 Dead-time output-voltage error

Dead-time output-voltage error is the difference between the intended switching-cycle average electric potential difference and the actual average produced when nonoverlap intervals alter the terminal waveform. Bridge switching dead time reduces H-bridge shoot-through, but during it an inductive load still carries electric current. Its recirculation path helps determine which rail clamps the output. The primary manufacturer discussion shows the bipolar/unipolar switching states and diode paths during that interval.^[ref]

An original event-accounting model avoids assuming a universal sign. Let an ideal half-bridge output take values 0 and $V_d$ over period $T$. During disjoint affected intervals of lengths $\Delta t_k$, suppose the intended normalized level is $q_k$ and the actual clamped level is $c_k$, each either 0 or 1. ThenAn interval replaced by the same rail contributes no error. An intended high interval replaced by low contributes negatively; the reverse contributes positively. Device drops require additional voltage terms.

For a stipulated single-pulse switching model, assume the load current keeps one sign throughout a cycle and that ideal recirculation clamps the midpoint to the low rail for current leaving the midpoint, or to the high rail for current entering it. With one effective high interval shortened or extended by $t_d$,For $V_d=24\mathrm{V}$, $T=50\mu \mathrm{s}$ and $t_d=100\mathrm{ns}$, the magnitude is $48\mathrm{mV}$. The corresponding ideal duty error magnitude is $t_d/T=0.002$. In a full H-bridge, subtract the two measured midpoint averages; their errors can reinforce or partly cancel according to their states.

Current-polarity dead-time compensation would add an opposing correction in that specified model. Near a current zero crossing, however, the sign may change within the interval, and the assumed clamping model can fail. Blindly applying the same signed offset throughout a crossing need not correct the actual waveform.

A proposed low-voltage test records both switch commands, actual midpoint potential and load electric current, integrates the difference from the intended waveform over a cycle, and compares it with the event sum. Repeat across current directions and pulse widths. Separate switching delay, diode drops and uncertain timing rather than fitting every discrepancy to one nominal dead-time number. The formulas above are illustrative switching models, not specifications for a particular driver.