Multiphase DC-DC Converter Phase Current Offset Compensation
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Solution Overview
Problem
Multiphase DC-DC power converters face instability and increased switching losses due to phase current offsets, making reliable low-load control and transition from PWM to PFM mode challenging.
Innovation Solution
A control circuit that operates constituent power converters in PWM mode, detects zero crossings, and switches low side switches to active diode operation to ensure all phase currents cross zero, allowing stable transition to PFM mode, reducing switching losses and improving energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the control transitions to PFM mode based on zero crossing detection of phase currents, then switching losses are reduced and energy efficiency is improved, but phase current offsets cause unreliable detection and instability
Solution Approach 1:
The control circuit proactively forces all phase currents to cross zero by operating low side switches as active diodes upon detecting the first zero crossing, before transitioning to PFM mode. This preliminary action ensures that all phase currents are synchronized at zero crossing, eliminating the reliability issue caused by phase current offsets while enabling efficient PFM operation.
Solution Approach 2:
The control circuit continuously monitors phase currents for zero crossing events and uses this feedback to trigger the active diode operation. When a zero crossing is detected in any phase, the control circuit activates the low side switches as active diodes to force other phases to also cross zero, creating a closed-loop control mechanism that ensures reliable detection before PFM transition.
2Productivity
If the low side switches are operated in complementary manner, then the converter operates efficiently in PWM mode, but phase current offsets prevent stable transition to PFM mode
Solution Approach 1:
The control circuit dynamically changes the operation mode of low side switches from complementary switching (during PWM mode) to active diode operation (when zero crossing is detected). This dynamic adaptation allows the system to maintain high productivity during PWM mode while ensuring stable phase current synchronization when transitioning to PFM mode, resolving the contradiction between output power and stability.
3Use of energy by moving object
If the control detects zero crossing to transition to PFM mode, then energy efficiency is improved, but phase current offsets lead to increased switching losses
Solution Approach 1:
The control circuit converts the harmful effect of phase current offsets into a beneficial outcome. Instead of allowing phase current offsets to cause unreliable detection and increased switching losses, the control circuit uses the first detected zero crossing as a trigger to force all other phases to cross zero through active diode operation. This transforms the potential harm of phase mismatches into a mechanism that ensures synchronized zero crossing for all phases, enabling efficient PFM mode operation with reduced switching losses.
Data Source
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AI summary
The present document relates to multiphase DC-DC power converters. In particular, the present document relates to the compensation of the phase offset incurred in multiphase DC-DC power converters which are controlled based on coil current zero crossing. A control circuit (115, 215) for a multiphase power converter (200) is described. The multiphase power converter (200) comprises a first and a second constituent switched-mode power converter, wherein the first and second constituent power converters provide first and second phase currents (331, 332), respectively. The first and second phase currents (331, 332) contribute to a joint load current (330) of the multiphase power converter (200). The first and second constituent power converters comprise first and second half bridges with first and second high side switches (201, 221) and first and second low side switches (202, 222), respectively. The control circuit (115, 215) is configured to operate the first and second constituent power converters in a pulse width modulation, pwm, mode with a constant commutation cycle rate; to operate the low side switches (202, 222) in a complementary manner with regards to the respective high side switches (201, 221); to detect a zero crossing of the first phase current (331) at a first time instant (333), when the first high side switch (201) is in off-state; and to operate the first low side switch (202) as an active diode, upon detecting the zero crossing of the first phase current (331).