Designing a residual current simulation system for testing in-cable control and protection device(IC-CPD)
[Objective]With the increasing popularity of new energy vehicles,ensuring the safety and convenience of their charging systems has become considerably important.In-cable control and protection device(IC-CPD)is a crucial protection device for ensuring household charging safety for these vehicles.Before entering the market,IC-CPD must undergo rigorous testing to ensure its effectiveness.According to the International Electrotechnical Commission(IEC)standards,the main protection function of IC-CPD is to provide residual current protection.Therefore,testing the residual current protection performance of IC-CPD is essential.For this purpose,a residual current simulation system specifically for IC-CPD testing has been designed.[Methods]The residual current simulation system designed in this study uses direct digital synthesis(DDS)technology to simulate current signals in digital form.To improve flexibility,two DAC chips controlled by a microprocessor adjust signal output:one for gain control and the other for generating arbitrary waveforms.The overall circuit design uses high-precision operational amplifiers and high current-driven operational amplifiers to improve the quality of simulated residual current.It also considers power conversion,signal isolation design,and timely detection and feedback of the IC-CPD protection status.In software design,linear interpolation functions modify the amplitude of AC signals,resulting in smooth output signals.The system uses an upper computer for control testing via an Ethernet connection.In addition,the testing system,upper computer,and high-precision multimeter are networked through a switch to perform real-time data measurement and accuracy calibration,thus ensuring the accuracy of IC-CPD testing.[Results]Signal measurement,waveform testing,and actual application results show that the simulation system can generate a maximum slope DC residual current of 75 mA and a maximum peak±75 mA amplitude gradient AC residual current,with smooth and nonjumping output waveforms.Calibration considerably improved the accuracy of the output signal.When the simulated residual current is below 40 mA,the error between the output signal set by the software and the actual measurement signal is minimal,with an output accuracy of up to 99.5％.At the same time,the system conducts AC signal symmetry calibration.After calibration,when the simulated residual current is below 40 mA,the output signal deviation error from the zero point is minimal,achieving an accuracy of up to 99.3％,meeting testing requirements.[Conclusions]The residual current simulation system developed in this study can generate slope DC residual currents and amplitude gradient AC residual currents.It features high system security and stability,flexible and smooth output waveforms,and high output accuracy.The system effectively performs residual current testing on IC-CPD products and has been applied in actual IC-CPD testing scenarios.Furthermore,the methods for simulating residual current and calibrating current accuracy used in this system can generate other high-precision current and voltage signals,offering the potential for broad application in different measurement and control systems.
in-cable control and protection deviceresidual current simulationdirect digital synthesis technologyaccuracy calibration
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