Wind Energy Systems - Wind Energy Systems for Electric Power Generation - page 106

Fig. 5.27 Circuit of a system
with step-up inverter

A simplified equivalent circuit is illustrated in Fig. 5.27, where the generator
is represented by the induced no-load voltage U o , is proportional to speed, and an
internal resistance. The step-up converter is modelled by an ideal transformer with
ratio 1 / (1- d ), an inductor in the input branch and a capacitor in the output branch.
The load side consists of a resistor and an e.m.f. representing the constant battery
voltage U B .
The performance of an example system for 4 kW at 350 min − 1 is illustrated by
calculated curves in Fig. 5.28. Characteristics are shown for battery loading oper-
ation, under the condition of continuous current. The duty ratio d is controlled to
keep torque proportional to speed, between 80 and 350 min − 1 . In the Figure part (a)
shows the course of the generator voltage vs. speed and input and output voltage of
the step-up inverter; part (b) depicts input and output currents, while (c) is the duty
ratio; eventually (d) is the course of input power.

a) b)

c) d)

Fig. 5.28 Performance of a system with step-up inverter and battery storage (example) (a-b) volt-
ages, currents; ( c ) duty ratio; ( d ) input power