Power Conversion Device Initial Charging Phase Control
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Solution Overview
Problem
Direct initial charging of an inverter without using current limiting resistors or reactors leads to overvoltage due to counter electromotive force from leakage inductance, causing potential breakage of components.
Innovation Solution
A power conversion apparatus that controls the closing phase angle of the circuit breaker to suppress overvoltage during initial charging, using a synchronous switching control device to manage the phase angle and prevent overcharge by optimizing the timing of power source switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct initial charging is performed without current limiting resistors or reactors, then apparatus compactification and cost reduction are achieved, but overvoltage occurs causing component breakage
Solution Approach 1:
The invention changes the timing parameter of power source switching to control the closing phase angle. By adjusting when the circuit breaker closes during the voltage cycle, the peak voltage applied to the smoothing capacitor is controlled to not exceed the rated voltage, eliminating overvoltage damage while maintaining direct charging without current limiting components.
Solution Approach 2:
The invention performs preliminary analysis and calculation of the optimal closing phase angle before switching operation. The control device determines the precise timing in advance based on system parameters, ensuring that when the circuit breaker closes, the voltage conditions are optimal for safe charging without requiring additional protective components.
2Reliability
If current limiting resistors or reactors are used for initial charging, then component safety is ensured, but apparatus size and cost increase
Solution Approach 1:
The invention extracts and eliminates the current limiting resistors and reactors from the charging circuit. Instead of using these physical components to limit current and prevent overvoltage, the solution removes them entirely and replaces their protective function with precise timing control of the circuit breaker closing phase angle.
Solution Approach 2:
The invention substitutes the mechanical/passive current limiting approach (using resistors and reactors) with an active control system. The control device uses electrical timing and phase angle detection to achieve the same protective effect without the physical bulk and cost of current limiting components.
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
Prevents overcharge and potential breakage of components by ensuring the DC voltage remains within safe limits, effectively managing the voltage peaks and maintaining component integrity.
Implementation Method 1
a voltage of not less than a peak value of an input voltage is applied to a smoothing capacitor of the inverter, by a counter electromotive force which is generated in a leakage inductance of the input transformer
Data Source
Figure 1
Figure 2
Figure 3(1)~3(3)
AI summary
To provide a power conversion apparatus and an initial charging method of the same which control a closing phase angle at the time of switching on a power source, to suppress an overvoltage of a DC voltage, and prevent overcharge and breakage of parts caused by the overvoltage. A peak voltage value V2m [V] of an input voltage V2, a total secondary side converted winding resistance R [Ω] of a primary side and a secondary side of an input transformer 10, a total leakage inductance L [H] of the primary side and the secondary side of the input transformer, a capacitor C [F], a power source frequency f [Hz] are substituted in a mathematical expression (6), and a closing phase angle θ [deg] is varied at each 5 - 10 [deg] interval from 0 to 180 [deg], to obtain first half-wave peak voltage values of the capacitor voltage Vc at the closing phase angles θ (S1). Next, in a graph in which the horizontal axis represents the closing phase angle θ, and the vertical axis represents the first half-wave peak voltage value of the capacitor voltage Vc, a phase angle (an optimum closing phase angle θ1) of a crossing point with a peak voltage value of an input voltage V2 is obtained. (S2). Next, using a synchronous switching control device 3, a circuit breaker 1 is closed at the optimum closing phase angle θ1 (S3).