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With increase in population there is a very high demand for electricity which has led to an extreme usage of fossil fuels, such as oil, gas and coal, results in a serious greenhouse effect and environmental pollution, which have a great influence in the world. Meanwhile, there is a big contradiction between the fossil supply and the global energy demand.
Renewable energy is becoming very popular to meet the global power demand and to reduce environmental pollution. The current more mature and widely used renewable energy sources include solar, wind and tidal energy sources. Solar PV is becoming a favourable choice amongst the other renewable sources and it will make one of the biggest contributions to electricity generation among the entire renewables energy candidate, because it is clean, emission free, and renewable electrical source with high reliability. Often these renewable sources have low-voltage output and must be pass through a set of high boost converter circuits to increase the voltage, and then through a DC-AC inverter to convert AC voltage from the main supply. Therefore, a DC-DC high boost converter plays an important role in overall efficiency of the system.The PV grid-connected power system in the residential applications is recently becoming a fast growing segment in Europe, Japan, and the U.S.
Unfortunately, the output voltage of the PV array is relatively low (24-48V). In order to satisfy the high 33 bus voltage requirements for the full-bridge, half-bridge, or multilevel grid inverters, the PV series-connected configuration is the conventional solution. However, the generated output power of the PV arrays is decreased greatly due to module mismatch and partial shading, especially in the urban areas. In the residential PV grid-connected system, the PV arrays are usually installed on the roof. Thus, the generated power of the PV arrays is reduced greatly with PV series connected configuration when they are covered by the shadows, which may be caused by the clouds, trees, neighbour’s house, and even the power line cables. In these situations, the PV parallel-connected configuration is more efficient than the series-connected configuration due to the PV performance.
On the other hand, only a low voltage is generated with the parallel-connected configuration, which makes it easy to satisfy the safety requirements in home applications. Thus, the new research trend is to employ the PV parallel-connected configuration rather than the series-connected configuration in the residential power generation system. Renewable energy such as Solar PV and fuel stack poses some other significant challenges such as optimal utilization of the sources due to their variable output. They are usually operated at low output voltage levels (typically 24-48V) when connected in parallel for residential application. This makes their application to grid connected systems and even some standalone loads difficult because a large voltage boosting at the output is required. The converters need to raise the low DC voltage (24-48V) to high DC voltage (380-400 V) for the PV inverters. This indicates that a DC-DC converter with high output voltage is essential right across the solar power panel.
Various topologies are available to achieve this high voltage gain. This high voltage of 400V is then fed to an inverter. The inverter input which is the DC link bus voltage of 400V is needed to be held constant for the inverter to invert the DC voltage to AC voltage. The inverter can either be grid tied or stand alone. The converter filter capacitor is designed based on a fixed inverter rating and the filter capacitor is rated based on that load.
Now there is a need to regulate the rated DC link voltage for the rated inverter in order to function properly. There are various feedback method used to regulate the output voltage. Then there can be cases when the inverter might fail and make the converter load go open. This will cause the output capacitor of the DC-DC converter to charge beyond its rated voltage this is because the constant current is being fed to the capacitor through the inductor. This may cause the damage to the output capacitor and breakdown of the whole DC-DC converter.
So there is a need to regulate the converter output voltage and also design a protection circuit which will take care of the converter when the load goes open. The protection circuit will not let the capacitor charge above its rated voltage level. This can be achieved by having a feedback network which sense the voltage level across the capacitor at all times and tries to maintains that voltage level.
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