Bridge Circuit Capacitance Precharging for Lower Switching Loss
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Solution Overview
Problem
Semiconductor switches in power electronic circuits experience significant switching losses and overvoltages due to the behavior of intrinsic diodes and voltage-dependent capacitances, particularly in hard-switching systems and bridge circuits, which are not effectively mitigated by existing zero-voltage or zero-current switching methods.
Innovation Solution
A method for forcibly precharging the capacitance of semiconductor switches, independent of operating conditions, using a charging current path that includes a diode in series with the switch and a series resonant circuit, allowing for reduced reverse voltage load and overvoltage prevention without increasing switching losses, by charging the capacitance before switching off and utilizing a low auxiliary voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If hard-switching is used in semiconductor switches, then circuit simplicity is maintained, but switching losses increase significantly
Solution Approach 1:
The patent applies preliminary action by precharging the drain-source capacitance of the MOSFET before the main switching event. A dedicated charging circuit activates during the dead time period to charge the capacitance to a predetermined voltage level before the next switching cycle begins. This precharging action reduces the voltage difference that must be overcome during switching, thereby reducing switching losses while maintaining circuit simplicity.
2Device complexity
If intrinsic diodes of MOSFETs are used as free-wheeling diodes, then device count is reduced, but reverse current chopping increases causing high switching losses and overvoltages
Solution Approach 1:
The patent converts the harmful reverse current chopping effect into a beneficial precharging mechanism. The reverse current that flows through the intrinsic diode during the dead time is deliberately utilized to charge the drain-source capacitance to a beneficial voltage level. This transforms what was previously a harmful effect (reverse current chopping causing overvoltages) into a useful function (precharging the capacitance to reduce switching losses).
Solution Approach 2:
The intrinsic diode serves a dual function: it continues to act as the free-wheeling diode for load current while simultaneously serving as the charging path for the drain-source capacitance during dead time. The circuit uses its own existing components (the intrinsic diode and the reverse current) to perform the additional function of capacitance precharging, eliminating the need for separate external charging components.
3Loss of energy
If resonant technologies are used for zero voltage switching, then switching losses are reduced, but switching expenditure and circuit complexity increase
Solution Approach 1:
The patent extracts and isolates the capacitance charging function from the main power switching path. By creating a separate, dedicated charging circuit that operates independently during dead time, the complex resonant switching mechanisms are eliminated while retaining the beneficial effect of capacitance precharging. The solution takes out only the essential function (capacitance charging) from the complex resonant system.
Solution Approach 2:
The patent changes the voltage parameter of the drain-source capacitance before the switching event by precharging it to a predetermined voltage level. This parameter change (voltage level adjustment) is achieved through a simple charging circuit during dead time, avoiding the need for complex resonant circuits while still achieving reduced switching losses through controlled voltage conditions.
4Object-affected harmful factors
If gate voltage is reduced to slow down switching process, then overvoltages are limited, but switch-on losses increase
Solution Approach 1:
Instead of modifying the gate voltage during switching to control overvoltages, the patent takes preliminary action by precharging the drain-source capacitance before switching. This precharging action prepares the capacitance in advance to accept the switching energy more gracefully, reducing overvoltages without requiring any modification to the gate voltage or switching speed control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces overvoltages and switching losses in semiconductor switches by precharging the capacitance before switching, allowing for efficient operation in hard-switching systems and bridge circuits without requiring additional inductances or capacitances, and can be implemented cost-effectively with few components.
Implementation Method 1
using a charging current path that is independent of the main current path, allowing for controlled precharging of the drain-source capacitance before switching, which reduces overvoltages and switching losses by utilizing a series diode and inductance to form a series resonant circuit
Data Source
AI summary
A method, circuit configuration and bridge circuit for charging a capacitance effective on the main current terminals of a semiconductor switch, in particular an intrinsic capacitance, in particular the drain-source capacitance of a MOSFET semiconductor switch or the collector-emitter capacitance of an IGBT semiconductor switch, the precharging, in particular the at least partial charging, of the effective capacitance being forcibly controlled via a charging current path.