Sensorless Brushless Motor Control via Neutral Point Voltage
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Solution Overview
Problem
Existing methods for controlling two-phase brushless motors without rotor position sensors face inefficiencies and noise issues due to non-sinusoidal current flow and high computational requirements, particularly in BLDC and sinusoidal commutation methods.
Innovation Solution
A method combining sinusoidal commutation and BLDC control, where one phase is supplied with sinusoidal current, and the non-sinusoidal phase is used to determine the rotor position, eliminating the need for sensors and reducing noise and computational effort by determining the rotor position based on phase voltage and neutral point voltage within a limited time window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless commutation is implemented by measuring EMF in stator coils, then position sensors are eliminated reducing cost and complexity, but this method is only possible above a certain minimum rotational speed
Solution Approach 1:
The patent introduces an intermediary measurement approach by measuring the voltage at the neutral point instead of directly measuring EMF in energized phases. This neutral point voltage serves as a mediator that contains information about rotor position through its relationship with the back-EMF of unenergized phases, enabling sensorless operation at low speeds without requiring direct EMF measurement
Solution Approach 2:
The patent replaces the mechanical/physical EMF measurement system with an electrical voltage measurement system at the neutral point. By substituting direct EMF sensing with neutral point voltage detection, the system achieves sensorless commutation capability that works across the entire speed range including very low speeds where traditional EMF measurement fails
2Extent of automation
If BLDC control method is used, then commutation is automated with optimal magnetic flux change, but non-sinusoidal current flow causes noise and efficiency issues
Solution Approach 1:
The patent merges the advantages of both BLDC control (automated commutation, optimal flux change) and sinusoidal control (smooth current flow, low noise) by using neutral point voltage detection to enable sinusoidal PWM control. The system combines the automated commutation capability of BLDC with the noise-reducing sinusoidal current characteristics
Solution Approach 2:
The patent changes the control parameter from rectangular PWM switching to sinusoidal PWM modulation. By changing the current waveform parameter from rectangular to sinusoidal while maintaining automated commutation through neutral point voltage detection, the system reduces noise and improves efficiency while retaining the benefits of automated control
3Loss of energy
If sinusoidal commutation is used, then noise is reduced and efficiency improved, but computational requirements increase and control complexity rises
Solution Approach 1:
The patent extracts the rotor position information from the neutral point voltage signal, separating the position detection function from complex computational algorithms. By taking out the position information directly from the neutral point voltage measurements, the system reduces computational requirements while maintaining sinusoidal commutation benefits
Solution Approach 2:
The neutral point voltage measurement system serves multiple functions simultaneously: it provides rotor position information for sinusoidal commutation, enables automated commutation switching, and reduces the need for separate position sensors. This self-service approach reduces overall control complexity while maintaining high efficiency
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
This approach enables effective current flow, reduces noise, and conserves energy by allowing longer sinusoidal energization, improving motor efficiency and extending the operation time with limited electrical energy, while simplifying the control unit and reducing costs.
Implementation Method 1
determining an electromotive force (EMF) of the phase not being energized in a purely sinusoidal manner from a difference between the determined phase voltage and the determined neutral point voltage
Implementation Method 2
The interaction between the stator field and the rotor field generates an electric torque that can lead to rotation
Data Source
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AI summary
The invention relates to a method for controlling a brushless motor (M) with at least two phases and without a rotor position sensor, comprising at least the following steps: • sinusoidal current supply (100) to at least one phase (U, V, W), wherein the phase voltage (UPhase) of the current supply (100) is preferably set by means of PWM control, • determination (200a) of the phase voltage (UPhase) of the phase (U, V, W) not being energized in a purely sinusoidal manner, • determination (200b) of the neutral point voltage, • determination (300) of a voltage difference (EMF) of the phase (U, V, W) not being energized in a purely sinusoidal manner from the difference between the determined phase voltage (UPhase) and the determined neutral point voltage, and • determination (400) of a rotor position based on the determined voltage difference of the phase (U, V, W) not being energized in a purely sinusoidal manner.