Multiphase Converter Frequency Control for Ripple Current Reduction
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Solution Overview
Problem
Conventional multiphase DC-DC converters experience increased ripple current when multiple phases are driven in sync, leading to larger capacitor sizes, which cannot be adequately reduced by phase shifting alone to meet modern size reduction demands.
Innovation Solution
A converter controlling apparatus that adjusts the driving frequency of each phase, setting a higher frequency for single-phase driving than for multiphase driving, and includes means to determine the number of phases based on load size, using soft switching converters with specific circuit configurations to minimize ripple current and capacitor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple phases are driven in sync in a multiphase DC-DC converter, then the power conversion capacity is improved, but the ripple current increases in proportion to the number of phases
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable based on operating conditions. The control unit dynamically changes the switching frequency of each phase according to the total output current, transitioning between high-frequency single-phase driving mode and low-frequency multiphase driving mode. This dynamic frequency adjustment resolves the contradiction by allowing the system to operate at high power capacity when needed while controlling ripple current through frequency modulation.
Solution Approach 2:
The patent changes the switching frequency parameter to resolve the contradiction. By setting different switching frequencies for different phases and adjusting the overall switching frequency based on load conditions, the system can achieve high power conversion capacity while maintaining acceptable ripple current levels. The control unit monitors output current and adjusts the frequency parameter accordingly.
2Object-generated harmful factors
If the switching frequency is increased to reduce ripple current, then the ripple current is reduced, but the switching loss increases
Solution Approach 1:
The system dynamically adjusts switching frequency based on load conditions. During light load conditions, high switching frequency is used to reduce ripple current. During heavy load conditions, the system transitions to multiphase driving with lower switching frequency, accepting higher ripple current in exchange for reduced switching losses and higher overall efficiency. This dynamic adaptation resolves the contradiction between ripple current reduction and switching loss minimization.
Solution Approach 2:
The switching frequency parameter is changed according to operating conditions. The control unit adjusts the frequency to optimize the balance between ripple current and switching loss, selecting appropriate frequency values based on the total output current and phase configuration.
3Object-generated harmful factors
If phase shifting is used to reduce ripple current, then the ripple current amplitude is attenuated, but the capacitor size reduction is limited and cannot meet further size reduction demands
Solution Approach 1:
The patent extends phase shifting from a static technique to a dynamic control strategy. The system dynamically adjusts both the phase shift amount and switching frequency based on operating conditions. By combining frequency modulation with phase shifting, the system achieves greater ripple current reduction than static phase shifting alone, enabling further capacitor size reduction to meet modern demands.
Solution Approach 2:
The patent combines multiple control techniques (phase shifting and frequency modulation) into a composite control strategy. This composite approach integrates the benefits of both techniques, achieving superior ripple current reduction and enabling more significant capacitor size reduction compared to using either technique alone.
4Object-generated harmful factors
If single-phase driving is used, then the ripple current is reduced, but the power conversion capacity is limited
Solution Approach 1:
The system dynamically transitions between single-phase and multiphase driving modes based on power demand. During light load conditions, single-phase driving with high switching frequency is used to minimize ripple current. During heavy load conditions, the system switches to multiphase driving with lower frequency to maximize power conversion capacity. This dynamic mode switching resolves the contradiction between ripple current reduction and power capacity.
Solution Approach 2:
The patent segments the operation into different modes (single-phase high-frequency mode and multiphase low-frequency mode). The control unit selects the appropriate segment based on load conditions, allowing the system to optimize for either ripple current reduction or power capacity depending on requirements.
Data Source
AI summary
A driving frequency setting portion is provided. The driving frequency setting portion sets a switching frequency of a switching element on the basis of a notification from a driving phase number switching portion. A ripple current detected by a current sensor is in inverse proportion to inductance of reactor. Since a ripple current becomes the largest in the single-phase driving, in this embodiment, considering both the ripple current and switching loss, a switching frequency for the single-phase driving is set higher than a switching frequency for multiphase driving.