Voltage Regulation in Weak Distribution Grids Using Transformerless Series Compensators

With increasing penetration of distributed generators (DGs), existing distribution grids are becoming weaker. As a result, voltage regulation in distribution grids impose a significant challenge and can be improved by introducing additional control apparatuses. In this paper, a transformerless static synchronous series compensator (T-SSSC) is adopted to maximise the power transfer between DGs and a weak grid by improving grid voltage stability. A new control strategy is introduced to reduce the number of switching events during the operation of a T-SSSC, thus limiting the switching losses. Furthermore, a new droop based control scheme is proposed to minimise the voltage unbalance between phases. A medium voltage distribution grid with embedded T-SSSCs modelled in Simulink has been used to verify the effectiveness of the proposed control schemes. For completeness, the performance a T-SSSC is investigated following a sudden change in grid short circuit level.