In this paper, a modular multiple DC (MMDC) transformer based DC transmission system, which is used for permanent magnetic synchronous generator (PMSG) based offshore wind farm grid connection, is proposed. The MMDC t...
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In this paper, a modular multiple DC (MMDC) transformer based DC transmission system, which is used for permanent magnetic synchronous generator (PMSG) based offshore wind farm grid connection, is proposed. The MMDC transformer is composed of input-parallel output-series (IPOS) DC/DC submodule groups, each of which consists of several input-series output-series (ISOS) LLC resonant converters (i.e., submodules). In the offshore wind farm, the electrical power generated by PMSG is converted to DC power by diode rectifier. Compared with the existing offshore wind farm grid-connection schemes, the proposed system has advantages of fewer conversion stages, higher efficiency and lower cost. The mathematical relationship of the system is studied, and then one kind of control strategy is proposed. Furthermore, a detailed DC transmission system simulation model containing a 160 submodules (LLC resonant converters) based MMDC transformer is built in PSCAD/EMTDC. Finally, a down-scaled experimental prototype of the DC system, which includes 9 submodules, is presented. Both simulation and experimental results validate the feasibility of the proposed DC system and effectiveness of the control strategy.
Electric Vehicles (EVs) play a significant role in the reduction of CO2 emissions and other health-threatening air pollutants Accordingly, several research studies are introduced owing to replacing conventional gasoli...
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Electric Vehicles (EVs) play a significant role in the reduction of CO2 emissions and other health-threatening air pollutants Accordingly, several research studies are introduced owing to replacing conventional gasoline-powered vehicles with battery-powered EVs. However, the ultra-fast charging (UFC) of the battery pack or the rapid recharging of the battery requires specific demands, including both: the EV battery and the influence on the power grid. In this regard, advanced power electronics technologies are emerging significantly to replace the currently existing gas station infrastructures with the EV charging stations to move from conventional charging (range of hours) to UFC (range of minutes). Among these power electronics conversion systems, the DC-DC conversion stage plays an essential role in supplying energy to the EV via charging the EV's battery. Accordingly, this paper aims to present possible architectures of connecting multiple Dual Active Bridge (DAB) units as the DC-DC stage of the EV fast charger and study their Small-Signal Modeling (SSM) and their control scheme. These are, namely, input-series output-series (ISOS), input-seriesoutput-Parallel (ISOP), input-Parallel output-Parallel (IPOP), and input-Parallel output-series (IPOS). The control scheme for each system is studied through controlling the output filter inductor current such that the current profile is based on Reflex Charging (RC). The main contribution of this paper can be highlighted in providing generalized SSM as well as providing a generalized control approach for the input-seriesinput-Parallel output-seriesoutput-Parallel (ISIP-OSOP) connection. The generalized model is verified with three different architectures. The control strategy for each architecture is studied to ensure equal power sharing, where simulation results are provided to elucidate the presented concept considering a three-module ISOS, IPOP, ISOP, and IPOS DC-DC converters.
input-series output-series (ISOS) modular dc-dc converters are suitable for applications involving high input and output voltages. input voltage sharing (IVS) and output voltage sharing (OVS) of the constituent module...
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input-series output-series (ISOS) modular dc-dc converters are suitable for applications involving high input and output voltages. input voltage sharing (IVS) and output voltage sharing (OVS) of the constituent modules must be guaranteed for an ISOS system. A duty cycle-based model predictive control (DC-MPC) scheme is proposed in this paper to achieve IVS and OVS for an ISOS system. The employed switching frequency in the DC-MPC scheme is fixed;duty cycles are optimized and then determined by minimizing a cost function, which is derived from an ISOS system aimed at achieving IVS and OVS. IVS and OVS can, therefore, be obtained by employing the optimized duty cycle within each sampling period. In addition, challenges and disadvantages of directly using traditional MPC to achieve IVS and OVS is briefly discussed, while the proposed DC-MPC can effectively avoid them. Compared with the existing proportional integral-based schemes in the literature, the proposed DC-MPC is better for IVS and OVS because it is a very simple and intuitive approach with lower cost and higher overall dynamic performance. Simulation and experiments are conducted to verify that the proposed DC-MPC scheme works well during both steady and transient states.
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