Refrigerating device for containers
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Solution Overview
Problem
Container refrigerators operating with generators as power supply can experience overheating or burnout due to excessive equivalent negative-phase-sequence current, especially when generators with insufficient capacitance are used without proper consideration of permissible current limits.
Innovation Solution
A container refrigerator system that includes calculators to determine the permissible equivalent negative-phase-sequence current and a restrictor to limit the generated current to this value, using a power converter and controller to adjust the frequency of the power supplied to prevent overheating, and accurately calculate the equivalent negative-phase-sequence current based on specific power consumption and device characteristics.
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 operating state of the generator and compressor motor, and adjusts the inverter output frequency and voltage accordingly. When the generator temperature rises or harmonic current exceeds thresholds, the system automatically reduces the equivalent negative-phase-sequence current to protect the generator while maintaining refrigeration function.
Solution Approach 2:
The system dynamically changes the operating parameters of the inverter device, specifically adjusting the output frequency and voltage to control the equivalent negative-phase-sequence current. By modifying these parameters in real-time based on generator conditions, the system prevents harmful heating while maintaining refrigeration capacity control.
2Quantity of substance
If a generator with small capacitance is connected to the container refrigerator, then the system can operate with smaller power supply, but the equivalent negative-phase-sequence current may exceed the permissible limit, causing generator overheating or burnout
Solution Approach 1:
The control device dynamically adjusts the inverter output characteristics based on the generator's actual capacitance and operating conditions. Rather than using fixed parameters, the system continuously adapts the frequency and voltage output to ensure the equivalent negative-phase-sequence current remains within safe limits for the specific generator connected, enabling reliable operation with generators of various capacitances.
Solution Approach 2:
The control device automatically detects the generator's permissible current limit and self-regulates the inverter output to maintain safe operating conditions. The system monitors its own performance and adjusts parameters without external intervention, preventing overheating and burnout while maximizing the utilization of the available generator capacity.
Data Source
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AI summary
In this container refrigerator, the permissible equivalent negative-phase-sequence current (Itg) 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 (It) 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.