A single-phase UPS system with harmonic suppression and reactive power compensation

This work proposes a control strategy applied to a single-phase uninterruptible power supply (UPS) system with series-parallel active power-line conditioning capabilities, allowing sinusoidal input current and sinusoidal output voltage, which results in an effective power factor correction. The UPS system is composed by two single-phase PWM converters in order to perform the active power line filter functions. The series converter acts as a series active power filter, which works as a sinusoidal current source in phase with the input voltage. The parallel converter acts as a parallel active power filter, which works as a sinusoidal voltage source in phase with the input voltage, providing sinusoidal voltage with low total harmonic distortion (THD). The detection of the angle-phase is performed using a single-phase PLL (phase-locked loop) structure, which is based on instantaneous active power theory. The PLL system has been implemented into two-phase stationary reference frame. Thereby, a fictitious quadrature voltage needs to be generated, which must be orthogonal to the measured utility voltage. Both the control algorithm of the UPS system, which uses synchronous reference frame (SRF) method, and the active power flow that occurs through the UPS system will be described and analytically studied. Mathematical analysis of the SRF-based algorithm is presented and simulation results are performed to validate the theoretical development and to verify the performance of the UPS system.