Mitigation of Circulating Currents for Parallel Connected Sources in a Standalone DC Microgrid

In a standalone DC microgrid, sources are interconnected in a parallel configuration. When sources of different power ratings are parallel connected, there arises a major issue of circulating currents which disturb current sharing by sources as per their capacity. Consequently, the voltage regulation becomes poorer. Additionally, connecting line resistances also play their part to contribute to abnormal current sharing. Droop controllers are normally preferred for the mitigation of circulating currents among parallel-connected sources. However, droop controllers cannot eliminate circulating currents for different rating sources. Hence, current sharing and voltage regulation cannot be ensured simultaneously. To address the issues, a distributed architecture-based Sliding Mode Control (SMC) technique is proposed in this paper. An analysis of the circulating currents for a two-source system is presented. Simulation results are presented to show the effectiveness and fail-safe operation of the proposed technique in a steady-state condition.

Effective reduction of magnetisation losses in copper-plated multifilament coated conductors using spiral geometry

We wound copper-plated multifilament coated conductors spirally on a round core to decouple filaments electromagnetically under ac transverse magnetic fields and measured their magnetisation losses. Although the coated conductors were plated with copper, which connects all filaments electrically and allows current sharing among them, the spiral geometry decoupled filaments similar to the twist geometry, and the magnetisation loss was reduced effectively by the multifilament structure. The measured magnetisation loss of a 4 mm-wide, 10-filament coated conductor with a 20 μm-thick copper wound spirally on a 3 mm-core was only 7% of that of the same 10-filament coated conductor with a straight shape under an ac transverse magnetic field with an amplitude and frequency of 100 mT and 65.44 Hz, respectively. We separated the measured magnetisation losses into hysteresis and coupling losses and discussed the influence of filament width, copper thickness, and core diameter on both losses. We compared the hysteresis losses with the analytical values given by Brandt and Indenbom and compared the coupling losses with the values calculated using a general expression of coupling loss with the coupling time constants and geometry factors.

Single loop PID controller design based on optimization algorithms for parallelly connected dc-dc converters

This paper addresses a viable single loop PID controller on the bases of optimization algorithms for parallelly connected DC-DC converters to improve current sharing, improve the systems dynamics and guarantee good steady-state performance simultaneously. Because of inconvenience and lack of accuracy of Ziegler-Nichols rule in tuning PID controller parameters, an optimized controller design strategy with the purpose of enhancing the system performance is introduced in this paper. The PID is tuned by the traditional Ziegler -Nichols technique along with three other different algorithms: Genetic algorithm, whale algorithm and grey wolf algorithm. A comparison has been established between these algorithms based on the objective function value, execution time, overshoot, settling time and current sharing. The simulation results were collected to authenticate effectiveness of the proposed techniques and to evaluate the advantages of these optimization algorithms over the traditional tuning method.