|PERS1||Three-Port DC–DC Converter for Stand-Alone Photovoltaic Systems||System efficiency and cost effectiveness are of critical importance for photovoltaic (PV) systems. This paper addresses the two issues by developing a novel three-port dc–dc converter
for stand-alone PV systems, based on an improved Flyback-Forward topology. It provides a compact single-unit solution with a combined feature of optimized maximum power point tracking
(MPPT), high step-up ratio, galvanic isolation, and multiple operating modes for domestic and aerospace applications. A theoretical analysis is conducted to analyze the operating modes followed by simulation and experimental work. This paper is focused on a comprehensive modulation strategy utilizing both PWM and
phase-shifted control that satisfies the requirement of PV power systems to achieve MPPT and output voltage regulation. A 250-W converter was designed and prototyped to provide experimental verification in term of system integration and high conversion
|PERS2||An Interleaved High-Power Fly back Inverter for Photovoltaic Applications||This paper presents analysis, design, and implementation of an isolated grid-connected inverter for photovoltaic (PV)
applications based on interleaved fly back converter topology operating
in discontinuous current mode. In today’s PV inverter technology, the simple and the low-cost advantage of the fly back topology is promoted only at very low power as micro inverter. Therefore, the primary objective of this study is to design the fly back converter
at high power and demonstrate its practicality with good performance as a central-type PV inverter. For this purpose, an inverter system rated at 2 kW is developed by interleaving of only
three flyback cells with added benefit of reduced size of passive filtering elements. A simulation model is developed in the piecewise linear electrical circuit simulator. Then, the design is verified and optimized for the best performance based on the simulation results. Finally, a prototype at rated power is built and evaluated
under the realistic conditions. The efficiency of the inverter, the total harmonic distortion of the grid current, and the power factor are measured as 90.16%, 4.42%, and 0.998, respectively. Consequently, it is demonstrated that the performance of the proposed
system is comparable to the commercial isolated PV inverters in the market, but it may have some cost advantage.
|PERS3||A Quasi-Uni polar SPWM Full-Bridge
Transformer less PV Grid-Connected Inverter with Constant Common-Mode Voltage
|The unipolar sinusoidal pulse width modulation (SPWM) full-bridge transformer less photovoltaic inverter with ac bypass brings low conduction loss and low leakage current. In order
to better eliminate the leakage current induced by the common mode
voltage, the clamping technology can be adopted to hold the common-mode voltage on a constant value in the freewheeling period. A full-bridge inverter topology with constant common-mode voltage (FB-CCV) has been derived and proposed in this paper, two unidirectional freewheeling branches are added into the ac
side of the FB-CCV, and the split structure of the proposed freewheeling
branches does not lead itself to the reverse-recovery issues for the freewheeling power switches and as such super junction MOSFETs can be utilized without any efficiency penalty. The passive clamping branches consist of a capacitor divider and two diodes, is added into the dc side of the FB-CCV, therefore, the weakness of active damping branch has been overcome, and the better clamping performance has been achieved in the freewheeling
period. In the dead time between the main switches and the freewheeling switches, the ant parallel diodes of diagonal main switches of the FB-CCV form the freewheeling path to clamp the
common-mode voltage at a constant value, and a quasi-unipolar SPWM strategy is presented. The operation principle, differential mode, and common-mode characteristics of the FB-CCV, Heric, H6, and HB-ZVR topologies are analyzed and compared in detail.
Finally, the viability of the FB-CCV is verified by a universal prototype inverter rated at 5 kW.
|PERS4||A Novel High Step-up DC/DC Converter Based on Integrating Coupled Inductor and Switched-Capacitor Techniques for Renewable Energy Applications||In this paper, a novel high step-up dc/dc converter is presented for renewable energy applications. The suggested structure consists of a coupled inductor and two voltage multiplier cells,
in order to obtain high step-up voltage gain. In addition, two capacitors
are charged during the switch-off period, using the energy stored in the coupled inductor which increases the voltage transfer gain. The energy stored in the leakage inductance is recycled
with the use of a passive clamp circuit. The voltage stress on the main power switch is also reduced in the proposed topology. Therefore, a main power switch with low resistance RDS(ON) can
be used to reduce the conduction losses. The operation principle and the steady-state analyses are discussed thoroughly. To verify the performance of the presented converter, a 300-W laboratory prototype circuit is implemented. The results validate the theoretical analyses and the practicability of the presented high step-up converter.
|PERS5||Interleaved Boost-Integrated LLC Resonant Converter With Fixed-Frequency PWM Control for Renewable Energy Generation Applications||This paper proposes a current-fed LLC resonant converter that is able to achieve high efficiency over a wide input
voltage range. It is derived by ntegrating a two-phase interleaved boost circuit and a full-bridge LLC circuit together by virtue of sharing the same full-bridge switching unit. Compared with conventional full-bridge LLC converter, the gain characteristic is improved
in terms of both gain range and optimal operation area, fixed-frequency pulse width-modulated(PWM)control is employed to achieve output voltage regulation, and the input current ripple
is minimized as well. The voltage across the turned-off primary side
switch can be always clamped by the bus voltage, reducing the switch voltage stress. Besides, its other distinct features, such as single-stage configuration, and soft switching for all switches also contribute to high power conversion efficiency. The operation principles are presented, and then the main characteristics regarding gain, input current ripple, and zero-voltage switching (ZVS) considering the nonlinear output capacitance of MOSFET are investigated and compared with conventional solutions. Also, the design procedure for some key parameters is presented, and two kinds of interleaved boost integrated resonant converter topologies are generalized. Finally, experimental results of a converter prototype with 120–240 V input and 24 V/25 A output verify all considerations.
|PERS6||A Step-up Resonant Converter for Grid-Connected Renewable Energy Sources||With the rapid development of large-scale renewable energy sources and HVDC grid, it is a promising option to connect the renewable energy sources to the HVDC grid with a pure dc system,
in which high-power high-voltage step-up dc–dc converters are the key equipment to transmit the electrical energy. This paper proposes a resonant converter which is suitable for grid-connected renewable energy sources. The converter can achieve high voltage
gain using an LC parallel resonant tank. It is characterized by zero-voltage-switching (ZVS) turn-on and nearly ZVS turn-off of main switches as well as zero-current-switching turn-off of rectifier diodes; moreover, the equivalent voltage stress of the semiconductor devices is lower than other resonant step-up converters. The
operation principle of the converter and its resonant parameter selection is presented in this paper. The operation principle of the proposed converter has been successfully verified by simulation
and experimental results.
|PERS7||Frequency-Coordinating Virtual Impedance for Autonomous Power Management of DC Micro grid||In this paper, the concept of frequency-coordinating virtual impedance is proposed for the autonomous control of a dc micro grid. This concept introduces another degree of freedom in the conventional droop control scheme, to enable both time-scale and power-scale coordination in a distributed micro grid system. As an example, the proposed technique is applied to the coordinating
regulation of a hybrid energy storage system composed of batteries and super capacitors. With an effective frequency-domain shaping of the virtual output impedances, the battery and super capacitor converters are designed to absorb low-frequency and
high-frequency power fluctuations, respectively. In this way, their
complementary advantages in energy and power density can be effectively
exploited. Furthermore, the proposed concept can be integrated into a mode-adaptive power management framework with autonomous mode transitions. The entire solution features highly versatile functions based on fully decentralized control. Therefore,
both flexibility and reliability can be enhanced. The effectiveness of the presented solution is verified by experimental results.
|PERS8||A Photovoltaic Array Transformer-Less Inverter With Film Capacitors and Silicon
|A new photovoltaic (PV) array power converter circuit is presented. This inverter is a transformer-less topology with grounded PV array and only film capacitors. The motivations are to reduce circuit complexity, eliminate leakage ground currents, and improve reliability. The use of silicon carbide (SiC) transistors is the key enabling technology for this particular circuit to attain reasonable (>97%) efficiency. Some background about the challenges
of ground currents and power decoupling to be addressed is first discussed. The proposed solution of a bidirectional buck boost converter, dynamically varying dc link, and half-bridge inverters is then presented along with details on the basic functionality. Some aspects of selecting passive components for the circuit are discussed. The average dynamic model and control system are then presented. Finally, simulation and experiment results are shown demonstrating that the proposed topology is a viable solution.