IEEE Power & Energy Magazine - March/April 2016 - 54

✔ shunt compensation (statCoM);
✔ series compensation as a static synchronous series

compensator on one or two lines
✔ a combination of the two configurations as a unified
power flow controller (UpfC), which permits power
flow control on one of two possible transmission lines
as well as bus voltage control
✔ the first in the world interline power flow controller
(ipfC), in which two VsCs are connected in series on
their respective transmission lines. the ipfC configuration permits simultaneous control of real and reactive power on two transmission lines.
operating experience has reinforced the need for enhanced
CsC performance during system faults when var support is figure 7. A CSC converter hall.
needed. the CsC statCoM is phase-angle controlled and
tailored to transmission-level applications with high output
voltage quality (48-pulse) and low converter losses. Unlike as inputs, it is called dual angle control. the DaC control
the pulsewidth-modulated statCoM, the angle-controlled structure is illustrated in figure 8.
statCoM is switched at the line frequency to achieve lower
experimental verification of the DaC performance has
system losses. Despite the superior synthesized voltage wave- been implemented on a transient network analyzer (tna)
form quality and converter efficiency, an angle-controlled hardware system, which is a scaled analogue equivalent
statCoM may show inadequate performance for close-in model of the actual transformers, switches, and the exact
faults. overcurrent, possible saturation of the interfacing trans- 48-pulse inverter topology installed at the 345-kV Marcy
formers caused by power system faults, and negative sequence substation. the interface of the inverters to the controllers
current during unbalanced conditions are contributing factors. and its connection to the ac system is shown conceptually
nYpa, in collaboration with north Carolina state Uni- in figure 9.
versity (nCsU), has researched ways to prevent the statthe performance of the proposed controller has been veriCoM from potentially tripping in the presence of power fied under very severe fault conditions. figure 10 indicates the
system faults by limiting the
negative sequence current and the
resulting dc-link voltage oscillation. the research resulted in
Iq+*
the development of a new control
α
+
Iq+ 120-Hz
αdc
-
PI
structure called the dual angle
STATCOM
Σ
Σ
Notch
Controller
+
controller (DaC).
+
S
Filter
αac
Ia
the only control input in the
abc to S
Ib
S
dq
angle-controlled statCoM is the
Second Harmonic
Ic
+
-
Oscillations
of
I
phase-angle difference between
q
+
Σ
the converter (VsC) and the ac
PI
bus instantaneous voltage vector
Controller
(a) . in this type of statCoM,
0
ωt
the ac output voltage of the conId-
60-Hz
X2
+
+
120-Hz
verter is controlled indirectly by
-
PLL
!
Σ
Σ
Iq- Notch
changing the dc-link voltage.
-1
+
S
2
S
S
Filter
X
Ib Ic
Ia
in the DaC, a is split into two
-ωt
parts, a dc and a ac . the dc part
S
Ia
abc
S
(a dc), which is the conventional
Ib
to dq
S
angle-controller output, controls
Ic
the positive sequence VsC output
voltage. the oscillating part (a ac)
controls the dc-link voltage oscillation at twice the line frequency
to limit the negative sequence current. since this control scheme
uses two control angles (a dc and a ac) figure 8. The control structure of the DAC.
march/april 2016

ieee power & energy magazine

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2016