BLDC Motor Control with Speed-Dependent Commutation Switching
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Solution Overview
Problem
Existing BLDC motor controllers face challenges in efficiently controlling torque output at both lower and higher speeds, leading to torque ripple, vibrations, and noise, while also being costly and complex to implement.
Innovation Solution
A motor controller using a modified trapezoidal control (MTC) approach that includes a single speed controller and a single current controller, utilizing position sensors and current sensors to determine duty cycles for PWM gate signals, thereby controlling the rotor speed smoothly and precisely across different sectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the trapezoidal approach is used for controlling BLDC motor, then the control structure is simple and widely used, but torque ripple occurs causing vibrations and noise especially at lower speeds
Solution Approach 1:
The patent applies dynamics by making the commutation approach speed-dependent. The controller dynamically switches between trapezoidal commutation at higher speeds and sinusoidal commutation at lower speeds. This resolves the contradiction by adapting the control strategy to operating conditions, eliminating torque ripple at low speeds while maintaining the simplicity of trapezoidal control at high speeds.
2Object-generated harmful factors
If the sinusoidal approach is used for controlling BLDC motor, then torque ripple is eliminated at lower speeds, but the control becomes inefficient at higher speeds and requires complex algorithms and expensive sensors
Solution Approach 1:
The controller dynamically selects the commutation strategy based on motor speed. At lower speeds where torque ripple is critical, sinusoidal commutation is applied to eliminate ripple. At higher speeds where efficiency is paramount, the system switches to simpler trapezoidal commutation. This dynamic adaptation resolves the contradiction by applying complex control only when necessary.
Solution Approach 2:
Different commutation strategies are applied to different speed ranges based on local requirements. The patent divides the operating range into low-speed and high-speed zones, applying sinusoidal control locally at low speeds to eliminate torque ripple, and trapezoidal control locally at high speeds for efficiency. This localized application resolves the contradiction without requiring complex control across the entire speed range.
3Productivity
If the field oriented control (FOC) approach is used for controlling BLDC motor, then torque output is efficiently controlled at both lower and higher speeds, but the controller becomes very complex requiring multiple current controllers and transforms
Solution Approach 1:
The patent implements dynamic commutation strategy selection based on speed thresholds. Instead of using complex FOC across all operating conditions, the system dynamically switches between sinusoidal and trapezoidal commutation depending on whether the motor operates in low-speed or high-speed range. This resolves the contradiction by achieving efficient torque control only when needed while maintaining simplicity during other operations.
Solution Approach 2:
The patent segments the speed range into distinct zones (low-speed and high-speed) and applies different commutation strategies to each segment. This segmentation allows the system to achieve FOC-level torque control efficiency in the low-speed segment while using simpler control in the high-speed segment, thereby resolving the contradiction without requiring full FOC complexity across the entire operating range.
4Device complexity
If a single commutation approach is used for all speed ranges, then the control structure remains simple, but the motor cannot operate smoothly at both lower and higher speeds
Solution Approach 1:
The controller implements dynamic switching between commutation strategies based on real-time speed feedback. When the motor speed crosses predefined thresholds, the controller automatically transitions between trapezoidal and sinusoidal commutation modes. This dynamic adaptation maintains structural simplicity while achieving versatile performance across the entire speed range, resolving the contradiction between simplicity and adaptability.
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
The MTC approach effectively minimizes torque ripple at all speed ranges, reducing motor noise and vibrations, and increasing the lifespan of the BLDC motor, while being simpler and more cost-effective compared to FOC approaches.
Implementation Method 1
an inverter operatively coupled to the power source and that converts direct current supplied by the power source into alternating current
Implementation Method 2
a brushless direct current (BLDC) motor is an electronically commutated motor powered by a direct current electric source via an external motor controller
Data Source
AI summary
A motor controller (100) is provided for smooth operation of an electric motor (102), which mitigates torque ripple, noise and vibration effects, and increases a life span of the motor (102). The motor controller (100) includes a speed controller (120), current transformation units (128 and 130), a current controller (132), and a pulse width modulation (PWM) signal generator (134). The current controller (132) determines a duty cycle of PWM gate signals used for controlling a rotor (104) speed within a particular sector (302A) of the motor (102) based on a reference quadrature-axis current and an actual quadrature-axis current. The PWM signal generator generates the PWM gate signals having the determined duty cycle, controls the rotor (104) speed, and incrementally varies a current speed of the motor (102) to achieve a target speed by modulating operations of a specific pair of inverter switches (502C and 502E) using the PWM gate signals.