Wind Energy 8-11

what are the years when the type 1 WECS was dominate?

1980-1995

what are some advantages of the type 1?

simple power conversion configuration; low initial maintenance cost; reliable operation (no power converter)

whare are some disadvantages of the type 1?

no adequate control of the reactive power; lower Cp efficiency because of “fixed” speed; changes in wind cause frequency stabilization issues; grid faults cause severe stress on mechanical components

what is the typical power range of the type 1?

< 1 MW

what are the main components of the type 1?

blades, gearbox, SCIG (squirrel-cage induction generator), soft-starter, capacitor bank, transformer, grid

what is stall control (type I0)?

a passive method used to limit aerodynamic power; this power shows an undesirable overshoot behavior

what is active stall control (type I1)?

passive control with adjustable rotor blades; blades rotate out of wind (negative angles) causing turbulence; no overshoot but higher price arising

what is involved in the drive train of the type 1?

rotor shaft, the gearbox, an elastic coupling and the generator

what are the loads of a type 1?

high loads due to stall control in blades; stiff coupling to grid with high loads and high variability in the active power

what are the power electronics of a type 1?

soft-starter using thyristors

what is the reactive power of the type 1?

no capability to control reactive power; capacitors are used to improve power factor

what are the control strategies of type 1?

ensuring safe turbine operation; in dual speed systems, maximizing energy production at low wind speeds; compensating power factor; responding to a higher level control to start/stop

what are the controllable processes in type 1?

development of aerodynamic torque; development of generator torque; conversion of electrical power from one form into another, using power electronics

when was the type 2 dominate?

1995-2000

what are the components of type 2?

blades, gearbox, WRIG (wound rotor induction generator), external variable rotor resistance, soft- starter, capacitators, transformer, grid

what are the advantages of the type 2?

reduces mechanical loads; smooths active power generation; some improvement in aerodynamic efficiency

what are the disadvantages of the type 2?

limited improvement in aerodynamic efficiency; losses in the variable resistance; no adequate control of reactive power; does not fulfill modern grid codes requirements

what is the typical power range for type 2?

600 kW- 2 MW

what is pitch control (type I2)?

blade is rotated actively into the wind (positive angles); avoids overshoot in power curve

what rotor control does type 2 use?

pitch control to limit and optimize the generated output power

what is the characteristic speed of type 2?

“limited” variable speed by modifying rotor resistance

what are the components of the type 2 drive train?

rotor shaft, gearbox, elastic coupling, generator

what are the loads of type 2?

reduced aerodynamic loads due to pitch control in blades; softer coupling to grid with high loads and medium variability in the active power

what is the generator of the type 2?

wounded rotor asynchronous generator

what are the power electronics in type 2?

external variable rotor resistance; soft-starter using thyristors

what is the reactive power of type 2?

no capability to control reactive power; capacitors used to improve power factor

what is the variable speed of the type 3?

30%

what are the advantages to the type 3?

improvement in aerodynamic efficiency; reduces mechanical loads; smoothes active power generation; control of active and reactive power; supports voltage dips; fulfills modern grid code requirements

what are the disadvantages of type 3?

stator generation is directly connected to the grid and feels any of its disturbance; speed range is smaller than type 4; maintenance cost with slip rings

what is the power range of type 3?

2-5 MW

what rotor control system does type 3 use?

pitch control

what are the speed characteristics of type 3?

variable speed (30%); Cp is aimed for low and medium wind speeds

what does are the components for drive train for type 3?

rotor shaft, gearbox, elastic coupling, generator

what are the loads of type 3?

reduced aerodynamic loads due to pitch control in blades; coupling to the grid is “soft”, reducing loads

what generator does type 3 use?

doubly fed induction generator (DFIG)

what is the reactive power of the type 3?

capability to control reactive power ± 0.9- 0.95 power factor

what are the control strategies of type 3?

ensuring safe turbine operation; speed control to maximize energy production w/in load constraints; pitch control; responding to a higher level control set-point

what is the purpose of the frequency converter in type 3 and 4?

enables control of both the active and reactive power delivered by the generator of the grid

which WECS does not need a gearbox?

type 4

what rotor control is used in type 4?

pitch control

what is the speed characteristics of type 4?

variable speed 50%; Cp is aimed for low and medium wind speeds

what components are a part of the drive train of type 4?

rotor shaft, elastic coupling, generator

what are the loads of the type 4?

loads are reduced by using pitch control; coupling to the grid is “soft”, reducing loads

what are the generators of type 4?

WRSG (wound rotor synchronous generator), PMSG (permanent magnet synchronous generator), IG (induction generator)

what are the power electronic of a type 4?

full rated power converter connected to the rotor (100% nominal power); a rectifier with a dc/ac boost converter

what is the reactive power of type 4?

capability to control reactive power (± 0.9-0.95 power factor)

equation for apparant power

S = P/ p.f. = 3 x V1 x I1*

equation for reactive power

Q = sqr(S² - P²)

operating speed equation

ns = (60 * f) / Pp

equation slip

s = ns - n/ ns

equation airgap power

Pd = Pmi/(1-s)

equation aerodynamic torque

Taero = Paero/ Otur = [½ x rho x A x U³x Cp(TSR, B)] / Otur

equation energy

E = P (power) x T (time)

equation tangent velocity

tangent velocity = w x R (w = rotational speed m/s, radius)

equation relative wind speed

Urel = sqr[(real-induced)² + Utan²]

equation tip speed ratio

TSR = O*R/ U = tangent velocity/free flow wind speed

equation area (not given radius)

A = mass flow rate/ (air density x wind speed)

equation equivalent impedance

Zeq = (jXm x R’2/s + jX’2)/ (jXm + R’2/s + jX’2)

equation stator current

I1 = V1 / Zt = V1 / (R1 + jX1 + Zeq)

equation rotor losses

Pcu2 = Pmi - Pd = 3 x R2 x I’2²

equation stator losses

Pcu1 = Pd - P1 = 3 x R1 x I1²

equation total efficiency

N = ne x nm x Cp

equation Vm

Vm = V1 - I1(R1 + jX1)

equation Im

Im = Vm / jXm

equation rotor current

I2’ = I1 - Im

equation internal mechanical power

Pmi = 3 x R2’ (1/s - 1) x I’2²

equation internal mechanical torque

Tmi = Pmi / Om