Overlap in Converter Operation due to Source Inductance

Introduction:
Converter operation refers to the process of converting electrical energy from one form to another. In power electronics, converters are widely used to control power flow, voltage, and current in various applications. However, during the operation of converters, certain phenomena can occur that affect their performance and efficiency.

Overlap in Converter Operation:
Overlap in converter operation refers to the occurrence of simultaneous conduction of two or more devices in a converter circuit. This can lead to several issues such as increased power losses, reduced efficiency, and increased stress on the devices. Overlap can occur due to various factors, including source resistance, source inductance, both source resistance and source inductance, and a high value of the firing angle.

Explanation:
Among the given options, the correct answer is option 'B', which states that overlap in converter operation is primarily caused by source inductance. Let's delve into why source inductance can lead to overlap in converter operation.

Impact of Source Inductance:
1. Delayed Current Zero Crossing:
- Source inductance causes a delay in the current zero crossing during the commutation process in converters.
- This delay can result in the conduction of two or more devices simultaneously, leading to overlap.

2. Increased Time for Device Turn-off:
- Source inductance stores energy in the form of a magnetic field during the device conduction.
- This stored energy prolongs the turn-off time of the devices when the commutation process begins.
- Consequently, the devices may not turn off completely before the next devices start to conduct, causing overlap.

3. Increased Voltage Stress on Devices:
- During overlap, the devices that are supposed to be turned off still carry a significant amount of current.
- This results in a voltage drop across the devices, leading to increased voltage stress.
- Higher voltage stress can degrade the devices' performance and reduce their lifespan.

4. Increased Power Losses:
- Overlap in converter operation leads to increased conduction losses as multiple devices are simultaneously conducting.
- These losses contribute to reduced converter efficiency and increased power dissipation.

Conclusion:
In conclusion, overlap in converter operation can occur due to various factors, including source resistance, source inductance, both source resistance and source inductance, and a high value of the firing angle. However, in this particular scenario, source inductance is the main cause of overlap. Source inductance delays the current zero crossing, increases the turn-off time of devices, and leads to increased voltage stress and power losses. By understanding the impact of source inductance, engineers can design converters with appropriate measures to minimize overlap and optimize converter performance.