Brushless Motor Control Reducing Torque Ripple
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Solution Overview
Problem
Existing brushless motor control systems face issues with sound and vibration due to torque ripple caused by rapid changes in coil energization, leading to complex circuit structures and inefficiencies, especially when applied to full-wave motors, and are not suitable for PWM control schemes.
Innovation Solution
A brushless motor control apparatus using a PWM signal generating means, a counter, and a control means to gradually change the voltage by counting down from a maximum value, generating a PWM signal that corresponds to a count value for a predetermined time period, thereby controlling the energization of the motor windings to reduce torque ripple and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the energization of one coil is turned off rapidly at the timing of changing the active phase to another phase, then the motor can operate with simple control, but a return current flows through the coil to generate torque ripple, resulting in sound and vibration
Solution Approach 1:
The patent applies dynamics by making the voltage waveform flexible and adaptable. Instead of using a fixed rectangular wave, the invention dynamically adjusts the voltage waveform to a non-axisymmetric pattern where the rising edge and falling edge have different time characteristics. This dynamic adjustment allows the system to maintain simple control while reducing torque ripple and sound by optimizing the voltage application timing and duration.
Solution Approach 2:
The patent changes the voltage waveform parameters from a symmetric rectangular wave to a non-axisymmetric waveform with asymmetric rise and fall times. Specifically, the voltage is applied for a longer duration on the rising edge and a shorter duration on the falling edge. This parameter change modifies the energization characteristics to reduce return current and torque ripple while maintaining control simplicity.
2Stability of the object's composition
If linear control schemes are used to change the voltage supplied to the motor, then the voltage can be smoothly adjusted, but the control is not suitable for PWM control schemes that change the time ratio of ON and OFF
Solution Approach 1:
The patent employs periodic action through PWM control, where the voltage is supplied in a series of pulses with varying duty ratios. The non-axisymmetric voltage waveform is generated by controlling the ON and OFF time ratios of the PWM signals. This approach combines the benefits of smooth voltage adjustment (through duty ratio modulation) with PWM control compatibility, allowing efficient motor control while maintaining voltage smoothness characteristics.
3Object-generated harmful factors
If techniques like Japanese Patent No. 3854186B are used to generate voltage of a bilaterally symmetric trapezoidal wave, then the energization can be gradually changed, but a control apparatus using a microcomputer is required, making the circuit structure complicated
Solution Approach 1:
The patent extracts and eliminates the microcomputer component from the control system. Instead of using a microcomputer to generate the non-axisymmetric voltage waveform, the invention uses a simplified control apparatus that directly generates the asymmetric PWM signals. This extraction of the complex microcomputer element reduces circuit complexity while maintaining the ability to gradually change energization and reduce torque ripple through the non-axisymmetric waveform design.
4Adaptability or versatility
If the technique of Japanese Patent No. 2692103B is applied to a full-wave motor, then the motor can operate, but the circuit size is disadvantageously doubled
Solution Approach 1:
The patent achieves universality by designing a control apparatus that can effectively control both half-wave and full-wave motors using the same non-axisymmetric voltage waveform technique. The control system is configured to generate asymmetric PWM signals that work across different motor types without requiring separate control circuits. This multi-functionality allows the same control approach to be applied to full-wave motors without doubling the circuit size, as the control logic remains unified and adaptable.
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 solution effectively reduces sound and vibration by gradually changing the energization of the motor coils, simplifying the circuit structure, and is applicable to both half-wave and full-wave motors without the need for additional counters or microcomputers, enhancing the motor's efficiency and reducing manufacturing costs.
Implementation Method 1
semiconductor elements (switching elements) are turned on and off to apply a voltage of a rectangular wave to each corresponding one of coils of multiple phases of the motor, so that a rotor of the motor is rotated
Implementation Method 2
When the energization of one of the coils is turned off at the timing of changing the active phase of the motor to another phase, a return current flows through the corresponding coil to generate a torque ripple
Data Source
AI summary
A slope counter starts countdown at timing of changing an output voltage of an FET to zero. A controller executes a nonsymmetrical energization control operation to control a PWM generator such that the PWM generator generates a PWM signal based on a count value of the slope counter and outputs the generated PWM signal to the FET. The countdown of the slope counter is terminated when a predetermined time period elapses or when a time period corresponding to an electrical angle of 40 degrees elapses before the elapsing of the predetermined period. Also, at this time, the controller terminates the nonsymmetrical energization control operation.