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This paper presents a system for compensating DC link current pulsation in four-wire inverters with energy storage operating under unbalanced load conditions. This phenomenon occurs when an inverter with an independent power control in each of the phases attempts to locally balance the voltage imbalance in the grid. Such a condition creates a DC link current pulsation, which is destructive for energy storage connected to the DC link. The conditions when this situation appears are presented in detail in the paper. A solution to this problem is proposed in the form of a dual active bridge converter and a capacitor bank to actively compensate this pulsation. The control algorithm is proposed based on a proportional-resonant controller. This paper presents the technical background and method by which the controller parameters were calculated, implemented and tested in a real-time system. The test results are presented and discussed, concluding that the proposed solution is an attractive option for protecting the energy storage from DC link current pulsation. The dual active bridge converter combined with resonant controller can compensate the DC link current pulsation almost entirely. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of the optimal selection of capacitor banks in electrical AC distribution systems for minimizing the costs of energy losses during a year of operation through a discrete version of the vortex search algorithm (DVSA). This algorithm works with a hypersphere with a variable radius defined by an exponential function where a Gaussian distribution is used to generate a set of candidate solutions uniformly distributed around the center of this hypersphere. This center corresponds to the best solution obtained at the iteration t, which is initialized at the center of the solution space at the iterative search beginning. The main advantage of combining the exponential function with the Gaussian distribution is the correct balance between the exploration and exploitation of the solution space, which allows reaching the global optimal solution of the optimization problem with a low standard deviation, i.e., guaranteeing repeatability at each simulation. Two classical distribution networks composed of 33 and 69 nodes were used to validate the proposed DVSA algorithm. They demonstrated that the DVSA improves numerical reports found in specialized literature regarding the optimal selection and location of fixed-step capacitor banks with a low computational burden. All the simulations were carried out in MATLAB software. [ABSTRACT FROM AUTHOR]

With many advantages, modular multilevel convert (MMC) has been extensively used in high and medium voltage power transmission projects. The thermal performance and reliability of components in MMC are key issues in system operation. However, in the current research on the reliability of MMC components, there are few methods to improve service lifetime expectancy of the components. This paper proposes a balance control algorithm, based on the cumulative fatigue damage of components, feedback to the control terminal for allocating the sub-module (SM) operating state and generating trigger pulses. Finally, the effectiveness of the proposed algorithm is verified and discussed in case studies. It is found that this algorithm is able to improve the aging degree of components in the meanwhile, the improvement in MMC reliability comes at the cost of slightly increasing capacitor voltage fluctuations and total harmonic distortion (THD). Due to the limitation of capacitor thermal performance, SM capacitor banks become a weak link in MMC reliability. [ABSTRACT FROM AUTHOR]

Reactive power compensation with Capacitor Banks (CBs) is one of the most successful approaches used in distribution systems, mainly due to their versatility, long-term acceptance in the power industry, and reduced costs. Most allocation methods, however, lack specific strategies to handle the limited discrete nature of CBs sizes seeking to improve the overall optimization and computational performance. We present an algorithm for the Optimal Placement of Capacitor Banks (OPCB) in distribution systems by means of a hybrid Flower Pollination Algorithm (FPA)–Exhaustive Search (ES) approach. The pollination process itself determines the sets of buses for placement, while CBs sizes and the final fitness values of each pollen are selected after a full-search is conducted in the sizing space. As the sizing phase works on the limited search space of predetermined discrete bank values, the computational effort to find the optimum CB capacity is greatly reduced. Tests were performed on distribution systems of 10, 34, and 85 buses with respect to the objective function, final losses, and voltage profile. The algorithm offers an excellent compromise between solution quality and computational effort, when compared to similar approaches. [ABSTRACT FROM AUTHOR]