Power Electronics in Solar PV System
Power electronics is a technology wherein power devices are used to convert electric power into the optimum characteristics efficiently. As a core component for increasing the energy efficiency and performance of various equipment, power electronic devices contribute in the power system development applying effective intelligent and sustainable techniques. Power electronics have significant contribution to the power generation, power transmission, power system harmonics control, power supply stability, etc.
For converting electricity from one form to another, power electronic devices are used. An Inverter is a power electronics device which converts direct current (DC) into alternating current (AC) electricity. In Solar PV System, solar panels produce direct current (DC) voltage. When we connect these solar panels to an electric circuit, they generate direct current (DC). Direct current (DC) is not useful in most devices and machines, because they are designed to run on alternating current (AC). A bi-directional converter converts DC electricity from battery storage into AC electricity during discharge for use on the electrical grid and AC to DC during battery charge. Electricity generated by Solar PV System must flow through a power electronic device. Inverters have the following functions:
- Solar PV Strings generate 1000 V which is converted to 220 volts for single-phase power grids and 400 volts for three-phase grids by using inverters. Inverters can also feed into the grid at medium-voltage up to 40 kV. The higher the grid voltage, the larger the transformer adjusting the AC voltage from the inverter needs to be. There also are solar parks that feed in at high voltage over 110 kV using large-scale inverters and substations. The frequency of the system is 50 Hz.
- Maximum Power Point Tracking (MPPT) is used to optimize the solar yields from the Solar PV strings which keeps the I-V curve of the voltage and the currents in the solar panels at maximum power and thus at maximum yield. There is a separate MPP tracker in every connected Solar PV string.
- Installation of Solar PV System helps to stabilize unstable power grids. The installation is taken offline if there is driving up voltage and frequency in the grid. The Solar PV System can feed in at full capacity when the voltage or frequency is too weak. Combing it with a large storage battery, can contribute in the grid-stabilizing significantly
- Inverters can also be used as a switching if the power grid suffers a short- or long-term break down. Solar PV System with the combination of a battery storage can function as an uninterruptible power supply. In commercial and industrial applications, it is very useful. It is also helpful in areas often effected by storms, flooding or other natural disasters.
- Inverter can optimize the self-consumption of Solar PV System in combination with battery storage. In this case, only the surplus electricity is fed back into the grid. It regulates a self-sufficient mini-grid which works fully independent of the public power grid.
- Smart inverters allow directly using the DC from the Solar PV System for charging batteries. Inverters play an important role for safeguarding the Solar PV System against voltage surges, lightning, electric arcs and disconnecting in case of fire.
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