BLDC Motor Current Detection Using PWM Synchronization
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Solution Overview
Problem
Conventional BLDC motor control apparatuses inaccurately detect driving current due to switching noise, leading to difficulties in accurate current control and degraded control performance.
Innovation Solution
A BLDC motor control apparatus that includes a current measurer with a resistor and bidirectional differential amplifier to measure driving current, a pulse width modulator with a counter and output circuit to minimize switching noise, and a controller that detects current when the counter reaches half the first value, ensuring accurate current detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the pulse width modulator changes driving voltage to drive the BLDC motor, then the motor can be controlled effectively, but switching noise occurs in the driving current
Solution Approach 1:
The patent applies preliminary action by having the controller determine the optimal current measurement timing in advance, based on the PWM switching cycle. The controller identifies when the switching noise is minimal and schedules current measurement at that specific moment, preventing noise contamination before it affects the measurement process.
Solution Approach 2:
The patent implements dynamics by making the current measurement timing adaptive rather than fixed. The controller dynamically adjusts the measurement moment according to the PWM switching state, selecting the optimal instant within each switching cycle when noise is minimized, thereby adapting the measurement process to the varying noise conditions.
2Device complexity
If the current control loop measures driving current independently from the pulse width modulator, then the control structure remains simple, but current detection becomes inaccurate due to switching noise
Solution Approach 1:
The patent applies feedback by having the controller receive information about the PWM switching state and use this feedback to determine the optimal current measurement timing. The controller continuously monitors the switching cycle and adjusts the measurement moment accordingly, creating a closed-loop system that improves measurement accuracy without adding complex hardware.
Solution Approach 2:
The patent merges the current measurement function with the PWM control function by having the controller perform both tasks in an integrated manner. Instead of having completely independent measurement and control loops, the controller combines knowledge of the PWM switching state with current measurement timing to achieve accurate measurements while maintaining a relatively simple overall structure.
3Productivity
If current is measured during PWM switching operation, then continuous control is maintained, but switching noise degrades control performance
Solution Approach 1:
The patent applies periodic action by measuring current at regular, periodic intervals that are synchronized with the PWM switching cycle. Instead of continuous measurement or random sampling, the system performs measurements at specific periodic moments within each PWM cycle when noise is minimized, maintaining rhythmical control while avoiding noise contamination.
Solution Approach 2:
The controller performs preliminary determination of the measurement timing based on the known PWM switching pattern. By calculating in advance when the optimal measurement moment occurs within each switching cycle, the system prepares the measurement schedule beforehand, ensuring continuous control is maintained without sacrificing accuracy to noise.
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 driving current with minimized switching noise, improving current control performance by selecting current with the same phase as the previous phase among coils, thus reducing noise and variation due to counter electromotive force.
Implementation Method 1
a bidirectional differential amplifier including input terminals connected to both ends of the resistor, may measure the amount and direction of currents flowing through coils of the BLDC motor
Implementation Method 2
The pulse width modulator that is used to change the driving voltage in the BLDC motor repeats an on/off switching operation
Implementation Method 3
a permanent magnet is installed on a rotor and a coil is installed on a stator and no commutator and brush are required, rotates the rotor including the permanent magnet installed thereon through a continuous rotating field that is formed by changing driving current
Data Source
AI summary
An apparatus and method to control a brushless direct current (BLDC) motor, which accurately detect driving current. To this end, the BLDC motor control apparatus includes a BLDC motor, a driver to generate driving current to drive the BLDC motor, a current measurer to measure the driving current, a pulse width modulator to change a driving voltage to drive the BLDC motor; and a controller to control the BLDC motor. The controller detects the amount of the driving current in synchronization with pulse width modulation of the pulse width modulator and determines current with a minimum change due to a variation of counter electromotive force, among currents flowing through a plurality of coils, as the driving current, thereby accurately detecting the driving current.