KR-20260065465-A - Method of Diagnosing Open-Circuit Fault of Dual Active Bridge Converter

KR20260065465AKR 20260065465 AKR20260065465 AKR 20260065465AKR-20260065465-A

Abstract

A method for diagnosing an open-circuit fault in a dual active bridge converter is disclosed. Among a pair of switches forming a positive current flowing from the primary side to the transformer and a pair of switches forming a negative current flowing out from the transformer to the primary side, a pair of switches causing an open-circuit fault is determined. After determining the pair of switches, a bridge causing an open-circuit fault among a first bridge and a second bridge is determined. Additionally, by applying a zero vector and an effective vector, an open-circuit fault is determined for the switch of the fault bridge.

Inventors

이준석
오현우

Assignees

단국대학교 산학협력단

Dates

Publication Date: 20260508
Application Date: 20250206
Priority Date: 20241030

Claims (7)

A method for diagnosing an open-circuit fault of a dual active bridge converter having a transformer connected between a first bridge and a second bridge, wherein the transformer is converted according to the primary side voltage connected to the first bridge that converts the input voltage and the winding ratio of the coil, and generates a secondary side voltage connected to the second bridge, A step of determining a switch pair having an open-circuit fault among a first switch pair forming a positive inductor current having a direction flowing from the first bridge to the transformer and a second switch pair forming a negative inductor current having a direction flowing out from the transformer to the first bridge; A step of determining the open fault bridge among the first bridge and the second bridge among the open fault switch pair: and An open fault diagnosis method comprising the step of determining a switch having an open fault within the above-mentioned open fault bridge.
In claim 1, the step of determining the open fault switch pair is An open-circuit fault diagnosis method characterized by comparing the average value of the inductor current sampled at the minimum value of the carrier wave and the inductor current sampled at the maximum value of the carrier wave with a switch pair threshold value, wherein the switch pair threshold value uses an offset current value modeled according to the open-circuit fault in the second bridge of the open-circuit fault switch pair.
A method for diagnosing open-circuit faults according to claim 2, wherein the determination of the open-circuit fault pair is characterized by determining the first switch pair as faulty if the following Equation 1 is satisfied, and determining the second switch pair as faulty if the following Equation 2 is satisfied. [Formula 1] [Equation 2] In the above Equations 1 and 2, i L,AVG is the average value of the sampled current, i L (t 1 ) is the inductor current at the point in time when the positive inductor current is generated during normal operation and the switches of the second bridge are in the off state, V pri is the primary side voltage of the transformer, n is the primary side winding ratio for the secondary side of the transformer, and V sec is the secondary side voltage of the transformer.
A method for diagnosing an open-circuit fault according to claim 1, wherein the step of determining the open-circuit fault bridge involves determining the inductor current sampled from the minimum value of the carrier wave by comparing it with a bridge threshold value, and the bridge threshold value utilizes the predicted current when an open-circuit fault occurs in the second bridge.
A method for diagnosing an open fault according to claim 4, wherein if the first switch pair has an open fault, the first bridge is determined to have an open fault according to the following Equation 3, and the second bridge is determined to have an open fault according to the following Equation 4. [Equation 3] [Equation 4] In the above Equations 3 and 4, i L_ZERO is the inductor current sampled at the minimum value of the carrier wave, i L (t 1 * ) is the inductor current predicted at the time when the switches of the second bridge of the first switch pair are opened after an open-circuit fault occurs, and i L (t 2 * ) is the inductor current predicted at the time when the switching operation through the second switch pair begins after an open-circuit fault occurs.
A method for diagnosing an open fault according to claim 5, characterized in that if the second switch pair has an open fault, the first bridge is determined to have an open fault according to the following formula 5, and the second bridge is determined to have an open fault according to the following formula 6. [Formula 5] [Equation 6]
An open fault diagnosis method according to claim 1, wherein the determination of the open fault switch is characterized by applying a zero vector to a terminal of a transformer connected to the open fault bridge and applying an effective vector to a transformer terminal opposite to the terminal to which the zero vector is applied.

Description

Method of Diagnosing Open-Circuit Fault of Dual Active Bridge Converter The present invention relates to a Dual Active Bridge (DAB) converter, and more specifically, to a method for diagnosing a fault in a DAB converter that can diagnose a fault within a short period of time. The DAB converter is a circuit widely used in power conversion systems due to its simple structure and ease of control. It offers the advantage of simultaneous power supply and recovery as it allows current to flow in both directions. Widely used in DC-DC converters, DAB converters are employed in various fields, such as electric vehicle charging systems and renewable energy systems, thanks to their high conversion efficiency and excellent power density. Figure 1 is a circuit diagram illustrating a conventional DAB converter. Referring to FIG. 1, the DAB converter has a first bridge (110), a transformer (120), and a second bridge (130). One bridge consists of four switches. Each bridge forms a current path according to the supplied switching signal, and the transformer (120) performs voltage conversion and current conversion operations according to the ratio of the number of turns. An input voltage V in is supplied, and an output voltage V out is formed through a transformer (120). The transformer (120), positioned between the input voltage V in and the output voltage V out , has a primary pole voltage V pri and a secondary pole voltage V sec according to the winding ratio n. The inductance L represents the leakage inductance of the transformer, and the inductor current i L flowing through it is substantially the current flowing through the primary coil of the transformer (120). If a specific switch constituting the two bridges (110, 130) has an open circuit fault, the current flowing through the transformer (120) is skewed to one polarity and causes inductance saturation. It is necessary to stop the power conversion system through fault diagnosis before the inductance saturates. To diagnose open-circuit faults in switches, current detection via a current sensor is required. In addition to the current sensor, additional circuitry and sensors for detecting voltage are also required. This places a significant circuit burden on systems employing DAB converters. Therefore, a fault diagnosis method is required that can rapidly determine open circuit failures in the DAB converter through an algorithm and accurately identify the fault switch. Figure 1 is a circuit diagram illustrating a conventional DAB converter. FIG. 2 is a graph showing the operating waveform of the DAB converter of FIG. 1 during normal operation according to a preferred embodiment of the present invention. Figure 3 is a circuit diagram illustrating the operating state of the switches of Figure 1 to explain the waveform diagram of Figure 2. FIG. 4 is a circuit diagram illustrating the operation when an open circuit fault occurs at switch S1 in FIG. 1 according to a preferred embodiment of the present invention. FIG. 5 is a graph showing the current-voltage characteristics according to the operation of the circuit of FIG. 4 in accordance with a preferred embodiment of the present invention. FIG. 6 is a circuit diagram illustrating the operation when an open circuit fault occurs at switch S6 in FIG. 1 according to a preferred embodiment of the present invention. FIG. 7 is a graph showing the current and voltage according to the operation of the circuit of FIG. 6 in accordance with a preferred embodiment of the present invention. The present invention is susceptible to various modifications and may take various forms; therefore, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Similar reference numerals have been used for similar components in the description of each drawing. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application. Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. Examples FIG. 2 is a graph showing the operating waveform of the DAB converter of FIG. 1 during normal operation according to a preferred embodiment of the present invention. Referring to FIG. 2, under the assumption that all switches of the bridge are operating normally, the voltage and current on the primar