Generalized Discontinuous PWM strategy applied to a grid-connected Modular Multilevel Converter

Abstract

This paper presents a new PWM strategy for the control of active and reactive power flow, applied to a three-phase power inverter connected to a microgrid. Power quality and reactive compensation are essential in the integration of renewable energy sources in small grids (stand-alone mode or connected to the utility grid). The control algorithm of the grid-connected system is applied for voltage control. This technique provides independent control of the active and reactive power flow in the utility grid while maintaining constant the DC-link voltage. As a novelty, a Generalized Discontinuous PWM technique is implemented in the control algorithm of the grid-connected converter. Losses in the converter are reduced while the efficiency of the equipment is increased. As a technological innovation, in addition to the power flow control technique, a modular multilevel converter (MMC) is introduced. The main purpose of the system is to improve voltage unbalance and harmonic compensation in stand-alone grids. Some advantages of the model developed here include the cellular concept, easy thermal design, increased system efficiency and improvement in the system expansion capacity. The simulation model has been developed and tested using MATLAB/Simulink software.