A Control Strategy for Parallel Three-Phase Inverters in Motor Drives

Parallel operation of inverters is one method to increase power ratings of motor drives for high power applications. This paper proposes a novel variation of Field-Oriented Control for parallel inverters driving AC machines. The proposed strategy is implemented directly in the natural (abc) reference frame and overcomes many issues faced by conventional controllers for parallel motor drives. At the core of this control strategy is a proposed Resonant Proportional Integral (RPI) controller, which uses integrated plant dynamics to achieve the functionality of a second-order Proportional Resonant (PR) controller using only a first-order Proportional Integral (PI) controller. Hence the proposed control strategy is very simple, requiring only an inner first-order RPI controller for the the stator currents, and an outer PI controller for motor speed and maximum torque per ampere (MTPA) operation. A theoretical analysis of the RPI controller is given, which is supported by simulation and experimental results.