Motor control circuit boosts EVs

Circuit technology from Renesas Electronics can reduce operation time by 10 per cent or less compared with software implementation for motor control in automotive microcontrollers for electric vehicles (EVs) and hybrid electric vehicles (HEVs). 

The Intelligent Motor Timer System (IMTS), a dedicated circuit block that can be integrated into the microcontroller, performs field-oriented-control operations essential to EV motor control, in just 0.8 micro seconds. This, says the company, is the world’s fastest rate and less than 10 per cent the operation processing time of software implementation on a CPU running at the same operating frequency. It adds that this contributes to the realisation 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 the functional safety support required for the automotive powertrain field.

To increase the range of EV and HEVs, it is necessary to boost the energy efficiency of motor control. This requires mechanical improvements to the motors, and enhancing the functions and performance of the electronic control units (ECUs) that control the motors. The additional functionality required results in a substantial increase in the operation processing load placed on the MCUs used in the ECUs. At the same time, automotive microcontrollers are required to restrict the amount of heat they generate to maintain a high level of reliability in high-temperature environments. It is necessary to keep the operating frequency of the MCUs’ internal circuits, including the CPU core or cores, relatively low, making them difficult to boost performance.

The IMTS is 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, to reduce the CPU load of the motor control microcontroller. The surplus CPU capacity can be allocated to advanced motor control algorithms designed to boost the energy efficiency.

It is configured in a tight linkage with a dedicated motor control timer circuit to control the succession of processing performed during each control period managed by the timer circuit. Operations such as obtaining the current value and angle value to PWM signal output, take place autonomously, independent of the CPU. The CPU capacity is therefore freed up to be allocated to software containing advanced control algorithms designed to boost energy efficiency.

A microcontroller with two CPUs in a lockstep dual-core configuration regularly monitors the internal operation of the IMTS circuit. This keeps the cost down while also achieving high-speed control and functional safety, says the company.

The IMTS has a configuration that makes it possible to correct errors in real time using software developed by the user. In addition, it performs this processing autonomously, so correction processing imposes no load on the CPU. The corrected sensor signal values are used for motor control operations, resulting in more accurate operation processing and better energy efficiency when operating the motor.

Renesas is now testing a prototype 40nm microcontroller with on-chip flash memory that incorporates the new technologies. It uses an actual motor drive system to confirm operation in an actual system. The company 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.


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