Separately Excited Synchronous Motor Rotor Position Detection
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Solution Overview
Problem
Synchronous machines with separately excited field windings face challenges in accurately determining the rotor's angular position at low speeds due to weak induced voltage signals, which are difficult to detect and control effectively.
Innovation Solution
A method involving the application of a unipolar current with an additional signal superimposed on the field winding, where the frequency of the additional signal is an integer multiple of the primary winding's current frequency, enhancing signal recognizability and allowing for synchronized current sampling to filter out noise, thereby improving control and position determination at low speeds or standstill.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a direct current is applied to the field winding, then the machine can operate at high speeds with strong induced voltage signals, but the induced voltage signal becomes very weak and difficult to detect at low speeds or standstill
Solution Approach 1:
An additional periodic signal with frequency f_z is superimposed on the unipolar current supplied to the field winding. This periodic modulation creates a corresponding periodic component in the induced voltage that can be easily detected even at low speeds or standstill, resolving the contradiction between high-speed operation and low-speed detection accuracy
Solution Approach 2:
The frequency of the additional signal is chosen to be an integer multiple of the supply frequency, creating a distinct frequency signature that allows reliable detection. This parameter change enables the system to maintain measurement precision across the entire speed range from standstill to high speeds
2Measurement precision
If an additional signal with high frequency is superimposed on the field winding current, then the signal-to-noise ratio is improved and signal recognizability is enhanced, but the device complexity increases due to additional signal generation and processing requirements
Solution Approach 1:
The additional signal serves multiple functions: it modulates the field current to enhance signal detectability, and its frequency is synchronized with the PWM frequency of the power semiconductors. This multi-functionality improves signal-to-noise ratio without requiring separate dedicated hardware for each function, thereby limiting the increase in device complexity
Solution Approach 2:
The control system uses synchronized current sampling that is coordinated with the additional signal frequency and PWM switching frequency. This feedback mechanism allows the system to distinguish the additional signal from noise and switching harmonics, improving measurement precision while using existing control infrastructure
3Loss of information
If the additional signal frequency is synchronized with the PWM frequency of power semiconductors, then the additional signal can be separated from controlled variables through synchronized sampling, but the control system complexity increases
Solution Approach 1:
The frequency of the additional signal is synchronized with the PWM frequency of the power semiconductors. This merging of frequencies allows the control system to use a single synchronized sampling clock for both the additional signal detection and the PWM control, improving signal separation accuracy while avoiding the need for separate synchronized sampling systems
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 provides a clear and recognizable signal with a high signal-to-noise ratio, enabling reliable and error-free determination of the rotor's angular position without additional sensors, achieving improved dynamics and reduced moment of inertia in the control system.
Implementation Method 1
the position of the rotor can be determined at high speeds by determining the voltage induced by the permanent magnets or, in the case of externally excited synchronous machines, by the field coils on the stator winding
Implementation Method 2
an additional signal is superimposed on the unipolar current, which is supplied to the field winding. In this case, the frequency of the additional signal is an integer multiple of the frequency of that current component
Data Source
AI summary
The invention relates to a method and a device for controlling a synchronous motor which is separately excited by an excitation winding, said excitation winding being supplied with a unipolar current on to which an additional signal is superimposed.