Second Quadrant Chopper or Type B Chopper or Class B Chopper

In this topic, you study Second Quadrant Chopper or Type B Chopper or Class B Chopper v-i plane, working principle, quadrant operation, Applications, waveforms, and Circuit diagrams. 

Type B chopper is basically equivalent to Step-Up Chopper.

Circuit Diagram

The Type B chopper circuit diagram as shown in Figure 1. Here the motor load is assumed, R_a and L_a armature resistance and inductance of the motor respectively. E_b is the back emf of the motor.

v_O – i_O plane

The Type B chopper operates in the Second quadrant of v_O – i_O plane as shown in Figure 2. Here v_O is the output voltage, V_O is the average output voltage, i_O is the output current and I_O is the average output current of Type B chopper circuit.

Quadrant II operation when Switch S₁ turned on

The Type B chopper circuit diagram for Quadrant II is shown in Figure 3 and the associated waveforms are shown below in Figure 5. Let us assume that the motor is running in the forward direction. When switch S₁ operated, Switch S₁ turned on and conducts, output voltage v_O is zero and E_b is responsible for the negative output current i_O, the machine behaves as generator and inductor stores energy.

Quadrant II operation when Switch S₁ turned off

The Type E chopper equivalent circuit diagram for Quadrant II is shown in Figure 4 and the associated waveforms are below shown in Figure 5. Switch S₁ turned off, diode FD conducts, output voltage v_O becomes positive and the output current i_O is negative, inductor release energy using diode FD, power flows from load to source and hence called as reverse braking.

Waveforms

Type B chopper associated waveforms are shown in Figure 5.

Application

This chopper is suitable for regenerative breaking application only.

Mathematical Analysis

Using the waveform as shown in Figure 1,  The average output voltage write as

\[{V_O} = {V_S}\left( {\frac{{{T_{OFF}}}}{T}} \right)….(1)\]

Also

\[\frac{{{T_{OFF}}}}{T} = 1 – \alpha ….(2)\]

Put Equation 2 in Equation 1 gives

\[{V_O} = {V_S}(1 – \alpha )….(3)\]

Equation 3 describe the realtion between input dc source voltage and average output voltage for Type B chopper.