Motor driving apparatus and refrigeration cycle equipment
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Solution Overview
Problem
Existing motor driving systems experience significant speed decreases during connection switching, leading to control failures and motor wear, particularly when switching between star and delta connections while rotating.
Innovation Solution
A motor driving apparatus that includes a control device to manage the inverter output and a connection switching device, allowing for zero current control during minimum torque phases, enabling seamless switching of motor connections without disrupting rotational speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If connection switching is performed while the motor is rotating, then the motor can operate continuously without stopping, but the speed of the motor greatly decreases at the time of switching causing control failure and motor wear
Solution Approach 1:
The control device identifies the minimum torque phase in advance before switching occurs, and pre-adjusts the inverter output to achieve zero current at that phase. This preliminary preparation ensures that when connection switching happens, the motor current is already zero, preventing speed drops and maintaining control stability throughout continuous operation.
2Productivity
If connection switching is performed while the motor is rotating, then the motor can operate continuously without stopping, but this causes wear of the shaft and control failures
Solution Approach 1:
The control device dynamically changes the inverter output parameters (voltage and frequency) to match the periodic variation of load torque. By adjusting these parameters so that current becomes zero during the minimum torque phase, the switching conditions are optimized to eliminate harmful effects like shaft wear and control failures while maintaining continuous operation.
3Manufacturing precision
If the inverter output is controlled to match periodic load torque variation, then the output torque follows load torque accurately, but this requires precise control during switching periods
Solution Approach 1:
The control device uses feedback from the periodic load torque characteristics to identify the minimum torque phase and adjust the inverter output accordingly. This feedback mechanism enables precise torque control that follows load torque variations accurately, while the automated nature of the feedback loop manages the complexity of coordinating inverter output with switching timing.
Data Source
AI summary
An inverter for driving a motor that has a switchable connection of windings and drives a load element having a periodically varying load torque is provided. The inverter is controlled so that an output torque of the motor follows the periodic variation of the load torque. The inverter is controlled so that a current flowing through the motor is zero during a period including a minimum torque phase at which the load torque is at or near a minimum value. The connection is switched while the current flowing through the motor is zero. It is possible to switch the connection of the windings while the motor is rotating, and avoid an increase in apparatus size.