Three key features of technology to improve the energy efficiency of electric vehicles

by:CTECHi     2021-08-06

In February of this year, Renesas Electronics Co., Ltd. (hereinafter referred to as 'Renesas Electronics'), the world's leading semiconductor solutions provider, announced that it has successfully developed a special circuit technology for motor control that can help car manufacturers meet more stringent requirements. Carbon emission standards.

This newly developed technology is called 'Intelligent Motor Timer System (IMTS)For the field-oriented control (FOC), which is very important in the control of electric vehicles, its operating time is only 0.8 microseconds (μs), which is the fastest speed in the world, and it is less than a CPU running at the same operating frequency. One-tenth of the processing time of the upper software. This will help develop high-speed electric vehicle motors with excellent energy efficiency and inverter systems with high-speed switching performance.

In addition, this unique circuit can also provide functional safety support for the automotive power system.

In recent years, with the continuous improvement of fuel efficiency requirements, the share of electric vehicles, hybrid vehicles and plug-in hybrid vehicles in the automotive market has gradually expanded. In order to further increase the application range of electric vehicles, it is necessary to enhance the energy efficiency of motor control.

Therefore, it is not only necessary to make mechanical improvements to the motor, but it is also very important to improve the function and performance of the electronic control unit of the motor. The electronic control unit that can be used to support the next generation of electric vehicles, hybrid electric vehicles and plug-in hybrid electric vehicles requires very advanced functions and complex control software, which will inevitably greatly increase the processing of the microcontroller in these electronic control units load.

At the same time, in order to ensure high reliability in high-temperature environments, it is also necessary to limit the heat generated by the automotive microcontroller. Therefore, it is necessary to keep the operating frequency of the internal circuits of the microcontroller (including the CPU core) at a relatively low level, which hinders the improvement of its performance.

In order to meet the above requirements, Renesas Electronics uses IMTS as a dedicated circuit module for static processing in many motor control performed by microcontrollers, because the processing process usually requires high response performance, such as collecting sensor data , Calculate and output the control value on this basis. IMTS is independent of the CPU and can run autonomously, which can significantly reduce the CPU load of the motor control microcontroller. The saved CPU performance can be allocated to advanced motor control algorithms to improve the energy efficiency of future electric vehicles, hybrid vehicles and plug-in hybrid vehicles.

Key features of dedicated motor control circuit technology:

(1) Develop dedicated circuit modules for static motor control processing and circuit technologies that support independent operation

Motor control A series of static processing involving field-oriented control (FOC) is required. In each control cycle, the MCU will collect the motor current value and angle value and calculate the control value of the next cycle; PWM will be generated on the basis of the control value Output.

When multiple motor control programs are running at the same time, for a Renesas 40nm automotive MCU running at a frequency of 320 MHz, the total processing load generated can account for up to 90% of its CPU performance. The newly developed IMTS is a dedicated circuit module that supports FOC operation and can share the processing load of the CPU to a large extent. It is configured in the form of a dedicated motor control timer circuit, and the link is compact, so a series of processing executed in the control cycle managed by each timer circuit—from obtaining the current value and angle value to the PWM signal output, can be independent of the CPU run.

This eliminates the load that should have been handled by the CPU before, and the released CPU performance can now be distributed to software containing advanced control algorithms to improve energy efficiency. By configuring a dedicated circuit for FOC, IMTS can reduce the operation processing time to 0.8μs, which is less than one-tenth of the time compared with the software configured on the CPU.

For power equipment made of new materials, the processing performance achieved by the new technology can meet the control requirements of inverters with high-speed switching performance (performance example: 100kHz switching frequency, control cycle 10μs), including use Inverters for power equipment made of new materials such as silicon carbide.

(2) The development of professional technology provides functional safety guarantee for automotive power system control

Automotive power system control must be able to Ensure functional safety, so as to detect component failures in time and automatically transfer the system to a safe state. This is generally achieved by using two microcontrollers to provide system redundancy, or an MCU with internal redundant circuits can also be used, but the cost of the latter will be relatively high.

The MCU used in the new technology has two dual-core lockstep configuration CPUs that can regularly monitor the internal operation of the IMTS circuit. This method can not only reduce costs, but also achieve high-speed control and functional safety. Functional safety will increase the load of the CPU, but in actual use, it only accounts for 2.4% of the total CPU processing capacity (Note 5).

(3) Circuit technology can flexibly correct external sensor signal errors

In order to achieve the precise processing performance of high-precision microcontrollers, it is necessary to collect high-precision sensor signal values. However, in actual operation, there will be errors caused by various reasons, such as errors caused by the installation position of the sensor. The newly developed IMTS can be loaded with user-developed software to correct errors in real time. In addition, IMTS can also perform the correction processing independently, without causing additional load on the CPU. The correct sensor signal value can achieve more accurate processing performance and higher energy efficiency in the operation of the motor.

Renesas Electronics is currently testing a 40nm MCU prototype (with on-chip flash memory) using this technology. It uses a real motor drive system to confirm the operation in the real system. Renesas Electronics aims to achieve higher energy efficiency for the electronic control units of electric vehicles, hybrid vehicles and plug-in hybrid vehicles through this dedicated motor control circuit technology.

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