Modeling and current control of modular multilevel converters considering actuator and sensor delays

Voltage source converter (VSC) technology becomes more and more common in high-voltage direct current (HVDC) transmission systems. Compared to conventional VSC technology modular multilevel design offers advantages such as higher voltage levels, modular construction, longer maintenance intervals and improved reliability. A multilevel approach can also help to reduce harmonics due to sinusoidal output voltages so that grid filters become dispensable. Modular multilevel converters (MMC) are a new circuit topology to realize multilevel converters that can be used for high-voltage transmission systems and offer the benefit of an only linearly rising hardware complexity for an increasing number of levels. To control the innovative MMC topology, special requirements exist which exceed classical converter control features. This paper presents a multivariable approach to realize an optimal current control considering actuator and sensor delays that occur in real converter control systems.