Selection of Ratings of Devices of a Chopper Converter: Chopper Converter – The waveforms of currents and voltages are useful in deciding the ratings of devices. The main thyristor carries the load current. Superimposed on this there is a current pulse during the recharging process of the capacitor through the resonating circuit. Therefore the peak …
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Two Quadrant Chopper: Sometimes a chopper may be required to provide a two quadrant operation by retaining the current direction in both motoring and braking modes. Such a Two Quadrant Chopper is shown in Fig. 3.86, and its waveforms in Fig. 3.87. The chopper permits a change in the polarity of terminal voltage keeping the …
Regenerative Braking: Sometimes the energy of the load may have to be fed to the supply system. A Chopper in this mode is called regenerative. The chopper working as a switch is connected across the load, which is normally a dc machine and the diode is connected in the line. The dc machine works as …
Methods of Controlling Chopper Circuit: The basic principle of control of a Chopper Circuit is the effective change of the value of the time ratio. This is done in two ways: 1.Time ratio control 2.Current limit control In the former, the ratio TON/T is varied. This can be achieved by varying TON, keeping the chopper …
Performance of Chopper in Steady State Condition: Assuming Steady State Condition of the chopper, we have during TON The solution of Eq. 3.89 is where Io is the current at the starting of TON. At TON = aT, the current is when the thyristor is OFF, free wheeling takes place and the operation is described …
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Chopper Circuit with Input Inductance: The preceding discussion of the chopper assumes ideal conditions and does not consider the effects of inductances in series with the thyristors. With choppers of large power, the leads connecting the Chopper Circuit to the supply have a definite amount of inductance (Le). Also, reactors are placed in series with …
DC Chopper: DC Chopper are mainly dc to dc single stage conversion devices which provide a variable voltage on the load side when fed from a constant dc voltage source. The commutation of the current from the thyristors cannot be achieved by means of supply voltage. The necessary reactive power for the converter must be …
Four Quadrants Converters: Four Quadrants Converters – The converters described in the previous sections are suitable either for one quadrant or two quadrant operation. In the former case stepless speed control is possible by changing the applied voltage. There is no regeneration. In the latter case both speed control and regeneration are possible. The converter …
Sequence control of Converters: Sequence control of Converters – We have shown that fully controlled converters take lagging reactive power from the mains. This requirement is less in half controlled converters and converters with a freewheeling diode, which however do not provide the process of inversion. In both cases the reactive power requirement increases as …
Three pulse converter with freewheeling diode: A Three pulse converter with freewheeling diode across the load terminals is depicted in Fig. 3.56. The diode is meant to provide an alternative path for the load current, which would otherwise have flown through the converter. The diode becomes positively biased when the load voltage becomes negative, and …