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

Abstract

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.

Evaluation of current ripple amplitude in five-phase PWM voltage source inverters

“…By introducing (20) in (4), and calculating v(t) by (11) and (12), the alternating component of inverter output voltage of the first phase can be written as…”

“…The effects of high-ripple currents on dead-time with adaptive compensation are studied in [19] and [20] as well, where the knowledge of peak-to-peak current ripple was of interest but it has not been properly addressed. Another example of application is referred to hysteresis current controllers and variable switching frequency PWM, for single-phase [21] and three-phase inverters [22], [23].…”

Elimination of zero-crossing distortion for high-precision amplifiers

“…These techniques rely on the detection of the polarity of the sampled output current of the converter [4]- [8], allow discontinuous conduction mode (DCM) during the output current zero crossing [3], or minimize dead-time to the absolute minimum [2]. All techniques mentioned achieve a reduction of the problem but, due to errors in the detection of current polarity changes or DCM during zero crossings, are not capable of completely removing it.…”

“…Extensive studies have been done on dead-time in PWM converters [1] and elimination [2], [3], minimization [4], [5], and compensation [6]- [8] of its effects. These techniques rely on the detection of the polarity of the sampled output current of the converter [4]- [8], allow discontinuous conduction mode (DCM) during the output current zero crossing [3], or minimize dead-time to the absolute minimum [2].…”

Analysis of Peak-to-Peak Current Ripple Amplitude in Seven-Phase PWM Voltage Source Inverters

“…In particular, the knowledge of the peak-to-peak current ripple distribution can be useful to determine the output voltage distortion due to the inverter dead-time in case of output currents with high ripple, by determining the multiple zero-crossing interval [21]. The effects of high-ripple currents on dead-time with adaptive compensation are studied in [22] and [23] as well, where the knowledge of peak-to-peak current ripple was of interest, but it has not been properly addressed. Another example of application is referred to hysteresis current controllers and variable switching frequency PWM, for single-phase [24] and three-phase inverters [25][26][27].…”