A Novel Adaptive Frequency Injection Method for Power Electronic System Impedance Measurement

Power electronic systems are prone to negative impedance instability due to the constant-power nature of the individual components. The impedance measurement, therefore, is very important during the system designing because of the close relationship between impedance and stability. However, traditional frequency sweep methods, by injecting a series of sinusoidal perturbation signals equidistantly, always select the frequency interval on experience accumulating without guiding theory, which result in low accuracy, low reliability, and low efficiency. In this paper, the relationship between measured results and the frequency interval is built first, then the frequency interval selection criteria of injection signals are derived accordingly. Afterward, based on the above analysis, a novel adaptive frequency injection method of impedance measurement is proposed to figure out the practical issues in power electronic system impedance measurement process. With this method, variable frequency interval can be selected according to characteristics of the measured network automatically. Compared to the traditional frequency sweep method, the proposed one can measure impedance more accurately and efficiently. The simulation and experimental results validate the effectiveness of the proposed method.