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In order to further improve the efficiency of dual-active-bridge (DAB) converter, a hybrid five-variable modulation scheme with minimal root mean square (rms) current is proposed in this article, which combines the traditional phase-shift and pulsewidth modulation schemes. By adopting the proposed optimal scheme, a wider zero-voltage switching (ZVS) operation range and lower rms current level are achieved simultaneously when compared with other modulation schemes, which significantly improves the efficiency of the DAB converter. Moreover, for the complexity of the proposed modulation scheme with five variables, the Fourier decomposition based analytical expressions are derived for the converter and a generalized performance analysis results are presented. Besides, in order to avoid the analysis error, especially at light-load condition, the optimization strategy takes the rms current as the optimal objective, which includes the eight harmonic component of the inductor current rather than just considers the fundamental component. And an offline particle swarm optimization algorithm is introduced to acquire the optimal operating points for the whole power range. To substantiate the effectiveness of the proposed modulation scheme, a comprehensive comparison among related works in terms of the rms value and ZVS range were carried out under various operation condition. Finally, a 1.2 kW experimental platform was built and the highest experimental efficiency under the proposed modulation scheme reaches 96.8%. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are widely used in street lighting, landscape lighting, liquid crystal display (LCD) backlighting, healthcare, etc. As an important part of LED lighting products, LED driver plays a vital role in maintenance costs reduction, energy saving and lifetime prolongation. In this paper, a single-stage LED driver is proposed, which is integrated by a totem-pole bridgeless power factor correction (PFC) unit and several modular LCL-T resonant rectifiers. The totem-pole bridgeless PFC unit and the LCL-T resonant rectifiers are integrated by sharing switches, which can simplify the circuit and reduce the system cost. The output current can be regulated by applying the variable inductor control. Constant duty cycle and fixed switching frequency operation can be achieved as well. The operating principle and the performance of the proposed converter are analyzed in this paper. In addition, a precise parameter design method is proposed by considering the high-order harmonics. At last, an experimental prototype is established to validate the proposed parameter design and variable inductor control method. [ABSTRACT FROM AUTHOR]

Unregulated LLC resonant converters operating at resonant frequency have been adopted in numerous applications due to its high efficiency characteristic. However, in practice, resonant frequency operation cannot always be guaranteed due to the tolerances and variations of circuit parameters. Therefore, in this brief, a simple resonant frequency tracking method based on the transformer secondary voltage is proposed. When LLC converter operating in the below resonant frequency region, the ratio of the average transformer secondary voltage and output voltage is less than unity, while the ratio is unity at resonant frequency. By adopting this characteristic, the resonant frequency tracking is achieved by comparing the calculated voltage ratio and unity, then the switching frequency is adjusted to track the resonant frequency. To reduce the sampling circuit complexity, the rectified transformer secondary voltage is sensed, and the voltage ratio becomes 0.5 at resonant frequency. The effectiveness of the proposed resonant frequency tracking method has been experimentally validated under different scenarios. [ABSTRACT FROM AUTHOR]

Asymmetric duty modulation (ADM), as a recently proposed modulation scheme, provides new chance to improve the performance of dual active bridge (DAB) converter. On this basis, an optimal ADM (OADM) scheme is proposed in this article to minimize the inductor peak-to-peak current over the whole voltage and power range. First, the DAB converter adopting ADM scheme is analyzed in frequency-domain and time-domain, and four operating modes are established. Then, the minimum peak-to-peak inductor current for each operating mode is obtained under Karush–Kuhn–Tucker condition, and the corresponding optimal closed-loop control with low calculation complexity is derived. Then, the key values and features of the OADM scheme are compared with recent state of the art, mainly including the inductor root mean square current and soft-switching performance. Finally, an experimental prototype was built to validate the efficiency enhancement of the converter by adopting the proposed OADM scheme. [ABSTRACT FROM AUTHOR]

In this article, an efficiency-oriented hybrid duty modulation (HDM) scheme is proposed for the dual active bridge (DAB) converter that can reduce the inductor root-mean-square (rms) current and extend the switch soft-switching range. First, a complete description of the combination forms of different modulation schemes is presented considering the allocation of the zero-voltage portion. A unified description for these combination forms is obtained in the frequency domain. Second, the symmetric–symmetric duty modulation (SSDM) scheme and asymmetric–symmetric duty modulation (A2SDM) scheme are established to minimize the inductor rms current by considering its fundamental component. Third, the characteristics of SSDM, A2SDM, and the traditional phase shift modulation schemes are compared from several aspects, mainly including the inductor rms current and the soft-switching performance. Furthermore, the loss breakdown analysis results for the three modulation schemes are presented and compared. According to these results, the HDM scheme is proposed to improve the overall efficiency of the DAB converter. Finally, an experimental prototype was built with a peak efficiency of 97%, which validates the effectiveness of the proposed modulation scheme. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge (CHB) inverter is one of the most attractive multilevel topologies for renewable energy applications. Due to the fact that CHB inverters employ a large number of components, they suffer from a higher probability of fault, which reduces the system reliability. A fault-tolerant operation for a CHB inverter is described in this article. New features ensure reliable and robust operation of the converter in the event of a fault. The proposed strategy uses an additional cross-coupled CHB (X-CHB) unit in companion with the existing CHB units to support the output voltage and ensure continuity of operation in the event of an open/short-circuit fault. The operation of the proposed X-CHB inverter is described in detail. Simulation and experimental verification of the proposed concept are demonstrated using a seven-level CHB. Both simulation and experimental results confirm the fault-tolerant operation of the X-CHB for a battery energy storage system in case of switch faults. [ABSTRACT FROM AUTHOR]

High step-up boost converters with coupled inductor have attracted much attention in the fuel cell or photovoltaic grid-connected generation system, however, there are few literatures elaborated on the construction ideas and derivation methods of them. Accordingly, in order to obtain a clear roadmap on the derivation and inner connection of these converters, a comprehensive review and analysis are presented in this paper. First, the basic boost converter with coupled inductor is regarded as the basic topology, and its merits and demerits are analyzed in detail. Then, in order to address these demerits, various step-up techniques are introduced, such as the rectifier circuit, the active-clamped circuit, the multi-winding coupled inductor, and the voltage doubler rectifier; and numerous new topologies are continuously proposed by combinations and equivalent simplifications. In addition to a detailed synthesis of each topology, a comparative and quantitative analysis among some important converters is presented, and the optimal one is chosen to build a 250 W prototype. Finally, based on comparisons and analysis, the main characteristics and inner connections of these high step-up boost converters with coupled inductor are identified and clarified. [ABSTRACT FROM AUTHOR]