Synchronous Motor Grid Switching at Predetermined Shaft Position
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Solution Overview
Problem
Existing variable frequency drivers (VFDs) switch synchronous motors to the electric grid without knowing the rotor position, leading to uncertainty in the operating position of connected machinery, such as reciprocating compressors.
Innovation Solution
A method and system that synchronize synchronous motors with the electric grid by performing the power switch only when the rotor is at a predetermined angular position, using an improved variable frequency driver and a switching enable unit that integrates shaft angular position detectors to ensure precise synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the power switch from VFD to electric grid is performed as soon as voltage alignment condition is reached, then the switching process is simple and quick, but the rotor position becomes unknown leading to loss of machine position information
Solution Approach 1:
The system performs preliminary detection of rotor position using shaft angular position detectors before the power switch from VFD to grid is executed. The control unit waits for the rotor to reach a predetermined angular position (such as zero degree) before enabling the switch, thus ensuring position information is known in advance of the switching action.
2Measurement precision
If the power switch is delayed until a predetermined rotor position is detected, then precise rotor position information is available, but the synchronization process takes longer
Solution Approach 1:
The system continuously monitors the shaft angular position through detectors and provides feedback to the control unit. The control unit compares the actual position with the predetermined target position and only enables the power switch when the rotor reaches the exact predetermined angular position, ensuring precise position information is obtained.
3Adaptability or versatility
If multiple voltage alignment conditions exist due to N/2 possible poles alignment, then the motor can be started flexibly, but it becomes impossible to determine which rotor position corresponds to which alignment
Solution Approach 1:
Shaft angular position detectors serve as an intermediary device that directly measures the physical position of the rotor shaft. This intermediary measurement system bridges the gap between the electrical voltage alignment conditions and the mechanical rotor position, providing unambiguous position information regardless of which of the N/2 pole alignment conditions is present.
Data Source
AI summary
The system (100) is used for starting and synchronizing synchronous motors (10) with power electricity of an electric grid (20). The system (100) includes a variable frequency driver (30) for starting the synchronous motors (10), and an electrical diverter (61, 63) for each synchronous motor (10). The electrical diverter (61, 63) has a control input electrically coupled to a control output of the variable frequency driver (30) so to selectively couple stator windings (12) of synchronous motors (10) with a power output (33) of the variable frequency driver (30) or with the electric grid (20) based on signals that are received at a control input of the variable frequency driver (30) and represent a position of the shafts of the synchronous motors (10). Therefore, switching occurs at desired shafts positions.