Voltage fluctuations resulting from variable output power of renewable energy sources are strictly challenging power quality in distributed generation systems. This paper presents a control method for Distributed-STATCOM (D-STATCOM) to alleviate variation of both positive-and negative-sequence voltages. The D-STATCOM simultaneously operates as fundamental positive-sequence admittance and fundamental negativesequence conductance to restore the positive-sequence voltage to the nominal value as well as reduce the negative-sequence voltage to an allowable level. Both admittance and conductance are dynamically tuned to improve voltage-regulation performances in response to load changes and power variation of renewable sources. A proportional-resonant current regulator with selectively harmonic compensation is realized to control the fundamental current of the D-STATCOM as well as reduce the harmonic current, which could be an advantage in practical applications due to high voltage distortion in low-voltage Microgrids. Voltage-regulation performances are discussed for different D-STATCOM location as well as different D-STATCOM current. Computer simulations and laboratory tests validate effectiveness.
The output power of the proposed dimmable ballast topology is self-regulated and insensitive to the lamp characteristics. Accurate dimming operation with rather constant filament power can be realized simply by open loop control of the switching frequency of the converter. It can provide reliable operation during lamp ignition with fault conditions or even short circuit without the need of current sensing circuits. Prototype was built for experimental verifications. For completeness, a simple ultra IOW dimming method i s also proposed together with the theoretical dimming limit considered.
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