Also, when a FC DG is connected to the grid, the amplitude (after applying a transformer), frequency, and phase angle of its voltage and the grid must be exactly equal, and these prerequisites are met simply by the inverter. Therefore, the output voltage, real and reactive power, frequency, and phase angle of the system can be adjusted by the parameters of the inverter. This action is done by adjusting the firing angle of the inverter. Also, as evaluated in the Example 5.6, drawing or injecting the desirable reactive power from the FC DG can be met by adjusting the output voltage amplitude.Īnother parameter in Example 5.6 which is set for injecting enough real power to the grid, is the phase angle ( δ) of the FC voltage with respect to the load voltage.
(5.51), the amplitude of the output voltage can be regulated by adjusting modulation index. When the FC system is under a heavy load as in Example 5.6, if the hydrogen flow rate is constant, the FC output voltage will be decreased. Circuit model of a three-phase six-switch PWM VSI. The harmonic components are merely shifted into the higher frequency range and are automatically filtered due to inductances in the AC system.įig. Notice that the root mean square value of the ac voltage waveform is still equal to the DC bus voltage, and hence the THD is not affected by the PWM process. The resulting chopped square waveform contains a replica of the desired waveform in its low-frequency components, with the higher-frequency components being at frequencies of a close to the carrier frequency. Note that over the period of one triangle wave, the average voltage applied to the load is proportional to the amplitude of the signal (assumed constant) during this period. Depending on whether the signal voltage is larger or smaller than the carrier waveform, either the positive or negative DC bus voltage is applied at the output. In the most straightforward implementation, generation of the desired output voltage is achieved by comparing the desired reference waveform (modulating signal) with a high-frequency triangular “carrier” wave as depicted schematically in Fig. 4.35.
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