Container Refrigerator Inverter Control for Generator Harmonic Heating
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Solution Overview
Problem
Container refrigerators using generators as power supply may generate excessive equivalent negative-phase-sequence current, leading to overheating or burnout, especially when the generator's capacitance does not meet the standard, and existing solutions do not adequately address this issue.
Innovation Solution
A container refrigerator that detects the permissible equivalent negative-phase-sequence current of the generator and controls the power converter to restrict the generated current within safe limits, using calculators to calculate and restrict the current, and a controller to adjust the frequency of the power converter to prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an inverter device is activated to control the number of rotations of the compressor motor, then the refrigeration capacity can be varied, but harmonic current is generated which heats the generator rotor and other parts, potentially causing burnout
Solution Approach 1:
The control device continuously monitors the equivalent negative-phase-sequence current generated by the inverter and compares it against the permissible current threshold. When the current exceeds the threshold, the control device automatically adjusts the inverter's operation to reduce the current, creating a closed-loop feedback system that prevents generator overheating while maintaining refrigeration control functionality
Solution Approach 2:
The system dynamically changes the operating parameters of the inverter device, specifically adjusting the frequency control and PWM switching parameters, to optimize the balance between refrigeration capacity control and harmonic current generation, ensuring the equivalent negative-phase-sequence current remains within permissible limits
2Adaptability or versatility
If a generator with small capacitance is connected without taking the permissible equivalent negative-phase-sequence current into consideration, then the container refrigerator can operate with available generators, but the equivalent negative-phase-sequence current could exceed the permissible current, resulting in overheat or burnout of the generator
Solution Approach 1:
Before operating the container refrigerator with a generator, the control device first detects and calculates the permissible equivalent negative-phase-sequence current of the connected generator. This preliminary assessment ensures that the generator's current-bearing capacity is known and accounted for before the inverter device is activated, preventing unsafe operation conditions
Solution Approach 2:
The control device continuously monitors the actual equivalent negative-phase-sequence current and compares it against the detected permissible current threshold, automatically adjusting operations to maintain safety margins and prevent generator overheating or burnout
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
Effectively prevents generator overheating or burnout by accurately calculating and restricting the equivalent negative-phase-sequence current, ensuring safe operation even with generators of insufficient capacitance.
Implementation Method 1
the power supplied to the built-in compressor needs to be converted through a frequency control such as a PWM control
Implementation Method 2
if, while the container refrigerator is operating, an inverter device is activated to control the number of rotations of its built-in compressor, then some harmonic current would be generated
Implementation Method 3
a generator (G) connected thereto as its power supply
Implementation Method 4
the harmonic current could be induced in the field winding of the generator connected, for example, thus heating the rotor and other parts to raise the temperature of the generator
Data Source
AI summary
In this container refrigerator, the permissible equivalent negative-phase-sequence current of a generator to be connected is calculated in Step S3 based on its capacitance. Next, in Step S4, the power consumption of an inverter device to generate the equivalent negative-phase-sequence current is calculated. Then, in Step S6, the equivalent negative-phase-sequence current generated by the container refrigerator is calculated based on the power consumption of this inverter device. Thereafter, in Step S9, It is compared to Itg. If It>Itg is satisfied, It is restricted until It≦Itg is met by lowering the output frequency of the inverter device repeatedly in multiple stages. Consequently, even if the generator connected has small capacitance, the operation may be continued at a number of rotations appropriate for that small capacitance without causing the generator to overheat or be burned out.