Brushless Motor Speed Calculation via Voltage Equation
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Solution Overview
Problem
Existing methods for calculating the rotation speed of brushless motors at low speeds are inefficient due to insufficient speed resolution and require additional components like optical encoders, increasing costs, and are prone to errors from noise and current disturbances.
Innovation Solution
A rotation speed calculation device that includes a current acquisition unit, a supply voltage acquisition unit, and a calculation unit using a voltage equation to calculate the rotation speed based on the current and supply voltage, without the need for differential current calculations, allowing for stable low-speed operation with a simple configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is added to suppress noise when reading motor current, then noise suppression is improved, but the error of the voltage drop value calculated from inductance and differential current increases
Solution Approach 1:
The patent extracts and eliminates the problematic differential current calculation from the speed estimation process. Instead of calculating dI/dt which requires filtering and introduces errors, the invention uses a simplified voltage equation (Eq. 14) that directly estimates speed from measured voltage and current values without differentiation, thereby removing the source of noise-related errors while maintaining measurement accuracy.
Solution Approach 2:
The patent replaces the need for expensive high-performance microcomputers with simple arithmetic operations that can be performed by low-cost microcontrollers. The complex differential calculations are replaced with basic algebraic computations using pre-calibrated constants, making the system affordable and suitable for cost-sensitive applications while maintaining adequate performance.
2Productivity
If differential value of current is calculated for speed estimation, then rotation speed can be calculated using voltage equation, but large calculation capability is necessary increasing costs
Solution Approach 1:
The patent replaces expensive high-performance microcomputers with simple arithmetic operations that can be performed by low-cost microcontrollers. The complex differential calculations are replaced with basic algebraic computations using pre-calibrated constants, making the system affordable and suitable for cost-sensitive applications while maintaining adequate performance.
Solution Approach 2:
The patent performs preliminary calibration to determine constants (such as inductance L and resistance R) that are then used in the simplified speed estimation equation. By pre-calculating and storing these constants, the system avoids complex real-time calculations during operation, reducing the computational burden on the microcontroller and enabling the use of lower-cost hardware.
3Measurement precision
If hall sensor pulse width is measured for speed control, then speed feedback is obtained, but speed resolution is insufficient at low speed
Solution Approach 1:
The patent enables the motor control system to estimate its own speed using readily available measurements (voltage and current) and a simplified mathematical model, without requiring external high-resolution sensors. This self-service approach allows the system to achieve adequate speed resolution at low speeds using only the existing hall sensors and basic measurements, avoiding the need for additional optical encoders or other expensive high-resolution sensors.
Data Source
AI summary
A rotation speed calculation device of a brushless motor includes: a current acquisition unit that acquires magnitude of current flowing through a coil of the brushless motor; a supply voltage acquisition unit that acquires supply voltage supplied to the brushless motor; and a calculation unit that calculates rotation speed of the brushless motor based on the magnitude of the current acquired by the current acquisition unit, the supply voltage acquired by the supply voltage acquisition unit, and a voltage equation calculating the rotation speed based on the magnitude of the current and the supply voltage. The voltage equation is an equation in which a member expressing a voltage drop due to inductance of a winding of the coil of the brushless motor is expressed by a product of a factor proportional to the current and a factor proportional to the rotation speed of the brushless motor.