Dead-time compensation for PWM amplifiers using simple feed-forward techniques

Dead-time effect is one of the dominant sources of output current and voltage distortion for pulse width modulated (PWM) amplifiers. Practical switching devices have finite turnon and turn-off time. To avoid short circuit a blanking time is added between turn-off and turn-on of the complementary working switches in a switching-leg. The blanking time, also referred to as dead-time, results in a nonlinear voltage error of the PWM output stage. Especially high-precision applications that require accurate input current for positioning systems suffer from the dead-time effect. Extensive studies have been done on the analysis and elimination, minimization and compensation of dead-time in PWM converters. Most of these techniques rely on the detection of the polarity of the output current of the converter. By using only the polarity of the output current, the inductor current ripple is neglected, which is not sufficient for high-precision applications. In this paper nonlinear feedforward of the current setpoint is used to compensate the dead-time effect. This simple feedforward technique leads to significant improvement of the current tracking during zero crossings over a high output current frequency range, as demonstrated by measurement results.