Electric vehicles (EVs) and hybrid electric vehicles (HEVs) are constantly evolving, and the electronics within them are also changing. An increasing number of Electronic devices play an important role in the overall construction and function of these vehicles. However, the driver has not changed. They still want their electric and hybrid electric vehicles to travel farther smoothly, become more affordable, charge faster, and keep them safe. So how can designers do more for them at a lower cost?
As requirements for safety, power density, and electromagnetic interference (EMI) become more stringent, different power architectures have emerged to address these challenges, including distributed power architectures with independent bias supplies for each critical load.
Traditional Power Architectures in Electric Vehicles
Automotive design engineers can design options for certain power architectures based on the power requirements of an electric vehicle. 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 HEV/EV Traction inverter
This solution has historically been popular due to its low cost, centralized architecture, but it can be difficult to manage faults and regulate voltages, and layout can be challenging. Centralized architectures are also susceptible to more noise, and the components within one system area are taller and heavier.
Finally, with reliability and safety a top priority, centralized architectures lack redundancy in power supplies, which can lead to large system failures if a single element in the bias supply fails. Deploying a distributed architecture protects against power failures, resulting in 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 the vehicle to suddenly fail or come to a complete stop. Safe redundancy and backup power within the powertrain system have become standard to ensure safety and reliability.
Distributed power architecture can assign each gate driver a dedicated, local, easily regulated bias supply close to it to meet reliability requirements in electric vehicle application environments, thus providing redundancy and improving system reliability. Responsiveness to a single point of failure. For example, if one of the bias supplies paired with the 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 functional, the motor can slow down and shut down in a well-controlled manner, or may continue to run. With this power system design, the occupants in the vehicle don’t even realize there is a problem.
External transformer bias supplies, such as flyback and push-pull controllers, are tall, heavy, and have a large footprint, preventing the use of distributed architectures in lightweight electronics. 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 transformers and components into an optimized, low-profile plane Magnetics module solution.
Integrating a planar transformer into an IC-sized package can drastically reduce the size, height, and weight of power systems. The UCC14240-Q1 integrates a transformer and isolation to provide simple control and low primary-to-secondary capacitance, improving common-mode transient immunity (CMTI) in dense and fast switching applications. Fully integrated primary and secondary side control and isolation enables a stable ±1.3% isolated DC/DC bias supply in one device. By achieving an output power of 1.5W, even at temperatures as high as 105°C, the UCC14240-Q1 can power gate drivers in distributed architectures, as shown in Figure 2.
Figure 2: Distributed Architecture in Electric/Hybrid Vehicle Traction Inverter Using UCC14240-Q1
Additional Considerations for Driving Powertrain Systems in a Distributed Architecture
Electric vehicles require high standards of reliability and safety, and this requirement permeates all power conversion electronics. Components must operate in a controlled and proven manner at ambient temperatures of 125°C and above. Isolated gate drivers need to be “smart,” including several safety and diagnostic features. The low-power bias supplies that power the gate drivers and other electronics in the system also need improvements, including achieving low EMI. The UCC14240-Q1 leverages TI’s integrated transformer technology, combined with a 3.5pF primary-to-secondary capacitive transformer, to reduce EMI from high-speed switching and easily achieve CMTI in excess of 150V/ns.
The proximity of the bias supply to the isolated gate driver in a distributed architecture ensures simpler printed circuit board layout and better regulation of the voltage powering the gate driver, which ultimately drives the gate of the power switch. These factors can improve the efficiency and reliability of traction inverters, which typically allow them to 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 the power requirements of these EV power systems increase, it is time to consider the use of silicon carbide and gallium nitride power switches for smaller, more efficient power supplies. Both semiconductor technologies each have some advantages, but require tighter gate-driver voltage regulation than well-established conventional insulated gate bipolar transistors. They also require components that provide low capacitance and high CMTI on the safety isolation barrier, as they switch high voltages faster than previously thought.
Electric vehicles will move towards higher reliability and longer driving distances in the future
Drivers will continue to expect vehicles with lower emissions, longer range, greater safety and reliability, and more features at lower prices. These demands for electric vehicles will likely only be met with advances in power electronics, including innovations in power architectures and their associated isolated gate drivers and bias supplies.
Switching to a distributed power architecture greatly improves reliability in isolated high-voltage environments, but the challenge is that additional components result in higher weight and size requirements. Fully integrated power solutions, such as the UCC14240-Q1 bias power module that switches at high frequencies, can save system-level space and enable lightweighting.
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