Electric Motor PWM Clock Signal EMI Reduction via Frequency Modulation
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Solution Overview
Problem
Electric motor control systems face challenges with electromagnetic interference (EMI) due to high-speed clocking signals, which existing methods like filtering and shielding are costly and time-consuming to address effectively.
Innovation Solution
Implementing Spread Spectrum Clock Generation (SSCG) technology, specifically using a triangular modulation wave with programmable frequency and modulation depth, to reduce EMI by spreading the clock signal across a broader frequency range, thereby reducing peak spectral energy and minimizing the need for additional EMI reduction measures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed clocking signals are used to control ICs, then system performance and processing speed are improved, but electromagnetic interference (EMI) increases
Solution Approach 1:
The patent applies periodic frequency modulation to the clock signal, varying the switching frequency in a periodic manner to spread spectral energy. This periodic action transforms the concentrated high-frequency clock signal into a modulated signal that maintains processing speed while reducing peak EMI emissions across specific frequency bands.
Solution Approach 2:
The patent dynamically changes the frequency parameter of the clock signal through modulation techniques. By varying the switching frequency around a nominal value, the system maintains high-speed operation while distributing electromagnetic energy across a broader spectrum, thereby reducing peak EMI levels that would otherwise interfere with motor control operations.
2Object-generated harmful factors
If traditional EMI reduction techniques (filtering, shielding) are implemented, then electromagnetic interference is reduced, but system cost and complexity increase
Solution Approach 1:
The patent converts the harmful effect of high-speed switching by intentionally modulating the clock frequency to spread spectral energy. Instead of trying to eliminate EMI through external filtering and shielding, the system uses frequency modulation to transform concentrated EMI into distributed, lower-level emissions that naturally comply with regulatory requirements without additional hardware complexity.
Solution Approach 2:
The patent replaces physical EMI mitigation mechanisms (filters, shields, specialized layouts) with a software-based frequency modulation approach. By implementing EMI reduction through clock signal processing in the digital domain, the system eliminates the need for additional passive components and complex physical design constraints, thereby reducing overall system complexity and cost.
3Object-generated harmful factors
If frequency modulation is applied to reduce EMI, then electromagnetic interference is reduced, but motor control precision may deteriorate
Solution Approach 1:
The patent applies frequency modulation in advance to the clock signal before it reaches the motor control circuits. By pre-modulating the clock frequency, the system reduces peak EMI emissions that could interfere with control precision, while the modulated signal continues to provide accurate timing references for PWM generation and motor control operations.
Solution Approach 2:
The system monitors motor control performance and adjusts the frequency modulation parameters accordingly. By implementing feedback control, the system maintains motor control precision despite frequency variations, ensuring that the modulated clock signal continues to provide accurate timing references while maintaining reduced EMI levels throughout operation.
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
This approach effectively reduces EMI throughout the system, mitigating the need for costly and time-consuming traditional EMI reduction techniques, ensuring stable operation of electric motor control systems while maintaining system performance.
Implementation Method 1
a first pulse-width modulated control signal having edge transitions occurring at one or more transition count values of pulses of a frequency-modulated clock signal
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5d
AI summary
An electric motor (M) id controlled by means of pulse-width modulated control signal (PWM, ADC) having edge transitions occurring at certain transition count values of the pulses of a clock signal (20) which is frequency-modulated with a step-wise frequency modulation (e.g. SSCG or Spread Spectrum Clock Generation). A frequency unmodulated clock signal (10) is provided having a fixed period (TPWM_NOM) indicative of the period of the pulse-width modulated control signals (PWM, ADC). The transition count values are set as a function of a predicted count value and/or a predicted frequency value for the frequency-modulated clock signal (20). Prediction occurs as a function of the frequency unmodulated clock signal (10), so that the transition count values are compensated against the step-wise (e.g. SSCG) frequency modulation.