Thyristor Inverters

Gate control in case of thyristor inverters only. 

Fully controlled thyristor inverter in anti-parallel to feedback energy... 

A typical basic circuit is shown in Figure 14.3 which consists of two main parts, a three-phase bridge-connected thyristor rectifier and a three-phase bridge-connected thyristor inverter. 

Diode bridge rectifier (converter) Inverter unit IGBT or thyristor, depending upon the size of machine,... 

The use of SCRs in an inverter circuit is intricate because of the absence of a natural commutation. Now only a forced commutation is possible, as it is connected to a d.c. source which provides no current zeros and hence facilitates no natural commutation. A forced commutation calls for a separate switching circuit, which is cumbersome, besides adding to the cost. As a result of this feature, they are also called forced commutated thyristors. 

U.sliifi ihyrisior devices (GTOs) Thyristor (GTO) inverter circuits are used for higher ratings of machines than above and to contiol larger powers such as lor those for reactive power conli ol. 

Figure 6.26(a) Basic IGBT or thyristor (GTO) inverter unit... 

A power diode reetifier unit feeding a fixed d.e. power to an inverter unit to control an a.c. motor, or a thyristor rectifier unit, directly controlling a d.e. motor, both contain... 

A relatively new innovation for use in electric motor compressor drives is the variable frequency power source. Fundamentally, the power source converts an existing three-phase source into DC then uses an inverter to convert back to a variable frequency supply. Thyristors or transistors are used to switch the output at the required frequency. 

This same rotor-cap-thyristor approach can also be used in the inverter-diode-induction coil approach noted above as the triggering mechanism instead of using the traditional points. This approach would allow for the switching on and off of the inverter and coil circuits together and for a determined firing period or multiple periods. 

The above diagram is a modified GDI approach that uses the pulsed DG from the inverter to charge an electrolyte capacitor (G1) which is discharged through the thyristor when the circuit is opened by the distributor cap/rotor timing. 

Figure 3.16 Schematic diagram of a SiC gate turnoff thyristor-based, dc-ac inverter power stage.

Tipton, C. W., et al., Half-Bridge Inverter Using 4H-SiC Gate Turn-Off Thyristors, IEEE Electron Device Letters, Vol. 23, 2002, pp. 194-196. 

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]. 

Most power systems in the oil industry do not have variable speed drives and so the AC supply is a highly dependable and simple source of sinusoidal voltage and current. Little or no harmonics are present. If a large variable speed drive is required, and an inverter or thyristor controller of some form is used, then the combination of these equipments will cause harmonic currents to be drawn from the supply. 

A special AC power system is required that will contain thyristor controllers, inverters or the like, that will produce harmonics. 

In this group there are several systems that use power electronics to provide a variable magnitude voltage at a variable frequency. Most of the systems use rectifiers and thyristors in the form of converters and inverters. 

Thyristor rectifier-inverter for variable voltage and variable frequency. 

Thyristors used in rectifier and inverter bridges are usually of two types. The first type is a three-terminal semiconductor that can only be turned on by a control or firing signal applied to its... 

High-power inverters were initially developed for the long-distance transmission of power from a three-phase source to a remote three-phase sink using a DC overhead transmission line or cable. Early DC power transmission used mercury arc thyratrons (gas-filled values or tubes), which functioned in a manner very similar to the early types of thyristors. The on state of the valves was controllable, but the off state was determined by natural commutation made available by the sinusoidal voltages of the sink power system, see Reference 13. A brief description of three-phase inverters follows. 

FIGURE 10.70 A single-phase current-source inverter using thyristors. 

Figure 10.70 shows a single-phase CSI using thyristors. A three-phase version of this type of inverter is widely used in induction motor drives. 

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