Compensating for dead time degradation of PWM inverter waveforms

The output voltage waveforms of a bridge inverter using some form of modulation strategy, such as pulse width modulation (PWM), are not the same as the ideal modulated waveforms because of the effect of `dead time´. This is the short period of time that is allowed to elapse for safety reasons between switching one device in an inverter leg off and the other device on. Methods of compensating for dead time are proposed and investigated and it is shown that its effects can be substantially eliminated. Tests with a compensated variable speed drive, using an inverter fed induction motor, demonstrate that the torque perturbations at a gear change are now negligible. Similarly, in a UPS application the low order harmonics are found to be removed from the filtered output voltage when dead time compensation is introduced