Q12Power Quality and FACTS
Question
Q.2. What is DVR? What are the component of DVR? Explain its operation. [8]
Answer
Definition of DVR
A Dynamic Voltage Restorer (DVR) is a series-connected custom power device installed between the supply and a sensitive load, which injects a controlled compensating voltage in series with the incoming supply voltage to correct voltage sags, swells, and imbalances before they reach the protected load.
Components of DVR
- Voltage source converter (VSC): IGBT-based converter that generates the compensating AC voltage waveform from a DC source
- Injection (series) transformer: couples the VSC output in series with the line and provides galvanic isolation and voltage matching
- Energy storage / DC-link capacitor: supplies the real power needed during voltage sag compensation (battery, capacitor bank, or flywheel)
- Harmonic filter: removes high-frequency PWM switching harmonics from the injected voltage
- Control and monitoring system: continuously senses supply voltage, detects sag/swell events, and computes the required injection voltage magnitude and phase
Operation
During normal operation, the DVR injects little or no voltage and the injection transformer is essentially transparent to load current. When the control system detects a voltage sag on the supply side, it rapidly (within a few milliseconds) commands the VSC to generate a compensating voltage of appropriate magnitude and phase so that, when added in series with the sagged supply voltage through the injection transformer, the resultant voltage delivered to the load is restored to its nominal rated value.
The required real power for this injected voltage is drawn from the DC-link energy storage. Once the sag or swell condition clears, the DVR ramps down its injected voltage smoothly to avoid transients and returns to standby mode. Because the DVR only needs to compensate for the difference (missing) voltage rather than supply the full load power, it can be rated at a fraction of the load rating, making it a cost-effective solution for protecting sensitive industrial loads from short-duration voltage disturbances.