DC / DC Converter

Abstract

To provide a flying DC / DC converter having a capacitor overheat protection function for preventing a temperature of a flying capacitor from excessively rising.SOLUTION: A DC / DC converter of the present invention, includes: a first capacitor; a first switch to a fourth switch, sequentially connected between both ends of the first capacitor in a serial relation; a second capacitor of which both ends are connected to a connection node of the first and second switches and a connection node of the third and fourth switches; an inductor in which one end is connected to the connection node of the second and third switches; and a controller that determines a control duty of the first switch to the fourth switch, estimates a temperature of the second capacitor on the basis of the control duty and a detection current obtained by detecting a current flowing in the inductor, and determines whether or not a delaying is performed on the basis of the temperature of the estimated second capacitor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a DC / DC converter, and more particularly to a flying DC / DC converter having a capacitor overheat protection function for preventing the temperature of a flying capacitor from rising excessively. [Background technology]

[0002] In general, a DC / DC converter is a device that converts the magnitude of an input DC voltage to a desired magnitude, and is widely used in various electrical and power fields.

[0003] A conventional DC / DC converter uses a semiconductor switch to control the amount of energy stored in and released from an inductor to convert DC to DC voltage. Such a conventional DC / DC converter has the disadvantage that the inductor used is large in size and heavy in weight.

[0004] In order to solve such problems of size and weight of inductors, a technology has been developed to reduce the inductance value provided by the inductor by reducing the voltage applied to the inductor using charging and discharging of a capacitor, thereby making the inductor smaller and lighter.

[0005] One such technique is a DC / DC converter in which a plurality of switches are connected in series and flying capacitors are provided between some of the switches.

[0006] A conventional DC / DC converter equipped with a flying capacitor is difficult to control because the voltage of the added flying capacitor must be controlled to a constant level.

[0007] In particular, the higher the temperature of a capacitor, the worse its characteristics become, and when the capacitor characteristics deteriorate, it can cause failures such as short circuits and disconnections. Therefore, in the case of a flying DC / DC converter, an overheat protection function is required to keep the temperature of the applied flying capacitor below a certain level in order to increase the reliability of the system.

[0008] Such overheat protection is accomplished by attaching a temperature sensor to the capacitor and adjusting the output based on the measured temperature value, but in this case, additional costs are incurred in designing the temperature sensor and associated circuitry. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 7,746,041 [Patent Document 2] Patent No. 6223609 specification Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in consideration of the above-mentioned problems in the conventional technology, and an object of the present invention is to provide a flying DC / DC converter having a capacitor overheat protection function for preventing the temperature of the flying capacitor from rising excessively. [Means for solving the problem]

[0011] In order to achieve the above object, a DC / DC converter according to one embodiment of the present invention includes a first capacitor; a first switch, a second switch, a third switch, and a fourth switch connected in series between both ends of the first capacitor; a second capacitor having both ends connected to a connection node between the first switch and the second switch and a connection node between the third switch and the fourth switch, respectively; an inductor having one end connected to the connection node between the second switch and the third switch; and a controller that determines control duties of the first switch to the fourth switch, estimates a temperature of the second capacitor based on the control duty and a detection current obtained by detecting a current flowing through the inductor, and determines whether to derate based on the estimated temperature of the second capacitor.

[0012] The controller generates a current command for the inductor based on a result of comparing a first detection voltage that detects the output voltage of the DC / DC converter with an output voltage command for the output voltage, determines control duties of the first switch to the fourth switch based on a value obtained by comparing a detection current that detects a current flowing through the inductor with the current command, calculates an RMS current of the second capacitor based on the control duty and the detection current, and estimates a temperature of the second capacitor based on the calculated RMS current, and the output voltage may be a voltage across both ends of the first capacitor, or a voltage between the other end of the inductor and a connection node between the first capacitor and the fourth switch.

[0013] The controller may perform derating by limiting the magnitude of the current command when the estimated temperature of the second capacitor is higher than a preset reference temperature. The controller can output whether or not to derate to a higher-level controller that generates the output voltage command. The controller may be configured to:

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[0014] The controller may include a voltage control unit that generates a current command for the inductor based on a difference between the first detected voltage and the output voltage command, a current control unit that generates a first control voltage command based on a difference between the current command and the detected current, a flying capacitor voltage control unit that generates a second control voltage command based on a difference between a second detected voltage that detects a voltage applied to the second capacitor and a second voltage command for the voltage applied to the second capacitor, and a capacitor protection unit that calculates an RMS current of the second capacitor based on the control duty obtained by dividing the first control voltage command by the output voltage and the detected current, estimates a temperature of the second capacitor based on the calculated RMS current, and decides whether to derate based on the estimated temperature of the second capacitor.

[0015] The capacitor protection unit may include a divider that divides the first control voltage command by the output voltage to calculate the control duty, a current calculation unit that calculates an RMS current of the second capacitor based on the control duty and the detected current, a temperature estimation unit that estimates a temperature of the second capacitor based on the RMS current of the second capacitor calculated by the current calculation unit, and an output decision unit that decides whether to derate based on a result of comparing the temperature of the second capacitor estimated by the temperature estimation unit with a preset reference temperature. The capacitor protection unit may further include a limiter for limiting a magnitude of a current command output from the voltage control unit and providing the limit to the current control unit when the output determination unit determines to perform derating. The output determination unit may output a signal indicating whether or not to perform derating to a higher-level controller that generates the output voltage command.

[0016] The current calculation unit is configured to calculate the current by the following formula:

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[0017] According to the DC / DC converter of the present invention, even if there is no temperature sensor, the temperature of the flying capacitor can be estimated by utilizing the switching duty and inductor current of the DC / DC converter to calculate the RMS value of the flying capacitor's conduction current.

[0018] As a result, the DC / DC converter according to the present invention can prevent overheating of the flying capacitor without incurring additional costs incurred by adding a temperature sensor, etc., and can ensure stability and reliability of control through overheating protection of the flying capacitor. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a circuit diagram of a DC / DC converter according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing in further detail the controller of the DC / DC converter according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing electrical flow states of a DC / DC converter according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing electrical flow states of a DC / DC converter according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram showing electrical flow states of a DC / DC converter according to an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing electrical flow states of a DC / DC converter according to an embodiment of the present invention. [Figure 7] 2 is a waveform diagram simply showing a flying capacitor conduction current included in the DC / DC converter shown in FIG. 1 when the pole voltage of the DC / DC converter is 0.75 or 0.25 of the output voltage. [Figure 8]2 is a waveform diagram simply showing a flying capacitor conduction current included in the DC / DC converter shown in FIG. 1 when the pole voltage of the DC / DC converter is 0.5 of the output voltage. [Figure 9] 4 is a graph showing a ratio of a conduction period of a flying capacitor according to a first control duty corresponding to a value obtained by dividing a first control voltage command by an output voltage of the DC / DC converter shown in FIG. 1; [Figure 10] 2 is a graph showing a value of an RMS determination coefficient of a flying capacitor conduction current according to a first control duty, which corresponds to a value obtained by dividing a first control voltage command of the DC / DC converter shown in FIG. 1 by an output voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A DC / DC converter according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] FIG. 1 is a circuit diagram of a DC / DC converter according to one embodiment of the present invention.

[0022] As shown in Fig. 1, the DC / DC converter according to an embodiment of the present invention is a DC / DC converter that boosts a DC voltage applied between the first input / output terminal T11 and the second input / output terminal T12 and provides it between the third input / output terminal T21 and the fourth input / output terminal T22, or conversely, that drops a DC voltage applied between the third input / output terminal T21 and the fourth input / output terminal T22 and provides it between the first input / output terminal T11 and the second input / output terminal T12. In the example shown in Fig. 1, a battery BAT is provided between the first input / output terminal T11 and the second input / output terminal T12, and the converter boosts the voltage of the battery BAT and provides it between the third input / output terminal T21 and the fourth input / output terminal T22. For example, a load is connected between the third input / output terminal T21 and the fourth input / output terminal T22.

[0023] Hereinafter, an example will be mainly described in which the voltage of the battery BAT is boosted and provided between the third input / output terminal T21 and the fourth input / output terminal T22. However, through the following explanation, a person skilled in the art can easily embody an example in which the opposite power flow, i.e., the voltage applied between the third input / output terminal T21 and the fourth input / output terminal T22 is stepped down and provided between the first input / output terminal T11 and the second input / output terminal T22.

[0024] The DC / DC converter according to an embodiment of the present invention includes a first capacitor C1 connected at both ends to a third input / output terminal T21 and a fourth input / output terminal T22. DC and the first capacitor C DC A first switch S connected in series between the two ends of the 1 , the second switch S 2 , the third switch S 3 , and the fourth switch S 4 and the first switch S 1 and the second switch S 2 and the third switch S 3 and the third switch S 4 A second capacitor C FC and the second switch S 2 and the third switch S 3 One end of the inductor L is connected to the connection node of the first switch S 1 ~ 4th Switch S 4 and a controller 10 that controls the on / off state of the light source.

[0025] First capacitor C DC is a type of smoothing capacitor connected between the third input / output terminal T21 and the fourth input / output terminal T22. Although not shown in FIG 1, an additional smoothing capacitor may be connected between the first input / output terminal T11 and the second input / output terminal T12.

[0026] First switch S 1 ~ 4th Switch S 4 is the first capacitor C DC are connected in series from one end to the other. 1~ 4th Switch S 4 Each of the first switches S is realized by an insulated gate bipolar transistor IGBT, and the on / off state is controlled by inputting an on / off control signal from the controller 10 to the gate of the IGBT. 1 ~ 4th Switch S 4 may be embodied with various switching elements known in the art that can replace IGBTs.

[0027] Second capacitor C FC is a flying capacitor, and the first switch S 1 and the second switch S 2 and the third switch S 3 and the fourth switch S 4 Each end is connected to a connection node.

[0028] Although not shown, in a DC / DC converter according to an embodiment of the present invention, the controller 10 controls the switch (S 1 ~S 4 The device is equipped with a number of sensors for detecting information within the circuit that is necessary for calculations to perform on / off control of the first input / output terminal T11 and the second input / output terminal T12, or the voltage V between the third input / output terminal T21 and the fourth input / output terminal T22. DC a voltage sensor for detecting a second capacitor C FC Voltage V FC and a current sensor for detecting the magnitude of the current flowing through the inductor L. The detected voltage and current detected by the voltage sensor and the current sensor are provided to the controller 10.

[0029] The controller 10 controls the first capacitor C DC The voltage across the inductor L and the first capacitor C DC and the fourth switch S 4Here, the first detection voltage corresponds to the output voltage output by the DC / DC converter after boosting or lowering a certain voltage. In the case of boosting, the first detection voltage corresponds to the voltage between the third input / output terminal T21 and the fourth input / output terminal T22 (i.e., the voltage between the first capacitor C DC The detected voltage V DC In the case of step-down, the voltage between the first I / O terminal T11 and the second I / O terminal T12 is detected.

[0030] The controller 10 also detects the first detection voltage V DC The control circuit 100 calculates an error between the voltage command and the DC / DC converter 102. ...

[0031] The controller 10 also controls the second capacitor C FC The voltage applied to the FC The second voltage command is a value that is preset by a higher-level controller, etc., and the first capacitor C DC In particular, in one embodiment of the present invention, the controller 10 controls the second capacitor C FC The voltage applied to the FC The error between the first and second voltage commands is multiplied by the detected current flowing through the inductor L, and the switch (S 1 ~S 4 ) on / off state.

[0032] FIG. 2 is a block diagram showing in more detail the controller of a DC / DC converter according to one embodiment of the present invention.

[0033] As shown in FIG. 2, a controller 10 of a DC / DC converter according to an embodiment of the present invention includes a voltage control unit 11, a current control unit 12, a flying capacitor voltage control unit 13, and a capacitor protection unit 150.

[0034] The voltage control unit 11 detects a voltage between the first input / output terminal T11 and the second input / output terminal T12, or a voltage between the third input / output terminal T21 and the fourth input / output terminal T22, and outputs a detected voltage V DC The first voltage command V DC * The controller 112 includes a subtractor 111 that calculates an error by comparing with the current command I L * Output.

[0035] The current control unit 12 receives a current command I L * and the detected current I L A subtractor 121 calculates the error between the first control voltage command V and the second control voltage command V DM * and a PI controller 122 that generates a first control voltage command V DM * is a switch (S 1 ~S 4 ) is used to determine the on / off duty.

[0036] FIG. 2 shows an example in which the voltage control unit 11 and the current control unit 12 perform proportional-integral control, but the present invention is not limited to this, and various control techniques known in the art may be applied.

[0037] The flying capacitor voltage control unit 13 controls the second capacitor C FC The voltage applied to the FC In response to the input, the second voltage command VFC * a subtractor 131 which calculates the error by comparing the output of the subtractor 131 with the output of the inductor L; a proportional controller 132 which outputs a control command to reduce the output of the subtractor 131 through proportional control; and a detection current I L and a reciprocal calculator 133 that calculates the reciprocal of V. CM * and a multiplier 134 that outputs

[0038] In addition, the controller 12 controls the first control voltage command V DM * and the second control voltage command V CM * The first duty command V 1 * a summation circuit 141 that generates a detection voltage V DC to the first control voltage command V DM * A subtractor 142 subtracts the second control voltage command V CM * The subtraction result of the subtractor 142 is added to the second duty command V 2 * A second summer 143 generates a first duty command V 1 * Based on the result of comparing the first switch S 1 and the fourth switch S 4 A first switching control unit (PWM) 144 that determines the on / off state of the second duty command V 2 * Based on the result of comparing the triangular wave having a preset frequency generated by the triangular wave generator 146 with the triangular wave having a preset frequency, the second switch S 2 and the third switch S 3 The inverter further includes a second switching control unit (PWM) 145 that determines the on / off state of the inverter.

[0039] According to the above-described configuration, the first duty command V 1 * and the second duty command V 2 * is the first control voltage command V DM * and the second control voltage command V CM * It is expressed by the following formula 1 using

[0040]

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[0041] Here, the first control voltage command V DM * is the output voltage V of the DC / DC converter DC A value that affects the output and is generated based on the second control voltage command V CM * is the flying capacitor voltage V FC A value generated based on the flying capacitor voltage V FC , or the output voltage V DC and the flying capacitor voltage V FC Difference with (V DC -V FC ) is affected. That is, the first control voltage command V DM * is used for output current control, and the second control voltage command V CM * is used to control the voltage of the flying capacitor.

[0042] 3 to 6 are diagrams showing states of electrical flows in the DC / DC converter according to one embodiment of the present invention.

[0043] Figure 3 shows the first switch S 1 and the second switch S 2 is on, and the third switch S 3 and the fourth switch S 4 The first state shows that the inductor L and the switch (S 2 or S3 ) and the capacitor C DC Voltage V DC is applied.

[0044] Figure 4 shows the first switch S 1 and the third switch S 3 is on and the second switch S 2 and the fourth switch S 4 The second state shows that the inductor L and the switch (S 2 or S 3 ) and the connection node, capacitor C DC Voltage V DC From flying capacitor C FC Voltage V FC This is the state in which a value obtained by subtracting

[0045] Figure 5 shows the second switch S 2 and the fourth switch S 4 is on, and the first switch S 1 and the third switch S 3 The third state shows that the inductor L and the switch (S 2 or S 3 ) and the connection node, the flying capacitor C FC Voltage V FC is applied.

[0046] Figure 6 shows the third switch S 3 and the fourth switch S 4 is on, and the first switch S 1 and the second switch S 2 The fourth state shows that the inductor L and the switch (S 2 or S 3 ) is in a state where no voltage is applied to the connection node.

[0047] In the states shown in FIGS. 3 to 6, the second capacitor C FC During the second and third states where current is conducted to the flying capacitor CFC During this state, a voltage change occurs on the flying capacitor C FC The energy charged and discharged to is affected by the ratio of the second state to the third state and the amount of current flowing through inductor L.

[0048] This can be expressed by the following Equation 2.

[0049]

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[0050] By summarizing the above Equation 2, the following Equation 3 is derived, and by calculating a transfer function based on this, the following Equation 4 is derived.

[0051]

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[0052]

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[0053] Therefore, in order to control the transfer function of Equation 4 in a closed loop in the form of a first-order low-pass filter, the relationship shown in Equation 5 below must be established.

[0054]

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[0055] According to Equation 5, it can be seen that linear control characteristics can be obtained only if the gain for proportional control has a characteristic that is inversely proportional to the inductor current.

[0056] Therefore, the flying capacitor voltage control unit 13 receives the inductor current I L By including a reciprocal calculator 133 that calculates the reciprocal of, it is possible to obtain stable control characteristics for the entire current.

[0057] Here, the controller in the flying capacitor voltage control unit 13 can be implemented as a proportional and integral (PI) controller instead of the proportional controller 132. When a proportional and integral (PI) controller is used, the value stored in the integrator generates a large duty pulsation according to the current direction, so that the inductor current I L Since there is a risk that controllability may be significantly deteriorated near where the current becomes zero, it is preferable to use a proportional controller.

[0058] On the other hand, the second capacitor C FC The output voltage in the second and third states where current is conducted to V DC -V FC ","V FC " and in the normal state, the intermediate voltage at the output of the three-level converter is 0.5V. DC Output.

[0059] Therefore, the output pole voltage of the flying converter (inductor L and switch (S 2 or S 3 ) and the voltage at the connection node) is 0.5V DC The closer the output pole voltage of the flying converter is to 0.5V, the more frequently the second and third states are utilized. DC The further away from the point, the more frequently the first or third state is utilized. FC is 0.5V DC When the valence electrons are stably controlled at 100 V, the proportion of the second and third states is equal (i.e., V CM * =0).

[0060] FIG. 7 is a waveform diagram simply showing the conduction current of a flying capacitor included in the DC / DC converter shown in FIG. 1 when the pole voltage of the DC / DC converter is 0.75 or 0.25 of the output voltage, and FIG. 8 is a waveform diagram simply showing the conduction current of a flying capacitor included in the DC / DC converter shown in FIG. 1 when the pole voltage of the DC / DC converter is 0.5 of the output voltage.

[0061] In Figs. 7 and 8, "T sw " is the first switch S 1 ~ 4th Switch S 4 The switching period is I L " is the inductor current and "T fc " is a flying capacitor C FC This is the time that current flows through the

[0062] As shown in FIG. 7 and FIG. 8, the total switching period T SW Among them, "T fc " is the percentage of "D fc " If we define "D fc " is expressed by the following formula 6.

[0063]

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[0064] Here, "D DM * " is the first control voltage command V DM * The duty value corresponds to the first control voltage command V DM * The output voltage V DC This is the same value as the value obtained by dividing the first control duty by the second control duty.

[0065] According to the above formula 6, the first control voltage command V DM * The output voltage V DC The first control duty D corresponds to the value obtained by dividingDM * "D fc " is represented in Figure 9.

[0066] FIG. 9 is a graph showing a ratio of a conduction period of a flying capacitor according to a first control duty corresponding to a value obtained by dividing a first control voltage command of the DC / DC converter shown in FIG. 1 by an output voltage.

[0067] Generally, the temperature of a capacitor is related to the cooling performance and heat generation amount according to the ambient temperature and temperature coefficient, and it is known that the heat generation amount has a characteristic that changes according to the RMS (Root Mean Square) value of the current flowing through the capacitor. That is, in the art, various methods are known for calculating the heat generation amount of a capacitor using the RMS value of the current flowing through the capacitor.

[0068] As shown in FIGS. 7 and 8, the RMS value of the bipolar pulse train is calculated by the following Equation 7.

[0069]

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[0070] "D" in the above formula 6 ft By applying the definition of " to Equation 7, the flying capacitor C FC The RMS value of the current flowing through I ft,rms is expressed by the following Equation 8.

[0071]

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[0072] In Equation 8, the RMS determination coefficient of the flying capacitor current, α fc " is the first control duty D DM * It is displayed as a function of

[0073] FIG. 10 is a graph showing the value of the RMS determination coefficient of the conducting current of the flying capacitor due to the first control duty corresponding to the value obtained by dividing the first control voltage command of the DC / DC converter shown in FIG. 1 by the output voltage.

[0074] As explained above, the RMS value of the flying capacitor conduction current is DM * and the inductor current I L is determined by.

[0075] The controller 10 according to an embodiment of the present invention determines a first control duty D DM * In order to derive the first control voltage command V DM * The output voltage V DC and a divider 151 for dividing the first control duty D DM * and the detected current I L The input of the flying capacitor C FC A current calculation unit 152 that derives the RMS value of the conduction current of the flying capacitor C FC Based on the RMS value of the conduction current of the flying capacitor C FC The capacitor protection unit 150 further includes a capacitor protection unit 150 having a temperature estimation unit 153 that estimates the temperature of the capacitor, and an output determination unit 154 that compares the estimated temperature with a preset reference temperature to determine whether or not to derate the output.

[0076] Here, the temperature estimation unit 153 may require information such as the coolant temperature (outside air temperature) to estimate the capacitor temperature, and the calculation for temperature estimation is implemented using various models or techniques known in the art.

[0077] Furthermore, when the output determination unit 154 determines that derating is necessary, it transmits a derating request to a higher-level controller or the like that generates a voltage command for the DC / DC converter. The higher-level controller or the like newly generates a voltage command for derating and provides it to the voltage control unit 11.

[0078] In order to perform output derating by the controller 10 itself, the capacitor protection unit 150 detects the current command I L * The limiter 155 limits the magnitude of the current command provided to the current control unit 12 to a preset level or less to limit the output of the DC / DC converter.

[0079] While particular embodiments of the present invention have been illustrated and described, it will be apparent to those having ordinary skill in the art that various modifications and variations can be made therein which remain within the scope of the invention. [Explanation of symbols]

[0080] 10 Controller 11 Voltage control section 111 Subtractor 112 Proportional-Integral Controller 12 Current control section 121 Subtractor 122 Proportional-integral controller 13 Flying capacitor voltage control section 131 Subtractor 132 Proportional Controller 133 Reciprocal calculator 134 Multiplier 141 Adder 142 Subtractor 143 Adder 144 First switching control section 145 Second switching control section 146 Triangle Wave Generator 150 Capacitor protection unit 151 Divider 152 Current calculation unit 153 Temperature estimation section 154 Output determination unit 155 Limiter

Claims

1. A DC / DC converter, comprising: A first capacitor; a first switch, a second switch, a third switch, and a fourth switch sequentially connected in series between both ends of the first capacitor; a second capacitor having both ends connected to a connection node between the first switch and the second switch and a connection node between the third switch and the fourth switch, an inductor having one end connected to a connection node between the second switch and the third switch; a controller that determines control duties of the first switch to the fourth switch, estimates a temperature of the second capacitor based on the control duties and a detected current obtained by detecting a current flowing through the inductor, and determines whether or not to perform derating based on the estimated temperature of the second capacitor, The controller: generating a current command for the inductor based on a result of comparing a first detected voltage obtained by detecting an output voltage of the DC / DC converter with an output voltage command for the output voltage; determining control duties of the first switch to the fourth switch based on a value obtained by comparing a detected current flowing through the inductor with the current command; calculating an RMS current of the second capacitor based on the control duty and the detected current, and estimating a temperature of the second capacitor based on the calculated RMS current; the output voltage is a voltage across both ends of the first capacitor, or a voltage between the other end of the inductor and a connection node between the first capacitor and the fourth switch, The controller: a voltage control unit that generates a current command for the inductor based on a difference between the first detected voltage and the output voltage command; a current control unit that generates a first control voltage command based on a difference between the current command and the detected current; a flying capacitor voltage control unit that generates a second control voltage command based on a difference between a second detected voltage obtained by detecting a voltage applied to the second capacitor and a second voltage command for the voltage applied to the second capacitor; a capacitor protection unit that calculates an RMS current of the second capacitor based on the control duty obtained by dividing the first control voltage command by the output voltage and the detected current, estimates a temperature of the second capacitor based on the calculated RMS current, and determines whether or not to perform derating based on the estimated temperature of the second capacitor.

2. The controller:

2. The DC / DC converter according to claim 1, wherein, when the estimated temperature of the second capacitor is higher than a preset reference temperature, the magnitude of the current command is limited to perform derating.

3. 2. The DC / DC converter according to claim 1, wherein the controller outputs whether or not to derate to a higher-level controller that generates the output voltage command.

4. The controller: The formula below: [0010] 2. The DC / DC converter according to claim 1, wherein the RMS current of the second capacitor is calculated by:

5. The capacitor protection unit includes: a divider that calculates the control duty by dividing the first control voltage command by the output voltage; a current calculation unit that calculates an RMS current of the second capacitor based on the control duty and the detected current; a temperature estimation unit that estimates a temperature of the second capacitor based on the RMS current of the second capacitor calculated by the current calculation unit; 2. The DC / DC converter of claim 1, further comprising: an output determination unit that determines whether to perform derating based on a result of comparing the temperature of the second capacitor estimated by the temperature estimator with a preset reference temperature.

6. The capacitor protection unit includes:

6. The DC / DC converter of claim 5, further comprising a limiter that limits a magnitude of a current command output from the voltage control unit and provides the limit to the current control unit when the output determination unit determines to derate.

7. 6. The DC / DC converter according to claim 5, wherein the output determination unit outputs whether or not to perform derating to a higher-level controller that generates the output voltage command.

8. The current calculation unit is The formula below: [0025] 6. The DC / DC converter according to claim 5, wherein the RMS current of the second capacitor is calculated by:

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