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Conventional phase‐shifting transformers (PST) have been utilized for power flow control in transmission networks for many years. Compared to the slow reacting PSTs, recently trending unified power flow controllers (UPFC) enable much faster power flow control. This paper introduces a decentralized power flow control scheme for power flow controllers (PFCs) without the need for communication between the PFCs. For each PFC, an influence area is defined. The line loading of the transmission lines in this influence area is monitored in real‐time operation and if there is an overloading of a line, a feedback control scheme is used to mitigate the overloading of the line. As the power flow control of UPFC is dependent of the network topology and the UPFC converter limit, additional control measures are introduced to circumvent potential critical scenarios. Supplementary control measures are also developed to increase the robustness of control scheme for the simultaneous operation of UPFC with slow reacting PST. Using RMS simulation in DIgSILENT PowerFactory, the developed control method is validated in the IEEE 68‐Bus NETS/NYPS test bench network. The method is also validated for UPFCs with overlapping influence areas and the combination of fast acting UPFCs and slow acting PST devices. [ABSTRACT FROM AUTHOR]

This paper proposes a transformer type dc power flow controller (DCPFC) based on stacks composed of sub‐modules (SMs). The converter can perform dc power flow control independently on point‐to‐point as well as multi‐terminal connection, which can be applied to either high voltage or medium voltage dc grids. In order to explain the operation principle, different operating states of the proposed DCPFC are analysed. With phase‐shift modulation and the closed‐loop current control, the proposed DCPFC can achieve bidirectional power flow regulation. Following the theoretical analysis of the proposed DCPFC, simulation results have verified the feasibility of bidirectional power flow control. A downscaled experimental prototype is also built to demonstrate the operation principle and performance of the proposed DCPFC. [ABSTRACT FROM AUTHOR]

The energy exchange between series and shunt converters is the basis for the powerful functioning of the unified distributed power flow controller, which can be realized through the 3rd harmonic current. In this paper, based on the established 3rd harmonic equivalent network of unified distributed power flow controller power system, the influence of the additional loss caused by the 3rd harmonic current on the line transmission capacity is analysed. The mathematical relationship between the neutral point voltage of the transformer and the 3rd harmonic current is constructed, and it is simplified according to the different 3rd harmonic currents. By analysing the power relationship of the 3rd harmonic equivalent network, it is found that there is a contradiction between improving the 3rd harmonic output efficiency of the shunt single‐phase converter and reducing the neutral point insulation voltage of the transformer. The constraint conditions of the 3rd harmonic current are simulated by the advanced digital power system simulator. Finally, the method of obtaining the economical and safe 3rd harmonic current value range is summarized, which provides a theoretical basis and reference for the device parameter design. [ABSTRACT FROM AUTHOR]

Deployment of battery energy storage (BES) in active distribution networks (ADNs) can provide many benefits in terms of energy management and voltage regulation. In this study, a stochastic optimal BES planning method considering conservation voltage reduction (CVR) is proposed for ADN with high-level renewable energy resources. The proposed method aims to determine the optimal BES sizing and location to minimise the total investment and operation cost considering energy saving achieved by CVR, while satisfying system operational constraints in the presence of stochastic renewable power generation. The uncertainty of load composition is also modelled through scenario analysis. The proposed planning scheme is tested in a modified IEEE 15-bus system and 43-bus radial system, respectively. The numerical results validate that the combination of CVR and BES can achieve more energy savings. [ABSTRACT FROM AUTHOR]

Topology verification supports effective management, loss reduction, and energy conservation strategies in low-voltage distribution networks across China. Of particular interest is the users-transformer connectivity relationship. Existing research shows that voltage profile similarity based on voltage data from the Advanced Metering Infrastructure (AMI) can determine the users-transformer connectivity relationship in a neighbourhood. This article analyses the electrical principles of the users-transformer connectivity relationship based on the similarity of voltage profiles and voltage data from the AMI and derives appropriate formulas that express those relationships. The results demonstrate that voltage profile similarity is not only related to electrical distance but also related to user load profiles. The validity of the derived formulas is validated in two scenarios: a correct relationship between a user and a transformer and a partial misjudgement between a user and a transformer. This article presents a theoretical foundation for analysing the connectivity relationship in low-voltage distribution networks using voltage data from AMI. [ABSTRACT FROM AUTHOR]

With the rapid growth of distributed generation (DG) in distribution systems, DG penetration limit is becoming a more emergent issue. The short-term voltage fluctuation resulting from the DG power fluctuation of intermittent DG sources, e.g. photovoltaic (PV) and wind power, could trigger excessive actions of a transformer with on-load tap changer (OLTC) or a feeder step-voltage regulator (SVR). In addition, DG tripping from feeder will cause sudden large voltage step change. These facts limit the maximum allowable penetration of DG in distribution networks. This study proposes the constraint models of voltage fluctuation limit on OLTC/SVR resulting from DG power fluctuation and generator disconnection to assess their impacts on the DG penetration limit. A simple optimal power flow methodology is built according to the practical criteria and applied to the practical feeder systems, to demonstrate the huge advantages of the proposed constraint models in the assessment of DG penetration limit, which also validates that both factors have significant impacts on DG hosting capacity. [ABSTRACT FROM AUTHOR]

For applications with hold-up time requirement, the conventional LLC converter requires a small magnetising inductance Lm to provide enough output voltage gain under the hold-up operation. However, it deteriorates the efficiency in normal operation. Different from the conventional one, the proposed converter has a bidirectional switch paralleled with the secondary winding of the transformer. In normal operation, the secondary bidirectional switch remains off, and the proposed converter works around the resonant frequency fr as the conventional one. While during the hold-up time, the converter provides sufficient output voltage gain with phase-shift control between primary and secondary switches. However, its output voltage gain is mainly determined by the phase shift angle ɸ and the normalised load pon but not the Lm. Then it can have a larger Lm than the conventional LLC converter, decreasing primary conduction and turn-off losses, and improving the efficiency in normal operation. A 200 V/420 W prototype was built, and experimental results show that the efficiency can be improved by 1% compared with the conventional LLC converter in normal operation, which has verified the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

A three-winding transformer based asymmetrical dual active bridge (TWT-ADAB) isolated dc-dc converter is proposed in this study. The converter comprises of three stages: primary, isolation, and secondary. The primary stage consists of an H-bridge converter, the isolation stage consists of a three-winding transformer with one primary and two secondary windings, and the secondary stage consists of a bridge converter having three legs and six active switches. The load current is shared equally by the secondary windings of the transformer resulting in reduced currents through switches of the secondary converter. Therefore, the turn-off losses of these switches get reduced. Further, zero voltage switching turn-on can be achieved for all switches of the TWT-ADAB converter to reduce the switching losses. A detailed analysis of the modelling and control of the proposed TWT-ADAB converter is presented. The theoretical analysis is verified using the simulation and experimental results. These demonstrated results show that the proposed TWT-ADAB converter offers wider ranges of the output voltages and powers and higher efficiency as compared with the existing dual bridge isolated dc-dc converters. Therefore, it can be an eminent structure for high-power isolated dc-dc power conversion applications. [ABSTRACT FROM AUTHOR]

Supplying non-linear loads causes increased losses in transformers which eventually leads to their reduced life spans. Therefore, transformers are derated in order to protect them against premature loss of life. To do this, load losses including ohmic loss and winding eddy current (WEC) loss need to be estimated. This study suggests an improved analytical approach using finite element method (FEM) which includes all material characteristics and geometrical structures in order to calculate WEC loss under non-sinusoidal load current in each winding individually. By adopting this procedure, harmonic loss factor as a dominant parameter in transformers derating is estimated. By emphasising the region in which the maximum WEC loss occurs, an additional factor (FMECL) based on the physical phenomena involved is introduced using FEM. On the basis of the aforementioned concepts, a new relationship is presented for transformer derating. Ultimately, the suggested method and the IEEE standard are applied to derate a distribution transformer and the results are discussed. In addition, the proposed method is validated using a thermal model and its advantages over the IEEE derating method is presented. [ABSTRACT FROM AUTHOR]