A Fibonacci-type switched-capacitor (SC) cell is modified in order to be suitable for an innovative, breakthrough switched-capacitor multilevel inverter (SCMLI) fitted for photovoltaics powered systems. Characteristic to such a cell, its capacitor voltages follow a Fibonacci series. Thus, with only a very few capacitors, a very large step-up of the input voltage is realized; and the staircase output waveform of a Modified Fibonacci -based inverter would feature a very large number of levels, being very close to a sinusoid. Such an inverter is necessary if its front-end is a green source of energy which provides only a relative low voltage. A common line-load ground two-output SC-based multilevel inverter is then developed, analyzed and designed. This inverter can feed two loads without interference with each other. The common ground (CG) effectively stops the leakage current of the solar cells. In order to get the same voltage step-up and the same number of levels as in a no-common ground inverter with the same structure, the Modified SC Fibonacci circuit is reinvented, by dividing it into two sub-networks, each one with another function. One of them together with the input source supply the positive half-sinusoids voltages of both outputs, thus assuring a permanent non-zero input current, as required by the front-end environmental-friendly sources of energy. The other SC sub-network supplies the negative half-sinusoids to both loads. The novel CG-SCMLI contains the smallest number of components per output among all the common ground SCMLIs able to provide the same number of levels in the output staircase waveform. The idea was implemented on a 400W 15-levels inverter providing two outputs of 220V rms, of a very small total harmonic distortion of 5.2%.

Answering the requirements of the environmental-friendly sources of energy when used as front end of the electrical local or national grid, a new switched-capacitor multilevel inverter (SCMLI) is proposed. The same structure can serve in multiple roles: voltage step-down; voltage step-up with a low dc boost factor; voltage step-up with a high dc boost factor. This SCMLI adapts itself for different levels of voltages provided by the MPPT (maximum power point tracking) stage which follows the photovoltaics array, voltages depending on the operating conditions (insolation, shadow, etc.). For all the input conditions, the inverter supplies the same ac 220V rms, 50 Hz voltage. A line-load common-ground (CG) is created for annihilating the typical leakage current of the solar cells. A new switched-capacitor (SC) structure is used, in which the switches are submitting to lower voltage stress compared with available step-down - step-up SCMLIs, resulting in a comparatively lower total standing voltage, and thus in a better efficiency and a lower cost function. A prototype able to invert a solar panel's MPPT voltage varying from 60V to 180V to a multilevel output featuring the total harmonic distortion (THD) of 17.2% is built. A standalone load of 484W is supplied. The experimental results show a nominal efficiency of 96.96% for the buck-type operation, of 96.19% for the boost-type operation with a dc gain of 4, and of 91.97% for the boost-type operation with a dc gain of 6.

A Switched-Capacitor Multilevel Inverter (SCMLI) is proposed. It concomitantly features: a) a permanent non-zero input current, b) a common line-load ground which eliminates the photovoltaic cell leakage current, c) two outputs, d) a high boost factor, equal to that in a similar no common ground inverter, and e) the smallest number of capacitors and switches per output and per boost factor compared to any available common ground SC inverter. Its basic structure is constituted by two SC sub-circuits. The originality of the proposed inverter allowing these features is due to a novel operation scheme in which one of the two SC sub-circuits supplies the positive half-sinusoid of both outputs, and the other SC sub-circuit supplies the negative half-sinusoid of both outputs. It was conceived as an inverter powered by a solar cell that supplies standalone ac loads of small powers. A real world application is implemented: a micro-inverter supplied by the solar cell of type TSM-DEG15MC.20(II) (with Vinin the range 40.2 - 41.5V, Poutin the range 390 - 415W) offering two outputs of opposite polarity of 110 Vrms, 60 Hz, according to an industrial requirement.

This paper presents a new soft-switched, current-driven full-bridge converter. A simple snubber is used in order to get ZVS for all the main switches. The soft-switching realization is independent of the load. The snubber is placed in parallel with the bridge. All the resonant circuit energy is recycled by the load in each half cycle. No additional current stresses appear on the main switches. A design-oriented steady-state analysis leads to the expressions of the dc voltage conversion ratio and ZVS analytical conditions, allowing for a trade-off design of the resonant inductor. A prototype has been built with a high energy transfer efficiency. The simulation and experiment results confirm the detailed theoretical analysis.

A step-up DC-DC converter is proposed by inserting a new switched-capacitor cell in a modified PWM boost circuit. The obtained hybrid PWM non-isolated converter is able to provide a large DC gain, as necessary for serving as front-end to electrical grids supplied by solar or fuel cells. It features low voltage stress on the switches compared with traditional boost converter, allowing for the use of low-voltage rated components, with smaller nominal parasitic on-resistances. Analysis, simulation and experimental data show the superiority of the proposed converter over other hybrid converters in a trade-off of complexity, components count, voltage ratio and voltage stress on the switches.

A new step-up basic switching cell formed by four passive elements and two diodes is proposed. It is inserted in a boost converter in order to obtain a new hybrid PWM non-isolated converter able to provide a large DC gain, as required as front-end to electrical grids supplied by solar or fuel cells. A family of converters can be created by inserting the defined switching structure in any step-up converter. Analysis, simulation and experimental data show the superiority of the proposed converter over other hybrid converters with similar complexity and the same voltage ratio: less voltage stresses on the switches.

For applications requiring power conversion from an input voltage of several kilovolts, like power supplies in railway systems, a new soft-switching PWM full-bridge converter of buck type is proposed. The active snubber used in this purpose is formed by two transistors operated alternatively in each half-cycle and one resonant capacitor, and is inserted in the secondary-side. All the main primary-side switches are turned-on and -off with ZCS, making them suitable for an IGBT implementation. The snubber's transistors are also turned-on and -off with ZCS. The resonant energy used to get soft-switching is recycled in each cycle to the load, by enhancing thus the effective duty-ratio. No additional resonant inductor is used, the transformer leakage inductance forms the resonant circuit with the snubber's capacitor. The soft-switching realization is independent of the load. The resonant capacitor is designed such that to assure ZCS starting from the required minimal input voltage. A design-oriented steady-state analysis leads to the expressions of the dc voltage conversion ratio and ZCS analytical conditions, allowing for a trade-off design of the resonant capacitance. The simulation and experimental results confirm the detailed theoretical analysis.

A simple switched-capacitor step-up cell formed by two capacitors and two diodes is inserted in a boost converter in order to get a large dc line-to-load voltage ratio. The output capacitor and output diode of the boost converter are eliminated, their role being taken by the elements of the switching block. The dc gain of the new structure is the same or larger than that of other converters with two capacitors and one inductor. The voltage stress of the transistor and diodes is just the difference between the output and input voltages. In both switching stages, a direct transfer path of energy from line to load is created, increasing thus the energy conversion efficiency. The new hybrid converter represents another solution for the interface between the alternative sources of energy and their loads or grid. The simulation and experimental results confirm the theoretical analysis.

A switched-capacitor (SC) circuit and a resonant inductor are integrated with a boost converter to create a conversion system designed to be used primarily with fuel cells or photovoltaic arrays. A very large dc voltage gain even at high load, continuous input current, and soft-switching of all switches are obtained. A resonance process is used to boost the output voltage of the SC circuit, i.e., a resonant voltage peak becomes a useful phenomenon that creates no undesired over-voltage stresses. A detailed steady-state analysis allows for a trade-off design of the system elements for maximizing the energy processing efficiency. Experimental results of a 22V/100V, 250 W prototype confirm the expected performance of the proposed circuit.

The switched-capacitor converters are ideal switching-mode power supplies for portable electronic consumers due to their light weight, small size, and high power density. However, they suffer from a discontinuous input current waveform with large di/dt, what leads to significant electromagnetic interference (EMI) emission. This paper proposes a configuration of switched-capacitor converters connected in parallel with their inputs and outputs interleaved. The interleaving times are calculated by taking into account the fast capacitor-charging characteristic, and the need to have the nominal operating point on its linear part for increasing the regulation range at changes in the input voltage and load. To improve control performance and avoid the use of small-signal linearization in the control design, a large-signal approach is adopted for modeling the converter, allowing for a design of a sliding mode control.

Three basic switching structures are defined: one is formed by two capacitors and three diodes; the other two are formed by two inductors and two diodes. They are inserted in either a Cuk converter, or a Sepic, or a Zeta converter. The SC/SL structures are built in such a way as when the active switch of the converter is on, the two inductors are charged in series or the two capacitors are discharged in parallel. When the active switch is off, the two inductors are discharged in parallel or the two capacitors are charged in series. As a result, the line voltage is reduced more times than in classical Cuk/Sepic/Zeta converters. The steady-state analysis of the new converters, a comparison of the DC voltage gain and of the voltage and current stresses of the new hybrid converters with those of the available quadratic converters, and experimental results are given

A ZVT boost converter is embedded in a power factor correction system. The control circuit of the converter assures soft-switching for all the MOSFETs and load regulation. The PFC system contains additional control circuits which assure: (a) the input current follows the input voltage in a sinusoidal form; (b) feedforward line voltage regulation; (c) overcurrent protection at the input of the converter; (d) overvoltage at the load. The main chip in the control system is a UNITRODE controller of type UC3855BN. The designed system features high power factor correction, good line and load regulation and high efficiency.

This paper presents the generalized circuit structure of a switched-capacitor DC/DC converter that can offer features of voltage step-down, voltage step-up, and bi-directional power flow, Starting with the derivation of a single-capacitor bidirectional converter cell, a converter string is created by cascading a required number of cells, which is determined by the input and output conversion ratio for optimizing the conversion efficiency. The input current is made continuous by operating two strings in parallel and in anti-phase. State-space averaging technique is applied to study the static and dynamic behaviors.

A method for finding the equilibrium points of closed-loop switching converters subjected to large-signal disturbances is developed. The position of the equilibrium points in the state-plane, in conjunction with the state-plane portrait, allow for the study of the stability of large-signal transients. For this purpose, a discrete-time model is formulated, starting from a time-domain analysis algorithm based on solving a set of algebraical modified nodal equations at each integration step. Due to the complexity of the formulas, the study of the large-signal stability is carried out here only for PWM converters operating in continuous conduction mode. An application to a boost regulator allows for favorably comparing our results to those available in literature.

A discrete-time dynamic model of closed-loop switched mode electronic regulators is derived. No small-ripple approximations are required. The same model serves for both local and global stability study: by discarding the nonlinear terms (like products of small-signal perturbations in the converter state variables) and using the z-transform, a local stability criteria is formulated. Applying the condition that the eigenvalues of the z-domain characteristic matrix have to be situated inside the unit circle, a design constraint on the feedback gains is found. An example of a boost converter operating in continuous conduction mode with inductor current and output voltage feedback is presented.