Rotary Machine Torque Control for Ground Fault Detection
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Solution Overview
Problem
In rotary machines, detecting a ground fault in an electric motor while minimizing the difference between the required torque and the actual sum torque of a turbine and an induction motor is challenging due to the existing torque mismatch between the turbine and the electric motor.
Innovation Solution
A control device that sets the induction motor to a minimum torque or higher when the turbine output torque is within its stable output range, allowing for ground fault detection and reducing torque differences by adjusting the turbine output torque based on the electric motor output torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is driven to detect ground fault, then ground fault detection capability is improved, but a difference between required torque and actual sum torque is generated
Solution Approach 1:
The control device preliminarily sets the electric motor output torque to a minimum value (e.g., 5% of rated torque) before ground fault detection. This preliminary action ensures the motor operates in a stable state suitable for detection while the control device subsequently calculates and applies torque correction to eliminate the difference between required and actual torque, thus resolving the contradiction between detection capability and torque accuracy
Solution Approach 2:
The control device implements feedback control by continuously monitoring the actual sum torque of turbine and electric motor, comparing it with the required torque, and adjusting the electric motor output torque accordingly. This feedback mechanism eliminates torque differences generated during ground fault detection, maintaining both detection capability and torque accuracy
2Adaptability or versatility
If the induction motor is synchronized with the turbine in unstable state, then the transition from turbine to combined output is achieved, but temporary useless decrease and increase in turbine output torque occurs
Solution Approach 1:
The control device sets a reference torque value in advance within the stable output range of the turbine before synchronization occurs. This preliminary setting prevents unstable synchronization by providing a predetermined torque reference, eliminating the need for temporary torque decreases and increases during the transition from turbine-only to combined output operation
Solution Approach 2:
The control device dynamically adjusts the electric motor output torque based on the turbine's operating state and the reference torque. By making the motor torque adjustable and responsive to real-time conditions, the system achieves smooth transition without temporary fluctuations, converting the static turbine output into a dynamically balanced combined output
Data Source
AI summary
A control device for a rotary machine, which is driven by a turbine output torque which is an output of a turbine and an electric motor output torque which is an output of an induction motor, includes: a required output setting unit configured to set a required torque for driving the rotary machine; and a drive source command unit configured to set the electric motor output torque to a minimum torque or higher of the induction motor and to set the turbine output torque to a value obtained by subtracting the electric motor output torque from the required torque when the turbine output torque is greater than or equal to a lower limit in a stable output range of the turbine.