Bidirectional Power Balance Control of Serial Voltage Injection Converter for Impedance Measurement of Grid-Connected Inverter

Serial voltage injection (SVI) converter is widely used in frequency-scan for the impedance measurement of the grid-connected inverter. The dc power supply is necessary for the SVI converter, which reduces device power density and cost performance. Meanwhile, the fundamental voltage variation brought by the varying operating capacity of the inverter and the voltage drop on the grid impedance decreases the impedance measurement precision in the traditional control scheme. In this article, the bidirectional power balance control strategy is first proposed to maintain the dc voltage without an additional dc power supply. Then, a voltage reference calculation method is proposed for regulating fundamental voltage. By the proposed method, the SVI converter can inject broadband-frequency voltage perturbations into the system under test with constant dc-side voltage and desired ac-side voltage. The impedance accuracy is not affected by the operating capacity of the inverter and the impedance of the grid with the proposed control method. The proposed power balance control with fundamental voltage control of the SVI converter is verified by the experimental tests.