Study of Thyristor controlled DC Drive.

A series DC machine is driven by a controlled rectifier. The control measures the input line voltages and calculates the correct moment of firing. The firing angle alpha is input on right side of the control block and the output from the control block directly triggers the thyristors in the controled rectifier.

The DC machine is connnected to a mechanical load where we specify the amount of power and inertia of the drive.

The current in the DC machine is measured and compared to a constant value of 200 Ampere. The error is fed into a PI controller, which results in the firing angle

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A cascaded control is build by including another PI controller for the speed loop. The measured angular speed is compared with a reference value of 100[Rad/s] and the error is input for a PI controller, whose output is now the required current in the DC link.

Notice a faster starting of the machine

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One block for the controlled rectifier, although the rectifier could also be build from discrete thyristors. The control block simplfies the gate control and allows synchronization with the grid. This is especially usefull if the grid contains impedance and higher harmonics. The current control loop is directly connected to the controlled rectifier and control block, simplifying the overall circuit diagram.


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