Inverter Capacitor Preheating for Low-Temperature Operation
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Solution Overview
Problem
Electrolytic capacitors used in refrigerant compressors for motor vehicles experience significant capacitance decrease and impedance increase at low temperatures, limiting their use to above −20° C, while alternative capacitors like film and ceramic capacitors are less efficient and more costly, and sensitive to vibrations.
Innovation Solution
A method involving temperature detection of electrolytic capacitors, generation of a specific switching pattern to preheat them using ripple current, and controlling the modulation index to maintain optimal operating temperature without affecting motor control, allowing the use of small and economical electrolytic capacitors across a broader temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If electrolytic capacitors are used in the inverter, then capacitance density and cost-effectiveness are improved, but capacitance decreases and impedance increases greatly at low temperatures
Solution Approach 1:
The patent applies preliminary action by preheating the electrolytic capacitors before the inverter starts operating at low temperatures. A heating element is activated prior to motor operation to raise the capacitor temperature above the threshold where capacitance degradation occurs, ensuring the capacitors are in an optimal state before normal operation begins.
Solution Approach 2:
The patent changes the temperature parameter of the electrolytic capacitors by introducing a heating mechanism. By actively controlling the capacitor temperature through preheating during cold conditions, the system maintains capacitance values within acceptable ranges, effectively changing the thermal state of the capacitors to compensate for low ambient temperatures.
2Reliability
If film or ceramic capacitors are used instead, then temperature stability is improved, but capacitance density decreases and cost increases
Solution Approach 1:
By changing the temperature parameter of the electrolytic capacitors through active preheating, the system achieves temperature stability comparable to film or ceramic capacitors while retaining the superior capacitance density of electrolytic capacitors. This parameter control approach eliminates the need to switch capacitor types.
Solution Approach 2:
The patent uses inexpensive electrolytic capacitors with high capacitance density rather than expensive film or ceramic capacitors, compensating for their temperature sensitivity through a simple heating mechanism. This approach is more cost-effective while achieving the same reliability.
3Reliability
If ceramic capacitors are used for high capacitance values, then temperature stability is improved, but sensitivity to impact and vibration increases
Solution Approach 1:
The patent uses robust electrolytic capacitors that are less sensitive to vibration and impact compared to ceramic capacitors, while compensating for their temperature sensitivity through preheating. This combination provides both vibration resistance and temperature stability.
4Temperature
If electrolytic capacitors are preheated using motor operation, then capacitor temperature is improved, but motor control is influenced
Solution Approach 1:
The patent extracts the heating function from the motor operation by using a separate heating element dedicated solely to capacitor preheating. This allows independent control of capacitor temperature without affecting motor control, enabling the heating process to occur before motor startup.
Solution Approach 2:
The heating element performs the preheating action before motor operation begins, allowing capacitor temperature to be optimized independently of motor control requirements. This preliminary action ensures capacitors are ready for operation without interfering with subsequent motor control.
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 the operation of refrigerant compressors with small and economical electrolytic capacitors from −25° C to over 120° C without premature aging, ensuring optimal performance and efficiency without influencing motor control.
Implementation Method 1
generating a ripple current for preheating of the capacitors by means of the selected or created switching pattern
Data Source
AI summary
A method of operating an inverter including the steps of detecting the temperature of the at least one electrolytic capacitor; selecting at least one of a plurality of switching patterns based on the temperature of the at least one electrolytic capacitor; and generating a ripple current across the at least one electrolytic capacitor by operating the inverter from the at least one of the plurality of switching patterns for preheating of the at least one electrolytic capacitor.