Investigation on the limitation of the BTB-VSC converter to control the active and reactive power flow

- The power boundaries of the three-phase back-to-back converter are established.
- The study allows the safe establishment of the power objectives.
- The boundary of the active power is set by the capacity of the lower VSC.
- The reactive power range is independent for each AC side.
- The operating area for positive reactive power is greater than for negative.

The back-to-back (BTB) converter based on voltage source converters (VSC) is a common topology used to control the electric power flow in several applications, including renewable power systems. The popularity of this converter lies in its flexibility to independently control active and reactive powers. This paper introduces an approach to establish the power limitations of the BTB-VSC converter in the linear region. The theoretical expressions are developed using the dq model of the system. The methodology is functional and identifies the capabilities and limitations of the BTB-VSC converter in controlling the active and reactive powers. The study is useful for (1) assigning appropriate references to the controllers and avoiding unreachable power references and (2) dismissing the attribution of possible failures to the control system. As a result, it is possible to establish whether the power application requirements are covered by the BTB-VSC converter. Results validate the boundaries of the active and reactive powers and an algorithm is implemented to construct the graphic areas of the active and reactive power regions. Moreover, a nonlinear control strategy based on input-output feedback linearization is implemented to corroborate the approach. Simulation and experimental tests are conducted with a 3 kVA system.