Compensation Algorithms Applied to Power Quality conditioners in three-phase four-wire systems

This work presents compensation algorithm schemes used in power quality conditioners applied to three-phase four-wire systems, allowing harmonic current suppression and reactive power compensation which results in an effective power factor correction. The strategies used to extract the three-phase compensation currents are based on the synchronous reference frame method. Although this method is itself based on balanced three-phase loads, it can also be used for single-phase loads, allowing independent control of all three phases. The compensation algorithms presented are implemented for two power conditioners, such as the Unified Power Quality Conditioner (UPQC) and the line-interactive Uninterruptible Power Supply (UPS) system, which allow the choice of a suitable compensation strategy resulting in either balanced or unbalanced sinusoidal source currents under balanced or unbalanced load conditions, respectively. Two, four-leg PWM converters are used to implement the UPQC and the UPS system to simultaneously perform the compensation of the load harmonic currents, utility voltage harmonics and the current and voltage unbalances. Mathematical analyses of the Synchronous Reference Frame (SRF)-based algorithms are presented and simulation results are performed to validate the theoretical development and confirm the performance of the power quality conditioners.