Protection mode: In order to isolate DVR from the system during fault current caused by short circuit, bypass switches are provided. The current is supplied to the system by another path as in figure 3.3.
Figure 3.3 Protection mode
3.3.2 Standby mode: In this mode, Low Voltage winding of injection transformer is shorted. No switching operation of semiconductors occurs in this mode. In this mode V_DVR= 0.
3.3.3 Injection mode:
In this modeV_DVR>0, figure 3.4 DVR injects the compensating voltage when there is a voltage difference through injection transformer.
DVR in this does following steps:
Find any voltage disturbance in the distribution network. This can be done by comparing the distorted voltage with load reference voltage. The difference is the desired voltage.
Initiate switching signals for Voltage Source Inverter (VSI), to track the desired voltage generated above by using sinusoidal pulse width modulation technique (SPWM).
Remove any harmonics by using filter, present in injected voltages.
Inject filtered voltage using injection transformers connected in series with the load