Bidirectional DC-DC converter, 12V - 300V, 1 kW?
Chill its only 1Kw so at 300 Volts the average current is about 3.3 Amps. SO you could do your power leveling at the 300 Volt level  There are lots of options so maybe BUCK BOOST or the SEPIC with the 1:1 coupled coil . I did a SEPIC for 1KW on Veroboard making 250VOLT at 4 amp   I used an E65 planar with 6 amp Bifilar Teflon wire and used scrap pcb as a spacer to make the airgap . I used 1200 Volt 80mohm SiC mosfet and got 95% efficiency from rectified mains . SO if you run it backwards you would get a Zeta with the same expected efficiency  .  Now that you can see how easy the high volts is, then you can transform this to your low isolated voltage with a ZVs isolated ROYER oscillator that has a synchronous rectifier to support bidirectional power flow  I would think that you will get better than 90% overall efficiency because I got 92% on 24 Volt NOT 12 and I used 150volt shottkys on the output because I didn't need bilateral power flow . Clearly there lots of ways to do this but I have stated the way that is close to what I have actually done.