Soft-Switching Triangular Current Mode Control for Three-Phase Converters
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Solution Overview
Problem
High switching frequency operation in power converters leads to dominant turn-on losses, especially in hard switching continuous conduction mode, which is not effectively addressed by existing technologies, and zero voltage switching (ZVS) turn-on is often required to mitigate these losses.
Innovation Solution
The implementation of triangular current mode (TCM) control with zero voltage switching (ZVS) turn-on, combined with discontinuous conduction mode (DCM) and clamped mode operation, allows for efficient soft-switching and phase synchronization in power converters, enabling ZVS turn-on without adding physical complexity, and is applicable to a wide range of power factors and converter topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high switching frequency operation is used in power converters, then productivity is improved, but turn-on losses increase significantly
Solution Approach 1:
The patent changes the switching parameter by implementing Zero Voltage Switching (ZVS) turn-on, where the switch turns on when the voltage across it is zero. This is achieved by allowing the inductor current to flow in both directions to discharge the parasitic capacitance before switching, thereby eliminating turn-on losses while maintaining high switching frequency operation
Solution Approach 2:
The patent employs Triangular Current Mode (TCM) control with periodic switching cycles that include both forward and reverse current flow phases. This periodic bidirectional current flow enables the parasitic capacitance to discharge completely before each switching event, ensuring ZVS conditions are met periodically at every switching cycle
2Loss of energy
If ZVS turn-on is implemented to reduce turn-on losses, then loss of energy is improved, but device complexity increases
Solution Approach 1:
The patent utilizes the inherent parasitic capacitance of the semiconductor switch itself as the resonant capacitor for ZVS operation. The inductor current naturally charges and discharges this parasitic capacitance during bidirectional operation, eliminating the need for external resonant capacitors or inductors that would increase device complexity
Solution Approach 2:
The patent makes the parasitic capacitance, which is normally a harmful element causing losses, serve a useful function as the resonant capacitor for achieving ZVS. This multi-functional use of existing components avoids adding extra elements while still achieving the desired soft-switching performance
3Loss of energy
If inductor current flows in both directions to achieve ZVS, then turn-on losses are reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements TCM control with feedback mechanisms that monitor the inductor current and adjust switching timing accordingly. This feedback ensures that the switching events occur at the precise moments when ZVS conditions are met, maintaining control precision despite the bidirectional current flow and varying operating conditions
Data Source
AI summary
Critical-mode soft-switching techniques for a power converter are described. In one example, a power converter includes a bidirectional converter electrically coupled between an alternating current (AC) power system and a direct current (DC) power system, where the bidirectional converter includes a number of phase legs. The power converter can also include a control system configured, during a portion of a 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).