Multi-Motor Inverter Soft Start to Prevent Inrush Current Damage
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Solution Overview
Problem
Existing inverter control methods for multiple motors, such as direct-on-line starting, cause large inrush currents and equipment damage, and require additional hardware for soft start, increasing costs and stress on piping systems.
Innovation Solution
An inverter system with 2n relays and output switches controls each motor's connection to either inverter or AC power source output, allowing soft start without additional components, preventing inrush currents and reducing stress on piping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct-on-line starting method is used for auxiliary motors, then motors can be started quickly and simply, but large inrush currents occur causing equipment damage and contact portion damage
Solution Approach 1:
The system performs preliminary action by having the inverter gradually accelerate the auxiliary motor from zero speed before connecting to the AC power source. This preliminary acceleration phase prevents the sudden inrush current that would occur with direct-on-line starting, while still achieving quick overall startup through the pre-accelerated state.
Solution Approach 2:
The inverter acts as an intermediary device between the AC power source and the auxiliary motor. It mediates the power transfer by controlling the motor acceleration process, transforming the direct connection into a controlled gradual connection, thereby eliminating the harmful inrush current while maintaining efficient power delivery.
2Object-affected harmful factors
If star-delta soft starter method is used, then inrush current is reduced, but additional hardware components and installation space are required
Solution Approach 1:
The inverter performs multiple functions: it serves as both the primary motor controller and the soft starter for auxiliary motors. By integrating the soft start capability into the existing inverter unit, the system eliminates the need for separate star-delta switching hardware, contactors, and additional control components, achieving inrush current reduction without increasing device complexity.
Solution Approach 2:
The patent merges the soft start function with the existing inverter control system. Instead of implementing separate star-delta starting hardware, the inverter's control unit is enhanced to manage auxiliary motor acceleration, combining multiple functions into a single integrated device and reducing overall system complexity.
3Stress or pressure
If multiple auxiliary motors are connected to AC power source, then system pressure requirement is met, but stress on piping system increases due to rapid flow rate change
Solution Approach 1:
The inverter applies periodic action by controlling the auxiliary motor acceleration in gradual stages rather than instant startup. The motor speed increases progressively through controlled frequency steps, which corresponds to gradual flow rate increase in the piping system, thereby meeting pressure requirements while avoiding sudden flow changes that cause piping stress.
Solution Approach 2:
The system provides beforehand cushioning by pre-accelerating the auxiliary motor through the inverter before full power connection. This gradual acceleration cushions the transition to full operating speed, preventing sudden flow rate changes in the piping system that would otherwise cause mechanical stress and potential damage.
4Ease of manufacture
If inverter controls multiple motors, then cost reduction is achieved, but control complexity increases
Solution Approach 1:
The control system applies segmentation by treating each motor (main and auxiliary) as a separate controllable unit with dedicated control logic. The control unit manages each motor independently through separate output switches and relays, allowing complex multi-motor control to be broken down into manageable segments, thereby reducing perceived complexity while maintaining cost efficiency.
Data Source
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AI summary
The present invention relates to a soft start control method for multiple motors, and an inverter using same. The inverter according to an embodiment of the present invention is an inverter which converts supplied alternating current into three-phase ((U, V, W)) alternating current and outputs same, the inverter comprising: 2n relays which operate on/off of respective output switches; and a control unit which controls the respective relays to operate the on/off of the respective output switches so as to control respective motors to be connected to the three phases ((U, V, W)) of the inverter or connected to three phases ((R, S, T)) of an alternating current power source unit.