Static power bridge motor drive circuit

[PhysicsTest]

TL;DR Summary

I am trying to understand the static power bridge section, but confused with the notation.

I am referring to the application note from TI, the below is the power bridge circuit.

The truth table is as below

a. I try the first values of A=0, B=0, C=0 the circuit would then become like this according to me

It is open above point O, then how the voltage of $\frac{-V_{DC}} 2$ will be applied at the point A,B,C as the table indicates.
b. I know these papers are written by experts but it confuses me , why should he consider a point "O"? Why did he not take just $V_{DC}$ instead of splitting into two power sources.
Note: I have attached the application note and it starts from page24.

 

[Tom.G]

Figure 12 on pg.24 shows that the motor is being treated as a 3-phase AC motor.

For that case, the point "O" would be equivalent to the Neutral of a 3-phase Wye connected source, such as at the transformer(s) on the power pole outside the building. Point "O" would then be the reference point from which each of the phase voltages are measured.

Summary:: I am trying to understand the static power bridge section, but confused with the notation.

It is open above point O, then how the voltage of will be applied at the point A,B,C as the table indicates.

To simulate the three sin wave voltages, the duty cycle (on time) of each switch is varied over time. This makes the voltage phases and amplitudes applied to the motor the equivalent of a typical 3-phase source.

The gory details are presented in the subsequent 6 pages of the application note. Not particularly easy to follow for most of us!

Cheers,
Tom