Variable Low-Pass Filter for Sensorless Motor Flux Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor control devices lack accurate estimation of magnetic flux in electric motors without position sensors, leading to inefficiencies in motor control.
Innovation Solution
A motor control device that includes a power converter, a magnetic flux estimator using a variable low-pass filter and phase adjuster to estimate stator magnetic flux, and a phase/velocity estimator to calculate motor velocity, enabling precise control of electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed low-pass filter is used to estimate stator magnetic flux, then the filtering is simple to implement, but the estimation accuracy deteriorates at different operating frequencies
Solution Approach 1:
The patent applies a variable cut-off frequency low-pass filter instead of a fixed one. The cut-off frequency is dynamically adjusted based on the operating frequency of the electric motor, allowing the filter to maintain optimal performance across different operating conditions. This resolves the contradiction by making the filter adaptive rather than static.
Solution Approach 2:
The patent changes the parameter of the low-pass filter (cut-off frequency) based on the operating conditions. By setting the cut-off frequency as a function of the motor's operating frequency, the filter maintains accurate magnetic flux estimation across varying speeds and loads, overcoming the limitation of fixed-frequency filters.
2Ease of manufacture
If integration is used to estimate magnetic flux from voltage difference, then the estimation is straightforward, but phase lag and accumulated errors occur
Solution Approach 1:
The patent transforms the integration operation into a differentiation operation in the frequency domain. By applying a low-pass filter with cut-off frequency equal to the motor's operating frequency and adjusting the phase, the system achieves magnetic flux estimation without the phase lag and error accumulation problems of time-domain integration.
Solution Approach 2:
The patent replaces the mechanical integration process with an equivalent frequency-domain filtering and phase adjustment process. This substitution eliminates the inherent drawbacks of integration (phase lag and error accumulation) while achieving the same mathematical objective of estimating magnetic flux from voltage and current measurements.
3Measurement precision
If position sensors are installed in electric motors, then control precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent enables the electric motor to estimate its own magnetic flux and position information using only voltage and current measurements from its own terminals. This self-service approach eliminates the need for external position sensors, maintaining control precision while reducing device complexity and cost.
Solution Approach 2:
The patent uses voltage and current measurements as intermediary signals to indirectly obtain magnetic flux and position information. Instead of directly measuring position with sensors, the system uses electrical measurements combined with mathematical processing (low-pass filtering and phase adjustment) to derive the necessary control information, avoiding the need for physical sensors.
Data Source
AI summary
A motor control device is provided, which includes a power converter for applying output voltage according to a voltage command to an electric motor, a magnetic flux estimator for estimating a vector of stator magnetic flux of the electric motor based on a difference between the output voltage and a voltage drop caused by a coil resistance of the electric motor, and a phase estimator for estimating a phase of the stator magnetic flux based on the vector of the stator magnetic flux estimated by the magnetic flux estimator. The magnetic flux estimator includes a variable low-pass filter for applying a low-pass filter to the difference at a cut-off frequency according to a frequency of the output voltage, and a phase adjuster for retarding at least one of an output phase of the variable low-pass filter and a phase of the difference before inputted into the variable low-pass filter.