“Electric vehicles (EV) and hybrid electric vehicles (HEV) are constantly evolving, and the Electronic devices in them are also changing. In terms of the overall structure and functions of these vehicles, more and more electronic devices are playing an important role. However, the driver has not changed. They still hope that their electric vehicles and hybrid electric vehicles can travel farther smoothly, become more economical, charge faster, and ensure their safety. So how can designers provide them with more services at a lower cost?
Electric vehicles (EV) and hybrid electric vehicles (HEV) are constantly evolving, and the electronic devices in them are also changing. In terms of the overall structure and functions of these vehicles, more and more electronic devices are playing an important role. However, the driver has not changed. They still hope that their electric vehicles and hybrid electric vehicles can travel farther smoothly, become more economical, charge faster, and ensure their safety. So how can designers provide them with more services at a lower cost?
As the requirements for safety, power density, and electromagnetic interference (EMI) become more and more stringent, different power architectures have emerged to meet these challenges, including distributed power architectures with independent bias power supplies for each critical load.
Traditional power architecture in electric vehicles
Automotive design engineers can design solutions for certain power architectures based on the power requirements of electric vehicles. The traditional method shown in Figure 1 is a centralized power architecture, which uses a central transformer and a bias controller to generate bias voltages for all gate drivers.
Figure 1: Centralized architecture in hybrid electric vehicle/electric vehicle traction Inverter
Centralized architecture has low cost, so this solution has always been popular, but this architecture may be difficult to manage faults and regulate voltage, and the layout is challenging. The centralized architecture is also susceptible to more noise, and the components in a system area are tall and heavy.
Finally, as reliability and safety become the top priority, the power supply of the centralized architecture lacks redundancy. If a single component in the bias power fails, it may cause a large-scale system failure. Deploying a distributed architecture can prevent power failures, thereby 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, everyone certainly does not want the vehicle’s engine to malfunction or stop completely. Safety redundancy and backup power in the powertrain system have become standard equipment to ensure safety and reliability.
The distributed power architecture can allocate a dedicated, local, and easily adjustable bias power supply close to each gate driver to meet the reliability requirements in the application environment of electric vehicles, so it can provide redundancy and improve system performance. The ability to react to a single point of failure. For example, if one of the bias power supplies matching the gate driver fails, the other five bias power supplies and their matching gate drivers can still operate normally. If five of the six gate drivers are still operating normally, the motor can be decelerated and turned off in a well-controlled manner, or it may continue to run. With this power system design, passengers in the vehicle will not even realize that there is a problem.
External transformer bias power supplies (such as flyback and push-pull controllers) are very tall, heavy, and occupy a large area, which hinders the use of distributed architectures in light-weight electronic devices. Electric vehicle power systems require more advanced components, that is, smaller integrated transformer modules, such as UCC14240-Q1 isolated DC/DC bias power modules, which can integrate transformers and components into an optimized, low-height plane Magnetic component module solution.
Integrating a planar transformer in an integrated circuit-sized package can greatly reduce the size, height, and weight of the power supply system. UCC14240-Q1 integrates transformer and isolation, provides simple control and lower primary to secondary capacitance, and improves common-mode transient immunity (CMTI) in dense and fast switching applications. The primary and secondary side control and isolation are fully integrated, and a stable ±1.3% isolated DC/DC bias power supply can be realized in one device. By achieving an output power of 1.5W, even at temperatures up to 105°C, UCC14240-Q1 can power gate drivers in a distributed architecture, as shown in Figure 2.
Figure 2: Distributed architecture in electric/hybrid vehicle traction inverter using UCC14240-Q1
Other considerations for driving the powertrain system in a distributed architecture
Electric vehicles require high standards of reliability and safety, and this requirement will permeate various power conversion electronic devices. The components must be operated at an ambient temperature of 125°C and above in a controlled and proven manner. Isolated gate drivers need to be “smart” and include multiple safety and diagnostic functions. The low-power bias power supplies that power the gate drivers and other electronic devices in the system also need to be improved, including achieving low EMI. UCC14240-Q1 utilizes TI’s integrated transformer technology, combined with a 3.5pF primary-to-secondary capacitor transformer, which can reduce the EMI generated by high-speed switching and easily achieve a CMTI exceeding 150V/ns.
The bias power supply is close to the isolated gate driver in the distributed architecture, which ensures a simpler printed circuit board layout and better regulation of the voltage supplying the gate driver, and finally drives the gate of the power switch. These factors can improve the efficiency and reliability of the traction inverter, which usually allows it to operate from 100kW to 500kW. These high-power systems require higher efficiency to ensure less heat loss, because thermal stress is one of the main causes of component failure.
With the increasing power requirements of these electric vehicle power systems, it is time to consider using silicon carbide and gallium nitride power switches to achieve smaller and more efficient power supplies. Each of these two semiconductor technologies has some advantages, but requires stricter regulation of the gate driver voltage than the mature traditional insulated gate bipolar transistor. They also need to provide low capacitance and high CMTI components on the safety isolation barrier, because they switch high voltage faster than previously thought.
Electric vehicles will move towards higher reliability and longer driving distances in the future
Drivers will continue to expect to buy vehicles with lower emissions, longer cruising range, higher safety and reliability, and more features at a lower price. Only with the continuous advancement of power electronics technology can these requirements for electric vehicles be met, including the innovation of power supply architecture and its related isolated gate drivers and bias power supplies.
Switching to a distributed power architecture greatly improves the reliability in an isolated high-voltage environment, but the challenge is that the additional components will 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 system-level space and achieve lighter weight.