LVRT - Low voltage ride through

Wind turbine control systems that comply with World Wide LVRT Demands

LVRT (Low Voltage Ride Through) and HVRT (High Voltage Ride Through), both also known as FRT - Fault Ride Through) have become a crucial feature of wind turbine control and power converter systems.

The LVRT-term is capturing the ability of a wind turbine (or in reality a wind park) to stay connected to the grid throughout a short mains voltage drop (a brownout) or a mains failure (a blackout), HVRT feature enables the wind turbine to stay connected during temporary voltage increase situations.

When the voltage of the grid is dropping it is essential that a wind park stays online in order to prevent major blackouts.  Equally, it is essential that the park is working actively to compensate for the faulty grid condition.

LVRT and the wind turbine control system

In China, major blackouts occur (as a result of entire wind parks tripping and getting offline as a result of a brownout).. This has increased the focus and need of the LVRT feature of the wind turbine control system.

It is a fact that many wind turbine control systems installed just a few years ago do not have the LVRT-feature and cannot in an economical way be upgraded in accordance with r the grid operator compliance.

Collaborating with power converter suppliers

That is why DEIF Wind Power Technology in close cooperation with power converter suppliers is enjoying a drastically increased interest for our control systems - not only for new installed turbines, but also for upgrading existing installed capacity.

In China and India, several wind parks are controlled with DEIF’s turbine control solutions and full-scale field tested and approved as being in full LVRT-feature compliance by grid-operators.

Whether the LVRT capability of a wind farm is satisfying for meeting the requirements is defined in grid codes issued by the grid operator. The capability of meeting these demands is decisive for whether the wind turbine/the wind park is allowed to be connected to the grid.

Examples of LVRT demands to the wind park (and derived from that – to the individual wind turbines) are;

• for short system faults (lasting up to 140ms) the wind farm has to remain connected to the grid. For super grid (HV-grids) voltage dips of longer durations the wind farm has to remain connected to the grid up to more than 3 minutes
• During grid faults or brownouts a wind farm has to supply maximum reactive current to the grid without exceeding the transient rating of the plant
• On super-grids during voltage dips lasting more than 140ms the active power output of a wind farm has to be retained at least in proportion to the retained balanced supergrid voltage

As mentioned above, the LVRT-demands are individually specified by the grid operators and might therefore vary from operator to operator and from country to country. For wind turbines the LVRT testing is described in the standard IEC 61400-21.

The LVRT-feature of wind turbine controls from DEIF WPT in combination with our Park Power Management solutions (including our forecasting solution) is all a wind park owner needs in order to comply with the demands of grid operators worldwide.

LVRT turn-key solution with power converter

Solutions for LVRT can be programmed outside of the wind turbine itself, e.g. by using usually by-passed air cooled full power converters, mostly applicable for older robust stall turbines.

Newer turbines that already have a power converter installed need a modification of the main control algorithms and additional power electronics hardware.

DEIF can support on all of these application with turn-key solutions.