Motor Speeds at higher RPM and input voltage relation

Please help me to understand this
Initially i observed distortions in the sinusoidal output when driving the motor at 400 RPM when the input voltage is 56V.
When i increased the input voltage to 64V then i found there are no distortions in the sinusoidal output and i applied torque upto 20NM.
Same issue it is happening at 500 RPM when i increase the voltage the voltage to 72V no distortion observed.
The motor RPM shall reach upto 700RPM and finding distortion again from 550 RPM, i don’t know if i can keep increasing the voltage. How do i solve the problem please help. The motor is 24 pole pair motor.

Did you also raise the motor.voltage_limit? It should be 50% of driver.voltage. But IMHO, you should consider the voltage drop under load and use a little less than 50%.
Otherwise the sine-wave is chopped

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The reason for distortion of the waveform is at higher RPM, when i observe the PWM, the lower legs are not getting ON, this is happening due to 100% modulation, now i reduce the modulation to 94% i could see some minimum duty on lower PWMs, but the RPM is getting limited and does not go beyond certain value, i still need to spin the motor by another 100 RPM to reach the expected levels, now i am enabling the flux weakening and see i can go to higher speeds.