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Motor control circuit for automotive MCUs targets next-gen EVs

Motor control circuit for automotive MCUs targets next-gen EVs

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By Christoph Hammerschmidt



Renesas says it will equip automotive microcontrollers with this dedicated motor control circuitry; objectives include boosting the energy efficiency of next-generation electric vehicles. Compared to a software implementation, the circuit block will reduces operation time to 10% or less while providing functional safety. Its functional block diagram is shown above, and contrasted with a conventional layout, below.

The IMTS performs field-oriented-control operations in 0.8 µsec, claimed as the fastest available. This contributes to the realization of next-generation high-speed EV motors with energy efficiency and inverter systems with high-speed switching performance to drive them. The circuit also enables functional safety support required for the automotive powertrain field.

With the increasingly stricter fuel efficiency requirements in the recent years, EVs, HEVs, and plug-in hybrid electric vehicles (PHEVs) have come to account for an increasing share of the total number of vehicles produced. To increase the range of such motor-driven vehicles, it is necessary to boost the energy efficiency of motor control.

Renesas implemented the IMTS as a dedicated circuit block for static processes requiring a high level of responsiveness such as acquisition of sensor data, calculation of control values based on it, and outputting of these values. The IMTS is independent of the CPU and capable of running autonomously, so it reduces the CPU load of the motor control MCU. The resulting surplus CPU capacity can then be allocated to advanced motor control algorithms designed to boost the energy efficiency of next-generation EVs, HEVs, and PHEVs.

Motor control requires a succession of static processing involving field-oriented-control operations, in which the motor current value and angle value are acquired during each control period managed by the MCU’s internal timer circuit and control values are determined for the next control period; and PWM output generated based on the control values. When multiple types of motor control are operating at the same time, the resulting processing load can consume up to the equivalent of up to approximately 90% of the capacity of the CPU in a Renesas 40 nm automotive MCU operating at 320 MHz.

The IMTS is a dedicated circuit block for these field-oriented-control operations. It is also configured in a tight linkage with a dedicated motor control timer circuit, resulting in a system in which the succession of processing performed during each control period managed by the timer circuit, from obtaining the current value and angle value to PWM signal output, all takes place autonomously, independent of the CPU. This means that the entire CPU load previously required for the above processing is eliminated.

Processing performance made possible by the new technology is sufficient to meet the demands of inverter control with high-speed switching (for example: switching frequency of 100 kHz, control period of 10 µsec) utilizing power devices fabricated from new materials such as silicon carbide (SiC).

The newly developed technology uses a MCU with two CPUs in a lockstep dual-core configuration that regularly monitors the internal operation of the IMTS circuit. This approach keeps the cost down while also achieving high-speed control and functional safety. Assuring functional safety places a load on the CPU, but in practical use cases this is estimated to amount to only 2.4% of the CPU’s total processing capacity.

High-precision MCU operation with highly accurate operation processing requires highly accurate sensor signal values. The IMTS has a configuration that makes it possible to correct errors in real time using software developed by the user. It performs this processing autonomously, so correction processing imposes no load on the CPU.

Renesas is now testing a prototype 40 nm MCU with on-chip flash memory that incorporates the new technologies. It uses an actual motor drive system to confirm operation in an actual system. Renesas aims to contribute to the realization of more energy efficient ECU systems for EVs, HEVs, and PHEVs through the use of this dedicated motor control circuit technology.

Renesas presented a paper on the new technology at International Solid-State Circuits Conference 2017 (ISSCC 2017), held in San Francisco, California.

Renesas Electronics Europe: www.renesas.com

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