| Title |
Control of DC-side Voltage Unbalance among Phases in Multi-level H-Bridge STATCOM with Unbalanced Load |
| Authors |
Byung-Ki Kwon ; Seung-Ki Jung ; Tae-Hyeong Kim |
| DOI |
10.6113/TKPE/2014.19.4.332 |
| Keywords |
STATCOM; dc-side voltage unbalance; unbalanced load; negative-sequence current; zero-sequence current |
| Abstract |
A cascaded H-bridge multi-level STATCOM(STATic synchronous COMpensator), which is composed of many cell inverters with independent dc-sources, generates inevitably dc-side voltage unbalance among phases when it compensates unbalanced load. It comes from the difference of flowing active power in each phase when this compensator makes negative-sequence current to eliminate the unbalance of source-side current. However, this unbalance can be controlled by injecting zero-sequence current which is decoupled with grid currents, so the compensator can work well during this balancing process. Both a feedback control algorithm, which produces zero-sequence current proportional to dc-side voltage unbalance within each phase, and a feedforward control algorithm, which makes zero-sequence current directly from the compensator's negative-sequence current, were proposed. The dc-side voltage of each phase can be controlled stably by these proposed algorithms in both steady-state and transient, so the compensator can have fast response to satisfy control performance under rapid changing load. These balancing controllers were implemented and verified via simulation and experiment. |