Robust Droop Control with Improved Voltage Quality - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 322

V DC

-

+

u f

i i o v o

L

CB

u

IGBT
H-bridge

PWM

C

AC bus

Figure 20.1 Single-phase inverter with a PWM block and an LC filter

of which the gain at frequency h is K h with zero phase. It is almost 1 everywhere apart from

at the frequencies around the harmonics. This is equivalent to reducing the output impedance
of the inverter

ω

sL + K i

Z o ( s ) =

1 + K R ( s )

+

to sL

K i

ω v o . The

at the frequency h . This helps improve the THD of the output voltage

1 + K h

damping factor ξ can be chosen as ξ = 0 . 01 to accommodate frequency variations and h can

v o

i

-

K i K R ( s )

-

u

v r

(a) The controller discussed in Chapter 8 to improve voltage THD

E *

-

K

RMS e

- E i

1

P i

n i

s

v o

v ri

Q i

1 i

m i

s

ω

i t+ δ i

*

ω

(b) Robust droop controller to generate the voltage reference

Figure 20.2 Robust droop control with improved voltage THD for R-inverters