Voltage requirements, electric motors

The centrifugal pump directly driven by a variable-speed electric motor is the most commonly used hardware comoination for adjustable speed pumping. The motor is operated by an electronic-motor speed controller whose function is to generate the voltage or current waveform required by the motor to make the speed of the motor track the input command input signal from the process controller. 

Motive power batteries are generally of higher quality than SLI batteries. Their most important characteristics are constant output voltage, high volumetric capacity at relatively low unit cost, good resistance to vibration and a long service life. Since electric motors used for motive power require... 

Most electronic equipment shares the television set s need for a number of differing voltages for the operation of individual components. This alone may be sufficient justification for the inclusion of a direct current to alternating current converter in fuel cell power systems. In addition, alternating current electric motors are more suitable in most applications. They tend to operate at a rotational speed controlled by the frequency of the current. If completely unloaded they speed up to this fixed velocity and accelerate no further. Many types of direct current motors, if operated unloaded, will continue to accelerate until they fail. A belt driven fan operated by an alternating current motor is undamaged by the failure of the belt. A direct current motor will require a special safety circuit to shut it down in case of belt failure. If the belt and the safety circuit both fail, the motor will speed up until it destroys itself. 

The stack output voltage ranges from 34 V at open circuit to 22 V at full load, while the electric motor is supplied at 48 V DC. For this reason, a DC-DC converter (see Sect. 5.2) is used to match the stack output voltage with that required by the engine. In Table 6.3, the technical specifications of the DC-DC converter are shown. 

Electrical power (AC of normal voltage and of voltage required by industrial motors e.g., 110-440V in the United States)... 

The required oxygen for proper function of the fuel cell stack is provided by an air module, which depending on requested power, provides the optimal air pressure and air flow. The main component of the air system is the compressor, which is mechanically driven from a high voltage electric motor. 

There are two fuel cell systems coimected in parallel. The electric motor used as the aircraft propulsion system is an AC brushless external rotor type. It can be operated within a voltage range between 210 and 330 V. If the upper limit of the cell voltage is set to 0.7 V, the total number of cells should be 834. Although MEAs can be customized from an economical perspective, an off-the-shelf product is favored. An MEA with 165 cm, which is commercially available, is adequate for cases 2, 3, and 4 in Table 23.4. The required power during takeoff is also estimated based on operational experience with the aircraft Antares DLR H2 and is believed to be 40 kW. Within the lower voltage limit of the motor, this power can be reached with 960 cells... 

The most frequently used starter systems are electric motors and air starters. The electric starters are usually 12- or 24-V dc cranking motors. The higher voltage is preferred on larger engines because of the high power required for annunciator controls and/or power circuit-... 

These may be used to feed the solenoid or the motor of an interrupting device (such as an electrically operated breaker), indicating lights and circuits, auxiliary contactors or relays, electrical or electronic timers, hooters or buzzers, and all such auxiliary components and devices mounted on a controlgear or a switchgear assembly requiring a specified control voltage. 

AC electric drives require more sophisticated converters when they are supplied with DC sources, because electric machines requires periodic voltage and current waves with a variable frequency depending on the load requirements. In Fig. 5.8, the scheme of an example of three-phase induction motor driven by a pulse-width-modulated inverter is reported. In this scheme a three-phase bridge connection with six power modules is shown to form the so-called inverter. Each power module can be composed by a number of power switches connected in parallel to carry higher currents. Across each power switch (IGBT) a parallel diode is connected to provide a return path for the phase current when the power module is switched off. 

In Fig. 5.20, the scheme for the configuration of a solar vehicle is reported. The DC-DC converter is required to adapt the voltage generated by the solar system to the voltage range proper of battery pack and electric drive. The converter is mono-directional because no energy flux goes from the battery and motor drive toward the solar panel [3, 4]. 

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