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

### 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 Vcmd ,
then V'cmd = T'1 * V1 + T'2 * V2 with T'1 = T1 and T'2 = T2 .

#### 1.2 OVM mode 1

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

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 .

### 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.