STATCOM and its application
Static synchronous compensator (STATCOM) is a power electronic based equipment to provide reactive power compensation and other options functionality, such as e.g. harmonic cancellation. In this blog post we look at how STATCOM works and how it can help to improve the performance in specific applications.
What is a STATCOM
The term STATCOM is an abbreviation from Static Synchronous Compensator. It is a power electronics-based equipment used to control the power flow and to improve transient stability of the grid. It is connected in parallel to the grid (as a shunt).
Knowing the variable frequency drives (VFD), one can imagine the STATCOM as basically an AFE rectifier and a dc capacitor bank. There is no inverter as STATCOM only exchanges reactive power with the grid and does not transfer any active power (see Fig. 1).
STATCOM provides bi-directional flow of the reactive power, unlike the classic SVC technologies (thyristor switched capacitor for supply of reactive power and thyristor switched reactor to consume reactive power).
Principle and functionality
A. Principle
STATCOM is a power electronic equipment used to compensate or control reactive power by either absorbing it or injecting it into the grid. The power hardware is basically an AC/DC converter that connects an AC grid with a DC capacitor bank (thus the similarity with the grid side of AFE type of VFD) The power semiconductors are self-commutated so that the phase angle between voltage and current can be adjusted as desired (→variable capacitive or inductive load from the grid perspective). The converter may use overmodulation to
better utilize the power components. Grid connection is realized through a dedicated coupling transformer. The short-circuit impedance of that transformer can be considered as a series inductance.
The power of STATCOM is defined at the network’s point of connection (POC) which is normally the HV side of the STATCOM transformer. The capability is therefore co-determined by the impedance of the transformer. The lower the transformer impedance the higher the power at POC that can be reached.
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B. Functionality
Reactive power compensation
Purpose is usually to minimize the total amount of reactive power to be transmitted in the grid and thus reducing the power losses and increasing the transmission capacity. STATCOM can either absorb or supply reactive power depending on actual demand. The reactive power balancing with a STATCOM is generally faster than conventional solutions such as Static VAR compensator (SVC).
Voltage control
The grid voltage is controlled indirectly by controlling the amount of injected or absorbed reactive power. Reactive power injection boosts the grid voltage while absorption of reactive power lowers the grid voltage.
▪ Reactive power injection:
- Overexcited operation (Q > 0)
- STATCOM terminal voltage > grid voltage
▪ Reactive power absorption:
- Underexcited operation (Q < 0)
- STATCOM terminal voltage < grid voltage
The voltage support is both quasi steady as well as dynamic support, e.g. during grid disturbances or faults.
Harmonic elimination
STATCOM has the capability to eliminate certain harmonics as well. The elimination works on the same principle as an active filter. However, for a STATCOM the harmonic elimination is a secondary function. Priority is put on the reactive power compensation. Some STATCOMs are quite limited with the highest order of harmonic that can be eliminated. The bandwidth is often linked with the topology and power rating. Low voltage based solutions at lower power operate with high switching frequency which translates into substantial bandwidth.
However, also high power modern STATCOMs based on multilevel converter platform can cover quite wide frequency range.
Load symmetrisation
Certain loads (e.g. direct railway supplies, arc furnaces, rural industrial facilities) are inherently asymmetric. If the load is of considerable size, it causes a grid unbalance. The load balancer is using both active and reactive power to minimize the unbalance.
C. Power part
The main power hardware sections of STATCOM are:
- AC/DC power converter: power semiconductor stacks based on IGBT or IGCT
- Capacitor based DC link:
- direct coupled capacitors plus eventually capacitor filters
- in case of power cells (MMC), capacitor inside each power cell
- Small “braking chopper” to stabilize dc voltage during transients and to discharge the dc bus
- Pre-charging system of the dc bus (optional)
STATCOM is often installed inside a dedicated container or E-house. Internally, the power part may be separated from the control section and cooling. A typical outdoor installation is shown in Figure 3.
D. Capability
The capability of STATCOM is usually depicted by means of P-Q curves, i.e. showing the amount of active and reactive power. For a specific grid voltage there is a corresponding P-Q envelope. As the grid voltage changes, the P-Q capability gets modified. Thus, the diagrams usually show at least three envelopes: for the nominal voltage, minimum continuous voltage and maximum continuous voltage.
The P-Q diagram normally does not have a circular shape. One reason is that the current capability changes with the power factor (different loading of active switch and anti-parallel diode), other reason is the voltage drop/increase over the coupling transformer. The inductive capability is higher than the capacitive reactive power which STATCOM can provide.
E. Topologies
Similar to VFDs, also STATCOM can be realized with several hardware topologies. In the low power/ low voltage range the platform is a 2-level converter. Many manufacturers then parallel multiple of those low voltage STATCOMs to scale the power. They usually use one common coupling transformer.
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Application areas
There are many areas that can benefit from using a STATCOM. In this chapter we briefly describe typical applications from utility, industry and renewables.
A. Solar (PV) plants
Solar (photovoltaic) power plants are sources with highly volatile power output. The variable power generation poses a challenge for voltage stability. STATCOM helps to reduce the voltage fluctuation.
B. Wind parks (onshore and offshore)
Wind parks are other generation units with fluctuating power output. Moreover, offshore wind parks are connected to the power grid through power cables with lengths of tens of kilometres. To manage the voltage variation and changing reactive power, a STATCOM is a suitable solution.
C. Steel industry (e.g. furnaces)
Electric arc furnace (EAF) is notoriously known as kind of load with major impact on the power quality of the grid. It is non-linear and with variable active power and therefore changing reactive power demand. Without any measures, the arc furnace causes voltage flicker and significant harmonic distortion. The STATCOM is a suitable solution to dynamically compensate the reactive power, suppress the flicker and eventually also re
duce certain harmonics. Typical rating of STATCOM is 60…80% of the power rating of the arc furnace.
D. Offshore oil and gas platforms
Offshore platforms need STATCOM as well, especially when they are supplied with power from shore [4]. In that case, the STATCOM is needed in steady state as well as in transient situation. Often, the STATCOM is installed onshore but in some configurations it may be located offshore as well. In steady state the STATCOM helps to optimize the reactive power flow and loading of the cable. Another case is a transient when the offshore load is tripped (load shadding) and there is a surplus of reactive power flowing towards onshore and
causing sudden voltage rise.
In this application, the STATCOM complements variable frequency drives (VFD) driving compressors and pumps on the platform.
E. Other unbalanced loads
Certain loads are inherently unbalanced with high negative sequence component. An example is railway grid supplied from a public grid. The railway grid is a single-phase load. On the three-phase side, only two phases are loaded. Additionally, when feeding directly the catenary, the power consumption is very variable (peak power when a train is passing through the railway section versus no-load condition when there is no train in the given section). Although there are solutions how to reduce the impact, the remaining unbalance is still significant. STATCOM in this application is aimed to further reduce the unbalance to an acceptable level (say below 2%).
F. Weak grids in remote areas
Grids in remote areas tend to be weak. The power generation units are faraway; there is an increased voltage drop across the long power line and the location is mostly supplied from a single point. Thus, the grid in such areas has larger voltage variation. An installation of STATCOM helps to stabilize the grid voltage and improve the power quality.
G. Improved fault ride through
Fault ride through is a very useful function of VFDs allowing them to withstand short-time grid undervoltages without tripping. However, not all VFDs are equipped with such functionality. A combination of a VFD without fault ride through capability and a grid prone to have frequent disturbances can have devastating consequences for the user. The drives are tripping, process is disturbed and productivity and quality suffer. If an upgrade of the VFDs is not in sight, the user may consider installing a STATCOM to dynamically boost the voltage during grid fault. The feasibility depends on the grid strength. For moderately strong grid the required size of the STATCOM likely makes the solution commercially not attractive. However, for a weak grid, the power rating of the STATCOM gets smaller and the solution may be viable.
Summary
STATCOM as a solution for reactive power compensation and voltage stabilization was briefly introduced. The blog post touched areas such as principle, functionality and application areas.
Acknowledgement
We would like to thank the Ingeteam company for authorizing us to use their picture showing typical STATCOM installation.
References
[1] N. G. Hingorani, L. Gyugyi, “Understanding FACTS; Concepts and Technology of Flexible AC Transmission Systems, IEEE ® Press Book, 2000.
[2] A matter of FACTS, ABB AB, 2016, document no. 1JNS018770 RevA
[3] Static compensator (STATCOM), Hitachi Energy, available online, https://www.hitachienergy.com/products-and-solutions/facts/statcom
[4] SFC for Power from Shore application, MB Drive Services, November 2022, available online, https://mb-drive-services.com/sfc-for-power-from-shore/
[5] Ingegrid STATCOM, Ingeteam, available online, https://www.ingeteam.com/us/en-us/sectors/energy-efficiency/p15_30_236/ingegrid-statcom.aspx
2 Comments
Sharan · February 23, 2026 at 8:02 am
I would like to sincerely appreciate the informative presentation on STATCOM and Its Applications. The session provided a clear and comprehensive understanding of the Static Synchronous Compensator (STATCOM) and its vital role in modern power systems.
admin · February 28, 2026 at 7:30 am
Thank you Sharan. Such feedback is our best motivation for future posts.