Three-Phase Motor Rotor Position Estimation With Polygonal Voltage Injection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining the rotor position of a three-phase motor without a rotary encoder are limited by measurement noise, especially at low speeds or standstill, and require knowledge of inductance values, which are difficult to obtain accurately due to variations with current and temperature.
Innovation Solution
A method using a field-oriented control system that determines a control voltage vector, transforms it using an inverse Park transform, and applies a regular polygonal voltage pattern through pulse width modulation to estimate rotor position from current measurements, eliminating the need for inductance knowledge and reducing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency voltage injection is used to increase signal-to-noise ratio, then measurement precision is improved, but audible noise increases
Solution Approach 1:
The patent applies periodic voltage injection with specific frequency selection. The injection frequency is chosen to be outside the audible range (typically above 20kHz) while maintaining sufficient signal strength for accurate position estimation. This periodic injection at optimized frequencies resolves the contradiction by achieving precise measurement without generating audible noise.
Solution Approach 2:
The patent changes the frequency parameter of the injected voltage signal to optimize performance. By adjusting the injection frequency to be ultrasonic (above human audible range) while maintaining adequate amplitude, the system achieves high measurement precision without producing audible noise, thus resolving the technical contradiction.
2Measurement precision
If inductance values are used for position estimation, then measurement precision is improved, but device complexity increases due to difficulty in obtaining accurate inductance values
Solution Approach 1:
The patent implements self-service by having the system automatically identify and adapt to the motor's inductance characteristics during normal operation. The injection-based method allows the system to self-calibrate and extract position information without requiring external inductance measurement equipment or complex pre-characterization procedures, thus reducing device complexity while maintaining precision.
Solution Approach 2:
The patent replaces the need for separate inductance measurement systems (locked rotor tests, rotational tests with instrumentation) with an electrical injection method that uses the motor's own operating currents. This substitution eliminates complex test equipment and procedures while achieving accurate position estimation.
3Measurement precision
If voltage pulses are made very narrow to improve position resolution at standstill, then measurement precision is improved, but reliability decreases due to switching transients and noise
Solution Approach 1:
The patent uses periodic voltage injection at optimized frequencies and durations. By selecting appropriate injection frequencies (ultrasonic range) and durations (sufficient to generate measurable current response but not excessively long), the system achieves high position resolution at standstill while avoiding the reliability issues associated with extremely narrow pulses, such as switching transients and noise susceptibility.
Data Source
AI summary
The present invention concerns a method and a device for determining a position of a rotor of a three-phase motor using a FOC system. The invention: —determines, by a proportional-integral controller, a first control voltage vector at a first instant, —transforms the first control voltage vector using an inverse Park transform, —sums the transformed first control voltage vector to a regular polygonal voltage pattern applied during a given duration, —performs a PWM from the sum of the transformed first control voltage vector and the regular polygonal voltage pattern, —controls the motor with the pulse-width modulation, —measures the current at each phase of the motor, —estimates the position of the rotor from the measured currents and from the regular polygonal voltage pattern, —determines, at a second instant, a second control voltage vector from the measured currents and from the estimated position.