How Do Boost and Buck Converters Work in a DC-AC Inverter?

[Chacabucogod]

I'm currently reading a paper given to me by my professor to expose to class. The problem is that I don't understand it very well! I'd like to see if you guys can help me. The paper I'm reading is "A boost dc-ac converter: Analysis, design, and experimentation" I've found the paper on the following link by looking it up on google. The funny thing is that the authors mention that the first boost converter acts as a boost and that the second one acts as a buck converter. I can't see how. They mention that the voltages are 180 out of phase of each other. How do they do that? With the PWM? The things I'm talking about are on the second page.

link to the paper

 

[Windadct]

They refer to Fig 1 as Buck and Fig 2 as Boost/Buck - I read through the first page and scanned the rest... I just see a DC/DC buck converter controlling a higher DC bus link and then a regular DC/AC inverter -- not really any thing unusual - very common in the Solar field today. ( If this was published in the 80s I would get it but seems pretty basic for '99?)
The DC/AC converter can be looked at as a "buck" converter - esp when considering short timeframe. Just the output modulation goes from -100% to 0 to + 100%