Three-Phase Bi-Directional AC/DC Converter Soft-Switching Control
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Solution Overview
Problem
Three-phase inverter/rectifier systems face challenges in achieving high-frequency operation with low switching-related loss due to wide switching frequency variation ranges, especially at high modulation indices, which limits their power density and efficiency.
Innovation Solution
The implementation of a high-frequency DPWM+CRM+Fs sync modulation control strategy, where DPWM is used for decoupling phases and switching frequency synchronization is applied to reduce switching frequency variation, enabling independent CRM control and achieving soft switching across all phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional PWM control is used in three-phase inverter/rectifier systems, then the system can operate at high switching frequencies, but switching frequency varies widely causing increased switching-related losses
Solution Approach 1:
The patent applies dynamics by making the switching frequency adaptive rather than fixed. The control system dynamically adjusts the switching frequency of each phase based on real-time operating conditions, specifically synchronizing it with the line frequency and power factor. This dynamic adjustment allows the system to maintain high switching frequencies for high power density while minimizing switching losses by reducing frequency variation ranges through coordinated control of all three phases.
Solution Approach 2:
The patent implements feedback mechanisms by continuously monitoring the line frequency and power factor, then using this information to adjust the switching frequency of each phase. The control system measures the actual operating conditions and feeds this information back to the switching frequency generation circuitry, enabling closed-loop control that optimizes the switching frequency to minimize losses while maintaining high-frequency operation for high power density.
2Power
If high modulation index is used to increase power output, then the power density improves, but switching frequency variation range increases causing higher switching losses
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the switching frequency parameter based on the modulation index and power factor. When high modulation index is used to increase power output, the control system simultaneously adjusts the switching frequency to optimize the trade-off between power density and switching losses. This parameter adaptation allows the system to maintain high power output while minimizing the adverse effects of wide switching frequency variation.
Solution Approach 2:
The patent implements universality by creating a control strategy that works across all operating conditions - different modulation indices, power factors, and load levels. The switching frequency synchronization mechanism provides a universal solution that adapts to various power density requirements while consistently minimizing switching losses through coordinated multi-phase control, making the system effective whether operating at high or low power levels.
3Volume of moving object
If switching frequency is increased to improve power density, then smaller passive components can be used, but switching-related losses increase
Solution Approach 1:
The patent applies dynamics by implementing variable switching frequency control that adapts to operating conditions. Instead of using a fixed high switching frequency that would always cause high switching losses, the system dynamically adjusts the frequency to be as high as needed for compact passive components but as low as necessary to minimize switching losses. This dynamic frequency adjustment allows the system to optimize the trade-off between component size and efficiency in real-time.
Data Source
AI summary
Critical-mode soft-switching techniques for a power converter are described. In one example, a power converter includes a converter electrically coupled between an alternating current (AC) power system and a direct current (DC) power system, where the converter includes a number of phase legs. The power converter can also include a control system configured, during a portion of a whole line cycle of the AC power system, to clamp a first phase leg of the converter from switching and operate second and third phase legs of the converter independently in either critical conduction mode (CRM) or in discontinuous conduction mode (DCM).