Inverter Switching Layout for Common-Mode Noise Reduction
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Solution Overview
Problem
Conventional power conversion devices experience significant noise issues due to parasitic capacitance between switching elements and the chassis, which are not effectively mitigated by existing EMI filters, leading to inefficient noise reduction.
Innovation Solution
The power conversion device reduces noise by minimizing parasitic capacitance between lower arm switching elements and the heatsink, using thicker insulating sheets for the lower arm elements, and controlling the conduction time of upper and lower arm switching elements to balance heat dissipation and noise reduction, with additional cooling and phase voltage adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large EMI filter is installed at the input part of the control circuit, then noise filtering capability is improved, but the wiring length becomes long and the filtering effect against common mode current is insufficient
Solution Approach 1:
The patent introduces a common mode coil as an intermediary component placed close to the switching element. This coil acts as a local filter that intercepts common mode current at its source, preventing it from traveling through long wiring to the EMI filter. The coil's inductance provides filtering action right at the noise generation point, making the wiring length irrelevant for common mode noise suppression.
Solution Approach 2:
The patent implements preliminary noise filtering by placing the common mode coil immediately adjacent to the switching element before the noise can propagate through the wiring. This preliminary action captures common mode current at its origin, preventing the need for long wiring runs to reach the main EMI filter and ensuring effective noise suppression at the source.
2Object-affected harmful factors
If a large common mode coil is inserted to achieve sufficient impedance, then noise reduction is improved, but device complexity and size increase
Solution Approach 1:
The patent applies local quality by differentiating the parasitic capacitance values for upper and lower arm switching elements. Specifically, the lower arm switching element is designed with smaller parasitic capacitance to the heatsink compared to the upper arm element. This asymmetric design allows targeted noise reduction at the lower arm without requiring uniformly large common mode coils across all switching elements, thereby reducing overall device complexity and size.
Solution Approach 2:
The patent changes the parasitic capacitance parameter of the lower arm switching element to be smaller than that of the upper arm element. This parameter modification reduces the magnitude of common mode current generated by the lower arm switching element, thereby reducing the required impedance and size of the common mode coil needed for effective noise filtering.
3Object-affected harmful factors
If thicker sheets are used between lower arm switching element and heatsink to reduce parasitic capacitance, then noise reduction is improved, but heat dissipation capability deteriorates
Solution Approach 1:
The patent applies local quality by making the sheet thickness between the lower arm switching element and heatsink larger than that between the upper arm switching element and heatsink. This localized increase in thickness specifically reduces parasitic capacitance at the lower arm where smaller capacitance is beneficial, while the upper arm maintains thinner sheets for better heat dissipation. The control device compensates for the heat dissipation reduction in the lower arm by adjusting conduction times.
Solution Approach 2:
The patent changes the physical parameter of sheet thickness to reduce parasitic capacitance between the lower arm switching element and heatsink. By increasing the thickness of the insulating sheet, the parasitic capacitance is reduced, which decreases common mode current. The control device compensates for the resulting heat dissipation reduction by adjusting switching element conduction times to balance thermal load.
4Temperature
If conduction time of upper arm switching element is made longer to balance heat dissipation, then thermal management is improved, but switching losses increase
Solution Approach 1:
The control device implements feedback control by monitoring thermal conditions and adjusting the conduction times of upper and lower arm switching elements accordingly. When the lower arm switching element has reduced heat dissipation capability due to thicker sheets, the control device increases its conduction time and decreases the upper arm conduction time to balance the thermal load, optimizing both thermal management and switching losses dynamically.
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 significantly reduces EMI noise while maintaining effective heat dissipation, even with thicker sheets, by concentrating heat generation in upper arm elements and using refrigerant cooling for lower arms, thus enhancing overall device performance.
Implementation Method 1
a parasitic capacitance between the lower arm switching element and a heatsink is smaller than a parasitic capacitance between the upper arm switching element and the heatsink
Implementation Method 2
the upper and lower arm switching elements of each phase are arranged in a heat exchange relation with a refrigerant sucked into the electric compressor
Data Source
AI summary
There is provided a power conversion device capable of easily reducing noise (common mode current) flowing out from a switching element via a parasitic capacitance. A power conversion device 1 applies a voltage at a connection point of upper and lower arm switching elements 18A to 18F to a motor 8. A parasitic capacitance between each of the lower arm switching elements 18D to 18F and a chassis 2 (partition wall 3: heatsink) is smaller than a parasitic capacitance between each of the upper arm switching elements 18A to 18C and the chassis 2 (partition wall 3: heatsink). Alternatively, a dielectric constant between each of the lower arm switching elements 18D to 18F and the chassis 2 (partition wall 3: heatsink) is smaller than a dielectric constant between each of the upper arm switching elements 18A to 18C and the chassis 2 (partition wall 3: heatsink).