Wideband RF PWM Inverter Synchronization for Harmonic Control
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Solution Overview
Problem
Existing wideband RF power supplies using single-phase PWM inverters face challenges in reducing switching loss and removing harmonic components, particularly in the RF frequency band, due to synchronization deviations between carrier and modulation waves.
Innovation Solution
The solution involves dividing the modulation wave frequency range into sections and adjusting the number of PWM pulses to maintain synchronism in frequencies and phases, using a carrier wave generation unit to generate a carrier wave that synchronizes with the modulation wave, and employing a low-pass filter to remove harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single-phase PWM inverter is used to output wideband sine wave in RF band, then frequency band coverage is improved, but synchronization deviation between carrier and modulation waves occurs causing increased switching loss
Solution Approach 1:
The patent dynamically adjusts the carrier wave frequency to maintain an integer multiple relationship with the modulation wave frequency across different operating conditions. This dynamic frequency adjustment ensures synchronization is maintained throughout the wide RF band, preventing the synchronization deviation that would otherwise cause increased switching loss.
Solution Approach 2:
The patent changes the carrier wave frequency parameter based on the modulation wave frequency to maintain the relationship fc=N×fs where N is an integer. By adjusting this parameter dynamically, the system achieves wideband operation while maintaining synchronization and minimizing switching losses.
2Adaptability or versatility
If a single-phase PWM inverter is used to output wideband sine wave in RF band, then frequency band coverage is improved, but harmonic component removal becomes difficult with single output filter
Solution Approach 1:
The patent dynamically controls the carrier wave frequency to maintain an integer multiple relationship with the modulation wave frequency. This dynamic control ensures that harmonic components are consistently positioned at frequencies that can be effectively filtered by a single output filter across the entire wide RF band, eliminating the need for multiple filters.
Solution Approach 2:
By changing the carrier wave frequency parameter to maintain fc=N×fs, the patent ensures that harmonic components remain at predictable frequency positions that can be removed by a single output filter, simplifying the filter configuration while maintaining wideband operation.
3Manufacturing precision
If carrier wave frequency is increased to reduce load loss from harmonic components, then waveform improvement is achieved, but switching loss in switching element increases
Solution Approach 1:
The patent optimizes the carrier wave frequency parameter by maintaining it as an integer multiple of the modulation wave frequency (fc=N×fs). This parameter relationship allows the system to achieve good waveform quality through PWM modulation while avoiding excessive switching losses by not unnecessarily increasing the carrier frequency beyond what is required for effective harmonic filtering.
Data Source
AI summary
A carrier wave generation unit comprising a wideband RF power supply divides a whole modulation wave variable frequency range into a plurality of modulation wave frequency sections associated with the number of PWM pulses N based on upper and lower limit frequencies of a carrier wave. In each modulation wave frequency section, an integer number of PWM pulses N associated to each modulation wave frequency section and the modulation wave frequency fs are used to vary a carrier wave frequency fc based on the relationship of fc=N·fs, thereby synchronizing the frequency between a carrier wave C and a modulation wave S to satisfy periodicity.