*5.3. LLC Converter Fed by Solar Panel*

An LLC converter powered directly with a solar panel is not preferred. On one hand, as the irradiance decreases, the maximum power that can be extracted from the solar panel also decreases. As the maximum power decreases, the voltage of the solar panel decreases. If the load is still constant, more current flows from the solar panel to the converter. This event is still well handled by the PID controller (Figure 13a). Sudden high-power consumption can cause the solar panel to reach its maximum current. In this case, the voltage of the solar panel is greatly reduced (below 25 V). This is handled by the PID controller by setting the frequency for maximum gain, however, the output voltage does not reach the setpoint. Once the overload has ceased, the output voltage stabilizes rapidly (Figure 13b). It is also possible to observe that the input current oscillates slightly under constant load. This is because the PID controller never controls the inverter with one frequency value, as the controllers also have oscillations. The oscillation amplitude depends on the value of the maximum power that can be extracted from the solar panel, so it depends on the irradiance. The oscillation of the PID controller changes the load on the solar panel, so the input voltage also changes.

### *5.4. LLC Converter Fed by Batteries and Solar Panel*

The measurement of the battery-powered LLC converter is shown in Figure 14. In the figure on the left, the motor torque changes only slightly, while in the figure on the right, it changes suddenly. In the case of measurement, Figure 14a, the output voltage varied to a lesser extent than in the case of solar power supply, because at high input current, the battery terminal voltage decreases only slightly. This allows the PID controller to hold the output voltage more stably. Furthermore, in the event of an overload, the voltage will not drop due to battery power as in the case of solar power, as shown in Figure 14b. The output voltage decreases greatly under dynamic load because the output filter capacitor is slightly discharged. When the output voltage exceeds 390 V, the converter is off. If the induction motor is started without a soft start, the output voltage can be greatly reduced. In this case, the PID controller needs more time to charge the output capacitor to the setpoint. Once the converter is turned on, it responds more quickly to dynamic loads. A decrease in output voltage will have a negligible effect on motor operation. In this case, the motor voltage also

decreases, with the result that the flux and, thus, the torque also decrease. A large drop in output voltage can be avoided if the motor is started softly and no mechanical load occurs instantaneously as shown in Figure 14a.

**Figure 13.** LLC converter fed by solar panel: (**a**) irradiance slightly decreasing; (**b**) solar panel overloaded operating condition.

**Figure 14.** LLC converter fed by batteries: (**a**) the torque changes slowly; (**b**) the torque changes suddenly.
