Interleaved PFC Converter Control for Phase Current Balancing
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Solution Overview
Problem
In multi-phase interleaved power factor correction (PFC) converters, current imbalances between phases are exacerbated by negative current flow back to the AC input at light loads or low input voltages, particularly near zero crossings.
Innovation Solution
A control circuit is implemented to manage the operation of switches in a multi-phase interleaved PFC converter, adjusting the on-time of synchronous switches based on the operating mode (continuous or discontinuous) to prevent negative current flow and maintain current balance across phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a synchronous switch is on for a full period of the off-time of its corresponding active switch, then the converter operates in continuous mode with good current balance, but negative current flows back to the AC input at light loads or low input voltages near zero crossing, greatly increasing current imbalance between different phases
Solution Approach 1:
The synchronous switch on-time is dynamically adjusted based on the detected operating mode. In continuous conduction mode, the synchronous switch remains on for the full off-time period to maintain current balance. In discontinuous conduction mode (detected at light loads or low input voltages), the synchronous switch on-time is reduced to prevent negative current flow back to the AC input, thereby eliminating current imbalance between phases.
Solution Approach 2:
The control circuit detects the operating mode (continuous or discontinuous conduction mode) based on current conditions and uses this feedback information to adjust the synchronous switch on-time accordingly. This feedback mechanism ensures that the converter adapts its operation to maintain current balance and prevent harmful negative current flow under varying load and input voltage conditions.
2Object-generated harmful factors
If the converter operates in discontinuous mode at light loads, then negative current flow is prevented, but current imbalance between phases increases if synchronous switch on-time is not adjusted
Solution Approach 1:
The synchronous switch on-time is dynamically adjusted based on the detected operating mode. In continuous conduction mode, the synchronous switch remains on for the full off-time period to maintain current balance. In discontinuous conduction mode (detected at light loads or low input voltages), the synchronous switch on-time is reduced to prevent negative current flow back to the AC input, thereby eliminating current imbalance between phases.
Solution Approach 2:
The control circuit detects the operating mode (continuous or discontinuous conduction mode) based on current conditions and uses this feedback information to adjust the synchronous switch on-time accordingly. This feedback mechanism ensures that the converter adapts its operation to maintain current balance and prevent harmful negative current flow under varying load and input voltage conditions.
Data Source
AI summary
A multi-phase interleaved PFC converter includes at least six switches coupled in a multi-phase interleaved circuit arrangement, and a control circuit. The control circuit is configured to turn on and turn off a first one of the switches according to a PWM signal to operate the first switch as an active switch having an off-time as a function of a duty cycle of the PWM signal, while turning on and turning off a second one of the switches as a synchronous switch. The control circuit is also configured to receive signal(s) indicative of currents in each phase of the interleaved circuit arrangement, set an on-time of the second switch equal to the off-time of the first switch when the signal(s) indicate continuous mode operation, and set the on-time of the second switch to a duration less than the off-time of the first switch when the signal(s) indicate discontinuous mode operation.