Protection circuit, DC-DC converter, battery charger and electric vehicle

Abstract

A protection circuit according to the present invention is for a DC-DC converter including a buck switch connected between a voltage input terminal and a first node and controlled by a switching period and a duty cycle of a switching signal, a buck inductor connected between the first node and a voltage output terminal, a buck capacitor connected between the voltage output terminal and ground, and a buck diode connected between a second node and the ground. The protection circuit is connected to the first node, the second node, and the ground. When the buck switch is switched between an on state and an off state in accordance with the switching signal, the protection circuit applies a protection voltage between the first node and the ground so that a voltage stress on the buck switch is smaller than an input voltage applied between the voltage input terminal and the ground.

Description

[Technical field]

[0001] The present invention relates to a technique for protecting a DC-DC converter from switching losses.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0111845, filed on September 2, 2020, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings. [Background technology]

[0003] In recent years, as the demand for portable electronic products such as laptops, video cameras, and mobile phones has grown rapidly and the development of electric vehicles, energy storage batteries, robots, and artificial satellites has accelerated, active research is being conducted on high-performance batteries that can be repeatedly charged and discharged.

[0004] Currently, various types of batteries, including nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium batteries, are commercially available. Among them, lithium batteries are attracting attention due to their advantages over nickel-based batteries, such as almost no memory effect, easy charging and discharging, a very low self-discharge rate, and a high energy density.

[0005] The electric vehicle includes a battery and a battery charger. When the battery charger is connected to an external power source through a charging cable, the battery charger generates charging power for the battery using power input from the external power source. In general, the battery charger includes a DC-DC converter that generates an output voltage that is smaller than the input voltage.

[0006] In recent years, in line with the trend toward weight reduction in electric vehicles, there is an increasing demand for lighter and smaller DC-DC converters. In order to reduce the size and weight of a DC-DC converter, the switching frequency of a switching signal must be increased rather than reducing the size of each physical element included in the DC-DC converter.

[0007] FIG 1 is a schematic diagram of a typical step-down DC-DC converter. Referring to FIG 1, the DC-DC converter has a voltage input terminal N i and the first node N 1 The buck switch SW connected between B and the first node N 1 and voltage output terminal N o The back inductor L connected between B and voltage output terminal N o A back capacitor C connected between B and the first node N 1 A back diode D is connected between B and, Buck switch SW B When the buck diode D B is turned on, and the first node N 1 A voltage substantially equal to 0 V is applied between the buck switch SW B When the buck diode D B is turned off, and the first node N i Between the input and ground, there is an input voltage V in As a result, the buck switch SW B Each time the is switched between the on and off states, the input voltage V in The voltage stress on the buck switch SW B It occurs towards both ends of the

[0008] However, because the switching loss of a DC-DC converter is proportional to the voltage stress, when the switching frequency increases, the power efficiency of the DC-DC converter decreases and the DC-DC converter may overheat. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above problems, and has an object to provide a protection circuit for protecting a DC-DC converter from switching loss, a battery charger including the protection circuit, and an electric vehicle including the battery charger.

[0010] Other objects and advantages of the present invention can be understood from the following description and will become more apparent from the embodiments of the present invention. Also, the objects and advantages of the present invention can be realized by the means and combinations thereof as set forth in the claims. [Means for solving the problem]

[0011] According to an aspect of the present invention, a protection circuit is provided for a DC-DC converter. The DC-DC converter includes a buck switch connected between a voltage input terminal and a first node and controlled by a switching period and a duty ratio of a switching signal, a buck inductor connected between the first node and a voltage output terminal, a buck diode connected between a second node and ground, and a buck capacitor connected between the voltage output terminal and the ground. The protection circuit is connected to the first node, the second node, and the ground. The protection circuit is configured to apply a protection voltage between the first node and the ground when the buck switch is switched between an on state and an off state according to the switching signal, such that a voltage stress of the buck switch is smaller than an input voltage applied between the voltage input terminal and the ground.

[0012] The protection circuit includes a first protection capacitor connected between the first node and the second node, a second protection capacitor connected between a third node and the ground, a protection inductor connected between the second node and the third node, and a protection diode connected between the first node and the third node.

[0013] The protection diode is maintained in an off state during a first period when the buck switch is in an on state, and the protection diode is maintained in an on state during a second period when the buck switch is in an off state.

[0014] The protection voltage may be equal to a voltage of a series circuit of the first protection capacitor and the back diode.

[0015] A voltage of a series circuit of the first protection capacitor, the protection inductor and the second protection capacitor may be equal to a sum of a voltage of the buck inductor and an output voltage during a first period in which the buck switch is in an on state, the output voltage being a voltage between the voltage output terminal and the ground.

[0016] The voltage of the first protection capacitor may be equal to the voltage of the series circuit of the protection inductor and the protection diode during a second time period when the buck switch is in an off state.

[0017] The voltage of the second protection capacitor may be equal to the voltage of the series circuit of the protection inductor and the buck diode during a second time period when the buck switch is in an off state.

[0018] A DC-DC converter according to another aspect of the present invention includes the above-mentioned protection circuit.

[0019] A battery charger according to yet another aspect of the present invention includes the above-mentioned DC-DC converter.

[0020] According to yet another aspect of the present invention, an electric vehicle includes the battery charger described above, and a battery connected between the voltage output terminal and ground. Effect of the Invention

[0021] According to an embodiment of the present invention, it is possible to reduce switching loss of a buck switch included in a DC-DC converter without using an additional switch that requires separate on / off control.

[0022] In addition, since the switching frequency can be increased in response to the reduction in switching loss of the buck switch, the DC-DC converter can be made lighter and more compact.

[0023] The effects of the present invention are not limited to the effects described above, and other effects of the present invention not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0024] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention described below, serve to further understand the technical ideas of the present invention. Therefore, the present invention should not be interpreted as being limited only to the matters described in the drawings. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram illustrating a general step-down DC-DC converter. [Diagram 2] 1 is a diagram showing an example of the configuration of an electric vehicle according to the present invention; [Diagram 3] 1 is a diagram illustrating an example of a configuration of a battery charger according to the present invention; [Figure 4] 4 is a diagram illustrating an example of the configuration of the DC-DC converter of FIG. 3. [Diagram 5] FIG. 5 is a schematic diagram illustrating the current waveforms of each component and the voltage waveform of the Buck switch over a single switching period when the DC-DC converter of FIG. 4 is operating in steady state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Prior to this, the terms and words used in the present specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best describe the invention.

[0027] Therefore, it should be understood that the embodiment described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can be substituted for them at the time of this application.

[0028] Terms including ordinal numbers such as first, second, etc. are used to distinguish one of various components from other components, and do not limit the components.

[0029] Throughout the specification, when a part "includes" a certain element, this does not mean to exclude other elements, but means that other elements may be further included, unless otherwise specified. Furthermore, terms such as "controller" described in the specification refer to a unit that processes at least one function or operation, and may be embodied in hardware, software, or a combination of hardware and software.

[0030] Furthermore, throughout this specification, when a part is referred to as being "connected" to another part, this includes not only a "direct connection" but also an "indirect connection" through other elements.

[0031] FIG. 2 is a diagram showing an example of the configuration of an electric vehicle according to the present invention.

[0032] Referring to FIG. 2, the electric vehicle 1 includes a battery pack 10 , an inverter 30 , an electric motor 40 , and a battery charger 50 .

[0033] The battery pack 10 includes a battery B, a relay 20, and a battery management system 100.

[0034] The battery B includes at least one battery cell. The type of each battery cell is not particularly limited as long as it can be repeatedly charged and discharged, such as a lithium ion cell. The battery B can be coupled to the inverter 30 through a pair of power terminals provided on the battery pack 10.

[0035] The relay 20 is connected in series to the battery B. The relay 20 is provided in a current path for charging and discharging the battery B. The relay 20 is controlled to be turned on and off in response to a control signal from the battery management system 100. The relay 20 may be a mechanical relay that is turned on and off by the magnetic force of a coil, or may be a semiconductor switch such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0036] The inverter 30 is provided to convert the direct current from the battery B to an alternating current in response to commands from the battery management system 100. The electric motor 40 may be, for example, a three-phase AC motor. The electric motor 40 is driven using the AC power from the inverter 30.

[0037] The battery management system 100 is provided to take charge of overall control related to charging and discharging of the battery B.

[0038] The battery management system 100 includes a sensing unit 110, a memory unit 120, and a control unit 140. The battery management system 100 may further include at least one of an interface unit 130 and a switch driver 150.

[0039] The sensing unit 110 includes a voltage sensor 111 and a current sensor 112. The sensing unit 110 may further include a temperature sensor 113.

[0040] The voltage sensor 111 is connected in parallel to the battery B and configured to detect a battery voltage applied across the battery B and generate a voltage signal indicative of the detected battery voltage. The current sensor 112 is connected in series to the battery B through a current path. The current sensor 112 is configured to detect a battery current flowing through the battery B and generate a current signal indicative of the detected battery current. The temperature sensor 113 is configured to detect the temperature of the battery B and generate a temperature signal indicative of the detected temperature.

[0041] The memory unit 120 may include at least one of the following recording media: a flash memory, a hard disk, a solid state disk (SSD), a silicon disk drive (SDD), a multimedia card micro, a random access memory (RAM), a static RAM (SRAM), a read only memory (ROM), an electrically erasable programmable ROM (EEPROM), and a programmable ROM (PROM). The memory unit 120 may store data and programs necessary for the arithmetic operation by the control unit 140. The memory unit 120 may store data indicating the result of the arithmetic operation by the control unit 140.

[0042] The interface unit 130 may include a communication circuit configured to support wired or wireless communication between the control unit 140 and the upper controller 2 (e.g., ECU: Electronic Control Unit). The wired communication may be, for example, CAN (Controller Area Network) communication, and the wireless communication may be, for example, ZigBee (registered trademark) or Bluetooth (registered trademark) communication. Of course, the type of communication protocol is not particularly limited as long as it supports wired or wireless communication between the control unit 140 and the upper controller 2. The interface unit 130 may include an output device (e.g., a display, a speaker) that provides information received from the control unit 140 and / or the upper controller 2 in a form that can be recognized by a user. The upper controller 2 may control the inverter 30 based on battery information (e.g., voltage, current, temperature, SOC (State of Charge)) collected through communication with the battery management system 100.

[0043] The control unit 140 may be operatively coupled to the upper controller 2, the relay 20, the sensing unit 110, the memory unit 120, the interface unit 130, and / or the switch driver 150. The control unit 140 may be embodied in hardware using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), microprocessors, and other electrical units for performing functions.

[0044] The switch driver 150 outputs a switching signal S to the relay 20 in response to a command from the control unit 140. 1 The switch driver 150 is configured to output a switching signal S to the battery charger 50 in response to a command from the control unit 140. 2The apparatus is configured to output:

[0045] FIG. 3 is a diagram showing an example of the configuration of a battery charger according to the present invention, and FIG. 4 is a diagram showing an example of the configuration of a DC-DC converter of FIG.

[0046] 3 and 4, a battery charger 50 is provided connectable to both ends of a battery B. The battery charger 50 includes a DC-DC converter 62. The battery charger 50 may further include a charging plug 51 and an AC-DC converter 52.

[0047] AC-DC converter 52 is configured to convert AC power from an AC charging station (not shown) connected to charging plug 51 into DC power having a predetermined voltage level.

[0048] DC-DC converter 62 is configured to generate charging power for Battery B using DC power from AC-DC converter 52 or a DC charging station (not shown).

[0049] The DC-DC converter 62 operates on an input voltage V in Steps down the input voltage V in Output voltage lower than V out The DC-DC converter 62 is a buck converter that generates a i , voltage output terminal N o , Back switch SW B , back inductor L B , back capacitor C B , back diode D B and a protection circuit 70. The protection circuit 70 may also be referred to as a "passive snubber."

[0050] Voltage input terminal N i Between the GND and the AC-DC converter 52 or the DC charging station, the input voltage V in can be applied to the voltage output terminal N oA battery B may be connected between the terminals.

[0051] Back switch SW B is the voltage input terminal N i and the first node N 1 The buck switch SW B is the switching signal S from the switch driver 150. 2 The back switch SW B A known switching element such as a MOSFET can be used as the switching signal S. 2 The switching period and duty ratio of S If D, the buck switch SW B is T S ×D, and is maintained in the on state during the first period of T S ×(1-D). The sum of the first and second periods is the switching period T S is equivalent to.

[0052] Back inductor L B is the first node N 1 and voltage output terminal N o The back inductor L is connected between B In the first period, the first node N 1 In the first period, the buck inductor L B The energy stored in the o In the first period, the buck inductor L B The energy charged in the buck inductor L B The state in which the energy discharged from and input to the DC-DC converter 62 is in balance may be referred to as the “steady state” of the DC-DC converter 62.

[0053] Back Capacitor C B is the voltage output terminal N o A back capacitor C is connected between the B is the voltage output terminal N o The output voltage V applied betweenout is provided to suppress ripple in the

[0054] Back Diode D B is the second node N 2 and ground. Specifically, a back diode D B The anode and cathode of the 2 are connected to the buck switch SW B During the first period when the second node N 2 The potential of the back diode D B The buck switch SW B During the second period when the second node N 2 The potential of the back diode D B The back diode D B While in the on state, a second node N 2 The current to the back diode D B It will flow through.

[0055] The protection circuit 70 is connected to the first node N 1 , the second node N 2 and ground. The protection circuit 70 is connected to the switching signal S 2 Back switch SW B When the first node N 1 The buck switch SW is configured to apply a protection voltage between the B The voltage stress at the voltage input terminal N i and the first node N 1 Since the voltage difference between B The voltage stress at the voltage input terminal N i The input voltage V applied between in will be smaller than

[0056] The protection circuit 70 includes a first protection capacitor C P1 , the second protection capacitor C P2, protective inductor L P , and protection diode D P Includes.

[0057] In Figure 4, I SW is the back switch B The current flowing through LB is the back inductor L B The current flowing through LP is the protective inductor L P The current flowing through CP1 is the first protection capacitor C P1 The current flowing through CP2 is the second protection capacitor C P2 The current flowing through DB is the back diode D B The current flowing through DP is the protection diode D P The current flowing through SW is the back switch B The voltage stress is shown.

[0058] First protection capacitor C P1 is the first node N 1 and the second node N 2 is connected between the

[0059] Second protection capacitor C P2 is the third node N 3 and ground.

[0060] First protection capacitor C P1 and the second protection capacitor C P2 is the back switch SW B When the first node N 1 By applying a protection voltage between the B Voltage stress of SW B Decrease the size of

[0061] Protection inductor L P is the second node N 2 and the third node N3 A protective inductor L is connected between P is the first protection capacitor C P1 and the second protection capacitor C P2 During charging and discharging of the first protection capacitor C P1 The current I CP1 and the second protection capacitor C P2 The current I CP2 is provided to suppress abrupt changes in

[0062] Protection diode D P is the first node N 1 and the third node N 3 Specifically, the protection diode D P The anode and cathode of the third node N 3 and the first node N 1 Protection diode D P is the first node N 1 The potential of the third node N 3 When the potential is lower than that of the protection diode D, it is turned on. P While the third node N 3 to the first node N 1 Current I DP flows through the protection diode DP. Protection diode D P is the first node N 1 The potential of the third node N 3 When the potential is higher than that of the protection diode D, it is in the off state. P While the first node N 1 and the third node N 3 The current between them is interrupted.

[0063] FIG. 5 is a schematic diagram illustrating the current waveforms of each component and the voltage waveform of the buck switch over a single switching period when the DC-DC converter 62 of FIG. 4 is operating at steady state.

[0064] Referring to FIG. 5, a single switching cycle begins with the buck switch SW B Status and protection inductor L PIn the first to fourth operation modes, the current I CP1 and current I CP2 and the current I DP and current I DB Since the current I CP2 Waveform and current I DB The waveforms of are omitted.

[0065] The first operating mode is the buck switch SW B The current I LP In the first operating mode, the current I LP The negative value of P1 and the second protection capacitor C P2 This means that the battery is discharged in the first operating mode.

[0066] The second operating mode is the buck switch SW B is maintained in the on state while the current I LP In this mode, the current I gradually increases from 0A. LP is a positive value greater than 0A, the first protection capacitor C P1 and the second protection capacitor C P2 is charged in the second operating mode.

[0067] In the first and second operating modes, the back diode D B and protection diode D P has an off state. Therefore, the first protection capacitor C P1 and the protective inductor L P and the second protection capacitor CP 2 The voltage in the series circuit with the input voltage V in is equivalent to.

[0068] The third operating mode is the buck switch SW B From the moment when the on-state is switched to the off-state, the current I LPThis is the operating mode from the point where the current goes from a positive value to 0A.

[0069] The fourth operating mode is the buck switch SW B is maintained in the off state while the current I LP This is an operating mode in which the current gradually decreases from 0A.

[0070] In the third and fourth operation modes, the back diode D B and protection diode D P Since has an on state, the first protection capacitor C P1 and back diode D B The series circuit with the first node N 1 A protection voltage greater than 0 V is applied between the first protection capacitor CP 1 and back diode D B The voltage applied across a series circuit of

[0071] Back switch SW B When the first node N 1 The voltage is the input voltage V in and the back inductor L B Voltage V LB is the input voltage V in and the output voltage V out Therefore, in the first and second operation modes, the relationships of the following Equations 1 and 2 are satisfied.

[0072] [Formula 1] V LP = V in -V CP1 -V CP2 = V in - 2V CP1

[0073] [Formula 2] V LB = V in -V out

[0074] Back switch SW B When the back diode D B and protection diode D P Since the first protection capacitor CP 1 , protective inductor L P and the second protection capacitor C P2 is the first node N 1 and ground. Thus, the back diode D B and protection diode D P Assuming that each forward voltage drop is 0 V, the relationships of the following Equations 3 and 4 are satisfied in the third and fourth operating modes.

[0075] [Formula 3] V LP = - V CP1 = - V CP2

[0076] [Formula 4] V LB = V CP1 -V out = V CP2 -V out = - V LP -V out

[0077] When the DC-DC converter 62 is operating in steady state, the buck inductor L B and protective inductor L P The average voltage of each must be 0 V. Therefore, the following Equation 5 is derived from Equation 1 and Equation 3, and the following Equation 6 is derived from Equation 2 and Equation 4.

[0078] [Formula 5] (V in - 2V CP1 )×D - V CP1 × (1 - D) = 0 [V]

[0079] [Formula 6] (V in -V out ) × D + (V CP1 -V out ) × (1-D) = 0 [V]

[0080] Formula 5 to V CP1 If we rearrange it, we get the following equation 5-1.

[0081] [Formula 5-1] TIFF0007631638000001.tif39133

[0082] Using formula 5-1, formula 6 is V out If we rearrange it, we get the following equation 6-1.

[0083] [Formula 6-1] TIFF0007631638000002.tif26142

[0084] In formula 6-1, G V is the voltage gain of the DC-DC converter 62.

[0085] Also, the back switch SW B The voltage stress when is switched from an on state to an off state is given by Equation 7 below.

[0086] [Formula 7] TIFF0007631638000003.tif26150

[0087] The duty ratio D is 0 to 1. Therefore, the voltage stress V of the DC-DC converter 62 SW The input voltage V in In other words, in the conventional DC-DC converter shown in FIG. 1, the input voltage V in A voltage stress of the same magnitude as that of the buck switch SW BOn the other hand, in the DC-DC converter 62 according to the present invention, the input voltage V in Voltage stress smaller than V SW is the back switch SW B In the DC-DC converter 62 according to the present invention, the duty ratio D increases as the buck switch SW B Voltage stress V SW When the battery B is charged using the DC-DC converter 62, the control unit 140 can increase the duty ratio D by a predetermined ratio every set time.

[0088] As described above, the present invention has been described using limited embodiments and drawings. However, the present invention is not limited thereto, and it goes without saying that various modifications and variations can be made by a person having ordinary knowledge in the technical field to which the present invention belongs within the technical spirit of the present invention and the equivalent scope of the claims.

[0089] Furthermore, the present invention described above is susceptible to various substitutions, modifications and alterations by those having ordinary knowledge in the technical field to which the present invention pertains, within the scope not departing from the technical spirit of the present invention, and is not limited to the above-described embodiments and the accompanying drawings, but may be configured by selectively combining all or part of each embodiment for various modifications.

Claims

1. A protection circuit for a DC-DC converter, comprising: a buck switch connected between a voltage input terminal and a first node and controlled by a switching period and a duty ratio of a switching signal; a buck inductor connected between the first node and a voltage output terminal; a buck diode connected between a second node and ground; and a buck capacitor connected between the voltage output terminal and the ground, a protection voltage is applied between the first node, the second node and the ground, such that when the buck switch is switched between an on state and an off state according to the switching signal, a voltage stress of the buck switch is smaller than an input voltage applied between the voltage input terminal and the ground; a first protection capacitor connected between the first node and the second node; a second protection capacitor connected between a third node and the ground; a protection inductor connected between the second node and the third node; a protection diode connected between the first node and the third node; the protection inductor is connected to the second protection capacitor via the third node; The first protection capacitor and the second protection capacitor are The protection circuit discharges in a first operating mode during a first period when the buck switch is on, and charges in a second operating mode during the first period.

2. The protection diode is The buck switch is maintained in an off state during a first period in which the buck switch is in an on state, 2. The protection circuit of claim 1, wherein the buck switch is maintained in an on state during a second period in which the buck switch is in an off state.

3. The protection voltage is 3. The protection circuit according to claim 1, wherein the voltage is equal to the voltage of a series circuit of the first protection capacitor and the back diode.

4. The voltage of the series circuit of the first protection capacitor, the protection inductor, and the second protection capacitor is During a first period in which the buck switch is in an on state, the voltage is equal to the sum of the voltage of the buck inductor and the output voltage; 4. The protection circuit according to claim 1, wherein the output voltage is a voltage between the voltage output terminal and the ground.

5. The voltage on the first protection capacitor is 5. The protection circuit according to claim 1, wherein during a second period in which the buck switch is in an off state, the voltage is the same as a voltage of a series circuit of the protection inductor and the protection diode.

6. The voltage on the second protection capacitor is 6. The protection circuit according to claim 1, wherein during a second period in which the buck switch is in an off state, the voltage is the same as a voltage of a series circuit of the protection inductor and the buck diode.

7. The protective inductor includes:

7. The protection circuit according to claim 1, wherein in a third operation mode in a second period in which the buck switch is in an off state, a current flows from the second node to the third node, and in a fourth operation mode in the second period, a current flows from the third node to the second node.

8. A DC-DC converter comprising a protection circuit according to any one of claims 1 to 7.

9. A battery charger comprising the DC-DC converter according to claim 8.

10. 10. An electric vehicle comprising the battery charger of claim 9.

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