IEEE Power & Energy Magazine - November/December 2016 - 33

Wind turbines have unique performance characteristics,
which are highly dependent on the power electronic devices
that enable their operation.
the voltage drop, and the wind turbine absorbed about
280 kVar of reactive power. It took about 1.3 s for the
active power to recover after the fault was cleared, and
the reactive power gradually returned to zero after voltage
recovery. These experiments show that the LVRT capability of the Jiuquan wind power cluster was successfully
transformed and that it now meets the basic requirements
of the new SERC standard.

Success
Regulatory organizations, grid companies, wind turbine manufacturers, and wind power developers have made great
achievements in formulating technical standards, improving
FRT capability of wind turbines, and conducting disturbance
experiments. Since 2013, there have been essentially no incidents with large-scale tripping of wind plants in China due
to lack of fault ride-through capability.

New Dynamic Challenges with High
Penetration of Renewable Power
Wind turbines have unique performance characteristics,
which are highly dependent on the power electronic devices
that enable their operation. As large-scale wind development
rapidly continues in China, with particularly high penetration in some regions, the influence of wind turbines and
clusters of wind farms on the grid continues to grow. With
that growth, new challenges emerge.

Sub-Synchronous Resonance (SSR) Due To
Transmission Series Compensation
To improve the power transmission capability of largescale wind power bases, series compensation is applied to
the power transmission line to reduce the electrical distance
between wind power clusters and the grid. Series compensation is an effective and economical method to improve power
transfer and manage voltage problems. However, the largescale transmission of wind power by a series compensationbased power transmission system can introduce subsynchronous resonance (SSR) risk. There have been some cases in
the field: the first SSR incident reported was an interaction
between a wind farm in Texas, United States, and series
compensation in September 2009.
Such incidents have taken place in China in recent
years. In 2013, wind power was injected to the main grid
after being connected in the Guyuan station in Hebei. The
500-kV Hangu and Gutai double-circuit lines were installed
with series compensation. This is a typical grid configuranovember/december 2016

tion with series compensated lines. Several SSR incidents
have taken place since the series compensation line of
Guyuan Station was put into operation. In these events, the
oscillation frequency was about 6-8 Hz. The oscillation
amplitude reached a maximum of 50% and continued for up
to 10 min. In some cases, a large number of wind turbines
were tripped.
SSR is caused primarily by the oscillatory interaction
between the wind turbine and the series compensation in
the transmission system. The wind turbine's control system
takes an active part in such interaction and, if not properly
designed, can inject negative damping to the modal oscillation. Therefore, it is important to accurately simulate the
control system and its parameters in the analysis. Oscillation frequency is dictated by the control system of the wind
turbine converter and transmission line parameters. The
risk and amplitude of SSR is influenced by the wind turbine
power output level (or wind speed), the degree of series compensation of the transmission lines, and the overall system
short circuit strength. While it has been demonstrated that
SSR involving wind turbines with either DFIG or full converter arrangements can be controlled and the risk mitigated,
a careful analysis of systems with series compensation
is needed.

Oscillation of Power System
with High Wind Power Penetration
To improve the voltage stability of the system when wind
power is integrated at a large scale, dynamic reactive-power
compensators (SVCs or SVGs) have been widely adopted.
These devices have the advantages of quick response and
flexible control. On one hand, electronic devices that are
integrated into the grid at a large scale are more controllable and can adapt to or change some basic operating
characteristics of the original power system. On the other
hand, their controllability depends highly on the external
grid environment due to the noninertia property of electronic power devices and their poor overload capability
and lack of robust response to grid disturbances. Thus,
electronically enabled devices interact strongly with one
another, and system oscillations can occur under weak
grid conditions.
In 2014, the wind power cluster in Kumul, Xinjiang,
Northwest China had several incidents in which a great
many wind turbines tripped off due to grid voltage oscillations. The voltage oscillations resulted in both overvoltage
and overcurrent and finally led to widespread wind turbine
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2016