Reversing the Power Flow in the Looped Electrical Distribution Network by Using a Cascaded H-bridge D-SSSC

In new configuration of electrical distribution network the distributed generation is connected directly to the medium voltage link. For achieving the total generation of DGs the distribution network radial configuration is changed to the loop or meshed configuration by using a power electronic device in the connection point to control the power flow. Distribution Static Synchronous Series Compensator (D-SSSC) is able to control the power flow between two feeders from different substations. Thanks to use the multilevel converter topology, D-SSSC is connected directly to the line, omitting bulky transformer. Cascaded H-bridge is the best option for this kind of realization. Controlling the power flow in new configuration of electrical distribution system is source of advantages. One of the great impacts of D-SSSC is balancing the power flows of connected feeders, avoiding congestion of feeders and cables damages. This system sometimes needs to reverse the power flow in the line despite of the phase angle between the feeders. The conventional SSSC control strategy uses current phase to inject a voltage in phase with the current to maintain the DC bus voltage at its reference value and a quadratic component to control the power flow. This control strategy is fail to operation while the power reference is reversing due to loosing the current phase track at low and zero line current. In this paper the feasibility of a DSSSC for reversing the power flow is discussed and a new control strategy based on voltage phase track is introduced.

Keywords:

Cascaded H-bridge , D-SSSC , power flow control , phase locked loop