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The intelligent substations should be developed to perform multifunction operations, including power flow control, voltage regulation, and cost-effective power quality (PQ) improvement. In this article, an intelligent substation by a distribution transformer integrated with a capacitive-coupling winding tap injection static synchronous compensator (CWTI-DSTATCOM) is proposed for balance and unbalance operations. Compared with the state-of-the-art approaches, CWTI-DSTATCOM can operate at a low dc voltage with a small active inverter rating, which also can provide distributed voltage, reactive, and unbalanced current compensation. The power rating reduction mechanism is mathematically revealed via balance and unbalance compensation analysis, which is further used to determine the optimal inverter power rating of unbalance operation via an optimal LC filter design method. Furthermore, a comprehensive compensation control strategy is developed to coordinate the transformer taps and the active inverter under balanced and unbalanced operations. Simulation and real-time digital simulator hardware-in-the-loop experiments are performed to prove the validity and effectiveness of the proposed topology over inverter rating reduction and PQ enhancement. [ABSTRACT FROM AUTHOR]

• A cost-efficient centralized topology integrated with distribution system is proposed to compensate the voltage drops. • Mathematical modelling is formulated to reveal the compensation mechanism, required compensation rating, and dc voltage. • A more generalized and practical power loss model based on scaling laws is formulated to analyze the loss reduction mechanism. • A comprehensive control scheme is developed to achieve the voltage quality improvement. Recently, an intelligent substation by the L-coupling static synchronous compensator integrated with a primary tapped transformer (L-STATCOM PTT) has been developed to perform multifunction operations, including stable power supply and desired power quality. While previous works mainly focus on current quality, the cost-effective compensation of voltage quality is still not involved. This paper firstly formulated the mathematical model of voltage compensation to reveal the compensation mechanism, and determine the required inverter rating and reasonable dc voltage for acceptable performance. Then its power rating reduction under different voltage drops has been mathematically revealed compared with conventional STATCOM. Furthermore, by considering the potential differences in IGBT switching time and collector-emitter on-state resistance, a more generalized and practical power loss model based on scaling laws is formulated. The proposed voltage compensation method can reduce compensator rating by 28.1% and power loss by 12.2% at the 10% voltage drop. Simulation and experiments are performed to prove the validity and effectiveness of the proposed topology over cost-effectiveness and load voltage support. [ABSTRACT FROM AUTHOR]

• Power quality management for 12-pulse rectifier is established to improve its voltage and current adaptability. • Power quality of distribution systems is managed based on the magnetic potential balance. • An energy-based control scheme is proposed to achieve the optimal power quality. • Lower dc-link voltage and better power quality can be achieved. This paper proposes an energy-based control scheme for optimal power quality management in 12-pulse rectifier integrated distribution systems. In this 12-pulse rectifier integrated distribution system, instead of using a step-down transformer for voltage matching, a back-to-back converter is connected to the taps of star and delta windings on 12-pulse rectifier transformer's secondary side via the coupling LC. Using the magnetic potential balance of harmonics and reactive components between the back-to-back converter and the load side of the 12-pulse rectifier, the power quality of distribution systems can be managed. This topology can improve the voltage and current adaptability of the converter, thereby saving the cost of voltage matching transformer and exploiting the filter converter capacity potential. To ensure global power quality performance, an energy-based control scheme is proposed to improve the power quality management performance by accelerating the energy dissipation of the system. Case studies are performed to verify the effectiveness and superiority of the proposed methodology on low dc-link voltage and power quality. [ABSTRACT FROM AUTHOR]