1 Overview
　　Static Var Generator (or SVG, for short) is the latest generation of reactive compensator and active power filter, representing the newest application of reactive compensation in electric field. It is also called the static compensator, known as STATCOM. It has replaced the traditional SVC due to the powerful function, small size and easy installation.
2 SVG principle
　　voltage source inverter is connected  in parallel to the power grid  through  reactor or transformer to adjust the the amplitude and phase of the output voltage at AC side of the inverter or directly control the amplitude and phase of its AC current in order to rapidly absorb or generate the required reactive power and realize the purpose of quick regulating the reactive power. When controlling by direct current, the device directly controls the AC side current, which could  not only track the shock current of the compensating impact load, but also track and compensate the harmonic current.
    No-load operation mode: Us= UI, IL =0, SVG does not absorb reactive power; capacitive mode:UI＞Us, IL is leading current, of which the amplitude can be continuously controlled by adjusting UI so as to continuously adjust the reactive power generated by SVG. inductive operation mode:UI＜Us, IL is lagging current, of which the amplitude can be continuously controlled by adjusting UI so as to continuously adjust the reactive power absorbed by SVG.

3 SVG electrical schematic

4,SVG Technical Features.

4.1 Advantages of the Device: SVG is the latest generation of reactive compensator and active power filter, representing the newest application of reactive compensation in electric field. With the voltage source inverter as its basis, SVG has improved the reactive compensation by leaps and bounds. Discarding the use of large capacitances and electrical inductances, SVG realize the switching of reactive energy through high-frequency switches of high power electric and electronic components.

4.2 Security of the Device:SVG is controllable current source compensation device, which is equivalent to a power source and not sensitive to system parameters, therefore ensuring no occurrence of harmonic amplification incidents; compensation current is totally controllable and there is no case of overcompensation of power factor. The device is also capable of tracking the frequency changes of power grid, thus the compensation performance is not influenced by the frequency changes of power grid..
4.3 Free Maintenance of the Device:SVG is in modular design, in which the power units are identical in terms of structure and electrical performance and thus interchangeable; The equipment adopts N+1 or N+2 redundant main circuit topology structure, capable of keeping operation at full load when one (or two) chain link unit is damaged.Equipment installation and commissioning are easy, provided with complete protection on overvoltage, undervoltage, overcurrent, and  overheating etc; Fiber optic transmission signals are adopted between the control system and inverter to completely resolve the problem of high and low voltage isolation, successfully avoiding the interference of electromagnetic signals and stabilizing SVG working performance.
4.4 Rapidity of the Device:The hardware system of SVG adopts full controllable IGBT, which may quickly turn off the semiconductor device; the software system adopts instantaneous reactive power algorithm, of which the response time can be shortened within 10ms.SVG may convert between the rated capacitive reactive power and the rated inductive reactive power in a very short timespan, suppressing voltage flicker rapidly and effectively, superior to any impact load compensation.     While the traditional SVC hardware system applies the thyristor that is switched off only when the current down to zero. The software system adopts the average value algorithm, so the response time is more than 20ms.
4.5 Superior Harmonic Output: SVG applies the carrier phase-shifting PWM technology and multilevel technology with power units  connected in series, which can output reactive current (Excluding harmonics) similar to the sine wave, or it can  output harmonic current with the set number of times (used for load harmonic filtering), which means that the SVG output current is totally controllable, meeting the demand of customers;  In comparison, SVC generates a large number of uncontrollable harmonic currents. To overcome it,  SVC has to generate a large amount of  uncontrollable reactive filtering branches only to filter the self-generated harmonic current.
4.6 Super compensation capacity:SVG output current does not rely on system voltage and shows the characteristics of constant current source. It outputs  the rated reactive current when the system voltage drops to 20%, ensuring a wider operation range; while the output current of SVC will decrease in direct proportion to the system voltage. When achieving the same compensation effect, the capacity of SVG can be 20% to 30% smaller than that of SVC.SVG may compensate the reactive power and harmonics at the same time. The compensated reactive power can be continuously adjusted from inductive reactive power to capacitive reactive power in both directions. If configured with fixed capacitor banks, it is able to meet the compensation range requirements of the system and the load, and to reduce the overall equipment cost.
4.7 Small Size: The inverter, as the core of SVG,  is composed of a fully controllable semiconductor power devices. SVG applies the DC capacitor as energy storage rather than the large filter branches and electric reactor  as of SVC; the installation size is generally 1/5 to 1/3 the size of SVC, thus especially suitable for sites with limited area. Besides, SVG can also be designed into portable box type.
4.8 High Efficiency: SVG applies a new type of low-cost IGBT power device with direct output voltage ranging form 1kV to 35kV. The efficiency  can achieve above 99.2%. Through the reactive power and harmonic compensation, it can increase the active power injecting into the devices in unit time, reduce the reactive power lose, increase the availability rate of electrical equipment, improve the working efficiency and reduce the energy consumption. The loss curve of SVG is superior to that of SVC (maximum loss is reached when SVC is idle), the equivalent running loss of SVG is usually only 1/3 to 1/2 of SVC, equivalent running loss is quite lower than that of SVC.
4.9 Multiple compensation functions:Suppress overvoltage of power system and improve voltage stability Improve the stability level of the system, reduce the released load when in low voltage  and avoid the transient voltage collapse. Maintain the voltage at the transmission line side dynamically and increase the power limit of the transmission lime and  its stability;Suppress the power shocks of power system;Suppress voltage flicker, compensate load imbalance, improve load power factor and filter out harmonics at the load side. 

5.SVG Application Field
5.1Reactive Var Compensation and Harmonic Filter of Industrial Loads in Metallurgical and Rolling Field
　　The reactive power impacts on power grid caused by symmetric loads in rolling mill and other industrial areas are as follows:It causes the voltage drop and voltage fluctuation of the power grid. In serious cases, the electrical equipment cannot work normally and the production efficiency decreases.Power factor drops;Harmful high-order harmonics will be produced in the load transmission device, mainly the 5th, 7th, 11st, 13rd odd harmonics and side frequency, which will cause serious distortion of the power grid voltage.SVG can solve the above problems perfectly, stabilizing the bus voltage stable and eliminating the harmonic interference. With sufficient compensation capacity, the power factor is close to 1. Comparing with traditional SVC, SVG has become the primary choice of reactive power compensation for industrial users such as rolling mill.

5.2 Voltage Fluctuation and Flicker Control of Electric Arc Furnace

    As a typical nonlinear large impact load, electric arc furnace will bring a series of adverse impacts on the power grid when connected to it.It will cause severe voltage fluctuations and flickers.Severe three-phase imbalance in the power grid may incur and produce the negative sequence current.Generate the harmonic, complex spectrum, which mainly presents 2-7 continuous harmonics.It may influence the ower power factor. The best way to solve the above-mentioned problem is to install reactive var power compensation device SVG. With fast response speed and response time less than 10ms, SVG can quickly provide reactive power supply to the electric arc furnace, stabilize the bus voltage,and increase the active power into the furnace so as to advance the production efficiency, eliminate the influence of flicker and compensate the harmonics as well as 3-phase unbalance. Comparing with the traditional SVC, SVG has great advantages when applying to arc furnace compensation. The sending procedure of voltage flicker is 4-5 times higher than that of traditional SVC. In the meanwhile, due to the good voltage stability  and not generating harmonics , the energy-saving and consumption reduction effect is also 1 time better than the traditional SVC.

5.3 Reactive Power Compensation and Comprehensive Harmonic Control of Mining Load like Hoist and Winch in Coal mining System
　　With the increase of mechanization and automation in coal mining, SVG can be applied to perform the following functions:it can reduce the reactive power loss and help energy saving when the power factor of coal power supply system is low, and the energy consumption per ton coal increases;The active harmonic filter can improve the quality of electricity supply when harmonic pollution is aggravated by the application of variable frequency speed and cascade speed control system. The device may stabilize the voltage and improve the power supply safety when power supply line is long, terminal voltage is low and driving force of mining machinery is insufficient.It may reduce the voltage fluctuation and flicker when large load starting
　　Application: Project Name: Kailuan (Group) Co., Ltd. Tangshan mine; operation time: August 2010; model: XDSVG-L06/04-04/H; equipment quantity: 3 sets; compensation effect: each bus power factor reached 0.99 or more; to solve the high load 6kV bus 1, paragraph 6 of the power factor is low, but in the equipment maintenance of low load, there have been compensation problems; to solve the harmonic problem of main and auxiliary hoist to 6kV 2 and 3 bus work; to solve the harmonic problem of 6kV 4, 5 coal washing plant at work and life for the load perceptual negative charge compensation.
5.4 SVG for reactive power compensation in wind power generation
　　The uncertainty of wind resources and running characteristics of wind turbines makes the output power of wind turbines fluctuate, resulting in subquality of grid power factor, voltage fluctuation and flicker and other problems,  the application of SVG can perform the following functions:Address problems in of wind power connection system, such as power factor, voltage fluctuation and flicker;Reduce the influence of system voltage fluctuation on the wind turbines, reduce the number of turbine switching;Solve the problems of unstablization when large capacity wind farm is connected to the system, it has good performance of  low voltage ride-through 
　　Application: Project Name: 35kV wind farm dynamic reactive power compensation; operation time: September 2011; model: XDSVG-L35/12-12/H; equipment quantity: 2 sets; compensation effect: the compensation of reactive power, improve the power factor; voltage control, voltage stability; energy saving, reducing transformer, line loss etc..
5.5 SVG for reactive power compensation of photovoltaic power generation:
Photovoltaic power generation is developing rapidly, bringing more diversified and clean power sources. But it also brings about many new problems, such as reactive power flow and voltage fluctuation. Light intensity and temperature changes affecting panels generating capacity may be caused by voltage fluctuation.Increasing photovoltaic power plant capacity will affect the stability of power grid operation, large-scale photovoltaic power plants must have some low voltage ride through capability.
　　Application: Project Name: saving Zhaoyuan Canzhuang photovoltaic power station; operation time: September 2011; model: XDSVG-L35/2-2/H; equipment quantity: 1 sets; compensation effect: the compensation of reactive power, improve the power factor; voltage control, voltage stability; energy saving, reducing transformer, line loss etc..
5.6 Hub substation of power grid system to improve the transmission capacity of the grid line
         Installing SVG devices at the load center station of the distribution network to achieve the following goals:Accurately adjust the reactive power output by following the load changes to avoid reverse transmission  of reactive power and improve the power factor of the system;Adjust the system voltage in real time to improve the quality of regional power grid;Provide voltage support in case of system failure to ensure the reliability and safety of power supply.
　　Application: the Shanghai Municipal Electric Power Company in order to improve the system transient voltage stability level, reduce the fault of low-voltage release load quantity, decided in the western suburbs of Huangdu partition of a ± substation; 50Mvar STATCOM device (by flexible transmission and distribution system of Tsinghua University is responsible for technology research and development work of the whole department), comprehensive control and realize there are 4 groups of fixed capacitors to achieve optimal compensation effect.

6.7 ports and shipbuilding industry:

　　   Loading and unloading equipments are mainly used in port such as  portal crane, off-shore cranes, gantry crane and bucket wheel machines etc, belonging to the reactive power impact load and featuring large load changes, quick speed changes and short time heavy load. With general application of SCR AC and DC drives, it will increase the mechanical performance of loading operations significantly and also bring about the problems such as increased demand for reactive power and harmonics pollution on grid and so on.Active filter may eliminate all kinds of harmonics less than 13 times which is produced by rectifier and frequency conversion device.Compensate reactive power generated by impact load in real time and improve the the system power factor;Increase voltage stability, improve system power quality, improve reliability of power supply
　　Application: name of project: the first phase project of Ganyu port area of Lianyungang port; operation time: August 2012; model: XDSVG-L10/2-2/H; equipment quantity: 1 sets; compensation effect: real-time compensation of reactive power, improve the power factor; voltage control, voltage stability; harmonic filter system.

6.SVG model naming　

Example of product model:
        XDSVG-L10/3-3/H represents that the rated voltage is 10kV, compensation capacitive capacity is 3Mvar, compensation inductive capacity is 3Mvar, with harmonic filter function.

7. SVG technical indicators

9 SVG cabinet arrangement diagram

10 Arrangement diagram of SVG connection reactor