IEEE Power Electronics Magazine - June 2022 - 54

These mathematical relationships in summary indicates
the case of a supercapacitor's capability to dissipate shortterm
surge energy in path resistances and/or ESR of the
device, compared to an electrolytic capacitor of a similar
can size. Based on the same theory, Figure 9 depicts what
happens to the voltage across the capacitor, with repeated
surges applied from a lightning surge simulator such as
Noiseken LSS 6230. It is important to note that the vertical
axis is in the units of millivolts, and hence do not tend to
exceed the rated dc voltage of the device.
106
105
1 F
Supercapacitors
104
103
102
101
100
Electrolytic Capacitors
1,500 µF
100 µF
470 µF
10-4
10-3
10-2
10-1
Capacitance (F)
FIG 8 Comparison of energy lost and stored for electrolytic capacitors and SCs
subjected to a 6 kV, 1.2/50 μs pulse. Capacitors chosen are 100, 470, and 1500 μF
electrolytic capacitors, and 1, 25, and 100 F SCs with 15, 100, 150, 700, 42, and
15 mΩ ESR, respectively.
20
15
10
5
6.5 kV
2.5 kV
1.5 kV
100
101
102
In summary this discussion provides the background to
use a SC based sub-circuit to develop a more effective SPD.
Problems with Supercapacitors as Shunt Devices
Referring to Figure 3, in a surge protector application, critical
load is safeguarded by the action of shunt devices such
as the MOVs and the BBDs. Given these conditions of the
MOV/BBD are kept in parallel to the ac utility mains line,
they should have a voltage rating that under nominal line
voltage and its worst case (RMS voltage) variation, they do
not fire into conduction, and they can withstand
the instantaneous line voltage.
Compared to this essential requirement,
100 F
25 F
since supercapacitors have very low voltage
dc ratings in the range of 2 to 4 V (for
single cell cases), they cannot directly re -
place MOVs or BBDs in a surge protector.
Also, at 50 or 60 Hz of power line frequency,
if you place a SC between live and the neutral
of the ac mains, it will show a very
small shunting impedance determined by
1/2πfC which will in turn create an effective
short circuit across the line and the
neutral. For example, 1 F SC will show
an impedance of approximately 3.1 mΩ at
50 Hz. However, a 1 µF film capacitor, will
show a shunt impedance of 3.1 kΩ. This
simply argues about the difficulty of using
a SC based shunt sub-circuit to absorb
transient surge voltages superimposed on
the power line.
Supercapacitor Assisted
Surge Absorber Concept
0 246 8101214161820
Number of Surges
(a)
1,200
1,000
800
600
400
200
1 F
5 F
25 F
Power electronics research group at the University
of Waikato, launched a PhD thesis
completed by the first author [10]-[14],
based on the preliminary investigations
which lead to the first patent [8]. As per
detailed research published in [12]-[16], a
uniquely new circuit topology as per Figure
10(d) was successfully developed by the
team at Waikato. This was based on a step
by step analysis of Figures 10(a) to 10(c).
Following paragraphs provide a summary of
the applicable theoretical concepts, and the
associated design and development process.
Based on the summaries provided in the
050
100
150
Number of Surges
(b)
FIG 9 Applying consecutive surges to supercapacitor. (a) different surge voltages
to a 5 F capacitor; (b) 6 kV peak surges to different capacitors.
54 IEEE POWER ELECTRONICS MAGAZINE z June 2022
200
250
300
above sections (Supercapacitors' Capability
to Absorb Transient Surges and Problems
with Supercapacitors as Shunt Devices),
while a SC and a resistor based circuit can
be used to dissipate transient energies associated
with high voltage transients superimposed
on the power line, the low voltage
dc rating and the extra-low ac impedance
Voltage (mV)
Voltage (mV)
Resistor Loss to Capacitor Ratio
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