ABSTRACT:
This paper describes the droop control method for parallel
operation of distributed electric springs for stabilizing ac power grid. It
provides a methodology that has the potential of allowing reactive power
controllers to work in different locations of the distribution lines of an ac
power supply and for these reactive power controllers to support and stabilize
the ac mains voltage levels at their respective locations on the distribution
lines. The control scheme allows these reactive power controllers to have
automatically adjustable voltage references according to the mains voltage
levels at the locations of the distribution network. The control method can be
applied to reactive power controllers embedded in smart electric loads
distributed across the power grid for stabilizing and supporting the ac power
supply along the distribution network. The proposed distributed deployment of electric
springs is envisaged to become an emerging technology potentially useful for
stabilizing power grids with substantial penetration of distributed and
intermittent renewable power sources or weakly regulated ac power grid.
KEYWORDS:
1.
Droop control
2.
Electric
springs
3.
Smart gird
4.
Voltage
regulation
SOFTWARE: MATLAB/SIMULINK
EXPECTED SIMULATION RESULTS:
Fig.
2. (a) Measured root-mean-square values of the mains voltage VS1,VS2
and VS3 (b) Measured root-mean-square values of the mains voltage VS1,VS2
and VS3 from 1800 to 1440 sec (ES activated without the proposed
droop control) (c) Measured root-mean-square values of the mains voltage VS1,VS2
and VS3 from 1800 to 2160 sec (ES activated with the proposed droop
control).
Fig.
3. Measured average value of reactive power generated by the 3 electric springs
(Qa1 ,Qa2 and Qa3 ).
Fig.
4. Measured modulation indexes of the electric springs M1,M2
and M3 .
Fig.
5. Measured average value of the critical load power PR1,PR2
and PR3 .
Fig.
6. Measured root-mean-square values of the non-critical load voltage Vo1
,Vo2 and Vo3 .
Fig.
7. Measured average value of the non-critical load power Po1,Po2
and Po3
.
CONCLUSION:
A control scheme has been successfully developed and
implemented for a group of electric springs. It enables individual electric
springs to generate their mains voltage reference values according to their
installation locations in the distribution lines and to work in co-operative
manner, instead of fighting against one another, therefore allowing the
electric springs to work in group to maximize their reactive power compensation
effects for voltage regulation. The control method also leads to more evenly
distribution of load power shedding among the non-critical loads. The
attractive features of the control scheme have been successfully verified in an
experimental smart grid setup.
With the droop control scheme,many electric springs
of small VA ratings could be embedded into non-critical loads such as electric
water heaters and refrigerators to form a new generation of smart loads that
are adaptive to power grid with substantial penetration of renewable energy
sources of distributed and intermittent nature. If many small electric springs
are deployed in the power grid in a distributed manner, their collective voltage
stabilizing efforts can be added together. Because the electric springs allow
these smart loads to consume power following the varying profile of
intermittent renewable energy sources, they have the potential to solve the
stability problems arising from the intermittent nature of renewable energy
sources and ensure that the load demand will follow power generation, which is
the new control paradigm for future smart grid. Since the electric appliances
embedded with the electric springs can share load shedding automatically, this
approach should be more consumer-friendly when compared with the on-off control
of electric appliances. For example, shutting down refrigerators is intrusive
and inconvenient to the consumers (and may involve consumers’ rights issues)
and requires some forms of central control. Allowing many smart refrigerators
to shed some load without being noticed and central control is more consumer- friendly.
The individual operations of the electric springs have
previously been evaluated. The successful implementation of the droop control
for 3 electric springs working as a group in a small distributed network in
this study is a just a step forward to confirm that multiple electric springs
can work together without ICT technology. The collective effects of electric
springs and their capacity are new topics that deserve further investigations. Extensive
simulation studies are needed to confirm the effectiveness of many such
electric springs working together in a large-scale power system model.
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