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I'm curious if anyone can validate the efficiency of a multilevel inverter. I've been thinking about them as a better solution for PV conversion. They seem to have many advantages, but when I look at it, a single phase output can seemingly only draw power from, on average, half of the panels at a time.

Voltage Ourput from MLI

I've seen this circuit both with and without caps across each individual source. I just can't see how this can do better than 50% efficiency especially without the caps.

Edit: I keep looking... I've found a ton of these that are grid tie. Lets say you have 6 panels that have an output voltage (after MPPT and DC-DC boost phases) of 30 V and each can provide 5 amps. So, I've got a peak voltage of 180V which gives me ~120Vrms. Now, the total available power from the panels is 180V*5A = 900W. But, my output power is 120V*5A = 600W. I feel like I'm missing something critical. Someone please tell me exactly how I'm being an idiot.

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Multilevel inverters is efficient (just google random 10 science articles about it). Instead, they have much more complex control logic. You've chose H-bridge based topology - it's good, but expensive. Look at diode-clamped ML inverter, maybe it's enough for your purposes?

For PV converter you better look for "multilevel inverters for PV applications", they're a bit different. For example, just one inverter may be not enough, most solutions i've met in articles uses additional boost converter on inverter's input.

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  • \$\begingroup\$ Ok, but I still don't see how they can match a standard string inverter, which takes all the power coming from the panels, inverts it into a square wave, then filters it. String inverters use all the panels, all the time. This h-bridge configuration (which lets keep for the sake of simplicity) hardly ever uses the top panel. Is the energy stored in the cap that's across it? I've seen this same circuit without it shown, but I suppose it could be implied. Still confused... \$\endgroup\$ Sep 12 '15 at 16:06
  • \$\begingroup\$ It's hard to recall for me, but as i remember, one of possible solutions works in such way: boost converter sets up MPPT for the panel (one DC-DC per 1 panel) by changing it's input impedance, and every DC-DC consequentially pumps up the DC-Link capacitor. Then, after capacitor we're using ML inverter to achieve AC output. P.S. One more nice article about PV - "A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules" (IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, 2005) \$\endgroup\$
    – Looongcat
    Sep 13 '15 at 16:44

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