Dynamic voltage restoration (DVR) is a method of overcoming

voltage sag Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...

s and swells that occur in

electrical power distribution Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmissio ...

. These are a problem because spikes consume power and sags reduce efficiency of some devices. DVR saves energy through voltage injections that can affect the

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform * Phase space, a mathematic ...

and wave-shape of the power being supplied. Devices used for DVR include static var devices, which are series compensation devices that use voltage source converters (VSC). The first such system in North America was installed in 1996 - a 12.47 kV system located in

Anderson, South Carolina Anderson is a city in and the county seat of Anderson County, South Carolina, United States. The population was 28,106 at the 2020 United States census, 2020 census, and the city was the center of an urbanized area of 75,702. It is one of the prin ...

Operation

The basic principle of dynamic voltage restoration is to inject a

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...

of the

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

and

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

necessary to restore the load side voltage to the desired

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...

and waveform, even when the source voltage is unbalanced or distorted. Generally, devices for dynamic voltage restoration employ gate turn off thyristors, (GTO) solid state power electronic switches in a pulse-width modulated (PWM) inverter structure. The DVR can generate or absorb independently controllable real and reactive power at the load side. In other words, the DVR is a solid state DC to AC switching power converter that injects a set of three-phase AC output voltages in series and synchronicity with the distribution and

transmission line In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmis ...

voltages. The source of the injected voltage is the commutation process for reactive power demand and an energy source for the real

power demand World energy supply and consumption is global production and preparation of fuel, generation of electricity, energy transport, and Electric energy consumption, energy consumption. It is a basic part of economic activity. It includes heat, but no ...

. The energy source may vary according to the design and manufacturer of the DVR, but DC

capacitors A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of a ...

and batteries drawn from the line through a

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...

are frequently used. The energy source is typically connected to the DVR through its DC input terminal. The amplitude and phase angle of the injected voltages are variable, thereby allowing control of the real and reactive power exchange between the dynamic voltage restorer and the distribution system. As the

reactive power Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactanc ...

exchange between the DVR and the distribution system is internally generated by the DVR without the AC passive reactive components.Ghosh, A. & Ledwich, G. (2002). Power quality enhancement using custom power devices (1st ed., pp. 7-8). Boston: Kluwer Academic Publishers.

Similar devices

DVRs use a technically similar approach as low voltage ride-through (LVRT) capability systems in wind turbine generators use. The dynamic response characteristics, particularly for line supplied DVRs, are similar to those in LVRT-mitigated turbines. Conduction losses in both kinds of devices are often minimized by using

integrated gate-commutated thyristor The integrated gate-commutated thyristor (IGCT) is a power semiconductor electronic device, used for switching electric current in industrial equipment. It is related to the gate turn-off (GTO) thyristor. It was jointly developed by Mitsubishi ...

(IGCT) technology in the inverters.

Applications

Practically, DVR systems can to inject up to 50% of nominal voltage, but only for a short time (up to 0.1 seconds). However, most

voltage sags Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

are much less than 50 percent, so this is not typically an issue. DVRs can also mitigate the damaging effects of voltage swells,

voltage unbalance Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

and other waveform distortions.

Drawbacks

DVRs may provide good solutions for end-users subject to unwanted

power quality Electric power quality is the degree to which the voltage, frequency, and waveform of a power supply system conform to established specifications. Good power quality can be defined as a steady supply voltage that stays within the prescribed range, ...

disturbances. However, they are generally not used in systems that are subject to prolonged reactive power deficiencies (resulting in low voltage conditions) and in systems that are vulnerable to

voltage collapse Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

. Because DVRs will maintain appropriate supply voltage, in such systems where incipient voltage conditions are present they actually make collapses more difficult to prevent and can even lead to cascading interruptions. Therefore, when applying DVRs, it is vital to consider the nature of the load whose voltage supply is being secured, as well as the transmission system which must tolerate the change in voltage-response of the load. It may be necessary to provide local fast reactive supply sources in order to protect the system, including the DVR, from voltage collapse and cascading interruptions.

SSSC and DVR

The SSSC’s counterpart is the Dynamic Voltage Regulator (DVR). Although both are utilized for series

compensation, their operating principles differ from each other. The static synchronous series compensator injects a balance voltage in series with the transmission line. On the other hand, the DVR compensates the unbalance in supply voltage of different phases. Also, DVRs are usually installed on a critical feeder supplying the active power through DC energy storage and the required reactive power is generated internally without any means of DC storage.

References

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External links

Dynamic Series Voltage Restoration for Sensitive Loads in Unbalanced Power Systems

Dynamic Voltage Restorer and Its application at LV & MV Level
Electric power distribution