ABSTRACT:
The use of ‘Electric Springs’ is a novel way of
distributed voltage control while simultaneously achieving effective
demand-side management through modulation of non-critical loads in response to
the fluctuations in intermittent renewable energy sources (e.g. wind). The
proof-of-concept has been successfully demonstrated on a simple 10 kVA test
system hardware. However, to show the effectiveness of such electric springs
when installed in large numbers across the power system, there is a need to
develop simple and yet accurate simulation models for these electric springs
which can be incorporated in large-scale power system simulation studies. This
paper describes the dynamic simulation approach for electric springs which is
appropriate for voltage and frequency control studies at the power system
level. The proposed model is validated by comparing the simulation results
against the experimental results. Close similarity between the simulation and
experimental results gave us the confidence to use this electric spring model
for investigating the effectiveness of their collective operation when
distributed in large number across a power system. Effectiveness of an electric
spring under unity and non-unity load power factors and different proportions
of critical and non-critical loads is also demonstrated.
KEYWORDS:
1. Demand side management
2. Reactive power control
3. Electric springs
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1: Block diagram of the test system with Electric Spring
EXPECTED SIMULATION RESULTS:
Fig.
2: Comparison between line voltages with ES operating in voltage support mode.
Reactive power consumption of the intermittent source is increased from 467 to
1100 Var at t=2.0 s (a) simulated response and (b) experimental results.
Fig.
3: Comparison between voltages injected by the ES. Reactive power consumption
of the intermittent source is increased from 467 to 1100 Var at t=2.0 s (a)
simulated response and (b) experimental results
Fig.
4: Comparison between voltages across the non-critical load. Reactive power
consumption of the intermittent source is increased from 467 to 1100 Var at
t=2.0 s (a) simulated response and (b) experimental results
Fig.
5: Comparison between line voltages with ES operating in voltage suppression
mode. Reactive power consumption of the intermittent source is reduced from 467
to 110 Var at t=2.0 s (a) simulated response and (b) experimental results
Fig.
6: Comparison between voltages injected by the ES. Reactive power consumption
of the intermittent source is reduced from 467 to 110 Var at t=2.0 s (a)
simulated response and (b) experimental results
Fig.
7: Comparison between voltages across the non-critical load. Reactive power
consumption of the intermittent source is reduced from 467 to 110 Var at t=2.0
s (a) simulated response and (b) experimental results
Fig.
8: Variation of active power consumeb by the non-critical and critical loads
under voltage support (subplot a) and suppression (subplot b) modes
Fig.
9: Simulated response following random variations in active power generation
and reactive power consumption of the intermittent source. ES is activated at t
= 720 s
Fig.
10: Experimental results following random variations in active power generation
and reactive power consumption of the intermittent source. ES is activated at t
= 720 s
Fig.
11: Simulated response for RL load (both critical load and non-critical load)
with a power factor of 0.95 lagging following random variations in active power
generation and reactive power consumption of the intermittent source. ES is
activated at t = 720 s
Fig.
12: System response for different distribution of non-critical and critical
loads (NC:C). Disturbance is increase in reactive power consumption of the
intermittent source from 467 to 1100 VAr at t=1.0 s
CONCLUSION:
The electric
spring is a new technology that has attractive features including dynamic
voltage regulation, balancing power supply and demand [8,9], power quality
improvement [14], distributed power compensation [15] and reducing energy
storage requreiments for future smart grid [16]. In order to fully explore
their full potentials in large-scale power system simulation, an averaged
simulation model for the electric spring is proposed here for the smart grid
research community. The simulation model is simple for inclusion into
large-scale system simulation platforms and yet accurate enough to capture the
dynamic behavior of interest in terms of studying voltage and frequency
stability. The case studies reported in the previous section exhibited close
match between simulation and experimental results confirming the accuracy. The
discrepancies, wherever applicable have been accounted for. These are due to
the fact that the DC link voltage control loop has been neglected. This results
in attaining a different operation point in terms of ES voltage in order to
obtain the same line voltage which is possible as suggested by the phasor
diagrams in Fig. 3. It is possible, of course, to include the DC link voltage
control loop in the model to eliminate these little discrepancies but only at
the expense of significant increase in simulation time for large systems. The
addition of DC link voltage control loop (with large number of ES distributed
across the system) makes the simulation much more complex with little improvement
in terms of accuracy.The use of ‘Electric Springs’ is a novel way of
distributed voltage control while simultaneously achieving effective
demand-side management through modulation of non-critical loads in response to
the fluctuations in intermittent renewable energy sources (e.g. wind). This
paper describes the simulation approach for electric springs which is
appropriate for voltage and frequency control studies at the power system
level. Close similarity between the simulation and experimental results gave us
the confidence to use this electric spring model for investigating the
effectiveness of their collective operation when distributed in large number
across a power system. The proposed dynamic model is generic enough to study
the performance of ESs under different load power factors and proportion of
critical and non-critical loads. The effectiveness of an ES improves with the
proportion of non-critical load.
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