In four-quadrant choppers, not only can the output current be positive and negative, but the output
voltage also can be positive and negative. These choppers are full-bridge DC-DC converters, as is shown
in Fig. 2.11. The main advantage of these converters is that the average of the output voltage can be
controlled in magnitude as well as in polarity. A four-quadrant chopper is a combination of two twoquadrant choppers in order to achieve negative average output voltage and/or negative average output
current.
The four-quadrant operation of the full-bridge DC-DC converter, as shown in Fig. 2.12, for the first
two quadrants of the (v–i) plane is achieved by switching S1
and S2
and considering D1
and D2like a
two-quadrant chopper. For the other two quadrants of the (v–i) plane, the operation is achieved by
switching S3
and S4
and considering D3
and D4as another two-quadrant chopper, which is connected to
the load in the opposite direction of the first two-quadrant chopper.