Power Conversion Device Switching Density Control
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Solution Overview
Problem
In power conversion devices for electric compressors, the cooling efficiency of switching elements varies along the refrigerant flow path, leading to uneven heat generation and a risk of thermal destruction, especially in inverter-integrated systems where complex structures complicate temperature leveling.
Innovation Solution
A power conversion device with a three-phase inverter circuit that uses sinusoidal modulation voltage command values to calculate discontinuous modulation voltage command values, allowing the inter-line modulation operation unit to set switching densities differently for each phase based on temperature, reducing switching losses and heat generation by adjusting the ON/OFF states and switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If discontinuous modulation method is used to reduce switching losses, then switching loss and heat generation are reduced, but temperature unevenness among switching elements increases due to varying cooling efficiency along refrigerant flow path
Solution Approach 1:
The patent applies local quality by setting different switching densities for switching elements based on their individual cooling conditions. Specifically, switching elements located downstream in the refrigerant flow path (with worse cooling efficiency) are assigned lower switching densities, while upstream elements (with better cooling efficiency) are assigned higher switching densities. This localized adjustment equalizes temperature across all switching elements while maintaining reduced overall switching losses compared to sinusoidal modulation.
Solution Approach 2:
The patent implements dynamics by dynamically adjusting the switching density of each phase's switching elements based on real-time temperature feedback. The control unit monitors temperature variations and modifies switching densities accordingly, creating a dynamic balance where hotter elements (typically downstream) reduce their switching activity while cooler elements (upstream) maintain higher activity, thereby equalizing temperatures across the system.
2Temperature
If refrigerant flow path is controlled to level temperature of switching elements, then temperature uniformity is improved, but device structure becomes complex
Solution Approach 1:
The patent replaces the mechanical approach of physically redistributing or redesigning the refrigerant flow path with a control-theory-based solution. Instead of modifying the physical cooling system to achieve temperature uniformity, the invention uses intelligent control algorithms that adjust switching densities based on detected temperature variations. This substitution maintains the simple original refrigerant flow path structure while achieving temperature leveling through electronic control.
Solution Approach 2:
The patent applies parameter changes by modifying the electrical operating parameters (switching densities) of the inverter circuit rather than changing the physical thermal parameters of the cooling system. By adjusting switching frequencies and duty cycles of individual phases based on temperature feedback, the system achieves temperature uniformity without altering the refrigerant flow path configuration or adding complex thermal management hardware.
3Productivity
If switching density is increased to improve motor drive performance, then motor performance is improved, but heat generation and risk of thermal destruction increase
Solution Approach 1:
The patent applies local quality by differentiating switching density assignments among switching elements based on their thermal conditions. High-performance switching elements (those with better cooling, typically upstream) operate at higher switching densities to maintain motor drive performance, while thermally vulnerable elements (downstream with worse cooling) operate at reduced densities. This localized differentiation maintains overall motor performance while preventing thermal destruction of vulnerable components.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the temperature of switching elements and using this information to dynamically adjust switching densities. When temperature sensors detect elevated temperatures in specific phases, the control unit automatically reduces switching density for those phases, creating a feedback loop that prevents thermal runaway while maintaining optimal performance in cooler phases. This feedback mechanism ensures reliability is maintained alongside performance.
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 effectively levels temperature across switching elements, preventing thermal destruction and potential device shutdowns by dynamically adjusting switching density according to temperature variations, thus enhancing the reliability of electric compressors.
Implementation Method 1
switching elements (semiconductor elements for power) of each phase of UVW are cooled by a suction refrigerant (low temperature gas refrigerant)
Data Source
AI summary
There is provided a power conversion device capable of eliminating a disadvantage of a sharp temperature rise in a switching element by using a discontinuous modulation method. The power conversion device includes a phase voltage command operation unit 33 which calculates a sinusoidal modulation voltage command value to be applied to a motor 8, an inter-line modulation operation unit 34 which, based on the sinusoidal modulation voltage command value, calculates a discontinuous modulation voltage command value for allowing an ON/OFF state of a switching element of one phase of a three-phase inverter circuit 28 to be fixed, and modulating ON/OFF states of switching elements of other two phases, and a PWM signal generation unit 36. The inter-line modulation operation unit sets a switching density of the switching element of at least one phase to a value different from that of the other phase.