Bridge converters are a type of power electronics circuit commonly used in electrical engineering applications. They are a type of AC/DC converter that can convert AC voltage into a DC voltage. A fully controlled bridge converter is a variant of the bridge converter that offers greater control over the output voltage.

In a fully controlled bridge converter, the four switches (usually thyristors) are used to control the flow of current through the load. By controlling the switching of these switches, the output voltage and current can be regulated. The converter operates by switching on and off the thyristors in a specific pattern, allowing current to flow through the load in the desired direction.

The operation of a fully controlled bridge converter can be divided into four quadrants, depending on the direction of the load current and the direction of the output voltage. These quadrants are:

1. Quadrant 1: In this quadrant, the load current is positive and the output voltage is positive. The thyristors in the converter are switched on in a specific pattern to allow current to flow from the input to the output, resulting in a positive output voltage.

2. Quadrant 2: In this quadrant, the load current is negative and the output voltage is positive. The thyristors in the converter are switched on in a different pattern to allow current to flow from the output to the input, resulting in a negative load current but still a positive output voltage.

3. Quadrant 3: In this quadrant, the load current is negative and the output voltage is negative. The thyristors in the converter are switched on in a different pattern to allow current to flow from the input to the output, resulting in a negative output voltage.

4. Quadrant 4: In this quadrant, the load current is positive and the output voltage is negative. The thyristors in the converter are switched on in a different pattern to allow current to flow from the output to the input, resulting in a positive load current but still a negative output voltage.

By operating in all four quadrants, a fully controlled bridge converter can regulate the output voltage and current in both positive and negative directions, making it a versatile and powerful device in electrical engineering applications.

In conclusion, a fully controlled bridge converter can operate in all four quadrants, allowing for the control of both positive and negative output voltages and load currents.

Introduction:
A fully controlled bridge converter is a power electronic device used to convert alternating current (AC) to direct current (DC) with the help of thyristors. It consists of four thyristors connected in a bridge configuration. The converter has the ability to control the direction and magnitude of the output DC voltage.

Explanation:
The operation of a fully controlled bridge converter can be divided into four quadrants based on the direction of current flow and voltage polarity. Each quadrant represents a different combination of the input and output voltage polarities. Let's discuss each quadrant in detail:

Quadrant 1:
- In this quadrant, the input voltage is positive and the output voltage is also positive.
- The thyristors in the upper arm of the bridge converter are forward biased and conducting, while the thyristors in the lower arm are reverse biased and non-conducting.
- The current flows from the positive terminal of the input source to the positive terminal of the load.
- The converter operates as a rectifier, converting AC to DC with a positive output voltage.

Quadrant 2:
- In this quadrant, the input voltage is negative and the output voltage is positive.
- The thyristors in the lower arm of the bridge converter are forward biased and conducting, while the thyristors in the upper arm are reverse biased and non-conducting.
- The current flows from the negative terminal of the input source to the positive terminal of the load.
- The converter operates as an inverter, converting AC to DC with a negative output voltage.

Quadrant 3:
- In this quadrant, the input voltage is negative and the output voltage is negative.
- The thyristors in the lower arm of the bridge converter are forward biased and conducting, while the thyristors in the upper arm are reverse biased and non-conducting.
- The current flows from the negative terminal of the input source to the negative terminal of the load.
- The converter operates as a rectifier, converting AC to DC with a negative output voltage.

Quadrant 4:
- In this quadrant, the input voltage is positive and the output voltage is negative.
- The thyristors in the upper arm of the bridge converter are forward biased and conducting, while the thyristors in the lower arm are reverse biased and non-conducting.
- The current flows from the positive terminal of the input source to the negative terminal of the load.
- The converter operates as an inverter, converting AC to DC with a positive output voltage.

Conclusion:
A fully controlled bridge converter can operate in all four quadrants. It can convert AC to DC with positive or negative output voltages depending on the input voltage polarity. Hence, the correct answer is option 'D' - it can operate in quadrants 1 and 4.