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Grid-Connected Systems
Published in Mukund R. Patel, Omid Beik, Wind and Solar Power Systems, 2021
Both the wind and PV systems interface the grid at the output terminals of a synchronizing breaker after the inverter. The power flows in either direction depending on the site voltage at the breaker terminals. The fundamental requirements on the site voltage for interfacing with the grid are as follows:The voltage magnitude and phase must equal that required for the desired magnitude and direction of the power flow. The voltage is controlled by the transformer turn ratio or the power electronic converter firing angle in a closed-loop control system.The frequency must be exactly equal to that of the grid or else the system will not work. To meet the exacting frequency requirement, the only effective means is to use the utility frequency as the inverter switching frequency reference.In the wind system, the base-load synchronous generators in the grid provide the magnetizing current for the induction generator.
Controlling Prime Movers
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
An isolated prime mover generator can operate in isochronous mode, changing speeds only temporarily in response to changes in load. The system can also operate in droop if a lower speed is permissible under loaded conditions. If, however, the generator is connected to an electric grid, the grid will determine the frequency. Should the governor speed reference be less than the utility frequency, power in the utility bus will flow to the generator and motor the unit. If the governor speed is even fractionally higher than the frequency of a utility bus, load will go to maximum in a futile attempt to increase the bus speed.
Transmission Photoplethysmograph
Published in Mesut Sahin, Howard Fidel, Raquel Perez-Castillejos, Instrumentation Handbook for Biomedical Engineers, 2020
Mesut Sahin, Howard Fidel, Raquel Perez-Castillejos
How many decades are there between the cutoff frequency of the circuit in Figure 8.3 and the frequency of the power line (also known as utility frequency)? Hint: a first-order filter does not have a very sharp transition band and thus a high-pass filter with a corner frequency that is much higher than 60 Hz may still pass signals at the power line frequency.
New DC Hybrid Filter for Attenuating Low-Frequency Ripple of AC-DC Power Converter
Published in Electric Power Components and Systems, 2019
Jinn-Chang Wu, Hurng-Liahng Jou, Tse-Yu Lin
In order to overcome the problem of using large electrolytic capacitors in single-phase AC-DC power converter, the active decoupling circuit is developed. The active decoupling circuit can be divided into series type [8], parallel type [9–14], and integrated type [15–17]. The series type active decoupling circuit is configured by inserting a power converter between the AC-DC power converter and the DC load. In the series type active decoupling circuit, the power converter generates a voltage to eliminate the twice-utility-frequency ripple of output voltage such that outputting a ripple-free DC voltage by using a small film capacitor. Since the twice-utility-frequency ripple of output voltage is significant, the controller of AC-DC power converter is critical. In addition, the twice-utility-frequency ripple is an AC voltage, and the power converter should be a full-bridge structure. In the parallel type active decoupling circuit, a power converter is connected to the output of AC-DC power converter in parallel. The power converter generates a pulsating power of twice-utility frequency and thus attenuates the twice-utility-frequency ripple of output voltage. The electrolytic capacitor is replaced by a high-voltage film capacitor in the DC bus of AC-DC power converter for the parallel type active decoupling circuit. However, the voltage stress of power converter is large and thus results in higher power loss. In addition, the current control of power converter is critical. The integrated type active decoupling circuit combines the function of decoupling circuit into the AC-DC power converter. Although the power circuit seems to be simplified, the diodes of AC-DC power converter should be replaced by power electronic switches. In addition, the power rating of power electronic switches is increased and the control circuit is complex.