DETAILED INVESTIGATION AND PERFORMANCE
IMPROVEMENT OF THE DYNAMIC BEHAVIOR OF
GRID-CONNECTED DFIG BASED WIND TURBINES
UNDER LVRT CONDITIONS
INTRODUCTION
In recent years, there has been a huge increase in global
demand for energy as a result of not only industrial
development, but also population growth. Consequently, the rise
in consumption of traditional fossil fuels has led to many serious
problems such as energy shortages, pollution, global warming,
the shortfall of traditional fossil energy sources, and energy
insecurity. These factors are driving the development of
renewable energy technologies, which are considered an
essential part of a well-balanced energy portfolio . Wind power
is thought to be the most promising near-term alternative energy.
As renewable energy sources grow in popularity, wind power is
currently one of the fastest growing renewable sources of
electrical energy . More than 54 GW of wind power was
installed in 2016, and it is expected to be higher in 2017 . With
the increased presence of wind energy in the power system over
the last decade, a serious concern about its influence on the
dynamic behavior of the electric power network has arisen .
Therefore, it becomes essential that grid-connected wind
turbines behave similarly to conventional power plants and
support the power network during normal and abnormal grid
conditions.
EXISTING SYSTEM:
In addition to the progress made in the creation of adequate
grid codes for the proper utilization of wind energy, a significant
improvement has been achieved in the design and
implementation of robust energy conversion systems that
efficiently transform wind energy. The Doubly-Fed Induction
Generator (DFIG)-based wind turbine has become one of the
most favorable choices in wind power generation. This is due to
the prominent advantages that it has compared to the other
energy conversion systems that are currently available in the
market. However, the dynamic response of the DFIG to grid
voltage transients is the most serious problem . DFIG-based
wind turbines are sensitive to voltage sags during grid faults.
This is due to the partial-scale back-back power converters that
connect the rotor of the generator to the power grid.
DRAWBACKS:
Faults in the power system, even far away from the location
of the turbine, can cause an abrupt drop of the grid voltage
which leads to an over-voltage in the DC bus and an over-
current in the rotor circuit of the generator .
Without any protection scheme, this can lead to power
converter damage. Moreover, it may also increase the speed
of the turbine above the rated limits if not properly
designed.
PROPOSED SYSTEM:
The DFIG is a perfect solution for systems with limited
variable-speed range, e.g. ±30% of the synchronous speed.The
back-to-back power converter in the DFIG system consists of
two converters, i.e., a Rotor-Side Converter (RSC) and a Grid-
Side Converter (GSC), which are connected backto- back by a
dc-link. Between the two converters, a dc-link capacitor is
placed as energy storage in order to limit voltage variations (or
ripple) in the dc-link voltage. With the RSC, it is possible to
control the torque, the speed of DFIG as well as the active and
reactive powers at the stator terminals. The main objective for
the GSC is to keep the dc-link voltage constant. It can also be
used to control the reactive power flowing from or to the power
grid . DC-link over-voltages may arise as a result of wind
turbine response to unbalanced grid faults or load shedding
situations. In this case, the direction of the power flow is
reversed and the current flows to the dc-link. Therefore, the DC-
link voltage must be limited to its rated value. This can be
achieved by using a DC-side crowbar circuit that consists of a
chopper and a resistor connected across the DC–link of the
converters, as shown in Fig. 2. This configuration can limit the
DC bus voltage from exceeding the safe operating range by
short-circuiting the dc-link through the chopper resistors.
ADVANTAGES:
The control strategy is directed at mitigating the rotor-side
voltage and current shock during abnormal grid conditions,
without any additional cost or reliability issues.
APPLICATIONS:
FACTS devices
Renewable resources
