Sensorless Motor Speed Estimation via Back-EMF Derivative
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Solution Overview
Problem
Existing sensorless speed estimation methods for electric motors, particularly in inverter-supplied systems, fail to accurately detect high motor speeds in asynchronous machines and synchronous machines, especially when the frequency of the fundamental wave of the supply voltage or current is unreliable, leading to potential overspeed and safety issues.
Innovation Solution
Monitoring the angular speed of the back-emf (electromotive force) of an electric motor by determining the time derivative of the stator current vector during a zero vector state of the inverter, allowing for reliable rotation speed estimation independent of the fundamental wave frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If speed estimation is based on fundamental wave frequency monitoring, then the system is simple and cost-effective, but it fails to detect high motor speeds in asynchronous machines and synchronous machines
Solution Approach 1:
The patent changes the estimation parameter from fundamental wave frequency to back-EMF angular speed. By monitoring the angular speed of the back-EMF vector instead of the fundamental wave frequency, the system achieves accurate speed estimation even at high speeds where traditional frequency-based methods fail. This parameter transformation resolves the contradiction by maintaining system simplicity while dramatically improving measurement accuracy across the full speed range.
2Reliability
If a separate safety circuit with alternative speed determination is used, then speed detection reliability is improved, but system cost increases
Solution Approach 1:
The patent makes the inverter's control system multi-functional by enabling it to perform both motor control and accurate speed estimation using back-EMF monitoring. This eliminates the need for a separate safety circuit while maintaining high reliability. The inverter's existing computational resources are utilized to calculate back-EMF angular speed, providing reliable speed detection across all operating conditions without adding separate hardware components.
Solution Approach 2:
The system uses its own internal measurements (stator currents and voltages) to generate accurate speed estimates through back-EMF calculation. The inverter monitors its own operational parameters and derives speed information without external sensors or separate measurement systems. This self-service approach maintains reliability while avoiding the costs and complexity of additional independent speed determination systems.
3Device complexity
If sensorless control is implemented, then system cost is reduced, but the system cannot reliably detect overspeed conditions
Solution Approach 1:
The patent transforms the speed estimation approach by changing from frequency-based parameters to back-EMF angular speed parameters. This allows sensorless control to maintain low system cost while achieving reliable overspeed detection. The back-EMF angular speed directly reflects the actual rotor speed regardless of the supply frequency, enabling accurate speed monitoring and overspeed protection without requiring mechanical sensors or complex additional circuitry.
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 speed estimation in scenarios where traditional methods fail, enhancing safety by preventing overspeed conditions and reducing costs associated with separate speed measurement systems.
Implementation Method 1
an inverter 40 is an inverter bridge implemented by means of transistors (e.g. IGBT, Insulated-gate Bipolar Transistor) or other semiconductor switches. The inverter 40 is typically used to adjust the power transferred from the intermediate circuit 30 to a motor 50 or other similar load.
Implementation Method 2
Monitoring the angular speed of the back-emf (electromotive force) of an electric motor by determining the time derivative of the stator current vector during a zero vector state of the inverter
Data Source
AI summary
A method is disclosed for estimating a rotation speed of an electric motor supplied by an inverter, by determining a time derivative of a stator current vector of the electric motor during a zero vector state of the inverter; and determining an estimate of the rotation speed of the electric motor on the basis of the determined time derivative of the stator current vector.