Active-Clamp Current-Fed Push-Pull Converter for Startup Runaway Control

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Solution Overview

Problem

Bidirectional power converters face challenges in converting low voltage to high voltage using phase shift full bridge topology due to inductor current runaway during startup, especially when the high voltage rail is smaller than the low voltage rail, leading to potential component damage.

Innovation Solution

Incorporating a clamp circuit with clamp switches and capacitors that provide a reset voltage to the inductor, ensuring volt-second balance and preventing inductor current runaway by active clamping during both forward and reverse operation modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If phase shift full bridge topology is used for low voltage to high voltage conversion, then bidirectional power transfer is enabled, but inductor current runaway occurs during startup when high voltage rail is smaller than low voltage rail

Engineering Contradiction:

Improvebidirectional power transfer capabilityVSAvoidinductor current stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The clamp circuit is activated before the main power conversion begins, pre-establishing a safe voltage reference and preventing inductor current runaway during startup. The clamp switches and capacitors are configured to engage automatically when voltage conditions indicate potential runaway, providing preliminary protection before full bidirectional operation commences.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The clamp circuit acts as an intermediary between the inductor and the rest of the power converter system. It introduces clamp switches and capacitors that mediate the voltage stress on the inductor, providing a controlled path for current during startup conditions and preventing direct runaway while enabling safe bidirectional power transfer.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If no clamp circuit is used, then device complexity is reduced, but inductor current runaway causes component damage

Engineering Contradiction:

Improvecircuit structure simplicityVSAvoidinductor current runaway damage

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The clamp circuit provides beforehand cushioning by pre-positioning clamp switches and capacitors to absorb and limit voltage spikes before they can cause inductor current runaway. This protective mechanism is built into the circuit architecture, cushioning against harmful effects before they manifest as component damage during startup or transient conditions.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If pre-biasing of high voltage rail is implemented, then inductor current runaway is prevented, but additional circuit complexity and control requirements are introduced

Engineering Contradiction:

Improveinductor current controlVSAvoidvoltage rail pre-biasing circuit

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The clamp circuit operates autonomously using self-service principles, automatically detecting voltage conditions and activating clamp switches when needed without requiring external pre-biasing control. The circuit monitors itself and provides necessary voltage clamping action based on real-time conditions, eliminating the need for complex pre-biasing control systems while maintaining reliability.

Inventive Principle:

Principle #25Self-service

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The clamp circuit effectively prevents inductor current runaway, enabling safe and efficient bidirectional power transfer without the need for pre-biasing the higher voltage rail, and allows operation in both forward and reverse modes without damage to components.

Implementation Method 1

an isolation transformer to electrically isolate the power converter output stage or secondary side from the input stage or primary side by arranging the isolation transformer between the primary side and the secondary side

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a clamp circuit coupled to the inductor and configured to provide a reset voltage to the inductor that prevents inductor current runaway

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11804782B2Active-clamp current-fed push-pull converter for bidirectional power transfer

Publication Date: 2023.10.31 ANALOG DEVICES INC

AI summary

An apparatus including a bidirectional power converter circuit. The power converter circuit includes a primary circuit side including a plurality of primary switches, an isolation transformer, and a secondary circuit side separated from the primary circuit side by the isolation transformer. The secondary circuit side includes an inductor, a rectifier circuit coupled to the inductor and configured to receive energy from the primary circuit side and provide energy to the primary circuit side, and a clamp circuit coupled to the inductor and configured to provide a reset voltage to the inductor that prevents inductor current runaway.