**5.2. Proportional integral control (PI)**

**5.1. Output voltage and current**

354 New Developments in Renewable Energy

Figure 28 below allows validating the stability of the voltage control loop of the converter that is, it can be seen that the output voltage, vout remains constant despite variations in the output current that is, in the load. This condition is valid to both situations namelly, the step-up of load corresponding to Figure 28 a) and the step-down of load corresponding to Figure 28 b).

(a) Step-up load condition.

(b) Step-down load condition.

**Figure 28.** Output voltage (Vout) and current (Iout).

The dynamics of the system can be evaluated by the analysis of the PI control signal. So, once considered both situations of load variation it appears that the stabilization time of the PI controller is approximately 7ms. In addition it presents a small oscillation which proves that the parameters of the PI control are well adapted to the system Figure 29 a) corresponds to the situation of a step-up load condition while Figure 29 b) corresponds to a step-down of load condition. The error of voltage is given by INA101 such as; ε =Vmeasured-Vreference and accordingly, the objective of the PI controller is to minimize this error for any load variation, as is shown in the two figures below.

(a) Step-up load condition.

(b) Step-down load condition.

**Figure 29.** PI Control.

#### **5.3. Resonant circuit operation**

Figure 30 corresponds to step-up and step-down load conditions. From its analysis it follows that the converter reacts to the load variation, varying its frequency of operation. Thus, for a small load level (Imin, Rmax) the frequency is low while for a high load (Imax, Rmin) the frequencyishigh.Indynamicterms itcanbeseenthatthetransitioninthefrequencyofoperation is instantaneous, hence, we conclude that the system has good dynamic characteristics. It can be also observed that in any of the load variations the output voltage Vout remains constant. This analysis validates the objective defined to the controller, that is it ensures a constant output voltage in order to satisfy the requirements imposed by the power system applications.

**6. Conclusions**

system MARK 1020.

**Nomenclature**

cell in its optimal operating point.

cell model and then for the whole system with load.

PEM – Proton exchange membrane fuel cell

IGBT – Insulated Gate Bipolar Transistor

SRC – Series resonant converter

ZVS – Zero voltage switching

tests made with the commercial system MARK 1020.

The main objective of the chapter is to discuss the design and implementation of a power generation system based on fuel cells. Accordingly, a methodology of designing and imple‐ menting an efficient high power converter system is presented. Moreover the chapter presents also an electrical equivalent model of the PEM fuel cell, which was validated by experimental

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

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

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Authors make considerations on the most suitable topologies of converters for this application type, and satisfying several criterions a series-resonant converter topology is selected, whose principle is based on soft-switching methodology. In this context the design and implemen‐ tation of the converter consisting of a input filter followed by the full-bridge inverter and the series resonant circuit on the primary side and a diode rectifier and output filter on the secondary side was based on the exploitation of their benefits as compared to other types of converters, namely: low component stresses, high frequency operation and soft-switching commutation. Converter design was done considering the operational constraints of the

A particular attention is done to the controller, which ensures a constant output voltage of the converter, in order to satisfy the requirements of the power system application and simulta‐ neously keeps the PEM operating within its optimum operating point. The control implemen‐ tation was divided into two parts namely: i) the voltage controller, which is responsible for keeping constant the output voltage of the converter even under loading variations and ii) the PEM controller, which is responsible for improving its performance by keeping the PEM fuel

Due to significance of the PEM cell behavior the results are firstly presented for the PEM fuel

The results demonstrate that the converter selected is a good solution to support the approach of improving the efficiency of PEM fuel cells because it allows an appropriated control of the power delivered by the fuel cell as it satisfies the requirements imposed by the load regulation

with minimum of losses due to adoption of soft switching commutation.

(a) Step-up load condition.

(b) Step-down load condition.

**Figure 30.** Output voltage and current and resonant circuit operation
