1) A hydrogen fuel cell is used as the source of a 120V/60Hz/2kW emergency AC power supply. The system consists of a Horizon H2000, a single-phase full-bridge inverter, a step-up transformer and an LC low pass filter as shown in the figure below. The plots of the output voltage and power as a function of the output current of the fuel cell are shown below. The fuel cell rated voltage is 28.8 V and its rated current is 70 A, for a total of 2016 W. Note that the voltage of the fuel cell varies with the output current and power. It decreases as the output power and current increase. A) Compute the turns ratio of the transformer for the fuel cell operating at the rated condition/power with the inverter operating with an amplitude modulation ratio (m) of 1. B) Calculate the value of ma when the load demanded from the AC power supply is null. Hint: Assume that the output voltage of the fuel cell at no-load (output current is zero) is 43 V. C) Compute the resonant, or cut-off, frequency of the second order LPF so that the magnitude of the dominant voltage harmonic across the load is 5% of the fundamental component. Assume that the inverter operates with unipolar SPWM with a triangular carrier of 900 Hz. + Vfc A + Vpri JZ JZ + Vsec + Vo Lf O + Cf Vo M > 50 45 40 35 30 25 20 15 10 5 0 2500 2000 1500 1000 500 0 0 0 10 10 20 20 30 30 H2000 U-I Curve 40 50 H2000 U-1 Curve H2000 P-I Curve 40 50 H2000 P-I Curve 60 60 70 70 80 80 90 A 90 A