Abstract
This paper presents the first experimental validation of the stability analysis based on the online measurement of harmonic impedances exploiting the linear time-periodic (LTP) approach applied to ac networks of power converters. Previous studies have provided the theoretical framework for the method, enabling the stability assessment of an unknown system adopting a black-box approach, relying only on injected perturbations and local measurements. The experimental case study considered in this paper comprises two single-phase converters, one acting as source subsystem and the other as load subsystem . A third converter, the stability measurement unit , is controlled to inject small current perturbations at the point of common coupling (PCC). From the measured small-signal perturbations of PCC voltage, source current, and load current, the harmonic impedances of source and load subsystems are calculated. The LTP Nyquist criterion is then applied to the ratio of the two harmonic impedances in order to assess the stability of the whole system. Theoretical and experimental results from a 5-kW laboratory prototype are provided and confirm the effectiveness of the method. In addition, the measurements do not require sophisticated equipment or control boards and can be easily performed from data sampled by commercial micro-controllers.
Highlights
S TABILITY analysis of interconnected power systems has been an interesting and challenging topic for researchers in the past decades, and it is still nowadays an open field for research [1], [2]
Focusing on a single-phase scenario, this paper proposes the experimental validation of the Harmonic State Space (HSS) method in combination with the Linear Time Periodic (LTP) Nyquist Criterion, already presented in detail in [21]
The experimental validation provided in this paper demonstrates that the method is fairly robust against implementation accuracy, since a good match with a theoretical prediction can be obtained with a simple implementation of the Stability Measurement Unit (SMU) for current injection, without the need for sophisticated control structures or high bandwidth current measurements
Summary
S TABILITY analysis of interconnected power systems has been an interesting and challenging topic for researchers in the past decades, and it is still nowadays an open field for research [1], [2]. One of the first investigations presented in the literature was provided by Middlebrook [3], who analysed the instability issues due to interactions between DC/DC converters and their input filters. The linearised input and output impedances of the system were first evaluated and the Nyquist Criterion was applied to assess the stability of the system. This approach was extended to AC power converters by. Cox is with the School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD, U.K
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