Learning the Types of STATCOM: A Journey through the Gym of Reactive Compensation

Imagine you are in a gym, each piece of equipment and exercise has its own characteristics and is intended to work specific muscles. In the same way, the different types of STATCOM are designed to improve the stability and quality of our electrical systems, each with its own characteristics and applications.

STATCOM classification

Based on Voltage Source Converters (VSC)
These equipment in voltage source mode are connected in series with the transmission line and function as a voltage source. They inject or absorb reactive power to maintain a stable voltage level and improve the power quality of the network. This mode is used in high voltage applications, such as large power plants or transmission grids.

1. Thyristor Technology
   At the time of the Industrial Revolution, thyristors were like free weights in the gym: robust and reliable. These devices pioneered reactive compensation, laying the foundation for what we know today as STATCOM. However, just as free weights have been supplemented by more advanced machines, thyristors have been overtaken by more modern technologies.
2. IGBT (Insulated Gate Bipolar Transistor) Technologies
   These modern devices use IGBTs, similar to the state-of-the-art machines in the gym. These devices allow for more efficient conversion and precise control of reactive power flow, providing fast and adaptive response to fluctuations in electrical demand. Imagine being able to adjust weight and exercise precisely to work exactly the muscle you need; that's how versatile the IGBTs in today's STATCOMs are.

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Based on Current Source Converters (CSC)
In this equipment based on Current Source Converters (CSC), the device is connected in parallel with the load and functions as a current source that can inject or absorb reactive power to maintain a stable current level and improve the power factor of the system. For the CSC to operate, it needs series-connected AC capacitors, which provide the reactance needed for DC to AC conversion and stabilize the current source bus voltage. It should be noted that these capacitors can cause resonances in the system if not properly designed.

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Comparison between VSC and CSC

Equipment based on Voltage Source Converters (VSC) and Current Source Converters (CSC) have different characteristics that make them suitable for different applications. The following is a detailed comparison of their main differences and uses:

• Efficiency: VSC (IGBT) based STATCOMs achieve 90-95% efficiency, making them ideal for maximizing power conversion in general applications. In contrast, CSCs have a moderate efficiency of 80-85%, which can be a limitation in applications where efficiency is critical.
• Response speed: VSCs respond quickly to network fluctuations with response times of less than 5 ms, allowing almost instantaneous reactive compensation. On the other hand, CSCs have a slower response speed, in the range of 10-20 ms, suitable for applications where accuracy is more important than speed.
• Precision control: VSCs offer precise control with ±3% variation, while CSCs excel in this area with ±1% precision control. This precision is particularly useful in applications where it is crucial to maintain specific electrical parameters within very narrow margins.
• Typical applications: VSCs with IGBTs are widely used in distribution systems, transmission, renewable generation and even industrial applications due to their high efficiency and fast response. CSCs, although less common, are ideal for industrial and specialized applications requiring precise current control

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STATCOM typologies

Two-Level STATCOM
In two-level equipment, the converter uses two voltage levels to produce the desired output waveform. This mode is simple, cost-effective and has a lower switching frequency, but produces more harmonics than other topologies.
Analogy: Think of a basic light switch that has only two positions: on and off. While it is simple and does its job, it may not be as precise or smooth in its operation as a dimmer that offers multiple levels of adjustment.

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Multilevel STATCOM
Multi-level equipment uses multiple voltage levels to produce the desired output waveform. This mode provides a smoother output waveform, reduces the number of harmonics and improves system efficiency. However, it is more complex and costly than the two-level topology.‍

Analogy: This type can be compared to an air conditioning system with variable temperature control. Instead of simply turning on or off, it gradually adjusts the temperature to maintain a comfortable environment more precisely.

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Modular Multilevel Converter (MMC) STATCOM
The modular multilevel converter (MMC) is a new generation of high-voltage converters that can produce high-quality output waveforms with low harmonics. It uses MMC topology to improve system efficiency and reliability. This type of equipment is commonly used in high voltage applications, such as offshore wind farms or large industrial plants. It is like a precision Swiss watch, where each component is designed to work in perfect harmony, offering exceptional efficiency and accuracy.

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Conclusion

Just as every piece of equipment and routine in the gym has its place in a balanced training program, each type of STATCOM has its ideal application in the electrical infrastructure.

While different types of STATCOMs offer varied solutions, VSC-based MMC STATCOMs prove to be superior in terms of flexibility and performance. This advanced technology, available through Diram, provides more efficient and reliable voltage regulation, better adapting to the modern demands of the power sector.

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Case Studies and Real Examples

To better understand how the different types of STATCOM are used, let's consider some real examples. To do so, we invite you to review the following link with our most recent STATCOM projects where we have helped different industries to make their operations more efficient, comply with energy regulations and improve their power quality: https://www.diram.com/en/statcom-projects

For more information about our products, send us a message and one of our experts will contact you.