Abstract
Performance degradation is, in general, regarded as a power quality problem. One solution to recover grid performance is through the application of a unified power quality conditioner (UPQC). Although these devices are multi-input/multi-output (MIMO) systems, the most common control strategies consist of two decoupled controllers, which neglect the coupling effects and add uncertainty to the system. For this reason, this paper proposes a multivariable resonant observer-based control strategy of a UPQC system. This method includes all significant coupling effects between this system and the grid. This strategy results in a stability-based compensator, which differs from recently proposed strategies that are based on signal calculation and cannot assure closed-loop stability. In addition, this paper introduces a simplified controller tuning strategy based on optimal conventional methods without losing closed-loop performance. It implies that the controller can be easily tuned, despite the complexity of the MIMO dynamic model. The UPQC with the resonant observer is verified on an experimental setup for a single-phase system, obtaining three relevant results for power quality improvement: (1) harmonics compensation tested with a total harmonic distortion limit of 5%; (2) sags and swells mitigation; and (3) power factor correction, achieving a unitary value on the grid side.
Highlights
Power quality (PQ), as defined in the recommended practice IEEE-1159-2019 [1], establishes some characteristics for both the voltage and current signals to achieve good performance for a grid and its connected load
To avoid unmodeled coupling effects, this paper proposes a MIMO model for a unified power quality conditioner (UPQC), and the control system uses a resonant extended state observer
The main results for the control system implementation were obtained in an experimental environment, describing five relevant functionalities related to a PQ improvement: (1) The UPQC compensates for the harmonics for both the load voltage and the grid current, obtaining a total harmonic distortion (THD) index if less than 5%, ac
Summary
Power quality (PQ), as defined in the recommended practice IEEE-1159-2019 [1], establishes some characteristics for both the voltage and current signals to achieve good performance for a grid and its connected load This concept provides some limits for electromagnetic phenomena based on the Electromagnetic Compatibility Standards defined by the International Electrotechnical Commission (IEC). To avoid unmodeled coupling effects, this paper proposes a MIMO model for a UPQC, and the control system uses a resonant extended state observer This design allows direct disturbance rejection and reference tracking. The intelligent control techniques are not oriented to achieve the internal stability of a grid-tied UPQC, while this paper describes a stability-based design Other recent advances, such as [14,16], provide signal-based control without any UPQC dynamic model. The following section describes the experimental setup for a single-phase system to verify the UPQC control architecture
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