STM32 MC SDK Overmodulation (new in V5.Y)

Revision as of 07:40, 8 June 2021 by Registered User
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)


1. Principle of SVPWM

STM32 MC Overmodulation new slide1 1.png

Space vector modulation index is limited to √3/2 but there is a way to extend this limit with the over-modulation. This technique is required when the modulation index, as the length of the reference space vector Us, exceeds the edges of the hexagon.


1.1. Linear mode

STM32 MC Overmodulation slide9 1.png

In the linear area, V'cmd can keep both the amplitude and angle of Vcmd ,
then V'cmd = T'1 * V1 + T'2 * V2 with T'1 = T1 and T'2 = T2 .

1.2. OVM mode 1

STM32 MC Overmodulation slide10 1.png

There are two cases:

  • In the green area: T1 + T2 ≤ 1 .
    Vcmd is unmodified and the timings remain unchanged T'1 = T1 and T'2 = T2 . In that region V'cmd follows the circle.
  • In the blue area: T1 + T2 > 1 .
    Then In order to keep V'cmd on the edge of the hexagon and keep the angle 𝜃, | V'cmd | is shrunk to make T'1 + T'2 = 1. V'cmd = T'1 * V1 + T'2 * V2 with T'1 = T1 / (T1 + T2) and T'2 = T2 / (T1 + T2).
    In that region V'cmd follows the hexagon edge.


1.3. OVM mode 2

STM32 MC Overmodulation slide11 1.png

There are three cases:

  • In the green area: T1 ≥ 1.0 .
    We only use V1 to generate theV'cmd .
    Then V'cmd = T'1 * V1 + T'2 * V2 with T1 = 1.0 and T2 = 0 .
  • In the yellow area: T2 ≥ 1.0 .
    We only use V2 to generate theV'cmd .
    Then V'cmd = T'1 * V1 + T'2 * V2 with T1 = 0 and T2 = 1.0 .
  • In the blue area: T1 < 1.0 && T2 < 1.0 .
    Then V'cmd = T'1 * V1 + T'2 * V2 with T'1 = (T1 / (T1 + T2) + 3 / 𝜋 . 𝛾) . (𝜋/6) / (𝜋/6 − 𝛾) and T'2 = 1.0 − T'1 .


2. Over-modulation timings sum-up

STM32 MC Overmodulation new slide5 1.png

3. Over-modulation activation in STM32 MC SDK V5.Y

STM32 MC Overmodulation new slide6 1.png

4. Over-modulation example

Example: F4 three shunt with Shinano motor at 4000 rpm

STM32 MC Overmodulation slide17.jpg
- In the middle of this snapshot: the blue curve shows the phase current
- Just bellow: the pink, yellow and green curves show the PWM channels

The over-modulation increases the total harmonic distortion, but it allows the modulation index to exceed √3/2.