Method for reducing the maximum inrush current of a compressor system comprising multiple asynchronous electrical motors and a compressor system for implementing this method
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Solution Overview
Problem
Compressor systems driven by asynchronous electric motors experience high inrush currents during startup, leading to increased costs and complexity in power delivery network design, and existing solutions like starter circuits or variable frequency drives are not cost-effective or efficient.
Innovation Solution
A method where asynchronous electrical motors are started one after another in an unloaded state, reaching nominal speed before being fully loaded, reducing the maximum inrush current by sequencing motor startups and load control operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple asynchronous motors are started simultaneously, then the compressor system reaches full operational capacity quickly, but the inrush current becomes excessively high requiring oversized power infrastructure
Solution Approach 1:
The system performs preliminary unloading of motors before startup by positioning load control units (inlet valves) to reduce mechanical load. This preliminary action allows motors to start with lower inrush current while still reaching full operational capacity, resolving the contradiction between quick startup and current reduction.
Solution Approach 2:
The startup process is segmented into distinct phases: unloading phase, sequential startup phase, and loading phase. Instead of simultaneous startup, motors are started one after another in a controlled sequence, dividing the inrush current problem into manageable segments that occur at different times.
2Object-affected harmful factors
If starter circuits are used to reduce inrush current, then the power delivery network requirements are reduced, but the device complexity and cost increase
Solution Approach 1:
The system uses its existing load control units (inlet valves) that are already part of the compressor architecture to perform the inrush current reduction function. These components serve dual purposes: normal load control and inrush current mitigation during startup, eliminating the need for separate starter circuits.
3Object-affected harmful factors
If variable frequency drives are added to control input current, then inrush current is reduced, but the cost and complexity of the compressor unit increase significantly
Solution Approach 1:
The existing load control units perform the current control function that would otherwise require variable frequency drives. By utilizing already-present components for dual purposes, the system achieves inrush current reduction without adding expensive and complex VFD hardware.
4Object-affected harmful factors
If motor size is reduced to lower inrush current, then the power delivery network requirements are reduced, but the motor may not have sufficient power for full load operation
Solution Approach 1:
By preliminarily unloading motors before startup, the system allows standard-sized motors to start with reduced inrush current while maintaining their full power capacity for load operation. The preliminary unloading action temporarily reduces the mechanical load during the critical startup phase, then full power is restored once the motor is running.
Data Source
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.