# Class E Chopper Operation

### Class E Chopper Operation:

In our previous posts, we have seen the basics of chopper, various types of choppers based on their working like Class-A, Class-B, Class-C, Class-D....

#### How Type E Chopper Works?

In this post, we will discuss about the Type E chopper working principle. It is a four quadrant chopper (ie, it operates in all 4 quadrants of the vO-iO plane shown below. The load current and load voltage can be both positive and negative.
Remember the following points:

1. Positive Load Current = Current flows from source to load
2. Negative Load Current = Current flows from load to source
3. When the chopper operates in the first and third quadrants, the motor receives energy and the motor operates in the driver mode.
4. When the motor operation is in second and fourth quadrant power is fed back to the supply and the motor operates in braking mode.

The four quadrant operation of class E chopper system can be achieved by means of two quadrant
choppers connected as shown in the below figure.
In class E chopper the load is active (ie, Motor load). The motor's direction of rotation can be reversed without reversing the polarity of its excitation.

In the circuit diagram, T1, T2, D4 and D3 constitute chopper-1 and chopper-2 consists of T4,T3, D1 and D2.

#### First Quadrant operation:

• In first quadrant forward motoring or rectifying operation will happen.
• Here switch (SCRs) T1 and T2 are turned ON.
• Now the voltage across the motor V0 = VS = supply voltage and load current IO starts to flow.
• Now both VO and IO are in positive direction.
• The load consumes the power from the source.
• When SCR T1 is turned OFF, the load current Io freewheels through T2, D4 as shown below figure.
• Inductance L stores energy during the time T2 is ON.
• Thus both VO and IO controlled to be in positive and thus in first quadrant.

#### Fourth Quadrant Operation:

• When the SCR T2 is turned off, the inductance forces the current through D3 and D4.
• This current flows through the supply Vs. ie, the energy is fed back to the supply.
• Note that at this moment, the (Vo=Ldi/dt) is more than the supply voltage Vs.
• Here load voltage is negative but load current is positive leading to the chopper operation in the fourth quadrant.

#### Third Quadrant Operation:

• To reverse the direction of rotation of the motor, T3 and T4 are turned ON.
• Polarity of load voltage VO reverses and the current flow is also reversed.
• Therefore the operation is in the third quadrant

Now the T3 is turned OFF, but T4 remains ON.
To maintain the current in the same direction inductance generates voltage and iO flows in the same direction through D2 and T4( freewheeling).
With T4 ON reverse current flows through L,T4, D2.
Inductance L stores energy during the time T4 is ON.

#### Second Quadrant Operation:

• When T4 is turned OFF, the inductance forces load current through D1 and D2.
• This current flows through supply. Because (VO = Ldi/dt) is more than the supply voltage VS.
• So energy is fed back to the supply.
• As load voltage VO is positive and Load current IO is negative, it is second quadrant operation of chopper.

Thanks for reading about Class E operation / Type E chopper working principle....

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