Modular Converter Control for Electric Train Efficiency
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Solution Overview
Problem
Modular converters for electric trains and trams face efficiency issues under low or no-load conditions due to persistent switching losses, leading to decreased efficiency and potential voltage oscillations when trying to manage DC-link voltages with existing threshold-based control methods.
Innovation Solution
A method that dynamically controls modular converters by switching between bypassed, active, and diode modes for AC-to-DC converters, using a DC-link capacitor and transformer-based resonant converters to optimize power transfer and reduce switching losses across varying load conditions, ensuring efficient operation from nominal to very low power ratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If AC-to-DC converters are operated in intermittent mode with threshold-based control under light-load conditions, then switching losses are reduced, but DC-link voltages oscillate between thresholds causing converter instability
Solution Approach 1:
The patent applies dynamics by making the converter cell configuration adaptive rather than static. The control method dynamically determines the number of converter cells in active, diode, and bypassed modes based on real-time power level detection. This dynamic reconfiguration allows the system to maintain stability across varying load conditions while minimizing switching losses, as the converter cells can transition between operational modes without causing voltage oscillations.
Solution Approach 2:
The patent utilizes parameter changes by detecting power level ranges and adjusting the operational parameters of converter cells accordingly. When power levels drop below certain thresholds, the control method changes the number of active converter cells and their operational modes (active, diode, or bypassed). This parameter adaptation prevents the DC-link voltage oscillation issue while maintaining efficiency under light-load conditions.
2Stability of the object's composition
If the difference between individual thresholds and further threshold is chosen relatively small, then voltage oscillations are reduced, but converter efficiency under low load operation remains unsatisfactory due to AC-to-DC converters remaining in active mode
Solution Approach 1:
The patent applies segmentation by dividing the converter system into multiple independently controllable converter cells. Each cell can be operated in different modes (active, diode, or bypassed) based on the detected power level. This segmentation allows the system to optimize efficiency under low load by placing some cells in diode or bypassed modes while maintaining voltage stability through coordinated control of the remaining active cells.
Solution Approach 2:
The patent implements partial action by activating only the necessary number of converter cells based on the current power level. Instead of keeping all AC-to-DC converters in active mode, the control method selectively deactivates or bypasses converter cells when power demand is low, thereby reducing switching losses and improving efficiency while maintaining sufficient voltage regulation through the remaining active cells.
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 maintains high efficiency and stability under low and very low load conditions, achieving sinusoidal input current and controlled DC output voltage, with no additional hardware required, allowing continuous adaptation of the switching strategy to meet power level demands.
Implementation Method 1
a DC-to-AC converter on a line side is connected via a resonant transformer with a further AC-to-DC converter on a motor side
Implementation Method 2
each converter cell comprises a resonant DC-to-DC converter
Data Source
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AI summary
A method is presented for controlling a modular converter, said modular converter in particular comprising a plurality of M converter cells (36), each converter cell comprising an AC-to-DC converter (40), a primary side of which represents a primary side of said converter cell, said AC-to-DC converter being an active AC-to-DC converter comprising a plurality of semiconductor switches (46a-d), and operable in one of a plurality of modes, the plurality of modes comprising a bypassed mode, an active mode, and a diode mode; a DC-to-DC converter (42), a secondary side of which represents a secondary side of said converter cell; with a secondary side of said AC-to-DC converter and a primary side of said DC-to-DC converter connected in parallel with a DC-link capacitor (50), wherein the primary sides of the converter cells are connected in series, with a first converter cell connected to a line (16), preferably a medium voltage line, providing an AC line voltage U(t) having a peak value Û, and an M-th converter cell connected to a ground (22); the method comprising the steps of: for a given allowable range [Umin, Umax] of a DC-voltage UDC at the DC-link capacitor determining whether any integer number N ≤ M exists for which and and if such integer number N exists: selecting an integer number L with L < N, selecting a first set of N-L converter cells, selecting a second set of L converter cells, putting the AC-to-DC converter of, preferably all, converter cells which have not been selected in steps ii) or iii) into bypassed mode, putting the AC-to-DC converter of, preferably all, converter cells from the first set into diode mode, putting the AC-to-DC converter of, preferably all, converter cells from the second set into active mode.