Influence of dead time on voltage harmonic spectrum of grid-connected PWM-VSC with LCL filter

In recent years, the three-phase pulse width modulation controlled voltage source converter (PWM-VSC) has found its way to wide range of applications, among which renewable energy sources and adjustable speed drives are the most common. In order to achieve low harmonic distortion of current at the point of common coupling (PCC), LCL filters are used for grid connection since they ensure higher damping of current harmonics than L-filters for the same volume. There are many different LCL filter design and optimization methods that are based on the assumption of an ideal converter. Since actual PWM-VSC includes many different sources of nonlinearities, their neglection can potentially lead to selection of inadequate LCL filter in terms of increased grid current harmonic distortion and decreased overall system performance. Research presented in this paper is part of ongoing effort to increase efficiency of adjustable speed drive for crane systems of which the PWM-VSC with LCL filter is a part. This paper focuses on influence of nonlinearities on voltage harmonic spectrum of PWM-VSC. Analysis is carried out by means of nonlinear models and it indicates that the dead time delay has the greatest impact on the system. Validation of simulation results by measurements suggest additional effects should be incorporated into the model. Such a model can then be used for development of more accurate non-iterative LCL filter design and optimization procedures as well as development of operating point optimization algorithms.