Introduction

The following topics are covered in this lecture:

•  First and Second Quadrant Converter

•  Four Quadrant Chopper

 

First and Fourth Quadrant Converter

In Figure 1a the configuration of two quandrant converter capable of operating in first and fourth quadrants is shown. Both the switches S₁ and S₂ are turned on for a duration t = 0 to t = T₁(Figure 1b) and off for a duration t = T₁ to t = T . The instantaneous output voltage appearing across the load is:

                                                                                             (1)

When the switches S₁ and S₂ are turned off , the current throught the inductor L continues to flow in the same direction, making the diodes D₁ and D₂ conduct thus feeding the load energy back to the dc source (Figure 1c). The average load voltage is obtained as

                                          (2)

From equation 2 it can be seen that for , is positive and the current flows from the DC source to load. Both the average load voltage and load current I_o being positive, the operation of the converter is in first quadrant (Figure 1d). When , is negative but I_o is positive and the converter operates in fourth quadrant (Figure 1e).

Figure 1a: First and Fourth quadrant converter	Figure 1b: When switches are on (First quadrant operation)
Figure 1c: When freewheeling diodes operate (Fourth quadrant operation)