Page 182 - Power Quality in Electrical Systems

164 Chapter Eleven

Vsd
Vcf Sin
Phase A Phase voltage
ABC Phase rotation PLL
estimation
Vcf Phase B Vsq identification (Fig. 4) Cos
DQ
Icfd
Phase capacitor
estimation
IL Phase A Icfq
IL Phase B ABC Isd Harmonic controllers
Phase current Isq 3rd, 5th, 7th, 9th, 11th, 13th
IL Phase C DQ estimation (Fig. 3)
– Q1
Pos + −
Vdc + + Esd seq
sq
P1 REG Pos D Kc Q2
p pe
DQ P1 REG DQ + +
– Q3
–
Ref Space vector modulation
Pos + – Q4
Pos Q
p
sq
+ Esq pe P1 REG DQ seq Kc
DQ
+ + Q5
n Neg D ne Q6
DQ P1 REG DQ
Limitation
ne Neg Q n Reset
DQ P1 REG DQ
Figure 11.11 Controller utilizing digital components [11.9].
[© 2005, IEEE, reprinted with permission]
Computers”. Where the controller requires phase information from
the supply line, such as for base drive signals in Figure 11.12, the con-
troller might be more sensitive to voltage sags than the personal
computer.

Correction measures
To keep a controller operating in the face of line-voltage sags and inter-
ruptions, the following equipment can be used:
■ Constant-Voltage Transformers (CVs): Used to correct for sags
down to 30 percent of rated line voltage for one cycle, and down to
70 percent continuously for a full load, as described in Chapter 8.
■ UPSs: For all conditions except line-voltage phase information.
Assume that the controlled load is operating from the supply line to
the UPS so that phase information from the UPS is of no use during
deep and long sags or interruptions.
■ Phase-Locked Loop: Used in the controller to provide phase
information.