# What Is a 2 Quadrant Drive?

Written by bert markgraf
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Two quadrant drive motor operation can be shown on a graph where speed is plotted on the horizontal axis and torque on the vertical axis. The most common operation is in quadrant one with forward speed and forward torque driving a load. The drive can make the motor operate in two quadrants if it can either make the motor reverse its speed to drive a load in the opposite direction or reverse the torque to apply braking to the load while the motor rotates in the forward direction. The terminology originated with DC motors, but is now often used for AC drives as well.

The simplest operation for a motor is for the drive to apply power so that the motor develops a forward torque, which drives the rotation of a load. To stop, power from the drive is reduced to zero and the load causes the motor to coast to a stop.

The simplest two quadrant drive powers a DC motor in single quadrant operation, but has an additional switch or contact to reverse the DC motor's field. This means that the drive can operate the motor in the forward direction or, with the field reversed, drive the motor in the reverse direction. In both cases, motor torque acts in the direction of the motor speed.

If reverse operation of the motor is not needed, the drive can still operate in two quadrants by adding regenerative braking. Operation in the braking quadrants means the drive must have a second rectifier bridge to conduct power back into the grid. In this case, operation in quadrant one is as before but, to stop the motor, torque is applied in the direction opposite to the speed, slowing the motor down and returning power to the grid. This type of two quadrant operation makes sense if the value of the power returned to the grid is greater than the cost of the additional rectifier bridge.

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