High Gain Transformer-less DC/AC Inverter for PV System

Investigation interests on many scientific aspects of photovoltaic (PV) trans-former-less inverter system has improved over the past decade. Using step-up transformer or high frequency transformer in electrical system has made the entire system expensive and voluminous. There is alternative topology to replace the transformer by implementing DC/DC quadratic boost converter to expand the voltage from 12VDC to 325VDC from the photovoltaic (PV) solar and convert it to AC applying H-bridge inverter circuit. This method will replace the conventional method of bulky transformer into a lighter converter with the same performance. The circuit is simulated using Power Sim (PSIM) software to initiate the design and study the circuit capability. The experimental result will project the exact voltage in the range of 230VACrms . The harmonic profile of the inverter is studies and compared with the normal inverter configuration.

Magneto-thermal coupling simulation and experimental verification for a three-winding high-frequency transformer

As a core component of the power electronic transformer (PET) in DC network, the multi-level high-frequency power transformer has received great attention due to the insulation material fatigue problems resulting from the hot-spot temperature rises. To solve this problem, a three-winding high-frequency transformer for 10 kVA PET application is designed and made in the laboratory, and the loss and temperature rise distribution is calculated by means of the finite element (FE) electromagnetic-thermal coupling simulation. The influence of temperature on the hysteresis and loss properties of core material has been carefully considered and measured. The influence of skin effect and end effect on the winding loss is taken into account through the establishing three-dimensional FE model. Besides, the convective heat transfer coefficient is solved based on the principle of heat transfer instead of the empirical coefficient method. By compared with the experimental results, the calculated results are validated to be effective in predicting the loss and hot-spot temperature rises of the transformer.

Design and simulation of a high-power double-output isolated Cuk converter

Among the transformer-less DC-DC converters, the superiority of the conventional Cuk converter is obvious in its good properties. However, the output power is limited for all transformer-less converter types including the conventional Cuk converter. In order to get more supplied power from this converter, some changes in its design were necessary. One of these modifications is to add a transformer to transfer more power and to separate the output side from the input side. Supply of some applications such as the DC link of modular multilevel inverters, e. g. cascaded H-bridge (CHB) topologies required more than one output. Hence, this paper is concerned with the design, analysis and simulation of an isolated dual-output modified Cuk converter. The proposed converter is designed to deliver a total output power of 2,000 W using only one modulating switch. A complete design and detailed analysis of the high-frequency transformer with the ANSYS Maxwell platform is presented in this paper. The modeling and simulation results of the high-frequency transformer are validated by the experimental implementation results and good agreement was obtained with a small percentage of errors less than 4 %. A set of analytical equations has been derived and presented in this paper to represent a mathematical model of the converter. In addition, the entire converter circuit was simulated and analyzed with MATLAB/Simulink. The simulation results were checked and compared to the findings of the mathematical model, yielding an excellent match with a percentage error of less than 2.15 %. Finally, when the presented converter was tested under various loads, including unbalanced load situations, a reasonable output voltage regulation was achieved, with the two output voltages being nearly identical with a deviation of less than 0.25 % under a severe unbalanced load condition of 150 %