How to solve the problem of charging electric vehicles? TI's answer is...
Latest update time：2021-04-14
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Pure electric vehicles account for a considerable proportion of new energy vehicles. In order to support this rapidly growing market, the construction of supporting infrastructure cannot lag behind. How to make the charging of electric vehicles as convenient and fast as refueling internal combustion engine vehicles has become a topic of concern for the entire new energy vehicle industry.
To solve this problem, we must first understand how electric vehicles are charged. As we all know, charging cars are usually charged through charging piles or charging stations. This charging infrastructure is also called electric vehicle service equipment (EVSE). Charging methods can be divided into two types: AC charging and DC charging.
AC charging is to connect the AC power in the grid to the on-board charger (OBC) inside the vehicle, and the OBC converts the AC power into high-voltage DC power through the built-in AC/DC and DC/DC circuits to charge the vehicle's power battery pack. DC charging requires the AC/DC and DC/DC power conversion of the AC power in the grid to be completed in the charging pile, and then bypasses the OBC inside the vehicle and directly connects to the battery for charging. Since these converters do not need to be installed inside the vehicle, they can be designed with high power levels, thereby achieving faster charging.
Figure 1: Electric vehicle AC charging and DC charging architecture (Source: TI)
These two types of charging methods are divided into three levels according to the size of the charging power. The higher the level, the greater the charging power and the faster the charging speed. Specifically:
1
Level 1:
Usually refers to AC charging from residential electricity, with a supply voltage of 120VAC/230VAC and a charging current of 12A to 16A. It takes about 12-17 hours to fully charge a 24kWH battery.
2
Level 2:
The main application scenario is to charge the battery with multi-phase 240VAC AC power through AC charging piles installed in commercial facilities (such as shopping malls). The charging current can reach 15A to 80A, and it takes about 8 hours to fully charge a 24kWH battery
.
3
Level 3:
Unlike the AC charging of the first two levels, the Level 3 EVSE uses DC charging. This solution can directly output 300V to 750V high-voltage DC power from the DC charging pile, and charge the on-board power battery with a current of up to 400A. Since the charging power is greatly improved, it takes less than 30 minutes to fully charge a battery with a capacity of 24kWH. This is the so-called "fast charging" technology of electric vehicles that everyone talks about.
Figure 2: Comparison between three EVSE charging levels (Source: TI)
Today, people are constantly exploring various technical paths to achieve faster charging and improve the experience of electric vehicle users, among which the design of three-level fast DC charging piles is one of the focuses.
Figure 3: System block diagram of a fast DC charging station (Source: TI)
So what key technologies are needed to design and develop a fast-charging DC charging station? Let's sort them out together.
Figure 4: Typical three-phase AC input DC charging pile topology (Source: TI)
Figure 4
is a typical three-phase AC input DC charging pile topology, in which we can see several key parts.
The first is the power conversion part, which includes a three-phase PFC power stage that converts the grid AC into DC, and a downstream DC/DC conversion module to obtain the high-voltage DC required for battery charging. High voltage and high energy efficiency are the core demands of power conversion circuits. In order to achieve these two goals, it is necessary to select the right topology and components for the power stage. Therefore, silicon carbide (SiC) MOSFETs with both high efficiency and high voltage characteristics are increasingly being adopted. They are highly efficient and can support the converter to operate at higher voltages, which can ensure higher charging power on the one hand, and reduce the required current at the same power on the other hand, so that less copper cables can be used to achieve higher power density.
Secondly, in
Figure 4
, we can also see that in order to accurately control the two power stages, a corresponding MCU is also required. In order to improve the overall efficiency and performance of the system, some innovative power topologies are introduced in the design of DC charging piles, such as the Vienna rectifier architecture used in the PFC power stage. These architectures require real-time MCUs with higher performance to provide fast and accurate sensing, specialized processing to reduce latency, and precise configurable driving.
Furthermore, between the MCU and the power stage circuit, a gate driver is also required to work with power devices such as IGBT and SiC MOSFET. In DC high-voltage systems such as DC charging piles, high-quality reinforced isolation is essential, so isolated gate drivers have become standard. They can provide basic isolation, functional isolation, and reinforced isolation to prevent any dangerous DC or uncontrolled transient current from flowing out of the power grid. At the same time, through the low-power input from the MCU, it generates suitable high-current gate drive for power switches such as IGBT and SiC MOSFET.
In addition, we can also see that in the DC charging pile system, some auxiliary power supply, communication interface and control, HMI human-computer interaction and other technologies are also needed. All these technologies must be organically integrated to complete a complete system development, which is not an easy task.
Texas Instruments (TI) has been committed to providing EVSE customers with advanced technology and solution support, especially overall solutions that meet the design specifications of Level 3 high-power charging piles. To this end, TI is also accelerating iterations on multiple product lines to provide products that are more suitable for fast charging pile requirements.
For example, in terms of digital control of the power stage, TI's C2000 real-time controller is a very suitable solution. This high-performance microcontroller product series is specifically designed for controlling power electronics, providing ultra-short delays, precision sensing, powerful processing and advanced drives to achieve efficient power control.
The TMS320F28004x
is a product in the C2000 real-time controller family that is very suitable for charging pile applications. It integrates key control peripherals, different analog and non-volatile memory on a single device. The real-time control subsystem is based on the TI 32-bit C28x CPU, which provides 100MHz signal processing performance. The new TMU extended instruction set further improves the performance of the C28x CPU, which can quickly execute trigonometric algorithms (common in conversion and torque loop calculations), as well as the VCU-I extended instruction set (reducing the delay of complex mathematical operations common in coding applications).
High-performance analog blocks are also integrated on the TMS320F28004x MCU to further improve system integration: three independent 12-bit ADCs can accurately and efficiently manage multiple analog signals, ultimately improving system throughput; seven PGAs on the analog front end can achieve on-chip voltage regulation before conversion; seven analog comparator modules can continuously monitor input voltage levels for trip conditions.
C2000 also provides configurable logic blocks (CLBs), which can be used to expand C2000 peripherals and implement custom logic, so that key functions can be integrated into a single C2000 MCU without external FPGA, CPLD or logic components. This unique "MCU+CPLD" architecture provides perfect support for customers' protection function design.
It is worth mentioning that the C2000 series has formed a very rich product portfolio, which can provide developers with great flexibility and scalability to explore different power topology architecture controls, which is of great benefit to the ever-evolving fast charging pile applications.
Figure 5: Overview of C2000 real-time controller series (Source: TI)
In terms of isolated gate drivers, TI's
UCC23513
is worth noting, which is an opto-compatible, single-channel, isolated gate driver suitable for IGBT, MOSFET and SiC MOSFET. The device has a peak output current of 4.5A and 5.3A for source and sink, respectively, a rated reinforced isolation value of 5.7KV
RMS
, a supply voltage range of up to 33V, and can drive low-side and high-side power FETs.
The UCC23513 input stage is an ediode, which means that it is more reliable and has better aging resistance than traditional LEDs. Other performance features of the device include high common-mode transient immunity (CMTI), low propagation delay and small pulse width distortion, as well as small performance offset between parts under strict process control. It can be said that compared with the gate driver based on the standard optocoupler, its key functions and features as well as reliability have been significantly improved, especially the operating temperature of the device is higher, so it can be used in applications that traditional optocouplers do not support.
Figure 6: Isolated gate driver UCC23513 (Source: TI)
Another TI product worth recommending in the overall solution for DC charging piles is the
ISO672xB/ISO672xB-Q1 digital isolator
, a high-performance dual-channel digital isolator that provides a 3000V
RMS
isolation rating in accordance with UL 1577 and is also certified by VDE, TUV, CSA, and CQC.
The logic input and output buffers of each isolation channel of the device are separated by TI's dual-capacitor silicon dioxide (SiO2
)
insulation barrier. While isolating CMOS or LVCMOS digital I/O, the ISO672xB provides high electromagnetic immunity and low radiation while also featuring low power consumption. These devices, combined with isolated power supplies, help prevent data buses such as UART, SPI, RS-485, RS-232 and CAN from damaging sensitive circuits, and enhanced electromagnetic compatibility can mitigate system-level ESD, EFT and surge issues and meet radiation standards.
Figure 7: ISO672xB/ISO672xB-Q1 digital isolator (Source: TI)
Finally, there is another isolated interface product recently launched by TI that is worth recommending -
ISO1042
is an electrically isolated CAN transceiver that complies with the ISO11898-2 (2016) standard specifications. It is used with an isolated power supply to provide high-voltage protection and prevent the noise current of the bus from entering the local ground. The device has ±70VDC bus fault protection and a ±30V common-mode voltage range, and supports a data rate of up to 5Mbps in CAN FD mode. Due to the use of
SiO2
insulation
barrier, ISO1042 can withstand a voltage of 5000
V
RMS
and an operating voltage of 1060
V
RMS
. Because the electromagnetic compatibility characteristics of the device have been significantly enhanced, it can ensure system-level ESD, EFT and surge protection and meet radiation standards.
Figure 7: ISO1042 isolated CAN transceiver (Source: TI)
With the development of the electric vehicle market, the construction of charging infrastructure will also accelerate. In the "new infrastructure" blueprint launched in China, charging piles are one of the seven core areas, and their importance and strategic significance can be seen from this. The development of charging piles, especially DC charging piles with fast charging characteristics, requires not only deep technical accumulation, but also the pace of rapid iteration and upgrading of technology products, which is a big challenge. The rich product portfolio and overall DC charging pile solutions provided by TI will undoubtedly help accelerate this development process.
The above products are just some of the more representative cases of TI's DC charging pile solutions. For more information on other products and complete solutions, Mouser Electronics' website can provide you with first-hand technical information. Come and have a look:
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