**3.1. Requirements for selecting the converter topology**

For the selection of the converter topology the following requirements are considered in order to ensure the maximum efficiency and minimum cost of the power generation system.


**Figure 9.** Switching loci trajectories of the different converter types.

340 New Developments in Renewable Energy

Figure 10 provides an arrangement for a soft-switching resonant converter. An inductor -Ls and a capacitor-Cs have been added to help the switch action. A similar *LdC*d pair is added to the diode. In any of these soft switching cases, switch action at a zero crossing cuts off the

ringing resonant waveform. This technique is often called quasi-resonance.

**Figure 10.** General structure of a resonant converter, where ZVS or ZCS can be obtained.

To create conditions for the ZCS or ZVS in DC-DC converters, the resonance or soft switching approach can be used. The ZVS or ZCS can be obtained by re-arranging the resonant compo‐ nent Figure 10, whose combinations offer several possibilities for resonant action as follows:

**5.** Incorporated filtering and storing possibilities

A comparative analysis of the major topologies of DC-DC converters described above is presented below.

### **3.2. DC-DC converter topologies**

Power electronic converters in general and DC-DC converters in particular have a great importance on the performance and efficiency of energy production process based on fuel cells. The control of the operation point of the fuel cell requires appropriate use of static power converters, capable of providing accurate support to the control methods. The main objective to beachievedwhenapplyingtheconverterstofuelcellsisobtainingthemaximumefficiencyusing the most appropriate control strategies, taking into account requirements described above. As described above, different converter topologies can be used as represented in figures 11 to 13 below.UsuallytheDC-DCconverterisputbetweenthefuelcellandtheinverter,whichperforms two functions,namely; 1) acts asDC isolationforthe inverter; and2)produces sufficient voltage for the inverter input so that the required magnitude of the AC voltage can be produced. The inverter can be single-phase or three-phase depending on the utility connection.

*3.2.1. Series resonant converter with capacitive output filter*

decreases with increase in input voltage.

**Figure 14.** Series Resonant converter with capacitive output filter.

*3.2.2. Series resonant converter with inductive output filter*

output filter. Its main characteristics can be summarized as follows:

**1.** The full range ZVS (full load to light load) is achieved.

also called series-parallel resonant converter (SPRC).

**2.** The full range ZVS (full load to light load) is achieved.

be summarized as follows:

voltage.

The converter topology shown in Figure 14 is in conformity with the considerations presented above. This is a modified series resonant converter (SRC), which uses an (L-C)||L resonant tank for soft switching of HF switches. The main characteristics of such type of converter can

Methodology of Designing Power Converters for Fuel Cell Based Systems: A Resonant Approach

http://dx.doi.org/10.5772/54674

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**1.** This configuration gives high efficiency at all varying load and line conditions but it

**3.** Switch peak current reduces with load but increases significantly with change in input

The converter topology shown in Figure 15 is an LCL type SRC with inductive output filter. This uses an LCL resonant tank for soft switching of high frequency switches and an inductive

**2.** Rectifier diode voltage rating is higher, but with application of ultra fast recovery diodes of high voltage rating with low forward voltage drop does not affect the efficiency much.

Note: This configuration can also be modified to a series resonant converter (SRC), which uses an (L-C)||C resonant tank for soft switching of high frequency switches, which, in this case is

**Figure 11.** Configuration of a DC-AC converter interfaced directly to the grid.

**Figure 12.** Configuration of a DC-DC followed by a DC-AC converter interfacing the grid.

**Figure 13.** Configuration of a DC-AC followed by a AC-AC converter interfacing the grid.
