Half-Bridge Power Converter Control for Full Zero-Voltage Switching
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Solution Overview
Problem
Existing power converters face challenges in achieving zero-voltage switching (ZVS) for all transitions in half-bridge topologies due to turn-on losses and inefficiencies in existing hardware and control-based approaches, limiting high switching frequencies and efficiency.
Innovation Solution
A system comprising a first and second half-bridge, with an auxiliary inductor and controller, that measures current and voltage values to compute dead times and duty cycles, ensuring ZVS for all transitions by adapting PWM control signals and using an auxiliary half-bridge as a current source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching frequency is increased to achieve higher power density, then productivity improves, but turn-on losses in transistors increase causing efficiency to deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-charging the transistor voltage to zero before switching occurs through the auxiliary resonance circuit. This prepares the circuit state in advance to eliminate turn-on losses, allowing high switching frequency operation without efficiency degradation. The auxiliary circuit creates conditions for ZVS to happen before the main switching event.
Solution Approach 2:
The patent introduces an auxiliary resonance circuit as an intermediary between the main half-bridge and the load. This auxiliary circuit acts as a mediator that provides the necessary current to charge/discharge the transistor output capacitances, enabling ZVS without directly affecting the main power conversion path. The intermediary circuit isolates the ZVS mechanism from the main power flow.
2Loss of energy
If hardware-based auxiliary resonance circuit is added to achieve ZVS, then turn-on losses are reduced, but device complexity increases and switching frequency is limited by hard-switching transistors in the auxiliary circuit
Solution Approach 1:
The patent makes the auxiliary half-bridge multi-functional by using it both for generating ZVS current and for power conversion. The same auxiliary transistors and inductor serve dual purposes: creating the resonance current needed for ZVS in the main bridge while also contributing to the overall power conversion function. This eliminates the need for separate dedicated ZVS components.
Solution Approach 2:
The patent merges the auxiliary ZVS circuit with the main power conversion circuit by using a combined half-bridge topology. The auxiliary inductor and transistors are integrated into the same circuit structure that performs power conversion, rather than being separate add-on components. This consolidation reduces overall device complexity while achieving ZVS.
3Loss of energy
If control-based critical conduction mode is used to achieve ZVS, then all transitions can operate at ZVS, but switching frequency range becomes too large making EMI filter and control design difficult
Solution Approach 1:
The patent implements feedback control by continuously monitoring the auxiliary inductor current and adjusting the PWM duty cycle to maintain the current within optimal bounds for ZVS. The controller uses this feedback to dynamically regulate the switching behavior, ensuring ZVS is achieved without requiring an excessively wide switching frequency range. This keeps the operating frequency range manageable for EMI filtering and control design.
4Loss of energy
If auxiliary half-bridge is used as current source for ZVS, then full ZVS capability is achieved, but component count and circuit footprint increase
Solution Approach 1:
The auxiliary half-bridge components serve multiple functions simultaneously: the auxiliary inductor provides both the ZVS current source and contributes to power conversion, while the auxiliary transistors generate ZVS current and participate in power switching. This multi-functionality reduces the need for separate dedicated ZVS components, thereby minimizing the overall circuit footprint while achieving full ZVS capability.
Data Source
AI summary
Disclosed is a system for zero voltage switching in a power converter with a first half-bridge and a second half-bridge. The first half-bridge has a first set of transistors and output inductor. The second half-bridge has a second set of transistors and auxiliary inductor. A current sensing means measures, at switching cycle scale, average and maximum current values of output inductor and average, minimum and maximum current values of auxiliary inductor. A voltage sensing means measures input and output voltages of first and second half-bridge. A controller is configured to compute dead times of pulse width modulation control signal of second half-bridge, generate pulse width modulation control signal of second half-bridge and to adapt dead times of first half-bridge.