Kerui Li

Generation of a Family of Very High DC Gain Power Electronics Circuits Based on Switched-Capacitor-Inductor Cells Starting from a Simple Graph

A simple graph with four nodes and eleven branches is defined. Its branches are filled in different ways with passive elements (capacitors, inductors, diodes) or replaced by short-circuits in order to get potential voltage step-up switching cells. These cells are inserted in boost converter, obtaining thus non-isolated power electronics circuits with a very high dc gain. Such circuits are necessary today in the green energy systems. The proposed circuits feature a lower voltage stress on its semiconductors (both switch and diodes) than that on the equivalent devices of a boost stage. A state-space-based dc and ac analysis allows for deriving the dc gain, the switches voltage and current stresses, and the frequency characteristics of the obtained converters. The steady-state analysis is performed for both the continuous and discontinuous conduction mode operations. The converters belonging to the new family are compared between them and then compared with available solutions of similar complexity as defined by the component count. Simulation and experimental results confirm the theoretical equations.

Large DC gain nonisolated converter based on a new L-C-D step-up switching cell

A new step-up basic switching cell formed by three passive elements and two diodes is proposed. It is inserted in a boost converter in order to obtain a new hybrid PWM nonisolated converter able to provide a large dc gain, as required in 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.

Generation of the Large DC Gain Step-Up Nonisolated Converters in Conjunction With Renewable Energy Sources Starting From a Proposed Geometric Structure

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.

Switched-inductor-based non-isolated large conversion ratio, low components count DC-DC regulators

Two switched-inductor cells are proposed. One of them is integrated into a boost structure, and the other one in a buck structure to get novel step-up, respectively step-down non-isolated converters with a large dc gain. The converters are operated at a high switching frequency, allowing for the inductors to be printed in PCB. Small size and high power density is obtained. The experimental results confirm the theoretical analysis. Comparison with converters with the same components count shows the advantages of the proposed regulators. The proposed cells are easily generalized by adding more inductors in order to obtain any required dc voltage gain.

Model predictive control of parallel distributed generation inverters in smart microgrids

In this paper, the parallel-connected three-phase voltage source inverter system is modeled and a state space model is obtained. A control algorithm based on finite control set model predictive control (FS-MPC) is proposed. It is applied to the distributed generation (DG) inverters that are able to provide high power quality, load current sharing and plug-n-play operation in microgrids. In this algorithm, the control objectives (voltage tracking and current sharing) are integrated into a weighted cost function. To reduce the computational burden, an alternate calculation scheme is adopted. Analysis and testing results verify the effectiveness and show the advantages of the proposed algorithm.

A new switched-capacitor based hybrid converter with large step-up DC gain and low voltage on its semiconductors

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.

Hybrid switched-capacitor quadratic boost converters with very high DC gain and low voltage stress on their semiconductor devices

By inserting a simple cell formed by a capacitor and diode into quadratic boost structures, new converters are obtained. They feature: a larger dc gain compared with that of quadratic boost converters and a smaller voltage stress on the switch and output diode, non-pulsating input current, as required for the use in conjunction with the environmental-friendly energy cells, easiness of the transistor driving, line-to-load common ground. The proposed cell can be easily generalized for enhancing the dc gain. The new converters compare favorably with available ones with the same reactive elements count. Simulations and experimental results confirm the theoretical analysis of the proposed converter.

Mixed switched-capacitor based high conversion ratio converter and generalization for renewable energy applications

A mixed switched-capacitor cell is proposed by integrating a voltage divider with a voltage multiplier. It is inserted in a boost stage for achieving a converter with high conversion ratio, low voltage stress on switches, non-pulsating input current as required as front-end to electrical grids supplied by renewable energy sources. The generalization of the proposed cell allows to achieve an ultra-high dc conversion ratio. Analysis and experimental data show the superiority of the proposed converter over other hybrid converters with similar complexity: higher dc voltage gain and less voltage stress on the switches.

A new ZVS-PWM current-fed full-bridge converter with full soft-switching load range

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.

From a voltage divider to a voltage doubler for a large DC gain converter

A classical step-down switched-capacitor cell is transformed into a step-up cell. By inserting it in a boost converter, a single-switch, low voltage stress, non-pulsating input current, large dc gain hybrid converter is proposed. The theoretical, simulation and experimental results prove the merits of the simple new solution in comparison with the available ones.