PWM Drive Control for MOSFET Switching Delay Ripple
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Solution Overview
Problem
PWM-based amplifiers face instability and current ripple issues near zero current due to MOSFET switching delays, leading to non-linear output and audible noise in applications requiring precise current regulation.
Innovation Solution
Implementing a system that identifies operational conditions and adjusts PWM signals by skipping or modifying pulses based on MOSFET turn-on and turn-off times to maintain accurate current control, using a monitor module and modified PWM signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM signals are used to control current at high frequencies, then power delivery efficiency is improved, but current ripple and instability occur near zero current due to MOSFET switching delays
Solution Approach 1:
The system dynamically adjusts the PWM frequency based on the operational conditions. When operating near zero current, the frequency is reduced to accommodate MOSFET switching delays, while at higher currents the frequency is increased for efficient power delivery. This dynamic frequency adjustment resolves the contradiction between power efficiency and control stability.
Solution Approach 2:
The patent changes the PWM signal parameters (frequency and duty cycle) based on the operating point. By monitoring the current level and adjusting the PWM frequency accordingly, the system maintains stable control near zero current while achieving high efficiency at higher power levels, thus resolving the contradiction between these two requirements.
2Stability of the object's composition
If PWM frequency is increased to smooth the output waveform, then the load perceives a smoother signal, but MOSFET switching delays cause greater current ripple and distortion
Solution Approach 1:
The system implements dynamic frequency modulation where the PWM frequency is not fixed but adapts based on the operating conditions. Near zero current, the frequency is lowered to allow complete MOSFET switching cycles, eliminating current ripple. At higher currents, the frequency is raised to smooth the waveform. This dynamic approach resolves the contradiction between waveform smoothness and current regulation accuracy.
3Device complexity
If standard PWM signals are provided at fixed frequency, then the control system is simple, but audible noise and chatter occur due to MOSFET turn-on and turn-off delays
Solution Approach 1:
The system uses periodic modulation of the PWM frequency, alternating between higher and lower frequencies based on the operating point. This periodic variation in frequency prevents the fixed-frequency-induced audible noise and chatter while maintaining relative system simplicity. The frequency modulation is implemented through a monitor module that adjusts the PWM generator parameters.
Data Source
AI summary
The subject matter of this specification can be embodied in, among other things, a method that includes receiving a first electrical current output setpoint, identifying a first operational condition based on the first electrical current output setpoint, providing, based on the identified first operational condition, a first pulse width modulated (PWM) signal having a first predetermined duty cycle, based on the first electrical current output setpoint, provided on a predetermined period, receiving a second electrical current output setpoint, identifying a second operational condition different from the first operational condition based on the second electrical current output setpoint, and providing, based on the identified second operational condition, a second PWM signal having a second predetermined duty cycle, based on the second electrical current output setpoint, provided on a predetermined multiple of the predetermined period.