Figure 1 shows qualitatively the reactive current versus connected voltage of such a solution. The reactive current depends linearly on the grid voltage and as a consequence the reactive power changes with the square of the grid voltage. Depending on the amount of switched component branches, the reactive current can only be altered in more or less large steps. Due to the limited switching time of capacitors, the dynamic performance of this solution is reduced. Furthermore, switching transients have to be accepted with this solution as well as regular maintenance of the breakers.

Figure 1 Reactive I-U of switched passive components	Figure 2 Reactive current versus voltage of an SVC

Figure 2 shows the reactive current versus connected voltage of a well known and widely used reactive power compensator: the SVC (Static Var Compensator). The SVC combines thyristor switched capacitors (TSC) with thyristor controlled reactors (TCR). Doing so, a smooth variation of reactive power over the complete installed power range is possible.

Figure 3 Reactive current versus voltage of a STATCOM	Figure 4 U-I of mixed STATCOM switched  passive components

Figure 3 shows the reactive current versus connected voltage of a STATCOM. The performance is similar to a SVC, i.e. it performs smooth variation of reactive current across its operating range with high dynamics. “it has advantages when compared to the Static Var Compensator (SVC), e.g., current injection independent of the system voltage, faster control and less of a space requirement.” The STATCOM is described more in detail further on. Finally, Figure 4 shows a combination of switched passive components with a small-sized STATCOM. This solution still includes disadvantages of switched passive components, e.g. switching transients and the need for regular maintenance of the breakers.

From an operator’s point of view, a solution for reactive power compensation without mechanically switched components is therefore preferred. ZDDQ’s product scope includes both SVC and STATCOM. Depending on the project set-up, SVC or STATCOM is the optimum solution. ZDDQ focuses on the STATCOM (Static Synchronous Compensator) as well suited “add-on” equipment to help wind parks to achieve Grid Code compliance.

ZDDQ Related power quality solutions,

Low voltage SVC

Low voltage SVG

High voltage SVC

High voltage SVG/STATCOM