Here, a single-stage cascaded H-bridge (CHB) inverter is presented for grid-connected photovoltaic (PV) systems. The CHB inverter has separate DC links and allows individual control of PV arrays. The conversion effici...
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Here, a single-stage cascaded H-bridge (CHB) inverter is presented for grid-connected photovoltaic (PV) systems. The CHB inverter has separate DC links and allows individual control of PV arrays. The conversion efficiency is high and the harmonic generation is lower than conventional PV inverters. Although the CHB inverter is a good candidate for injection of solar power into grid, its control issues have not been completely solved. One of the main challenges in the CHB inverter is the harmonic generation when the connected PV arrays to the H-bridge cells have different amounts of insolation. This study deals with the asymmetrical operating conditions of PV arrays (or H-bridge cells) in the CHB inverter and presents an analytical equation for determination of cells' modulation indices based on PV arrays data. Then, a control loop is added to the tracking algorithm of conventional control systems to determine whether an H-bridge cell is in the linear modulation or not. In the case of overmodulation, the corresponding DC link voltage is increased by the controller to bring it back to the linear region. The validity of new method is confirmed by simulations and experiments on a seven-level 1.7kW CHB inverter.
Hybrid energy storage system (HESS) consists of different electrical storage devices with complementary characteristics to satisfy both the energy and power requirements of the load. This study presents an improved fr...
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Hybrid energy storage system (HESS) consists of different electrical storage devices with complementary characteristics to satisfy both the energy and power requirements of the load. This study presents an improved frequency sharing algorithm for battery/ultracapacitor (UC) HESS in the presence of delay. Time delay is inevitable with the digital implementation of controlalgorithms. Presence of delay deteriorates the transient response of the system by limiting the bandwidth of inner current loops. The DC-link voltage will settle only after settling of the slower loop, i.e. battery loop, hence the presence of delay will make the system response slower in conventional methods. However, the improvedalgorithm shares battery current loop error during transients with faster UC current loop and hence DC-link voltage settling becomes faster. Furthermore, for safe and efficient operation, an energy management algorithm (EMA) has been designed that ensures nominal UC voltage and other operational constraints as described in the study. To analyse the effect of UC voltage control loop on the operation of the DC-link voltage control loop during transients, UC voltage control loop with different bandwidths have been designed and tested. Microcontroller based implementation was done for experimental verification of the improved control algorithm and EMA.
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