Power conditioners

Although a fuel cell produces electricity, a fuel cell power system requires the integration of many components beyond the fuel cell stack itself, for the fuel cell will produce only dc power and utilize only processed fuel. Various system components are incorporated into a power system to allow operation with conventional fuels, to tie into the ac power grid, and often, to utilize rejected heat to achieve high efficiency. In a rudimentary form, fuel cell power systems consist of a fuel processor, fuel cell power section, power conditioner, and potentially a cogeneration or bottoming cycle to utilize the rejected heat. A simple schematic of these basic systems and their interconnections is presented in Figure 9-1. 

The cell and stacks that compose the power section have been discussed extensively in the previous sections of this handbook. Section 9.1 addresses system processes such as fuel processors, rejected heat utilization, the power conditioner, and equipment performance guidelines. System optimization issues are addressed in Section 9.2. System design examples for present day and future applications are presented in Sections 9.3 and 9.4 respectively. Section 9.5 discusses research and development areas that are required for the future system designs to be developed. Section 9.5 presents some advanced fuel cell network designs, and Section 9.6 introduces hybrid systems that combine fuel cells with other generating technologies in integrated systems. 

This section starts by examining the fuel cell unit operation, and continues on to the fuel processors and power conditioners. Other more common unit operations, such as pumps and heat exchangers, will be left to the reader to investigate with the help of standard engineering handbooks. 

Like a battery, a fuel cell produces direct current (DC). However, fuel cells come in a complete package in which the fuel cell stack is integrated with an inverter to convert DC to alternating current and a reformer to provide the hydrogen-rich fuel. Thus, a complete fuel cell system includes a fuel reformer, a fuel cell stack, and a power conditioner. A 200-kW PAFC unit by United Technologies Company is illustrated in Fig. 7. 

The power conditioner was an 18-pulse, stepped-wave, gate-turn-off thyristor (GTO) converter manufactured by GE. It was capable of four-quadrant operation, i.e., it was bi-directional and VAR capable. It was configured with three, six-pulse converters which were connected in series on the a.c. side and in parallel on the d.c. side. It was rated at 10 MW, and the input window voltage was rated 1750 Vdc to 2800 Vdc. A Westinghouse monitoring and control system provided the BESS with a highly automated supervisory control and data-acquisition capability [18,19]. 

The power-conditioning system was built by GE and consists of paired, six-pulse converters that form a 12-pulse converter module, and three of these are paralleled to achieve the required power rating. The switches are GTO thyristors. The power conditioner incorporates harmonic filtering and provides for four-quadrant operation, i.e., the equipment is bi-directional and provides VAR control [21,22]. 

All power sources, earthing requirements and power conditioners required by computer hardware. This includes protection and emergency devices such as surge suppressors and uninterruptible power supplies (UPS). 

FIGURE 10.140 Installation details for a computer-room UPS power conditioner. 

FIGURE 10.172 Interior view of a high-capacity hybrid power conditioner. (Courtesy of Control Concepts.) Active Power Line Conditioner... 

Figure 8-12 Fuel cell power conditioner control system for powering dedicated loads...

Unintentional islanding the fuel cell power conditioner must detect islanding and cease to energize the area electric power system within 2 seconds of the formation of an island. 

Corrective measures for limiting fuel cell ripple current The following corrective measures are suggested for limiting the fuel cell ripple current (especially for power conditioners with single phase AC output) ... 

Uninterruptible Power Supplies Power Conditioner for Critical Equipment, David C. Griffith... 

Therefore, the DC output from the stack is 0.442 259 = 114.5 kW. Let us take a reasonable figure for the efficiency of a state-of-the-art power conditioner of 95%, which means that the alternating current (AC) power from the stack is 114.5 0.95 = 109.8 kW. 

A power conditioner that converts the output from the power section to the type of power and quality required by the application. This subsystem could range from a simple voltage control to a sophisticated device that converts the DC power to an AC power output. 

Power Conditioner. A fuel cell produces DC power that must be converted to AC. The power conditioning section also reduces voltage spikes and harmonic distortions. 

In the following sections, system components such as fuel processors, heat management, and utilization the power conditioner units and auxiliary equipment are introduced. 

---