I am going to guess that you are not familiar with the prinicples of AC electricity.
First, the nominal 440V AC system is rated according to the RMS value of the system voltage, which is aproximately 70.7% of the peak value. This means that in a 440 Volt system, the peak voltage applied to the load (motor) is around 630 volts. This corresponds very closely to the filtered DC voltage you will see in the controller between the rectifier and the IGBT switching circuit. A motor rated for 460VAC is designed to live with these peak voltages ( 630 to 680V) as a normal condition.
Consequently, The motor does not see excessive voltages, at least when operated at it's design speed (60 hz). The PWM nature of the output of this controller produces an applied voltage to the motor with a constant peak value, but with a varying duration. The result is the motor sees this applied voltage as not much different from a sine wave power supply.
However, to maintain the torque performance of a motor that is operated at speeds less that the 60HZ rated speed, you will need to reduce the voltage to maintain the ratio of voltage to frequency that the motor is rated for. For a 460V motor designed for 60 HZ, this ratio is around 7.67:1. (460V / 60 HZ).
I also assume you are working on this just for your own amusement. There are ready made, all the bugs worked out, complete with warranty controllers available for about what the parts would cost.
Have fun!
Wes