Abstract
During the direct touch of the inverter output voltage or with the ungrounded shield of the cable connecting the inverter to the motor or other type of load, the nonsinusoidal ground currents with a basic harmonic frequency between 1.5 and 16 kHz, flow via a human’s body. Here was proved that Residual Current Device (RCD) (I_{triangle n} = 30 mA) does not switch off the power supply when a ground current with a value of about some hundred milliamps occurs. Because RCDs do not disconnect the power supply, the touch on the inverter’s voltage is dangerous to health and life. For the authors, the RCD usage in the Voltage Frequency Converters (VFCs) is not a good engineer practice when high-frequency common-mode distortion currents flow through it. The paper presents tests of RCD operation in the event of a resistance ground fault (via human body) during EV battery charging where the PWM voltage inverter is connected to the external rectifier to provide DC charging battery voltage. Finally, the authors propose a method of eliminating common-mode (CM) current from short protection system by using a separate circuit in which the parasitic leakage current omits an RCD.
Highlights
In drive voltage frequency converters (VFCs), the PWM (Pulse Width Modulation) voltage inverter is a DC/ AC converter that is usually connected to the motor
The safe operation of an EV battery charging station depends on the presence of appropriate protections on the supply side, including a fuse or an overcurrent circuit breaker, correct connection to the ground cables screens and the components metallic chassis right usage Residual Current Device (RCD) for disconnecting the power supply if the ground leakage current or ground fault current is greater than a specified value (e.g. 30 mA)
Measurements of the RCD tripping were performed at the stationary electrical switching station equipped with an RCD type AC (Fig. 8a), which is the supplementary part of the basic protection system
Summary
In drive voltage frequency converters (VFCs), the PWM (Pulse Width Modulation) voltage inverter is a DC/ AC converter that is usually connected to the motor. In the event of a resistive ground fault to the phase voltage of the inverter, the resulting short-circuit current has a limited effective value and does not stop the inverter, there is a risk of electric shock. √ Since the maximum value of rectifier CM voltageUCM−REC1 does not exceed 81 V ( 2Up : 4)[19] and the frequency of this triangular waveform has tripled the supply voltage frequency 3×50 Hz or 3×60 Hz, it is usually ignored in the analysis of ground leakage currents in converters and PWM inverters.
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