Bridge Converter Switching at Zero Voltage to Suppress Surge Current
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Solution Overview
Problem
In bridge circuits, switching the ON/OFF of relays during operations leads to surge currents that reduce the durability and service life of relays and connected electrical elements due to voltage differences across their terminals.
Innovation Solution
A converter device with a bridge rectification circuit, capacitors connected in parallel and series, and a switching element controlled by a control unit to switch between low-voltage and high-voltage modes at a timing where the voltage difference across the switching element is zero, suppressing surge currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a relay is switched ON/OFF during bridge circuit operation, then rectification mode switching is achieved, but surge current flows through the relay and connected electrical elements due to voltage difference across contact points
Solution Approach 1:
The control unit detects the zero-crossing timing of the alternating current power supply in advance and schedules the relay switching to occur at this predetermined timing, thereby avoiding surge current before it can damage the relay and electrical elements
Solution Approach 2:
The invention changes the switching timing parameter from arbitrary or demand-based switching to zero-crossing-based switching, which fundamentally eliminates the voltage difference across relay contact points during switching, thereby preventing surge current
2Ease of operation
If relay switching is performed without considering voltage difference, then control flexibility is maintained, but excessive surge current reduces service life of switching components
Solution Approach 1:
The control unit continuously monitors the alternating current power supply waveform to detect zero-crossing timing, using this feedback information to precisely control when the relay should be switched, thereby protecting components while maintaining control functionality
Solution Approach 2:
The system determines the optimal switching timing in advance by detecting zero-crossing points, preparing the switching event to occur precisely when voltage difference is zero, thus preventing surge current before it can affect component longevity
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
The solution effectively reduces surge currents through the switching element and connected electrical components, enhancing their durability and service life.
Implementation Method 1
a bridge rectification circuit including a plurality of rectification elements D1 to D4 that rectify alternating-current power supplied from an alternating-current power supply 2
Implementation Method 2
capacitors C1 and C2 that smooth direct-current power output by the bridge rectification circuit 5
Data Source
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AI summary
The purpose of the present invention is to provide a converter device with which it is possible to suppress a surge current flowing in a switching element and an electric element connected to the switching element, and a motor drive device comprising the same. This converter device comprises: a bridge rectification circuit including a plurality of rectification elements (D1-D4) for rectifying power supplied from an AC power supply; a plurality of capacitors (C1, C2) connected in parallel to an output side of the bridge rectification circuit and connected in series with each other; a switching element (SW1) having a first terminal connected to a midpoint (P1) between the plurality of rectification elements connected in series and having a second terminal connected to a midpoint (P2) between the plurality of capacitors; and a control unit (24) that, by controlling the state of the switching element, switches between low-voltage control in which a current is supplied from one direction to all the capacitors, and high-voltage control in which a capacitor charged for each half cycle of the AC power supply is switched. The control unit turns on the switching element at a switching timing at which a difference between voltages at both ends of the switching element becomes substantially zero.