Page 50 - Hybrid-Renewable Energy Systems in Microgrids

34 Hybrid-Renewable Energy Systems in Microgrids

droop control is also found to be slow. Various improved versions of droop control-
lers are available in literature, wherein an attempt has been made to overcome these
drawbacks.

6 Simulation study

A MATLAB-based study of a parallel inverter-based AC microgrid system has been
performed to demonstrate the operation and control of an autonomous microgrid. Load
share between the two inverters is controlled using droop control scheme. A voltage
control in association with a current control provides necessary PWM switching sig-
nal for controlled operation of both the inverters. Table 2.1 presents the microgrid data
used for simulation study.
Under dynamic load condition, loads at bus 1 and bus 2 are changing. A simulation
period of 2.5 s has been taken, and the active and reactive load demands at individual
buses have been plotted in Fig. 2.7 and Fig. 2.8.
With the operation of droop controller along with voltage and current controller,
instantaneous active and reactive power supply from both inverters is maintained in a
desired ratio. The desired ratio is adjusted with the help of droop coefficients. From
the data given in Table 2.1, it can be deduced that the desired active power share
between two inverters is in the ratio of 1:5. The reactive power demand is shared
equally between two inverters. Figs. 2.9 and 2.10 present the active and reactive load
sharing between two inverters. Results validate that the active power share has been
achieved in a ratio of 1:5 as desired.

Table 2.1 Microgrid data for parallel inverter-based AC microgrid

Parameter Values
Reference AC bus voltage for both AC 120 V
buses
Reference frequency 314 rad/s
R si 0.1 Ω
L si 4 mH
R 12 0.04 Ω
L 12 1 mH
C di 200 µF
R Li 10 Ω
0.0352 H
L Li
Switching frequency 5 kHz
Active power droop coefficients (m p1 , m p2 ) 0.0095, 0.0019
Reactive power droop coefficients 0.012
(n q1 = n q2 )