Modular Converter Control for Light-Load Switching Loss Reduction
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Solution Overview
Problem
Modular converters used in electrical trains and trams experience reduced efficiency under light-load or no-load conditions due to persistent switching losses, despite lower power transfer, as the control methods currently used do not effectively manage switching operations at varying power ratings.
Innovation Solution
A method for controlling modular converters that adjusts operation modes based on transferred power, activating or deactivating converter cells to minimize switching losses, including selective operation of DC-to-DC and AC-to-DC converters, and short-circuiting unnecessary cells, thereby reducing energy consumption and maintaining high efficiency across a range of power ratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the modular converter operates with zero voltage switching (ZVS) to achieve soft-switching of DC-to-DC converter semiconductors, then switching losses are reduced at nominal power ratings, but circulating current persists under light-load or no-load conditions causing switching losses to remain high when power transfer is low
Solution Approach 1:
The control method dynamically adapts the switching strategy based on the operating point. At nominal power ratings, ZVS is maintained for low switching losses. Under light-load or no-load conditions, the control automatically transitions to a different mode where converter cells are deactivated or operated in a reduced mode, eliminating the need for circulating current and thus removing switching losses when they are not needed for power transfer.
Solution Approach 2:
The invention changes the operational parameters of the converter cells based on load conditions. By monitoring the power transfer level and comparing it with threshold values, the system adjusts the switching behavior and activation state of converter cells, transitioning from ZVS mode at high power to a deactivated or reduced-power mode at low power, thereby optimizing efficiency across the entire operating range.
2Reliability
If converter cells are continuously operated to maintain readiness for power transfer, then the converter can respond to load changes, but switching losses persist under light-load or no-load conditions reducing overall efficiency
Solution Approach 1:
The modular converter is divided into multiple independent converter cells that can be individually controlled. This segmentation allows the system to activate only the necessary number of cells based on the current power transfer requirements. When power transfer is low, fewer cells are activated, reducing switching losses while maintaining sufficient capacity to handle load changes. The modular structure enables flexible configuration of active cells based on real-time conditions.
3Ease of operation
If the modular converter is operated in normal load operation mode across all power ratings, then consistent control is maintained, but efficiency decreases under light-load or no-load conditions due to unchanged switching losses
Solution Approach 1:
The control method transitions from a static normal load operation mode to a dynamic control strategy that adapts to the actual power transfer level. By continuously monitoring the transferred power and comparing it with threshold values, the system dynamically switches between normal load operation mode and low load operation mode, ensuring optimal efficiency at each operating point while maintaining stable and predictable converter behavior through structured mode transitions.
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 method significantly reduces switching losses and improves overall efficiency of modular converters under light-load or no-load conditions, ensuring high efficiency and stable operation across varying power ratings, while supporting bi-directional energy flow and maintaining control objectives like sinusoidal input current and stable DC output voltage.
Implementation Method 1
a resonant DC-to-DC converter, in which a DC-to-AC converter on the line side is connected via a resonant transformer with an AC-to-DC converter on the motor side
Data Source
Figure 1
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AI summary
A modular converter (10) comprises a plurality of converter cells (36), which are connected in series on a first side and are connected on a second side, wherein each converter cell (36) comprises an AC-to-DC converter (40) connected to the first side and a DC-to-DC converter (42) connected to the second side. A method for controlling the modular converter (10) comprises the steps of: estimating the power transferred by the modular converter (10); comparing the transferred power with a threshold value; when the transferred power is bigger than the threshold value, operating the modular converter in a normal load operation mode (1 16, 122, 128); when the transferred power is smaller than the threshold value, operating the modular converter in a low load operation mode (1 14, 120, 126), in which the converter cells (36) are operated, such that switching losses are reduced with respect to the normal load operation mode.