/// CURRENT MEASUREMENT\\\


Leak measurement for EV chargers


A new sensor uses fluxgate technology to measure EV charging station current leakage


I


n the rush to move the world over to elec- tric vehicles and conform to legislation that has been developed in scores of coun-


tries, the requirement for charging infras- tructure is growing at a rate not currently matched by reality. According to the latest fig- ures from Bloomberg, at the end of 2020, there were just 1.4 million public charging points worldwide, most of which are in China and the EU. In the UK, estimates from EDP En- ergy put the figure at 35,000 currently in ex- istence in around 13,000 locations. However, public charging points are just


part of the picture with the majority of charg- ing locations being in the EV owners’ own homes or privately owned chargers in the workplace. According to electrical measurement spe- cialist LEM, 2019 saw around 6.5 million pri- vate charging points worldwide: not nearly enough to meet the expected growth in own- ership. Of course, plugging the car into a mains socket will do the job, albeit slowly and in the least effective way, so there is huge pressure on charger manu- facturers to sup- ply more effective products to the home market. LEM believes


that to support the massive de- ployment of EVs, driven by ambi- tious policies to phase out sales of internal combustion engine (ICE) vehicles, the charging infras- tructure must increase by thirteen times.


Meeting the standard \\\ Due to this, manufacturers must develop


chargers that are affordable, easy to install and conform to standards criteria, both for safety and robustness of the product. Since 2016, IEC standards and more specif- ically IEC 62955 / IEC 62752, require the de-


28 /// DAQ, Sensors & Instrumentation \\\ 2021


Fluxgate-based leakage current detector ensures home EV charging systems conform to standards requirements


tection of a direct leakage current at 6mA DC to avoid the home residual current device (RCD) type A being ineffective. The blinding ef- fect, as it is known, appears when an EV de- velops an insulation fault. EV architecture integrates a battery pack,


powered by direct current (DC), which can generate a leakage current that can deacti- vate a home RCD. To protect the RCD and avoid the need to install an RCD type B in the electrical panel of home EV owners, EV charg- ers include a device to detect the DC leakage current.


Leakage current detection \\\ This detection is the role of a new leakage


current sensor based on open-loop fluxgate technology. Called the CDSR, the sensor is in- novative, extremely compact and safe, allowing manufac- turers to opti-


mise the electronic design of their charger products. The CDSR has been developed to meet mar-


ket demand for a residential and commercial charging station, offering a version for single- phase architecture and another for three- phase topology. With a maximum current per phase of 32A rms, the CDSR can be integrated into AC chargers from 3.7kW to 22kW. Following the trend towards digital elec-


tronics, the CDSR provides not only an ana- logue communication output but also a serial peripheral interface (SPI), enabling simple in- terfacing of hardware. The CDSR operates from a +3.3VDC supply and has a typical cur- rent consumption of just 50mA when mea- suring 150mA as a maximum primary residual current.


The ratio-metric be- haviour of the CDSR ensures it can resist power supply drift and maintain a sta- ble output measure- ment.


Being extremely


robust, the CDSR can operate inside all EV chargers. It has an operating tempera- ture between -40°C to 85°C, can withstand acceleration forces up


to 10G while maintaining nominal performance, and


has a very high level of insula- tion between its primary and


measurement circuits, thanks to long


creepage and clearance distances (13.2mm). Designed to ensure a high level of safety, the CDSR provides a default detection output signal with a reaction time below 200μs. Com- bined with an independent test winding, charger manufacturers can test the perfor- mance of the sensor in real time to guaran- tee maximum safety. DS&I


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