265
Coupling with Batteries and Fuel Cells
The simplest manner of HESS integration is through direct connection.
The direct integration of a supercapacitor with primary power sources benefits from a power requirement less than that necessary for a DC–DC converter operation. As an alternative to converter use, a diode can be applied
as a replacement to assist in power control while achieving high efficiency.
However, the terminal voltage of the FC will then determine the UC bank
voltage and therefore limit full utilization of its power capabilities.
For simple design purposes, the total resistance between these two energy
systems connected in such a manner determines their respective roles in
power sharing. By following this notion, a primary control strategy often
used is summarized here.
1. At periods of low power demand (<5 kW), the FC supports the load
up to its limit. Any excess power is directed to charge the supercapacitor, while the terminal load voltage requirements determine
supercapacitor charging or discharging.
2. At periods of high power demand (>50 kW), the FC supplies its rated
power in addition to discharging the supercapacitor to deliver the
necessary supplementary power beyond the FC capability.
3. Interrupted power for small time intervals is supplied only by the
supercapacitor bank.
4. Design of the UC requires avoiding conditions that permit overcharging or undercharging of the bank.
5. Control of the operating voltage of supercapacitor V initial to ½V initial
permits ~75% of the stored energy to be used.
Achieving these control strategies requires the implementation of PI controllers, ideal switching elements, and sensors to monitor currents and voltages;
all of which can be evaluated via integration into a simulation model.
The load requirements of an application may call for either DC or AC
electrical energy. HESSs produce DC energy; back-up power and residential applications operate under AC conditions, and therefore necessitate the
inclusion of a DC–AC inverter. In the model presented for a residential power
supply using a power conditioning unit (PCU), a simplified inverter is presented. In addition, although a DC–DC converter is included in real-world
systems, it is not included in the following model due to its negligible effects
on the dynamic response and the complications and numerical instabilities
associated with its integration.
6.6.4 Optimization of Models
The integration of a battery–supercapacitor ESS with FCs continues to
develop along with topologies that can be used to integrate these systems
and their applications. Four common topologies are reviewed along with
Coupling with Batteries and Fuel Cells
The simplest manner of HESS integration is through direct connection.
The direct integration of a supercapacitor with primary power sources benefits from a power requirement less than that necessary for a DC–DC converter operation. As an alternative to converter use, a diode can be applied
as a replacement to assist in power control while achieving high efficiency.
However, the terminal voltage of the FC will then determine the UC bank
voltage and therefore limit full utilization of its power capabilities.
For simple design purposes, the total resistance between these two energy
systems connected in such a manner determines their respective roles in
power sharing. By following this notion, a primary control strategy often
used is summarized here.
1. At periods of low power demand (<5 kW), the FC supports the load
up to its limit. Any excess power is directed to charge the supercapacitor, while the terminal load voltage requirements determine
supercapacitor charging or discharging.
2. At periods of high power demand (>50 kW), the FC supplies its rated
power in addition to discharging the supercapacitor to deliver the
necessary supplementary power beyond the FC capability.
3. Interrupted power for small time intervals is supplied only by the
supercapacitor bank.
4. Design of the UC requires avoiding conditions that permit overcharging or undercharging of the bank.
5. Control of the operating voltage of supercapacitor V initial to ½V initial
permits ~75% of the stored energy to be used.
Achieving these control strategies requires the implementation of PI controllers, ideal switching elements, and sensors to monitor currents and voltages;
all of which can be evaluated via integration into a simulation model.
The load requirements of an application may call for either DC or AC
electrical energy. HESSs produce DC energy; back-up power and residential applications operate under AC conditions, and therefore necessitate the
inclusion of a DC–AC inverter. In the model presented for a residential power
supply using a power conditioning unit (PCU), a simplified inverter is presented. In addition, although a DC–DC converter is included in real-world
systems, it is not included in the following model due to its negligible effects
on the dynamic response and the complications and numerical instabilities
associated with its integration.
6.6.4 Optimization of Models
The integration of a battery–supercapacitor ESS with FCs continues to
develop along with topologies that can be used to integrate these systems
and their applications. Four common topologies are reviewed along with