Sensorless Motor Speed Estimation Using PLL Voltage Vector Analysis
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Solution Overview
Problem
Existing methods for estimating the rotational speed of a freewheeling electric motor without a speed sensor are either costly due to the need for high-dynamic voltage measurement circuits or slow due to frequency sweeping, and require knowledge of motor parameters, making them impractical for quick and simple implementation in variable speed drives.
Innovation Solution
A software method that calculates the rotational speed using a PLL phase-locked loop circuit to evaluate the angle of rotation of reference alternating voltages generated from measured flux and torque currents, without requiring motor parameters or passing current through the motor, allowing for rapid and accurate speed estimation during motor control recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage measurement circuit is used to measure phase voltages for speed estimation, then speed estimation accuracy is improved, but device complexity and cost increase due to high-dynamic requirements and cable disturbance immunity
Solution Approach 1:
The patent replaces the hardware voltage measurement circuit with a software-based method. Instead of measuring actual phase voltages with complex hardware, the system calculates reference voltages using motor model equations based on measured currents and estimated speed, then uses the phase difference between these calculated reference voltages to determine rotor position and speed. This substitution eliminates the need for high-dynamic voltage measurement circuits while maintaining speed estimation accuracy.
2Device complexity
If frequency sweeping is performed to estimate motor speed, then speed estimation is achieved without voltage measurement circuit, but response time deteriorates due to several seconds sweeping duration
Solution Approach 1:
The patent performs preliminary action by continuously estimating motor speed and updating the speed model even during normal operation, not just when coasting occurs. The system maintains an up-to-date speed estimate by processing current measurements through the motor model equations in real-time, so when coasting begins and speed estimation is needed, the value is already available or can be quickly determined without performing a time-consuming frequency sweep.
3Loss of information
If current is passed through motor during frequency sweep for speed estimation, then speed information is obtained, but motor speed deteriorates due to braking effect during search phase
Solution Approach 1:
The patent replaces the mechanical current injection method with an electrical calculation-based approach. Instead of passing physical current through the motor windings to elicit a response, the system uses electrical equations to calculate what the voltages should be at the current operating point, then compares these calculated values with actual measurements or uses the relationship between calculated reference voltages to infer speed. This eliminates the need to physically interact with the motor during estimation.
4Measurement precision
If motor parameters are required for speed estimation using simplified equations, then implementation complexity increases, but measurement precision may be improved
Solution Approach 1:
The patent implements self-service by having the system automatically adapt and update its own motor parameters during operation. The motor model equations include parameters such as resistance and inductance that can be estimated online using standard identification routines or adaptive observers. This allows the system to maintain accurate speed estimation without requiring manual parameter input or complex hardware, as the motor itself provides the necessary information through its electrical characteristics during normal operation.
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 quick and accurate estimation of motor speed with minimal disturbance, eliminating the need for costly hardware and motor parameter knowledge, and is applicable to both synchronous and asynchronous motors, facilitating on-the-fly motor control resumption.
Implementation Method 1
Due to the residual electromotive force due to the rotation of the motor, these voltages are sinusoids shifted by +/-60° whose frequency corresponds to the electrical speed of the motor.
Implementation Method 2
The calculation step uses a PLL phase-locked loop circuit which receives the AC reference voltages Va, Vb as input and which delivers the speed of rotation ω as output.
Data Source
Figure 1~4
AI summary
The method involves measuring a current flow (Id) and a torque current (Iq) of an electric motor (M) in an orthogonal diphase line. Reference alternating current (AC) voltages (Va, Vb) are determined by executing a current regulation from the measured flow, the current, and two reference currents. Rotational speed (omega) of the motor is calculated with the help of a phase lock loop (PLL) circuit by evaluating a rotational angle (thetaE) of a voltage vector, whose components are fixed, where the circuit receives the voltages at its input and delivers the rotational speed at its output. An independent claim is also included for a device for estimating a rotational speed of an electric motor.