A method for reducing the maximum inrush current of a compressor system comprising multiple asynchronous electrical motors and a compressor system for implementing this method
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Compressor systems driven by multiple asynchronous electrical motors experience high inrush currents during startup, leading to increased costs and complexity in power delivery network design, as well as potential limitations imposed by public utilities, with existing solutions like starter circuits and variable frequency drives being costly and inefficient.
Innovation Solution
A method where asynchronous electrical motors are started one after another in an unloaded state, reaching nominal speed before loading, to minimize inrush current, using load control units to manage mechanical load and reduce electrical current draw during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple asynchronous electrical motors are started simultaneously, then the compressor system achieves full capacity operation, but the inrush current increases significantly requiring oversized power infrastructure
Solution Approach 1:
The patent applies preliminary action by unloading the motors before startup and keeping them unloaded during the acceleration phase. The load control units are activated in advance to ensure motors start in an unloaded state, which prevents high inrush current while maintaining the ability to achieve full capacity operation once all motors are running.
Solution Approach 2:
The patent applies dynamics by dynamically controlling the load on motors during different operational phases. The load control units adjust the mechanical load based on the startup sequence and operational status, allowing motors to accelerate with minimal load and then progressively apply full load once running, thereby managing inrush current while maintaining productivity.
2Object-affected harmful factors
If starter circuits are used to reduce inrush current, then the power infrastructure cost decreases, but the motor efficiency at maximum speed is significantly reduced
Solution Approach 1:
The patent uses dynamic load control to maintain motor efficiency. Unlike fixed starter circuits that alter winding connections and reduce efficiency, this invention dynamically adjusts the mechanical load via load control units while maintaining optimal electrical connection patterns, ensuring motors operate at maximum efficiency during full-load conditions.
Solution Approach 2:
The patent introduces load control units as intermediaries between the motors and the mechanical load. These units decouple the electrical startup process from the mechanical load application, allowing motors to start and accelerate without heavy mechanical burden while maintaining their electrical efficiency characteristics during operation.
3Object-affected harmful factors
If variable frequency drives are added to each motor to control input current, then the inrush current is reduced, but the cost and complexity of the compressor unit increases
Solution Approach 1:
The patent extracts the load control function from the electrical drive system and places it in mechanical load control units. This separation allows simple on/off control of mechanical load without complex frequency conversion electronics, reducing system complexity while still achieving inrush current reduction through unloaded startup sequences.
Solution Approach 2:
The patent uses simple, cost-effective load control units instead of expensive variable frequency drives. These load control units provide the necessary function of reducing startup current through mechanical load management without the high cost and complexity of electronic frequency conversion systems.
4Reliability
If the power delivery network is designed for high inrush current, then reliable motor startup is ensured, but the cost and complexity of the fixed infrastructure increases
Solution Approach 1:
The patent ensures reliable motor startup through preliminary unloading actions. By activating load control units before startup to ensure motors begin in an unloaded state, the system maintains startup reliability without requiring oversized power infrastructure, as the unloaded condition naturally limits inrush current to acceptable levels.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
This method for controlling asynchronous electrical motors of a compressor system, comprises: - receiving an order to start a first asynchronous electrical motor and a second asynchronous electrical motor of a compressor system; - unloading said first and second motors, by operating respectively a first load control unit of the first motor and a second load control unit of the second motor, in order to reduce the mechanical load associated to said motors; - starting the first motor and, only once the first motor is running at nominal speed, starting the second motor, - loading both the first and second electrical motor only once the second motor has started and is running at nominal speed, by operating the first load control unit and the second load control unit, in order to increase the mechanical load associated to said motors.