Line Converter Control for Track-Bound Vehicle Noise Reduction
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Solution Overview
Problem
Line converters in track-bound vehicles generate significant audible noise and high power losses due to current harmonics, particularly at low loads and when the vehicle is stationary, as a result of conventional Pulse Width Modulation control schemes.
Innovation Solution
The method involves controlling semiconductor devices to prevent current through the transformer's secondary winding from reaching zero and changing direction only at the start of a new AC line voltage half period, making the current discontinuous and eliminating harmonics, with a control scheme switching to Pulse Width Modulation at higher loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional Pulse Width Modulation control scheme is used for line converter, then the converter can operate at all load levels, but significant audible noise and high power losses occur due to current harmonics especially at low loads
Solution Approach 1:
The patent applies different control strategies to different operating conditions: discontinuous current control is used specifically for low load conditions (below threshold) where noise is problematic, while continuous PWM control is used for higher loads. This localized application of different control qualities resolves the contradiction by optimizing performance for each specific operating regime rather than using a single control method across all conditions.
Solution Approach 2:
The control system dynamically switches between discontinuous current control mode and continuous PWM control mode based on the detected load level. The control strategy is not static but adapts in real-time to changing operating conditions, enabling the system to maintain low noise operation at idle while preserving full functionality under load.
2Object-generated harmful factors
If discontinuous current control is used to eliminate harmonics at low loads, then noise and power losses are reduced, but the control complexity increases due to switching between control modes
Solution Approach 1:
The control system includes a threshold detection mechanism that anticipates the need for control mode switching by monitoring the load level. When the load exceeds the predetermined threshold, the system proactively transitions from discontinuous to continuous control mode, and vice versa when the threshold is crossed in reverse. This preliminary detection and pre-planned switching reduces the perceived complexity by making the control transitions predictable and automated rather than requiring complex real-time decision-making.
3Reliability
If current is allowed to reach zero and change direction with conventional PWM, then the converter maintains continuous operation, but current harmonics are generated causing audible noise
Solution Approach 1:
Instead of allowing the current to naturally follow the PWM waveform and pass through zero crossings (conventional approach), the invention inverts the approach by actively preventing the current from reaching zero during the conduction period. The control method ensures current continues to flow in the same direction even when the voltage polarity changes, thereby eliminating the zero-crossing harmonics that cause audible noise while maintaining reliable operation.
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 eliminates noise and reduces power losses by up to 20% at low loads, improving operational efficiency and reducing disturbing noise, especially when the vehicle is stationary or idling.
Implementation Method 1
The vehicle has a transformer 3 for transforming the voltage from the supply line 2 to a suitable level. The transformer has here a primary winding 40 and two secondary windings 4, 5
Implementation Method 2
Each current valve comprises a semiconductor device of turn-off type 28-31, such as an IGBT (Insulated Gate Bipolar Transistor), and a rectifying member 32-35, such as a diode, connected in anti-parallel therewith
Data Source
AI summary
In a method for controlling a line converter on board a track-bound vehicle semiconductor devices of current valves of the line converter are controlled to be turned on and off so as to prevent the current (I) through a secondary winding of a transformer to which midpoints of phase-legs of the converter are connected to pass zero and shift direction other when the voltage across the secondary winding shifts direction by a start of a new half period of an AC line voltage across the windings of the transformer.