Active Bridge Rectifier Circuit With Dead Time Control
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Solution Overview
Problem
Conventional active bridge rectifier circuits face safety issues due to simultaneous turning on of upper and lower bridge arms caused by noise interference and non-ideal input voltage waveforms, leading to short circuits, which reduces efficiency and controllability.
Innovation Solution
An active bridge rectifier circuit with a rectifier unit comprising upper and lower bridge switches and a control unit that includes signal comparators to generate comparison signals for controlling the switches, a reference voltage unit to adjust dead time, and a protection unit using an AND gate circuit to prevent simultaneous switching, ensuring safe operation and maximizing duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional control methods use voltages to compare with reference voltage to generate drive signals, then the bridge rectifier circuit can be controlled, but noise interference or non-ideal input voltage waveform causes upper and lower bridge arms to be simultaneously turned on, leading to short circuit
Solution Approach 1:
The patent introduces a dead time control mechanism as an intermediary between the voltage comparison and bridge arm switching. A dead time generator creates a time delay between the turn-off of one bridge arm and the turn-on of the other, preventing simultaneous conduction. This mediator resolves the conflict by adding a temporal buffer that eliminates the short circuit risk caused by noise or waveform irregularities.
Solution Approach 2:
The patent implements preliminary action by pre-establishing dead time intervals before the actual switching occurs. The control circuit proactively schedules the turn-off of upper bridge arms and turn-on of lower bridge arms with a predetermined time offset, ensuring that even if noise or waveform anomalies occur, the bridge arms cannot be simultaneously on. This preventive timing strategy eliminates the short circuit hazard before it can manifest.
2Reliability
If reference voltage is increased to prevent simultaneous turning on of upper and lower bridge arms, then short circuit is prevented, but effective duty cycle is reduced, affecting utilization rate and controllability
Solution Approach 1:
The patent applies dynamics by making the dead time adjustable rather than fixed. The dead time generator allows dynamic adjustment of the time interval between bridge arm switching based on operating conditions. This enables the system to optimize the balance between safety (preventing short circuits) and productivity (maximizing duty cycle) by adapting the dead time to actual runtime requirements, rather than using a conservative fixed reference voltage that permanently limits duty cycle.
Solution Approach 2:
The patent changes the parameter of dead time duration to resolve the contradiction. Instead of increasing reference voltage (which permanently reduces duty cycle), the system adjusts the temporal parameter of switching intervals. By optimizing the dead time parameter, the system achieves short circuit prevention while minimizing the impact on effective duty cycle, thereby maintaining both reliability and productivity.
3Loss of energy
If semiconductor switches are used to substitute rectifier diodes, then efficiency is improved, but losses become significant and require careful management
Solution Approach 1:
The patent employs periodic action through synchronized PWM control of the semiconductor switches. The control circuit generates periodic gate drive signals with precise timing to ensure switches operate in optimal conduction modes. This periodic switching strategy minimizes switching losses and conduction losses by maintaining switches in their most efficient states throughout the AC cycle, thereby reducing overall rectifier losses while managing the complexity through systematic timing control.
Data Source
AI summary
An active bridge rectifier circuit includes a rectifier unit and a control unit. The rectifier unit includes a first upper bridge switch, a second upper bridge switch, a first lower bridge switch, and a second lower bridge switch. The control unit includes a first signal comparator and a second signal comparator. The first signal comparator compares a live wire signal provided from a live wire end with a neutral wire signal provided from a neutral wire end to generate a first comparison signal. The second signal comparator compares the live wire signal with the neutral wire signal to generate a second comparison signal. The first comparison signal controls the first upper bridge switch and the first lower bridge switch. The second comparison signal controls the second upper bridge switch and the second lower bridge switch.