68 Interconnection and Control 681 Power Conditioning

Power conditioning for a fuel cell power plant includes power consolidation, current control, direct current (DC) to alternating current (AC) inversion

FIGURE 6.7

Typical relationship between voltage and power for fuel cells.

FIGURE 6.7

Typical relationship between voltage and power for fuel cells.

(unless the application is DC), and stepping the voltage up through a transformer. In addition, power quality aspects such as maintaining consistent voltage and frequency with low harmonic distortion, as well as the transient response of the power conditioning equipment, should be considered. When connected to the utility grid, additional considerations may include interconnection equipment and switch-gear, synchronization, real power ramp rate, and reactive power (VAR) support capabilities.

An important aspect of power conditioning equipment is the efficiency of the power conversion and conditioning. These efficiencies vary widely with system design but are typically on the order of 94 to 98% (Hirschenhofer et al., 1998). Fuel cells can be used to supply DC to power systems such as DC-driven motors, batteries, UPS systems, solenoids, controls, electronic equipment, or other DC equipment. In fact, most of the consumer electronics equipment (e.g., televisions, stereos, telephones, video cameras, etc.) and all computers and computer-based equipment and controls use DC electricity. In most cases, this DC voltage is provided by a connection to an AC supply followed by conversion of the AC voltage to DC voltage in an AC-to-DC converting power supply. Even with the direct use of fuel cell DC current, quality power conditioning equipment is required to maintain voltage levels and accommodate fluctuations in desired current flow. This could be accomplished at much lower cost and higher efficiencies. Fuel cells offer the opportunity of direct use of DC electricity and the elimination of many of these power supplies and concomitant energy losses in the future. However, since current technologies are already designed to accommodate the AC electricity that is standard, most fuel cell systems are designed with inverters to convert DC current to AC electricity. The power conditioning system that is required includes the capability of delivering real power and reactive power to the user. The power conditioning system also usually includes the provision of power to the fuel cell system auxiliaries and controls.

Power conditioning equipment can be designed and constructed in many different manners and can include the use of solid-state inverters, voltage transformers, and controls. Typically, fuel cell operating parameters such as fuel flow rate and demanded electrical output must be controlled by the power conditioning equipment to maintain power quality. In addition, the power conditioning equipment and wiring are typically designed to withstand utility grid or user disturbances in voltage and current including voltage spikes, voltage shorts, and overcurrent disturbances.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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