Simple Control Method Tames Flux Saturation In High-Frequency Transformer-Link Full-Bridge DC-DC Converters

Focus:

The high-frequency transformer-link dc-dc converter is the preferred topology for low- and medium-power plasma-cutting applications since it is compact, light and provides good dynamic response along with galvanic isolation. However, such systems suffer from transformer-core flux saturation, which leads to problems such as an increase in converter switching loss and noise, power supply shutdown or even a catastrophic failure in some cases. Several solutions have been proposed, but each has its drawbacks as described in this article. The simple method of transformer-flux control proposed in this article overcomes many of those disadvantages. This method maintains tight control of the transformer flux by steering the PWM output signal to the appropriate converter switch without affecting the main control loop. This enables full utilization of the transformer core without compromising the system’s dynamic response. Furthermore, it can be retrofitted into an existing power supply with minimal impact on its circuitry. This article begins with a review of the conventional full-bridge-converter plasma- cutting system, and then discusses the mechanics of transformer flux saturation, explaining both its causes and effects. With that as background, the principle of operation of the proposed control method and its circuit implementation are described. This is a conceptual discussion, but simulation and experimental results will be presented in a later article.

What you’ll learn:

• How to understand causes of transformer flux saturation in high-frequency transformer-link full- bridge dc-dc converters
• How to understand possible control options for preventing transformer flux saturation in high- frequency transformer-link full-bridge dc-dc converters

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Author & Publication:

Girish R. Kamath, Hypertherm, Hanover, NH, How2Power Today, Jun 29 2012

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