Abstract
Power electronic converters, together with their loads, sources, and controls, form a coupled system that includes many nonlinear interactions, for instance due to pulse-width modulation (PWM) and feedback control. In this paper we develop a complete, nonlinear modeling approach for voltage-source inverters in the frequency domain, taking into account the harmonic components introduced into the system from the inputs and from the nonlinear digital PWM. The most important contribution is a method for analyzing how these harmonics propagate through the nonlinear system in steady state. To enable this, an analytic model of PWM with arbitrary, multiple-frequency input is necessary. A revised model of Asymmetrical regularly-sampled double-edge PWM (AD-PWM) is proposed and its incorporation into the system model regarding sampling effects is discussed. The resulting nonlinear equation system is numerically and simultaneously solved, yielding the spectra of all relevant signals in the converter. The results are validated with time-domain simulations and with measurements, proving the effectiveness of the proposed approach.
Highlights
The accurate assessment of current and voltage harmonics of power electronic systems is studied to meet a variety of design goals, including determination of dc-link capacitor size and lifetime [1,2], compliance with grid codes [3], avoidance of the excitation of resonances [4], and design of active power filters [5,6]
The FPGA incorporates the low-level control of the power converters, whereas the high level control was implemented in the processor
A numerical comparison of the two models presented in Figure 6a,b was performed, using the model by Song and Sarwate ([11], (61)) for ND-pulse-width modulation (PWM) and the proposed model for Asymmetrical regularly-sampled double-edge PWM (AD-PWM) in (26)
Summary
The accurate assessment of current and voltage harmonics of power electronic systems is studied to meet a variety of design goals, including determination of dc-link capacitor size and lifetime [1,2], compliance with grid codes [3], avoidance of the excitation of resonances [4], and design of active power filters [5,6]. A need for research was identified to develop a frequency-domain method that models a power electronic system including its harmonic interactions. These interactions concern the mutual dependencies between the continuous signals of the power stage, the digital signals of the control, and the influence of nonlinear effects such as modulation, sampling, and aliasing. The complexity and novelty of this paper lies in the PWM model’s correct consideration of the sampling process and the interactions of the subsystems This stands in contrast to the prevailing models found in the presented literature, which either model the components with their input-to-output behavior neglecting the closed-loop interactions or with a linearized behavior. The work presented here is a part of the author’s dissertation [27]
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