Electrical loads both generate and absorb reactive power. Since the transmitted load often varies considerably from one hour to the next, the reactive power balance in a grid varies as well. This can result in unacceptable variations in voltage amplitude, including voltage depression or even voltage collapse.
Like an SVC, the STATCOM instantly and continuously provides variable reactive power in response to voltage transients, supporting the stability of grid voltage. The STATCOM operates according to voltage source principles, combining unique PWM (pulse width modulation) switching in IGBTs (insulated gate bipolar transistors). The unit`s effective rating and response speed is unequalled, and can be dedicated to active harmonic filtering and voltage flicker mitigation. Its components mean the STATCOM`s footprint can be extremely small, and ABB has branded this downsized, high-performance STATCOM concept SVC Light.
Installing a STATCOM at one or more suitable points in a grid will increase power transfer capability by enhancing voltage stability and maintaining a smooth voltage profile under different network conditions. The STATCOM also enables improvements in power quality.
STATCOM/SVC Light technology
SVC Light is based on a technology platform also used in high-voltage direct current (HVDC) power transmission applications, namely HVDC Light®. The most important component is the modular voltage source converter (VSC), equipped with insulated gate bipolar transistors (IGBTs) that are controlled by pulse width modulation (PWM). A VSC is capable of both generating and consuming reactive power. If required, switched or fixed air core reactors and high-voltage AC capacitors can be used with the VSC as additional reactive power elements to achieve any desired range.
STATCOM/SVC Light principle
SVC Light can be considered a voltage source behind a reactance. Physically, it is built as a modular multilevel inverter operating with distributed DC link or, operating at constant direct current (DC) voltage (depending on VSC topology). It generates and absorbs reactive power by electronically processing voltage and current waveforms in a voltage source converter (the grid views it as a synchronous machine without inertia). As a result, capacitor banks and shunt reactors are not needed for SVC Light to generate and absorb reactive power, which enables a compact design and small footprint. The high overall effective switching frequency of the IGBTs provides extremely fast control and a smooth output voltage. It is particularly useful in applications such as mitigating the voltage flicker created by electric arc furnaces, voltage balancing, harmonic filtering and grid voltage recovery. The built in DC capacitors are utilized to support and stabilize the controlled DC voltage needed to operate the converter. Voltage source converters connected in "back-to-back configuration" between two AC busbars can operate with active power, making a dual purpose scheme feasible. A back-to-back configuration enables active power transfer between two AC grids (synchronous or asynchronous, or even with different frequencies) while the converters simultaneously provide reactive power support to the AC networks.