Distributed architecture enables high reliability to drive next generation electric vehicle drive systems

Electric vehicles (EVs) and hybrid electric vehicles (HEVs) are evolving, and so are the electronics in them. More and more electronics are playing a major role in the overall build and functionality of these vehicles. But drivers haven’t changed. They still expect their EVs and HEVs to go farther, be more affordable, charge faster, and keep them safe. So how can designers give them more at a lower cost?

As requirements for safety, power density, and electromagnetic interference (EMI) become increasingly stringent, different power architectures have emerged to address these challenges, including distributed power architectures with independent bias supplies for each critical load.

Traditional power architecture in electric vehicles

Automotive design engineers can design for certain power architectures based on the power requirements of electric vehicles. The traditional approach shown in Figure 1 is a centralized power architecture that uses a central transformer and a bias controller to generate bias voltages for all gate drivers.

Figure 1: Centralized architecture in a HEV/EV traction inverter

Centralized architectures have historically been a popular solution due to their lower cost, but they can be difficult to manage faults and regulate voltages, and layout is challenging. Centralized architectures are also susceptible to more noise, and components within one system area are tall and heavy.

Finally, as reliability and safety become top priorities, centralized architectures lack redundancy in power supplies, which can lead to large system failures if a single component in the bias supply fails. Deploying a distributed architecture protects against power supply failures, creating a more reliable system.

High reliability through distributed architecture

If a small electronic component in the traction inverter motor fails while the car is traveling at 65 mph, you don’t want your vehicle to suddenly lose its engine or come to a complete stop. Safety redundancy and backup power within the powertrain system have become standard to ensure safety and reliability.

Distributed power architectures provide redundancy and improve the system's ability to respond to single-point failures by assigning each gate driver a dedicated, local, and easily regulated bias supply close to it to meet the reliability requirements of electric vehicle application environments. For example, if one of the bias supplies associated with a gate driver fails, the other five bias supplies and their associated gate drivers can still operate normally. If five of the six gate drivers are still operating normally, the motor can be decelerated and shut down in a well-controlled manner, or it may continue to operate. With this power system design, passengers in the vehicle will not even be aware that there is a problem.

External transformer bias supplies, such as flyback and push-pull controllers, are tall, heavy and take up a large area, hindering the use of distributed architectures in lightweight electronic devices. Electric vehicle power systems require more advanced devices, namely smaller integrated transformer modules, such as the UCC14240-Q1 isolated DC/DC bias power module, which integrates the transformer and components into an optimized, low-profile planar magnetics module solution.

Integrating planar transformers in IC-sized packages can significantly reduce the size, height, and weight of power systems. The UCC14240-Q1 integrates transformers and isolation to provide simple control and lower primary-to-secondary capacitance, improving common-mode transient immunity (CMTI) in dense and fast switching applications. Fully integrating primary and secondary side control with isolation enables a stable ±1.3% isolated DC/DC bias supply in one device. By achieving 1.5W of output power, even at temperatures up to 105°C, the UCC14240-Q1 can power gate drivers in distributed architectures, as shown in Figure 2.

Figure 2: Distributed architecture in an electric/hybrid vehicle traction inverter using the UCC14240-Q1

Additional Considerations for Driving Powertrain Systems in Distributed Architectures

Electric vehicles require high standards of reliability and safety, and this requirement will permeate the various power conversion electronics. Components must operate in a controlled and verified manner at ambient temperatures of 125°C and above. Isolated gate drivers need to be "smart" and include multiple safety and diagnostic features. The low-power bias supply that powers the gate driver and other electronics in the system also needs to be improved, including achieving low EMI. The UCC14240-Q1 uses TI's integrated transformer technology, combined with a 3.5pF primary-to-secondary capacitance transformer, to reduce EMI generated by high-speed switching and easily achieve CMTI in excess of 150V/ns.

The proximity of the bias supply to the isolated gate drivers in a distributed architecture ensures simpler PCB layout and better regulation of the voltage that powers the gate drivers, which ultimately drive the gates of the power switches. These factors can improve the efficiency and reliability of traction inverters, which typically operate at 100kW to 500kW. These high-power systems require higher efficiency to ensure less heat loss, as thermal stress is one of the main causes of component failure.

As these electric vehicle power systems demand more power, it’s time to consider using silicon carbide and gallium nitride power switches to achieve smaller, more efficient power supplies. Both semiconductor technologies have some advantages on their own, but require tighter regulation of gate driver voltages than the established traditional insulated gate bipolar transistors. They also require components that provide low capacitance and high CMTI across the safety isolation barrier because they switch high voltages faster than previously thought.

Electric vehicles will move towards higher reliability and longer driving distance in the future

Drivers will continue to expect lower emissions, longer range, greater safety and reliability, and more features at lower prices. Meeting these demands on electric vehicles will only be possible with continued advances in power electronics technology, including innovations in power architectures and their associated isolated gate drivers and bias supplies.

Moving to a distributed power architecture greatly improves reliability in isolated high voltage environments, but the challenge is that the additional components lead to higher weight and size requirements. A fully integrated power solution, such as the UCC14240-Q1 bias power module that switches at high frequencies, can save space and achieve lightweighting at the system level.