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An introduction is presented in which the guest editors discuss the theme of the issue, Applications of Predictive Control in Micro grids.

A very simple geometric structure whose branches can be filled by inductors, capacitors, diodes, short-circuits, or open-circuits is proposed. It serves for generating large dc gain-purposed switching cells by making different choices of the type of component on each branch. The switching cells are integrated in basic converters. It is shown that almost all the high dc gain nonisolated converters based on switched-capacitor-inductor cells proposed in the last years, regardless of their complexity, can be derived through this method. From the same geometric structure, new high dc gain boosting converters can be derived in a systematic manner. The available and the new converters in each class as defined by the number of reactive components are compared in terms of their performance: dc gain, semiconductor elements count, voltage and current stress on transistors and diodes, character of the input current, easiness of the transistor driving, and easiness of the control as determined by common/uncommon line-load ground, power stage efficiency. This comparison allows us to choose the optimal solution for each specific application in conjunction with the green sources of energy, multisource microgrids, electric vehicles, data and communications systems, and so on. The geometric structure is generalized in different ways, allowing for the development of ultrahigh dc gain converters. One of the proposed generalized ultrahigh dc gain converters is fully analyzed and built in the laboratory, with the experimental results verifying the theoretical analysis. [ABSTRACT FROM AUTHOR]

A very simple, low component count snubber is used in order to get ZCS for all the switches of a three-level voltage step-down converter. ZCS allows for the implementation of the switches with insulated-gate bipolar transistor which are able to withstand large input voltages at large power. The snubber is placed in the secondary-side, before the rectifier. The transformer leakage inductance is used in the ZCS-purposed resonant process, eliminating thus the need for an additional resonant inductor. All the resonant circuit energy is recuperated to the load. No voltage stresses appear on the switches, and the current stress is limited in a tradeoff components design. The proposed solution allows for a boost of the effective duty cycle. As a result, the proposed converter operates with a high efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a phase-shift interleaving control method for variable-phase switched-capacitor (SC) converters that can perform voltage conversions with little electromagnetic interference over a wide range of operating condition. This is achieved by having multiple units of SC converter connected in parallel and an N-state hysteresis unit selection control scheme which works along the interleaving control to vary the number of converters in operation. By having the capacitors of inactive units connected to the output and the converters operating with output interleaving operation, the output capacitor that is typically required in SC converters for maintaining a small voltage ripple is made redundant in this configuration. A three-unit SC converter of the proposed configuration is described in this paper. Experimental results show that the proposed solution works satisfactorily with good regulation, input and output interleaving operations, and dynamic response for a wide operating range. [ABSTRACT FROM PUBLISHER]

The energy-efficiency issue of switched-capacitor converters is still a controversial topic that requires a more in-depth discussion. In this paper, we address the issue by dividing the analysis of the entire efficiency problem into two parts. In the first part, the efficiency of a capacitor-charging RC circuit under different aspects (partial charging, full charging, at zero capacitor voltage, at nonzero capacitor voltage, etc.) will be conducted. The efficiency analysis of a capacitor-discharging RC circuit with a resistor, capacitor, and paralleled resistor–capacitor loads will be covered. A complete evaluation of the overall efficiency is then performed in terms of both the charging and discharging efficiencies. Based on the analysis, some design rules useful for developing high-efficiency switched-capacitor converters is suggested. Additionally, it is shown that the belief that quasi-switched-capacitor converters are more lossy than switched-capacitor converters is a common misconception. [ABSTRACT FROM AUTHOR]

A new concept of high-voltage dc-dc power conversion is presented in this paper. Its distinctive feature lies in distributing the high input voltage asymmetrically between two primary-side series-connected switch pairs. This allows using switches of optimal ratings in their respective class: the low-voltage switch pair implemented with MOSFETs only, and the high-voltage switch pair implemented with insulated gate bipolar transistors (IGBTs) only. As the switches in a switch pair are of the same type and voltage rating, they are maximally utilized. With an active snubber on the secondary side of the isolation transformer, a hybrid zero-voltage-switching-zero-current-switching (ZCS) scheme, which is different from the zero-voltage and zero-current-switching technique, is realized and makes all IGBTs be zero-current-switched and all MOSFETs be zero-voltage-switched from very light load to full load condition with minimal circulating energy. The ZCS snubber energy is completely released to the load, leading also to a duty-cycle gain. The operating principles, dc analysis, and design guidelines will be given. A 2-kW, 1500/48-V experimental prototype has been built and evaluated. The measured efficiency of the converter is found to be 92.4% at the rated condition. [ABSTRACT FROM AUTHOR]

Power conversion from an input voltage of several kilovolts to a low load voltage is of great significance in various applications, but poses serious challenges. In this paper, a new converter, which is able to realize such a large step-down conversion in a single step, is proposed by introducing a novel concept of dc–dc multiphase conversion and n-phase interleaving rectification. The proposed structure is formed by n switch pairs in the primary side, an n-phase isolation transformer with the primary windings connected to dc blocking capacitors, and an n-phase current multiplier in the output side. The switching patterns applied to the switch pairs have a phase difference of 360^\circ \mathord\left/ \vphantom 360^\circ n \right. \kern-\nulldelimiterspace n, and the output inductor currents are interleaved correspondingly, making necessary a smaller output filter. For a V_i input voltage and I_o load current, the converter features V_i/n voltage stress on the primary-side switches, and I_o/n current stress on the secondary-side inductors and diodes. Thus, the magnetic size of the inductors is considerable reduced. The primary-side switches are commutated with zero-voltage-switching (ZVS). Therefore, rather than using insulated-gate bipolar transistors (IGBTs) or MOSFETs with higher voltage ratings, the most available, notable performing 500/600 V MOSFETs can be used in the proposed converter with several kilovolts supply voltage, allowing for a higher operation frequency and lower conduction losses. Compared with an input-series–output-parallel (ISOP) connection of full-bridge (FB) isolated converters, for the same voltage stress on the switches, the proposed converter requires half of the number of transistors and inherently balances the input voltage among the switch pairs. The switching mechanism of a typical switch pair in the kth interval T_s/n of a switching cycle is analyzed. A dc analysis was carried out to determine the dc conversion ratio and the ZVS conditions in an analytical form. It allows for a tradeoff design of the converter, such that to minimize the duty-cycle loss and maximize the ZVS load range. A 1500/48-V, 2-kW prototype with four switch pairs was designed, implemented, and evaluated. The experimental results prove the soft switching of the switches, the low voltage stress across the primary-side switches, and the low current flowing through the rectifier's diodes and inductors. The efficiency measured at nominal power rating was 90.75%. [ABSTRACT FROM AUTHOR]

The switched-capacitor (SC) converters are ideal switching-mode power supplies for consumer portable electronic devices due to their nature of being light weight, small size, and high-power density. However, they suffer from a discontinuous input-current waveform with large di/dt, which leads to significant electromagnetic interference emission. This paper proposes a configuration of SC converters connected in parallel, with their inputs and outputs interleaved and adaptively controlled. The interleaving operation is performed by using an original type of control in which both the capacitors’ charging time TON and switching frequency are adjusted to get the line and load regulation. It is shown that, for a given range of variation of the supply voltage and load, there always exists a solution [TON, TS] that assures both output-voltage regulation and perfect interleaving. Experimental results are provided to validate the feasibility of the proposed scheme. Precise interleaving, and good line and load regulation are maintained for all the designated range, including the transient periods. [ABSTRACT FROM PUBLISHER]

A new current-driven soft-switched full-bridge converter is presented in this paper. By connecting a switchedcapacitor snubber in parallel with the primary winding of the coupling transformer, all main switches are zero-current-switched (ZCS) and the switches in the snubber are zero-voltage-switched (ZVS). The proposed converter has the following key features. First, the transformer leakage inductance is utilized as a part of the resonant circuit for the soft-switching actions. Second, the snubber capacitor voltage is adaptively controlled: the capacitor is charged to the minimum necessary energy for switching the main switches at zero current, depending on the actual value of the input/load current. Thus, less resonant energy is circulated. Third, there is no extra voltage stress on the switches and the current through the switches is limited to the value of the input current. Consequently, the conduction losses are kept minimum. The cyclical switching operation and control of the converter are described. A tradeoff design of the snubber circuit is given: the requirement of reducing the duration of the resonant intervals for minimizing the dutycycle loss is superimposed on the requirement of getting ZCS for a very large range of the line voltage and load. A 530-V/15-kV, 5-kW prototype has been built and evaluated. The experimental results confirmed the theoretical predictions. A comparative study on the converter efficiency with and without the proposed snubber circuit is given, showing the superiority of the proposed solution. [ABSTRACT FROM AUTHOR]

A new soft-switched, current-driven full-bridge converter is presented. The structure utilizes a simple snubber formed by two unidirectional switches and a capacitor to realize soft-switching operation over a wide line and load range. All primary-side switches are operated with zero-current switching (ZCS) and the snubber switches are operated with zero-voltage switching. The energy used for soft-switching is self-adaptable. For a given input current, the snubber capacitor is charged to the minimum required energy for ZCS of the switches. Thus, less resonant energy is used and the conduction loss can be kept minimal. The cyclical switching operation and control of the converter will be discussed. By compromising the voltage stress on the switches and loss of duty cycle (i.e., the regulation range), an optimized design procedure of the circuit elements is derived. The input voltage range and load variation that ensure both output voltage regulation and soft switching are determined. By studying the small-signal characteristics of the entire system, a current-controlled feedback control circuit has been implemented with a DSP. The experimental results measured on a 5-kW, 530-V/15-kV prototype confirms the advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

A new circuit is proposed for a steep step-up of the line voltage. It integrates a switched-capacitor (SC) circuit within a boost converter. An SC circuit can achieve any voltage ratio, allowing for a boost of the input voltage to high values. It is unregulated to allow for a very high efficiency. The boost stage has a regulation purpose. It can operate at a relatively low duty cycle, thus avoiding diode-reverse recovery problems. The new circuit is not a cascade interconnection of the two power stages; their operation is integrated. The simplicity and robustness of the solution, the possibility of getting higher voltage ratios than cascading boost converters, without using transformers with all their problems, and the good overall efficiency are the benefits of the proposed converter. [ABSTRACT FROM AUTHOR]

Presents a generalized circuit structure of bi-directional switched-capacitor dc/dc converters that feature voltage step-down, voltage step-up, and bi-directional power flow. Derivation of two structures of single-capacitor bi-directional converter cells; Control scheme applied in the capacitor-charging phase; Formulation of a converter string by cascading a number of converter cells.

Presents a technique for calculating the alternating current line-to-output and control-to-output transfer characteristics of direct current (dc)/dc converters. Algorithm description; Illustrative examples; Conclusion.

Proposes a direct current (dc)-dc boost converter operating under zero-voltage-transition (ZVT) conditions. Information on ZVT-pulse-width modulation boost converter; DC analysis and time-domain simulation; Discussion on alternating current small signal analysis; What the proposed converter achieves.