How Dynamic voltage restorer (DVR) can be useful to overcome Power quality problems

What is a dynamic voltage restorer

Power quality is an important factor while distribution of the electric power, so uninterrupted flow of power is required for the customers. To achieve this power quality the bus voltage should maintain its voltage to be a sinusoid at rated voltage and frequency

Problems associated with power quality

  • Transients
  • Long duration power variations
  • Sustained interruptions
  • Short duration voltage variations
  • Voltage swag
  • Voltage swells

Among the power quality problems, the voltage swag is the most severe disturbances, so in order to overcome these disturbances DVR can be used in a power distribution network

Normally it is installed in a distribution system between the supply and the critical load feeder at the point of common coupling. It can compensate voltage sags and swell, it can also do line voltage harmonics compensation and reduction of transients in voltage and fault current limitations. The primary function of the DVR is to minimize the voltage sags on the lines that affect the sensitive equipment

Why do we need DVR

  • If the voltage sag is not controlled it will have a severe impact on sensitive load
  • DVR acts as a filter between distribution line and the feeder to receive clean power
  • It can work as a harmonic isolator to prevent the harmonics in the source voltage reaching the load

DVR operation

A DVR is a solid-state power electronics switching device consists of either GTO or IGBT, a capacitor bank is used as an energy storage device and injection transformers will be useful for the voltage compensation

Compensation capacity of the DVR is depended upon the maximum voltage injection capability and the active power that can be supplied by the DVR. DC system has large capacitor energy storage and its advantage is that it has the potential to supply high current pulses for hundreds of thousands of cycles

Configuration of DVR

  • Injection or Booster transformer
  • Harmonic filter
  • Storage devices
  • Voltage source converter
  • DC charging circuit
  • Control & protection

Injection booster transformer

This is a specially designed transformer which could limit the coupling noise and transient energy from the primary side to the secondary side

  • It does the isolation of the load from the system
  • It connects DVR to the distribution network via the HV windings and transforms and couples the injecting compensation voltages generated by the voltage source converters to the incoming supply voltage

Harmonic filter

Its main function is to keep the harmonic voltage generated by the voltage source converter to a normal level

Voltage source converter (VSC)

A VSC consists of a storage and a switching device which could be useful to generate a sinusoidal voltage at required frequency, magnitude, and phase angle VSC is used in DVR to supply voltage temporarily or to generate parts of the supply voltage which is missing

DC charging circuit

The two important tasks of the DC charging circuit is

  • After a sag compensation event energy source will be charged
  • It maintains the DC link voltage at the nominal Dc link voltage

Control & protection

The control mechanism generally consists of hardware and programmable logic. Protective functions like differential current protection of the transformer or short circuit on the customer load side

Advantages of DVR over other custom power device

  • DVR has higher energy capacity and lower cost compared to SMEs
  • Smaller in size and less costly than the DSTATCOM
  • Very sensitive to the system load level
  • DVR can control the active power flow

Industrial application of DVR

  • Automotive manufacturers
  • Electronics (consumer electronics and computer manufacturers)
  • Chemical and steel plant
  • Process industries like semiconductor plants and plastic mills