Compressor Preheating PWM Control to Suppress AC Noise and Vibration
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Solution Overview
Problem
Conventional air-conditioning apparatuses experience vibrations and noise during preheating due to differential component frequencies generated by inverter usage, leading to performance degradation and potential compressor malfunction.
Innovation Solution
An air-conditioning apparatus with a control unit that includes a liquefaction detecting unit, a first PWM signal generating unit for asynchronous operation, and a second PWM signal generating unit for synchronous high-frequency preheating, allowing for selective switching to prevent low-frequency noise and vibrations by using synchronous PWM for preheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If asynchronous PWM is used for inverter control during preheating, then the motor winding can be warmed to prevent coolant liquefaction, but differential component frequencies cause vibrations and noise in the compressor
Solution Approach 1:
The patent changes the PWM control parameters by switching from asynchronous PWM to synchronous PWM during preheating operation. This parameter change eliminates the differential component frequencies that cause vibrations and noise, while still achieving the necessary motor winding temperature increase to prevent coolant liquefaction.
Solution Approach 2:
The patent dynamically switches between different PWM control modes based on the operational state. During preheating, synchronous PWM is selected to minimize vibrations and noise. During normal operation, asynchronous PWM can be used. This dynamic adaptation resolves the contradiction between reliability and harmful factors.
2Reliability
If high-frequency open-phase current is passed to motor winding for preheating, then liquid compression is prevented, but the differential component frequency causes prominent vibrations and noise when motor is not running
Solution Approach 1:
The patent changes the frequency relationship between output voltage and PWM carrier during preheating by using synchronous PWM. This ensures that the differential component frequencies are eliminated or shifted to less problematic ranges, reducing vibrations and noise while maintaining the protective preheating function.
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
Enables preheating of coolant without causing vibrations or noise, ensuring efficient and reliable operation by stabilizing the frequency spectrum and reducing noise within the audibility range.
Implementation Method 1
a control unit that receives the output signal passes a high-frequency open-phase current of low intensity to a motor winding so that the motor winding is warmed
Implementation Method 2
due to the interference between an output voltage frequency fo and a PWM carrier frequency fc, a differential component frequency m·fo±n·fc (m and n are integers) is generated. If the differential component appears in a low-frequency region, then that causes vibrations of bearings or noise in the compressor motor
Data Source
AI summary
The air-conditioning apparatus includes a coolant circuit configured by sequentially connecting a compressor, an indoor heat exchanger, an expansion valve, and an outdoor heat exchanger; a motor that operates a compressor mechanism disposed inside the compressor; an inverter for driving the motor; and a control unit that controls the inverter. The control unit includes a liquefaction detecting unit that detects coolant liquefaction in the compressor; includes a first PWM signal generating unit that generates an inverter control signal for driving the motor; includes a second PWM signal generating unit that generates an inverter control signal for making the motor perform a preheating operation; and includes a switching unit that performs switching in such a way that the first PWM signal generating unit or the second PWM signal generating unit outputs the corresponding inverter control signal to the inverter.