LLC resonant converter and charging system having LLC resonant converter

Abstract

The present disclosure relates to an LLC resonant converter and a charging system having the LLC resonant converter. Based on the characteristics of the LLC resonant converter whose output is determined by LC resonance, the LLC resonant converter and the charging system having the LLC resonant converter can solve the overcurrent generation and output voltage deviation occurring at the initial startup.

Description

Technical Field

[0001] The present disclosure relates to an LLC resonant converter and a charging system having the LLC resonant converter, and more particularly, to an LLC resonant converter and a charging system having the LLC resonant converter, which are capable of resolving overcurrent generation and output voltage deviation occurring during initial startup based on the characteristics of the LLC resonant converter, wherein the output of the LLC resonant converter is determined by LC resonance. Background Art

[0002] An environmentally friendly vehicle that needs to charge a battery, which is an energy source for a driving motor in a vehicle such as an electric vehicle or a plug-in hybrid vehicle, has an on-board charger that converts external AC power and outputs DC power for charging the battery.

[0003] Generally, the on-board charger includes: a power factor correction circuit for compensating the power factor of the external AC power and outputting the power as DC; and a DC-DC converter for converting the DC outputted by the power factor correction circuit into a DC voltage for charging the battery. Here, an LLC resonant converter using LC resonance (e.g., a combination of two inductors and one capacitor ("LLC")) may be employed as the DC-DC converter.

[0004] The resonant frequency determined by two inductors and one capacitor (i.e., the resonant cavity outside the transformer) determines the characteristics of the LLC resonant converter. The advantage of the LLC resonant converter is that by using the resonant current generated by two inductors and one capacitor, the switching loss and the diode loss can be greatly reduced. Further, the LLC resonant converter controls the switching frequency (rather than the duty cycle of the switching element included therein) to determine the input / output relationship, and thus obtains a nonlinear input / output voltage gain characteristic curve. Accordingly, the LLC resonant converter has the disadvantage that it is difficult to control.

[0005] Specifically, because the LC resonance clearly defines the gain curve, it is not feasible to control the LLC resonant converter in any area outside the input and output areas. For example, when the output terminal of the charger using the LLC resonant converter is connected to the battery to be charged through a relay during initial charging, an overcurrent may flow and the capacitor provided at the output terminal of the charger may be burned out. Thus, before connecting the relay, the voltage and current control of the LLC resonant converter should be performed under no-load conditions. However, because the output voltage of the LLC resonant converter is not formed, the LLC resonant converter is switched to the maximum switching frequency. Accordingly, an overcurrent may be generated due to the LC resonance, and the components constituting the circuit may be burned out. Under no-load conditions, the switching frequency should be infinite to produce a minimum load, but the limitation of the maximum frequency generated by the microcomputer controlling the switching element causes the output voltage to continue to increase and deviate.

[0006] The contents described as the related technical field are only provided to help understanding the background technology of the present disclosure, and the contents described as the related technical field should not be considered to correspond to the related technical field known to those of ordinary skill in the art. Summary of the invention

[0007] The objective of the present disclosure is to provide an LLC resonant converter and a charging system having the LLC resonant converter, which can solve the overcurrent generation and output voltage deviation that occur when controlling the voltage and current in a no-load state during initial startup based on the characteristics of the LLC resonant converter, wherein the output of the LLC resonant converter is determined by LC resonance.

[0008] According to an exemplary embodiment of the present disclosure, an LLC resonant converter may include: a plurality of switching elements connected to an input terminal and constituting a bridge circuit; a resonant cavity receiving power formed by switching the plurality of switching elements for resonance; a transformer having a primary coil connected to the resonant cavity and a secondary coil connected to a load side; a rectifier circuit connected between the secondary coil and an output terminal; an output capacitor connected to the output terminal; and a controller determining whether to switch the plurality of switching elements and a switching duty ratio of the plurality of switching elements based on an output voltage sensing value obtained by detecting a voltage at the output terminal, a voltage of a load connected to the output terminal, and a preset output voltage command value.

[0009] The LLC resonant converter may further include a relay having two ends connected to the output terminal and the load, respectively, and the controller may perform short-circuiting of the relay when a voltage at the output terminal is within a normal voltage range required by the load.

[0010] Before short-circuiting the relay, the controller may adjust the switching duty ratio to have a smaller value than the switching duty ratio preset to be applied after the relay is short-circuited.

[0011] When the output voltage sense value is less than or equal to a preset reference value, before the relay is short-circuited, the controller may adjust the switching duty ratio to have a smaller value than the switching duty ratio set to be applied in a normal state in which the load is connected to the output terminal.

[0012] The reference value may be a value that is a basis for determining a connection state of the load based on the characteristics of the load connected to the output terminal.

[0013] The load may be a battery that is charged by receiving power from the output terminal, and the reference value may correspond to a minimum voltage value output when the battery is in a normal state.

[0014] The controller may determine whether to switch the plurality of switching elements based on a difference between the output voltage sense value and the output voltage command value.

[0015] When the output voltage sensing value is less than a value obtained by adding a first preset margin value to the output voltage command value, the controller may perform switching on the switching element, and when the output voltage sensing value is equal to or greater than a value obtained by adding the first preset margin value to the output voltage command value, the controller may stop switching on the switching element.

[0016] After stopping the switching of the switching element, when the output voltage sense value decreases to a value obtained by subtracting the second preset margin value from the output voltage command value, the controller may resume the switching of the switching element.

[0017] The first preset margin value may have a size equal to or greater than a fluctuation size of an output voltage generated in a normal operation state in which a load is connected to the output terminal after the initial startup is terminated and may be less than a preset upper limit value.

[0018] According to another exemplary embodiment of the present disclosure, a charging system may include: an LLC resonant converter, including: a plurality of switching elements connected to an input terminal and constituting a bridge circuit; a resonant cavity, receiving power formed by short-circuiting and opening the plurality of switching elements for resonance; a transformer, having a primary coil connected to the resonant cavity and a secondary coil connected to a load side; a rectifier circuit, connected between the secondary coil and an output terminal; and an output capacitor, connected to the output terminal; a relay, having one end connected to the output terminal; a battery, connected to the other end of the relay to be charged; and a controller, when battery charging is started, controlling the relay to be in an open state to operate an initial charging mode, and determining whether to switch the plurality of switching elements and the switching duty ratio of the plurality of switching elements based on an output voltage sensing value obtained by detecting a voltage at the output terminal in the initial charging mode, a voltage of the battery, and a preset output voltage command value.

[0019] The controller may adjust the switching duty ratio applied in the initial charging mode to have a smaller value than the switching duty ratio preset to be applied in a normal state in which the relay is short-circuited after the initial charging mode is terminated.

[0020] When the output voltage sense value is less than or equal to the reference value of the initial charging mode, the controller may adjust the switching duty ratio to have a smaller value than the switching duty ratio set to be applied in a normal state where the relay is short-circuited after the initial charging mode is terminated.

[0021] The reference value may correspond to a minimum voltage value output by the battery during normal operation.

[0022] The controller may determine whether to switch the switching element based on a difference between the output voltage sense value and the output voltage command value.

[0023] When the output voltage sensing value is less than a value obtained by adding a first preset margin value to the output voltage command value, the controller may perform switching on the switching element, and when the output voltage sensing value is equal to or greater than a value obtained by adding the first preset margin value to the output voltage command value, the controller may stop switching on the switching element.

[0024] After stopping the switching of the switching element, when the output voltage sense value decreases to a value obtained by subtracting the second preset margin value from the output voltage command value, the controller may resume the switching of the switching element.

[0025] The first preset margin value may have a magnitude equal to or greater than a fluctuation magnitude of an output voltage generated in a normal operation state in which a battery is connected to an output terminal after initial startup is terminated and may be less than a preset upper limit value.

[0026] When the output capacitor is charged to a preset charging voltage in the initial charging mode, the controller may short-circuit the relay to terminate the initial charging mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a circuit diagram of a charging system having an LLC resonant converter according to an exemplary embodiment of the present disclosure.

[0028] Figure 2 is a diagram showing a general LLC resonant converter and input / output voltage gain curves of corresponding operating regions.

[0029] Figure 3 is a block diagram illustrating a controller of an LLC resonant converter according to an exemplary embodiment of the present disclosure in more detail.

[0030] Figure 4 is a flowchart illustrating a method of switching duty cycle control performed by a controller of an LLC resonant converter according to an exemplary embodiment of the present disclosure.

[0031] Figure 5 is a diagram for explaining a method of controlling whether to perform pulse width modulation performed by a controller of an LLC resonant converter according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] Hereinafter, an LLC resonant converter and a charging system having the same according to various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0033] Figure 1 is a circuit diagram of a charging system having an LLC resonant converter according to an exemplary embodiment of the present disclosure.

[0034] refer to Figure 1 According to an exemplary embodiment of the present disclosure, a charging system with an LLC resonant converter may include: an electromagnetic interference (EMI) filter 11, which removes noise components of external AC power; a rectifier circuit 13, which rectifies the power filtered by the EMI filter 11; a smoothing capacitor Cs, which is used to smooth the output of the rectifier circuit 13; a power factor correction circuit 15, which receives the power smoothed by the smoothing capacitor Cs and improves the power factor of the received power to output the power as DC power; an LLC resonant converter 17, which converts the voltage amplitude of the DC power output from the power factor correction circuit 15 and outputs a charging voltage Vo for charging a battery 19; the battery 19, which is charged by receiving the voltage provided by the LLC resonant converter 17; and a resonant cavity 171, which is located in the LLC resonant converter 17.

[0035] The EMI filter 11 is configured to remove the noise of the high frequency component of the input external AC power, and is a circuit already known in the art. The rectifier circuit 13 can be implemented in the form of a bridge circuit implemented by using a plurality of diodes, and the smoothing capacitor Cs is connected between both ends of the rectifier circuit 13. The rectifier circuit 13 and the smoothing capacitor Cs are also circuit elements already known in the art.

[0036] You can use an inductor including L BS , Switching element Q BS , and diode D BS The topology of a boost converter is used to implement a power factor correction circuit 15 configured to improve the power factor of AC power. The operating mechanism of such a power factor correction circuit 15 using the topology of a boost converter is generally known.

[0037] Capacitor C BS It can be connected to the output terminal of the power factor correction circuit 15 to form a DC connection terminal. Figure 1 In the embodiment, two DC link capacitors C having the same capacitance value are BS It can be connected in series to connect the half-bridge LLC resonant converter 17 in the subsequent stage of the power factor correction circuit 15, and connect the two DC connection capacitors C BS The terminals of can be connected to the resonant cavity 171 of the half-bridge LLC resonant converter 17 in a subsequent stage.

[0038] The LLC resonant converter 17 may include: a switching element Q 1 and Q 2 , connected to its input terminal to form a bridge circuit; the resonant cavity 171 receives the short-circuited and open-circuited switching element Q 1 and Q 2 The power formed; a transformer 173 having a primary coil connected to the resonant cavity 171 and a secondary coil connected to the output side, and the charged object is connected to the output side; a rectifier circuit 175 connected to the secondary coil of the transformer 173; and an output capacitor Co connected to the output terminal.

[0039] Figure 2 is a diagram showing a general LLC resonant converter and an input / output voltage gain curve for a corresponding operating region. Figure 2 In FIG. 1 , the dotted line shows the input / output voltage gain according to the resonance generated by the inductor Lr and the capacitor Cr and is a gain curve at a low load, and the solid line shows the input / output voltage gain according to the resonance generated by the inductors Lr and Lm and the capacitor Cr and is a gain curve at a high load.

[0040] refer to Figure 2, LLC resonant converter mainly has three operating regions.

[0041] The first operating region is the switching element Q 1 and Q 2 The area corresponding to the point where the switching frequency fsw is equal to the resonant frequency fsr generated by the inductors Lr and Lm and the capacitor Cr. This area is the part where the switching frequency fsw is set equal to the resonant frequency fsr and is the fsw with the minimum switching loss. Because the switching frequency fsw and the resonant frequency fsr should be exactly the same, this area exists in a very small part.

[0042] The second operating region is the switching element Q 1 and Q 2 The switching frequency fsw is greater than the resonant frequency fsr generated by the inductors Lr and Lm and the capacitor Cr. This region is a region where the switching frequency fsw is greater than the resonant frequency fsr and is a region where the zero voltage switching (ZVS) loss can be reduced but the zero current switching loss can be generated.

[0043] The third operating region is the switching element Q 1 and Q 2 The switching frequency fsw is less than the resonant frequency fsr generated by the inductors Lr and Lm and the capacitor Cr, and is greater than the resonant frequency fpr generated by the inductor Lr and the capacitor Cr. This region is a region where the switching frequency fsw is less than the resonant frequency fsr and the switching loss is small, thereby improving efficiency.

[0044] As described above, the LLC resonant converter 17 can be used to switch the switching element Q in the bridge circuit. 1 and Q 2 The switching frequency is adjusted to determine the operating region and gain and thereby determine the size of the charging voltage Vo. Specifically, by making the switching element Q 1 and Q 2 The switching frequency of the LLC resonant converter 17 is adjusted by controlling the switching frequency while keeping the switching duty cycle fixed (for example, the switching duty cycle is 50%).

[0045] However, a general method of controlling an LLC resonant converter has a problem in that when no-load control is performed at initial startup, the switching frequency of the switching element is maximized, and thereby an overcurrent is generated due to LC resonance and the output voltage continues to increase and deviates.

[0046] Accordingly, the present disclosure provides a control technology capable of solving the problems of overcurrent generation and output voltage deviation due to LC resonance under no-load conditions at the initial startup of an LLC resonant converter.

[0047] Return to reference Figure 1 The controller 100 is an element for performing control to solve the above-mentioned problems of the general LLC resonant converter, and can be implemented in the form of, for example, a microcomputer, which includes a processor for performing calculations required for algorithm processing and control; and a memory for storing information required for the algorithm processing and calculations performed by the processor.

[0048] First, the controller 100 can control the switching element Q in the LLC resonant converter 17 1 and Q 2 Further, the controller 100 can control the switching element Q in the power factor correction circuit 15. BS The power factor correction circuit 15 is provided in a charger including an LLC resonant converter 17, and the relay RLY determines the electrical connection state between the LLC resonant converter 17 and the battery 19. The present disclosure solves the problem that occurs during the control in a no-load state at the initial startup of the LLC resonant converter. Therefore, the present description will focus on the control of the LLC resonant converter 17 mainly performed by the controller 100.

[0049] Figure 3 is a block diagram showing a controller of an LLC resonant converter according to an exemplary embodiment of the present disclosure in more detail. Further, Figure 4 is a flowchart illustrating a method of switching duty cycle control performed by a controller of an LLC resonant converter according to an exemplary embodiment of the present disclosure, and Figure 5 is a diagram for explaining a method of controlling whether to perform pulse width modulation performed by a controller of an LLC resonant converter according to an exemplary embodiment of the present disclosure.

[0050] refer to Figure 3 According to an exemplary embodiment of the present disclosure, the controller 100 of the LLC resonant converter may include: a voltage controller 110 and a switching element Q1 in the LLC resonant converter. 1 and Q 2 The current controller 130 of the switching frequency; the duty cycle determination unit 150, determines the switching element Q in the LLC resonant converter 1 and Q 2 and a pulse width modulation (PWM) signal generating unit 151, generating a PWM signal having a switching frequency determined by the current controller 130 and a switching duty ratio determined by the duty ratio determining unit 150.

[0051] The controller 100 of the LLC resonant converter according to the exemplary embodiment of the present disclosure may include a PWM execution determination unit 170 for determining whether to execute the switching element Q in the LLC resonant converter. 1 and Q2 and PWM execution determination unit 190, according to the determination result of the PWM execution determination unit 170, determines that the PWM signal generated by the PWM signal generating unit 151 is sent to the switching element Q 1 and Q 2 The PWM signal generated by the PWM signal generating unit 151 is also blocked.

[0052] The controller 100 may perform various functions of the above-mentioned units 150, 151, 170, and 190. The units 120, 130, 140, and 150 described below are implemented using software instructions running on a processor of the controller 100.

[0053] The voltage controller 110 and the current controller 130 in the controller 100 are elements for controlling a circuit device that converts electric power by applying general switching elements such as a converter and an inverter. More specifically, the voltage controller 110 can receive an output voltage sensing value obtained by detecting the output voltage of the LLC resonant converter using a sensor or the like, and an output voltage command value corresponding to a desired voltage output by the LLC resonant converter, and generate a specific output value for minimizing the error between the output voltage sensing value and the output voltage command value by using a general controller such as a proportional integral (PI) controller or a proportional integral differential (PID) controller. Figure 3 In the embodiment of the present invention, the voltage controller 110 may generate an output current command value for minimizing the error between the output voltage sensed value and the output voltage command value. The current controller 130 may receive the output current command value provided from the voltage controller 110 and the output current sensed value detected at the output terminal of the LLC resonant converter by a sensor or the like, and determine the switching element Q in the LLC resonant converter by using a general controller such as a proportional integral (PI) controller or a proportional integral derivative (PID) controller. 1 and Q 2 The switching frequency is set to minimize the error between the output current sense value and the output current command value.

[0054] The voltage controller 110 and the current controller 130 are used in the related art to control the switching element Q 1 and Q 2 , so that the output voltage of the LLC resonant converter is a general technology of a desired value (output voltage command value). Therefore, additional detailed description will be omitted.

[0055] like Figure 4As shown, the duty ratio determination unit 150 in the controller 100 compares the output voltage sensing value obtained by detecting the output voltage of the LLC resonant converter (S11) by a sensor or the like with a preset reference value (S12), and then, when the output voltage sensing value is greater than the reference value, determines that the switching element Q is switched to a predetermined value. 1 and Q 2 The switching frequency is used as a normal first switching duty cycle (eg, 50%) (S13), or when the output voltage sensed value is less than or equal to the reference value, the switching element Q is determined. 1 and Q 2 The switching frequency is used as a second switching duty ratio (eg, 15%) (having a smaller value than the first switching duty ratio) (S14).

[0056] In an exemplary embodiment of the present disclosure, when the output voltage sense value is less than a specified reference value, that is, when the output voltage is not formed or the output voltage is low, in order to prevent overcurrent generation due to LC resonance in a state where the output voltage of the LLC resonant converter is not formed, the duty ratio determination unit 150 turns off the switching element Q in the LLC resonant converter. 1 and Q 2 The duty cycle of is changed to have a smaller value than the preset basic duty cycle. According to an exemplary embodiment of the present disclosure, the LC resonant current from the resonant cavity in the LLC resonant converter may not reach a maximum value and only send a low current, thereby preventing internal components from being burned due to overcurrent.

[0057] Here, the reference value input to the duty ratio determination unit 150 and compared with the output voltage sensed value may be set as a value for determining the basis of the no-load state at the initial startup of the LLC resonant converter. That is, the reference value may be a value for determining the basis of the no-load state based on the characteristics of the load connected to the output terminal of the LLC resonant converter after the initial startup state is terminated.

[0058] For example, considering that in a charging system including an LLC resonant converter, the output of the LLC resonant converter is connected to the battery 19 being charged, when the detected output voltage value of the LLC resonant converter is less than the minimum voltage value that the battery 19 can output when operating normally (as defined by the specifications of the battery 19), it can be estimated that the LLC resonant converter is in a no-load state. That is, the reference value used in the duty cycle determination unit 150 can be the minimum voltage value that the battery can output in a normal state.

[0059] The first switching duty cycle is provided to the internal switching element Q when the output of the LLC resonant converter is normally connected to the load. 1 and Q 2The duty cycle of the PWM signal. For example, the first switch duty cycle can be determined in advance to be approximately 50%. The second switch duty cycle has a smaller value than the first switch duty cycle and can be changed according to the LC resonance amount of the resonant cavity 171 in the LLC resonant converter. For example, the second switch duty cycle can be determined to be a value that makes the maximum value of the LC resonance less than the value of the rated current preset based on the specifications of the LLC resonant converter under the condition that the output voltage of the LLC resonant converter is 0V.

[0060] The PWM signal generating unit 151 of the controller 100 generates a PWM signal having a switching frequency determined by the current controller 130 and a switching duty ratio determined by the duty ratio determining unit 150. The PWM signal is provided to the switching element Q in the LLC resonant converter. 1 and Q 2 The gate of the switching element is used to adjust the Q 1 and Q 2 On or off, and can therefore be called a gate signal.

[0061] The PWM execution determination unit 170 in the controller 100 may receive the output voltage sensing value and the preset second reference value, and determine whether to execute the switching element Q in the LLC resonant converter. 1 and Q 2 Reference Figure 5 The PWM execution determination unit 170 compares the output voltage sensed value obtained by detecting the output voltage of the LLC resonant converter (S11) by a sensor or the like with a preset reference value (output voltage command value + first margin value), and when the output voltage sensed value is less than the reference value, determines whether to continue switching the switching element Q in the LLC resonant converter. 1 and Q 2 On the contrary, when the output voltage sense value is greater than or equal to the reference value (output voltage command value + first margin value), the PWM execution determination unit 170 determines to stop the switching element Q in the LLC resonant converter. 1 and Q 2 Switch.

[0062] In the PWM execution determination unit 170, the reference value compared with the output voltage sensing value at the initial startup may be a value obtained by adding a first preset margin value (α) to the output voltage command value. The first preset margin value (α) may be determined based on the fluctuation magnitude of the output voltage generated in a normal operating state in which the load is connected to the output terminal of the LLC resonant converter after the initial startup of the LLC resonant converter. This is because the voltage of the output terminal in a normal state may be a value of the output voltage plus the fluctuation, and thus the value obtained by adding the value corresponding to the fluctuation to the output voltage should be regarded as normal. More specifically, the first preset margin value (α) may be determined to be equal to or greater than the fluctuation magnitude of the output voltage generated in a normal operating state in which the load is connected to the output terminal of the LLC resonant converter after the initial startup of the LLC resonant converter, and equal to or less than a preset upper limit value that does not have a bad effect on the converter or the parts constituting the load.

[0063] When the output voltage sense value at the initial startup is equal to or greater than a value obtained by adding the first preset margin value (α) to the output voltage command value, the switching element Q is stopped. 1 and Q 2 After the switching, when the output voltage sense value decreases to a value obtained by subtracting the second preset margin value (β) from the output voltage command value, the PWM execution determination unit 170 may restore the switching element Q 1 and Q 2 Switch.

[0064] Here, the first preset margin value (α) and the second preset margin value (β) may be positive values ​​appropriately selected by an experimental method.

[0065] The PWM execution determination unit 190 of the controller 100 sends the PWM signal generated by the PWM signal generation unit 151 to the switching element Q according to the determination result of the PWM execution determination unit 170. 1 and Q 2 , to continue switching element Q 1 and Q 2 or the PWM execution determination unit 190 of the controller 100 blocks the PWM signal generated by the PWM signal generation unit 151 according to the determination result of the PWM execution determination unit 170 to stop the switching element Q 1 and Q 2 Switch.

[0066] According to an exemplary embodiment of the present disclosure, when the output voltage continues to increase and becomes greater than a predetermined reference value (output voltage command value+α) due to the limitation of the maximum switching frequency provided to the switching element when the LLC resonant converter is initially started, the controller 100 is capable of preventing the PWM signal from being provided to the switching element Q in the LLC resonant converter. 1 and Q 2 And solve the problem of output voltage deviation.

[0067] As described above, by reducing the duty cycle of the PWM signal provided to the LLC resonant converter at the initial startup of the LLC resonant converter using the voltage / current in the no-load state to stop overcurrent generation, and by blocking the PWM signal to prevent deviation when the output voltage of the LLC resonant converter increases to a predetermined level or above, various embodiments of the present disclosure enable the capacitor at the output terminal of the LLC resonant converter to be charged at the initial startup under no-load conditions.

[0068] like Figure 1 As shown, when the LLC resonant converter is applied to the charging system, once the operation of the charging system starts, as shown in FIG. Figures 3 to 5 As explained in the above, the controller 100 controls the switching element Q in the LLC resonant converter 17. 1 and Q 2 The duty cycle of the PWM signal is adjusted, and it is determined whether to send the PWM signal when the relay RLY is in the disconnected state, thereby making it possible to stably charge the output capacitor Co of the LLC resonant converter 17 in a no-load state before the relay RLY is short-circuited. When the charging of the output capacitor Co is terminated and the output voltage of the LLC resonant converter 17 at the output terminal of the LLC resonant converter 17 is formed to a preset voltage required by the load (battery), the controller 100 short-circuits the relay RLY so that the charging power can be stably supplied to the battery 19.

[0069] According to the LLC resonant converter and the charging system having the above-mentioned LLC resonant converter, it is possible to prevent the generation of overcurrent due to LC resonance in the process of controlling the output voltage and current in a no-load state at the initial startup of the LLC resonant converter and solve the output voltage deviation caused by switching frequency limitation.

[0070] According to the LLC resonant converter and the charging system having the LLC resonant converter, it is also possible to stably charge the capacitor at the output terminal of the LLC resonant converter in a no-load state at the initial startup of the LLC resonant converter.

[0071] Effects obtained from the present disclosure are not limited to the above-mentioned effects, and other effects not mentioned above can be clearly understood by those skilled in the art from the following description.

[0072] While the present disclosure has been shown and described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims

1. An LLC resonant converter, comprising: a plurality of switching elements connected to the input terminals and forming a bridge circuit; a resonant cavity receiving power formed by switching the plurality of switching elements for resonance; a transformer having a primary coil connected to the resonant cavity and a secondary coil connected to a load side; a rectifier circuit connected between the secondary coil and the output terminal; an output capacitor connected to the output terminal; as well as a controller that determines whether to switch the plurality of switching elements and a switching duty ratio of the plurality of switching elements based on an output voltage sensing value obtained by detecting a voltage at the output terminal, a voltage of a load connected to the output terminal, and a preset output voltage command value; a relay, both ends of which are connected to the output terminal and the load, respectively, wherein when the voltage at the output terminal is within a normal voltage range required by the load, the controller performs a short circuit of the relay; Wherein, before the relay is short-circuited, the controller adjusts the switch duty cycle to have a smaller value than a switch duty cycle preset to be applied after the relay is short-circuited.

2. The LLC resonant converter according to claim 1, wherein: When the output voltage sense value is less than or equal to a preset reference value, the controller adjusts the switching duty ratio to have a value smaller than a switching duty ratio set to be applied in a normal state in which the load is connected to the output terminal.

3. The LLC resonant converter according to claim 2, wherein: The reference value is a value that is a basis for determining the connection state of the load based on the characteristics of the load connected to the output terminal.

4. The LLC resonant converter according to claim 3, wherein: The load is a battery that is charged by receiving power from the output terminal, and the reference value corresponds to a minimum voltage value output when the battery is in a normal state.

5. The LLC resonant converter according to claim 1, wherein: The controller determines whether to switch the plurality of switching elements based on a difference between the output voltage sense value and the output voltage command value.

6. The LLC resonant converter according to claim 1, wherein: When the output voltage sense value is less than a value obtained by adding a first preset margin value to the output voltage command value, the controller performs switching on the switching element, and When the output voltage sense value is equal to or greater than a value obtained by adding the first preset margin value to the output voltage command value, the controller stops switching of the switching element.

7. The LLC resonant converter according to claim 6, wherein: After stopping the switching of the switching element, the controller resumes the switching of the switching element when the output voltage sense value decreases to a value obtained by subtracting a second preset margin value from the output voltage command value.

8. The LLC resonant converter according to claim 6, wherein: The first preset margin value has a magnitude equal to or greater than a fluctuation magnitude of an output voltage generated in a normal operation state in which the load is connected to the output terminal after initial startup is terminated, and is smaller than a preset upper limit value.

9. A charging system comprising: An LLC resonant converter, comprising: a plurality of switching elements connected to an input terminal and constituting a bridge circuit; a resonant cavity receiving power formed by short-circuiting and opening the plurality of switching elements for resonance; a transformer having a primary coil connected to the resonant cavity and a secondary coil connected to a load side; a rectifier circuit connected between the secondary coil and an output terminal; and an output capacitor connected to the output terminal; a relay having one end connected to the output terminal; a battery connected to the other end of the relay to be charged; and a controller that controls the relay to be in an open state to execute an initial charging mode when charging of the battery starts, and determines whether to switch the plurality of switching elements and switching duty ratios of the plurality of switching elements based on an output voltage sensing value obtained by detecting a voltage at the output terminal in the initial charging mode, a voltage of the battery, and a preset output voltage command value; The controller adjusts the switch duty ratio applied in the initial charging mode to have a smaller value than the switch duty ratio preset to be applied in a normal state where the relay is short-circuited after the initial charging mode is terminated.

10. The charging system according to claim 9, wherein: When the output voltage sense value is less than or equal to a preset reference value, the controller adjusts the switching duty ratio to have a smaller value than the switching duty ratio set to be applied in a normal state in which the relay is short-circuited after the initial charging mode is terminated.

11. The charging system according to claim 10, wherein: The reference value corresponds to a minimum voltage value output by the battery when the battery operates normally.

12. The charging system according to claim 9, wherein: The controller determines whether to switch the switching element based on a difference between the output voltage sense value and the output voltage command value.

13. The charging system according to claim 9, wherein: When the output voltage sensing value is less than a value obtained by adding a first preset margin value to the output voltage command value, the controller switches the switching element, and when the output voltage sensing value is equal to or greater than a value obtained by adding the first preset margin value to the output voltage command value, the controller stops switching the switching element.

14. The charging system according to claim 13, wherein: After stopping the switching of the switching element, the controller resumes the switching of the switching element when the output voltage sense value decreases to a value obtained by subtracting a second preset margin value from the output voltage command value.

15. The charging system according to claim 13, wherein: The first preset margin value has a magnitude equal to or greater than a fluctuation magnitude of an output voltage generated in a normal operation state in which the battery is connected to the output terminal after initial startup is terminated, and is smaller than a preset upper limit value.

16. The charging system according to claim 9, wherein: When the output capacitor is charged to a preset charging voltage in the initial charging mode, the controller short-circuits the relay to terminate the initial charging mode.

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