Boost Circuit Drive Pulse Control for Backflow Current Prevention
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Solution Overview
Problem
The existing rectifier circuits in power converting apparatuses suffer from backflow currents when the voltage of the smoothing capacitor exceeds the power supply voltage, leading to increased conduction losses and inefficient energy transfer.
Innovation Solution
A power converting apparatus is designed with a boost circuit comprising a reactor, first and second legs with switching elements, and voltage detecting units to control the drive pulses such that the width of the second drive pulse for the first upper-arm switching element is larger than the first drive pulse for the first lower-arm switching element when the smoothed voltage is higher than the supply voltage, preventing backflow currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the MOSFET is kept ON all the time when the power supply voltage is positive to enable rectification, then the rectification function is improved, but a backflow current flows from the smoothing capacitor to the power supply side when the capacitor voltage exceeds the supply voltage, increasing conduction losses
Solution Approach 1:
The patent applies dynamic control by switching the MOSFET between ON and OFF states based on the voltage relationship between the smoothing capacitor and the power supply. When the capacitor voltage is lower than or equal to the supply voltage, the MOSFET is turned ON for rectification. When the capacitor voltage exceeds the supply voltage, the MOSFET is turned OFF to prevent backflow current, thus dynamically adapting to voltage conditions to minimize energy losses while maintaining rectification function.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the voltage of the smoothing capacitor and comparing it with the power supply voltage. Based on this feedback information, the control circuit adjusts the MOSFET switching state accordingly, ensuring that the MOSFET is ON only when necessary for rectification and OFF when the capacitor voltage exceeds the supply voltage, thereby preventing backflow current and reducing conduction losses.
2Loss of energy
If the MOSFET is turned OFF to prevent backflow current, then energy losses are reduced, but the rectification function may be compromised
Solution Approach 1:
The system dynamically adjusts the MOSFET switching state based on real-time voltage conditions. The MOSFET is turned ON when the capacitor voltage is lower than or equal to the supply voltage to enable efficient rectification, and turned OFF when the capacitor voltage exceeds the supply voltage to prevent backflow current. This dynamic control ensures optimal rectification efficiency while minimizing energy losses.
Solution Approach 2:
The control system uses feedback from voltage sensors to continuously monitor the relationship between capacitor voltage and supply voltage. Based on this feedback, the control circuit intelligently decides when to turn the MOSFET ON for rectification and when to turn it OFF to prevent backflow, thereby maintaining high rectification efficiency while reducing energy losses.
3Loss of energy
If synchronous rectification is implemented to reduce losses, then energy efficiency is improved, but the control complexity increases due to the need for precise timing and voltage monitoring
Solution Approach 1:
The patent employs feedback control by using voltage sensors to monitor both the power supply voltage and the smoothing capacitor voltage. The control circuit compares these voltages and generates appropriate gate drive signals for the MOSFET based on the comparison result. This feedback mechanism enables synchronous rectification with reduced control complexity, as the control decisions are based on simple voltage comparison rather than complex timing requirements.
Solution Approach 2:
The control system achieves self-service by using the voltage information from the smoothing capacitor and power supply to automatically control the MOSFET switching. The system monitors its own operating conditions and adjusts the rectification process accordingly, eliminating the need for external complex control signals or precise timing mechanisms, thereby reducing control circuit complexity while maintaining energy efficiency.
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 configuration effectively prevents backflow currents and ensures efficient energy transfer by controlling the switching elements to manage voltage differences between the smoothing capacitor and the power supply, reducing conduction losses and maintaining sinusoidal current output.
Implementation Method 1
a boost circuit comprising a reactor, a first leg, and a second leg, and boosting a first voltage output from an alternating-current power supply
Implementation Method 2
a smoothing capacitor connected to both ends of the boost circuit and smoothing a voltage output from the boost circuit
Data Source
AI summary
A power converting apparatus includes: a boost circuit including a reactor supplied with first voltage output from an alternating-current power supply, a first leg including first upper-arm and lower-arm switching elements connected in series, and a second leg connected in parallel with the first leg and including second upper-arm and lower-arm switching elements connected in series, and boosting the first voltage; a first voltage detecting unit detecting the first voltage; a smoothing capacitor smoothing voltage output from the boost circuit; and a second voltage detecting unit detecting second voltage smoothed by the smoothing capacitor. When the second voltage is larger than the first voltage and is lower than or equal to twice the first voltage, a width of a second drive pulse to turn on the first upper-arm switching element is larger than a width of a first drive pulse to turn on the first lower-arm switching element.