This paper considers the problem of designing a multilevel pulse width modulated waveform (PWM) with a prescribed harmonic content. Multilevel PWM design plays a major role in many diverse engineering disciplines. In power electronics, multilevel PWM design corresponds to determining the inverter switching times and levels for selective harmonic elimination and harmonic compensation. In mechatronics, the same design corresponds to shaping input signals to damp residual vibrations in flexible structures. More generally, in most applications, the aim of PWM design is to minimize the total harmonic distortion while adhering to a prescribed harmonic content. The solution approach presented in this paper is based on linear programming with the objective of minimizing the total harmonic distortion. This objective is achieved within an arbitrarily small bound of the optimal solution. In addition, the linear programming formulation makes the design of such switching waveforms computationally tractable and efficient. Simulations are provided for corroboration.
In this article, the feasibility of selective harmonic elimination for grid-connected operation of low voltage DC sources is presented. An appropriate fixed switching pattern is able to achieve good quality current while minimizing switching operations, thereby improving the inverter efficiency. In an attempt to establish the potential advantages over conventional PWM techniques, this article demonstrates the application of SHE in grid connect applications, especially in high power levels while maintaining the ability to provide an independent control of active and reactive powers. The problem formulation is based on using a fixed switching pattern that provides a certain fundamental voltage and eliminates 5 th , 7 th , 11 th , 13 th , 17 th , 19 th , 23 rd , 25 th , 29 th , and 31 st harmonic order. A power structure consisting of two-stage power conversion is proposed to make this possible, enabling amplitude and phase control of the generated AC voltage from the inverter. An LCL filter has been used for grid interface. The switching pattern and the development of control structure are presented. Simulation studies are discussed and experimental results shown validate the proposed scheme.
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