Motor Controller Spread Spectrum Oscillator EMI Reduction
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Solution Overview
Problem
Conventional motor controllers generating PWM signals cause electromagnetic interference (EMI), and existing solutions to mitigate this issue either increase costs or affect efficiency and precision.
Innovation Solution
A motor controller with a spread spectrum oscillator and comparators that generate a varying frequency ramp signal, allowing the PWM signal to be compared and adjusted, thereby reducing EMI without additional components and maintaining efficiency and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PWM signal with fixed frequency is generated to control the direct current motor, then the motor control is precise and efficient, but electromagnetic interference (EMI) is generated in the high frequency band
Solution Approach 1:
The patent applies dynamics by making the PWM signal frequency variable rather than fixed. The spread spectrum oscillator continuously varies the frequency of the ramp signal within a range centered on a base frequency, causing the PWM signal frequency to dynamically change. This dynamic frequency variation disperses the electromagnetic energy across a broader frequency spectrum, reducing peak EMI while maintaining motor control precision through the compensator's feedback mechanism.
Solution Approach 2:
The patent changes the frequency parameter of the PWM signal from a fixed value to a varying value within a specified range. The spread spectrum oscillator modifies the ramp signal frequency parameter dynamically, which directly changes the PWM signal frequency parameter. This parameter change approach reduces EMI by spreading the spectral energy while the compensator ensures the average frequency remains appropriate for precise motor control.
2Object-generated harmful factors
If shielding housing or anti-EMI components are added to reduce electromagnetic interference, then EMI is reduced, but cost and material consumption increase
Solution Approach 1:
The patent applies self-service by making the motor controller itself generate the solution to its EMI problem through the spread spectrum oscillator integrated within the PWM unit. Instead of requiring external shielding housing or separate anti-EMI components, the controller internally varies the PWM frequency to dispersE electromagnetic energy. This self-service approach reduces EMI without adding external components, thereby reducing device complexity and material consumption.
Solution Approach 2:
The patent extracts the EMI reduction function from external components (shielding housing, anti-EMI components) and integrates it into the core PWM generation mechanism itself. By embedding the spread spectrum oscillator within the PWM unit, the EMI mitigation capability is extracted from separate physical components and realized through signal processing within the existing controller architecture, reducing overall device complexity.
3Object-generated harmful factors
If the PWM signal frequency is reduced to minimize EMI, then electromagnetic interference is reduced, but motor control efficiency and precision deteriorate
Solution Approach 1:
The patent uses dynamics to vary the PWM frequency around an optimal base frequency rather than using a constantly reduced frequency. The spread spectrum oscillator dynamically adjusts the frequency up and down within a spread range, ensuring that the average frequency remains at the base frequency optimized for motor control efficiency. This dynamic variation reduces peak EMI while maintaining overall control productivity.
Solution Approach 2:
The patent changes the frequency parameter from a reduced constant value to a varying value centered on the optimal base frequency. The spread spectrum technique modifies the frequency parameter within a range that includes the base frequency, ensuring that the average frequency maintains the efficiency and precision required for motor control while the instantaneous frequency variations reduce EMI through spectral spreading.
Data Source
AI summary
The present invention provides a motor controller for controlling a DC motor according to a reference signal. The motor controller includes a compensator, a pulse width modulation unit, and a motor driving unit. The compensator generates a control signal according to the reference signal and a sensing signal from the DC motor. The pulse width modulation unit generates a motor control signal by comparing the control signal and a ramp signal having a varying frequency. The motor driving unit receives the motor control signal and drives the DC motor according to the motor control signal.