**5. Experimental setup and results**

**4. Control**

352 New Developments in Renewable Energy

The control consists of two loops; the loop of the voltage or the fast loop and the loop of he PEM or the slow loop. The voltage controller is responsible of controlling the output voltage of the converter, keeping this in a constant value defined by the user even for load variations. The PEM controller is responsible of controlling the operation of the PEM, keeping it in its optimal point that is, producing the electrical power requested by the load with a minimum current and consequently with a minimum of hydrogen consumption. The control structure

of the converter as described is represented in Figure 26.

**Figure 26.** Control structure of the SRC.

The experimental setup is represented in Figure 27. It is used to test the all system composed by the PEM Mark 1020, the SRC and the load. The load is composed by a set of several resistors connected in series, whose variation is performed by a manual switch. The fuel pressure that provides a PEM stack is monitored by a standard dial pressure gauge, which maintains it constant in the range of 0.3 to 0.5bar. The ventilator is used to inject the oxidant flow necessary into the stack in order to produce the electrochemical reaction. The voltage of 26.06V repre‐ sented by the multimetter corresponds to the open-circuit voltage of the PEM.

The experimental results corresponding to the output voltage and current, the PI controller and the resonant current, are presented in this section to validate experimentally the SRC in its stability and dynamics.

**Figure 27.** Experimental setup of the system.

#### **5.1. Output voltage and current**

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).

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

in the two figures below.

**Figure 29.** PI Control.

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

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

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

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(a) Step-up load condition.

(b) Step-down load condition.

(a) Step-up load condition.

(b) Step-down load condition.
