BLDC motor taking excessive current
The BEMF voltage is related to the rotating speed of the motor, not the supplied voltage. So, it is normal that motor speeds up when you increase the voltage (or duty cycle ratio): \$V_{Supply}=V_{BEMF} + I\cdot R\$, \$V_{BEMF}=K\cdot \Omega\$. 

If you change the duty cycle is like changing V_supply. 

Possible causes:


the rotor flux is not properly oriented, by means of hall comutation scheme 
MOSFETs have long rise/fall switch times and they overheat, poor MOSFET gate driving mechanism


Add a schematics and some scope trace.

EDIT:

The transistors could be cross conducting, because you don't have a dead time circuit generator in between HIN_x and LIN_x. The optocouplers have an additional propagation delay, so it is plausible that you have a cross conduction of HI and LO IGBT while switching. 

What you can do: 


Introduce a new circuit with comparators and logic gates with RC delay in order to make a dead time generator, between optocouplers and gate drive IC.
Eliminate the optocouplers and use a MCU with a time process unit that already has dead time generator and all logics for hall sensors. Known to me, these are series of STM32 for motor control MCU.
Eliminate the IR2110 gate driver and optocoupler, use an isolated gate driver, all in one device, with a built-in dead time generator. link
Expand your logic circuit and add dead time.


Questions:


Does your circuit have the recirculation path? The depicted IGBTs don't have a body diode built in (intrinsic diode in the MOSFET)
Are you sure that Roff is 100 ohm and diode 1N1418 is adequate? The 100 ohm will not significantly reduce the turn off resistance, with additional diode it can just add some more capacitance, so you better eliminate both.
Why not replacing IGBT with MOSFET, because the IGBT is suitable for HV.