Notes on Rectifier Power Flow Modeling
Voltage Control Mode
The rectifier has two control modes. The first is voltage control. In this mode, the output of the rectifier is held at the specified voltage set point unless the following limiting conditions occur:
- Diode rectifier: The control mode is disabled. The rectifier will produce a DC voltage in accordance with Kimbark’s DC equations. This mode is also the same as forcing Alpha to zero.
- Thyristor rectifier: Voltage control will hold the specified voltage, and a change in Alpha is calculated to hold the specified voltage. The DC voltage will be the result of Kimbark’s DC equations.
Note that the combination of the input AC voltage and the thyristor control’s attempt to change Alpha can create limiting conditions. Consider these two limiting conditions:
- Alpha Max: If the AC voltage is too high and the thyristor control increases the Alpha and hits Alpha Max, the rectifier will stop at Alpha Max, and the DC voltage will be calculated for this condition using Kimbark’s equations.
- Alpha Min: If the AC voltage is too low and the thyristor control hits Alpha Min, the Rectifier will stop at Alpha Min, and the DC voltage will be calculated for this condition using Kimbark’s equations. When Alphas Min is equal to zero, this is basically the same conditions as a diode rectifier.
IGBT rectifier: Since the controls and limiting conditions for IGBT’s are not well known and vary significantly between manufacturers, the DC voltage is held like a SWING bus. No AC input voltage condition has any effect on the DC voltage.
Current Control Mode
In Current Control Mode, the rectifier holds the DC current on the rectifier output at the specified current level unless a limit is hit. If a limit is hit, the DC current is determined by Kimbark’s equations and the DC system on the output of the rectifier.
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