Search

The output power of long strings of photovoltaic (PV) modules are vulnerable to the effect of mismatching and partial shading among different level PV elements such as cells, sub-modules and modules. In this paper, a sub-module synchronous buck converter (SBC) with the distributed maximum power point tracking (DMPPT) control is presented in order to achieve optimal output power of the PV module, low system cost, and high efficiency even under partial shading conditions. Main shading patterns in a PV module are classified and their typical characteristics are illustrated. In order to improve the efficiency, a series-connected DC optimizer structure is implemented and a two-switch synchronous buck converter is delicately designed for each sub-module. A two-step perturb & observe based MPPT algorithm is adopted: firstly, a coarse tracking is implemented with large step size in order to improve the tracking speed and followed by a refined tracking process with a small step size with aim to minimizing the static oscillations. Furthermore, a bypass mode is triggered in order to maximize the system efficiency when no mismatch among sub-modules is detected. In the proposed sub-module DMPPT PV system, only the output voltage is sampled, which reduces the current sensor and simplifies the implementation difficulty. A PV system with the proposed sub-module DMPPT algorithm and SBC power interface was built in Matlab/Simulink. Main simulation results were provided for various shading patterns and working scenarios. A 100 W low-cost and high efficiency sub-module integrated synchronous buck converter was designed. The experimental measured efficiency of the SBC was high up to 98.7 % . By comparing the actual power yield under shading conditions, an average 27.55 % output power improvement was achieved with the proposed sub-module DMPPT algorithm. [ABSTRACT FROM AUTHOR]

For Fuel Cell Electric Vehicles, DC-DC power converters are essential to provide energy storage buffers between fuel cell stacks and the traction system because fuel cells show characteristics of low-voltage high-current output and wide output voltage variation. This paper presents a hybrid-mode two-phase interleaved boost converter for fuel cell electric vehicle application in order to improve the power density, minimize the input current ripple, and enhance the system efficiency. Two operation modes are adopted in the practical design: mode I and mode II are used with each boost converter operating in continuous conduction mode and discontinuous conduction mode. The operation, design and control of the interleaved boost converter for different operating modes are discussed with their equivalent circuits. The boundary conditions are distinguished with respect to switching duty ratio and load conditions. Transitions between continuous conduction mode and discontinuous conduction mode are illustrated for the whole duty ratio range. The expressions for inductor current ripple, input current ripple and output voltage ripple are derived and verified by simulation and experimental tests. The efficiency and power density improvements are illustrated to verify the effectiveness of the proposed design scheme. [ABSTRACT FROM AUTHOR]

Due to the intermittent nature of the renewable energy sources including photovoltaic and wind energy, the energy storage systems are essential to stabilize dc bus voltage. Considering the discharge depth of super-capacitors and energy-storage batteries, the bidirectional isolated power interface will operate for a wide range of voltage and power. This study focuses on in-depth analysis of the dual-active-bridge dc–dc converter that is controlled by the dual-phase-shift scheme to improve the conversion efficiency in distributed power system. The power flow of each operating mode with dual-phase-shift control is characterized based on a detailed analysis of the effects of “minor parameters”, including the deadtime and power device voltage drops. The complete output power plane of the dual-active-bridge converter with dual-phase-shift control is obtained and compared with experimental results. The optimal operating mode is determined according to the practical output power range and the power flow characteristics. Experimental evaluation shows the effectiveness of the proposed power flow model with dual-phase-shift control and significant efficiency improvement using the optimal mode of dual-phase-shift compared with the conventional phase shift control. [ABSTRACT FROM AUTHOR]

A new model of the optimum tilt angle of a soiled photovoltaic (PV) panel is proposed in this paper. The tilt angle is a key factor that influences the output power of PV panel, while dust deposition is an inevitable external element to be considered. In this paper, the solar radiation model is studied by analysing the Hay, Davies, Klucher, Reindl (HDKR) model. The cell temperature of a PV panel is also investigated to evaluate the power output. A fitting formula is derived to express the relationship between the dust deposition density and the tilt angle, and it is integrated in the output model of a fixed-type PV panel. Besides, the effect of dust deposition on the transmittance is analysed. An inverse correlation between the dust deposition density and tilt angle can be obtained, and the optimum tilt angle is calculated to maximize the power output of a soiled PV panel. Simulation is conducted by Matlab to demonstrate the validity of the proposed model of the optimum tilt angle with the shielding effect by dust. Furthermore, the relationship between dust deposition and the working temperature of PV panel is investigated by indoor experiments. [ABSTRACT FROM AUTHOR]