Control of a transformerless static synchronous series compensator for unbalanced voltage compensation

This paper explores a transformerless static synchronous series compensator (TL-SSSC) for mitigating voltage distortion in a power distribution line with renewable generations. A novel deadbeat current control scheme with time delay compensation is proposed which models the a-b-c three phase line with TL-SSSC plus its LC filters and predicts the compensating voltages to be injected by the TL-SSSC. Without resolving measured voltages and currents into positive and negative sequences, the scheme is computationally efficient and effective in mitigating voltage distortion due to faults occurring at different locations along the distribution line. It also eliminates the problem of inaccurate compensation voltage caused by inverter filter choking voltage drop. The paper also analyses the power controllable ranges for a TL-SSSC under different unbalanced voltage ratios. The proposed TL-SSSC and control scheme is validated using Typhoon Hardware-In -Loop (HIL) device. Experimental results on mitigation unbalanced voltages of a 11kV transmission line confirm the effectiveness and high performance.