Independent operation of parallel three-phase converters for motor drive applications

A motor drive consisting of two parallel voltage-sourced converters was developed and implemented. A parallel converter arrangement allows the system to be constructed in a modular fashion to gain economies of scale and redundancy. The converters are connected to common ac- and dc-buses without isolation and are controlled without inter-converter communication or a master/slave arrangement. The system was simulated and the results validated against an experimental setup. Both steady-state and dynamic load sharing were achieved through the use of drooped PI speed regulators. PI controllers were used to regulate the quadrature currents provided by each converter. Circulating 0-sequence current was regulated using P controllers. A linearized state-space model of the system was developed and an eigenvalue analysis was performed, showing system stability. Speed steps in simulation and in the laboratory demonstrated good response. The loss of one converter's gating was emulated. The system continued to operate, showing an advantage of system redundancy.