Use in Inverters in solar power system

Sep 9, 2017   //   by admin   //   Knowledge Base  //  No Comments

A solar photovoltaic system harness solar energy to generate electricity. Inverters are the main component of a solar power system. They convert DC current from solar panels into AC current that can be supplied to the utility grid.

They can be classified in to mainly three types:-

  • Grid tie Inverters:

They are not connected to batteries and is designed to protect the system from Islanding. They automatically shut down when there is no power supply.

  • Stand-alone Inverters:

Stand-alone inverters draw DC current from batteries charged by charge controllers of PV systems. They are normally need not connected to the utility grid and do not need anti-islanding protection.

  • Battery Backup Inverters:

These can manage battery charge via on-board charger. These inverters are capable of supplying AC energy to selected loads when utility fails, and are required to have anti-islanding protection.

Solar inverters must supply electricity in sine wave form, which co-ordinated with frequency of the utility grid on the AC side of inverters, feed limited voltage into the grid which normally less than or equal to the frequency of grid.

On DC side, the power output of a module varies in such a way the output produced is maximum. For achieving this purpose inverters use Maximum Power Point Tracking or MPPT technology via charge controller. Charge controllers are devices which regulate the voltage supply, store excess power in battery and supply a regulated power in to the grid.

And MPPT can be defined as a technique by which solar power system tends to gain maximum output by a solar panel. The PV system applies the following three techniques to obtain MPPT:

  • Perturb and observe:

In this method the charge controllers adjust the voltage by small amount from the system, and measures power supply if the supply of power increases it makes further needed adjustments until there is no power supply.

–       Incremental conductance:

In this method the controller measures the increase in the current and voltage in the system and predicts the effect of change in voltage on the system. This method is more fast and efficient than perturb and observe method.

–       Constant voltage:

The power delivered to the load is momentarily interrupted and the open-circuit voltage with zero current is measured. The controller then resumes operation with the voltage controlled at a fixed ratio, of the open-circuit voltage, which has empirically been determined as the estimated maximum power point.

Some PV systems use solar micro inverters for each panel. It is a type of solar inverter which is connected to single solar panel and converts AC input from that single panel to DC output. The key feature of solar micro inverter is it’s control over the single panel and mounting which allows the panel to increase its output. Each Micro-Inverter has individual has MPPT technique for its panel.

Micro inverters have become much popular in the places where array are small in size and every panel is concerned. It is useful for residential purposes where there is a problem of shading and it is advised to not to connect the panels.

Solar inverters may sometimes fail due to following reasons:-

·      Capacitor failure:-

–       Electrolytic materials age faster than polycarbonate and other dry dielectric materials

–       Voltage stress

–       Continuous operation under maximum voltage conditions

–       Frequent short-term voltage transients

–       Current stress

–       High current increases the internal temperature

–       Thermal stress on component terminals

–       Improper Charge and discharge rates

–       Not operating in ambient temperatures

–       Mechanical stress

–       Vibrations

·      Inverter bridge failure

–       Excess use beyond the operating limit

–       Excess of voltage and current supply

–       Malfunctioning of components

–       Thermal shock

–       Thermal overload

·      Electro-mechanical wear

–       Component stress

–       Impurity at contacts

–       Temperature variations

 

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