a thermal management system is essential for electric vehicles. This is particularly because the extreme climatic conditions can hamper the performance and reliability of power electronics products.

The thermal management system must maintain the proper temperature for the electric motor, power electronics, and battery. Any malfunction in thermal control will cause electric motors to burn out, age, lose efficiency, and demagnetize magnets. It will also shorten their lifespan. In addition to extending the battery cells’ lifespan, an effective thermal management system is a crucial safety measure that averts thermal runaway.

For EVs to operate safely and effectively, designers must take these conditions into account and include the proper thermal management systems.

3. High-power density converters – Increased power per cubic centimetre

High-power density converters are crucial to the powertrain’s ability to maximize vehicle mobility and reduce power consumption. The passive component size in all power converters is inversely proportional to the switching frequency. The most common method for minimizing the size of passive components and lowering the thruster’s volume and weight is to increase the switching frequency.

The size of passive components and switching losses can be reduced in these converters by using WBG semiconductors and raising the switching frequency. However, when passive component volume is decreased, the surface area available for cooling them is also decreased. This could lead to new challenges in high-power density converters.

4. WBG semiconductor impact on EMI

WBG semiconductor-based inverters’ high switching frequency and quick switching present difficulties for EMI problems in the vehicle and shorten the lifespan and operation of the traction motor. While the problems may be resolved by slowing down WBG devices to the same pace as conventional switching devices, doing so will also result in the loss of the efficiency and power density gains that come with switching to WBG devices.

5. Affordability and cost reduction

As the need for luxurious loads grows, so will the number of power electronic converters in the vehicle. PECs result in a rise in the price and dimensions of the car. Electric vehicles need to be affordable for widespread adoption. The challenge is to reduce costs by using smaller and more affordable PEC units in electric vehicles.

6. Unreliable power supply

India’s power supply is unstable, with frequent power outages and variations in voltage.  It will be a challenge for power electronics designers to provide for safe and effective operation of EVs by designing suitable power conditioning and protection mechanism for power electronic products.

7. Life cycle analysis

Life cycle analysis of power electronic converters includes challenges in thermal, insulation, testing, manufacturing, and cost reduction as well as recycling to ensure the sustainability of power electronic products.

Conclusion

In the quest for EV supremacy, overcoming challenges is the name of the game. Addressing hurdles related to range worries and charging infrastructure is the key to unleashing the full potential of electric vehicles. And the advancements in power electronic converters is crucial here.

Thanks to groundbreaking strides in semiconductor materials like AlN, GaN, and SiC, power electronics devices have undergone a metamorphosis. Now, they boast of superior thermal properties and compact dimensions, paving the way for more efficient mobility.

We’re not far from a future where wireless power transfer technology and lightning-fast charging come together, slashing wait times at charging stations and transforming EV journeys into seamless adventures.

Get ready to buckle up for a ride into the future—where every charge is a step closer to a cleaner, greener world!

This entry was posted in Embedded Blog, Blog by Embitel. Bookmark the permalink