Abstract
The three-phase voltage source inverter (VSI) is de facto standard in power conversion systems. To realize high power density systems, one of the items to be correctly addressed is the design and selection of the dc-link capacitor in relation to the voltage switching ripple. In this paper, effective formulas for designing the dc-link capacitor as a function of the switching voltage ripple amplitude are obtained, considering the operating conditions such as the modulation index and the output current amplitude. The calculations are obtained considering the requirements and restrictions referring to the high (switching)-frequency dc-link voltage ripple component. Analyses have been performed considering the dc source impedance (non-ideal dc voltage source at the switching frequency) and a balanced load. Analytical expressions are derived for the dc-link voltage switching ripple amplitude and its maximum value over the fundamental period. Different values of modulation index and output phase angle have been considered and different diagrams are presented. Analytical results were validated both by simulations and comprehensive experimental tests.
Highlights
Three-phase inverters are customarily adopted, due to their wide availability, in many different applications, such as variable speed ac drives, uninterruptible power supplies (UPS), stand-alone and grid-connected systems, etc
The primary target is the reduction in total harmonic distortion (THD) of output currents and the dc bus utilization, EMI, and switching losses reduction, etc
Analyses dc refer to supply; they are valid in the case of most dc supplies since the dc source impedance at the case of a non-ideal dc voltage source, representing an input inductive filter or photovoltaic dc the inverter switching frequency becomes usually much higher than the dc-link capacitor impedsupply; they are valid in the case of most dc supplies since the dc source impedance at ance
Summary
Three-phase inverters are customarily adopted, due to their wide availability, in many different applications, such as variable speed ac drives, uninterruptible power supplies (UPS), stand-alone and grid-connected systems, etc. Comprehensive calculations of the dc-link voltage ripple for single-phase H-bridge PWM inverters were first reported in [9], considering both the high- (~10 kHz) and the low-frequency (100 Hz) components. In [19,20,21], different modulation methods aimed at reducing the input current harmonics flowing through the dc-link capacitor of the three-phase VSIs have been proposed. Theoretical analysis of the dc-link voltage switching ripple in a three-phase PWM voltage source inverter with dc source impedance and balanced load has been presented in [22]. The peak-to-peak dc voltage ripple envelope is analytically defined as a function of the output current amplitude, its phase angle, and the modulation index over the fundamental period. Based on the proposed calculations, simple and practical expressions for the dc-link capacitor design are proposed
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