PMP22650: Question about 800-V, bi-directional on-board charger

I view the video of the high voltage seminar about the benefits of 650-V GaN FETs for 800-V power converters on the web. I have some questions and hope to receive kind answers.

The figure shown below mentioned the 800V bi-directional on-board charger. For 800V battery, the presenter says that the series stacked half-bridge approach on the secondary side can reduce the voltage of used devices, from 1200V to 650V. From my knowledge, the output voltage of CLLLC secondary side is positive-negative voltage. Does it means that only the positive-half cycle charges one of the capacitors? To balance the voltage of two capacitors, is the next positive-half cycle charges the other capacitor? How the energy of the negative-half cycle is used? Is the negative-half cycle used to adjust the overvoltage of the battery? or the controller will not deliver power on the negative-half cycle (by reducing the duty cycle)?