Compressor Preheating Control for Low-Standby Heat Pumps
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Solution Overview
Problem
Existing heat pump devices face inefficiencies in heating the compressor, leading to inadequate prevention of coolant buildup and increased standby power consumption due to high-frequency current regeneration and high-efficiency motor designs that require increased direct current, resulting in elevated inverter losses.
Innovation Solution
A heat pump device with an inverter control unit that selectively applies direct-current or high-frequency energization to the motor based on the coolant's sleeping amount, optimizing heating efficiency and reducing standby power by switching between direct-current and high-frequency energization modes according to the necessary heating amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-frequency single-phase alternating-current voltage is supplied to the compressor, then the liquid coolant can be vaporized and discharged, but the heating efficiency of the compressor is deteriorated due to long total-off sections and current regeneration
Solution Approach 1:
The patent changes the voltage type parameter from high-frequency alternating-current to direct-current during constraint energization. By supplying direct-current voltage to the motor winding wire, the system eliminates the total-off sections inherent in alternating-current waveforms, preventing current regeneration and improving heating efficiency while maintaining the ability to vaporize and discharge liquid coolant.
Solution Approach 2:
The patent dynamically selects the energization method based on the detected state of the compressor. The control unit determines whether constraint energization is needed based on compressor temperature and operating conditions, then switches between normal operation mode and constraint energization mode (using direct-current), allowing the system to adapt to varying conditions and optimize heating efficiency.
2Temperature
If direct current is fed to the motor winding wire for preheating, then heating can be achieved, but the electric current flowing to the inverter increases causing higher losses and deteriorated heating efficiency
Solution Approach 1:
The patent changes the voltage frequency parameter by supplying high-frequency voltage (higher than normal operation frequency) during constraint energization. This high-frequency voltage generates sufficient heat through copper loss in the motor winding wire to vaporize liquid coolant, while the high frequency allows for reduced current magnitude, thereby reducing inverter losses compared to traditional direct-current preheating methods.
3Loss of energy
If a small motor with small copper loss is used, then efficiency is improved, but the heat value with respect to applied voltage is small making it difficult to obtain necessary heating amount
Solution Approach 1:
The patent changes the voltage frequency parameter to high-frequency during constraint energization mode. This allows small motors with low copper loss to generate sufficient heat by operating at high frequencies, where the reactance increases and enables effective heating even with reduced current, thus maintaining both motor efficiency and adequate heating capability.
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
The solution enables efficient heating of the compressor, prevents coolant buildup, and reduces standby power consumption by optimizing energy usage, thereby improving heating efficiency and contributing to energy savings and environmental sustainability.
Implementation Method 1
heating the compressor to thereby vaporizing and discharging the liquid coolant... supplying a single-phase alternating-current voltage having a frequency of about 25 kilohertz higher than a normal frequency... a heat value is obtained as a product of a winding resistance and a square of the electric current
Data Source
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AI summary
A heat pump device surely prevents a coolant from being held up in a compressor and attains a reduction in standby power, by efficiently carrying out heating to the compressor according to a necessary heating amount. An air conditioner, a heat pump water heater, a refrigerator, and a freezing machine including the heat pump device are provided. An inverter control unit 10 includes a constraint-energization control unit 12 that, during operation standby of the compressor 1, determines whether heating to the compressor 1 is necessary, on the basis of a coolant sleeping amount in the compressor 1, and, when having determined that heating to the compressor 1 is necessary, selects, according to the coolant sleeping amount, any one of direct-current energization for supplying a direct-current voltage to the motor 8 and high-frequency energization for supplying a high-frequency voltage having a frequency higher than a frequency during a normal operation to the motor 8, so as to output a constraint energization command for carrying out constraint energization of the motor; and a driving-signal generating unit 13 that generates a driving signal on the basis of the constraint energization command.