Method and apparatus for setting air gap and turns ratio of transformer of low voltage DC-DC converter

Abstract

The present disclosure relates to a method and apparatus for setting an air gap and a turns ratio of a transformer of a low-voltage DC-DC converter. The method includes: setting power switching elements based on voltage / current capacity and parasitic capacitance; setting a minimum inductance to ensure zero-voltage switching operation of the power switching elements; adjusting the air gap and the turns ratio in a core region of the transformer based on an input voltage range of the transformer; calculating a leakage inductance of the transformer; comparing the minimum inductance with the leakage inductance; and adaptively performing an adjustment based on a comparison result.

Description

[0001] This application is a divisional application of the application with the filing date of July 17, 2019, application number 201910645666.5, and invention title "Low-Voltage DC-DC Converter and Its Driving Method", the entire content of which is incorporated herein by reference.

[0002] Cross-Reference to Related Applications

[0003] This application claims the priority and benefit of Korean Patent Application No. 2018-0083575 filed on July 18, 2018, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a low-voltage DC-DC converter and a driving method thereof. Background Art

[0005] A low-voltage direct current (DC)-direct current (DC) converter (LDC) is a power supply component that needs to be responsible for supplying power to an electrical load and charging a low-voltage auxiliary battery installed in an eco-friendly vehicle.

[0006] According to the driving method, such low-voltage DC-DC converters are classified into various types, and high power is transformed in a full-bridge manner to perform an isolation switching operation.

[0007] However, during the control switching operation of the power switching element, switching power loss occurs in a conventional LDC.

[0008] Meanwhile, to solve this problem, Korean Unexamined Patent Publication No. 1998-040074 (title: Zero-Voltage Switching DC-DC Buck Converter) discloses a zero-voltage switching technology for a power switching element.

[0009] That is, the prior art uses zero-voltage switching operation to reduce switching power loss.

[0010] However, in the prior art, a zero-voltage switching inductor should be additionally installed to ensure zero-voltage switching operation.

[0011] However, since the zero-voltage switching inductor generates heat during the high-speed switching operation of the power switching element, a heat dissipation structure using a heat sink is required, and a large space is required from the perspective of the system. Summary of the Invention

[0012] The present invention aims to provide a method for setting an air gap and a turns ratio in a core region of a transformer of a low-voltage DC-DC converter, which can reduce the size and cost of a product and increase the power density by increasing an air gap in the core region of the transformer and adjusting the turns ratio of the transformer.

[0013] However, the technical objectives of this embodiment are not limited to the above technical objectives, and there may be other technical objectives.

[0014] According to one aspect of the present invention, a method for setting the air gap and turns ratio in the core region of a transformer of a low-voltage DC-DC converter is provided, including: setting power switch elements based on voltage / current capacity and parasitic capacitance; setting a minimum inductance to ensure zero-voltage switching operation of the power switch elements; adjusting the air gap and turns ratio in the core region of the transformer based on the input voltage range of the transformer; calculating the leakage inductance of the transformer; comparing the minimum inductance with the leakage inductance; and performing the adjustment again based on the comparison result.

[0015] The minimum inductance is set based on the parasitic capacitance of the power switch elements.

[0016] The turns ratio is set based on the primary input current, secondary input current, and magnetizing current of the transformer.

[0017] The air gap in the core region is set based on the magnetizing inductance, primary turns, magnetic resistance of the core region, and magnetic resistance of the air gap.

[0018] The leakage inductance is calculated based on the primary leakage inductance, primary turns, and primary circuit resistance. Description of the Drawings

[0019] By referring to the accompanying drawings and describing in detail the exemplary embodiments of the present invention, the above and other objects, features, and advantages of the present invention will become more apparent to those of ordinary skill in the art, where:

[0020] Figure 1 is a view showing a low-voltage direct current (DC)-DC converter operating in a full-bridge manner according to the prior art;

[0021] Figure 2 is a configuration diagram of a low-voltage DC-DC converter according to an embodiment of the present invention;

[0022] Figure 3 is a view for describing a low-voltage DC-DC converter according to an embodiment of the present invention;

[0023] Figure 4 is a view showing a transformer of a low-voltage DC-DC converter according to an embodiment of the present invention;

[0024] Figure 5 is a flowchart of a method for driving a low-voltage DC-DC converter according to an embodiment of the present invention.

[0025] Figure 6It is a flowchart of a method for setting a transformer of a low-voltage DC-DC converter according to an embodiment of the present invention.

[0026] Figure 7 It is a view showing the internal structure of a transformer of a low-voltage DC-DC converter according to each prior art and an embodiment of the present invention;

[0027] Figure 8A It is a view showing the output waveform of a low-voltage DC-DC converter according to each prior art, Figure 8B It is a diagram showing the output waveform of a low-voltage DC-DC converter according to an embodiment of the present invention; and

[0028] Figure 9 It is a table showing the output values of a low-voltage DC-DC converter according to each prior art and an embodiment of the present invention. Detailed Embodiments

[0029] Hereinafter, embodiments that can be easily implemented by those skilled in the art will be described in detail with reference to the accompanying drawings. However, the embodiments of the present invention can be implemented in several different forms and are not limited to the embodiments described herein. In addition, in order to clearly illustrate the embodiments of the present invention, parts irrelevant to the description are omitted in the drawings.

[0030] Meanwhile, the terms used herein are provided only for the purpose of describing the embodiments of the present invention and not for the purpose of limitation. Unless the context clearly indicates otherwise, the singular forms include the plural forms. It should be understood that when the terms "comprises" and "comprising" are used herein, they specify some stated components, steps, operations, and / or elements, but do not exclude the presence or addition of one or more other components, steps, operations, and / or elements.

[0031] The present invention relates to a low-voltage direct current (DC)-DC converter 100 and a driving method thereof.

[0032] In an eco-friendly vehicle, a low-voltage DC-DC converter is a necessary device for charging a low-voltage auxiliary battery using a high-voltage output from a high-voltage main battery and supplying power to various electrical loads installed in the vehicle. In addition, high-power conversion is performed using a full-bridge method to perform an isolation switching operation.

[0033] Hereinafter, reference will be made to Figure 1 Describe the operation of a conventional low-voltage DC-DC converter.

[0034] Figure 1 It is a view showing a low-voltage DC-DC converter operating in a full-bridge manner according to the prior art.

[0035] In this case, since power losses occur during the operation of the power switching elements Q1, Q2, Q3, and Q4, zero-voltage switching operation is used to minimize the switching power losses.

[0036] Zero-voltage switching operation is a high-speed switching technology for power elements and is an important factor contributing to achieving high efficiency in the field of converters, but a zero-voltage switching inductor Lzvs is required.

[0037] However, since the zero-voltage switching inductor Lzvs generates heat during the switching operation of the power switching elements Q1, Q2, Q3, and Q4, a heat dissipation structure using a heat sink or its cooling system is required, so a large space is required from the perspective of the system, and the size of the product needs to be increased.

[0038] In one embodiment of the present invention, an air gap is added to the core region of the transformer 120, and the turns ratio of the transformer 120 is adjusted to replace the conventional zero-voltage switching inductor.

[0039] Hereinafter, reference will be made to Figures 2 to 4 describe the low-voltage DC-DC converter 100 according to one embodiment of the present invention.

[0040] Figure 2 is a configuration diagram showing the low-voltage DC-DC converter 100 according to one embodiment of the present invention. Figure 3 is a view for describing the low-voltage DC-DC converter 100 according to one embodiment of the present invention. Figure 4 is a view showing the transformer 120 of the low-voltage DC-DC converter 100 according to one embodiment of the present invention.

[0041] As Figure 2 shown, the low-voltage DC-DC converter 100 according to one embodiment of the present invention includes a switch 110, a transformer 120, and a power supply 130.

[0042] The switch 110 converts the high voltage supplied from the high-voltage battery of the vehicle into an AC voltage.

[0043] See Figure 3 , the power switching elements Q1, Q2, Q3, and Q4 are arranged in the switch 110 in a full-bridge manner, and zero-voltage switching operation can be performed using the leakage inductance Llk1 to be described below.

[0044] In addition, the inductor Lzvs installed for zero-voltage switching operation according to the prior art is removed from the switch 110, an air gap is added to the core region of the transformer 120, and its turns ratio is adjusted to replace the primary leakage inductance Llkl of the transformer 120, thereby reducing the material cost and product size. In addition, since the size of the product is reduced, the power density of the product can be increased.

[0045] The transformer 120 reduces the AC voltage output from the switch 110 to a low voltage and transmits the reduced voltage to the power supply 130.

[0046] Reference Figure 4 , since an air gap is added to the core region of the transformer 120, the magnetizing inductance Lm is reduced according to Equation 1.

[0047] [Equation 1]

[0048]

[0049] Here, Lm is the magnetizing inductance of the transformer 120, N1 is the number of primary turns of the transformer 120, Rc is the magnetic resistance of the core region, and Rg is the magnetic resistance of the air gap.

[0050] Since the core of the transformer 120 according to an embodiment of the present invention is formed of a magnetic material and may not perform a normal function when a current exceeding the saturation characteristic inherent in the magnetic material is applied thereto, it is considered that the turns ratio of the transformer 120 reduces the magnetizing current.

[0051] Therefore, by adjusting the turns ratio of the transformer 120, the following effects can be achieved: the magnetizing current im of the transformer 120 is reduced according to Equation 2, and the primary leakage inductance Llkl of the transformer 120 is increased according to Equation 3.

[0052] [Equation 2]

[0053]

[0054] Here, im is the magnetizing current of the transformer 120, i1 is the primary input current of the transformer 120, N1 is the number of primary turns of the transformer 120, N2 is the number of secondary turns of the transformer 120, and i2 is the secondary output current of the transformer 120.

[0055] [Equation 3]

[0056]

[0057] Here, Llkl is the value of the primary leakage inductance of the transformer 120, N1 is the number of primary turns of the transformer 120, and R1 is the primary circuit resistance of the transformer 120.

[0058] The power supply 130 rectifies the low-voltage output from the transformer 120 and supplies the rectified low voltage to the load.

[0059] Hereinafter, a method for driving the low-voltage DC-DC converter 100 will be described with reference to Figure 5 a description of driving the low-voltage DC-DC converter 100.

[0060] Figure 5 FIG. is a flowchart of a method for driving the low-voltage DC-DC converter 100 according to an embodiment of the present invention.

[0061] Referring to Figure 5 , first, in the method for driving the low-voltage DC-DC converter 100, the high voltage supplied from the high-voltage battery of the vehicle is converted into an AC voltage (S110).

[0062] At this time, according to an embodiment of the present invention, the power switch elements may be arranged in a full-bridge manner to convert the high voltage of the vehicle into an AC voltage.

[0063] Then, the AC voltage is reduced to a low voltage using the transformer 120 in which an air gap is added in the core region and the turns ratio is adjusted.

[0064] At this time, since a specific description of adding an air gap in the core region of the transformer 120 and adjusting the turns ratio has been described with reference to Figure 4 Equations 1 to 3 above, the specific description will be omitted below.

[0065] Finally, the low voltage is rectified and supplied to the low-voltage auxiliary battery and the electrical load of the vehicle (S130).

[0066] In the above description, the operations of S110 to S130 may be further divided into additional operations or combined into a reduced number of operations. Additionally, some operations may be omitted as needed, or the order of the operations may also be changed. Additionally, even though Figure 4 other omitted operations described with reference to Figure 5 may also be applied to the method for driving the low-voltage DC-DC converter 100.

[0067] Meanwhile, the transformer 120 of the low-voltage DC-DC converter 100 according to an embodiment of the present invention may be set by Figure 6 a method.

[0068] Figure 6 FIG. is a flowchart of a method for setting the transformer 120 of the low-voltage DC-DC converter 100 according to an embodiment of the present invention.

[0069] Referring to Figure 6, first, set the power switch element (S210) by considering the voltage / current capacity and parasitic capacitance.

[0070] Then, set the value of the minimum inductance Lmin to ensure zero-voltage switching operation (S220).

[0071] Here, the minimum inductance value is the minimum value of the zero-voltage switching inductor to ensure the zero-voltage switching operation of the power switch element, and is set such that the parasitic capacitance of the power switch element is less than the energy stored in the zero-voltage switching inductor.

[0072] Then, according to an embodiment of the present invention, set the turns ratio of the transformer 120 and adjust the air gap (S230).

[0073] At this time, consider the input voltage range to set the turns ratio of the transformer 120 and adjust the air gap in the core region.

[0074] Then, calculate the value of the leakage inductance Llk1 of the transformer 120 using the above equation 3 (S240).

[0075] Then, compare the set value of the minimum inductance Lmin with the calculated value of the leakage inductance Llk1 (S250).

[0076] In the case where the value of the minimum inductance Lmin is less than the value of the leakage inductance Llk1 in the comparison result, the transformer 120 formed under the conditions of a reduced magnetizing current and magnetizing inductance and an increased leakage inductance value is applied to the product (S260).

[0077] On the contrary, in the case where the value of the minimum inductance Lmin is greater than the value of the leakage inductance Llk1, perform the operation S230 of setting the turns ratio and adjusting the air gap again.

[0078] Hereinafter, with reference to Figures 7 to 9 Describe the internal structure of the transformer 120 according to the prior art, the internal structure of the transformer 120 according to an embodiment of the present invention, and the change in the output value according to the increase in the air gap and the adjustment of the turns ratio in the core region of the transformer 120.

[0079] Figure 7 is a view showing the internal structure of the transformer 120 of the low-voltage DC-DC converter 100 according to each of the prior art and an embodiment of the present invention.

[0080] Refer to Figure 7, in an embodiment of the present invention, the zero-voltage switching inductor that was additionally installed in the transformer 120 according to the prior art is removed from the transformer 120, an air gap is added to the core region of the transformer 120, and the turns ratio of the transformer 120 is adjusted to replace the zero-voltage switching inductor. Therefore, compared with the conventional transformer, the number of components can be reduced, thereby reducing the material cost and product size. In addition, since the size of the product is reduced, the power density of the product can be increased.

[0081] Figure 8A is a view showing the output waveforms of the low-voltage DC-DC converters according to the respective prior arts. Figure 8B is a view showing the output waveform of the low-voltage DC-DC converter 100 according to an embodiment of the present invention, and shows results that can be easily compared between multiple execution results. Figure 9 is a table showing the output values of the low-voltage DC-DC converter 100 according to the respective prior arts and an embodiment of the present invention.

[0082] Figure 8A shows the waveform formed using the output values according to the prior art, Figure 8B shows the waveform formed using the output values after adding an air gap to the core region of the transformer 120 and adjusting the turns ratio.

[0083] According to an embodiment of the present invention, the turns ratio can be adjusted to 11:1:1.

[0084] See Figure 9 , the input voltage and input current according to an embodiment of the present invention are the same as the input voltage and input current according to the prior art. The magnetizing inductance of 800 μH according to the prior art is reduced to 210 μH after adding an air gap to the core region of the transformer 120 and adjusting the turns ratio according to an embodiment of the present invention. In addition, the leakage inductance of the transformer 120 increases from 2.8 μH to 4.3 μH.

[0085] In the simulation results, it can be seen that as the magnetizing inductance decreases, the magnetizing current decreases, and the operating performance of the low-voltage DC-DC converter 100 is higher than or equal to the operating performance of the conventional low-voltage DC-DC converter, and since the magnetizing current decreases, the input current decreases compared with the conventional low-voltage DC-DC converter, so that an effect of improved system efficiency can be expected. In addition, it can be seen that a margin of the duty ratio of the transformer 120 can also be ensured.

[0086] According to an embodiment of the present invention, by increasing the air gap in the core region of the transformer and adjusting the turns ratio, the cost and size of the product can be significantly reduced.

[0087] The power density of the low-voltage DC-DC converter can also be increased according to the reduction in the size of the product.

[0088] The above description is merely exemplary, and those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical scope and basic features. Therefore, the above embodiments should be regarded only as examples in all aspects and not for the purpose of limitation. For example, each component described as a single type can be implemented in a distributed manner, and similarly, components described as distributed can be implemented in a coupled manner.

[0089] The scope of the present invention is defined by the appended claims and includes all modifications or variations that come from the meaning, scope, and equivalents of the appended claims.

Claims

1. A method for setting an air gap and a turn ratio in a core region of a transformer of a low-voltage DC-DC converter, the method comprising the following steps: Setting a power switch element based on voltage / current capacity and parasitic capacitance; Setting a minimum inductance to ensure zero-voltage switching operation of the power switch element; Adjusting the air gap and the turn ratio in the core region of the transformer based on the input voltage range of the transformer; Calculating the leakage inductance of the transformer; Comparing the minimum inductance with the leakage inductance; and Performing the adjustment again based on the comparison result, wherein the air gap in the core region is set based on magnetizing inductance, primary turns, reluctance of the core region, and reluctance of the air gap.

2. The method according to claim 1, wherein the turn ratio is set based on the primary input current, secondary input current, and magnetizing current of the transformer.

3. The method according to claim 1, wherein the leakage inductance is calculated based on primary leakage inductance, primary turns, and primary circuit resistance.

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