Abstract
This chapter presents a fuzzy logic approach for reactive power and voltage control in grid-connected wind farms with different types of wind generator units to improve steady state voltage stability of power systems. The load buses' voltage deviation is minimized by changing the reactive power controllers according to their sensitivity using fuzzy set theory. The proposed approach uses only a few high sensitivity controllers to achieve the desired objectives. A 297-bus-equivalent grid-connected wind system and a 417-bus-equivalent grid-connected wind system are considered to present the simulation results. To prove the effectiveness of the proposed approach, a comparative analysis is also carried out with the conventional linear-programming-based reactive power optimization technique. Results demonstrated that the proposed approach is more effective in improving the system performance as compared with the conventional existing techniques.
TopNotations
a: Transformer off-nominal tap
j: Complex operator
α: Angle of the primitive admittance of the line
y: Primitive admittance of the line
Y: Admittance matrix
B: Line charging susceptance
∆Q: Incremental change in bus reactive power
∆V: Incremental change in bus voltage magnitude
∆T: Incremental change in transformer tap
θ: Angle of the bus admittance matrix
δ: Voltage phase angle
Vdj: Desired voltage at load bus j
Vaj: Actual voltage at load bus j
Ve: Error or difference voltage at load bus
Vmin: Minimum or lower limit on bus voltage
Vmax: Maximum or upper limit on bus voltage
X: Row vector of the voltage/reactive power controllers
[C]: Controlling ability of the controller matrix
m: Controller index
tg: Number of grid OLTC transformers
tpcc: Number of OLTC transformers at the point of common coupling of wind farm
g: Number of generators
svc: Number of switchable VAr compensators
vswg: Number of variable speed wind generators
r: Number of remaining buses
M: Voltage/reactive power controller step size
[H]: Voltage deviation sensitivity matrix
[S]: Linearized sensitivity matrix relating dependent and control variable
L-index: Static voltage stability index
n: Number of total buses
Ploss: System active power loss
Qloss: System reactive power loss
Lmax-index: Maximum value of voltage stability index
Key Terms in this Chapter
Voltage Stability: Voltage stability refers to the ability of a power system to maintain steady voltage at all buses in the system after being subjected to a disturbance from a given initial operating condition.
Standard Deviation (STDEV): The standard deviation of the load voltage is used to quantify the amount of variation or dispersion of a set of load voltages.
Contingency: Contingency is an outage of a transmission line or transformer that may lead to overloads in other branches and/or sudden system voltage drop.
Fuzzy System: It is a component of machine learning techniques that takes membership values within 0 to 1 unlike crisp sets.
Electric Grid: An electric grid is a network of synchronized power providers and consumers that are connected by transmission and distribution lines and operated by one or more control centers.
Wind Farm: An area of land with a group of energy producing windmills or wind turbines.
Reactive Power: In electric power transmission and distribution, volt ampere reactive (VAR) is a unit by which reactive power is expressed in an AC electric power system.
Optimization: A mathematical method to find the solution of a problem towards achieving better performance either in form of minimum or maximum under one or more given constraints.
Wind Turbine: A wind turbine is a device that converts the wind's kinetic energy into electrical power.