Abstract
As a result of increasing variability of network impedance, interest in impedance estimation techniques is growing. This review contextualises local impedance estimation techniques by providing a historical prospective on the uses of these techniques, from the early implementations designed to monitor power quality to the latest techniques integrated into converters designed to update the controller with the most recent network information. This is followed by clear and consolidated descriptions, a complete classification and comparison tables of local estimation techniques intended to assist engineers and researchers choose an estimation technique that is suitable to their application. The discussed techniques are then ranked for a range of application priorities such as accuracy, least disruptive to the network, most suitable for wide frequency spectrum estimations and rapidity of estimation. Practical applications of impedance estimation are discussed, such as network characterisation, anti-islanding detection, filter resonance avoidance and controller tuning. To conclude the review, future trends are identified.
Highlights
E ARLY impedance estimation literature focused on harmonic content due to power quality concerns [1], [2]
3) LC and LCL filter resonance avoidance A number of papers use impedance estimation techniques to avoid resonating with the network, especially when passive damping has been avoided for efficiency reasons
Some PRBS-type literature claim that their estimations can be used for adaptive control tuning [21], [82], but it is not specified what control aspect is being tuned. [25] uses the P/Q variation technique to update the value of a virtual impedance within the phaselocked loop (PLL), intended to stabilise the controller in weak grids
Summary
E ARLY impedance estimation literature focused on harmonic content due to power quality concerns [1], [2]. Recent literature is interested in online controller tuning for improved stability [19]–[25] Many of these articles are driven by increased network impedance variability and resulting voltage stability issues [26], increasing the importance of appropriate control tuning [27]. There is an alternative approach to online controller tuning, and that is to use impedance agnostic control [23], [36]–[42] These techniques may require stability studies as part of the commissioning, studies which could be based on the estimation techniques discussed in this article. While these quantities are interchangable, it is decided to Passive methods Section III
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