PWM Signal Frequency Multiplier for BLDC Motor Speed Control
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Solution Overview
Problem
Existing mechatronic assemblies for controlling brushless direct current (BLDC) motors in automotive applications face limitations in maximum setpoint speed due to frequency constraints of pulse-width modulated (PWM) control signals, leading to errors in signal interpretation and inefficiencies in energy transmission, particularly at extreme duty cycle values.
Innovation Solution
A mechatronic assembly with a frequency multiplier and electronic modulation circuit that increases the frequency of PWM signals beyond the motor's electrical frequency, allowing for higher control frequencies and efficient energy transmission, while eliminating dead zones in duty cycle ranges to prevent misinterpretation and fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the frequency of PWM control signal is increased to achieve higher motor speed, then the maximum setpoint speed is improved, but the controller hardware must be modified which increases device complexity
Solution Approach 1:
The system is divided into two independent parts: a simple controller that generates low-frequency PWM signals with direction and torque information, and a separate frequency multiplier circuit that increases the frequency to the required level for high-speed motor control. This segmentation allows the controller to remain simple while achieving high-speed operation through the frequency multiplication stage.
Solution Approach 2:
A frequency multiplier circuit is introduced as an intermediary component between the controller and the motor. This intermediary takes the low-frequency PWM signal from the controller, multiplies its frequency, and outputs the high-frequency signal needed for high-speed motor control, thereby resolving the conflict between simple controller design and high-speed operation requirements.
2Adaptability or versatility
If separate channels are used for transmitting direction and speed information, then the control flexibility is improved, but signal synchronization errors occur which worsens measurement precision
Solution Approach 1:
Direction and speed information are merged into a single PWM control signal where direction is encoded in the polarity and speed is encoded in the duty cycle. This unified signaling approach eliminates synchronization errors between separate channels while maintaining full control flexibility, as both pieces of information are transmitted simultaneously in one synchronized signal.
3Reliability
If extreme duty cycle values are used for fault detection, then the reliability is improved, but the usable control range is reduced which worsens the loss of information
Solution Approach 1:
The system moves from using only the duty cycle dimension for control to using both polarity and duty cycle dimensions. Fault detection is performed using extreme polarity values (±100% duty cycle), while the full range of duty cycle values (0-100%) remains available for speed control. This dimensional expansion allows simultaneous fault detection capability and full control range without conflict.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a mechatronic assembly (2) for driving a body, which is designed to be connected to a continuous electrical power source (4) and an electronic control unit (1) comprising a computer for running a power-assistance algorithm supplying a pulse-width modulation input signal having discrete states and a cyclic ratio encoding the steering and torque/speed information (6).