12-10-2012, 03:21 PM
I NEED advance power semiconductor devices ppt
12-10-2012, 03:21 PM
I NEED advance power semiconductor devices ppt
16-05-2013, 04:49 PM
Power Semiconductor Devices
Power Semiconductor.pdf (Size: 188.35 KB / Downloads: 72) Introduction This lesson provides the reader the following: (i) Create an awareness of the general nature of Power electronic equipment; (ii) Brief idea about topics of study involved, (iii) The key features of the principal Power Electronic Devices; (iv) An idea about which device to choose for a particular application. (v) A few issues like base drive and protection of PE devices and equipment common to most varieties. Power Electronics is the art of converting electrical energy from one form to another in an efficient, clean, compact, and robust manner for convenient utilisation. A passenger lift in a modern building equipped with a Variable-Voltage-Variable-Speed induction-machine drive offers a comfortable ride and stops exactly at the floor level. Behind the scene it consumes less power with reduced stresses on the motor and corruption of the utility mains. Power Electronics involves the study of • Power semiconductor devices - their physics, characteristics, drive requirements and their protection for optimum utilisation of their capacities, • Power converter topologies involving them, • Control strategies of the converters, • Digital, analogue and microelectronics involved, • Capacitive and magnetic energy storage elements, • Rotating and static electrical devices, • Quality of waveforms generated, • Electro Magnetic and Radio Frequency Interference, How is Power electronics distinct from linear electronics? It is not primarily in their power handling capacities. While power management IC's in mobile sets working on Power Electronic principles are meant to handle only a few milliwatts, large linear audio amplifiers are rated at a few thousand watts. The utilisation of the Bipolar junction transistor, Fig. 1.2 in the two types of amplifiers best symbolises the difference. In Power Electronics all devices are operated in the switching mode - either 'FULLY-ON' or 'FULLY-OFF' states. The linear amplifier concentrates on fidelity in signal amplification, requiring transistors to operate strictly in the linear (active) zone, Fig 1.3. Saturation and cutoff zones in the VCE - IC plane are avoided. In a Power electronic switching amplifier, only those areas in the VCE - IC plane which have been skirted above, are suitable. On-state dissipation is minimum if the device is in saturation (or quasi-saturation for optimising other losses). In the off-state also, losses are minimum if the BJT is reverse biased. A BJT switch will try to traverse the active zone as fast as possible to minimise switching losses. Power Semiconductor device - history Power electronics and converters utilizing them made a head start when the first device the Silicon Controlled Rectifier was proposed by Bell Labs and commercially produced by General Electric in the earlier fifties. The Mercury Arc Rectifiers were well in use by that time and the robust and compact SCR first started replacing it in the rectifiers and cycloconverters. The necessity arose of extending the application of the SCR beyond the line-commutated mode of action, which called for external measures to circumvent its turn-off incapability via its control terminals. Various turn-off schemes were proposed and their classification was suggested but it became increasingly obvious that a device with turn-off capability was desirable, which would permit it a wider application. The turn-off networks and aids were impractical at higher powers. Silicon Controlled Rectifier (SCR) The Silicon Controlled Rectifier is the most popular of the thyristor family of four layer regenerative devices. It is normally turned on by the application of a gate pulse when a forward bias voltage is present at the main terminals. However, being regenerative or 'latching', it cannot be turned off via the gate terminals specially at the extremely high amplification factor of the gate. There are two main types of SCR's. Converter grade or Phase Control thyristors These devices are the work horses of the Power Electronics. They are turned off by natural (line) commutation and are reverse biased at least for a few milliseconds subsequent to a conduction period. No fast switching feature is desired of these devices. They are available at voltage ratings in excess of 5 KV starting from about 50 V and current ratings of about 5 KA. The largest converters for HVDC transmission are built with series-parallel combination of these devices. Conduction voltages are device voltage rating dependent and range between 1.5 V (600V) to about 3.0 V (+5 KV). These devices are unsuitable for any 'forced-commutated' circuit requiring unwieldy large commutation components. |
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