Direct AC Power Converter Inrush Current Control
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Solution Overview
Problem
In direct AC power converting apparatuses, increasing the electrostatic capacitance of clamp capacitors to suppress voltage caused by regenerative currents leads to higher inrush currents, which is undesirable.
Innovation Solution
Incorporating a resistor on the neutral phase input line and connecting reactors in parallel with the resistor, along with a diode configuration that allows for voltage doubler rectification and parallel connection of capacitors to manage the inrush current effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrostatic capacitance of the clamp capacitor is increased to suppress the voltage between both ends of the capacitor, then the voltage suppression is improved, but the inrush current increases
Solution Approach 1:
The clamp capacitor is divided into two separate capacitors (first clamp capacitor and second clamp capacitor) connected in series. This segmentation allows the total capacitance to be distributed, reducing the inrush current while maintaining the voltage suppression capability across the series combination.
Solution Approach 2:
A neutral line switch is introduced as an intermediary component to control the connection between the neutral line and the series-connected clamp capacitors. This switch enables selective connection/disconnection, allowing the system to manage inrush current by controlling when the capacitors are connected to the power source.
2Reliability
If the electrostatic capacitance of the clamp capacitor is increased to suppress regenerative current voltage, then the voltage control is improved, but the device complexity increases
Solution Approach 1:
The series-connected clamp capacitors serve multiple functions: they suppress regenerative current voltage, divide the voltage across two components, and reduce inrush current. This multi-functionality achieves voltage control reliability without proportionally increasing device complexity.
Solution Approach 2:
The neutral line switch is used to preliminarily disconnect the clamp capacitors from the power source during startup or voltage transitions. This preliminary action prevents inrush current before it occurs, while the capacitors remain in place to provide voltage suppression when needed.
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 prevents inrush currents from flowing to the capacitors, reduces voltage pulsations, and ensures efficient operation by managing the charging and discharging of capacitors, thereby maintaining capacitor voltage within safe limits.
Implementation Method 1
a series circuit in which a power source, a reactor, a resistor, and a capacitor are connected in series
Implementation Method 2
When an inductance of the reactor is defined as L
Implementation Method 3
an electrostatic capacitance of the clamp capacitor is defined as C
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The present invention is directed to a direct AC power converting apparatus capable of reducing an inrush current. A control section (5) controls a current-source converter 1 while a switch (S1) is conducting, to render conducting a pair of a high-arm side transistor and a low-arm side transistor (for example, transistors (Srp, Srn)) which are connected to any one of input lines (ACLr, ACLs, ACLt), performs voltage doubler rectification on a voltage between a neutral phase input line (ACLn) on which a resistor (R1) is provided and any one of the input lines (ACLr, ACLs, ACLt), to serve for charging of clamp capacitors (Cc1, Cc2).