Regenerative braking in DC drives requires controlling the firing angle of the controlled rectifier. The DC machine is driven by an auxilairy machine with constant negative speed. As a result, the back emf of the DC machine is also negative. The current thought the machine is controlled such, that it is still positive and lagrer than zero. Because of the thyristors only a positive current direction is possible. Therefore the voltage accross the DC machine has to be negative in order to make the power flow in the DC link from machine to grid. A negative output voltage is possible for larger values of the firing angle alpha.
The losses in the series winding resistance of the DC machine are also modeled and displayed in the scopes.
Compared to the previous simulation, the controlled rectifier is build from discrete components. In this way you can see the current path in the controlled rectifier and you can see the commutation of the thyristors taking place. It clearly shows that the current can only flow in one direction.
Rectifiers and controlled rectifiers used in DC machine control can be modeled as a single block or using discrete components. A block for control of the gating signals that is synchronized to the grid simplifies modeling.
