Zimmar Physics Accelarator Notes-259.pdf - The H-bridge...

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The H-bridge topology allows to operate in the 4-quadrant. When the magnet gives back its energy, the return energy can be dissipate in a brake chopper or store in the capacitor bank of the DC-link. Another possibility is to replace the diode rectifier by an active front end done with IGBT. In this case, the energy can return to the grid. The main advantage of this topology is to use IGBT semiconductor which are widely pro- duced at low price. They can be easily controlled with PWM (pulse-width modulation) technique at a switching frequency above few kHz which helps to reduce the current ripple and improve the feed- back loop performance. The IGBT rating starts from 600 V up to 6.5 kV and from 50 A to 3 kA which allows covering a large scale of the needs. Switch-mode power converter with high fre- quency transformer One of the main interests of using a high frequency transformer is to reduce the volume of the power converters. Ferrite cores are widely produced which allow using high fre- quency transformer at a competitive price. A clas- sical topology can be found in Fig.5. Figure 5: Switch-mode power converter with high fre- quency transformer. The diode bridge is directly connected to the grids. An inverter drives a high frequency trans- former. A diode bridge is connected at the out- put of the secondaries of the transformer to obtain a DC voltage to apply to the magnet. This type of power converter operates only in one-quadrant. 4-quadrant operation can be obtained by adding another stage but the return energy has to be dis- sipated at this level (Fig.6), [3].

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