A three-phase PWM method is used to provide a 208V. 60Hz voltage across a three

Question

A three-phase PWM method is used to provide a 208V. 60Hz voltage across a three phase wye connected series R-L load with R = 5 Ohm and L = 4mH. The DC supply voltage is 400V. The frequency modulation is 47. Determine the switching frequency. Determine the required modulation index, ma. Determine the three highest levels of harmonic current harmonics, their respective harmonic orders and calculate the resultant RMS harmonic currents. Calculate the total harmonic distortion. Also, determine the highest modulation index that is possible without going into overmodulation. The determine the highest modulation index possible while in overmodulation that will produce the highest possible RMS output voltage in six-step mode. What is that highest line to line RMS output voltage that can be produced? Finally, sketch waveforms for the line to midpoint voltages, the line to neutral voltages (where the neutral is at the midpoint of the wye-connected load). Assume that the neutral point is where the system is grounded

Explanation / Answer

the methods to generate different PWM waveforms for 3-phase
AC induction motor using an Infineon 16-bit microcontroller XC164CS are introduced.
For better understanding, the basic operation and control principle of 3-phase AC
induction motors is described in Section 2. The content of Section 3 is the respective
explanation of the theory of four popular PWM schemes frequently utilized in AC induction
motor control, SPWM (Sinusoidal PWM), THIPWM (Third-Harmonic Injection PWM),
SAPWM (Saddle-wave PWM), SVPWM (Space Vector PWM). In Section 4, XC164CS
DAvE configurations and codes programming for different PWM schemes realization are
discussed in detail and illustrated with flow charts. At the end of this article some
experimental results including simulator waveforms and figures measured by oscilloscope
are shown to validate the algorithms and some conclusions are drawn.
Furthermore, two sets of source codes for SPWM and SVPWM with 10KHz carrier
frequency and output frequency from 0 to 50Hz in 10 seconds respectively as well as an
EXCEL file on calculation tables for all PWM modes are attached.

Basic Operation Theory
The 3-phase stators and 3-phase rotors are considered as two fundamental parts of a 3-
phase AC induction motor. When the 3-phase stators are energized by the 3-phase AC
power source, current flow is generated in the stators. The magnetic field synthesized by
3-phase stator current is always rotating incessantly with the variation of the current. This
rotating magnetic field cuts the rotor and the current generated in it interacts with the
rotating magnetic field and thus produces the magnetic torque which makes the rotor
rotate (Figure 1). The rotating speed of the rotor n should be less than that of the rotating
magnetic field n0. Reverse rotating of the rotor will be realized by two of the 3-phase power
source positions exchanged.

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