The classification of STATCOM

Static synchronous compensator (STATCOM or SVG) is a kind of dynamic reactive power compensation equipment based on voltage source converter (VSC). It is a typical representative of the second generation facts device. This article will briefly introduce the classification of Static synchronous compensator.

The following is a list of contents

• Theoretical classification of Static synchronous compensator

• Classification by the inverter modules of basic unit

• Classification by component

• Classification by voltage class

Theoretical classification of Static synchronous compensator

Theoretically, STATCOM can be divided into voltage source type and current source type. In terms of its circuit structure, the DC side of voltage source STATCOM has large capacitance in parallel, which ensures that the voltage will not change greatly in the process of continuous charge and discharge or device commutation, and the bridge side series inductance, while the current source STATCOM is a DC side series large inductance, which ensures that there will be no large fluctuation in the current of device commutation or charging and discharging devices, and the bridge side parallel inductance.

In practical application, the commonly used high-capacity STATCOM basically adopts voltage source structure. However, the SVG can be controlled as a current source for reactive power compensation. A new STATCOM control strategy is proposed in the domestic literature, that is, the strategy of voltage controlled current source (VCCS) and the strategy of improved voltage controlled voltage source (VCVS) are used to compensate the voltage imbalance at the point of common coupling (PCC), especially when the capacity is small, the VCCS method will achieve the best compensation effect.

Classification by the inverter modules of basic unit

According to the basic unit inverter module, STATCOM can be divided into single-phase bridge two-level, three-phase bridge two-level and three-phase bridge multi-level. In the application of large capacity and high voltage level, it is often necessary to couple multiple low-voltage and small capacity converters through transformers, that is, multiplicity. Or the transformer is used to boost or depressurize the AC input and output side, which will have the disadvantages of energy consumption, large harmonic content and low system efficiency. The switching devices of multilevel converter bear small voltage stress. For example, the voltage stress of each switching device of three-level converter is half of that of two-level converter, with less harmonic content and lower loss. Therefore, it has been widely used and developed in large capacity occasions.

Classification by component

According to the components, STATCOM can be divided into GTO type, IGBT type, IGCT type, SCR type, GTR type and MOSFET type. Facts equipment based on power conversion generally adopts fully controlled devices, which are mainly selected from GTO, improved GTO (IGBT, MTO, ETO, etc.) and (HV) IGBT. STATCOM, the first one in the world to use GTO as inverter power device, was developed by EPRI and Westinghouse Electric Company, with a capacity of 1mvar. 20mvar STATCOM in China and 80mvar STATCOM in Inuyama switching station of Kansai power system in Japan use GTO as power devices. IGBT is suitable for small capacity occasions. The distribution STATCOM developed by ABB company adopts multiple IGBTs in series.

Classification by voltage class

According to the voltage level, STATCOM can be divided into high-voltage transmission network compensation and low-voltage distribution network compensation. In high voltage transmission network, STATCOM needs to be connected to the power grid through transformer. In the low-voltage distribution network, D-STATCOM is connected in parallel or directly in parallel through reactors. The basic working principle of D-STATCOM is to connect the bridge circuit to the power grid through the reactor or directly in parallel, appropriately adjust the amplitude or phase of the output voltage on the AC side of the circuit, or directly control the current on the AC side of the circuit, so that the circuit system can harvest and send out reactive current that meets the requirements, so as to realize the purpose of dynamic compensation of reactive power. In addition, specific harmonics can be eliminated by pulse width modulation.

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