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This paper deals with compensation algorithm schemes used in single-phase Power Quality Conditioners (PQC's), allowing harmonic suppression and sag/swell compensation of the input voltage. In addition, reactive power compensation and harmonic suppression of the input current are also carried out, resulting in an effective power factor correction. Two single-phase PQC's are discussed, namely, the single-phase Unified Power Quality Conditioner (UPQC) and the single-phase line-interactive Uninterruptible Power Supply (UPS) system. To compensate the input current and the output voltage, Synchronous Reference Frame (SRF) based controllers are used. Although the SRF method is itself based on balanced three-phase loads, it can be adapted for use in single-phase loads. Both the UPS and UPQC are composed of two single-phase PWM converters to perform the active power line filter functions. The single-phase PQC's can be implemented by adopting two different operation modes. In the first mode the series converter acts as a sinusoidal current source, while the parallel converter acts as a sinusoidal voltage source. In the second mode, the series converter acts as a non-sinusoidal voltage source, while the parallel converter acts as a non-sinusoidal current source. A comparative analysis of the two operation modes is made, in which the advantages and disadvantages of each are discussed. Validation results are presented to confirm the theoretical development and performance of the single-phase PQC's.