Power Electronic Converters

Smart grids will provide more electricity to meet rising demand, increase reliability and quality of power supplies, increase energy efficiency, is able to integrate low carbon energy sources into power networks. This paper deals with the development and control of a smart grid-connected PV/WT hybrid system model. This model consists of wind turbine, photovoltaic array, asynchronous (induction) generator, controllers and converters (Sepic & Cockcroft). It is developed by using MATLAB/SIMULINK software package. In order to maximize the generated power, Cockcroft & Sepic convertors are used. Under various operating conditions, the dynamic behavior of the proposed model is examined. The inputs given to the developed system are the real-time measured parameters. The wind speed, solar irradiance and temperature data are collected from a grid connected solar power system located in Manchester. The control strategy of the proposed model results a better tool for smart grid performance optimization.

Multilevel inverters with less number of components and power supplies play important role in most of power electronic applications. In this paper, a new switched capacitor multilevel inverter (SCMLI) is presented which can generate more output voltage levels with less number of components and one required dc power supply in contrast to some of existing topologies. This structure uses a new switched capacitor converter (SCC) which includes several capacitors that can be charged by binary asymmetrically algorithm as self-balancing. At the next, proposed SCMLI is connected to another SCMLI unit as hybrid form and then, the output voltage levels are increased with good quality using hybrid modulation technique. Several simulation results by PSCAD/EMTDC software and comparisons in different aspects such as number of required switches, capacitors, number of components that are in current path and total blocked voltage is given to confirm the effectiveness of proposed topology.

The quest for a green electrical power system has increased the use of renewable energy resources and power electronic converters in the existing power system. These power electronic converters, however, are a major cause of harmonics and result in the degradation of power quality. In the last two decades, researchers have proposed various designs of multilevel converters to minimize these harmonic distortions, however, a comprehensive solution for stand-alone solar photovoltaic (PV) systems with low total harmonic distortion (THD) is still missing in the present body of knowledge. This paper proposes a single-phase 17-level cascaded H-bridge multilevel converter (CHMC) model for a stand-alone system using solar PV arrays. The proposed model employs eight different flexible PV arrays that can be replaced with DC voltage sources when required to meet the load demand. The proposed model does not include any capacitor and filter thus saving a lot of cost in the overall system. The model has been implemented in the Simulink environment using a model-based design approach. The simulation results show that the proposed model has reduced the THD to almost 7% as compared to the existing models. The cost comparison of the proposed converter also proved its economic benefit over other types.

The pre-charging control scheme of the Modular Multilevel Converters is an important research subject. At the start-up of the MMC, all capacitors in each submodule of the MMC are required to be equally charged to a certain voltage value before transferring to the normal operation, otherwise a large inrush current may occur at the instant of the start-up threatening the safe operation of the IGBTs and the capacitors. Basically, to start-up an MMC, two phases need to be considered, Uncontrollable pre-charging phase and Controllable pre-charging phase, the Uncontrollable pre-charging phase, which is our main focus has been overlooked for a while. The conventional solution for limiting the huge inrush current during the aforementioned phase was using a limiting resistor and magnetic contactor arrangement as stated in plenty of papers for the last decade. In this paper, two new methods are introduced in order to pre-charge the capacitors, at the uncontrollable pre-charging phase to their nominal voltage without using the traditional solution. Detailed design algorithms of the proposed methods are introduced. Simulation results of the proposed methods are presented to show how employing these new methods would drastically limit the surge of the circulating current during the uncontrolled start-up phase.

INDEX TERMS : Charging process model, modular multilevel converter (MMC), pre-charging control scheme, single phase MMC, start-up control, subsequent capacitors charging.

ABSTRACT Real-time simulation of Power Electronic Converters (PECs) allows a first realistic validation of their digital controllers and avoids experimental constrains (cost, damage risks, reliability ...). However, to increase the realism of validation, the real-time model has to reach a high level of accuracy. This objective is balanced by, among others, the computational time ensured by the used digital technology. This is one of the main reasons why Field Programmable Gate Array (FPGA) devices are preferred. The proposed paper summarizes the hardware FPGA design of PECs real-time model. The Associate Discrete Circuit (ADC) modeling technique is used for each power switch. To make the necessary functional validation, the Matlab/Simulink SimPowerSystems based model has been taken as a reference design. The proposed case study consists of a H-bridge DC-AC converter that supplies an AC load with a sinusoidal back-EMF. The corresponding FPGA-based real-time model is validated at open loop condition and at closed loop with a digital current controller. In addition to functional simulation results, real-time Hardware In the Loop (HIL) simulation results are provided.