Compared with SVC, SVG is superior to SVC in the following aspects:
First, the working principle is different
(1) SVC can be seen as a dynamic source of reactive power. According to the requirements of accessing the grid, it can provide capacitive reactive power to the grid, and can also absorb excess inductive reactive power of the grid. The capacitor bank is usually connected to the grid by a filter bank, and can provide reactive power to the grid. When there is not much reactive power, these excess capacitive reactive power is absorbed by a parallel reactor. The reactor current is controlled by a thyristor valve group. By adjusting the phase angle of the thyristor, the current value of the current flowing through the reactor can be changed to ensure that the reactive power of the SVC at the grid access point is just right. The voltage of the point can be stabilized within the specified range, which acts as a reactive power compensation for the power grid.
(2) SVG takes the high-power voltage-type inverter as the core, and quickly absorbs or emits the required reactive power by adjusting the amplitude and phase of the inverter output voltage, or directly controlling the amplitude and phase of the AC-side current. To achieve the purpose of quickly and dynamically adjusting reactive power.
Second, the response speed is fast
Generally, the response speed of SVC is 2040ms; while the response speed of SVG is no more than 5ms, it can better suppress voltage fluctuations and flicker. Under the same compensation capacity, SVG has the best compensation effect on voltage fluctuation and flicker.
Third, the low voltage characteristics are good
SVG has the characteristics of a current source, and the output capacity is little affected by the bus voltage. This advantage makes SVG have great advantages when used for voltage control. The lower the system voltage, the more dynamic reactive voltage adjustment is needed. The low voltage characteristic of SVG is good. The reactive current of the output has nothing to do with the system voltage. It is a controllable constant current source. When the system voltage is reduced, it can still output rated reactive current and has strong overload capability. While SVC is impedance type, the output capacity is greatly affected by the bus voltage, and the system voltage is lower. The ability to output reactive current is proportionally reduced and does not have overload capability. Therefore, the reactive power compensation capability of SVG is independent of the system voltage, and the reactive power compensation capability of SVC decreases linearly with the decrease of system voltage.
Fourth, the operation safety performance is improved
SVC uses thyristor-regulated reactance plus multi-group capacitor as the main means of reactive power compensation, which is prone to resonance amplification, resulting in safety accidents. When system voltage fluctuation is large, the compensation effect is greatly affected, and the running loss is large; SVG matching capacitor There is no need to set the filter bank, there is no resonance amplification phenomenon, SVG is an active type compensation device, which is a current source device composed of IGBTs that can turn off the device, thereby avoiding the resonance phenomenon and greatly improving the operation safety performance.
Five, harmonic characteristics
SVC uses the equivalent fundamental impedance of the thyristor to control the reactor, which is not only affected by the system harmonics, but also generates a large number of harmonics. It must be matched with a filter bank to filter out the harmonic content generated by the SVC itself; SVG Adopting three-level single-phase bridge technology, single-phase can output 5-level voltage waveform, and adopts carrier phase-shifting pulse modulation method, which is not only affected by system harmonics, but also can suppress system harmonics. Compared with SVC, SVG uses measures such as multiplexing, multi-level or pulse width adjustment technology to greatly reduce the harmonic content in the compensation current.
Six, small footprint
Under the same compensation capacity, the SVG footprint is reduced by 1/2 to 2/3 compared to SVC. Since SVG uses fewer reactors and capacitors than SVC, it greatly reduces the size and footprint of the device; The reactors are not only relatively large in size, but also take into account the installation interval between each other, and the overall footprint is large.
In summary, the SVG reactive power compensation device can greatly improve the power quality of the power grid due to its fast response, low harmonic content, and strong reactive power adjustment capability. It has become the development direction of reactive power compensation technology.
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