Modeling and Control of a Battery Connected Standalone Photovoltaic System

Nowadays, due to the decrease of conventional energy sources and growing problem of environmental pollution, renewable energy sources are playing a big role in producing electricity. Among them solar and wind are popular renewable energy sources, that have concerned with more and more attention. Solar energy has become a promising, popular and alternative source because of its advantages such as abundance, pollution free, renewability and maintenance free. This work is based on a standalone photovoltaic (PV) system in which a storage device is used as a backup source. The remote areas, which are isolated from utility grid,standalone operation of PV system is the best option. But due to diurnal cycle of the earth and weather condition, solar energy in not constant throughout the day and also sometimes the PV generation is not sucient to full the power demand of the varying local load. Hence PV system cannot give a steady power to the load connected in standalone PV system, which makes the system unstable. So the use of dedicated energy storage systems needs to be taken into account to make this intermittent PV power more dispatchable and stable. Here, the storage device is mainly taken as a lead-acid battery, as it is more convenient to use in high power applications such as solar and wind systems because of its low cost and availability in large size. For controlling the standalone PV system, its mathematical modelling is very much necessary. So the modelling of PV system and lead-acid battery by using the corresponding equivalent circuits are discussed. As we know, to increase the eciency of PV array maximum power should be extracted from it. Here an analog MPPT controller is used for extracting the optimal power available at PV module,by controlling the duty cycle of a boost converter. This analog MPPT control technique shows fast and robust behavior even in changing environmental and load condition compared to conventional MPPT control techniques. For charging and discharging of the lead-acid battery, a bidirectional buck-boost converter is used, which is capable of transferring power in both the direction with appropriate voltage level. To provide electrical power to any load or appliances, the inverter converts the DC bus voltage to a single phase AC voltage with appropriate amplitude and frequency. In this work a current-controlled single phase VSI with bipolar pulse width modulation is used to maintain the stable voltage and current at local load. Thus here three independent control loops are used to control the whole standalone system. Those are MPPT control loop for extracting maximum power from PV module, battery control loop for bidirectional power ow between battery and DC-link through bidirectional buck-boost converter and inverter control loop for maintaining stable voltage and current at local load. The stability analysis is performed by using bode plots for both the inverter control loop and buck-boost converter control loop and these control loops are stable for our tuned controller parameters. The system is simulated in MATLAB/SIMULINK and simulation results shown to full the objectives of the standalone PV system. The simulation results prove the e ectiveness of the proposed controllers

A new family of high gain boost DC-DC converters with reduced switch voltage stress for renewable energy sources

In this paper, a new family of non-isolated boost dc-dc converters with high voltage gains is proposed. The proposed boost topologies exhibit very high voltage gains at moderate duty cycles and lower switch voltage/current stresses with reduced component counts. Here, a total of four new non-isolated boost topologies are proposed using four-terminal PWM high-gain switch cells with an inductor-switch network. Among these four topologies, two converters have identical voltage gain with opposite load voltage polarities and likewise other two exhibit similar nature (i.e., equal but opposite load voltage) but have higher gain than the former topologies. The detailed operating principle, steady-state analysis, and design methodology are presented for the proposed positive output very high-gain converter, which can be easily extended to the rest of the topologies. An exhaustive comparison study has been presented for the proposed topologies with the existing step-up converters to highlight their advantages. Finally, the mathematical analysis, analytical studies, and high boosting feature of the proposed positive output high-gain boost converter are verified using a 250 W, 50 kHz prototype. The experimental results are presented for different duty cycles with fixed input voltage to verify the efficacy of the proposed structures in terms of higher boosting capability. 2022 John Wiley & Sons Ltd.Scopu