Internal Control System

SVC models need to be provided with some form of control for proper operation of both the TCR and the TSC components and also for synchronous coordination between the two.  Control signals for the firing angle order (AO) to the TCR, and capacitor switch ON/OFF order (CSW) for TSC should be provided by a properly designed SVC controller.

The exact instant of valve firing for the TCR is determined when a reference angle derived from a Phase Locked Oscillator (PLO) equals the angle order.  A built-in dq0-transformation based PLO is provided as the default PLO and is used to generate firing pulses for the TCR thyristors (whenever Firing Pulses From: | Internal PLO is selected in the SVC input parameters).

However, the internal control systems for the SVC may not meet the requirements of the sophisticated user, who may desire unique control characteristics, or a special configuration.  The internal mechanism for generation of firing pulses for the TCR thyristors may be replaced with a user defined model providing a correct sequence of 12 pulses (6 for the D and 6 for the Y thyristors in the TCR).  The firing pulses can then be passed as inputs (whenever Firing Pulses From: | External is selected in the SVC input parameters).  In this case, AO has no effect on the operation of the TCR but the blocking signal KB would still cause all of the pulses to be zero (as it was when they are generated internally).

A correct sequence of the 12 pulses for TCR thyristors must take into account the thyristor order, as indicated above in the general circuit diagram, and provides proper phase shift between the pulses as shown below.

NOTES:  Added compensation will be required to confine all angles between 0° and 360°.  q is a reference angle such as the one derived from the PLO.  Capacitors are switched on when the voltage difference between the system and the capacitor to be switched is a minimum.  Capacitors are switched off only at current zero.