High power, high performance parallel connected multiconverters: analysis and control

Recently, there has been an increasing demand for high power, high performance converters for power system applications, motor drives, etc. The low switching frequency of existing devices poses a severe limitation that can be overcome by the use of interconnected smaller power converters (multiconverter) with appropriate control. This paper concentrates on the transformerless parallel connection of three-phase power converters, that offers interesting features like simplicity, gracefully degrading operation, high reliability, easy expandability and easy maintenance. Based on its state space model, the decoupling and the behavior of the balanced and zero sequence currents are explained. The PWM is explained as a special sample and hold element. After showing the requirements for the current controller of a parallel connected multiconverter, and discussing individual and centralized control, the use of an individual deadbeat controller is discussed. Influence of the sampling times displacement is analyzed, and the harmonics minimization by optimum zero sequence is proposed. Both are confirmed by simulation results