Alternative Solutions to Thyristors in Three Phase Rectifier Bridges - With Inductive Load
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Thyristor bridge rectifiers are probably the rectifier topology that aremost used in applications where control of the DC voltage is needed. Inaddition to the fact that thyristors beginning to get yesterdays technology,they also generate a lot of unwanted harmonic distortion on the AC side,and the time is in to look at other topologies that can replace the thyristorbridge.IGBT (Insulated Gate Bipolar Transistor)is a power electronic componentwhich has become popular to use in many applications the lastyears, also in rectifiers. Thus the IGBT has become a popular component,it is less used in high power applications such as controlled three phaserectifiers. This thesis are looking at three different rectifier topologies, onetraditional thyristor bridge rectifier, and two with IGBTs. Comparisonbetween the three rectifiers are done, with pros and cons for each of them.To verify the theory, each topology has been simulated in Simulink.The first topology which is proposed to replace the thyristor bridge is adiode bridge rectifier with a H IGBT-bridge across the load. This topologywas investigated in the pre project of this author the last semester. Thenew topology that has been proposed in this thesis is a rectifier bridgeconsisting of six RB-IGBT (reverse blocking IGBT), controlled with aSPWM signal (sinusoidal pulse width modulation).The greatest advantage with the IGBTs is that they can be switchedon and off in milliseconds, independent of the voltage polarity. By usingSPWM control of the IGBT rectifier, sinusoidal current draw from thesource are possible. If this is achieved, the harmonic distortion in thesource will be minimal. The simulations of this topology shows that theresponses to changes in load voltage are equal to the responses with thediode and thyristor bridges. The source harmonics are significantly lesswith the IGBT rectifier. To verify the work and simulations done in thisthesis a physical model of the system should be made and tested.