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The engineer said that | RH850C1M-Ax MCU solved the complex control problem in the integrated dual traction inverter

Renesas Electronics

Latest update time: 12:48, November 12, 2021-12

Number of readings:

Author: Sam Gold

Senior Manager

Almost every region in the world is striving for more stringent environmental regulations. Europe is the leader among them, while the greenhouse gas (GHG) standards in other regions are closely followed. As another influencing factor, the United States is expected to have more stringent greenhouse gas emission standards under the leadership of the current new government, which may lead to Hybrid electric vehicle As this vehicle category can serve as an early available solution in the transition to BEV. Although mild hybrid vehicles (48V system) can help to meet the new greenhouse gas emission standards, from the perspective of OEMs, they are not enough to avoid fines due to non-compliance with their respective national CO emission regulations.

Figure 1: Greenhouse gas regulations per country (source: ICCT, 2020)

With the acceleration of the greenhouse gas trend, the global xEV market may enter a long period of expansion, and the battery cost will also decline. From 2025, more stringent restrictions (fuel economy standards/BEV sales regulations) will lead to increased demand for xEV in various countries. Then, as the price of core technologies (including batteries) gradually decreases, the transition to independent growth mode will begin in 2025.

Figure 2: Global light vehicle xEV market demand forecast (excluding 2/3 wheelers, medium/heavy buses and trucks) Source: Strategy Analytics - Automotive Electronics System Demand - April 2021-

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HEV system requirements and concepts

In particular, PHEV and FHEV depend on their respective system concepts. From the perspective of collaborative control strategies (ICE and electric drive), they have higher complexity. In addition, due to the combination/addition of ICE and electric drive functions, they are more sensitive to the space constraints of application components. This applies not only to electromechanical components, but also to electronic devices such as digital chipsets, analog and power supply components.

The system complexity described above comes from the following upper functions: when the vehicle decelerates, the kinetic energy is converted into electric energy through the motor and stored in the battery. During acceleration, the electric energy from the battery is used to assist ICE, thus saving fuel consumption. FHEV with high power motor means high generator capacity, so more kinetic energy can be recovered (or recovered) during deceleration, thus improving fuel efficiency by tens of percent.

HEV control: concept of complexity

Figure 3: HEV classification

HEVs have several hybrid architectures, of which Figure 3 describes the broad categories:

The simplest thing is Parallel hybrid system 。 The motor is placed in parallel with ICE. The motor/generator assists in acceleration by using electrical energy from the battery, and charges the battery during deceleration by using the motor as a generator. The advantages of this system are lower cost and lower control complexity.

stay Series Hybrid system In the case of, the kinetic energy generated by ICE is converted into electric energy through the generator, and then the electric energy is used again by another motor to generate kinetic energy. This seems like a waste of cost and energy. However, the advantage of this method is that it can run ICE in the most fuel efficient speed/torque range. This is due to ICE's low fuel efficiency in low speed (e.g.<1500rpm) or high speed (e.g.>4000rpm) and low torque range.

Series/Parallel hybrid system It is the most complex system. When ICE operates in the range of fuel saving speed/torque, ICE output can be directly transmitted to the wheels through the clutch and gearbox. If torque assistance is required, the motor can assist in acceleration, and ICE can save fuel like a parallel hybrid system. When the vehicle speed is very slow, the clutch will release. At this time, the function of the system is similar to that of the series hybrid system to avoid running ICE in the range of low fuel efficiency.

In the case of series and series/parallel hybrid power system configurations, a combination of two motor/generator devices that strictly and interdependently control is usually required.

HEV control: key challenges and solutions

From the concept of traction motor system introduced earlier, it is obvious that due to the heavy communication load between the two entities and the need to increase diagnosis efforts to maintain the ASIL level, especially in the case of series/parallel hybrid power systems, their respective control and synchronization work tends to be complex.

An obvious solution to optimize these works is to integrate two inverter control systems into one ECU controller (MCU). By using this concept, the synchronization between the two inverter control loops can be achieved in a single microcontroller, resulting in high communication bandwidth and reduced latency. In addition, by selecting target devices that meet the security level ASIL, the diagnostic and functional safety concepts will become simpler and more direct. Another benefit of the integrated solution is of course the highly optimized bill of materials (BOM), while reducing the space requirements for parts, which is very beneficial for the entire system concept.

Solution: MCU with integrated xEV support function

One of the keys of HEV dedicated MCU is to shunt the vector mathematical calculation process of motor control algorithm to the dedicated processing IP. By using this method, MCU can be equipped with a small number of CPU cores and undertake other software tasks mentioned above.

Enhanced motor control unit (EMU3)

The embedded "Enhanced Motor Control Unit" (EMU Gen3) is a group of separate motor controlled accelerator modules. These modules use vector control algorithms to calculate three-phase PWM comparison values and generate them based on the motor current measured by the A/D converter Rectangular wave pattern. In addition, the angle value of the motor is obtained by performing the integrated Resolver to Digital Converter (RDC3A) of the position sensor interface function. Three phase motor The timer TSG3 uses the calculation result of EMU3 to output PWM and rectangular wave.

Figure 4: Enhanced Motor Control Unit (EMU3)

The IP of EMU3 can combine its specific function block and user specific software intervention to exercise motor control function. Therefore, the flexible control concept that combines hardware acceleration and individual user software can be realized.

Figure 5: Flexible control of motor based on user specific software intervention

Dual motor/generator control

The key solution to realize the dual motor/generator control capability is based on how the motor control IP ("EMU3") and embedded position sensor interface are integrated into the microcontroller system previously introduced.

The following figure shows the actual method of controlling two motors (refer to the abbreviation definition in the appendix):

CPU2 and CPU3 control one motor respectively. By using EMU3, the processing of performance intensive motor control algorithms (such as Park/Clark transform for generating PWM mode) has been transferred from CPU to EMU3. This allows other important software tasks, such as diagnostic processing, to be performed by the CPU.

CPU1 can also be used for other functions: for example, to realize DC/DC converter control as an optional integrated additional function to optimize the layout of the entire HEV system.

RDC3A is MCU integrated (equivalent to Tamagawa AU6805) dual Resolver The digital converter interface, or more generally, the motor position sensor interface, can be connected to the analog resolver or inductive position sensor signal.

Figure 6: Example of a system that controls a dual motor/generator

Solution provided by Renesar

In Renesas, the 40 nm microcontroller RH850/C1M-Ax has been verified for many years as a HEV control concept. This device and the upcoming 28nm next generation device focus on the inverter control function of traction motor. Appropriate PMICs, grid drivers, IGBT devices and inverter turnkey solutions can greatly reduce the R&D work of customers (see Figure 7).

Figure 7: Rexa xEV product portfolio

Summary

Due to the increase of system complexity, the hybrid electric vehicle (HEV) based on the combination of electric drive and ICE system needs a cost-effective and size optimized propulsion system. The high-performance microcontroller (MCU) dedicated to the traction inverter has a dedicated hardware accelerator function for vector mathematical calculation, which can help to achieve the overall optimized electronic and electromechanical system design.

END

About us

Renesa Electronics Group (TSE: 6723), which provides professional and reliable innovative embedded design and complete semiconductor solutions, aims to improve people's work and lifestyle through the use of billions of networked intelligent devices of its products. As a global supplier of microcontroller, simulation, power supply and SoC products, Rexa Electronics provides comprehensive solutions for various applications such as automobile, industry, home, infrastructure and the Internet of Things, and looks forward to working with you to create an infinite future. For more information, please visit renesas.com.

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