Sensorless PMSM Control via Phase Angle Torque Estimation
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Solution Overview
Problem
Existing closed-loop control systems for permanent magnet synchronous motors (PMSMs) face challenges at low speeds due to imprecision in back-EMF-based methods and reliance on motor characteristics, which affect reliability and accuracy, especially in applications requiring high positional accuracy and stability.
Innovation Solution
A method that measures phase current and voltage to estimate external load torque as a factor of the cosine of the phase angle, allowing for accurate control and compensation, independent of motor characteristics, and accounts for dead-zone play in actuation systems by determining a reference position relative to mechanical limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If back-EMF-based sensorless control methods are used, then control simplicity is improved, but measurement precision deteriorates at very low speeds because back-EMF disappears when rotor speed approaches zero
Solution Approach 1:
The patent changes the measurement parameter from back-EMF (which depends on speed) to phase voltage and phase current measurements. By using the relationship between voltage, current, and impedance angle, the system can estimate load torque independently of rotor speed, enabling accurate low-speed operation without relying on back-EMF signals.
2Measurement precision
If position-dependent inductance variation methods are used, then low speed operation is improved, but adaptability deteriorates because these methods cannot be used in stepper motors with very small inductance variation
Solution Approach 1:
The patent implements a feedback mechanism where phase voltage and phase current are continuously measured, and the impedance angle is calculated to estimate external load torque. This feedback loop allows the system to adapt to different motor types regardless of inductance variation characteristics, making the method universally applicable to both PMSMs and stepper motors.
3Ease of operation
If predetermined motor characteristics (phase resistance and inductance) are used for control, then ease of operation is improved, but reliability deteriorates because these characteristics vary with temperature, speed and load
Solution Approach 1:
The patent enables the control system to self-adapt by continuously measuring phase voltage and current and calculating the impedance angle in real-time. This eliminates the need for predetermined motor characteristics, allowing the system to automatically compensate for variations in resistance and inductance due to temperature, speed, and load changes without requiring external calibration or adjustment.
4Measurement precision
If external position or torque sensors are used, then measurement precision is improved, but device complexity and cost increase while reliability decreases
Solution Approach 1:
The patent uses phase voltage and phase current measurements as intermediary quantities to indirectly estimate external load torque. Instead of directly measuring torque or position with sensors, the system uses electrical measurements (voltage and current) as mediators to derive mechanical information, achieving sensorless control with high precision.
5Measurement precision
If complex calculation methods are used to address low speed operation, then measurement precision is improved, but device complexity increases and responsiveness may be affected
Solution Approach 1:
The patent segments the control problem into distinct measurable components: phase voltage measurement, phase current measurement, and impedance angle calculation. By breaking down the complex task of load torque estimation into these manageable segments, the system achieves accurate low-speed control without requiring overly complex calculations, maintaining both precision and responsiveness.
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
The solution provides robust, reliable, and accurate control of PMSMs at low speeds, reducing errors due to dead-zone play and material/ manufacturing tolerances, enabling precise positioning without external sensors, and is easily configurable across different motor series.
Implementation Method 1
calculating a phase angle φ between the measured phase current i(t) and phase voltage u(t), and estimating external load torque τ as a factor of the cosine of the phase angle φ
Implementation Method 2
permanent magnet synchronous motor (PMSM), such as a stepper or BLDC (brushless DC) motor
Data Source
Figure 1a~1c
Figure 2a~3
Figure 4~5a
AI summary
Method of controlling a PMSM, comprising measuring phase current i(t) of at least one phase of the PMSM, calculating a phase angle ϕ between the measured phase current i(t) and a phase voltage u(t) of said at least one phase, and estimating external load torque z as a function of the cosine of the phase angle ϕ.