Phase Shift Control for Boost Converter Sub-Harmonic Oscillations
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Solution Overview
Problem
The phase shift disconnection method in paralleled boost converters experiences sub-harmonic oscillations due to conduction timing errors, leading to power runaway and unstable operation, especially when the duty ratio of the second switch is less than 0.5.
Innovation Solution
A phase shift control method that adjusts the slave-phase charge time interval based on the conduction timing error calculated from the master-phase charge time interval and the peak value of the slave-phase inductor current, ensuring accurate switching timing to prevent sub-harmonic oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the phase shift disconnection method is used to control the slave phase switching timing, then the converter operates in critical current conduction mode, but conduction timing errors cause sub-harmonic oscillations and power runaway when duty ratio is less than 0.5
Solution Approach 1:
The patent implements feedback control by detecting the actual current waveform and comparing it with the expected critical conduction mode waveform. The control unit adjusts the slave phase switching timing based on the detected conduction timing error, creating a closed-loop control system that eliminates sub-harmonic oscillations and prevents power runaway while maintaining stable operation in critical current conduction mode.
2Ease of operation
If fixed time lag is used for phase shift conduction method, then the control is simple to implement, but the slave phase cannot adapt to current state variations causing mode deviation
Solution Approach 1:
The patent transitions from a static fixed time lag control method to a dynamic control method where the slave phase switching timing is continuously adjusted based on real-time detection of the current state. The control unit dynamically modifies the switching timing to maintain optimal operation, enabling the system to adapt to variations in load, input voltage, and other operating conditions while keeping the control implementation relatively simple.
3Device complexity
If the slave phase timing is not precisely controlled, then the control circuit complexity is reduced, but conduction timing errors accumulate causing sub-harmonic oscillations
Solution Approach 1:
The patent employs a self-correcting mechanism where the control system automatically detects conduction timing errors and adjusts the slave phase switching timing without requiring complex external intervention. The system uses its own operational parameters (current waveforms, switching timings) to generate correction signals, achieving precise timing control through self-service feedback rather than through complex predetermined control circuits.
Data Source
AI summary
A phase shift control method for a boost converter and circuit implementation comprises a master phase and at least one slave phase. A master-phase inductor current flowing through the master phase has a master-phase charge time interval and a master-phase discharge time interval; a slave-phase inductor current flowing through the slave phase has a slave-phase charge time interval and a slave-phase discharge time interval. The method comprises: calculating an ideal switching timing whereat the slave-phase inductor current descends to a zero-current judgment value; obtaining a physical switching timing whereat the slave-phase charge time interval starts; calculating a conduction timing error between the physical switching timing and the ideal switching timing; determining the time length of the slave-phase charge time interval in the same cycle according to the conduction timing error and the master-phase charge time interval.