Train Traction Converter Startup for Inrush and Harmonic Noise
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Solution Overview
Problem
The existing traction systems for electric trains generate harmonic noise and inrush currents that can interfere with trackside safety and communication equipment, compromising their operation.
Innovation Solution
The traction system employs a sequential closing of switches to reduce inrush currents and delays the start of power conversion by AC/DC converters until all switches have closed, ensuring simultaneous startup and phase-shifting of PWM operations to cancel out harmonic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If AC/DC converters are started sequentially to avoid simultaneous inrush currents, then inrush current noise is reduced, but there is a lead-in period with insufficient converters operating for proper phase shifting
Solution Approach 1:
All first switches are closed in advance before any AC/DC converter starts power conversion. This preliminary connection of all transformers eliminates the lead-in period problem, ensuring that when converters start simultaneously after the delay, all necessary converters are available for proper phase-shifting and harmonic noise cancellation.
Solution Approach 2:
The control device employs periodic PWM switching with coordinated phase shifts across all converters. By delaying the start until all switches are closed, the system ensures that the periodic switching actions of all converters work together from the beginning to achieve effective harmonic noise cancellation.
2Productivity
If all first switches are closed simultaneously to enable immediate power conversion, then power delivery is faster, but inrush currents reinforce each other creating noise current interference
Solution Approach 1:
The control device closes all first switches in advance as a preliminary action before starting power conversion. This sequencing approach maintains fast power delivery by minimizing the delay, while the coordinated timing ensures that inrush currents do not reinforce each other, thus reducing noise current interference.
Solution Approach 2:
The system uses coordinated periodic switching of first switches followed by simultaneous converter startup. This periodic action pattern with precise timing control enables fast power delivery while preventing inrush current reinforcement through proper sequencing of the switching operations.
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 reduces the peak levels of combined noise currents and harmonic noise, minimizing interference with trackside safety and communication equipment while allowing for earlier power delivery to train motors.
Implementation Method 1
each converter unit includes AC/DC convertors 101 for converting the stepped down AC electric power to DC electric power... The control device 9 controls: the timing of the start of power conversion using pulse width modulation by the AC/DC converters
Implementation Method 2
transformer equipment 2 for stepping down electric voltage level from high voltage of the overhead wire, the AC/DC converters operating on the stepped down voltage
Data Source
Figure 1
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Figure 4
AI summary
A traction system for a train is provided. The traction system has plural transformers for stepping down a voltage level of AC electric power provided from an overhead wire. The traction system further has plural converter units for supply of electric power to motors of the train. Each converter unit includes an AC/DC convertor for converting the stepped down AC electric power provided by one of the transformers to DC electric power. The AC/DC converters are configured to use pulse width modulation to convert the stepped down AC electric power on the basis of respective pulse signals which each have the same switching frequency but are phase shifted from each other to substantially cancel out second order harmonic noise from the pulse signals. The traction system further has plural first switches which are closable to respectively connect high voltage sides of the transformers to the overhead wire, the closing of each first switch provoking an inrush current into the respective transformer. The traction system further has a controller that is configured to control the timing of the closing of the first switches such that the first switches are closed in sequence with a first predetermined time interval between closures. The controller is further configured to control the timing of the start of power conversion using pulse width modulation by each of the AC/DC converters such that the starts are simultaneous and after the first switches have closed.