3 Static voltage support based on reactive power


In order to protect the connected loads, the voltage must be kept within defined limits – that applies to the distribution grid in par- ticular. With their ability to provided control- led inductive or capacitive reactive power, PV inverters can help guarantee the voltage quality required in EN 50160.


Reason: the increasing feed-in at low and medium-voltage levels can result in voltage increases which caused problems for the previous grid operation method (flow of energy from central generator to decen- tralized loads). Using reactive power, PV inverters can now reduce undesirable volt- age increases significantly. Reactive pow- er-compatible inverters can also be used to compensate for existing phase shift. As even reactive power reduces efficiency, this reduces the load on the grid infrastructure, whose capacity limits may already have been reached. Typical causes of phase shifts include transformers, large motors or even simply long cable sections.


There are several options for adjusting the percentage of reactive power: Plant opera- tors can use set points specified by utility operator, or various reactive power values can be set via an agreed schedule or re- motely programmed via the SMA Power Reducer Box. The third option is regulation of the percentage of reactive power via a characteristic curve depending on the grid voltage measured at the connection point or the active power output of the inverter.


4 Dynamic grid support


Until now, PV plants had to disconnect from the grid immediately, even during tem- porary drops in grid voltage. This meant that many plants were deactivated in the event of grid failure, unbalancing the grid even further. Inverters with dynamic grid support functions act within milliseconds in such events, preventing the grid failure spreading further. The so-called restricted dynamic grid support ensures that the in- verter is ready to feed energy into the grid immediately after a drop in the grid volt- age. Devices with full LVRT or FRT behavior


(Low-Voltage or Fault Ride Through) can also feed reactive power into the grid dur- ing grid voltage drops. LVRT is already supported by the new Sunny Central CP series.


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