Wideband Measurement of High-Frequency Coupling Admittances for Single-Phase VSC Considering Grid Impedance

The wideband impedance measurement is a powerful tool to quickly grasp the input admittance characteristics of a voltage-source converter (VSC). However, the influence of frequency coupling characteristics needs to be carefully considered when the observation frequency is higher than half the VSC switching frequency. The frequency coupling features bring challenges to wideband-excitation-based measurement of VSC coupling admittances. In addition, the measured VSC coupling admittances are affected by the nonzero grid impedance, which means VSC coupling admittances cannot be obtained by the traditional impedance measurement method. This paper analyses the frequency distribution characteristics of high-frequency coupling admittances for a single-phase VSC. Then a decoupling test method for VSC coupling admittances by injecting a series of linearly independent excitation signals is proposed. It eliminates the influence of grid impedance on the measurement results of VSC coupling admittances. On this basis, in order to improve the test efficiency, a wideband measurement method based on the multi-tone signal is further proposed. The frequency of the wideband excitation signal is alternately distributed in odd and even numbers, which effectively avoids the influence of VSC frequency coupling phenomena. Hardware-in-the-loop simulation results validate the effectiveness of the proposed wideband measurement method.