Sensorless Synchronous Motor Start-Up Using Adaptive Rotor Position Estimation
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Solution Overview
Problem
Existing synchronous electric machines face challenges in controlling torque and position without angular position sensors, particularly at low rotational speeds and under high torque conditions, due to sensor reliability issues, environmental stress, and limitations in estimating rotor position using back electromotive force (EMF) at low speeds.
Innovation Solution
A control device with a closed-loop adaptive angle estimator that injects a non-zero direct current to estimate rotor position based on stator flux, using a non-linear stator flux observer to adapt to changes in rotational speed, and an adaptive angle estimator to correct angular errors, enabling reliable starting and operation from standstill to maximum speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotor angle sensor (encoder or resolver) is used to detect rotor position, then the exact rotor position and speed are known, but the device complexity increases, reliability decreases due to sensor failure under thermal stress, and cost increases
Solution Approach 1:
The patent extracts the position detection function from the physical sensor and implements it through software-based estimation algorithms. The sensorless control method eliminates the need for mechanical sensors by deriving rotor position information from electrical measurements (currents and voltages) processed through mathematical models, thereby removing the unreliable sensor component while maintaining position detection capability
Solution Approach 2:
The patent replaces the mechanical sensor system (encoder or resolver) with an electrical/software-based estimation system. Instead of using physical sensors to measure rotor position, the system uses electrical measurements and mathematical algorithms (such as back-EMF estimation or observer-based methods) to calculate rotor position and speed, substituting mechanical measurement with electrical computation
2Device complexity
If back EMF-based position estimation is used, then the control device complexity is reduced, but the measurement precision deteriorates at low rotational speeds due to diminished back EMF magnitude
Solution Approach 1:
The patent implements a dynamic switching strategy where the control method adapts based on operating conditions. At low speeds, it uses alternative estimation techniques (such as current-based observers or injection methods) that remain effective when back-EMF is small, and transitions to back-EMF-based estimation at higher speeds. This dynamic adaptation maintains measurement precision across the entire speed range while keeping the control device relatively simple
Solution Approach 2:
The patent changes the estimation parameters and algorithms based on rotational speed. Instead of relying solely on back-EMF magnitude, the system adjusts the estimation approach according to speed conditions, using different mathematical models or measurement techniques appropriate for low-speed versus high-speed operation, thereby maintaining detectability across all speeds
3Power
If high torque is applied, then the power output increases, but the rotor shaft slips relative to the rotor body, causing absolute position error and degrading control accuracy
Solution Approach 1:
The patent replaces mechanical position sensing (which is vulnerable to shaft slip) with electrical-based position estimation. By using current and voltage measurements combined with mathematical models to estimate rotor position, the system eliminates the mechanical connection between the position sensing element and the rotor shaft, thereby preventing position errors caused by shaft slip under high torque conditions
4Device complexity
If an open-loop starting sequence is used, then the starting process is simplified, but the transition to closed-loop control requires perfect knowledge of inertia and load, and may cause stalling
Solution Approach 1:
The patent implements feedback mechanisms that allow the system to adapt during the transition from open-loop to closed-loop control. By continuously monitoring actual system response and comparing it with expected behavior, the controller can adjust parameters in real-time, eliminating the need for perfect prior knowledge of inertia and load. This feedback-based adaptation ensures reliable transition without stalling while maintaining relatively simple control structure
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
Enables reliable and robust sensorless, closed-loop starting and control of synchronous electric machines from standstill to maximum rotational speed, correcting angular position errors and maintaining torque accuracy.
Implementation Method 1
One solution exists for estimating the angular position of the motor using an approach that estimates the back electromotive force (EMF) between stator phases.
Implementation Method 2
a closed-loop adaptive angle estimator, for estimating the estimated angular position value of the rotor, based on a difference between at least one data point of a reference stator flux vector
Data Source
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AI summary
One aspect of the invention relates to a control device (2) for starting up a synchronous electric motor (1) up to a predetermined threshold speed, comprising: a current regulator (4) that delivers a voltage setpoint (V#dq) in accordance with a regulation current setpoint (l#dq'), a computing unit (5) for computing a current feedback (Idq) in accordance with measurements of the phase currents (lu, Iv, Iw), an estimator (6) for estimating an angular position of the rotor (θelec), in accordance with a difference between a reference stator flux vector (λq) that depends on the feedback currents (Iq) and an adaptive stator flux vector (λqv) that depends on the voltage setpoint (V#dq), on the feedback currents (Iq, Id), and on an estimated electrical speed (ωelec), a setpoint current modifier (7) that computes, when the estimated electrical speed (ωelec) is lower than the predetermined threshold speed, a regulator setpoint DC current (l#d) having a non-zero value.