BLDC Phase Current Regulation via FET Drain-Source Voltage
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Solution Overview
Problem
Existing methods for controlling and monitoring brushless direct current (BLDC) motors require high calculation efforts and RAM usage, leading to limited dynamics and inefficiencies, especially in applications requiring rapid speed changes or load regulation.
Innovation Solution
A method that determines the phase current direction and zero-crossing moment by measuring drain source voltages over high side and low side field effect transistors, allowing for reduced computation power and alignment of phase current with back-electromotive force (BEMF) voltage, thereby optimizing energy efficiency and noise behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional BEMF-based phase current control methods are used, then rotor position synchronization is achieved, but calculation efforts and RAM usage become excessively high
Solution Approach 1:
The patent extracts only the essential information needed for phase current control by measuring drain-source voltages of FETs to determine current direction and zero-crossing moments, rather than computing complete phase current waveforms. This selective extraction of critical parameters dramatically reduces calculation complexity while maintaining control precision.
Solution Approach 2:
Instead of measuring phase current directly and deriving direction, the patent inverts the approach by measuring the voltages across the switching FETs and inferring current direction from these voltage measurements. This indirect measurement method simplifies the computational burden while providing accurate current direction information.
2Measurement precision
If high calculation efforts are applied for precise phase current control, then control accuracy is improved, but system dynamics and response speed are limited
Solution Approach 1:
The patent extracts only the critical zero-crossing moment and current direction information needed for phase alignment, avoiding computationally intensive complete waveform processing. This enables rapid detection and response to changing load conditions while maintaining precise phase current alignment with BEMF voltage.
Solution Approach 2:
The system uses the existing FET switching signals and drain-source voltage measurements that are already present in the power circuit, eliminating the need for separate current sensors and their associated signal processing. This self-service approach reduces computational overhead and accelerates response time.
3Measurement precision
If phase current is kept high during BEMF sensing, then sufficient signal strength is obtained, but electromagnetic compatibility and acoustic noise performance deteriorate
Solution Approach 1:
The patent implements periodic BEMF sensing during specific intervals when phase current is naturally minimal (at zero-crossing moments), rather than attempting continuous sensing during high current periods. This periodic measurement approach during low-current intervals provides sufficient signal strength while minimizing electromagnetic interference and acoustic noise generation.
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 reduces processing power and RAM requirements, enhances dynamic behavior, and improves electromagnetic compatibility (EMC) and acoustic noise performance by aligning phase current and BEMF voltage, enabling faster response to load changes and energy-efficient operation.
Implementation Method 1
measuring the drain source voltage over the high side field effect transistor and low side field effect transistor
Implementation Method 2
measuring the back-electromotive force (BEMF) voltage in the undriven coils
Data Source
Figure 1~3
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Figure 5~6
AI summary
A method (1010) for determining a phase current (101) direction and a zero-crossing moment (T1) of the phase current (101) in a sinusoidally controlled brushless direct current motor (451). The brushless direct current motor (451) comprises a coil (452) per phase and the phase of the brushless direct current motor is driven by a half bridge driver (453). The half bridge driver comprises a high side field effect transistor (454) and a low side field effect transistor (455). The method comprising the following steps: - measuring (1011) the drain source voltage over the high side field effect transistor (454) and low side field effect transistor (455), - determining (1012) the zero crossing moment (T1) of the phase current by determining the current direction based on the measured drain source voltages and by determining the moment the current changes direction.