Harmonic spectrum of unipolar inverter

Thread Starter


Joined Apr 20, 2021
Hi everyone,
I'm building low power 600w grid following inverter. Scheme is standard with DC-link capacitor at 400v, full bridge H-bridge with 4 power mosfets and LCL filter. LCL filter is designed to filter high switching harmonics. Switching frequency of mosfets is 30kHz and I'm using unipolar modulation so that harmonic spectrum of voltage exiting h-bridge has double that frequency. As I understand, theoretically speaking, spectrum of current and voltage shouldn't consist harmonic at 30kHz but in experimental set up I measured it. It is noticeable even at grid voltage. I'm wondering could that harmonic be electromagnetic interference caused by mosfet switching. If it is EMI, is that component really in real spectrum of my current and voltage or is that just noise that my measuring equipment picks up? I'm using oscilloscope voltage and current probes. Also harmonic at 60kHz is higher than I expected with that LCL filter. Does it affect THD of my current?
I'm looking forward to any help and clarification.
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