Outdoor AC Inverter Cooling Control for Switching Element Heat
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Solution Overview
Problem
Conventional air conditioners face challenges in preventing thermal breakdown of switching elements due to rapid temperature changes, which can occur before the cooling fan's rotational speed is adequately increased to manage heat generated by high-power semiconductor devices like MOSFETs.
Innovation Solution
An outdoor air conditioner unit incorporates a compressor-driving inverter circuit that converts DC power to pseudo three-phase AC power using switching elements, along with a fan rotational speed detection unit and ambient temperature detection unit, allowing the compressor inverter drive unit to control the compressor rotational speed based on fan speed and ambient temperature to prevent thermal breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermistor is used to detect temperature for controlling fan speed, then the control system can regulate cooling performance, but the thermistor cannot detect rapid temperature changes within a short time period, causing delayed response to thermal breakdown risks
Solution Approach 1:
The control unit proactively increases fan rotational speed based on compressor current magnitude before thermal breakdown occurs. By detecting current as a leading indicator of heat generation and preemptively adjusting fan speed, the system prevents the delayed response problem of thermistor-based temperature detection.
Solution Approach 2:
The patent replaces thermistor-based temperature measurement with a current-based thermal management approach. Instead of mechanically measuring temperature after heat accumulation, the system uses electrical current detection to infer thermal risk and triggers preventive cooling action, substituting direct thermal measurement with an indirect but faster electrical parameter measurement.
2Temperature
If the fan rotational speed is increased rapidly to cool switching elements, then cooling performance improves, but the thermistor cannot keep up with the rapid temperature change, leaving switching elements in a dangerous temperature range
Solution Approach 1:
The control unit acts as an intermediary between compressor operation and fan speed control. It uses compressor current as a mediator parameter to infer thermal conditions and adjusts fan speed accordingly, bypassing the need for direct thermistor measurement during rapid transient conditions. This intermediary approach enables accurate thermal management without relying on slow thermistor response.
3Productivity
If the compressor output is increased to improve cooling performance, then more heat is generated in switching elements, but this increases the risk of thermal breakdown without adequate cooling response
Solution Approach 1:
The system implements feedback control by continuously monitoring compressor current and adjusting fan speed in real-time. The control unit uses current feedback as an indicator of heat generation rate and dynamically adjusts cooling capacity to match thermal load, enabling the compressor to operate at high output without causing thermal breakdown in switching elements.
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 solution effectively prevents thermal breakdown of switching elements by dynamically adjusting compressor and fan speeds in response to temperature and ambient conditions, ensuring stable operation and enhanced cooling performance.
Implementation Method 1
an inverter circuit for converting direct current (DC) power into three-phase alternating current (AC) power using a plurality of switching elements. Such an inverter circuit sequentially turns on and off the switching elements to generate three-phase AC power
Implementation Method 2
a fan rotational speed detection unit to detect a fan rotational speed of a fan that cools the switching elements
Implementation Method 3
an increase in the output of the compressor motor increases the current flowing to the switching elements and thus increases the amount of heat generated in the switching elements
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An outdoor unit 100 of an air conditioner includes a compressor-driving inverter circuit 2 to convert direct current power for driving a compressor 3 into pseudo three-phase alternating current power using a plurality of switching elements; a fan rotational speed detection unit 7 to detect the fan rotational speed of a fan that cools the switching elements; an ambient temperature detection unit 12 to detect the ambient temperature at a location where the air conditioner is located; and a compressor inverter drive unit 9 to control the compressor rotational speed of the compressor 3 by controlling the compressor-driving inverter circuit 2. The compressor inverter drive unit 9 controls the compressor-driving inverter circuit 2 on the basis of the fan rotational speed and the ambient temperature.