PWM Switching Frequency Harmonic Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional pulse width modulation (PWM) control of electrical consumers generates harmonics that interfere with radio reception, particularly in the medium wave band, due to a fixed switching frequency that can match or closely align with the carrier frequency, causing audible noise and interference.
Innovation Solution
Adapting the actual switching frequency to the closest value where the harmonic amplitude is smaller than its neighboring harmonics, and adjusting the duty cycle to a ratio of natural numbers, ensuring that the frequency is an integer multiple of the carrier frequency, thereby minimizing interference on the carrier frequency and its harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed switching frequency is used for PWM control, then the control is simple and stable, but interference with radio reception occurs when the switching frequency or its harmonics align with the carrier frequency
Solution Approach 1:
The patent applies dynamics by making the PWM switching frequency adjustable rather than fixed. The control unit dynamically selects from multiple predetermined switching frequencies to find one that minimizes radio interference, transforming a static parameter into a dynamic one that adapts to minimize harmful effects.
Solution Approach 2:
The patent changes the switching frequency parameter from a single fixed value to multiple predetermined values. By varying this parameter and selecting the optimal one based on interference levels, the system resolves the contradiction between operational simplicity and radio reception quality.
2Object-affected harmful factors
If the switching frequency is adjusted to align with radio carrier frequency, then interference is reduced, but the control precision and stability may be compromised
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing multiple predetermined switching frequencies that are known to minimize radio interference. Instead of performing complex real-time analysis, the system selects from pre-prepared frequency values that have been optimized to reduce harmonics affecting radio carriers.
Solution Approach 2:
The patent uses a simplified approach by selecting from a limited set of predetermined frequencies rather than implementing complex continuous frequency adjustment. This discrete selection method sacrifices some precision for simplicity and reliability, using a 'good enough' solution from pre-defined options rather than optimizing continuously.
3Object-affected harmful factors
If the switching frequency is changed to reduce interference, then radio reception improves, but additional control complexity and calculation are required
Solution Approach 1:
The control unit performs preliminary selection of optimal switching frequencies from a predetermined set. By pre-defining acceptable frequency values that minimize harmonic interference with radio carriers, the system reduces the complexity of real-time frequency adjustment while still achieving interference reduction.
Solution Approach 2:
The system uses its own predetermined frequency data to automatically select the optimal switching frequency without requiring external intervention or complex external analysis. The control unit self-regulates by choosing from its pre-stored frequency options based on interference minimization criteria.
Data Source
AI summary
A method for controlling an electrical load by means of pulse width modulation, wherein a setpoint switching frequency fsetpoint and a setpoint duty ratio dsetpoint are prescribed, wherein the carrier frequency fch of a selected radio transmitter is determined, and wherein the actual switching frequency fsw is matched to the carrier frequency fch of the radio transmitter such that a multiple k*fsw of the actual switching frequency fsw is the same as the carrier frequency fch with an integer factor k, is characterized, according to the invention, in that the actual switching frequency fsw is defined as that value closest to the setpoint switching frequency fsetpoint for which the amplitude of the harmonic k* fsw in the harmonic spectrum of the actual switching frequency fsw is smaller than the amplitudes of its closest lower (k-1 )* fsw and upper (k+1 )* fsw adjacent harmonics.