ABSTRACT:
Unbalanced
grid voltage sags are the severe challenge for wind power generation system
which connected to the grid successfully. The dc bus voltage and output power
will fluctuate under unbalanced grid voltage. Moreover, the voltage sags will
lead to the increase of peak current, which will bring potential safety hazards
to the operation of wind power system. This paper proposes a simple current
limiting control scheme without auxiliary equipment, which based on the
detailed analysis of the excessive peak current. In this scheme, the machine
side converter (MSC) controller adjusts the electromagnetic power according to the
power transmitted to the grid by the grid side converter (GSC). Meanwhile, it
converts the unbalanced power on the dc-link into the rotor kinetic energy,
avoiding the dc-link overvoltage. The GSC controller can not only ensure that
the three-phase inverter currents are in the maximum safe range that the
converters can bear, but also provide reactive power support for the grid.
Furthermore, the fluctuations on dc bus voltage and output power can be
eliminated effectively by using the GSC controller. The feasibility of the
proposed scheme and the superiority over the traditional control schemes have
been verified by simulations under different types of unbalanced voltage.
KEYWORDS:
1. Unbalanced
grid voltage
2. Peak current
3. Current
limiting control
4. Rotor kinetic energy
Reactive power support
SOFTWARE: MATLAB/SIMULINK
SCHEMATIC DIAGRAM:
Figure 1. The Simplified System Structure.
EXPECTED SIMULATION RESULTS:
Figure 2. (A)The Three-Phase Unbalanced Voltages
With 3956 90_, 5636 30_, 5636 150_Under Case 1, (B) The
Three-Phase
Unbalanced Voltages With 3956 86_, 5406 28_, 5886 148_ Under Case 2, (C) Wind Speed.
Figure 3. Control Performance Of
Different Control Schemes Under Case 1 (A) Control Strategy I, (B) Control Strategy
Ii, (C) Proposed Control Strategy.
Figure 4. Control Performance Of
Different Control Schemes Under Case 2 (A) Control Strategy I, (B) Control
Strategy Ii, (C) Proposed Control Strategy.
CONCLUSION:
This
paper presents a new power and current limiting control of wind turbine based
on PMSG for enhanced operation performance under unbalanced grid voltage. The
contributions of this work mainly includes the following parts: 1) Based on the
detailed analysis of the output current, a peak current limiting scheme is
proposed to ensure the three-phase currents are within the safe range; 2) The
unbalanced power in the system is converted into rotor kinetic energy, which
solves the problem of dc bus overvoltage; 3) The fluctuations on dc bus voltage
and output power are eliminated effectively. The advantages of the proposed
scheme for this work are as follows: 1) No additional auxiliary equipment is
needed, avoiding high costs; 2) There is no need to exchange the control
functions of MSC controller and GSC controller, which avoids the problem of
resetting the control parameters; 3) The control of three-phase inverter
currents is realized in αβ coordinate system, without the separation of
positive and negative sequence of current and complex rotating coordinate transformation,
the structure is simple. The effectiveness and superiority of the proposed control
strategy have been verified by comparing the simulation results with the other
two control strategies under the two different grid faults.
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