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An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50\% for all Power Factors
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| Author(s) |
Roland UNRUH, Joachim BÖCKER, Frank SCHAFMEISTER |
| Abstract |
Star-connected cascaded H-bridge Converters require large DC-link capacitors to buffer the second-order harmonic voltage ripple. First, it is analytically proven that the DC-link voltage ripple is proportional to the apparent converter power and does not depend on the power factor for nominal operation with sinusoidal reference arm voltages and currents. A third-harmonic zero-sequence voltage injection with an optimal amplitude and phase angle transforms the 2nd harmonic to a 4thharmonic DC-link voltage ripple. This reduces the voltage ripple by exactly 50\% for all power factors at steady-state at balanced conditions. However, this requires 54\% additional modules for unity power factor operation and even 100\% for pure reactive power operation to account for the increased reference arm voltages due to the large amplitude of the optimal third-harmonic injection. If notenough modules are available, an adaptive discontinuous PWM is utilized to still minimize the voltage ripple for the given number of modules and power factor. With a very limited number of modules (modulation index is 1.15), the proposed method still reduces the DC-link voltage ripple by 24.4\% for unity power factor operation. It requires the same number of modules as the commonlyutilized 3rd harmonic injection with 1/6 of the grid voltage amplitude and achieves superior results. Simulations of a 10kV/1MVA system confirm the analysis. |
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| Filename: | 0416-epe2023-full-12023305.pdf |
| Filesize: | 2.305 MB |
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| Type |
Members Only |
| Date |
Last modified 2023-09-24 by System |
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