Introduction:
A single-phase dual converter is a power electronic device that allows bidirectional power flow between an AC source and a DC load. It consists of two converters, one working as a rectifier and the other as an inverter. The converters are connected back-to-back, allowing power to flow in either direction.

Explanation:
In circulating current mode of operation, the converters are controlled in such a way that both of them work simultaneously. However, their roles differ, with one converter working as a rectifier and the other as an inverter.

Working of the converters:
1. Rectifier converter:
- The rectifier converter converts AC input voltage into a DC output voltage.
- It operates in the rectification mode, where it allows the current to flow from the AC source to the DC load.
- The rectifier converter uses thyristors or diodes to control the flow of current.

2. Inverter converter:
- The inverter converter converts the DC input voltage into an AC output voltage.
- It operates in the inversion mode, where it allows the current to flow from the DC source to the AC load.
- The inverter converter also uses thyristors or diodes to control the flow of current.

Working together:
- In circulating current mode, both converters work simultaneously.
- One converter acts as a rectifier, allowing power to flow from the AC source to the DC load.
- The other converter acts as an inverter, allowing power to flow from the DC source to the AC load.
- The converters are connected back-to-back, which enables bidirectional power flow.
- The circulating current flows between the converters, ensuring power transfer in both directions.

Advantages of circulating current mode:
- Improved power quality: The circulating current mode helps in maintaining a constant and smooth power flow between the AC source and the DC load.
- Bidirectional power flow: The ability to transfer power in both directions allows for flexibility in the system operation.
- Regenerative braking: The circulating current mode enables regenerative braking, where the energy generated during braking is fed back to the AC source.

Conclusion:
In a single-phase dual converter operating in circulating current mode, one converter always works as a rectifier, allowing power flow from the AC source to the DC load, while the other converter works as an inverter, allowing power flow from the DC source to the AC load. This configuration enables bidirectional power flow and offers advantages such as improved power quality and regenerative braking.

Introduction:
A single-phase dual converter is a power electronic device that allows bi-directional power flow between two voltage sources. It consists of two converters connected back-to-back, with one converter operating as a rectifier and the other as an inverter. The operation of the dual converter can be categorized into two modes: circulating current mode and non-circulating current mode. In this discussion, we will focus on the circulating current mode.

Circulating Current Mode:
In the circulating current mode, the converters are designed to share the load current between them in a controlled manner. This mode is used when there is a need for bidirectional power flow between two voltage sources. The circulating current mode allows power to flow from the input source to the output source and vice versa.

Working of Converters:
In the circulating current mode, one converter always operates as a rectifier, and the other converter always operates as an inverter. Let's understand how this works:

- Rectifier: The rectifier converter is connected to the input voltage source and is responsible for converting the input AC voltage into DC voltage. It controls the power flow from the input source to the output source.

- Inverter: The inverter converter is connected to the output voltage source and is responsible for converting the DC voltage into AC voltage. It controls the power flow from the output source to the input source.

Simultaneous Operation:
Both converters work simultaneously, but their roles are different. The rectifier converter operates as a rectifier, allowing power flow from the input source to the output source. At the same time, the inverter converter operates as an inverter, allowing power flow from the output source to the input source. In this way, power can circulate between the two voltage sources.

Control of Circulating Current:
To ensure proper operation and control of the circulating current, a control system is used. The control system adjusts the firing angles of the converter switches to control the power flow and maintain the desired circulating current. By varying the firing angles, the load current can be shared between the rectifier and the inverter according to the desired power flow direction.

Conclusion:
In the circulating current mode of a single-phase dual converter, one converter always operates as a rectifier, and the other converter always operates as an inverter. Both converters work simultaneously but perform different functions. This mode allows bidirectional power flow between two voltage sources and requires a control system to maintain the desired circulating current.