Abstract:The three-port converter has three H-bridge ports that can interface with three different energy sources and offers the advantages of flexible power transmission, galvanic isolation ability and high power density. The three-port full-bridge converter can be used in electric vehicles as a combined charger that consists of a battery charger and a DC-DC converter. Power transfer occurs between two ports while the third port is isolated, i.e., the average power is zero. The purpose of this paper is to apply an optimal phase shift strategy in isolation control and provide a detailed comparison between traditional phase shift control and optimal phase shift control under the proposed isolation control scheme, including comparison of the zero-voltage-switching range and the root mean square current for the two methods. Based on this analysis, the optimal parameters are selected. The results of simulations and experiments are given to verify the advantages of dual-phase-shift control in isolation control.
The capacity of an energy storage device configuration not only affects the economic operation of a microgrid, but also affects the power supply's reliability. An isolated microgrid is considered with typical loads, renewable energy resources, and a hybrid energy storage system (HESS) composed of batteries and ultracapacitors in this paper. A quantum-behaved particle swarm optimization (QPSO) algorithm that optimizes the HESS capacity is used. Based on the respective power compensation capabilities of ultracapacitors and batteries, a rational energy scheduling strategy is proposed using the principle of a low-pass filter and can help to avoid frequent batteries charging and discharging. Considering the rated power of each energy storage type, the respective compensation power is corrected. By determining whether the charging state reaches the limit, the value is corrected again. Additionally, a mathematical model that minimizes the daily cost of the HESS is derived. This paper takes an isolated micrgrid in north China as an example to verify the effectiveness of this method. The comparison between QPSO and a traditional particle swarm algorithm shows that QPSO can find the optimal solution faster and the HESS has lower daily cost. Simulation results for an isolated microgrid verified the effectiveness of the HESS optimal capacity configuration method.
The operating characteristics of a dual-active-bridge (DAB) converter are generally poor when using the singlephase-shift (SPS) control strategy while working with a light load or when the input voltage and the output voltage are not matched with the transformer ratio. To improve DAB operating characteristics when working under such undesirable conditions, a novel one-side single half-bridge pulse-width-modulation plus phase-shift (HPPS) switching strategy is proposed in this study. The operational principle of the strategy is demonstrated, and a suitable power mathematical model is also established. Based on this model, a detailed contrast analysis is conducted to compare HPPS control with SPS control, and includes zero-voltage-switching range comparison, circulating power comparison and root-mean-square current value comparison. A laboratory prototype is constructed, and the validity and feasibility of the proposed HPPS control strategy is verified by the experimental results.
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