The complete version of the electric vehicle DC charging pile design guide is here, full of practical information!

Currently, more than 20 models equipped with 800 V systems have been launched or are about to be launched worldwide, and fast charging stations that provide more than 350kW charging power have become widely popular. It is expected that charging modules will develop towards higher power and higher efficiency. By adopting suitable power components, topologies, and rugged controllers, we will have more high-power charging stations, solving users' range anxiety while reducing carbon emissions. This article will introduce solutions for the design of DC charging piles for electric vehicles.

This is a common two-level EV charging circuit, consisting of a three-phase half-bridge power stage and a second dual active bridge (DAB) power stage. The system has a simple structure, high operating efficiency and is easy to control. It uses phase-shift modulation to achieve zero voltage switching (ZVS) at high loads while maximizing efficiency over a wide charging voltage range of 200V to 1000V. In the design of a 25kW EV DC charger, seven half-bridge power modules are used.

ON Semiconductor's full silicon carbide (SiC) half-bridge power integrated module (PIM) is ideal for the design of electric vehicle DC charging piles. It has an easy-to-install package and form factor, greatly reducing thermal resistance and parasitic inductance, helping to achieve higher system operating efficiency and power density.

EliteSiC, Full Silicon Carbide Power Integrated Module, M3S NXH004P120M3F2, Half Bridge, 1200V, 4mΩ

■ Built-in new third-generation silicon carbide chip

■ Excellent Figure of Merit (FOM) = [RDS(ON) × EOSS]

■ Using HPS or DBC substrate, low thermal resistance

■ Pre-applied thermal interface material

Converters consisting of a bridge using wide bandgap components run the risk of self-turning on the low-side MOSFET. The main causes are Miller capacitance, gate resistance and high dv/dt. One solution is to use a gate driver that provides a negative gate voltage.

The NCP51752 is a single-channel isolated gate driver with peak source and sink currents of 4.5 A/9 A respectively. It provides short and matched propagation delays for fast switching applications. The most important feature of the NCP51752 is the innovative embedded negative bias rail mechanism (-2/-3/-4/-5 V).

When operating in a high-power state, it is critical to monitor the status of power modules and other key components, especially their temperature. ON Semiconductor's EliteSiC full silicon carbide (SiC) power integrated module (PIM) integrates a negative temperature coefficient thermistor (NTC), which can achieve real-time monitoring and quickly switch the operating mode or activate cooling devices. At the same time, in order to prevent damage caused by short circuits and high currents, the current measurement circuit needs to be placed on the bridge. This solution is cost-effective and provides better flexibility than the desaturation (DESAT) protection in the gate driver.

ON Semiconductor offers a variety of signal conditioning and control products. The NCS2007x series of operational amplifiers offer rail-to-rail output operation, 3MHz bandwidth, and are available in single, dual, and quad configurations. Its variety of compact packages and wide supply voltage range of 2.7V to 36V make it suitable for a variety of applications. For high-precision current monitoring, the NCS21x is recommended, which has a low supply voltage and low-bias zero-drift architecture to maximize current detection on the shunt resistor, with a full-scale voltage drop as low as 10mV.

In the design of auxiliary power supply for 25 kW DC charging pile of electric vehicle, NCV890100 is used to power some low-voltage components. NCV890100 is a fixed frequency, monolithic step-down switching regulator. It is suitable for systems requiring low noise and small size. NCV890100 can convert the typical 4.5 V to 18 V input voltage to an output voltage as low as 3.3 V at a constant switching frequency above the amplitude modulation (AM) band, eliminating the need for expensive filters and electromagnetic interference countermeasures.

The NCP3064 is another DC-DC regulator suitable for both step-up and step-down applications, designed to minimize the number of external components. Both products integrate thermal shutdown protection (TSD).

EliteSiC, 1200 V MOSFET, M3S Series New 1200 V M3S planar SiC MOSFET series:

■ Optimized for high temperature operation

■ Improve parasitic capacitance, suitable for high frequency operation

■ RDS(ON) =22 mΩ @VGS =18 V*

■ Ultra-low gate charge (QG(TOT)) = 137 nC*

■ High-speed switching with low capacitance (COSS = 146 pF)*

■ Provides Kelvin source connection

Field Stop 7th Generation, IGBT, 1200 V:

■ New 1200V trench field stop seventh generation IGBT series

■ Groove narrow terrace and proton implantation multiple buffer technology

■ Provide fast switching and low saturation voltage drop VCE(SAT) type

■ Improved parasitic capacitance, suitable for high frequency operation

■ General packaging

■ Target applications - Energy infrastructure, factory automation

EliteSiC, Full Silicon Carbide Power Integrated Module, 900V/1200V:

■ Available configurations: Vienna, half bridge, full bridge

■ Low thermal resistance

■ Built-in NTC thermistor

■ Improved RDS(ON) at higher voltage

■ Higher efficiency and higher power density

■ Flexible high reliability thermal interface solution

How to select a gate driver

Current drive capability: The on and off of the switch is actually the charging and discharging process of the input and output capacitors. Higher current sinking and sourcing capabilities mean faster turn-on and turn-off speeds, ultimately resulting in smaller switching losses.

Fault detection: Gate drivers are not only used to drive switches, but also to protect switches and even the entire system. For example, undervoltage lockout (UVLO) ensures that the power supply to the gate driver is in good condition, desaturation (DESAT) is used to detect short circuits, and active Miller clamping prevents false turn-on in fast switching systems.

Immunity: Common-mode transient immunity (CMTI) refers to the maximum allowable rate at which the common-mode voltage between the gate driver input and output circuits rises or falls, and it determines whether the product can be used in fast switching systems. High-power systems operate at very fast change rates, such as greater than 100 V/ns, which can generate very large voltage transients. Isolated gate drivers need to be able to withstand CMTI above the rated level to prevent noise from being generated on the low-voltage circuit side and prevent the isolation barrier from failing.

Propagation delay: Propagation delay is the time delay from 10% of the input to 90% of the output (it may vary between vendors). This delay affects the switching timing between devices, which is critical in high-frequency applications. Setting dead time can avoid breakdown and further damage. The smaller the dead time is set, the smaller the switching loss will be.

Compatibility: In new projects, pin-to-pin replacement is always preferred if there is no major design change. Selecting gate drivers with similar specifications and packages facilitates quick design.

Of course, not every point needs to be followed. For example, unlike IGBT, the output characteristics of SiC MOSFET are more like variable resistors, without saturation region, which means that the ordinary desaturation detection principle does not work. As one of the solutions, current sensors are usually used to detect overcurrent, or temperature sensors are used to detect abnormal temperature.

Silicon Carbide (SiC) Isolated Gate Driver NCP51561:

■ 4.5 A/9 A peak source/sink current

■ 36 ns propagation delay, 8 ns maximum delay matching

■ 5 kV electrical isolation, CMTI ≥ 200 V/ns

■ Dual channel design

■ SOIC-16WB package with 8mm creepage distance

Isolated high current gate driver NCD57080:

■ High current peak output (6.5 A/6.5 A)

■ Undervoltage lockout (UVLO), active Miller clamp

■ 3.5 kV electrical isolation, CMTI ≥ 100 V/ns

■ Typical 60 ns propagation delay

■ Single channel design

■ SOIC-8WB package with 8mm creepage distance

Common AC-DC Power Factor Correction (PFC) Topologies

Active front end:

■ No bridge conduction loss

■ Simple circuit, easy to control, few components

■ The switch needs to withstand full bus voltage and spike voltage

■ Wide bandgap (WBG) components are preferred to reduce total harmonic distortion (THD)

■ Reduce inductor size

■ Allows bidirectional conversion

Vienna Rectifier and T-NPC:

■ Three-level configuration reduces total harmonic distortion (THD) and voltage stress on switches

■ Easy to control, only one drive signal is needed for each phase to drive back-to-back switching

■ Switch bus voltage is halved

■ Conduction loss caused by bridging

■ Bidirectional conversion through full switch replacement

Interleaved parallel boost circuit, single phase:

■ Reduce inductor size, current stress and EMI

■ Easy to control, simple circuit, double/triple components

■ Easy to increase output power

■ Conduction loss caused by bridging.

■ One-way operation only

Totem Pole PFC, Single Phase:

■ Improve efficiency, reduce electromagnetic interference (EMI), lower total harmonic distortion (THD), and reduce the number of switches per conduction cycle

■ Small number of switches, high power density

■ Wide bandgap components are required to reduce recovery losses

■ Zero crossing noise, common mode noise

■ Supports bidirectional conversion

Common topologies for DC-DC conversion

LLC resonant converter:

■ Frequency modulation, resonant converter achieves soft switching to improve efficiency

■ Primary side zero voltage switching (ZVS), secondary side zero current switching (ZCS)