AC–DC Converter – II | Three-Phase Active Front End (AFE) Converter | 180° & 120° Conduction | Electric Vehicles | Lecture 14

Three-phase Active Front End (AFE) converters have become an integral part of modern high-power electric vehicle charging systems due to their capability of bidirectional power flow, regulated DC output, and near-unity power factor operation. In this lecture, we begin with an overview of different operating modes of DC–AC converters, including Square Wave, Quasi Square Wave, Multi-Pulse, PWM, Sine PWM, 180° Conduction, and 120° Conduction, before introducing the three-phase Active Front End converter used in EV charging applications.

The lecture explains the construction and operating principle of the Three-Phase Active Front End (AFE) Converter, develops its equivalent circuit, and demonstrates how active control enables bidirectional power flow between the AC grid and the DC link. The role of phase difference between the source voltage and converter voltage in controlling the direction of power transfer is discussed using phasor diagrams and equivalent circuit analysis. The lecture also presents the operation of the inverter under 180° conduction and 120° conduction modes, along with the corresponding switching sequences and output voltage waveforms.

Finally, the lecture introduces the fundamentals of closed-loop control for Active Front End converters. It discusses the advantages of closed-loop operation, including accurate output voltage regulation, improved dynamic response, disturbance rejection, reduced steady-state error, and unity power factor operation. The lecture concludes with the concept of the rotating resultant space vector and its representation in the stationary αβ reference frame, providing the foundation for advanced vector control techniques used in modern power electronic converters.

Topics Covered

Modes of Operation of DC–AC Converters
Three-Phase Active Front End (AFE) Converter
Equivalent Circuit of AFE Converter
Bidirectional Power Flow Control
Phase Angle Control of Power Flow
180° Conduction Mode
120° Conduction Mode
Output Voltage Waveforms
Closed-Loop Control of AFE Converter
Advantages of Closed-Loop Control
Rotating Resultant Space Vector
Stationary αβ Reference Frame

Who Should Watch?

B.Tech. and M.Tech. students
Power Electronics learners
Electric Vehicle enthusiasts
GATE and ESE aspirants
Researchers working on EV charging systems and motor drives
Engineers designing grid-connected converters and Active Front End systems

Recommended References

D. W. Hart, Power Electronics, McGraw-Hill, 2011.
P. S. Bimbhra, Power Electronics, 5th Edition, Khanna Publishers, 2012.
R. W. Erickson and D. Maksimović, Fundamentals of Power Electronics, 2nd Edition, Springer.

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