Project Background

A national new energy vehicle charging service operator is building a new generation of 240kW liquid-cooled supercharging network, aiming to cover major cities and highway service areas across the country. The super charging pile adopts liquid-cooled charging gun technology, which can realize the user experience of ”charging in 5 minutes, range of 200 kilometers”.

As a power metering equipment for external business, the charging pile must meet the requirements of the national metrology and calibration regulations JJG1148-2018 "Electric Vehicle Non-vehicle Chargers", in which the power metering accuracy needs to reach 1.0 level. As the core link of electric energy measurement, the accuracy of current detection directly determines the accuracy of charging billing.

Technical specification requirements:

• Output voltage range: 200-1000V DC (compatible with 400V and 800V models)
• Maximum output current: 600A
• Current measurement accuracy: ±0.5% (to meet the requirements of 1.0 level power measurement)
• Operating ambient temperature: -30℃ ~ +55℃ (outdoor installation)

Technical challenges faced

1. Measurement level accuracy requirements

JJG1148-2018 stipulates that the power measurement error limit for level 1.0 charging pile is ±1.0%, and considering other error components such as voltage measurement and time measurement, the current measurement accuracy needs to reach ±0.5% or higher.

2. Wide voltage range compatibility

The supercharger pile needs to be compatible with 400V platform and 800V platform electric vehicles with an output voltage range of 200-1000V, and the current detection system needs to maintain stable operation over the entire voltage range.

3. Outdoor harsh environments

Charging piles are installed outdoors, facing harsh environments such as high temperature, cold, rain, snow, dust, etc., with a temperature range of -30℃~+55℃. At the same time, there are high-power electric and electronic equipment inside the charging pile, and the electromagnetic environment is complicated.

4. High-current heat dissipation

The power consumption of the shunt is about 36W at 600A, which is not particularly large, but still requires effective heat dissipation in the closed charging pile cabinet.

Technical Solutions

1. Shunt sizing

Select FL-2 type shunt, key parameters:

• Resistance value: 100µΩ ±0.5%
• Rated current: 750A (25% margin for 600A operating current)
• Rated voltage drop: 75mV @750A, 60mV @600A
• Temperature coefficient:<30ppm>
• Power loss: 36W @600A

2. High-precision signal chain design

• Four-terminal wiring eliminates the effects of lead resistance
• Matching TI INA190 high precision current sense amplifier, offset voltage<15µV
• 24-bit high precision ADC with >20-bit effective resolution
• MCU implementation of temperature compensation algorithms for dynamic correction of shunt temperature based on NTC measurements

3. Anti-interference design

• Voltage sampling line using twisted shielded wire, shield single-ended grounding
• Signal conditioning circuit with differential input, common mode rejection ratio >80dB
• PCB layout optimized to separate analog signal ground from digital ground
• RC filtering and TVS protection added to inputs

4. Liquid-cooled thermal integration

The mounting position of the shunt cooperates with the liquid cooling system of the charging module to take away the heat through the liquid cooling plate. During 600A continuous operation, the temperature of the shunt is stabilized at about 45℃, which is far below the material limit temperature.

Project results

• Measurement accuracy:Current measurement accuracy of ±0.3% over the full temperature range of -30℃~+55℃, better than ±0.5% design requirements
• Metrological certification:Products through the provincial metrological institute type evaluation test, to obtain the type approval certificate of measuring instruments
• Batch consistency:Consistency of batch products, no need to calibrate for operation after field installation
• Scale of deployment:More than 80,000 sets have been supplied and deployed in more than 2,000 supercharging stations nationwide.
• User satisfaction:Billing Dispute Rate Drops by 85%, Significantly Improving User Satisfaction

Summary of technical parameters