DAB converter apparatus capable of eliminating DC bias

Abstract

The present invention relates to a dual active bridge converter device capable of removing DC bias, and more specifically, to a dual active bridge converter device capable of removing DC bias by switching the switching elements of the primary circuit and the secondary circuit using only the output current in a steady state or a transient state.

Description

Technology Field

[0001] The present invention relates to a dual active bridge converter device capable of removing DC bias, and more specifically, to a dual active bridge converter device capable of removing DC bias by switching the switching elements of the primary circuit and the secondary circuit using only the output current in a steady state or a transient state. Background Technology

[0002] Over the past few years, the power electronics sector has witnessed rapid advancements in bidirectional power conversion technology. The importance of this technology is becoming increasingly evident in various applications, including electric vehicle charging and discharging, energy storage systems (ESS), and smart grids.

[0004] In the aforementioned application fields, efficient energy conversion and management play a pivotal role in highlighting the importance of bidirectional power converters. Among bidirectional converters, the Dual Active Bridge (DAB) converter stands out for its relatively simple circuitry, zero-voltage switching capabilities, and high efficiency in high-power systems. While previous research has primarily focused on topics such as zero-voltage switching solutions, phase-shift (PS) control strategies, current stress minimization, topology expansion, hardware design, and optimization, the characteristics related to the DC bias of dual active bridge converters have received less attention.

[0006] During the operation of a dual active bridge converter, variations in load under the same output conditions can cause phase shifts and lead to flux imbalance, which may result in DC bias. This DC bias can saturate the transformer, potentially causing overcurrent in the system and posing a risk of damage to power components.

[0008] Therefore, it is necessary to remove this DC bias, and existing methods use blocking capacitors to achieve this. However, this presents the problem of increased system cost and volume due to the use of additional capacitors. The problem to be solved

[0009] The present invention was created to resolve such problems, and the objective of the present invention is to provide a dual active bridge converter device capable of removing DC bias by switching the switching elements of the primary circuit and the secondary circuit using only the output current in a steady state or a transient state. means of solving the problem

[0010] A dual active bridge converter device capable of removing DC bias according to the present invention for achieving the above-mentioned purpose comprises: a primary circuit having a primary switching element; a secondary circuit having a secondary switching element; a transformer located between the primary circuit and the secondary circuit; a controller that removes DC bias when in a normal state or a transient state by switching the primary switching element and the secondary switching element; and an output current sensor that detects the output current of the output terminal of the secondary circuit.

[0011] In addition, the first switching element comprises a first switching element, a second switching element, a third switching element, and a fourth switching element connected in a full-bridge configuration, and the second switching element comprises a fifth switching element, a sixth switching element, a seventh switching element, and an eighth switching element connected in a full-bridge configuration.

[0012] In addition, the controller is characterized by obtaining an output current (Io) through the output current sensor when in a normal state, obtaining a control value (D) from the following mathematical formula using the output current (Io), and switching the first switching element and the second switching element to either the first switching technique or the second switching technique according to the control value (D) to remove the DC bias.

[0013]

[0014] Here, Io is the output current, Vo is the output voltage, RL is the load-side resistance, n is the transformer ratio, V1 is the transformer primary voltage, fs is the switching frequency, and L is the series inductance.

[0015] In addition, the controller is characterized by obtaining an output current (Io) through the output current sensor in the event of a transient state, deriving the following mathematical formulas through the RPS method, obtaining control values ​​(D2, D'2) from the following mathematical formulas using the output current (Io), and switching the first switching element and the second switching element to either the first switching technique or the second switching technique according to the control values ​​(D2, D'2) to remove the DC bias.

[0016]

[0017]

[0018]

[0019]

[0020] Here, Io is the output current, V2 is the transformer secondary voltage, n is the transformer ratio, V1 is the transformer primary voltage, fs is the switching frequency, and L is the series inductance.

[0021] In addition, the first switching technique is characterized by controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be ON, the second switching element (112) and the third switching element (113) to be OFF, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be ON, and the sixth switching element (212) and the seventh switching element (213) to be OFF.

[0023] In addition, the second switching technique is characterized by controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be turned ON, the second switching element (112) and the third switching element (113) to be turned OFF, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be turned OFF, and the sixth switching element (212) and the seventh switching element (213) to be turned ON.

[0025] In addition, the third switching technique is characterized by controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be turned off, the second switching element (112) and the third switching element (113) to be turned on, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be turned on, and the sixth switching element (212) and the seventh switching element (213) to be turned off.

[0027] In addition, the above-described fourth switching technique is characterized by controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be OFF, the second switching element (112) and the third switching element (113) to be ON, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be OFF, and the sixth switching element (212) and the seventh switching element (213) to be ON. Effects of the invention

[0028] The dual active bridge converter device capable of removing DC bias according to the present invention has the effect of removing DC bias by switching the switching elements of the primary circuit and the secondary circuit using only the output current in a normal state or a transient state.

[0030] The problems solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below. Brief explanation of the drawing

[0031] FIG. 1 is a circuit diagram of a dual active bridge converter device capable of DC bias removal according to an embodiment of the present invention. FIG. 2 is an implementation diagram of a switching method of a controller according to an embodiment of the present invention. FIG. 3 is an example diagram of the switching period of a controller according to an embodiment of the present invention. FIG. 4 is an example diagram of voltage characteristics according to switching in a steady state according to an embodiment of the present invention. FIG. 5 is an example diagram of current characteristics according to switching in a steady state according to an embodiment of the present invention. FIG. 6 is an exemplary diagram of a method for calculating DC bias current during a transient state according to an embodiment of the present invention. FIG. 7 is an explanatory diagram of an RPS method according to an embodiment of the present invention. FIG. 8 is a simulation result diagram using PSIM according to an embodiment of the present invention. Specific details for implementing the invention

[0032] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to ensure that the spirit of the present invention is sufficiently conveyed to those skilled in the art.

[0034] In describing the present invention, terms such as first, second, etc. may be used to describe various components, but the components may not be limited by the terms. The terms are intended solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0036] When it is mentioned that a component is connected to or coupled with another component, it can be understood that it may be directly connected to or coupled with that other component, or that there may be other components in between.

[0038] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions may include plural expressions unless the context clearly indicates otherwise.

[0040] In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0042] Hereinafter, specific technical details to be implemented in the present invention will be described in detail with reference to the attached drawings.

[0044] FIG. 1 is a circuit diagram of a dual active bridge converter device capable of DC bias removal according to an embodiment of the present invention. As shown in FIG. 1, the dual active bridge converter device capable of DC bias removal according to the present invention may include a primary side circuit (100), a secondary side circuit (200), a transformer (300), a controller (400), and an output current sensor (500).

[0046] The above primary side circuit (100) includes a primary switching element (110), and the primary switching element (110) may include a first switching element (111), a second switching element (112), a third switching element (113), and a fourth switching element (114) configured in a full-bridge form. Additionally, it may further include an input capacitor.

[0048] The above secondary circuit (200) includes a secondary switching element (210), and the secondary switching element (210) may include a fifth switching element (211), a sixth switching element (212), a seventh switching element (213), and an eighth switching element (214) configured in a full-bridge form. Additionally, it may further include an output capacitor.

[0050] The above transformer (300) may include a series inductor (310) and an inductor block (320), and the inductor current refers to the current flowing through the inductor block (3230).

[0052] The controller (400) switches the primary switching element (110) and the secondary switching element (210) of the primary side circuit (100) and the secondary side circuit (200).

[0054] The output current sensor (500) detects the output current output from the output terminal of the secondary circuit (200) and is typically a configuration required for constant current control or power device protection in a dual active bridge converter device.

[0056] FIG. 2 is an illustration of a switching method of a controller according to an embodiment of the present invention. As shown in FIG. 2, the controller (400) can switch the first switching element (110) and the second switching element (210) using any one of a first switching technique, a second switching technique, a third switching technique, or a fourth switching technique.

[0058] The first switching technique means controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be turned ON, the second switching element (112) and the third switching element (113) to be turned OFF, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be turned ON, and the sixth switching element (212) and the seventh switching element (213) to be turned OFF.

[0060] The second switching technique means controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be turned ON, the second switching element (112) and the third switching element (113) to be turned OFF, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be turned OFF, and the sixth switching element (212) and the seventh switching element (213) to be turned ON.

[0062] The third switching technique means controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be turned off, the second switching element (112) and the third switching element (113) to be turned on, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be turned on, and the sixth switching element (212) and the seventh switching element (213) to be turned off.

[0064] The fourth switching technique means controlling the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be turned off, the second switching element (112) and the third switching element (113) to be turned on, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be turned off, and the sixth switching element (212) and the seventh switching element (213) to be turned on.

[0066] FIG. 3 is an example diagram of the switching cycle of a controller according to an embodiment of the present invention.

[0067] As illustrated in FIG. 3, when the controller (400) switches the first switching element (110) and the second switching element (210) according to the first switching technique, the second switching technique, the third switching technique, or the fourth switching technique, the switching period can be divided into four sections.

[0069] Meanwhile, the dual active bridge converter device capable of removing DC bias according to the present invention can remove DC bias by performing switching depending on the normal state or transient state. First, the method for removing DC bias in the normal state is explained through FIGS. 4 to 6.

[0071] FIG. 4 is an example diagram of voltage characteristics according to switching in a normal state according to an embodiment of the present invention, and FIG. 5 is an example diagram of current characteristics according to switching in a normal state according to an embodiment of the present invention.

[0072] As shown in FIGS. 4 and 5, when the controller (400) performs switching using the first switching technique or the second switching technique in a normal state, the characteristics of the primary side transformer voltage, secondary side transformer voltage, inductor voltage, inductor current, and output current for each section of the switching cycle can be checked.

[0074] By utilizing the characteristics of the primary side transformer voltage, secondary side transformer voltage, inductor voltage, inductor current, and output current for each section of the above switching cycle, the following mathematical formula 3 can be derived by subtracting section 3 from section 2 of FIG. 5 as in the following mathematical formula 1, and adding section 1 to the result as in the following mathematical formula 2.

[0075]

[0076]

[0077]

[0078] Here, Io is the output current, Vo is the output voltage, RL is the load-side voltage, n is the transformer ratio, V1 is the transformer primary-side voltage, fs is the switching frequency, and L is the series inductance.

[0080] The controller (400) obtains an output current (Io) through the output current sensor (500), obtains a control value (D) in the above mathematical formula 3 using the output current (Io), and can remove the DC bias by switching the first switching element (110) and the second switching element (210) according to the control value (D) using any one of the first switching technique, the second switching technique, the third switching technique, or the fourth switching technique.

[0082] Next, the method for removing DC bias in the case of a transient state is explained through Figures 6 and 7.

[0084] FIG. 6 is an example diagram of a method for calculating DC bias current during a transient state according to an embodiment of the present invention.

[0085] As shown in FIG. 6, when a DC bias occurs during a transient state, the DC bias current can be calculated through the peak currents I1, I2, I3, and I4 at the point where the DC bias occurs. The peak currents I1, I2, I3, and I4 are given by Equation 4 below, and the section where the DC bias occurs is expressed as Equation 5 below. Through Equations 4 and 5 below, the DC bias current can be calculated as Equation 6 below.

[0086]

[0087]

[0088]

[0089] Here, V2 is the secondary voltage of the transformer, n is the transformer ratio, fs is the switching frequency, and L is the series inductance.

[0091] FIG. 7 is an explanatory diagram of an RPS method according to an embodiment of the present invention.

[0092] The controller (400) of the dual active bridge converter device according to the present invention uses a Recovery Phase Shift (RPS) method to remove DC bias when in a transient state, wherein the RPS method means dividing the phase change for the ground voltage into two parts as shown in FIG. 7 and adding it to the rising edge and falling edge of one cycle of the ground voltage.

[0094] When using the above-described RPS method, the peak currents I1, I2, I3, and I4 at the DC bias point are given by Equation 7 below, and the section where the DC bias occurs is expressed as Equation 8 below.

[0095]

[0096]

[0097] Here, V2 is the secondary voltage of the transformer, n is the transformer ratio, fs is the switching frequency, and L is the series inductance.

[0099] By applying the above-mentioned peak currents I1, I2, I3, and I4 and the DC bias current calculation method, the controller (400) can derive the following mathematical formulas 9 to 12.

[0100]

[0101]

[0102]

[0103]

[0104] Here, Io is the output current, V2 is the transformer secondary voltage, n is the transformer ratio, V1 is the transformer primary voltage, fs is the switching frequency, and L is the series inductance.

[0106] The controller (400) obtains an output current (Io) through the output current sensor (500), obtains control values ​​(D2, D'2) in the above mathematical formulas 9 to 12 using the output current (Io), and can remove the DC bias by switching the first switching element (110) and the second switching element (210) according to the control values ​​(D2, D'2) to any one of the first switching technique, the second switching technique, the third switching technique, or the fourth switching technique.

[0108] Figure 8 is a simulation result diagram using PSIM according to an embodiment of the present invention. As shown in Figure 8, after implementing a dual active bridge converter device capable of DC bias removal according to the present invention through PSIM (Power Electronics Simulation Software) and performing a simulation, Figure 8a shows that the DC bias of the inductor current was 4.98A with a peak of 37.5A, and it took 30 cycles to return to a steady state. Figure 8b shows that the DC bias of the inductor current was -0.923A with a peak of 27.2A, and it took 4 cycles to return to a steady state. In the above simulation, the main parameter values ​​are an input voltage (Vs) of 750V, an output voltage (Vo) of 350V, a switching frequency (fs) of 50kHz, a transformer ratio (n) of 0.5, and a series inductance (L) of 50uH. In addition, Fig. 8a shows that DC bias removal was performed only in the normal state, and Fig. 8b shows that DC bias removal was performed in both the normal state and the transient state.

[0110] Accordingly, as described above, it can be confirmed that the dual active bridge converter device capable of removing DC bias according to the present invention can remove DC bias by switching the switching elements of the primary circuit and the secondary circuit using only the output current in a steady state or a transient state, and since this can be realized through only the output current sensor essential for the dual active bridge converter device, the volume of the device can be reduced compared to conventional methods, and it is economical and efficient.

[0112] In the foregoing, although all components constituting an embodiment of the present invention have been described as being combined or operating as a single unit, the present invention is not necessarily limited to such an embodiment. That is, within the scope of the purpose of the present invention, all components may be selectively combined and operated in one or more ways. Furthermore, while all components may each be implemented as a single independent piece of hardware, some or all of the components may be selectively combined to be implemented as a computer program having a program module that performs some or all of the combined functions on one or more pieces of hardware. The codes and code segments constituting the computer program can be easily inferred by those skilled in the art of the present invention. An embodiment of the present invention may be implemented by storing such a computer-readable storage medium and reading and executing it by a computer.

[0114] Meanwhile, although preferred embodiments illustrating the technical concept of the present invention have been described and illustrated above, the present invention is not limited to the configuration and operation as illustrated and described, and those skilled in the art will understand that numerous changes and modifications are possible to the present invention without departing from the scope of the technical concept. Accordingly, all such appropriate changes, modifications, and equivalents should be deemed to fall within the scope of the present invention. Accordingly, the true scope of technical protection of the present invention should be determined by the technical concept of the appended claims. Explanation of the symbols

[0115] 100 : Primary side circuit 110: Primary switching element 111 : First switching element 112 : Second switching element 113 : Third switching element 114 : 4th switching element 200 : Secondary circuit 210 : Secondary switching element 211 : 5th switching element 212 : 6th switching element 213 : 7th switching element 214 : 8th switching element 300: Transformer 310: Series Inductor 320: Inductor Block 400 : Controller 500 : Output current sensor

Claims

Claim 1 A dual active bridge converter device capable of removing DC bias, comprising: a primary side circuit having a primary switching element; a secondary side circuit having a secondary switching element; a transformer including a series inductor and an inductor block located between the primary side circuit and the secondary side circuit; a controller that removes DC bias in a steady state or transient state by switching the primary switching element and the secondary switching element; and an output current sensor that detects the output current of the output terminal of the secondary side circuit, wherein, in the steady state, the controller obtains an output current (Io) through the output current sensor, obtains a control value (D) from the following mathematical formula using the output current (Io), and removes DC bias by switching the primary switching element and the secondary switching element to any one of a first switching technique, a second switching technique, a third switching technique, or a fourth switching technique according to the control value (D). Here, Io is the output current, Vo is the output voltage, RL is the load-side resistance, n is the transformer ratio, V1 is the transformer primary-side voltage, fs is the switching frequency, ΔQ is the amount of charge transferred by the inductor current during the switching period, Ts is the switching period, φ is the phase difference between the primary and secondary bridges, and L is the inductance of the series inductor. Claim 2 A dual active bridge converter device capable of DC bias removal according to claim 1, wherein the first switching element comprises a first switching element, a second switching element, a third switching element, and a fourth switching element connected in a full-bridge configuration, and the second switching element comprises a fifth switching element, a sixth switching element, a seventh switching element, and an eighth switching element connected in a full-bridge configuration. Claim 3 delete Claim 4 A dual active bridge converter device capable of removing DC bias according to claim 1, wherein the controller, in the event of a transient state, obtains an output current (Io) through the output current sensor, derives the following mathematical formulas through the RPS method, obtains control values ​​(D2, D'2) from the following mathematical formulas using the output current (Io), and removes DC bias by switching the first switching element and the second switching element to any one of the first switching technique, the second switching technique, the third switching technique, and the fourth switching technique according to the control values ​​(D2, D'2). Here, Io is the output current, V2 is the transformer secondary voltage, n is the transformer ratio, V1 is the transformer primary voltage, fs is the switching frequency, ITdc is the DC bias current component, I2 and I4 are the inductor current values ​​during the switching period, D1 is the control value, and L is the inductance of the series inductor. Claim 5 A dual active bridge converter device capable of DC bias removal, wherein, in claim 1 or 4, the first switching technique controls the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be ON, the second switching element (112) and the third switching element (113) to be OFF, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be ON, and the sixth switching element (212) and the seventh switching element (213) to be OFF. Claim 6 A dual active bridge converter device capable of DC bias removal, wherein, in claim 1 or 4, the second switching technique controls the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be ON, the second switching element (112) and the third switching element (113) to be OFF, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be OFF, and the sixth switching element (212) and the seventh switching element (213) to be ON. Claim 7 A dual active bridge converter device capable of DC bias removal, wherein, in claim 1 or 4, the third switching technique controls the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be OFF, the second switching element (112) and the third switching element (113) to be ON, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be ON, and the sixth switching element (212) and the seventh switching element (213) to be OFF. Claim 8 A dual active bridge converter device capable of DC bias removal, wherein, in claim 1 or 4, the fourth switching technique controls the first switching element (111) and the fourth switching element (114) of the first switching element (110) to be OFF, the second switching element (112) and the third switching element (113) to be ON, the fifth switching element (211) and the eighth switching element (214) of the second switching element (210) to be OFF, and the sixth switching element (212) and the seventh switching element (213) to be ON.

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