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In order to make new energy enthusiasts and junior R & D personnel better understand the core technology of new energy vehicles, the author combined with the summary of experience in the research and development process, the classification of new energy vehicles, module planning, electronic control technology and charging facilities were analyzed.

1 Classification of new energy vehicles

In the classification of new energy vehicles, the different classification methods of "weak mixing, strong mixing" and "series and parallel" make non-industry people confused, in fact, these names are explained from different angles and are not contradictory.

1.1 Consumer Perspective

The consumer perspective is usually divided according to the mixing degree, which can be divided into start-stop, weak mixing, medium mixing, strong mixing, plug-in and pure electric, fuel saving effect and cost increase and other indicators are added as shown in Table 1. The "-" in the table means that there is no such function or it is weak, and the more the number of "+" means the better the effect. It can be seen from the table that with the improvement of fuel saving effect, the cost increase is also more.

Table 1 Consumer perspective classification

1.2 Technical Perspective

Figure 1 Technical classification

From a simple to complex technical perspective, it can be divided into pure electric, series hybrid, parallel hybrid and hybrid hybrid, as shown in Figure 1. Where P0 stands for BSG(Belt starter generator, start-stop device with drive) system, P1 stands for ISG(Integrated starter generator, starter and generator integration device) system, the motor is between the engine and the clutch. In P2, the motor is located between the clutch and the transmission input, P3 indicates that the motor is located at the transmission output or in the rear axle, and P03 indicates a combination of P0 and P3. It can be seen from the statistical table that various structures are widely used in passenger or commercial vehicles at home and abroad, P2 is relatively popular in Europe, planetary structure dominates in Japanese and American vehicles, P03 and other combination structures are widely used in four-wheel drive vehicles, Outland and Peugeot 3008 have achieved mass production. The selection of new energy models should consider the structural complexity, fuel saving effect and cost increase, such as the three-planet row dual-mode system jointly developed by GM, Chrysler and BMW, although the fuel saving effect is better, but due to the complex structure and high cost, the market performance in the past ten years is not satisfactory.

2 New energy vehicle module planning

Although the classification of new energy vehicles is complex, there are many shared modules, and a modular approach can be adopted in the development process to share the platform and improve the development speed. In general, the whole new energy vehicle can be divided into three module system, as shown in Figure 2. The first-level module mainly refers to the execution system, including charging equipment, electric accessories, energy storage system, engine, generator, clutch, drive motor and gearbox. The second-level module is divided into two parts: the execution system and the control system. The execution part includes the ground charger of the charging equipment, the collector and the vehicle charger, the monomer, the electric box and the PACK of the energy storage system, the gas engine, the gasoline engine and the diesel engine of the engine, the permanent magnet synchronous and AC asynchronous of the generator, the dry type and the wet type in the clutch, and the permanent magnet synchronous and AC asynchronous of the driving motor. The gearbox part of the stepped automatic transmission (including AMT, AT and DCT, etc.), the planetary bank and reduction gear; The control system of the secondary module includes BMS, ECU, GCU, CCU, MCU, TCU and VCU, which respectively represent the battery management system, the engine electronic control unit, the generator controller, the clutch control unit, the motor controller, the transmission control system and the vehicle controller. In the three-level module system, including the power type and energy type of the battery unit, the water-cooled and air-cooled forms of permanent magnet and asynchronous motors, the three-level module of the control system mainly includes the hardware, the bottom layer and the application layer software.

Figure 2 three-level module system

According to the similarity of function and control, some modules of the three-level module system can be composed of three platform architectures: pure electric (including extension program), plug-in parallel hybrid and plug-in hybrid. For example, pure electric (including extension program) is composed of charging equipment, electric accessories, energy storage system, drive motor and gear box. The versatility of each platform module is strong, and the development method of platform and module can share core component resources, improve the safety and reliability of the new energy system, shorten the cycle, and reduce research and development and procurement costs

3. Three core technologies of new energy

In the three-level module system and platform architecture, the vehicle controller (VCU), motor controller (MCU) and battery management system (BMS) are the most important core technologies, which have an important impact on the power, economy, reliability and safety of the vehicle.

3.1 VCU

VCU is the core electronic control unit to achieve vehicle control decision-making, generally only equipped with new energy vehicles, traditional fuel vehicles do not need this device. VCU determines the driver's driving intention by collecting signals such as gas pedal, gear and brake pedal. By monitoring vehicle status (speed, temperature, etc.) information, VCU judges and processes, sends vehicle operation status control commands to the power system and power battery system, and controls the working mode of the on-board accessories power system; VCU has the function of vehicle system fault diagnosis protection and storage.

Figure 3 shows the structure of VCU, including shell, hardware circuit, underlying software and application layer software. Hardware circuit, underlying software and application layer software are the key core technologies of VCU.

Figure 3 VCU composition

VCU hardware adopts standardized core module circuit (32-bit main processor, power supply, memory, CAN) and VCU special circuit (sensor acquisition, etc.). Among them, the standardized core module circuit can be applied in MCU and BMS, and the platform hardware will have very good portability and scalability. With the development of automotive processor technology, VCU has gradually transitioned from 16-bit to 32-bit processor chips, and 32-bit has become the mainstream product in the industry.

The underlying software takes AUTOSAR automotive software open system architecture as the standard to achieve the development goal of a common platform for the development of electronic control units (ECU) and supports different control systems of new energy vehicles. Modular software components aim at software reuse to effectively improve software quality and shorten software development cycle.

The application layer software is developed according to the V-shaped development process and based on the model, which is conducive to team collaboration and platform expansion. Use rapid prototyping tools and model-in-the-loop (MIL) tools to validate software models and speed up development; Policy documents and software models are managed with dedicated version tools to enhance traceability; Driver's torque analysis, shift rule, mode switching, torque distribution and fault diagnosis strategy are the key technologies in the application layer, which have an important impact on vehicle power, economy and reliability.

Table 2 shows the technical parameters of the world's mainstream VCU suppliers, representing the development dynamics of VCU.

3.2 MCU

MCU is a unique core power electronic unit of new energy vehicles. By receiving vehicle driving control instructions from VCU, the MCU controls the motor to output the specified torque and speed to drive the vehicle. To realize the conversion of the DC energy of the power battery into the required high voltage alternating current, and drive the motor body output mechanical energy. At the same time, MCU has the function of motor system fault diagnosis protection and storage.

The MCU consists of a shell and cooling system, power electronic unit, control circuit, underlying software and control algorithm software. The specific structure is shown in Figure 4.

Figure 4 MCU composition

MCU hardware circuit adopts modular and platform-based design concept (core module and VCU are on the same platform), the power drive part adopts multi-diagnostic protection function circuit design, and the power loop part adopts automotive IGBT module parallel technology, customized bus capacitor and integrated bus design. The structure part adopts high protection level and integrated liquid cooling design.

Similar to VCU, the MCU underlying software takes AUTOSAR open system architecture as the standard to achieve the development goal of a common platform for ECU development, and the modular software components aim at software reuse.

Application layer software can be divided into four modules according to function design: state control, vector algorithm, demand torque calculation and diagnosis module. Among them, vector algorithm module is divided into MTPA control and weak magnetic control.

The key technologies of MCU include: based on 32-bit high-performance dual-core main processor; Automotive parallel IGBT technology, customized thin film bus capacitor and integrated power loop design, based on AutoSAR architecture platform software and advanced SVPWM PMSM control algorithm; High protection grade housing and integrated water cooling design.

Table 3 shows the technical parameters of the world's mainstream MCU hardware suppliers, representing the development dynamics of MCU.

Table 3 MCU technical parameters

3.3 Battery Packs and BMS

The battery pack is the core energy source of new energy vehicles, which provides driving electric energy for the whole vehicle. It mainly forms the main body of the battery pack through the envelope of the metal shell. The modular structure design realizes the integration of the battery cell. The thermal management performance of the battery pack is optimized through thermal management design and simulation. The electrical components and wiring harness realize the safety protection and connection path of the control system for the battery. Through BMS, the management of the battery cell is realized, as well as the communication and information exchange with the vehicle.

The composition of the battery pack is shown in Figure 5, including the cell, module, electrical system, thermal management system, box and BMS. BMS can improve the utilization rate of the battery, prevent the battery from overcharging and overdischarging, extend the service life of the battery, and monitor the status of the battery.

Figure 5 Battery pack composition

BMS is the most critical component of the battery pack, similar to VCU, the core part is composed of hardware circuit, underlying software and application layer software. However, the BMS hardware is composed of two parts: the main board (BCU) and the slave board (BMU), and the slave board is installed inside the module to detect the voltage, current and balance control of the unit. The motherboard installation position is flexible for relay control, state of charge (SOC) estimation, and electrical damage protection.

The BMU hardware measures the battery voltage and temperature and transmits commands and data bidirectionally with the BCU module over reliable data transmission channels. BCU can use the 32-bit microprocessor based on the automotive functional safety architecture to complete the total voltage acquisition, insulation detection, relay drive and condition monitoring.

The underlying software architecture conforms to AUTOSAR standard, and modular development is easy to achieve expansion and transplantation, improving development efficiency.

Application layer software is the control core of BMS, including modules such as battery protection, electrical damage protection, fault diagnosis management, thermal management, relay control, slave board control, equalization control, SOC estimation and communication management. The application layer software architecture is shown in Figure 6.

Figure 6 Application layer software architecture

Table 4 shows the technical parameters of mainstream BMS suppliers at home and abroad, representing the development dynamics of BMS.

Table 4 BMS technical parameters

4 Charging Facilities

Imperfect charging facilities are an important factor hindering the market promotion of new energy vehicles. The successful solutions of Tesla are analyzed, and the charging solutions of new energy vehicles are proposed and the components of the charging system are analyzed.

4.1 Analysis of Tesla charging scheme

The Tesla Supercharger represents the most advanced charging technology in the world today, and it charges the MODEL S much faster than most charging stations. Table 5 shows the Tesla battery and charging parameters.

Table 5 Battery and charging parameters

Tesla has 5 kinds of charging methods, using ordinary 110/220V mains socket charging, 30 hours full; Integrated 10kW charger, 10 hours full; Integrated 20kW charger, 5 hours full; A fast charger can be installed in the home wall or parking lot, charging time can be shortened to 5 hours; With an 80% charge in 45 minutes and no electricity charges, this fast charging device is only common in the North American market.

Tesla's charging stations use solar panel awnings to both offset energy consumption and shade from the sun. Unlike filling up at a gas station, which requires a fee, a properly configured MODEL S can be charged for free at any open charging station.

The characteristics of Tesla charging technology can be summarized as follows: 1) The Tesla charging station has added solar charging technology, which enables the charging station to use clean energy as much as possible, reduce the dependence on the grid, and also reduce the interference to the grid. This technology can also be realized in China. 2) Tesla's short charging time is not surprising, Tesla's charger capacity is large 90~120kWh, charging rate 0.8C, like ordinary fast charging, and does not use a larger charging rate, so it will not affect the battery life; Charging to 40% in 20 minutes can meet the battery life requirements, mainly because of the large battery capacity.

4.2 Charging Solution

Figure 7 Charging system composition

Figure 7 shows a new energy vehicle charging solution for reference. The charging system consists of distribution system (high voltage distribution cabinet, transformer, reactive power compensation device and low voltage switch cabinet), charging system (charging cabinet and charger terminal) and energy storage system (energy storage battery and inverter cabinet). The reactive power compensation device solves the influence of the charging system on the power factor of the power grid, and the charging machine in the charging cabinet generally has the active filter function to solve the harmonic current and power factor problems. The energy storage battery and inverter cabinet solve the problem that the old distribution system cannot meet the capacity requirements of the charging station, and play the role of peak cutting and valley filling, storing energy when there is no charging, charging with large capacity and releasing stored energy for charging when the distribution system capacity is insufficient. If the capacity of the new power distribution system is sufficient, the energy storage battery and inverter cabinet can not be selected. Wind power and photovoltaics provide clean energy for the charging system, minimizing withdrawals from the grid.

5 Summary

From the perspective of consumers and technology, the structure of new energy vehicles is summarized and classified, and the advantages of various structures are analyzed, as well as the application of various Oems at home and abroad. The module composition and platform architecture of new energy vehicles are analyzed, and the relevant execution system and control system in the three-level module system are introduced in detail. Analyze the structure and key technologies of VCU, MCU and BMS, as well as the technical parameters and development trends of the world's mainstream suppliers. The successful solutions of Tesla were analyzed, and the charging solutions of new energy vehicles were proposed.