Power Conversion Device Current Control Stability
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Solution Overview
Problem
Existing power conversion devices with multi-level circuits and low inductance values face instability in current control due to high gain of the control system, leading to unstable operation when the inductance value of the AC inductor is reduced.
Innovation Solution
A power conversion device with a series connection of switching units, an input LC filter, and a control unit that measures and stabilizes the current using feedback control, selecting a current with a low element value within a gain margin to maintain system stability, even when the inductance value is low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the inductance value of the AC inductor is reduced to decrease filter size, then the device size is reduced, but the current control becomes unstable due to high gain
Solution Approach 1:
The patent applies feedback control by measuring the current through the AC inductor and using this measurement to adjust the switching control. The control unit performs feedback control based on the measured current value to stabilize the current control when the inductance value is low, preventing instability while maintaining reduced filter size.
Solution Approach 2:
The patent changes the control parameter from voltage-based control to current-based feedback control. By measuring the actual current through the AC inductor and using this current value as the feedback parameter for control, the system adapts to low inductance conditions and maintains stability.
2Volume of moving object
If the inductance value Lf is made lower than system impedance Ls to reduce filter size, then the device size is reduced, but the current control becomes unstable
Solution Approach 1:
The patent implements feedback control specifically designed for the case where Lf < Ls. The control unit measures the current through the AC inductor and performs feedback control based on this measurement, which stabilizes the system even when the filter inductance is lower than the system impedance, enabling reduced filter size without sacrificing stability.
Solution Approach 2:
The patent makes the control system dynamic by continuously measuring the current and adjusting the control based on real-time conditions. This dynamic feedback approach allows the system to adapt to the specific condition where filter inductance is lower than system impedance, maintaining stability under varying operating conditions.
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 prevents input current control instability and maintains stability by selecting an appropriate current for feedback control, ensuring stable operation even with reduced inductance values.
Implementation Method 1
a capacitor 4 and an inductor 3 that constitute an input filter together
Implementation Method 2
a plurality of switching units 40a, 40b and 40c that are connected in series between a positive terminal and a negative terminal of an AC source 11 and that output, to loads 14a through 14c, an input current Iin that is from the AC source 11 and a DC output voltage E that is generated through ON/OFF control of semiconductor switching elements 41a through 41c
Data Source
AI summary
A power conversion device including an alternating current (AC) source, a plurality of switching units connected in series between positive and negative terminals of the AC source, each including a semiconductor switching element and having a load connected thereto, each switching unit outputting, to the load connected thereto, an input current from the AC source and a direct current (DC) output voltage that is generated through ON/OFF control of the semiconductor switching elements, a capacitor connected in parallel with the AC source and with the switching units, an inductor inserted between the capacitor and the switching units, and between the AC source and the switching units, a current measurement unit that measures a value of a current flowing from the AC source to the capacitor, and a control device that performs the ON/OFF control on the semiconductor switching elements on the basis of the measured current value.