UPQC-Based High Precision Impedance Measurement Device and its Switching Control Method

When the relative size of the measured grid-connected inverter of renewable energy power generation equipment's impedance and the grid's impedance changes in different frequencies, only using the current-injected impedance measuring device or the voltage-injected impedance measuring device can not accurately measure the wide-bandwidth frequency impedance of the measured equipment. In this paper, the basic theory of impedance measurement under single current-disturbed injection method and single voltage-disturbed injection method is introduced. Then, aiming at the problem of low measurement precision under single perturbation injection method, the impedance measurement of grid-connected three-phase LC-type inverter is taken as the research object, and a UPQC (Unified Power Quality Conditioner) -based impedance measurement device and its switching control method is proposed. The proposed method can realize the switch of the perturbation injection mode: when the impedance of the grid is higher than that of the measured equipment, the impedance measurement device works on the current injection mode; when the impedance of the grid is lower than that of the measured equipment, the device works on the voltage injection mode. So that the high proportion of the perturbation is distributed on the side of the measured equipment to improve the precision of impedance measurement. After measuring the impedance of resistance and grid-connected inverter of renewable energy power generation equipment, the effectiveness of the proposed device is verified by comparison and analysis.