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Electrochemical Supercapacitors for Energy Storage and Delivery
6.4.2 ES–Battery Indirect Coupling: Active Control
Indirect coupling of a supercapacitor and battery via the addition of a DC–
DC power converter affords a means of stepping the voltage up or down.
This can provide HESS systems with supplementary degrees of freedom
for operation and rectify problems and constraints surrounding the passive
direct coupling described earlier. These advantages are:
1. The supercapacitor and battery voltages can now differ from one
another, providing design flexibility for both types of arrays.
2. The weight of the power source to meet peak power requirements is
now readily reduced compared with passive direct coupling.
3. A greater power capacity is realizable while circumventing a battery
current that may surpass the safety limit.
4. A constant terminal voltage (with small variation) can be maintained for the HESS.
5. Regulated recharging of the battery can be achieved through a DC–
DC converter without a need to introduce a separate charger.
Several topologies exist for implementing a power converter into the HESS
circuit in conjunction with the benefits and challenges arising from their use.
By reviewing a system that requires the HESS and power converter through
a top-down approach, high level interfaces where energy and data flow are
exchanged can be defined, and an early estimation of the “intelligence”
required by the unit and subsequent control system can be made.
Topologies often vary based on control scheme, switch rating, component
count, and circuit complexity. While various topologies have been compared
and presented in the literature, the robust buck–boost (half-bridge) DC–DC
converter remains the most popular for use in hybrid battery–supercapacitor
systems as a result of its simplicity and efficiency.
Utilizing a DC–DC converter with an ES requires that it be bidirectional
to permit the governance of both discharge and charge cycles. Depending
on the configuration chosen, either the supercapacitor or the battery is connected to the DC bus (load). This is beneficial for controlling the battery current supplied to the DC bus, but the bus voltage will fluctuate according to
the state of charge (SOC) of the supercapacitor. Furthermore, several ES cells
are required to match the DC bus voltage.
Through introduction of a DC–DC converter, active control can be implemented by a microcontroller. The active control design, control settings, and
rules vary, depending on the applications. For the additional topology shown
in Figure 6.3, the average smaller current (relative to the peak) demanded by
the load is met by the feedback-controlled buck DC–DC converter to discharge the battery at a steady rate, independent of the battery voltage variations that may occur.
Electrochemical Supercapacitors for Energy Storage and Delivery
6.4.2 ES–Battery Indirect Coupling: Active Control
Indirect coupling of a supercapacitor and battery via the addition of a DC–
DC power converter affords a means of stepping the voltage up or down.
This can provide HESS systems with supplementary degrees of freedom
for operation and rectify problems and constraints surrounding the passive
direct coupling described earlier. These advantages are:
1. The supercapacitor and battery voltages can now differ from one
another, providing design flexibility for both types of arrays.
2. The weight of the power source to meet peak power requirements is
now readily reduced compared with passive direct coupling.
3. A greater power capacity is realizable while circumventing a battery
current that may surpass the safety limit.
4. A constant terminal voltage (with small variation) can be maintained for the HESS.
5. Regulated recharging of the battery can be achieved through a DC–
DC converter without a need to introduce a separate charger.
Several topologies exist for implementing a power converter into the HESS
circuit in conjunction with the benefits and challenges arising from their use.
By reviewing a system that requires the HESS and power converter through
a top-down approach, high level interfaces where energy and data flow are
exchanged can be defined, and an early estimation of the “intelligence”
required by the unit and subsequent control system can be made.
Topologies often vary based on control scheme, switch rating, component
count, and circuit complexity. While various topologies have been compared
and presented in the literature, the robust buck–boost (half-bridge) DC–DC
converter remains the most popular for use in hybrid battery–supercapacitor
systems as a result of its simplicity and efficiency.
Utilizing a DC–DC converter with an ES requires that it be bidirectional
to permit the governance of both discharge and charge cycles. Depending
on the configuration chosen, either the supercapacitor or the battery is connected to the DC bus (load). This is beneficial for controlling the battery current supplied to the DC bus, but the bus voltage will fluctuate according to
the state of charge (SOC) of the supercapacitor. Furthermore, several ES cells
are required to match the DC bus voltage.
Through introduction of a DC–DC converter, active control can be implemented by a microcontroller. The active control design, control settings, and
rules vary, depending on the applications. For the additional topology shown
in Figure 6.3, the average smaller current (relative to the peak) demanded by
the load is met by the feedback-controlled buck DC–DC converter to discharge the battery at a steady rate, independent of the battery voltage variations that may occur.