1. Principle of SVPWM
Space vector modulation index is limited to (√3)/2 but there is way to extend this limit with the over-modulation. This technique is required when the modulation index (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. TOVM mode 1
There are two cases:
- In the green area: T1 + T2 ≤ 1 .
- 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 .
- 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
1.4. Example: F4 three shunt with Shinano motor at 4000rpm