DC-Link RL Decoupling Circuit for Parallel Inverter Resonance
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Solution Overview
Problem
In electric locomotives with multiple inverters connected in parallel to a common DC power supply, resonance issues between input capacitors and stray inductances lead to malfunctioning of both motors if one inverter fails, resulting in loss of traction, which existing solutions attempt to address through oversizing capacitors or using low parasitic inductance bus bars, but these methods are costly and inefficient.
Innovation Solution
A DC-link decoupling circuit with an RL filter, comprising inductors and resistors connected in series and parallel, respectively, is introduced between the common power supply line and input capacitors of each inverter, allowing for resonance damping and enabling separation of faulty inverters from the power supply, thereby preventing loss of traction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple inverters are connected in parallel to a common DC power supply line, then the power supply efficiency is improved and each inverter can independently control different motors, but resonance occurs between the input capacitors and stray inductances causing system malfunction when one inverter fails
Solution Approach 1:
An RL filter is introduced as an intermediary component between the common DC power supply line and each inverter's input capacitor. The filter comprises an inductor L connected in series with the power supply line and a resistor R connected in parallel to the inductor. This intermediary structure dampens resonance oscillations by providing a controlled impedance path that prevents harmful resonance between capacitors and stray inductances, while maintaining the parallel connection architecture for improved power supply efficiency.
2Reliability
If switch means are provided for separating faulty inverters from the power supply line, then the reliability is improved by isolating failures, but the device complexity increases due to additional switching components and control circuitry
Solution Approach 1:
The system is segmented into independent inverter units, each equipped with its own switch means (contactors or circuit breakers) that can independently open to isolate that specific inverter from the common DC power supply line. This segmentation allows failure isolation without requiring complex system-wide shutdown mechanisms, as each inverter can be independently disconnected while others continue operating.
3Reliability
If oversizing capacitors is used to address resonance issues, then the resonance frequency is shifted, but the cost and device complexity increase significantly
Solution Approach 1:
Instead of changing the capacitor size parameter, the invention introduces an RL filter that changes the overall impedance parameter of the circuit. The inductor L and resistor R create a damped oscillation system with a controlled time constant (L/R), which actively suppresses resonance oscillations at the existing capacitor values. This parameter change approach avoids the cost and complexity of oversized capacitors while achieving the same resonance control objective.
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 proposed solution effectively decouples resonance between input capacitors and allows for isolation of malfunctioning inverters, ensuring continued traction by damping oscillations and maintaining system efficiency and reducing costs.
Implementation Method 1
resonance oscillation attenuating/damping means in the form of an RL filter (resistor-inductor filter) decoupling the resonance condition of the inverters
Implementation Method 2
a resistor which is connected in parallel to said inductors and in parallel to the inputs of said two inverters, and which connects the two branches connecting the two inverters with each other
Implementation Method 3
an inductor for each branch of the power supply line connecting one of the inverters, which is connected in series between said common power supply line and said inverter
Data Source
Figure 1~2
Figure 3~5
AI summary
A DC-link decoupling circuit is provided in combination with two inverters which are connected in parallel to a common DC power supply line and each of which inverter driving one different traction motor, switch means being provided for each of said two inverters, for separating the corresponding inverter from said power supply line in case of failure. The said DC-link decoupling circuit is provided with resonance oscillation attenuating/damping means in the form of an RL filter (resistor-inductor filter). The invention relates also to an electric locomotive comprising at least two electric motors, each motor being controlled by one of two inverters, each of which inverters is powered by a common power supply line, switch means being provided for each of said two inverters, for separating the corresponding inverter from said power supply line in case of failure. DC-link decoupling means are provided for decoupling the resonance condition of inverters, which means consist of an RL filter having a damping inductor and a damping resistor in parallel.