Control and Power Electronics

DC machines are simpler and cheaper, because their speed regulation is based on scalar controls. For that reason they need simple electronic boards to control the DC electric drive operations. Moreover, they have the advantage that they can be fed by the DC supply already on board. On the other hand, the principal disadvantage is represented by the maintenance required, since for instance brushes need to be periodically checked and changed. Another point to take in consideration is that fuel cell electric vehicles equipped with brushed electric machines would require specific safety devices to avoid that sparks of the collector during the commutation might interact with the hydrogen used as fuel on board. 

Variable speed drives are generally based on a set of an electric machine driven by power electronic converters and controls, which are implemented in electronic cards. The whole system makes possible the speed regulation of the electric machine. 

In Fig. 5.7, the scheme of a generic DC electric drive supplied by a battery pack is shown, and it also represents the traction drive for a BEV. 

The DC-DC converter changes the electric characteristics of voltage and current supplied by the electric source in order to feed the electric machine and satisfy the load mechanic requirements. 

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. 

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Haake MARS Rheometer This is a modular instrument designed to allow all application assemblies, including the measuring head and electronics systems, to be interchanged. The main control and power electronics are separated from the instrument itself, thereby preventing thermal and mechanical interference from heat sources, fans, and other equipment. A variety of temperature control units are available to control temperatures from -150 C up to 600X. 

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