Abstract
Normally unbalanced grid voltage dips may lead to unbalanced non-sinusoidal current injections, DC-link voltage oscillations, and active and/or reactive power oscillations with twice the grid fundamental frequency in three-phase grid-connected Photovoltaic (PV) systems. Double grid frequency oscillations at the DC-link of the conventional two-stage PV inverters can further deteriorate the DC-link capacitor, which is one of the most important limiting components in the system. Proper control of these converters may efficiently address this problem. In such solutions, Current Reference Calculation (CRC) is one of the most important issues that should be coped with the reliable operation of grid-connected converters under unbalanced grid faults. Therefore, this paper proposes and simulates CRC methods and presents the results in order to improve the quality of the grid-connected PV system under unbalanced grid voltage fault.
Highlights
With the fast increase of grid-connected PV generation [1, 2], PV systems should contribute to the grid stability by providing ancillary services, beyond the basic power delivery
The new grid requirements demand the grid-connected PV systems, single- or three-phase, to have the capability to operate in power factors other than unity
Based on the recently revised grid codes, PV inverters are preferred to stay connected during grid voltage faults [3,4,5,6]
Summary
With the fast increase of grid-connected PV generation [1, 2], PV systems should contribute to the grid stability by providing ancillary services, beyond the basic power delivery. The revised grid codes require the PV systems to inject a certain amount of reactive power in case of low voltage fault [7, 8]. Current limitation, current reference calculation [9], active and reactive power oscillation, and DC-link voltage oscillation are such important issues. They are the key issues to the proper operation of grid-connected PV converters under faults. This control strategy may offer a new solution to solve the voltage sag issue on a power system due to the PV plants connected to the grid by streaming their reactive power to the grid to enhance its power quality
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