Encoderless Synchronous Machine Control via Squirrel Cage Damping
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Solution Overview
Problem
Existing control methods for synchronous machines struggle to operate effectively in the lower speed range without angular position information, leading to instability and oscillation, and fail to provide reliable emergency operation when energy supply is disrupted.
Innovation Solution
The method employs an encoderless control strategy for a separately excited synchronous machine with a squirrel cage rotor, using an inverter-controlled stator voltage and current space vectors to regulate operation below critical speed, and switches to field-oriented control above critical speed, leveraging the squirrel cage for damping and energy supply via a contactless exciter winding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If encoderless control is used in the lower speed range, then the device complexity is reduced by eliminating angle sensors, but the stability deteriorates due to lack of angular position information
Solution Approach 1:
The squirrel cage acts as an intermediary element that provides damping torque to stabilize rotor operation at low speeds without requiring angle sensors. The cage windings generate eddy currents that produce a stabilizing electromagnetic field, serving as a mediator between the control system and the rotor position.
Solution Approach 2:
The patent replaces the mechanical/physical angle sensor system with an electronic control system that uses current space vectors and flux models to achieve encoderless control. This substitution eliminates mechanical components while maintaining control capability through mathematical modeling and feedback control.
2Ease of operation
If regulated operation is enabled in the lower speed range without angular position information, then the ease of operation is improved, but the measurement precision deteriorates due to lack of angle data
Solution Approach 1:
The control system performs self-position estimation by using the measured current space vectors and the flux model to determine rotor position indirectly. The system serves itself by calculating position information from electrical measurements rather than requiring external sensors, enabling operation without angular position information.
3Stability of the object's composition
If the squirrel cage is used for damping at low speeds, then the stability is improved, but the loss of energy increases due to ohmic losses in the cage
Solution Approach 1:
The squirrel cage provides partial damping action that is sufficient to stabilize low-speed operation without requiring full engagement of the excitation field winding. The cage windings are partially active during low-speed operation, providing just enough damping torque to maintain stability while minimizing ohmic losses.
4Productivity
If field-oriented control is used above critical speed, then the productivity is improved through better control accuracy, but the device complexity increases due to switching control strategies
Solution Approach 1:
The control system dynamically switches between encoderless control with squirrel cage damping for low speeds and field-oriented control for higher speeds. The control strategy adapts to the operating conditions, using the most appropriate method for each speed range to optimize both productivity and simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables stable and dynamic speed control in the lower speed range, reduces oscillation tendencies, and allows seamless transition to asynchronous operation during energy failures, with improved signal quality and control accuracy.
Implementation Method 1
If the rotor deviates from the desired angular position, the squirrel cage dampens. Because when slip occurs, the ohmic loss in the short-circuit cage also increases with the slip.
Implementation Method 2
Because when slip occurs, the ohmic loss in the short-circuit cage also increases with the slip.
Implementation Method 3
a stator voltage space vector being set and a stator current space vector being determined by a unit feeding the electric machine, in particular comprising an inverter controlled by an electronic circuit
Implementation Method 4
the electric machine comprises a rotor movable relative to a stator winding, in particular rotatably mounted, rotor, in particular wherein the rotor is a Has excitation winding
Data Source
AI summary
The invention relates to a method for operating an electrical machine, especially a separately excited synchronous machine having an additional squirrel cage. The electrical machine comprises a rotor which is mobile relative to a stator winding, especially a rotatably mounted rotor, the rotor especially having an excitation winding and/or a squirrel cage. A unit supplying the electrical machine and especially having an inverter controlled by an electronic control unit, provides a stator voltage space vector and determines a stator current space vector. The stator current space vector so determined is controlled towards a rated value when the rotor is below a critical speed, especially the rate of the stator current space vector determined is controlled towards a rated value for the rate and the direction and/or speed of the stator current space vector is controlled towards a corresponding rated value for the direction and/or speed.