Parallel PI Voltage-H Current Control of a Neutral Leg - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 211

P

i N

i C

plant

u=p

C

Figure 13.3 Block diagram of the H ∞ current control scheme

13.2 Design of an H ∞ Current Controller
13.2.1 Controller Description
The H ∞ current control scheme is shown in Figure 13.3, where P is the transfer function
of the independently-controlled neutral leg and C is the transfer function of the controller.
The controller C is designed by solving a weighted sensitivity H ∞ problem (Zhou and Doyle
1998), as formulated later, to assure the stability of the entire system. The neutral current i N
is regarded as an external disturbance and the control signal is u

= p .

13.2.2 Formulation as a Standard H ∞ Problem
A measurement noise n is introduced when measuring the current i C , as shown in Figure 13.4.
The components of the current i C are expected to be within a certain frequency range so
a weighting function W is introduced to reflect this. A weighting factor

μ

is introduced to

i N

~

n

P

ξ

1

i L

+ +

V u N i C

p

+

W

DC

sL + R

-

+

2 +

N N

z

μ

1

V c

s ( C

+ +

C )

N N −

u=p y

C

Figure 13.4 Formulation of the H ∞ problem to control the current flowing through the split DC
capacitors