BLDC Motor Driver Back-EMF Sampling for High-Speed Torque Control
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Solution Overview
Problem
Conventional BLDC motor systems face challenges in accurately detecting back electromotive force voltage at high driving speeds, leading to increased power consumption and difficulty in controlling torque ripple.
Innovation Solution
A motor driver incorporating an analog-to-digital converter (ADC) that samples and converts voltage sensing signals into digital data during a floating period, allowing for accurate detection of back electromotive force voltage using a back electromotive force voltage determination unit, which calculates an average based on multiple digital samples, and a speed control unit that adjusts motor speed based on the detected voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional back electromotive force voltage detection circuit is used, then the circuit can detect voltage at low speeds, but power consumption increases and detection accuracy deteriorates as driving speed increases
Solution Approach 1:
The patent extracts the back electromotive force voltage detection function from the conventional complex detection circuit and implements it using a simplified approach: utilizing the existing ADC resource and a dedicated detection period (floating period) to sample the phase voltage, thereby detecting the back electromotive force voltage without requiring additional complex circuitry that would increase power consumption
Solution Approach 2:
The system uses its own operational characteristics (the floating period when all switches are off and phase current is zero) to perform self-detection of the back electromotive force voltage. During this self-generated detection window, the phase voltage directly reflects the back electromotive force voltage, allowing the system to detect voltage using its own operational phases without external assistance
2Speed
If a conventional back electromotive force voltage detection circuit is used, then the circuit can operate at low speeds, but detection becomes difficult at high driving speeds
Solution Approach 1:
The patent introduces a predetermined floating period (detection period) in advance within each control cycle, during which all switches are turned off and the phase voltage is sampled. This preliminary preparation of a dedicated detection window ensures that the back electromotive force voltage can be accurately captured regardless of the motor's driving speed, as the detection timing is pre-planned and synchronized with the motor phases
Solution Approach 2:
The system performs back electromotive force voltage detection periodically by utilizing the floating period that occurs regularly in each control cycle. By sampling the phase voltage during these periodic detection windows and averaging multiple samples, the system achieves accurate detection at varying speeds without being constrained by speed-dependent detection difficulties
3Reliability
If a complex back electromotive force voltage detection circuit is used, then detection coverage is improved, but the circuit complexity increases
Solution Approach 1:
The patent makes the ADC resource universal by using it for both normal phase voltage measurement and back electromotive force voltage detection. The same ADC that measures phase voltages during switching operations is also used to sample the phase voltage during the floating period for back electromotive force detection, thereby achieving multiple functions with a single component and reducing overall circuit complexity
Solution Approach 2:
The patent extracts the back electromotive force voltage detection capability from the need for separate dedicated detection hardware. By utilizing the existing ADC and the naturally occurring floating period, the system obtains reliable detection coverage without adding complex external detection circuits, keeping the overall system simple while maintaining comprehensive detection capability
4Measurement precision
If the floating period is extended to improve detection accuracy, then more sampling data is obtained, but torque ripple increases
Solution Approach 1:
The patent applies partial action by performing ADC sampling at specific sampling points within the floating period rather than continuously throughout. By selecting optimal sampling points (such as when the phase voltage most accurately reflects the back electromotive force voltage) and taking a limited number of samples during the floating period, the system achieves sufficient detection accuracy while minimizing the duration of the detection window, thereby reducing torque ripple
Solution Approach 2:
The system adjusts the sampling parameters (sampling points and number of samples) within the floating period to optimize the balance between detection accuracy and torque ripple. By changing the timing and quantity of samples taken during the floating period, the system achieves accurate back electromotive force voltage detection while keeping the floating period duration optimized to minimize its negative impact on motor performance
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 accurate detection of back electromotive force voltage even at high speeds, minimizing torque ripple and power consumption, while maintaining efficient motor control.
Implementation Method 1
an analog-to-digital converter (ADC) which, when a voltage sensing signal detected at a phase voltage of a specific coil in a floating period is input, samples the input voltage sensing signal at a sampling point and converts the input voltage sensing signal into digital voltage sampling data
Implementation Method 2
a back electromotive force voltage determination unit which determines a back electromotive force voltage of the specific coil on the basis of a plurality of pieces of the digital voltage sampling data input for N periods
Data Source
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Figure 3~4
AI summary
The present application relates to motor driver and method of driving motor. A motor driver according to one embodiment of the present disclosure includes an analog-to-digital converter (ADC) which, when a voltage sensing signal detected at a phase voltage of a specific coil in a floating period is input, samples the input voltage sensing signal at a sampling point and converts the input voltage sensing signal into digital voltage sampling data and a back electromotive force voltage determination unit which determines a back electromotive force voltage of the specific coil on the basis of a plurality of pieces of the digital voltage sampling data input for N periods.