Control system and method for low voltage DC-DC converter

Abstract

The present invention relates to a control system and method for a low-voltage DC-DC converter, and the control system may include a low-voltage DC-DC converter unit, which includes a power semiconductor element and converts power supplied by a high-voltage battery of a vehicle into low-voltage power. A switching frequency changing unit changes the switching frequency of the power semiconductor element, and a microcomputer generates a final PWM signal based on an input voltage value input from the high-voltage battery and an output voltage value of the switching frequency changing unit to apply a maximum duty cycle command voltage to a PWM controller. The PWM controller applies a PWM voltage to the power semiconductor element to operate the power semiconductor element to work in a manner less than a maximum duty cycle based on the maximum duty cycle command voltage applied from the microcomputer.

Description

Technical Field

[0001] The present invention relates to a control system and method for a low voltage DC-DC converter, and more particularly, to a control system and method for a low voltage DC-DC converter that prevents damage to a clamping capacitor and a power semiconductor in the low voltage DC-DC converter when a control abnormality caused by interference or the like occurs. Background Art

[0002] A low voltage DC-DC converter (LDC) that powers an auxiliary battery and electric field loads of an environmentally friendly vehicle needs to have a high power density because it is installed in the engine room of the vehicle, and needs to have a high efficiency because the efficiency of the LDC directly affects the vehicle fuel efficiency. Therefore, research on LDC has been actively carried out.

[0003] Traditionally, various topologies have been studied to meet the high power density and high efficiency of LDCs. Recently, Figure 1 The active clamp forward (ACF) converter shown in FIG. 1 has a reduced component count, zero volt switching (ZVS) characteristics, and low conduction loss. However, the conventional ACF converter has a high voltage stress because the input voltage and the clamp capacitor C C The voltage of is applied to the switching element due to the structure of the active clamp. In addition, when the switching duty ratio of the switching elements S1 and S2 increases due to a control failure caused by interference, etc., the voltage of the clamp capacitor increases, so that the voltage applied to the clamp capacitor and the switching element exceeds the withstand voltage and may cause damage to the LDC.

[0004] Meanwhile, in order to protect the clamping capacitor and the switching element of the ACF converter in the conventional technology, a method of limiting the maximum switching duty cycle of the switching element has been developed. However, according to the conventional method, since the maximum duty cycle limit value is fixed even when the input voltage changes, when a control failure occurs due to interference, etc. at a high input voltage, the switching element may operate at the maximum duty cycle. Therefore, the voltage may exceed the withstand voltage of the clamping capacitor and the switching element, which may cause damage to the corresponding elements. Therefore, it is necessary to develop a technology that can prevent damage to the clamping capacitor and the switching element in the LDC even when a control abnormality occurs due to interference, etc. Summary of the invention

[0005] The present invention provides a control system and method for a low voltage DC-DC converter (LDC), which limits the maximum duty cycle of the switch of the power semiconductor element of the LDC based on the input voltage input from the high voltage battery and the output voltage of the switching frequency change unit, thereby preventing the clamping capacitor and the power semiconductor in the LDC from being damaged even when a control abnormality occurs due to interference or the like.

[0006] In order to achieve the above-mentioned objectives, according to the present invention, a control system of a low-voltage DC-DC converter (LDC) may include: a low-voltage DC-DC converter unit, which includes a power semiconductor element and is configured to convert power supplied by a high-voltage battery of a vehicle into low-voltage power; a switching frequency changing unit, which is configured to change the switching frequency of the power semiconductor element; a microcomputer, which is configured to generate a final pulse width modulation (PWM) signal based on an input voltage value input from the high-voltage battery and an output voltage value of the switching frequency changing unit to apply a maximum duty cycle command voltage to a PWM IC; and a PWM IC (e.g., a PWM controller), which is configured to apply a PWM voltage to the power semiconductor element to prevent the power semiconductor element from exceeding a maximum duty cycle based on the maximum duty cycle command voltage applied from the microcomputer.

[0007] The microcomputer may include: a temporary PWM signal generating unit configured to generate a duty cycle of a temporary PWM signal, the duty cycle of the temporary PWM signal being used to generate a maximum duty cycle command voltage input to the PWM IC based on an input voltage input from a high voltage battery; a PWM adjustment factor generating unit configured to generate an adjustment factor value based on an output voltage of the switching frequency changing unit; a multiplier configured to multiply the duty cycle of the temporary PWM signal generated in the temporary PWM signal generating unit by the adjustment factor value generated in the PWM adjustment factor generating unit; and a final PWM signal generating unit configured to generate the maximum duty cycle command voltage based on a result of a multiplication operation by the multiplier.

[0008] The system may further include a storage unit configured to store duty cycle information and factor value information of a PWM signal, the duty cycle information of the PWM signal being used to generate a maximum duty cycle command voltage input to the PWMIC by an input voltage input from a high-voltage battery, and the factor value information being used to eliminate a maximum duty cycle change portion of the power semiconductor element based on an output voltage of the switching frequency change unit. The microcomputer may be configured to: derive a duty cycle value and a factor value of a temporary PWM signal based on an input voltage value input from a high-voltage battery, an output voltage value of the switching frequency change unit, and information stored in the storage unit, the duty cycle value of the temporary PWM signal being used to generate a maximum duty cycle command voltage input to the PWMIC based on an input voltage, and the factor value being based on the output voltage of the switching frequency change unit; and generate a final PWM signal for generating a maximum duty cycle command voltage based on the duty cycle value of the temporary PWM signal and the above-derived factor value, thereby applying the maximum duty cycle command voltage to the PWM IC.

[0009] The maximum duty cycle command voltage may be a voltage value for limiting the maximum duty cycle of the power semiconductor element. In addition, the system may include a filter unit, which is disposed between the microcomputer and the PWM IC and configured to smooth the voltage output from the microcomputer. The system may further include a voltage sensor configured to detect the voltage input from the high voltage battery and the voltage output from the switching frequency changing unit, respectively. The microcomputer is configured to generate a final PWM signal for generating a maximum duty cycle command voltage by multiplying a duty cycle value of a temporary PWM signal for generating a maximum duty cycle command voltage input to the PWM IC according to an input voltage by a factor value based on the output voltage of the switching frequency changing unit.

[0010] In order to achieve the above-mentioned another object, according to the present invention, a control method of an LDC may include: detecting a voltage input from a high-voltage battery and a voltage output from a switching frequency changing unit; deriving a duty cycle value of a temporary PWM signal for generating a maximum duty cycle command voltage input to a PWM IC according to the input voltage value based on an input voltage value input from the high-voltage battery and information stored in a storage unit; deriving a factor value based on the output voltage of the switching frequency changing unit based on an output voltage value of the switching frequency changing unit and information stored in the storage unit; generating a final PWM signal for generating a maximum duty cycle command voltage based on the duty cycle value of the temporary PWM signal and the above-derived factor value, thereby applying the maximum duty cycle command voltage to the PWM IC; and operating a power semiconductor element based on the applied maximum duty cycle command voltage without exceeding the maximum duty cycle.

[0011] Before detecting the voltage input from the high-voltage battery and the voltage output from the switching frequency changing unit, the method may further include storing duty cycle information and factor value information of the PWM signal, the duty cycle information of the PWM signal being used to generate a maximum duty cycle command voltage input to the PWM IC by the input voltage input from the high-voltage battery, and the factor value information being used to eliminate a maximum switching duty cycle change portion of the power semiconductor element based on the output voltage of the switching frequency changing unit. When generating the final PWM signal, the final PWM signal for generating the maximum duty cycle command voltage is generated by multiplying the duty cycle value of the temporary PWM signal by the factor value, the duty cycle value of the temporary PWM signal being used to generate the maximum duty cycle command voltage input to the PWM IC based on the input voltage, and the factor value being based on the output voltage of the switching frequency changing unit.

[0012] According to the present invention, by limiting the maximum duty cycle of the switch of the power semiconductor element of the LDC based on the input voltage input from the high-voltage battery and the output voltage of the switching frequency changing unit, damage to the clamping capacitor and the power semiconductor in the LDC can be prevented even when a control abnormality occurs due to interference, etc. In addition, by eliminating the maximum duty cycle change portion of the power semiconductor element according to the output voltage of the switching frequency changing unit and by increasing the operating duty cycle of the LDC, a higher output can be ensured. In addition, when the voltage range of the high-voltage battery is changed according to the vehicle type, there is no need to redesign the LDC and the power semiconductor element, so that a unified LDC can be used in various types of vehicles. Therefore, the manufacturing cost of the LDC can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and other advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1 is a schematic diagram illustrating a conventional ACF converter according to the prior art;

[0015] Figure 2 is a block diagram schematically illustrating a structure of a control system of an LDC according to an exemplary embodiment of the present invention;

[0016] Figure 3 is a circuit diagram of a switching frequency changing unit in a control system of an LDC according to an exemplary embodiment of the present invention;

[0017] Figure 4 is a table including duty ratio information of a PWM signal, wherein the duty ratio information stored in the storage unit is used to generate a maximum duty ratio command voltage input to a PWM IC by an input voltage input from a high voltage battery in a control system of an LDC according to an exemplary embodiment of the present invention;

[0018] Figure 5 is a table including factor value information stored in a storage unit of a control system of an LDC according to an exemplary embodiment of the present invention, the factor value information being used to eliminate a maximum duty ratio change portion of a power semiconductor element according to an output voltage of a switching frequency change unit;

[0019] Figure 6 is a graph illustrating a PWM IC output maximum limit duty cycle, a power semiconductor element reference maximum limit duty cycle, and a power semiconductor element reference operating duty cycle based on a change in a switching frequency of a power conversion element in a conventional control system according to an LDC in the prior art;

[0020] Figure 7 is a graph illustrating a PWM IC output maximum limit duty ratio, a power semiconductor element reference maximum limit duty ratio, and a power semiconductor element reference operating duty ratio based on a change in a switching frequency of a power conversion element in a control system according to an exemplary embodiment of the present invention;

[0021] Figure 8 is a flowchart illustrating the flow of a control method of an LDC according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0022] It should be understood that the term "vehicle" or "vehicle-based" or other similar terms used herein generally include motor vehicles, such as passenger cars including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, ships including various boats, vessels, aircraft, etc., and include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources). As referred to herein, a hybrid vehicle is a vehicle having two or more power sources, such as both gasoline-powered and electric-powered vehicles.

[0023] Although the exemplary embodiments are described as using multiple units to perform the exemplary processes, it is understood that the exemplary processes can also be performed by one or more modules. In addition, it is understood that the term "controller / control unit" refers to a hardware device including a memory and a processor. The memory is configured to store the modules, and the processor is specifically configured to execute the modules to perform one or more processes further described below.

[0024] In addition, the control logic of the present invention can be implemented as a non-volatile computer-readable medium, which is a computer-readable medium including executable program instructions executed by a processor, a controller / control unit, etc. Examples of computer-readable media include, but are not limited to: ROM, RAM, compact disk (CD)-ROM, magnetic tape, floppy disk, flash drive, smart card, and optical data storage device. The computer-readable recording medium can also be distributed in a network-coupled computer system so that the computer-readable medium is stored and executed in a distributed form (for example, through a telematics server or a controller area network (CAN)).

[0025] The terms used in this article are only used to describe specific embodiments, and are not intended to limit the present invention. As used herein, the singular forms "a", "one" and "said" are intended to include plural forms as well, unless the context clearly indicates that plural forms are not included. It will also be further understood that when the terms "include" and / or "include" are used in this book, it is indicated that there are the features, numerical values, steps, operations, elements and / or components, but it is not excluded that there are or add one or more other features, integral bodies, steps, operations, elements, components and / or their groups. As used herein, the term "and / or" includes any and all combinations of one or more related enumeration items.

[0026] Unless otherwise stated or clearly indicated from the context, the term "approximately" as used herein is understood to be within the normal permissible range in the art, such as within 2 standard deviations of the mean value. "Approximately" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% or 0.01% of the value. Unless the context indicates otherwise, the term "approximately" modifies all numerical values ​​provided herein.

[0027] Hereinafter, a control system and method of a low voltage DC-DC converter (LDC) according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0028] Figure 2 is a block diagram schematically illustrating a structure of a control system of an LDC according to an exemplary embodiment of the present invention, Figure 3 is a circuit diagram of a switching frequency changing unit in a control system of an LDC according to an exemplary embodiment of the present invention, Figure 4 is a table including duty cycle information of a PWM signal, wherein the duty cycle information stored in the storage unit is used to generate a maximum duty cycle command voltage input to a PWM IC using an input voltage input from a high voltage battery in a control system of an LDC according to an exemplary embodiment of the present invention, Figure 5is a table including factor value information stored in a storage unit of a control system of an LDC according to an exemplary embodiment of the present invention, the factor value information being used to eliminate a maximum duty ratio change portion of a power semiconductor element according to an output voltage of a switching frequency change unit.

[0029] like Figure 2 As shown in FIG. 1 , the control system of the LDC according to the exemplary embodiment of the present invention may include: an LDC unit 100, a switching frequency changing unit 300, a microcomputer 500, and a PWM IC 600, and may include a storage unit 400. Specifically, the LDC unit 100 may include a power semiconductor element 110 and may be configured to convert power supplied from a high-voltage battery 200 of a vehicle into low-voltage power. According to an exemplary embodiment, the power semiconductor element 110 may be a field effect transistor (FET), and in the present invention, other power semiconductor elements may be used as power semiconductors.

[0030] In addition, the high-voltage battery 200 is a high-output and large-capacity battery that can be configured to supply power for driving the motor, and can be configured to supply power for charging the auxiliary battery and supply power to the vehicle electric field load. The high-voltage battery 200 may include a plurality of battery cells. Therefore, the high-voltage battery 200 can be configured to output high-voltage power of several hundred volts or more by taking the sum of the output voltages of the battery cells as the output voltage. More specifically, the LDC unit 100 can be configured to convert the power supplied from the high-voltage battery 200 into a low voltage to provide power to at least one of the auxiliary battery (not shown) and the electric load (not shown) of the vehicle. For example, when a 12V auxiliary battery and an electric load are used in the vehicle, the LDC unit 100 can be configured to reduce the high voltage of the power supplied from the high-voltage battery 200 to 12V, and provide power to the auxiliary battery and the electric field load.

[0031] The switching frequency changing unit 300 may be configured to change the switching frequency of the power semiconductor element 110 to reduce the switching noise of the power semiconductor element 110 in the LDC unit 100. Specifically, the switching frequency changing unit 300 of the present invention may be used as a Figure 3 In addition, according to an exemplary embodiment, the switching frequency changing unit 300 may be a spread spectrum frequency modulation (SSFM) device. Since the SSFM device and the relaxation oscillator are well-known technologies, their detailed description will be omitted.

[0032] The duty cycle information and factor value information of the PWM signal can be stored in the storage unit 400, the duty cycle information of the PWM signal is used to generate the maximum duty cycle command voltage input to the PWM IC 600 through the input voltage input from the high voltage battery 200, and the factor value information is used to eliminate the maximum duty cycle change part of the power semiconductor element 110 according to the output voltage of the switching frequency change unit 300. Specifically, as Figure 4 As shown in FIG. 1 , the input voltage (V in ) to generate the duty cycle (D temp ) information can be stored in the storage unit 400.

[0033] Specifically, the table includes duty cycle information of the PWM signal, which is stored in the storage unit 400 for generating a maximum duty cycle command voltage by means of an input voltage input from the high-voltage battery 200. The table can be generated based on the following operations: selecting a maximum operating duty cycle of the power semiconductor element 110 capable of generating a maximum output or a rated output while taking into account the withstand voltage specifications of the clamping capacitor (not shown) in the LDC 100 and the power semiconductor element 110 when controlling the duty cycle margin; deriving a final maximum output duty cycle of the PWM IC 600 by means of the input voltage (which includes a duty cycle loss between the PWM IC 600 and the power semiconductor element 110); and deriving a maximum duty cycle command voltage value applied to the PWM IC 600 by means of the input voltage input from the high-voltage battery 200.

[0034] In addition, the maximum duty cycle instruction voltage in the present invention may be a voltage value for limiting the maximum duty cycle, and the power semiconductor element 110 operates at this value. Figure 5 As shown in FIG. 4 , factor value information for eliminating the maximum duty ratio change portion of the power semiconductor element 110 according to the output voltage of the switching frequency changing unit 300 may be stored in the storage unit 400. Specifically, the switching frequency of the power semiconductor element 110 may be changed according to the output voltage of the switching frequency changing unit 300. For example, when the output voltage of the switching frequency changing unit 300 is large, the switching frequency of the power semiconductor element 110 may be reduced, and when the output voltage of the switching frequency changing unit 300 is small, the switching frequency of the power semiconductor element 110 may be increased.

[0035] In addition, as described above, when the output voltage of the switching frequency changing unit 300 changes, the switching frequency of the power semiconductor element 110 may change, and when the switching frequency of the power semiconductor element 110 changes, the maximum duty cycle value of the power semiconductor element 110 may change. In other words, when the output voltage of the switching frequency changing unit 300 changes, the maximum duty cycle value of the power semiconductor element 110 may change. Therefore, the voltage applied to the power semiconductor element 110 and the clamping capacitor (not shown) in the LDC 100 may be affected. In severe cases, the power semiconductor element 110, the clamping capacitor (not shown), etc. may burn out or be damaged in other ways. Figure 5 As shown in , in the present invention, a factor value for eliminating a maximum duty cycle change portion of the power semiconductor element 110 based on an output voltage value of the switching frequency changing unit 300 can be stored in the storage unit 400, and when a final PWM signal is generated in the microcomputer 500 as described below, the stored factor value can be utilized.

[0036] The microcomputer 500 (e.g., a processor) may be configured to generate a final PWM signal based on an input voltage value input from the high voltage battery 200 and an output voltage value of the switching frequency changing unit 300, thereby applying a maximum duty cycle command voltage to the PWM IC. Specifically, the microcomputer 500 may include: a temporary PWM signal generating unit 510 configured to generate a duty cycle of a temporary PWM signal for generating a maximum duty cycle command voltage input to the PWM IC based on an input voltage input from the high voltage battery 200; a PWM adjustment factor generating unit 520 configured to generate an adjustment factor value based on the output voltage of the switching frequency changing unit 300; a multiplier 530 configured to multiply the duty cycle of the temporary PWM signal generated in the temporary PWM signal generating unit 510 by the adjustment factor value generated in the PWM adjustment factor generating unit 520; and a final PWM signal generating unit 540 configured to generate a maximum duty cycle command voltage based on a result of a multiplication operation by the multiplier 530.

[0037] In addition, the microcomputer 500 including the above-mentioned structure may be configured to generate a duty cycle value of a temporary PWM signal for generating a maximum duty cycle command voltage input to the PWM IC 600 according to an input voltage value input from the high voltage battery 200 and the information stored in the storage unit 400. Figure 4For example, when the input voltage input from the high voltage battery 200 is about 180V, the microcomputer 500 may be configured to generate a PWM signal having a duty cycle of about 38.1%, and thus may generate a maximum duty cycle command voltage input to the PWM IC 600. According to another exemplary embodiment, when the input voltage input from the high voltage battery 200 is about 310V, the microcomputer 500 may be configured to generate a PWM signal having a duty cycle of about 56.2%, and thus may generate a maximum duty cycle command voltage input to the PWM IC 600.

[0038] In addition, the microcomputer 500 may be configured to derive an adjustment factor value according to the output voltage of the switching frequency changing unit 300 and information previously stored in the storage unit 400. Figure 5 For example, when the output voltage value of the switching frequency changing unit 300 is about 1.5V, the microcomputer 500 can be configured to obtain a factor value of about 1.06, and when the output voltage of the switching frequency changing unit 300 is about 3.5V, the microcomputer 500 can be configured to obtain a factor value of about 0.94.

[0039] In addition, the microcomputer 500 may be configured to generate a final PWM signal for generating a maximum duty cycle command voltage based on the duty cycle of the temporary PWM signal and the adjustment factor value obtained according to the above method, thereby applying the maximum duty cycle command voltage to the PWM IC 600. Specifically, the microcomputer 500 may be configured to generate a final PWM signal for generating the maximum duty cycle command voltage by multiplying the duty cycle value of the temporary PWM signal (which is used to generate the maximum duty cycle command voltage input to the PWM IC 600 based on the input voltage) by the adjustment factor value based on the output voltage of the switching frequency changing unit 300.

[0040] The PWM IC 600 may be configured to apply a PWM voltage to the power semiconductor element 110, and thus the power semiconductor element 110 of the LDC 100 may operate without exceeding the maximum duty cycle based on the maximum duty cycle command voltage applied from the microcomputer 500. In the present invention, the microcomputer 500 may be configured to generate a maximum duty cycle command voltage that limits the maximum duty cycle of the operation of the power semiconductor element 110 based on the input voltage input from the high-voltage battery 200 and the output voltage of the switching frequency changing unit 300, and may be configured to apply the maximum duty cycle command voltage to the PWM IC 600. Then, the PWM IC 600 may be configured to operate the power semiconductor element 110 without exceeding the maximum duty cycle based on the maximum duty cycle command voltage applied thereto. Therefore, even when a control failure occurs due to interference or the like at a high input voltage from the high-voltage battery 200, the power semiconductor element 110 may operate without exceeding the maximum duty cycle (for example, it may operate at a less than maximum duty cycle). Therefore, the clamping capacitor and the power semiconductor element 110 in the LDC may be prevented from exceeding their withstand voltage and being damaged.

[0041] In addition, the control system of the LDC according to the exemplary embodiment of the present invention may further include a filter unit 700, which is provided between the microcomputer 500 and the PWM IC 600 and is configured to smooth the maximum duty cycle command voltage output from the microcomputer 500. At this time, according to the exemplary embodiment, the maximum duty cycle command voltage output from the microcomputer 500 may be a 5-volt PWM voltage having a final PWM signal for generating the maximum command voltage. In addition, the 5-volt PWM voltage having the final PWM signal output from the microcomputer 500 may be smoothed by the filter unit 700 (for example, noise, abnormal values, etc. may be removed) and applied to the PWM IC 600 with a direct current (DC) voltage. In addition, the control system of the LDC according to the exemplary embodiment of the present invention may further include a voltage sensor 800, which is configured to detect the voltage input from the high-voltage battery 200 and the voltage output from the switching frequency changing unit 300, respectively.

[0042] also, Figure 6 is a graph illustrating a PWM IC output maximum limit duty cycle, a power semiconductor element reference maximum limit duty cycle, and a power semiconductor element reference operating duty cycle based on a change in switching frequency of a power conversion element in a conventional control system according to the prior art LDC. Figure 7 is a graph illustrating a PWM IC output maximum limit duty ratio, a power semiconductor element reference maximum limit duty ratio, and a power semiconductor element reference operating duty ratio based on a change in a switching frequency of a power conversion element in a control system according to an exemplary embodiment of the present invention.

[0043] like Figure 6 and Figure 7 As shown in, based on the control system of the LDC according to the present invention, by limiting the maximum duty cycle of the power semiconductor element 110 according to the input voltage input from the high-voltage battery 200, even in the case of a control failure due to interference or the like when a high input voltage is input from the high-voltage battery 200, the power semiconductor element 110 can operate without exceeding the maximum duty cycle. Therefore, the clamping capacitor and the power semiconductor element 110 in the LDC can be prevented from exceeding their withstand voltage and being damaged. In addition, by eliminating the change portion of the maximum duty cycle of the operation of the power semiconductor element 110 according to the output voltage of the switching frequency changing unit 300 and by increasing the maximum operable duty cycle of the LDC, a higher output than the conventional output can be ensured, so that the output of the LDC can be ensured in a state where the voltage of the high-voltage battery is low.

[0044] Figure 8 1 is a flow chart illustrating the process of a control method of an LDC according to an exemplary embodiment of the present invention. The method described below may be executed by a processor of a controller. Figure 8 As shown in , a control method of an LDC according to an exemplary embodiment of the present invention may include: detecting a voltage input from a high-voltage battery and a voltage output from a switching frequency changing unit; deriving a duty cycle value of a temporary PWM signal for generating a maximum duty cycle command voltage input to a PWM IC according to the input voltage value based on an input voltage value input from the high-voltage battery and information stored in a storage unit; deriving a factor value according to an output voltage of the switching frequency changing unit and information stored in the storage unit; generating a final PWM signal for generating a maximum duty cycle command voltage based on the duty cycle value of the temporary PWM signal and the above-derived factor value, thereby applying the maximum duty cycle command voltage to the PWM IC; and operating a power semiconductor element without exceeding the maximum duty cycle based on the maximum duty cycle command voltage applied to the PWM IC.

[0045] In addition, before detecting the voltage input from the high-voltage battery and the voltage output from the switching frequency changing unit, the control method of the LDC according to the exemplary embodiment of the present invention may further include: storing the duty cycle information and factor value information of the PWM signal, the duty cycle information of the PWM signal is used to generate the maximum duty cycle command voltage input to the PWMIC by the input voltage input from the high-voltage battery, and the factor value information is used to eliminate the maximum switching duty cycle change part of the power semiconductor element according to the output voltage of the switching frequency changing unit. In addition, when generating the final PWM signal, the final PWM signal for generating the maximum duty cycle command voltage can be generated by multiplying the duty cycle value of the temporary PWM signal (which is used to generate the maximum duty cycle command voltage input to the PWM IC according to the input voltage) by the factor value based on the output voltage of the switching frequency changing unit.

[0046] The technical features in the detailed steps of the control method of the LDC according to the present invention are the same as the technical features of the detailed structure in the control system of the LDC according to the present invention described above, so the detailed description thereof will be omitted.

Claims

1. A control system for a low voltage DC-DC converter, comprising: a low-voltage DC-DC converter unit including a power semiconductor element and configured to convert power supplied from a high-voltage battery of the vehicle into low-voltage power; a switching frequency changing unit configured to change the switching frequency of the power semiconductor element; as well as a microcomputer configured to generate a final pulse width modulation signal based on an input voltage value input from a high voltage battery and an output voltage value of a switching frequency changing unit to apply a maximum duty cycle command voltage to a pulse width modulation controller, The pulse width modulation controller is configured to apply a pulse width modulation voltage to the power semiconductor element to drive the power semiconductor element to operate in a manner less than a maximum duty cycle based on a maximum duty cycle instruction voltage applied from a microcomputer.

2. The control system of the low voltage DC-DC converter according to claim 1, wherein: The microcomputer comprises: a temporary pulse width modulation signal generating unit configured to generate a duty cycle of a temporary pulse width modulation signal, the duty cycle of the temporary pulse width modulation signal being used to generate a maximum duty cycle command voltage input to the pulse width modulation controller based on an input voltage input from a high voltage battery; a pulse width modulation adjustment factor generating unit configured to generate an adjustment factor value based on an output voltage of the switching frequency changing unit; a multiplier configured to multiply the duty cycle of the temporary pulse width modulation signal generated in the temporary pulse width modulation signal generating unit by the adjustment factor value generated in the pulse width modulation adjustment factor generating unit; and The final pulse width modulation signal generating unit is configured to generate a maximum duty ratio command voltage based on a result of the multiplication operation by the multiplier.

3. The control system of the low voltage DC-DC converter according to claim 1, further comprising: A storage unit is configured to store duty cycle information and factor value information of a pulse width modulation signal, wherein the duty cycle information of the pulse width modulation signal is used to generate a maximum duty cycle command voltage input to a pulse width modulation controller by an input voltage input from a high voltage battery, and the factor value information is used to eliminate a maximum duty cycle change portion of a power semiconductor element based on an output voltage of a switching frequency change unit.

4. The control system of the low voltage DC-DC converter according to claim 3, wherein: The microcomputer is configured as follows: deriving a duty cycle value and a factor value of a temporary pulse width modulation signal based on an input voltage value input from a high voltage battery, an output voltage value of a switching frequency changing unit, and information stored in a storage unit, wherein the duty cycle value of the temporary pulse width modulation signal is used to generate a maximum duty cycle command voltage input to a pulse width modulation controller based on the input voltage, and the factor value is based on the output voltage of the switching frequency changing unit; A final pulse width modulation signal for generating a maximum duty cycle command voltage based on the duty cycle value of the temporary pulse width modulation signal and the derived factor value is generated, thereby applying the maximum duty cycle command voltage to the pulse width modulation controller.

5. The control system of the low voltage DC-DC converter according to claim 1, wherein: The maximum duty cycle instruction voltage is a voltage value used to limit the maximum duty cycle of the power semiconductor element.

6. The control system of the low voltage DC-DC converter according to claim 1, further comprising: A filter unit is provided between the microcomputer and the pulse width modulation controller and is configured to smooth a voltage output from the microcomputer.

7. The control system of the low voltage DC-DC converter according to claim 1, further comprising: A voltage sensor is configured to detect a voltage input from the high voltage battery and a voltage output from the switching frequency changing unit, respectively.

8. The control system of the low voltage DC-DC converter according to claim 1, wherein: The microcomputer is configured to generate a final pulse width modulation signal for generating a maximum duty ratio command voltage by multiplying a duty ratio value of a temporary pulse width modulation signal for generating a maximum duty ratio command voltage input to the pulse width modulation controller according to an input voltage by a factor value based on an output voltage of a switching frequency changing unit.

9. A control method for a low voltage DC-DC converter, comprising: detecting, by a processor, a voltage input from a high voltage battery and a voltage output from a switching frequency changing unit; Based on the input voltage value input from the high voltage battery and the information stored in the storage unit, the processor derives the duty cycle value of the temporary pulse width modulation signal, and the duty cycle value of the temporary pulse width modulation signal is used to generate a maximum duty cycle command voltage input to the pulse width modulation controller according to the input voltage value; deriving the factor value by the processor based on the output voltage of the switching frequency changing unit and the information stored in the storage unit; generating, by the processor, a final pulse width modulation signal for generating a maximum duty cycle command voltage based on the duty cycle value of the temporary pulse width modulation signal and the derived factor value, thereby applying the maximum duty cycle command voltage to the pulse width modulation controller; Based on the maximum duty cycle command voltage applied to the pulse width modulation controller, the processor operates the power semiconductor element to be driven at a duty cycle less than the maximum duty cycle.

10. The method according to claim 9, wherein: Before detecting the voltage input from the high voltage battery and the voltage output from the switching frequency change unit: A processor is used to store duty cycle information and factor value information of a pulse width modulation signal, wherein the duty cycle information of the pulse width modulation signal is used to generate a maximum duty cycle command voltage input to a pulse width modulation controller through an input voltage input from a high-voltage battery, and the factor value information is used to eliminate the maximum switching duty cycle change portion of the power semiconductor element according to the output voltage of the switching frequency change unit.

11. The method according to claim 9, wherein: When generating a final pulse width modulation signal, the final pulse width modulation signal for generating a maximum duty cycle command voltage is generated by multiplying the duty cycle value of the temporary pulse width modulation signal by a factor value, wherein the duty cycle value of the temporary pulse width modulation signal is used to generate the maximum duty cycle command voltage input to the pulse width modulation controller according to the input voltage, and the factor value is based on the output voltage of the switching frequency changing unit.

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