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Developing microcontrollers (MCUs) for motor control in electric vehicles requires an optimal combination of performance, integration, networking and functional safety. Engineers must design these processors to efficiently control the traction inverter while keeping in mind the need for miniaturization and low cost to meet carmaker requirements. On top of these concerns, there are issues around reliability, safety and security.
EV traction inverters are used to convert DC power from the high-voltage battery into AC power to drive the motor. Using an MCU to control the traction inverter effectively controls the spinning of the traction motor and the propulsion of a vehicle.
“The MCU provides the brain of the EV motor by accepting torque control commands from other sources across the vehicle, such as the accelerator/brake pedals, ADAS control, chassis and vehicle dynamics/electronics stability control, and intelligently controlling the switching of the high-voltage DC battery to rotate the EV motor with multi-phase AC current through electromagnetics,” said Brian Carlson, director of global product and solutions marketing at NXP Semiconductors.
In addition, advanced EV motor control can synchronize the motor control across multiple motors to support torque vectoring, which provides improved handling and vehicle control for a better driving experience, Carlson added.
Key challenges
The biggest concerns in EV motor control include requirements for higher efficiency and further miniaturization, which are also related to the need to extend EV range. Cost is another big issue as carmakers look for new ways to reduce their overhead.
“The major challenges in this application are having high efficiency, the need for miniaturization and having low cost,” said Steve Van Singel, director of the U.S. automotive MCU product marketing and application engineering group at Renesas Electronics. “Product reliability is also important.”
The two primary issues are cost reduction of EVs and addressing the range anxiety of consumers, NXP’s Carlson added.
“Carmakers are looking for ways to design EVs more cost-effectively to extend the range of EVs into lower-tier vehicles as they plan to shift from internal-combustion engines to EVs over the next 10 to 15 years,” he said. “EV motor control and related technologies are evolving rapidly to address multiple industry challenges and concerns.”
One way to address these concerns is to pack the MCUs with high-performance CPU cores. Renesas’s MCUs use high-performance cores and motor control accelerator hardware. “These elements enable high-speed, high-efficiency motor control applications,” Van Singel said.
How does this translate into higher power efficiency for EV traction inverters?
“In order to achieve high-power–efficiency inverter control, it is necessary to acquire the values of the current sensor and angle sensor without much delay and to perform feedback calculations of the next PWM output values at the appropriate time,” Van Singel said. “Feedback calculations should be able to be calculated for more advanced motor control algorithms. These algorithms require CPUs capable of high-speed calculations and/or auxiliary accelerators, A/D converters and sensor interfaces that are tightly integrated.
“In addition, the feedback frequency tends to become shorter as the motor rotates at higher speeds. As power semiconductors evolve in the future, computing performance must increase even more to support these trends,” he added. “If the frequency of the CPU is increased in order to increase the processing power, power consumption including device heating will become important, so a well-balanced MCU that can withstand in-vehicle conditions is required.”
High-performance MCUs for EV motor control can perform machine-learning (ML) inferencing and advanced control algorithms that improve over time to provide higher efficiency and performance, with secure connections to the cloud for data and over-the-air (OTA) updates back to the MCU, according to NXP’s Carlson.
Carmakers are also addressing these issues by “leveraging new technologies to reduce the number of components, weight and size of the EV motor, as well as increasing the power efficiency and power density [more power in less area] to offer vehicles with longer range and smaller, more efficient motors that can also free up precious space in their vehicles to provide more room and features for their customers,” Carlson said.
“Being able to support entry vehicles with a single motor, premium vehicles with dual motors, performance vehicles with three motors and off-road/4WD vehicles with four motors is also a challenge, so they need solutions that can scale across their fleets with a different number of motors in a coordinated way for highest efficiency,” he added.
Higher integration
Integration plays a key role, with the need to incorporate higher functionality and reduce PCB space as well as cost. MCU makers have continually integrated more functions into their devices.
“In the areas of cost and size reduction, integration becomes important to remove external components and support the new types that can inherently reduce the physical size of the motors through higher switching rates that allow for the use of smaller discrete supporting components, thereby increasing power density and the ability to extend range,” Carlson said. “New requirements, such as high resolution, pulse-width modulation and sigma-delta analog-to-digital conversion, drive the need for new interfaces and analog integration in modern EV motor control ECUs.”
More analog and interface integration can reduce the number of external components, thereby reducing bill-of-materials (BOM) cost and improving the control of the power conversion required to drive the motors, Carlson explained. “It is key to the success and the improvements of the EV motor and driving experience over time and must be able to scale to support the OEM’s fleet needs from low- to high-tier vehicles and one- to four-wheel–drive applications.”
In addition, with the increased use of wide-bandgap technologies in automotive applications, more integration is happening in motor control ECUs to address the higher performance needed to drive silicon carbide (SiC) and gallium nitride (GaN) power switches, Carlson added.
Another area of integration is the resolver-to-digital converter (RDC), which has traditionally been an external IC. Renesas, for example, has integrated the RDC for several MCU generations, which reduces both the ECU circuit board area and the BOM cost. “Since the RDC is implemented in dedicated hardware, it is possible to measure motor position angles for high motor-rotation speeds, which enables the motor to be miniaturized in size considerably,” Van Singel said.
Integration also plays a role in reliability and safety. “If the MCU malfunctions, the EV’s traction motor will become uncontrollable,” Van Singel added.
This higher integration includes incorporating functional safety features. The ISO 26262 functional safety standard for automotive electrical and electronic systems defines guidelines and a framework to ensure that automotive components work correctly.
Renesas MCUs used for traction motor control applications incorporate several built-in functions for ISO 26262 functional safety, along with the integrated RDC, which can accommodate both resolver and inductive position sensor signals.
“Inductive position sensing of the motor position is gaining popularity due to its lower cost, weight and complexity,” Van Singel said.
One example is Microchip Technology’s recently launched LX34070 inductive position sensor IC for EV motor control applications. The new device includes features that make it functional-safety–ready for ISO 26262 compliance in the Automotive Safety Integrity Level (ASIL)-C classification.
LX34070 enables lighter, smaller and more reliable motor solutions compared with alternative technologies, such as Hall-effect position sensors and older magnetic resolver solutions, eliminating the cost, weight and size of the magnetics, according to Microchip.
Further complicating motor control design is the automotive industry’s move to zonal architectures, which leads to a need for higher scalability and reusability.
“Additional functions may be added to a zonal ECU that is responsible for motor control in the EV; these functions may or may not be related to EV specific requirements [DC/DC, etc.],” Van Singel said. “The MCUs must be scalable to be able to accommodate these added functions based on customer requirements.”
Scalability and reusability become highly important, as zonal architectures may cause task reallocation among the ECUs and MCUs located within them, he added.
NXP also reports challenges with zonal architectures.
“Zonal architectures change the landscape of automotive MCUs to address consolidation, vehicle-wide networking and new safety and security requirements, so MCUs for EV control have to adapt with more modern solutions for zonal architectures,” Carlson said.
Zonal architectures are driving cross-domain software integration, as well as the need and use of time-sensitive networking (TSN) Ethernet to support determinism and quality of service needed to support real-time control of distributed EV motors (one to four motors), he added.
“Zonal architectures inherently must support multi-tenancy or multiple applications from multiple vendors, such as OEMs, Tier 1s and partners, which drives the need for new MCU technologies that can support isolation or freedom from interference,” Carlson said. “Isolation and dedication of specific interfaces is needed, along with isolation that includes the processor, memory, peripherals and inputs/outputs.”
What’s next
MCU makers are focusing more on providing scalability, as well as boosting performance and optimizing devices for motor control. Both NXP and Renesas agree that scalability is key to supporting carmakers as they transition to EVs, requiring them to meet different performance and cost targets for low- to high-tier vehicles.
“Investment in an MCU needs to be leveraged across these fleets, so the MCU solution needs to be able to scale appropriately,” Carlson said.
Renesas’s RH850/U2Bx is an example of a new series currently in development for motor control, all while delivering scalability. The MCUs feature up to eight 400-MHz performance cores, up to 32-MB flash and functions specialized for motor control like the RDC and a motor control (FOC) accelerator that works in combination with multiple dedicated motor control timer structures. The series also provides functions for the latest communication interfaces, security and functional safety.
“Scalability of the device peripheral functions is important for integrating previously separated applications; in addition, since the optimum memory size changes, a lineup of devices with different flash memory sizes is also required,” Van Singel said. “Cost optimization of sensor interfaces including the RDC is a challenge that has recently arisen that was not present in conventional inverters. Renesas is solving this concern by implementing the built-in RDC that can handle both resolver and inductive position sensor signals.
“For system optimization and miniaturization, in the future, EVs will include e-axles and X-in-1 [e-axle + DC/DC + other functions] integration,” he added. “In this trend as well, an MCU roadmap with motor control scalability is important.”
Van Singel also reiterated that inductive position sensing is emerging as a method to sense the motor angle position, thanks to its cost and weight savings and lower complexity.
For NXP, the company provides higher performance with a combination of Arm processor cores, a DSP core and dedicated motor control accelerators. The company also offers “a higher level of analog integration, TSN Ethernet and higher resolution of pulse-width modulation for higher-performance and more accurate EV motor control that is needed to support the new technologies coming into the space like SiC and GaN power switches,” Carlson said. “NXP is taking EV motor control—and electrification in general—into the future with a ‘modern MCU’ approach that supports new zonal architectures that leverage Ethernet TSN, the ability to control multiple e-motors, support high-security OTA updates and provide more efficient traction inverter [motor] control, along with an increased safety offering with an ASIL-D software resolver that additionally reduces system BOM cost.”
NXP introduced the S32 Automotive Platform processors in 2022 that address these trends. The S32E real-time processors with actuation and the S32K39 dual-traction inverter control MCUs address the emerging EV motor control needs for higher performance, higher integration and scalability. They also support ASIL-D functional safety that is required for this safety-critical application, and both processors can work together to provide the scalability and vehicle-wide control of electric motors.
Carlson expects future EV motor control designs will leverage the new level of performance, integration and scalability offered by these new MCUs and processors.
“With more performance and improved analog integration, they can better support more advanced control algorithms, integrate AI/ML to monitor and improve motor performance and efficiency, and add new value-add features over time through OTA updates,” he said.
Carlson also expects SiC to replace IGBT devices in the near future, followed by GaN power switches to help increase power efficiency and driving range and decrease the size and weight of the EV motors.
“Gate drivers will become more advanced, not only to support the higher switching-speed demands of SiC/GaN, but providing additional functional safety and aging monitoring, as well as higher-efficiency power control, such as [a] dynamic strength drive that adapts to the driving situation to help improve driving range,” he added.
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