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DC microgrid is gaining attraction and a recent trend in distribution power generation system due to penetration of renewables (especially photovoltaic or fuel cell). In this paper, a new triple-switch-triple-mode high step-up converter (TSTM-HS converter) is presented for dc microgrid applications. In the proposed converter, voltage lift technique is employed and range of duty cycle is extended by incorporating an additional switch in converter circuitry. By doing this, high voltage conversion ratio is achieved without using a transformer, coupled inductor, and multiple stages of switched capacitors. Moreover, the TSTM-HS converter operated in three modes with two types of the duty cycles to achieve low to high voltage conversion without using high duty cycle for each switch. The effects of difference in the inductance values on the regulation and operating behavior of the TSTM-HS converter are discussed. The continuous conduction mode and discontinuous conduction mode characteristics of the TSTM-HS converter are discussed in detail with steady-state analysis and boundary condition. The comparison is provided to highlight the benefits of the TSTM-HS converter. The selection of semiconductor devices and the design of reactive components are discussed for the TSTM-HS converter. The experimental results of the proposed converter are provided which validate the theoretical approach, performance, and feasibility of converter. [ABSTRACT FROM AUTHOR]

Direct power control (DPC) has been proposed as an effective control method for pulsewidth modulated (PWM) converters. The recent development focuses on the integration of the model predictive (MP) control and DPC to obtain better steady-state performance. In most MP-DPCs, duty cycle optimization (DCO) is a common technique to achieve the power error minimization. However, the periodic occurrence of a duty cycle larger than one (D > 1) deteriorates the performance of the PWM converter by inducing current spikes and power surges. To address this problem, this paper conducts an in-depth examination on the “D > 1” case common in MP-DPC using DCO. It is found the “D > 1” case is caused by the wrong control action of the active power in the starting period of each sector. Furthermore, a new table containing an additional pre-calculated interval in every sector is developed to eradicate the “D > 1” case and its associated power quality issues. Both simulation and experimental results are provided to demonstrate the effectiveness of the new table. [ABSTRACT FROM AUTHOR]

In this paper, a highly efficient isolated resonant converter with a novel modulation method is proposed for delivering power from photovoltaic (PV) modules to the dc microgrid. The proposed modulation method allows the converter to boost low input voltages and regulate a wide input voltage range. The converter design is based on a series resonant converter (SRC) that operates at the resonant frequency to achieve highest efficiency under nominal input voltage condition. Under shadowed or low irradiance conditions of PV panels, the converter will operate with the proposed “double-pulse duty cycle” modulation method to step up the voltage for the dc microgrid connection. With the proposed modulation method, the output switches serve for both synchronous rectification and voltage boost function. This method enables a higher voltage boost ratio than the SRC without adding additional switches while operating at the resonant frequency. A 300-W hardware prototype with gallium-nitride devices is built to verify the performance of the proposed converter and modulation method. The converter achieved a peak efficiency of 98.9% and a California Energy Commission weighted efficiency of 98.7% under nominal input voltage condition. [ABSTRACT FROM AUTHOR]

The conventional predictive duty cycle control (CPDCC) of three-phase full-bridge ac/dc converters selects adjacent nonzero vector pair based on the grid-voltage vector location, then the duration for each vector is calculated. Though the vector selection method is quite simple, it has a significant disadvantage that the values of calculated durations could be frequently less than zero due to nonoptimal vector selection, which results in high current harmonics and power notches. It could be improved with improved predictive duty cycle control (IPDCC) by reselecting the nonzero vector pair when negative duration exists; however, the whole vector selection and calculation procedure are repeated. By theoretical verification that the power variation rates of reversible vector pair are symmetrical with respect to that of zero vector, this paper proposes the reversible predictive duty cycle control (RPDCC) simply by replacing the original vector with its opposite vector and the recalculation of vector duration is eliminated compared with IPDCC. Thus, the calculation effort is almost not increased compared with CPDCC while system performance is significantly improved. The proposed control is theoretically derived and verified with the simulation and experimental results showing that RPDCC has better steady and dynamic performance than CPDCC and IPDCC methods. [ABSTRACT FROM AUTHOR]

This paper presents a new interleaved active clamp forward converter for low and wide input, and high current output applications. In the proposed converter, the operating duty ratio can be extended over 0.5 due to the additional powering path resulting from additional series-connected secondary windings from each transformer. As a result, the proposed converter can be designed with large transformer turns ratio. Thus, since the proposed converter can reduce not only the primary RMS current but also switch turn-off current, it can achieve high efficiency. Moreover, since all secondary switches can operate without floating gate drivers, the proposed converter can maintain simple structure and low complexity of gate driving circuits in the secondary side. The validity of this proposed converter is verified by the experimental results from 36V–72 V input and 12 V/500 W output for the dc/dc prototype. [ABSTRACT FROM AUTHOR]