Current Issue : July - September Volume : 2017 Issue Number : 3 Articles : 5 Articles
In this study, a novel high step-up DC-DC converter was successfully integrated using\ncoupled inductor and switched capacitor techniques. High step-up DC-DC gain was achieved using\na coupled inductor when capacitors charged and discharged energy, respectively. In addition, energy\nwas recovered from the leakage inductance of the coupled inductor by using a passive clamp circuit.\nTherefore, the voltage stress of the main power switch was almost reduced to 1/7 Vo (output voltage).\nMoreover, the coupled inductor alleviated the reverse-recovery problem of the diode. The proposed\ncircuit efficiency can be further improved and high voltage gain can be achieved. The operation\nprinciple and steady-state analysis of the proposed converter were discussed. Finally, a hardware\nprototype circuit with input voltage of 24 V, output voltage of up to 400 V, and maximum power of\n150W was constructed in a laboratory; the maximum efficiency was almost 96.2%....
Microgrid frequency and voltage regulation is a challenging task, as classical generators\nwith rotational inertia are usually replaced by converter-interfaced systems that inherently do not\nprovide any inertial response. The aim of this paper is to analyse and compare autonomous primary\ncontrol techniques for alternating current (AC) and direct current (DC) microgrids that improve this\ntransient behaviour. In this context, a virtual synchronous machine (VSM) technique is investigated\nfor AC microgrids, and its behaviour for different values of emulated inertia and droop slopes is\ntested. Regarding DC microgrids, a virtual-impedance-based algorithm inspired by the operation\nconcept of VSMs is proposed. The results demonstrate that the proposed strategy can be configured to\nhave an analogous behaviour to VSM techniques by varying the control parameters of the integrated\nvirtual-impedances. This means that the steady-state and transient behaviour of converters employing\nthese strategies can be configured independently. As shown in the simulations, this is an interesting\nfeature that could be, for instance, employed for the integration of different dynamic generation or\nstorage systems, such as batteries or supercapacitors....
This paper presents the experimental verification of a 2kW battery energy storage system (BESS). The BESS comprises a full-bridge\nbidirectional isolated dc-dc converter and a PWM converter that is intended for integration with a photovoltaic (PV) generator,\nresulting in leveling of the intermittent output power from the PV generator at the utility side. A phase-shift controller is also\nemployed tomanage the charging and discharging operations of the BESS based on PVoutput power and battery voltage.Moreover,\na current controller that uses the ...
Direct current (DC) distribution systems and DC microgrids are becoming a reliable and\nefficient alternative energy system, compatible with the DC nature of most of the distributed energy\nresources (DERs), storage devices and loads. The challenging problem of redesigning an autonomous\nDC-grid system in view of using energy storage devices to balance the power produced and absorbed,\nby applying simple decentralized controllers on the electronic power interfaces, is investigated in this\npaper. To this end, a complete nonlinear DC-grid model has been deployed that includes different\nDC-DERs, two controlled parallel battery branches, and different varying DC loads. Since many loads\nin modern distribution systems are connected through power converters, both constant power loads\nand simple resistive loads are considered in parallel. Within this system, suitable cascaded controllers\non the DC/DC power converter interfaces to the battery branches are proposed, in a manner that\nensures stability and charge sharing between the two branches at the desired ratio. To achieve this\ntask, inner-loop current controllers are combined with outer-loop voltage, droop-based controllers.\nThe proportional-integral (PI) inner-loop current controllers include damping terms and are fully\nindependent from the system parameters. The controller scheme is incorporated into the system\nmodel and a globally valid nonlinear stability analysis is conducted; this differs from small-signal\nlinear methods that are valid only for specific systems, usually via eigenvalue investigations. In the\npresent study, under the virtual cost of applying advanced Lyapunov techniques on the entire\nnonlinear system, a rigorous analysis is formulated to prove stability and convergence to the desired\noperation, regardless of the particular system characteristics. The theoretical results are evaluated by\ndetailed simulations, with the system performance being very satisfactory....
In modular uninterruptible power supplies (UPSs), several DC/AC modules are required\nto work in parallel. This structure allows the system to be more reliable and flexible. These DC/AC\nmodules share the same DC bus and AC critical bus. Module differences, such as filter inductor,\nfilter capacitor, control parameters, and so on, will make it possible for the potential zero sequence\ncurrent to flow among the modules. This undesired type of circulating current will bring extra losses\nto the power semiconductor devices in the system, which should be paid special attention in high\npower application scenarios. In this paper, plug�n�play modules and cycle control are discussed and\nvalidated through experimental results. Moreover, potential zero sequence circulating current impact\non power semiconductor devices thermal performance is also analyzed in this paper....
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