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One unique feature in parallel three-phase converters is a potential zero-sequence circulating current. To avoid the circulating current, most present technology uses isolation approach, such as transformers or separate power supplies. This paper proposes a parallel system where individual converters connect both ac and dc sides directly without additional passive components to reduce size and cost of the overall parallel system. In this case, the control of the circulating current becomes an important objective in the converter design. This paper 1) develops an averaged model of the parallel converters based on a phase-leg averaging technique; 2) a zero-sequence model is then developed to predict the dynamics of the zero-sequence current; 3) based on the zero-sequence model, this paper introduces a new control variable, which is associated with space-vector modulation; 4) a strong zero-sequence current control loop is designed to suppress the circulating current; 5) simulation and experimental results validate the developed model and the proposed control scheme. Index Terms--Boost rectifier, parallel three-phase converters, phase-leg, space vector modulation (SVM), variable zero-vectors, zero-sequence circulating current.

The interwinding capacitance of the transformer and the primary-side circuit nodes to ground capacitance are critical coupling path for common-mode (CM) noise in isolated power converters. In order to analyze the CM noise, the transformer interwinding capacitance is usually equivalent to lumped capacitance. In this paper, a generalized lumped capacitance model for constructing the CM noise equivalent circuit that is valid at low frequencies is derived. By simplifying the CM noise equivalent circuit based on Thevenin’s theorem, the equivalent noise source (ENS) for CM noise is proposed. The ENS is expressed by a linear combination of voltages in the converter, where the coefficients of these voltages are determined by transformer winding structure and the circuit configuration. With the help of ENS, the CM noise of the converter under different circuit configuration can be systematically analyzed and conveniently compared, which develops an effective reference for selecting a proper circuit configuration. Finally, the lumped capacitance model and the ENS for CM noise are verified by the experimental results. [ABSTRACT FROM PUBLISHER]

In an isolated power converter, the interwinding capacitance of the transformer is the critical coupling path for the generating of common-mode (CM) noise. The shielding technique, for the purpose of blocking the electric coupling between the adjacent windings, has been widely used to deal with the CM noise. For the transformer with a single shielding layer, the displacement current that flows between the shielding layer and its adjacent windings still causes CM noise. In this paper, the shielding-cancelation (SC) technique is proposed by combining the shielding technique and the winding cancelation method together: The shielding layer is adjusted to have the same turns number and winding direction with its adjacent windings. In this way, the $dv/dt$ on the interwinding capacitance is always zero; thus, the CM noise can be effectively suppressed. A flyback converter prototype is built in the laboratory, and the performance of the SC technique on suppressing the CM noise is verified by experiments. [ABSTRACT FROM PUBLISHER]

In a photovoltaic (PV)- or fuel-cell-based grid-connected power system, a high step-up dc–dc converter is required to boost the low voltage of a PV or fuel cell to a relatively high bus voltage for the downstream dc–ac grid-connected inverter. To integrate the advantages of the high voltage gain of a switched-capacitor (SC) converter and excellent output regulation of a switching-mode dc–dc converter, a method of combining the two types of converters is proposed in this paper. The basic idea is that when the switch is turned on, the inductor is charged, and the capacitors are connected in series to supply the load, and when the switch is turned off, the inductor releases energy to charge multiple capacitors in parallel, whose voltages are controlled by a pulsewidth modulation technique. Thus, a high voltage gain of the dc–dc converter can be obtained with good regulation. Based on this principle, a series of new topologies are derived, and the operating principles and voltage gains of the proposed converters are analyzed. Finally, the design of the proposed converter is given, and the experiment results are provided to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

In this paper, the differential-mode (DM) electromagnetic interference (EMI) noise of a single-phase boost power factor correction converter operating in critical current mode was analyzed. The DM noise spectra are calculated based on the mathematical model of EMI receiver and the required corner frequencies of DM filter are obtained. It can be seen that the minimum corner frequencies are determined by the maximum noises at 150 kHz. With the relation between the magnitude of the inductor current ripple and the DM noise, the characteristics of noise at 150 kHz are obtained by analyzing the current ripple magnitude at 150 kHz; thus, the worst conditions which have the maximum noise value are figured out. Meanwhile, the maximum noises at 150 kHz for different input voltages are identical, so the DM filter can be designed based on one worst spectrum at one input voltage without testing the spectra in other conditions. [ABSTRACT FROM AUTHOR]

A discontinuous-current-mode (DCM) boost power factor correction (PFC) converter features zero-current turn-on for the switch, no reverse recovery in diode, and constant–frequency operation. However, the input power factor (PF) is relatively low when the duty cycle is constant in a half line cycle. This paper derives the expressions of the input current and PF of the DCM boost PFC converter, and based on that, variable-duty-cycle control is proposed so as to improve the PF to nearly unity in the whole input–voltage range. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. Other than a higher PF, the proposed variable-duty-cycle control achieves a lower output–voltage ripple and a higher efficiency over constant-duty-cycle control. The experimental results from a 120-W universal input prototype are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]