combinepdf

voltage across the
critical load.
So far, three generations
o f E S s h a v e b e e n
developed. The first
generation, consisting of
a single-phase inverter
w i t h a c a p a c i t o r
installed on the dc-link
side, is connected in
series with a non-critical
load and drawback is its
limited reactive power
c o m p e n s a t i o n
capability. The second
generation is proposed
and it replaces the
capacitor with a battery,
which enables the active
p o w e r r e g u l a t i o n .
However, the battery
brings other problems
such as larger size,
shorter service life and
higher cost. The third
generation solves the
battery problem using
t w o b i d i r e c t i o n a l
inverters connected
back-to-back through a
dc bus, but additional
transformers are
required to isolate the
inverters from the grid.
It is expected that the
ES, as a decentralised
approach, can also be
used to improve the
power quality of the
d i s t r i b u t i o n ( l o w -
voltage) power grids.
Conventionally, single
centralised techniques
such as the series and
s h u n t V A R
compensators are used
at the high voltage level
t o i m p r o v e t h e
performance of AC
p o w e r s y s t e m s b y
p r o v i d i n g 1 ) l o a d
compensation and 2)
voltage support.
There is a growing
interest in using dc
power systems and
micro grids for our
electricity transmission
a n d d i s t r i b u t i o n ,
particularly with the
increasing penetration
of photovoltaic power
systems. ES’s Dispersed
throughout the
distribution system can
provide a strong and
cost effective
m e c h a n i s m f o r
distributed voltage
control that emerged as
a novel way of DSM on
the real time basis.
******
Positive Emotions
and Math
-Learning Reinforce each
other
Positive emotions and success at
learning in math reinforce each
other, according to a new study by
Ludwig-Maximilians University in
Munch on students emotional
attitudes to mathematics.
Research shows that learning and
cognitive performance of students
can b influenced by emotional
reactions to learning, like
enjoyment, anxiety and boredom.
The finding appears in the journal
Child Development.
“ We f o u n d t h a t e m o t i o n s
i n f l u e n c e d s t u d e n t s ’ m a t h
achievement over the years “,
explains Prof. Reinhard Pekrun,
who led the research. “Students
with higher intelligence had better
grades and test scores, but those
who also enjoyed and took pride
i n m a t h h a d e v e n b e t t e r
achievement. Students who
experienced anger , anxiety,
shame, boredom, or-hopelessness
had lower achievement”