Type-E four-quadrant chopper

A Type-E (Class-E) chopper is a four-quadrant chopper: it can give both polarities of average load voltage and both directions of load current. It uses four switches (CH1–CH4) with anti-parallel diodes (D1–D4) in a full-bridge arrangement, and is used to drive a dc motor in forward motoring, forward braking, reverse motoring and reverse braking.

       +  o-------+---------------+
                  |               |
            CH1 / D1        CH3 / D3
                  |    load       |
                  A---R--L--E-----B
                  |  (+vo, +io: A->B)
            CH2 / D2        CH4 / D4
                  |               |
       -  o-------+---------------+
 dc supply Vs between the + and - rails
 CH: switch;  D: anti-parallel diode
 E: back emf of the dc motor

           vo
            ^
  Q2        |        Q1
 (+vo,-io)  |   (+vo,+io)
 fwd brake  |   fwd motor
 -----------+-----------> io
  Q3        |        Q4
 (-vo,-io)  |   (-vo,+io)
 rev motor  |   rev brake

Quadrant I: forward motoring ($+v_o$, $+i_o$)

• CH4 is kept ON, CH2 and CH3 OFF; CH1 is chopped.
• CH1 ON: $V_s \to$ CH1 $\to$ A $\to$ load $\to$ B $\to$ CH4; $v_o = +V_s$, $i_o$ rises.
• CH1 OFF: current freewheels through CH4 and D2; $v_o = 0$.
• $V_o = DV_s$ (positive), power flows from source to motor. Works like a Type-A chopper.

Quadrant II: forward braking / regeneration ($+v_o$, $-i_o$)

• Motor emf $E$ is positive at A (machine running forward, the same polarity as in motoring); CH2 is chopped, others OFF.
• CH2 ON: $E$ drives current B $\to$ A (negative) through the load, CH2 and D4; energy is stored in L.
• CH2 OFF: the inductor emf adds to $E$ and current flows through D1, the source and D4, so $v_o = +V_s$ while $i_o$ is negative: energy is returned to the source. Works like a Type-B chopper.

Quadrant III: reverse motoring ($-v_o$, $-i_o$)

• CH2 is kept ON, CH1 and CH4 OFF; CH3 is chopped.
• CH3 ON: $V_s \to$ CH3 $\to$ B $\to$ load $\to$ A $\to$ CH2; $v_o = -V_s$, current negative.
• CH3 OFF: current freewheels through CH2 and D4; $v_o = 0$.
• The motor runs in the reverse direction.

Quadrant IV: reverse braking ($-v_o$, $+i_o$)

• Motor emf is now positive at B (machine running in reverse); CH4 is chopped, others OFF.
• CH4 ON: $E$ drives current A $\to$ B (positive) through the load, CH4 and D2; energy is stored in L.
• CH4 OFF: current flows through D3, the source and D2; $v_o = -V_s$ with $i_o$ positive, so power is fed back to the source.

Summary

Thus by choosing which switch is chopped and which is held ON, the Type-E chopper gives full speed and torque control of a dc motor in all four quadrants, including regenerative braking in both directions.