Compressor Envelope Control Using Inverter Speed Regulation
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Solution Overview
Problem
Transport refrigeration systems in vehicles face challenges in maintaining optimal compressor operation across varying engine speeds, leading to inconsistent discharge pressure and temperature, which can compromise the preservation of perishable cargo.
Innovation Solution
A control apparatus with temperature and pressure sensors, a microprocessor, and an inverter that adjusts electrical power to the compressor based on sensed discharge and suction pressures, as well as return air temperature, to maintain a stable compressor envelope and efficient cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the compressor is directly driven by the main engine drive, then the system structure is simple, but the compressor speed varies with engine speed causing discharge pressure and temperature to fall outside the compressor envelope
Solution Approach 1:
The patent applies dynamics by making the compressor drive system adjustable and adaptable to different operating conditions. The inverter allows the compressor speed to be dynamically controlled based on actual system needs, transitioning from a fixed direct-drive configuration to a flexible variable-speed configuration that maintains reliable operation across varying engine speeds.
Solution Approach 2:
The patent changes the operational parameters of the compressor drive system by introducing an inverter that can vary the electrical power frequency and voltage supplied to the compressor motor. This enables independent control of compressor speed from engine speed, allowing the system to maintain optimal discharge pressure and temperature within the compressor envelope regardless of engine operating conditions.
2Productivity
If the compressor speed is increased to meet peak cooling demands, then the cooling capacity is improved, but the discharge temperature and pressure may exceed safe operating limits
Solution Approach 1:
The patent implements feedback control by continuously monitoring discharge temperature and pressure sensors and using this information to adjust compressor speed via the inverter. When discharge parameters approach unsafe limits, the system automatically reduces compressor speed to maintain operation within the safe envelope, while still responding to cooling demands. This closed-loop control enables the system to maximize cooling capacity without exceeding safe operating parameters.
3Reliability
If the compressor speed is reduced to maintain safe discharge parameters, then the compressor envelope is protected, but the cooling capacity decreases
Solution Approach 1:
The patent applies dynamics by enabling the compressor speed to be dynamically adjusted based on real-time system conditions. Rather than operating at a fixed reduced speed, the system can vary compressor speed continuously to match actual cooling demands while maintaining discharge parameters within safe limits. This dynamic response allows the system to maximize cooling capacity within the safe envelope for each operating condition.
Solution Approach 2:
The patent achieves multi-functionality by having the inverter-based control system perform multiple roles: protecting the compressor envelope, meeting varying cooling demands, improving energy efficiency, and enabling flexible operation across different engine speeds. This universal control approach allows the system to optimize for different priorities (protection vs. capacity) depending on actual operating conditions.
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 provides improved temperature control and reduced compressor speed variability, enhancing the reliability and efficiency of the refrigeration system by maintaining desired temperature and pressure ranges, especially during peak cooling demands.
Implementation Method 1
an inverter configured to receive an inverter control signal from the microprocessor and to receive electrical power from the generator and to provide a level of electrical power to the compressor in response to the inverter control signal
Implementation Method 2
a generator driven by an engine with the generated electrical power being supplied to a compressor
Data Source
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AI summary
A transport refrigeration system is provided with a control apparatus including an inverter and a microprocessor, with the microprocessor receiving signals representative of sensed values of the compressor discharge temperature and pressure, as well as the suction pressure, and controlling the inverter to responsively provide a selective level of electrical voltage and frequency to the compressor in order to maintain a desired compressor envelope.