Driving device, compressor, air conditioner, and driving method
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Solution Overview
Problem
Existing motor driving systems face challenges in reducing demagnetization of permanent magnets, especially during special operation states where current flows only in two of three-phase coils, due to varying connection states between Y and delta connections.
Innovation Solution
A driving device and method that includes an inverter and a connection switching unit to manage the connection state between Y and delta connections, with specific threshold settings for the inverter current to prevent demagnetization, where the second threshold for the delta connection is set lower than the square root of three times the first threshold for the Y connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overcurrent protection level is set based on the conventional relationship (B = √3 × A) between Y connection and delta connection, then the motor can operate efficiently in normal three-phase conditions, but demagnetization occurs in special operation states where current flows only in two phases
Solution Approach 1:
The patent changes the overcurrent protection parameter B for delta connection from the conventional value (√3 × A) to a reduced value (0.95 to 0.98 times √3 × A). This parameter adjustment ensures that in special operation states where current flows only in two phases, the protection level is low enough to prevent demagnetization while maintaining appropriate protection in normal three-phase operation.
2Reliability
If the overcurrent protection level B for delta connection is reduced below 0.95 times √3 × A, then demagnetization is prevented in special operation states, but the motor output capacity is unnecessarily limited
Solution Approach 1:
The patent optimizes the protection parameter B to be 0.95 to 0.98 times √3 × A, finding the optimal balance point. This range is high enough to maintain motor output capacity close to the theoretical maximum, yet low enough to prevent demagnetization in special two-phase operation states. The specific value within this range can be selected based on the desired trade-off between protection and output capacity.
3Power
If the overcurrent protection level B for delta connection is set to √3 × A or higher, then the motor output capacity is maximized, but demagnetization occurs in special operation states where current flows only in two phases
Solution Approach 1:
The patent applies preliminary anti-action by proactively reducing the overcurrent protection level B before demagnetization can occur in special operation states. By setting B to 0.95 to 0.98 times √3 × A, the system preemptively prevents the harmful effect of demagnetization that would otherwise occur when current flows only in two phases during delta connection operation.
Data Source
AI summary
A driving device includes an inverter to output a voltage to coils, a connection switching unit to switch a connection state of the coils between a Y connection and a delta connection, and a controller. The controller causes the inverter to stop outputting, when the connection state of the coils is the Y connection and a current value of the inverter reaches a first threshold A, or when the connection state of the coils is the delta connection and the current value of the inverter reaches a second threshold B. The first threshold A and the second threshold B satisfy B<√3×A.