Rectifier Bridge Circuit Inrush Current Limitation
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Solution Overview
Problem
Existing controlled rectifier bridge circuits face issues such as high cost, poor reliability, risk of undesired relay opening, acoustic noise, and high current consumption in electromechanical solutions, and increased design complexity and cost in electronic solutions, particularly due to the need for galvanic isolation and opto- or magnetic couplers.
Innovation Solution
A rectifier bridge circuit using conventional electronic switches like SCRs or IGBTs, biased from an auxiliary DC bus and interfaced with a microcontroller unit without magnetic or opto-couplers, employing a circuit architecture with a high-voltage low-valued capacitor and a level shifter/current source circuit to control the switches, thereby reducing costs and complexity while enabling inrush current limitation through progressive time conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electromechanical solutions using relays are used to implement controlled bridges, then galvanic isolation is achieved, but cost increases, reliability decreases, and acoustic noise is generated
Solution Approach 1:
The patent replaces electromechanical relay switches with electronic switches (SCRs or IGBTs) that are directly controlled by a microcontroller unit. This substitution eliminates mechanical moving parts, thereby improving reliability while removing the need for complex galvanic isolation mechanisms such as opto- or magnetic couplers, thus reducing device complexity.
2Device complexity
If electronic solutions using SCRs are used to implement controlled bridges, then cost is reduced, but design complexity increases due to the need for floating supply and opto- or magnetic couplers
Solution Approach 1:
The patent replaces the complex galvanic isolation mechanism with a direct electronic control interface. The microcontroller unit directly drives the gate of the SCR or IGBT without requiring opto- or magnetic couplers, thereby simplifying the circuit design while maintaining cost-effectiveness.
Solution Approach 2:
The patent employs a single auxiliary DC bus that serves multiple functions: it provides the holding current for the electronic switches during the positive half-cycle and the gating current during the negative half-cycle. This multi-functional approach eliminates the need for separate floating supplies and complex isolation mechanisms, reducing design complexity.
3Reliability
If relays are used as switches in electromechanical solutions, then galvanic isolation is achieved, but cost increases due to expensive relays and sense resistors
Solution Approach 1:
The patent replaces expensive electromechanical relays with solid-state electronic switches (SCRs or IGBTs) that have lower on-resistance and no mechanical wear. This substitution reduces power losses while improving reliability, as electronic switches do not suffer from contact erosion or mechanical failure.
4Productivity
If a resistor is used to limit inrush current to a capacitor, then inrush current is controlled, but power losses increase and efficiency decreases
Solution Approach 1:
The patent employs dynamic control of the electronic switch conduction angle to limit inrush current. By progressively increasing the conduction angle of the SCR or IGBT during capacitor charging, the circuit limits inrush current without the continuous power dissipation associated with resistive limiting. Once the capacitor is charged, the switch is fully conductive, eliminating power losses.
Data Source
AI summary
A rectifier bridge circuit includes a first SCR/IGBT switch and a second SCR/IGBT switch coupled to a circuit input to receive an ac input voltage. The first and second SCR/IGBT switches are alternatively switchable to generate a rectified voltage at a circuit output. Control currents coupled to control terminals of the first and second SCR/IGBT switches are power supply sourced from an auxiliary dc source generated by rectifying the ac input voltage. The control currents are generated by current sources coupled between the auxiliary dc source and the control terminals of the first and second SCR/IGBT switches. The current sources are selectively activatable to produce gating currents for switching on and off the first and second SCR/IGBT switches. A controller unit is provided to control the current sources via level shifter circuits. The control implements progressive conduction time of the first and second SCR/IGBT switches so as to provide inrush current limitation.