You could throttle it with a constant-current source (essentially an active electronic variable resistance), set to something just less than the solar controller can manage, and put that between the 48v bat and the solar controller.

Linear ones are fairly simple to design but at high currents can get quite hot so would need heat-sinking.

Switch-mode ones run cool but are more complicated to design and might mismatch with your solar controller which is essentially a big switch-mode device itself.

The simplest version of this is just a big power resistor sized to restrict the input current below the 58 amp limit (130% of 45 amps).

A few simple calculations show that the worst case voltage drop would be 24 volts and at 58 amps this would need a 0.413 ohm resistor.

Nearest standard value of 0.47 ohms would limit to 51 amps at 24 volts.

If used continuously it would then dissipate 1.2KW, but the chances are that the voltage drop is less than 24 volts and the Pulse Width Modulation of the solar controller will limit the time it is dissipating to a small % of that.

Try a 50 watt resistor if you can get one. And fit a 60 amp fuse.

When testing my solar inverter I simulated a solar source with a variable voltage, current-limited, bench power supply.

Soar PV is essentially a current-limited variable voltage power source.

The current-limiting bit is what seems to be missing in your setup.

Hope you haven't blown it up too bad.

Good luck.

Dave.