Approved version. Approved on: 08:53, 25 May 2021

- Last edited one month ago ago

# STM32 MC SDK Overmodulation (new in V5.Y)

## Contents

### 1 Principle of SVPWM

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

In the linear area, *V' _{cmd}* can keep both the amplitude and angle of

*V*,

_{cmd}then

*V'*with

_{cmd}= T'_{1}* V_{1}+ T'_{2}* V_{2}*T'*and

_{1}= T_{1}*T'*.

_{2}= T_{2}#### 1.2 OVM mode 1

There are two cases:

- In the green area:
*T*._{1}+ T_{2}≤ 1

*V*is unmodified and the timings remain unchanged_{cmd}*T'*and_{1}= T_{1}*T'*. In that region_{2}= T_{2}*V'*follows the circle._{cmd} - In the blue area:
*T*._{1}+ T_{2}> 1

Then In order to keep*V'*on the edge of the hexagon and keep the angle 𝜃,_{cmd}*| V'*is shrunk to make_{cmd}|*T'*._{1}+ T'_{2}= 1*V'*with_{cmd}= T'_{1}* V_{1}+ T'_{2}* V_{2}*T'*and_{1}= T_{1}/ (T_{1}+ T_{2})*T'*._{2}= T_{2}/ (T_{1}+ T_{2})

In that region*V'*follows the hexagon edge._{cmd}

#### 1.3 OVM mode 2

There are three cases:

- In the green area:
*T*._{1}≥ 1.0

We only use V1 to generate the*V'*._{cmd}

Then*V'*with_{cmd}= T'_{1}* V_{1}+ T'_{2}* V_{2}*T*and_{1}= 1.0*T*._{2}= 0 - In the yellow area:
*T*._{2}≥ 1.0

We only use V2 to generate the*V'*._{cmd}

Then*V'*with_{cmd}= T'_{1}* V_{1}+ T'_{2}* V_{2}*T*and_{1}= 0*T*._{2}= 1.0 - In the blue area:
*T*._{1}< 1.0 && T_{2}< 1.0

Then*V'*with_{cmd}= T'_{1}* V_{1}+ T'_{2}* V_{2}*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

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

### 4 Over-modulation example

Example: F4 three shunt with Shinano motor at 4000 rpm

- 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.