Cascade Chopper Circuit With Split Inductors for Low-Loss DC Conversion
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Solution Overview
Problem
The existing chopper circuits for DC electric railways face challenges in miniaturization and lightweight design, leading to increased weight and volume, which results in higher costs and lower reliability, along with switching losses and potential overvoltages due to the inductor's high inductance and square wave current flow.
Innovation Solution
A chopper circuit design that includes semiconductor power converters and an inductor connected in series, with a control unit to manage power conversion and switch control, allowing for the output current to be controlled below a predetermined value, thereby reducing switching losses and preventing overvoltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If the inductance of the inductor is reduced to achieve miniaturization and lightweight design, then the weight and volume of the inductor are reduced, but the ripple currents in the inductor current increase, degrading power quality and causing unstable converter operation
Solution Approach 1:
The inductor is divided into a first inductor and a second inductor connected in series, allowing the total inductance to be distributed across multiple components. This segmentation enables reduced individual inductor sizes while maintaining total inductance requirements, addressing the weight reduction goal without compromising stability.
Solution Approach 2:
The patent implements dynamic control of switching timing based on current detection. The control unit detects inductor current and dynamically adjusts switch activation timing to ensure current continuity, preventing instability even when inductance is reduced. This dynamic adaptation maintains reliable operation with smaller inductors.
2Volume of stationary object
If the inductance of the inductor is reduced for miniaturization, then the volume of the inductor is reduced, but the ripple currents increase, degrading power quality
Solution Approach 1:
By splitting the inductor into series-connected first and second inductors, the patent reduces the volume of each individual inductor component while the combined inductance maintains smoother current characteristics, thereby reducing ripple currents and preserving power quality.
Solution Approach 2:
The control unit employs periodic switching control with carefully timed intervals to ensure continuous current flow through the series inductors. This periodic action with optimized timing reduces current ripple by preventing discontinuities that would otherwise occur with reduced inductance.
3Ease of operation
If hard switching is performed in the first and second switch units, then the chopper circuit operates with simple control, but switching losses occur, reducing converter efficiency
Solution Approach 1:
The control unit performs preliminary detection of inductor current before activating switches. By detecting current status in advance and timing switch activation to coincide with zero or near-zero current moments, the patent enables soft switching that reduces switching losses while maintaining relatively simple control architecture.
Solution Approach 2:
The control unit uses feedback from inductor current detection to dynamically adjust switching timing. This feedback mechanism allows the system to adapt switching moments based on actual current conditions, achieving soft switching that reduces energy losses while keeping the control system relatively simple through automated current-based timing.
4Device complexity
If a high-voltage side current with square wave characteristics flows, then the chopper circuit operates with simple topology, but overvoltages occur due to wiring inductance, reducing reliability
Solution Approach 1:
The series connection of first and second inductors segments the current path, creating a more gradual current transition profile compared to a single inductor configuration. This segmentation smooths current waveforms, reducing the severity of square wave characteristics and minimizing overvoltage generation from wiring inductance while maintaining relatively simple circuit topology.
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 achieves a compact, lightweight, and reliable chopper circuit with reduced switching losses and no overvoltages, enhancing power quality and efficiency.
Implementation Method 1
an inductor connected to a connection point between the first switch unit and the second switch unit
Implementation Method 2
Each of the first switch unit and the second switch unit is formed by a semiconductor switching element which conducts electricity in one direction in the ON state
Data Source
AI summary
This chopper circuit 1 performs voltage conversion between a first DC voltage at a first external connection terminal and a second DC voltage at a second external connection terminal and is provided with: a first switch portion 11 having the first external connection terminal; a second switch portion 12 connected in series with the first switch portion 11 so that the conducting direction during ON-time matches that of the first switch portion 11 and having the second external connection terminal on the opposite side to the side where the first switch portion 11 is connected; one or a plurality of semiconductor power converters 13 cascade-connected to each other, which are provided on a wire branched from the wire for connecting the first switch portion 11 and the second switch portion 12; and an inductor 14 connected in series with the semiconductor power converters 13 on the wire branched from the wire for connecting the first switch portion 11 and the second switch portion 12.