SVG and SVC reactive power compensation principle difference?

I, the working principle is different

(1) SVC can be regarded as a dynamic reactive power source. According to the demand for access to the grid, it can provide capacitive reactive power to the grid, but also can absorb the excess inductive reactive power of the grid, the capacitor bank is usually connected to the grid as a filter bank, it can provide reactive power to the grid, when the grid does not need too much reactive power, these excess capacitive reactive power, it is absorbed by a shunt reactor.

The reactor current is controlled by a thyristor valve group, with the help of the thyristor triggered phase angle adjustment, you can change the RMS value of the current flowing through the reactor, so as to ensure that the amount of reactive power of the SVC at the grid access point is just enough to stabilize the voltage of the point in the specified range, and play the role of grid reactive power compensation.

(2)SVG takes the high-power voltage inverter as the core, through adjusting the amplitude and phase of the inverter output voltage, or directly controlling the amplitude and phase of the AC side current, it can rapidly absorb or send out the required reactive power, and realize the purpose of fast dynamic regulation of reactive power.

Second, the response speed

Generally, the response speed of SVC is 20-40ms; while the response speed of SVG is not more than 5ms, which can better inhibit voltage fluctuation and flicker, and under the same compensation capacity, SVG has the best compensation effect on voltage fluctuation and flicker.

Three, low voltage characteristics

SVG has the characteristics of a current source, the output capacity by the bus voltage is very small. This advantage makes SVG has a great advantage when used for voltage control, the lower the system voltage, the more need for dynamic reactive power regulation of voltage, SVG's low voltage characteristics are good, the output reactive current has no relationship with the system voltage, it can be regarded as a controllable constant current source, when the system voltage is lowered, it still outputs the rated reactive current, and it has a strong overload capacity;

While SVC is an impedance type, the output capacity is affected by the busbar voltage. The SVC is impedance type, the output capacity is greatly affected by the bus voltage, the lower the system voltage is, the output reactive current capacity decreases proportionally, and it does not have the overload capacity. Therefore, the reactive power compensation capacity of SVG is independent of the system voltage, while the reactive power compensation capacity of SVC decreases linearly with the drop of system voltage.

Fourth, the operation of safety performance improvement

SVC to thyristor-controlled adjustable reactance plus a number of capacitors as the main means of reactive power compensation, very easy to resonance amplification phenomenon, resulting in safety accidents, system voltage fluctuations, the compensation effect is affected by the big, big operating losses;

SVG supporting capacitors do not need to set up a filter bank, there is no resonance amplification phenomenon!

SVG is an active compensation device, which is a current source device composed of switchable device IGBT, thus avoiding the resonance phenomenon and greatly improving the operation safety performance.

V. Harmonic characteristics

SVC uses SCR to control the equivalent fundamental impedance of the reactor, which is not only affected by the system harmonics, but also produces a large number of harmonics, and must be matched with the use of filters to filter out the harmonic content of the SVC itself;

SVG adopts the three-level single-phase bridge technology, and single-phase can output 5-level voltage waveforms, and adopts carrier wave and phase-shift pulse modulation method. The pulse modulation method of phase shifting is not only less affected by system harmonics, but also can suppress system harmonics. Compared with SVC, SVG greatly reduces the harmonic content in the compensation current after adopting measures such as multiplication, multi-level or pulse width regulation technology.

Sixth, footprint

In the same compensation capacity, SVG footprint than the SVC is reduced by 1/2 to 2/3. Because SVG uses less reactor and capacitor than SVC, so it greatly reduces the size of the device and footprint; SVC reactor is not only a large volume itself, but also taking into account the installation of the spacing between each other, overall footprint larger.

Summary of the above, SVG reactive power compensation device due to the advantages of fast response speed, low harmonic content, reactive power regulation ability, etc., can greatly improve the power quality of the grid, has become the development direction of reactive power compensation technology.

SVG is a typical power electronic equipment, consists of three basic functional modules: detection module, control computing module and compensation output module.

The working principle is to detect the current information of the system by external CT, and then analyze the current current information, such as PF, S, Q, etc., by the control chip; then the controller will give the driving signal for compensation, and finally the inverter circuit composed of power electronic inverter circuits will send out the compensation current. The most advanced SVG product in the world is STATCOM --- dynamic reactive power compensation device.

SVG static reactive power generator adopts a switchable power electronic device (IGBT) to form a self-commutated bridge circuit, which is connected in parallel to the power grid through a reactor, and appropriately adjusts the amplitude and phase of the output voltage on the AC side of the bridge circuit, or directly controls its AC side current. It rapidly absorbs or sends out the required reactive power, realizing the purpose of fast dynamic regulation of reactive power.

Reference:

Baidu Encyclopedia of SVG