Power Converter Inrush Current Prevention via Predictive Control
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Solution Overview
Problem
Existing power conversion devices face issues with inrush currents when the capacitor voltage drops below the alternating current power supply voltage during power failures or interruptions, leading to potential semiconductor element damage, especially when using wide bandgap semiconductor materials, which complicates achieving a small-sized and low-cost design.
Innovation Solution
A power conversion device with a power detecting unit and a control unit that predicts capacitor voltage decreases based on input power changes, causing the device to stop operations before the capacitor voltage falls below the input voltage, thereby preventing inrush currents and allowing the use of semiconductor materials with lower current resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the capacitor breakdown voltage is reduced to decrease size and cost, then the capacitor voltage when operating is near the alternating current power supply voltage, but the capacitor voltage drops below the input voltage during power failure, causing inrush current
Solution Approach 1:
The control unit performs preliminary detection of input power changes and predicts capacitor voltage decrease before the actual voltage drop occurs. By detecting power failure or interruption in advance and predicting the voltage trajectory, the system can prepare protective actions (such as opening switches or activating protection circuits) before the capacitor voltage drops below the alternating current power supply voltage, thereby preventing inrush current while allowing the use of capacitors with lower breakdown voltage
Solution Approach 2:
The control unit continuously monitors input power and capacitor voltage, establishing a feedback mechanism that detects changes in input power and uses this information to predict future capacitor voltage levels. This feedback loop enables the system to adjust its state in real-time based on the predicted voltage trajectory, ensuring protection against inrush current while optimizing capacitor selection for size and cost
2Ease of operation
If the load operation is stopped only after capacitor voltage drops to reference value, then the reference value must be set near maximum input voltage, but the detection and control time delay causes large inrush current to occur
Solution Approach 1:
Instead of waiting for capacitor voltage to actually drop to a reference value, the control unit detects changes in input power in advance and predicts the future voltage trajectory. This preliminary detection and prediction allows the system to take protective action before the dangerous voltage drop occurs, eliminating the harmful time delay between detection and protection while maintaining simple control logic
Solution Approach 2:
The control unit acts as an intermediary that bridges the gap between simple voltage threshold detection and complex real-time prediction. By using input power change detection as an intermediate indicator, the system can infer future voltage conditions and trigger protection mechanisms in advance, effectively bridging the time delay problem without requiring complex control algorithms
3Reliability
If wide bandgap semiconductor materials are used, then current resistance is lower, but the device complexity increases due to inrush current protection requirements
Solution Approach 1:
The control unit utilizes existing detection and control functions to perform inrush current protection, rather than requiring separate dedicated protection circuits. By using the same control infrastructure for both normal operation control and protection functions, the system achieves reliable protection for wide bandgap semiconductor materials without significantly increasing device complexity
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 effectively prevents inrush currents and allows for the use of wide bandgap semiconductor materials, resulting in a smaller, lower-cost power conversion device configuration.
Implementation Method 1
a capacitor that smooths an output
Implementation Method 2
a power detecting unit that detects power input into the power converting unit
Data Source
AI summary
In response to a problem wherein a voltage of a capacitor of a power conversion device decreases when a voltage of an alternating current power supply is restored after once decreasing, the voltage of the capacitor drops below a maximum value of the voltage of the alternating current power supply when power is restored, and an inrush current occurs, the power conversion device, provided between an alternating current power supply and a load, is such that a decrease in an input voltage or an input current of a power converting unit is detected, a change in the voltage of the capacitor is predicted, and operations of the power converting unit are caused to stop before the voltage of the capacitor drops to or below the maximum value of the voltage of the alternating current power supply, thereby restricting an occurrence of an inrush current.