Modulation techniques for cascaded H-bridge multilevel converters based on analytical methods

Over the last two decades, digitally controlled power electronic converters, have become a key enabling technology in important areas such as renewable energy and distributed generation, smart grids, transportation, industry, robotics, consumer electronics, etc.Power electronic converters are required to fulfil many demanding tasks, but they all share some basic requirements, including optimisation of energy conversion, high flexibility and low cost, according to the concept of Life Cycle Assessment (LCA).Multilevel converters (MLCs), first proposed for high power and high voltage applications, are gaining popularity and applications at all power levels, demonstrating unusual flexibility even at low power levels. Key features of MLCs are their ability to overcome voltage limitation of power devices, to offer modularity and fault tolerance capability, moreover, they are capable to reduce the harmonic content affecting their input/output currents and voltages.Their modulation patterns can be generated in many different ways and often are imposed by algorithms that consist of off-line pre-calculations followed by real-time application of the pre-calculated patterns through look-up tables. These approaches require large amounts of memory, can reduce the accuracy of the commutation angles, and are not very flexible in closed-loop operation. Analytical methods, on the other hand, offer significant advances: exact problem formulation, simple and effective real-time implementation, the ability to selectively eliminate or mitigate harmonics, the possibility of cascading the modulator with the external control loops.