AC–DC Converter – III | Clarke & Park Transformation | dq Control | Active Front End (AFE) | Electric Vehicles | Lecture 15

Modern three-phase Active Front End (AFE) converters employ advanced reference frame transformations to simplify control, achieve fast dynamic response, and maintain unity power factor. In this lecture, we continue the study of three-phase AC–DC converters by revisiting 180° conduction, 120° conduction, and Sinusoidal PWM (SPWM), followed by the introduction of the Clarke (αβ) and Park (dq) transformations, which form the foundation of vector control in modern power electronic converters and electric vehicle charging systems.

The lecture explains how three-phase quantities are transformed into a stationary αβ reference frame using the Clarke Transformation and subsequently into a rotating dq reference frame using the Park Transformation. The significance of aligning the rotating reference frame with the resultant voltage vector is discussed, demonstrating how AC quantities are converted into constant DC quantities that are easier to regulate using conventional PI controllers. Mathematical derivations of both transformations are presented along with their physical interpretation.

Finally, the lecture develops the closed-loop control model of the Active Front End converter in the dq reference frame. The dynamic equations of the converter are derived, followed by the expressions for active and reactive power in the dq frame. The lecture concludes with the implementation of PI-based current controllers, illustrating how independent control of d-axis and q-axis currents enables precise DC-link voltage regulation, unity power factor operation, and high-performance control of grid-connected converters used in electric vehicle charging applications.

Topics Covered

Review of 180° and 120° Conduction Modes
Sinusoidal Pulse Width Modulation (SPWM)
Resultant Space Vector Concept
Clarke Transformation (abc → αβ)
Stationary αβ Reference Frame
Park Transformation (αβ → dq)
Rotating dq Reference Frame
Decoupling of Three-Phase Quantities
Closed-Loop Control of Active Front End (AFE) Converter
dq-Axis Dynamic Equations
Active and Reactive Power in dq Frame
PI-Based Current Control Strategy

Who Should Watch?

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

Recommended References

D. W. Hart, Power Electronics, McGraw-Hill, 2011.
P. S. Bimbhra, Power Electronics, 5th Edition, Khanna Publishers, 2012.
R. Krishnan, Electric Motor Drives: Modeling, Analysis, and Control, Prentice Hall, 2001.

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