Motor Drive Capacitor Switching for TVS Voltage Ripple Control
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Solution Overview
Problem
In at least partly electrically operated vehicles, the isolated Traction Voltage System (TVS) experiences voltage swings relative to chassis ground due to stray capacitance, leading to common mode voltage ripple and electromagnetic interference, which current passive filter capacitors are insufficient to mitigate effectively.
Innovation Solution
A motor drive configuration with a dedicated capacitor connected to the Traction Voltage System (TVS) in opposite phase to the motor windings, and optionally to a second chassis ground, to counteract voltage swings and reduce common mode TVS voltage ripple and electromagnetic interference, with the capacitor size dynamically adjusted to match the existing stray capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a passive filter capacitor is connected between the TVS pole and chassis ground to counteract voltage swing, then the TVS to chassis voltage swing is reduced, but the capacitor dimension is not large enough to effectively mitigate the electromagnetic interference
Solution Approach 1:
The patent introduces a dedicated capacitor as an intermediary component specifically configured to counteract the stray capacitance effect. This capacitor is connected between the TVS pole and chassis ground, acting as a mediator to balance the voltage swing caused by motor drive switching. The intermediary capacitor provides a controlled capacitive path that compensates for the unwanted parasitic capacitance, thereby reducing common mode voltage ripple and electromagnetic interference more effectively than conventional filter capacitors.
Solution Approach 2:
The patent applies parameter changes by carefully selecting and adjusting the capacitance value of the dedicated capacitor to match or balance the stray capacitance value. By changing the capacitance parameter of the dedicated capacitor, the system achieves optimal cancellation of voltage swing. The capacitance value is chosen based on the specific stray capacitance measurement, allowing the system to dynamically adapt the filtering capability to match the actual interference conditions.
2Power
If the motor drive switches current through motor windings to operate the electric machine, then the electric machine delivers power to driving wheels, but stray capacitance pulls chassis potential towards TVS potential causing common mode voltage ripple
Solution Approach 1:
The patent converts the harmful effect of stray capacitance into a beneficial effect by introducing a dedicated capacitor that mimics and counteracts the stray capacitance behavior. The dedicated capacitor is intentionally designed to create an equal and opposite voltage swing that cancels out the harmful common mode ripple. This approach transforms the problem of capacitance-induced voltage swing into a solution where controlled capacitance is used to balance and eliminate the harmful effects.
3Stability of the object's composition
If no direct connection to chassis ground is provided in the isolated TVS, then the TVS system operates independently, but voltage swings or jumps occur in TVS voltages relative to chassis ground when motor drive is active
Solution Approach 1:
The patent applies segmentation by separating the grounding function from the power delivery function. The dedicated capacitor provides a localized capacitive reference between the TVS pole and chassis ground without creating a direct galvanic connection. This segmented approach allows the TVS system to maintain its isolated architecture while still providing voltage reference stability through the capacitive coupling, thereby eliminating voltage swings without compromising system independence.
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 configuration effectively minimizes voltage swings and reduces electromagnetic interference, enhancing the operational stability and reducing noise in the vehicle's electrical system.
Implementation Method 1
A motor drive configuration with a dedicated capacitor connected to the Traction Voltage System (TVS) in opposite phase to the motor windings, and optionally to a second chassis ground, to counteract voltage swings and reduce common mode TVS voltage ripple
Data Source
AI summary
A motor drive in a an at least partly electrically operated vehicle. Motor windings are connected to a positive pole of a TVS and a capacitor is connected to a negative pole when a first, third and sixth connecting units are in connected state and when a second, fourth and fifth connecting units are in disconnected state. The motor windings are connected to a negative pole of the TVS and the capacitor is connected to the positive pole when the first, third and sixth connecting units are in disconnected state and when the second, fourth and fifth connecting units are in connected state.