Investigation of Control Methods for Electric Vehicle Charging to Reduce Voltage Unbalance
摘要
This paper includes investigations of characteristic-based regulations for voltage unbalance reduction, which were tested in a laboratory environment for the charging of electric vehicles at the low-voltage level. With the regulations, the phase-precise setting of the active and reactive power is performed separately for each phase conductor during charging processes of electric vehicles. The focus is on the investigation of a voltage-dependent active power regulation P(V), a voltage-dependent reactive power regulation Q(V) and a reactive power provision depending on the phase shift of the voltages Q(Δφu). A laboratory setup was created that contains a low-voltage grid, which is generated with a grid simulator and a line impedance, and a device under test with which AC charging processes can be performed and in which the regulations are integrated. In addition to power transfer, charging communication is also implemented for realistic charging processes. For the investigations of the regulations, different voltage unbalance cases were generated with the grid simulator, which contain both changes in the RMS values and changes in the phase angles. The results of the tests show that with the phase-precise P(V) regulation unbalance of the RMS voltage values and with the Q(Δφu) unbalance of the phase shift of the voltages can be reduced. This also leads to a reduction in the voltage unbalance factor. With R/X ratios greater than 1, which are typically present in low-voltage networks, active power is more suitable for influencing the RMS voltage values and reactive power is more suitable for adjusting the phase angles.