DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

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Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

This paper introduces a non-isolated high step-up dc–dc converter with dual coupled inductors suitable for distributed generation applications. By implementing an input parallel connection, the proposed dc–dc structure inherits shared input current with low ripple, which also requires small capacitive filter at its input. Moreover, this topology can reach high voltage gain by using dual coupled inductors in series connection at the output stage. The proposed converter uses active clamp circuits with a shared clamp capacitor for the main switches. In addition to the active clamp circuit, the leakage energy is recycled to the output by using an integrated regenerative snubber. Indeed, these circuits allow soft-switching conditions, i.e., zero voltage switching and zero current switching for active and passive switching devices, respectively. The mentioned features along with a common ground connection of the input and output make the proposed topology a proper candidate for transformer-less grid-connected photovoltaic systems. The operating performance, analysis and mathematical derivations of the proposed dc–dc converter have been demonstrated in the paper. Moreover, the main features of the proposed converter have been verified through experimental results of a 1-kW laboratory prototype.

High-Efficiency High Step-Up DC–DC Converter With Dual Coupled Inductors for Grid-Connected Photovoltaic Systems

The main contribution of this paper is the derivation rules summarized from existing high-performance inverters with H6-type configuration, which makes novel topologies possible. In addition, a novel high-efficiency single-phase transformerless photovoltaic inverter with hybrid modulation method is also proposed and evaluated as an example. Without input split capacitors, common-mode voltage and leakage current issues in a nonisolated system with H6-type configuration are eliminated, and the feature of a three-level output voltage in the inverter bridge's middle point helps inductors and power quality optimization. The detailed operation principles with hybrid modulation strategy combined with unipolar and bipolar pulsewidth modulation schemes are presented. Experimental results of a 2200VA prototype verify the proposed topology with hybrid modulation method.

High-Efficiency Single-Phase Transformerless PV H6 Inverter With Hybrid Modulation Method

In this paper, we present a distributed economic dispatch (ED) strategy based on projected gradient and finite-time average consensus algorithms for smart grid systems. Both conventional thermal generators and wind turbines are taken into account in the ED model. By decomposing the centralized optimization into optimizations at local agents, a scheme is proposed for each agent to iteratively estimate a solution of the optimization problem in a distributed manner with limited communication among neighbors. It is theoretically shown that the estimated solutions of all the agents reach consensus of the optimal solution asymptomatically. This scheme also brings some advantages, such as plug-and-play property. Different from most existing distributed methods, the private confidential information, such as gradient or incremental cost of each generator, is not required for the information exchange, which makes more sense in real applications. Besides, the proposed method not only handles quadratic, but also nonquadratic convex cost functions with arbitrary initial values. Several case studies implemented on six-bus power system, as well as the IEEE 30-bus power system, are discussed and tested to validate the proposed method.

Distributed Economic Dispatch for Smart Grids With Random Wind Power

A review of photovoltaic systems: Design, operation and maintenance

A power distribution grid exhibits the characteristics of a weak grid owing to the existence of scattered high-power distributed power-generation devices. The grid impedance affects the robust stability of grid-connected inverters, leading to harmonic resonance, or even instability in the system. Therefore, a study of the stability of grid-connected inverters with high grid impedance based on impedance analysis is presented in this paper. The output impedance modeling of an LCL -type single-phase grid-connected inverter is derived, where the effects of the PLL loop and the digital control delays on the output impedance characteristics have been taken into account. To enhance the stability of grid-connected inverters with different grid impedance, a novel impedance-phased compensation control strategy is proposed by increasing the phase margin of the grid-connected inverters. Specifically, a detailed implementation and parameter design of the impedance-phased compensation control method is depicted. Finally, an impedance-phased dynamic control scheme combined with online grid impedance measurement is introduced and also verified by the experiment results.

Impedance-Phased Dynamic Control Method for Grid-Connected Inverters in a Weak Grid

High voltage gain dc-dc converters are required in many industrial applications such as photovoltaic and fuel cell energy systems, high-intensity discharge lamp (HID), dc back-up energy systems, and electric vehicles. This paper presents a novel input-parallel output-series boost converter with dual coupled inductors and a voltage multiplier module. On the one hand, the primary windings of two coupled inductors are connected in parallel to share the input current and reduce the current ripple at the input. On the other hand, the proposed converter inherits the merits of interleaved series-connected output capacitors for high voltage gain, low output voltage ripple, and low switch voltage stress. Moreover, the secondary sides of two coupled inductors are connected in series to a regenerative capacitor by a diode for extending the voltage gain and balancing the primary-parallel currents. In addition, the active switches are turned on at zero current and the reverse recovery problem of diodes is alleviated by reasonable leakage inductances of the coupled inductors. Besides, the energy of leakage inductances can be recycled. A prototype circuit rated 500-W output power is implemented in the laboratory, and the experimental results shows satisfactory agreement with the theoretical analysis.

A High Gain Input-Parallel Output-Series DC/DC Converter With Dual Coupled Inductors

Variable-speed fixed-pitch (VSFP) wind turbines have good prospects in small-to-medium-scale wind power markets due to their simple structure, low cost, and high reliability. One difficulty with VSFP concept wind turbines is to prevent overspeeding and overloading problems at excessive wind velocities, which has rarely been reported in literatures until now. This paper first proposes a sensorless overall power control strategy for a commonly used permanent-magnet-synchronous-generator-based VSFP concept wind power system, with which maximum power point tracking operation, constant speed stalling operation, and constant power soft-stalling operation are all realized. The proposed control scheme has a special advantage of simple structure, i.e., only two regulators are used to realize the three operational modes and also the natural transition between them. An aerodynamic power observer is adopted in the proposed scheme to fasten the MPPT speed. In addition, to enhance system robustness to parameter variations and optimize dynamic and static speed-control performance, an adaptive PI-like fuzzy logic controller is proposed and used as speed regulator in the overall power control scheme. The proposed strategy is verified by simulation and experimental results performed by a 1.2-kW VSFP concept wind turbine prototype.

New Overall Power Control Strategy for Variable-Speed Fixed-Pitch Wind Turbines Within the Whole Wind Velocity Range

Micro-dc grid is a novel power system focused on the development of renewable resources. However, two-wire transmitting power mode is generally accepted in a micro-dc grid, which is usually not suitable for the requirements of the input voltage levels of different power converters and loads. In order to meet the requirements, a half-bridge voltage balancer was introduced in a micro-dc grid, which can convert a two-wire mode into a three-wire mode in a micro-dc grid via a neutral line. However, the shoot-through problem existing in bridge-type converters degrades the reliability of the voltage balancer. In this paper, a dual-buck half-bridge voltage balancer and a control strategy are proposed, which can avoid the shoot-through problem. The small-signal model of the voltage balancer is derived for designing the control parameters and the current relationships of the inductors; the capacitors and the unbalanced loads are analyzed particularly. Finally, a prototype, which can deal with 2-kW unbalance ability, is built to verify that the proposed voltage balancer may have a good ability of balancing the voltage by building a neutral line.

Dual-Buck Half-Bridge Voltage Balancer

This paper studies a three-level dc converter for balancing the dc input voltage, which has a similar topology with the conventional three-level dc converter. It can easily build a neutral line for changing a dc voltage source into two dc voltage-level sources. A control strategy of conducting time extension of partial switch devices is also presented for achieving three-level states of each power switch. The operating principle of the converter is analyzed in detail based on the presented control strategy. The small-signal model and the effects of the proposed control strategy are also driven. Finally, a prototype is fabricated and tested in the lab and the experimental results verify the converter to achieve three-level characteristics and to have a good ability of balancing the input voltage.

Chunying Gong

Papers

Impedance-Phased Dynamic Control Method for Grid-Connected Inverters in a Weak Grid

A High Gain Input-Parallel Output-Series DC/DC Converter With Dual Coupled Inductors

New Overall Power Control Strategy for Variable-Speed Fixed-Pitch Wind Turbines Within the Whole Wind Velocity Range

Dual-Buck Half-Bridge Voltage Balancer

Three-Level DC Converter for Balancing DC 800-V Voltage