STATCOM - SVC Light®
Static compensator (STATCOM) – SVC Light®
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 a Static Var Compensator (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 switching of high-power semiconductors like IGBTs (Insulated Gate Bipolar Transistors) and IGCTs (Integrated Gate Commutated Thyristors). The use of these powerful components means the STATCOM`s footprint can be extremely small, and Hitachi Energy has branded this 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 in heavy industry like steel-making.
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 powerful semiconductors performing switching. SVC Light is available for system voltages up to 69 kV and converter ratings over -/+ 400 Mvar. For higher voltages, a step-down transformer is used to connect SVC Light to the grid. SVC Light provides a symmetrical operating range. For asymmetrical operations and in order to optimize performance, thyristor-switched reactors and capacitors are operated in parallel to form hybrid solutions.
SVC Light® principle
SVC Light is a VSC concept, based on a chain-link modular multilevel converter (MMC), particularly adapted for power system applications. Physically, SVC Light can be considered a voltage source behind a reactance. It generates and absorbs reactive power by electronically processing voltage and current waveforms in the VSC, rendering unnecessary to include physical capacitor and reactor branches for generating/absorbing reactive power. It is capable of yielding a high reactive power input to the grid more or less unimpeded by possible suppressed grid voltages, and with a high dynamic response.
This is particularly useful, for instance, to support weak grids and to improve the performance of large wind farms under varying grid conditions, as well as of grids loaded by a large percentage of air conditioners in hot and humid climates. SVC Light´s effective rating and speed of response is unequalled. For instance, for high-speed rail systems and heavy industrial plants it is applied for voltage balancing of asymmetrical loads, mitigating voltage flicker created by electric arc furnaces, and active harmonic filtering.
The power semiconductors (IGBT/IGCT) are key components in SVC Light. The multilevel chain-link solution is built up by linking H-bridge modules in series with one another to form the phase legs of the VSC. Fig. 1a shows a single H-bridge with four IGBTs, and Fig. 1b shows a configuration in which four H-bridge modules make up each of the three phase legs. A photograph of modular H-bridge units, two stacks of four modules each, is displayed in Fig. 2. The compactness of the IGBT valves, the absence of physical capacitor and reactor branches for generating/absorbing reactive power, plus the minute need for harmonic filters enable a very compact lay-out of SVC Light.