Male cat fights female cat

Hi, 

I know there are topics similar to this on here but if there is any specific advice it would be much appreciated.

I have two cats that we adopted as a bonded pair. Since we've had them (almost 3 years now) our male cat picks on our female cat, corners her, bites her, sometimes we're awakened in the middle of the night by her screams while he's attacking her. I do think her vocalizations are slightly exaggerated but still, he beats her up.

They also cuddle, sleep together, snuggle, seem bonded. They are both fixed. My female cat is an all around scared cat (with humans and cats) because they were feral and for whatever reason the male cat just got more used to people. 

I don't understand why they fight. We have two feeding bowls, two litter boxes. They use the same litter box and eat out of the same dish most of the time still anyway. She never fights back- just hisses and try to get away. We always clap loudly and just break it up. And then separate them for awhile. 

It's relatively manageable but now I'm worried because we're leaving for almost 3 weeks for the first time since we've had them. We will have someone check on them daily but no one to break up the fights. We've left for up to 4 days before, and everything has been fine. But who knows what she went through while we were gone.

We have almost 2 months to try some stuff out before we leave. Does anybody have any suggestions? Any experience with those pheromone diffusers? I almost bought them but heard they sometimes burn up and i wouldn't want to leave it plugged in while we're gone due to fire risk. Any experience with the collars, spray, or other products?

Thank you!

I would really work on building her confidence. A confident cat is less likely to be picked on.

We build confidence using play, food, height and love. I would really step up playing with her in all areas of the house. After play feed treats or food. Try to give a number of places for both of them to go high. Cat trees, maybe window perches, maybe cat shelving. And try to give as much love as possible. If she can't be held or pet just sit with her, talk softly to her. 

I would also add more comfy and warm bedding. 

Is there certain places that she gets cornered? If so, try to get a cat tree or something so that she has multiple escape routes (both horizontally and vertically).

Please do not ignore the boy during this and try to play with him and after play feed.

This should help. If yous tart now hopefully you can see a difference before you leave. And please feel free to ask anything and hopefully we can see what works and how we could adjust things.