Semiconductor switches

Semiconductor switches. 3. Switching power supplies. I. Title. 

Voltage peaks also arise from the semiconductors switching in the inverter stressing the insulation of connected motors. For this reason, motors intended for inverter operation are better insulated. Sometimes - depending on the length of the motor cable - output filters are provided between the frequency converter and the motor to protect the latter. Such measures should be undertaken when standard motors used initially at constant speed on the mains are retrofitted with an inverter for variable drive. 

Another alternative starting aid is the softstarter. In a softstart, starting current is limited by semiconductor switches via phase control. Since the softstart is also bridged following startup, it does not have to be configured for full power. 

A-Si H memory switches do not have counterparts in standard crystalline semiconductor technology, unlike the sensors, TFTs and LEDs. However, amorphous semiconductor switching devices have a... 

McGinness J., Corry P. and Proctor P. (1974), Amorphous semiconductor switching in melanins , Science 183, 853-855. 

Before 1990s, thyristors and transistors were used as power modules for AC drive systems. Since then other semiconductor switching power modules have been used, such as GTO, MOSFETs, IGBTs, and combination of them. Nowadays IGBT and MCT-based inverters are used by electric drives manufacturers for the electric car market. The key characteristics of the different types of technology used for power electronic component are reported in Table 5.1. However, other power switching modules are currently under development [12]. 

We mentioned that all semiconductor switches suffer losses. Despite their advantages, they are certainly not the perfect or ideal switches we may have imagined them to be at first sight. 

As indicated previously, a real-world semiconductor switch can also be considered as having a parasitic resistance strapped across it. This parallel resistor in effect models the leakage current path, and thus the leakage loss term. Similarly, the forward drop across the device can also, in a sense, be thought of as a series parasitic resistance — leading to a conduction loss term. 

Now, had we taken a semiconductor switch instead of a mechanical one, we would have had a non-zero forward voltage drop, of say Vsw. This forward drop effectively just subtracts from the applied dc input during the on-time. So, had we done the above calculations symbolically, we would get... 

This concept of information is similar to the memory of a computer, which is made up of small semiconductor switches, each of which has two positions—on and off. The ability of computers to do an ever-increasing number of tasks depends on the ability of engineers to design chips that have more and more switches in a small space. Similarly, the ability of cells to do so many biochemical tasks depends on the large number of DNA nucleotides in the small space of the chromosomes. 

Schwarze, G. E. Frasca, A. J. 1990. Neutron and gamma irradiation effects on power semiconductor switches, NASA Technical Memorandum, 103200. 

McGinness J, Cony P, Proctor P (1974) Amtaphous Semiconductor Switching in... 

Switching devices, e.g. semiconductor switches in power electronic systems that are explicitly represented by a component model can be more easily identified in a bond graph in comparison to a representation that accounts for switches by controlled junctions. An initial not simplified bond graph is more close to a system schematic (cf. Chap. 4, Figs.4.2 and 4.3). 

Semiconductor switches in power electronic inverters are commonly made up of a transistor together with a diode in anti-paraUel connection as depicted in Fig. 2.13a for a bipolar transistor to provide a path for an inductive load current when conducting switches are turned off and thus to avoid damage of the transistors in an inverter. MOSFET transistors have a built-in diode. Figure2.13b shows a bond graph model of such a transistor-diode pair. 

Figure4.2 shows a diagnostic bond graph (DBG) of the switched network in Fig.4.1 with the semiconductor switch explicitly modelled by an element Sw b, i.e. an MTF-R pair.

In comparison to the BG in Fig.4.2, the BG in Fig.4.3 reproduced from [9] does not reflect the series connection of a resistor and a semiconductor switch. The latter one is not explicitly visible in the BG. Additional information must be known that junction I3 is a controlled junction. Moreover, detectors are not in inverted causality although sensors deliver a measured and thus known variable into a DBG. Also note that an auxiliary resistor R Rs2 is needed to determine the effort at junction O4. 

The decomposition of the system matrix A into a matrix A with nominal parameters and a matrix AA accounting for parameter changes is illustrated for the example network with one semiconductor switch and the previously considered abrupt change of resistance at f = 2s. 

Example Simple Network with a Semiconductor Switch... 

The current system mode of a healthy system can be identified by evaluating all ARRs for all feasible switch state combinations. This may require considerable computational effort. The computational time, however, can be reduced by distributing the task on multiple parallel processors. Moreover, this task is only necessary if an initial system mode is not known or if the last known system mode is no longer valid because rapid system modes have taken place while system mode identification is still in progress. Once the current system mode is known, the all-mode FSM can be consulted to identify a subset of ARRs that is to be evaluated to identify the new current system. This has been illustrated by application to a simple circuit with three semiconductor switches. 

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