Direct-current-direct-current converter

Abstract

The present invention relates to a DC-DC converter. The flying capacitor DC-DC converter has a capacitor protection function that prevents the flying capacitor from overheating. The flying capacitor DC-DC converter estimates the temperature of the capacitor based on the inductor current and the switching duty ratio determined in accordance with the comparison result between the output voltage and the voltage command value, and determines whether to perform derating.

Description

TECHNICAL FIELD

[0001] The present application relates to a DC-DC converter, and more particularly, to a flying capacitor DC-DC converter having a capacitor protection function that prevents overheating of a flying capacitor. BACKGROUND

[0002] DC-DC converters that convert a direct current (DC) power source from one voltage level to another voltage level are widely used in various electronic devices.

[0003] With regard to a conventional DC-DC converter, a technology is known that converts a voltage of a DC power source to another voltage by controlling an energy accumulation amount and an energy release amount of an inductor using on / off operations of a semiconductor switch. This type of DC-DC converter has a disadvantage of being large in size and heavy.

[0004] To solve this problem, that is, to reduce the size and weight of the inductor, it is necessary to reduce the inductance value of the inductor. To this end, a technology has been developed that reduces a voltage applied to the inductor by charging and discharging a capacitor.

[0005] Among various DC-DC converters using this technology, there is a DC-DC converter that includes a series of switches and a flying capacitor disposed between two of the switches.

[0006] This DC-DC converter having a flying capacitor has a problem in that it is difficult to control because it is necessary to maintain a voltage of the flying capacitor at a constant level.

[0007] Specifically, a capacitor characteristic deteriorates as a temperature increases, and when the capacitor characteristic deteriorates, a failure such as a short circuit or an open circuit occurs. Therefore, in the case of a flying capacitor DC-DC converter, a function of overheat protection is required to control a temperature of the flying capacitor to a certain temperature or less to improve system reliability.

[0008] The overheat protection function can be implemented by attaching a temperature sensor to the capacitor and adjusting an output voltage of the capacitor based on a measured temperature. However, this method generates an additional cost of designing the temperature sensor and related circuits.

[0009] The above statements are merely intended to help understand the background of the present application and are not intended to mean that the present application falls within the scope of the related art known to those skilled in the art. SUMMARY

[0010] An object of the present application is to provide a flying capacitor DC-DC converter having a capacitor protection function that prevents a temperature of a flying capacitor thereof from excessively increasing.

[0011] To achieve this object, according to one aspect of the present application, there is provided a DC-DC converter including: a first capacitor; first, second, third, and fourth switches connected in series between first and second electrodes of the first capacitor; a second capacitor having first and second electrodes connected to connection nodes of the first and second switches and the third and fourth switches, respectively; an inductor having a first terminal connected to a connection node of the second and third switches; and a controller that determines control duty ratios of the first to fourth switches, estimates a temperature of the second capacitor based on the control duty ratios and a detection current that is an actually measured inductor current, and determines whether to perform derating according to the temperature of the second capacitor.

[0012] According to one embodiment of the present application, the controller generates a current command value based on a comparison result between a first detection voltage that is a measured output voltage of the DC-DC converter and an output voltage command value that is a target voltage to be output from the DC-DC converter, determines control duty ratios of the first to fourth switches based on a comparison result between the detection current and the current command value, calculates a root mean square (RMS) current of the second capacitor based on the control duty ratios and the detection current, and estimates the temperature of the second capacitor based on the calculated RSM current. The output voltage is a voltage between the first and second electrodes of the first capacitor or a voltage between a second terminal of the inductor and a connection node of the first capacitor and the fourth switch.

[0013] According to one embodiment of the present application, the DC-DC converter can further include a voltage sensor for obtaining the measured output voltage.

[0014] According to one embodiment of the present application, when the estimated temperature of the second capacitor is higher than a predetermined reference temperature, the controller can perform derating by imposing a limit on the current command value.

[0015] According to one embodiment of the present application, the controller can output a decision on whether to perform derating to a higher-level controller that generates the output voltage command value.

[0016] According to one embodiment of the present application, the controller can calculate the RMS current (I of the second capacitor using an equation ft，rms : second capacitor RMS current, I L : detection current, control duty ratios).

[0017] According to one embodiment of the present application, the controller can include a voltage controller that generates a current command value as a target current to be flowed through the inductor according to a difference between a first detected voltage and an output voltage command value, a current controller that generates a first control voltage command value according to a difference between the current command value and a detected current, a flying capacitor voltage controller that generates a second control voltage command value according to a difference between a second detected voltage and a second voltage command value, and a capacitor protector that calculates an RMS current of the second capacitor based on the detected current and a control duty obtained by dividing the first control voltage command value by the output voltage, estimates a temperature of the second capacitor based on the calculated RMS current, and determines whether to perform derating according to the temperature of the second capacitor.

[0018] According to one embodiment of the present application, the capacitor protector can include a divider that calculates a control duty by dividing the first control voltage command value by the output voltage, a current calculator that calculates an RMS current of the second capacitor based on the control duty and the detected current, a temperature estimator that estimates a temperature of the second capacitor according to the calculated RMS current of the second capacitor, and an output determiner that determines whether to perform derating according to a comparison result between the estimated temperature of the second capacitor obtained by the temperature estimator and a predetermined reference temperature.

[0019] According to one exemplary embodiment of the present application, when the output determiner determines to perform derating, the capacitor protector can further include a limiter that applies a limit to the current command value output from the voltage controller and provides the limited current command value to the current controller.

[0020] According to one exemplary embodiment of the present application, the output determiner can output a decision of whether to perform derating to a superior controller that generates the output voltage command value.

[0021] According to one exemplary embodiment of the present application, the current calculator can calculate the RMS current (I of the second capacitor using an equation ft，rms : RMS current of the second capacitor, I L : detected current, : control duty.

[0022] According to one exemplary embodiment of the present application, the DC-DC converter can further include a current sensor for obtaining an actually measured inductor current.

[0023] According to the present application, even in the case where a temperature sensor is not provided, the DC-DC converter can calculate the current RMS value of the flying capacitor based on the inductor current and the switching duty ratio of the flying DC-DC converter, thereby estimating the temperature of the flying capacitor.

[0024] Therefore, with this configuration of the DC-DC converter, it is possible to prevent overheating of the flying capacitor without incurring additional costs due to the addition of a temperature sensor or the like, and it is possible to ensure stability and reliability of control through protection against overheating of the flying capacitor.

[0025] The effects and advantages achievable by the present application are not limited to the above-mentioned effects and advantages, and other effects and advantages not mentioned above but achievable by the present application will be apparent to those skilled in the art from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and other objects, features and other advantages of the present application will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0027] Figure 1 FIG. 1 shows a circuit diagram of a DC-DC converter according to an embodiment of the present application;

[0028] Figure 2 FIG. 2 shows a block diagram of a controller of the DC-DC converter according to an embodiment of the present application;

[0029] Figures 3 to 6 FIG. 3 shows a schematic diagram of the flow of current in the DC-DC converter according to an embodiment of the present application;

[0030] Figure 7 FIG. 4 shows a waveform diagram of the current of the flying capacitor included in the DC-DC converter shown in FIG. 1 when the pole voltage of the DC-DC converter is 0.75 times or 0.25 times the output voltage; Figure 1

[0031] Figure 8 FIG. 5 shows a waveform diagram of the current of the flying capacitor included in the DC-DC converter shown in FIG. 1 when the pole voltage of the DC-DC converter is 0.5 times the output voltage;

[0032] Figure 9 FIG. 6 shows a graph of the ratio of the on-interval of the flying capacitor according to the first control duty ratio, which corresponds to a value obtained by dividing the first control voltage command value by the output voltage of the DC-DC converter shown in FIG. 1; and Figure 1

[0033] Figure 10 ​​To show a graph of the RMS determining coefficient of the flying capacitor's current according to the first control duty ratio, which corresponds to a value obtained by dividing the first control voltage command value by the output voltage of the DC-DC converter shown in FIG. 1. Figure 1 DETAILED DESCRIPTION

[0034] Hereinafter, a DC-DC converter according to various embodiments of the present application will be described in detail with reference to the accompanying drawings.

[0035] Figure 1 A circuit diagram of a DC-DC converter according to one embodiment of the present application.

[0036] Reference Signs Figure 1 The DC-DC converter according to one embodiment of the present application converts a voltage applied between a first input / output (I / O) terminal T11 and a second I / O terminal T12 into a higher voltage, and provides the raised voltage between a third I / O terminal T21 and a fourth I / O terminal T22. Conversely, the DC-DC converter converts a voltage applied between the third I / O terminal T21 and the fourth I / O terminal T22 into a lower voltage, and provides the generated lower voltage between the first I / O terminal T11 and the second I / O terminal T12. Figure 1 An exemplary converter is shown, which includes a battery BAT disposed between the first I / O terminal T11 and the second I / O terminal T12, the converter raising a voltage of a supply current of the battery BAT into a higher voltage, and providing the generated higher voltage between the third I / O terminal T21 and the fourth I / O terminal T22. For example, a load is connected between the third I / O terminal T21 and the fourth I / O terminal T22.

[0037] The following description relates to an example in which a voltage obtained by boosting an output voltage of the battery BAT is applied between the third I / O terminal T21 and the fourth I / O terminal T22. However, it will be understood by those skilled in the art that the opposite case is also possible. That is, a voltage applied between the third I / O terminal T21 and the fourth I / O terminal T22 is stepped down, and the resulting lowered voltage is applied between the first I / O terminal T11 and the second I / O terminal T12.

[0038] The DC-DC converter according to one embodiment of the present application includes a first capacitor C DC , first to fourth switches S1, S2, S3, and S4, a second capacitor C FC , an inductor L, and a controller 10; the first capacitor C DC ​The first and second electrodes are respectively connected to the third I / O terminal T21 and the fourth I / O terminal T22; the first to fourth switches S1, S2, S3 and S4 are connected in series to the first capacitor C. DC Between the first electrode and the second electrode; the second capacitor C FC The first and second electrodes are respectively connected to the connection node between the first switch S1 and the second switch S2 and the connection node between the third switch S3 and the fourth switch S4; the first terminal of the inductor L is connected to the connection node between the second switch S2 and the third switch S3; the controller 10 controls the on / off state of each of the first to fourth switches S1 to S4. In one example, the outputs S1 to S4 of the controller 10 can be connected to the gates of the first to fourth switches S1 to S4 respectively.

[0039] First capacitor C DC It is a smoothing capacitor connected between the third I / O terminal T21 and the fourth I / O terminal T22. Although Figure 1 It is not shown in the figure, but an additional smoothing capacitor can be connected between the first I / O terminal T11 and the second I / O terminal T12.

[0040] The first switch S1 to the fourth switch S4 are connected to the first capacitor C. DC The first electrode side is connected in series with the second electrode side. Each of the first switches S1 to the fourth switches S4 is implemented by an insulated gate bipolar transistor (IGBT). Each switch is turned on or off according to an on / off control signal input from the controller 10 to its gate. Alternatively, each of the first switches S1 to the fourth switches S4 can be implemented using any switching element known in the art instead of an IGBT.

[0041] Second capacitor C FC It is a flying capacitor, whose first electrode and second electrode are respectively connected to the connection node between the first switch S1 and the second switch S2 and the connection node between the third switch S3 and the fourth switch S4.

[0042] Although not shown in the accompanying drawings, a DC-DC converter according to one embodiment of the present invention may include multiple sensors for detecting internal circuitry information used by a controller 10 to generate an on / off control signal for each of the first switch S1 to the fourth switch S4. The multiple sensors may include: sensors for measuring the voltage V between the first I / O terminal T11 and the second I / O terminal T12 or the voltage V between the third I / O terminal T21 and the fourth I / O terminal T22. DC A voltage sensor is used to measure the second capacitor C. FC voltage V FCa voltage sensor for measuring a voltage across the inductor L L a current sensor for measuring a current flowing through the inductor L. The voltage value and the current value measured by the voltage sensor and the current sensor are referred to as a detected voltage and a detected current, respectively. The detected voltage and the detected current are input to the controller 10.

[0043] The controller 10 receives a first detected voltage, which is an actual measured voltage between the first electrode and the second electrode of the first capacitor C DC or between the second terminal and the first capacitor C DC The first detected voltage corresponds to an output voltage generated by a step-up operation of the DC-DC converter or an output voltage generated by a step-down operation. In the case of the step-up operation, the first detected voltage corresponds to a voltage between the third I / O terminal T21 and the fourth I / O terminal T22 (i.e., a voltage of the first capacitor C DC In the case of the step-down operation, the first detected voltage corresponds to a voltage between the first I / O terminal T11 and the second I / O terminal T12.

[0044] The controller 10 compares the first detected voltage with a first voltage command value, and calculates a difference therebetween. The first voltage command value represents a target voltage set to be output from the DC-DC converter. The first voltage command value is set by a higher-level controller. In one example, a set value or a preset value can be stored in a storage device, and can be read by the controller 10, or can be transmitted to the controller 10 from the higher-level controller.

[0045] The controller 10 receives a detected voltage V FC applied to the second capacitor C FC , which is a measured voltage, compares a second detected voltage V FC with a preset second voltage command value, and calculates a difference therebetween. The second voltage command value is preset by the higher-level controller, and is approximately half of a voltage of the first capacitor C DC According to one embodiment of the present application, the controller 10 controls the on / off state of each of the switches S1 to S4 based on a product of the actual measured current (i.e., the detected current) of the inductor L and the difference between the detected voltage V FC applied to the second capacitor C FC and the second voltage command value.

[0046] Figure 2 is a block diagram of a controller of a DC-DC converter according to one embodiment of the present application.

[0047] Reference will now be made in detail to the embodiments of the present application, examples of which are illustrated in the accompanying drawings. Figure 2According to one embodiment of the present invention, the controller 10 of the DC-DC converter includes a voltage controller 11, a current controller 12, a flying capacitor voltage controller 13, and a capacitor protector 150.

[0048] The voltage controller 11 includes a subtractor 111 and a PI controller 112. The subtractor 111 detects the voltage V, which is the actual measured voltage between the first I / O terminal T11 and the second I / O terminal T12. DC Or the detection voltage V, which is the actual measured voltage between the third I / O terminal T21 and the fourth I / O terminal T22. DC With the preset first voltage command value V DC * Compare and calculate the detection voltage V DC With the first voltage command value V DC The difference between * is calculated by the subtractor 111. The PI controller 112 performs proportional-integral control to reduce the difference calculated by the subtractor 111. By performing proportional-integral control, the PI controller 112 outputs an inductor current command value I representing the target current of the inductor L. L * This reduces the difference calculated by subtractor 111.

[0049] The current controller 12 includes a subtractor 121 and a PI controller 122. The subtractor 121 calculates the inductor current command value I provided by the voltage controller 11. L *The actual detected current I flowing through inductor L L The difference between them. PI controller 122 performs proportional-integral control to generate a first control voltage command value V that can reduce the output value of subtractor 121. DM *. First control voltage command value V DM *Used to determine the on-off duty cycle of switches S1 to S4.

[0050] Figure 2 An example of voltage controller 11 and current controller 12 performing proportional-integral control is shown. However, the control technique is not limited to this. Various techniques known in the art can be utilized.

[0051] The flying capacitor voltage controller 12 includes a subtractor 131, a proportional controller 132, a reciprocal calculator 133, and a multiplier 134. The subtractor 131 receives the voltage applied to the second capacitor C. FC Detection voltage V FC The detection voltage V FC With the preset second voltage command value V FC The subtractor 131 compares the values ​​and calculates the difference. The proportional controller 132 performs proportional control and outputs a control command value to decrease the output value of the subtractor 131. The reciprocal calculator 133 calculates the measured inductor current I. Lthe reciprocal of the output value of the proportional controller 132 and the multiplication of the reciprocal output from the reciprocal calculator 133, and outputs the calculated product as a second control voltage command value V CM *.

[0052] In addition, the controller 10 can further include an adder 141, a subtractor 142, a second adder 143, a first switch controller 144, and a second switch controller 145; the adder 141 adds the first control voltage command value V DM * output from the current controller 12 and the second control voltage command value V CM * output from the flying capacitor voltage controller 13, and generates a first duty command value V1*; the subtractor 142 subtracts the first control voltage command value V DC * from the detection voltage V DM * detected between the I / O terminals; the second adder 143 adds the result value output from the subtractor 142 and the second control voltage command value V CM *; the first switch controller 144 determines the on / off state of the first switch S1 and the fourth switch S4 according to the comparison result between the first duty command value V1* and a triangular wave signal having a predetermined frequency generated from a triangular wave generator 146; and the second switch controller 145 determines the on / off state of the second switch S2 and the third switch S3 according to the comparison result between the second duty command value V2* and the triangular wave signal having a predetermined frequency output from the triangular wave generator 146.

[0053] With regard to the above configuration, the first duty command value V1* and the second duty command value V2* can be expressed by Equation 1 using the first control voltage command value V DM * and the second control voltage command value V CM *.

[0054] [Equation 1]

[0055] V1* = V CM * + V DM *

[0056] V2* = V CM * + (V DC - V DM ).

[0057] wherein the first control voltage command value V DM * is a value generated based on the output voltage V DC of the DC-DC converter and has an influence on the output, and the second control voltage command value V CM * is a value generated based on the voltage V FC of the flying capacitor and has an influence on the voltage VFC or the output voltage V of the DC-DC converter DC and the voltage V of the flying capacitor FC between them V DC -V FC has an influence. That is, the first control voltage command value V DM *is used to control the output voltage of the DC-DC converter, while the second control voltage command value V CM *is used to control the voltage of the flying capacitor.

[0058] Figures 3 to 6 is a schematic diagram showing the flow of current in the DC-DC converter according to one embodiment of the present application.

[0059] Figure 3 shows a first state in which the first switch S1 and the second switch S2 are on, and the third switch S3 and the fourth switch S4 are off. When the voltage V DC of the capacitor C DC is fully applied to the connection node of the inductor L and the switch S2 or S3, the first state is established.

[0060] Figure 4 shows a second state in which the first switch S1 and the third switch S3 are on, and the second switch S2 and the fourth switch S4 are off. When the voltage V DC corresponding to the voltage V DC of the capacitor C FC and the voltage V FC of the flying capacitor C FC is applied to the connection node of the inductor L and the switch S2 or S3, the second state is established.

[0061] Figure 5 shows a third state in which the second switch S2 and the fourth switch S4 are on, and the first switch S1 and the third switch S3 are off. When the voltage V FC of the flying capacitor C FC is applied to the connection node of the inductor L and the switch S2 or S3, the third state is established.

[0062] Figure 6 shows a fourth state in which the first switch S1 and the second switch S2 are off, and the third switch S3 and the fourth switch S4 are on. When no voltage is applied to the connection node of the inductor L and the switch S2 or S3, the fourth state is established.

[0063] In the states shown in Figures 3 to 6 , in the second and third states in which current flows through the second capacitor C FC called the flying capacitor C FC , the flying capacitor C FCThe voltage change. During the total duration of the second and third states, the flying capacitor C is charged. FC In or from the flying capacitor C FC The electrical energy released depends on the current flowing through the inductor L and the ratio of the second state to the third state.

[0064] This can be represented by Equation 2.

[0065] [Equation 2]

[0066] I FC =sC FC V FC

[0067] I FC =D CM ·I L

[0068]

[0069] Among them, “D” CM "This indicates that current flows through the flying capacitor C" FC The duty cycle, which is determined by the proportional control of the flying capacitor voltage controller 13, and is expressed by the third line of Equation 2. The third line of Equation 2 indicates that without utilizing the inductor current I... L The duty cycle in the case of the reciprocal of K. In Equation 2, "K P "" indicates the gain of the proportional controller 132.

[0070] Equation 2 can be reduced to Equation 3, and Equation 4 can be obtained by calculating the transfer function based on Equation 3.

[0071] [Equation 3]

[0072]

[0073] [Equation 4]

[0074]

[0075] In order to control the transfer function of Equation 4 in the closed-loop form of a first-order low-pass filter, the relationship in Equation 5 must be established.

[0076] [Equation 5]

[0077]

[0078] Equation 5 shows that linear control characteristics can only be obtained when the gain of the proportional control is inversely proportional to the inductor current.

[0079] Therefore, the flying capacitor voltage controller 13 includes a method for obtaining the inductor current I. LThe configuration of the reciprocal of the reciprocal of the flyback capacitor voltage controller 133 enables stable control characteristics of the total current to be obtained.

[0080] Here, the controller in the flyback capacitor voltage controller 13 can be implemented using a proportional-integral (PI) controller instead of the proportional controller 132. However, when a PI controller is used, depending on the direction of the current, a large duty pulsation can be generated from the value accumulated in the integrator. This means that the controllability of the inductor current I L near zero deteriorates greatly. Therefore, it is preferable to use a proportional controller.

[0081] The current flows through the second capacitor (i.e., the flyback capacitor) C FC The output voltages of the second state and the third state are "V DC -V FC " and "V FC ", respectively. In the normal state, the intermediate voltage 0.5*V DC in the output of the output three-level converter.

[0082] Therefore, when the output pole voltage of the flyback converter approaches 0.5*V DC , the frequency of use of the second state and the third state increases, and when the output pole voltage of the flyback converter differs greatly from 0.5*V DC , the frequency of use of the first state or the third state increases. In addition, when the flyback capacitor C FC is stably controlled to output a voltage of 0.5*V DC , the ratio of the second state to the third state is 1:1 (i.e., V CM * = 0).

[0083] Figure 7 To briefly show the waveform of the current of the flyback capacitor included in the DC-DC converter when the pole voltage of the DC-DC converter shown in Figure 1 is 0.75 times or 0.25 times the output voltage, Figure 8 To briefly show the waveform of the current of the flyback capacitor included in the DC-DC converter when the pole voltage of the DC-DC converter is 0.5 times the output voltage.

[0084] In Figure 7 and Figure 8 , T sw denotes the switching period of the first switch S1 to the fourth switch S4, I L denotes the inductor current, and T fc is the duration of the current flowing through the flyback capacitor C FC .

[0085] As Figure 7 and Figure 8As shown, when the duration T fc Relative to the total switching period T sw The ratio is defined as D fc When, the ratio D fc It can be represented by Equation 6.

[0086] [Equation 6]

[0087] D fc =0.5-|D DM *-0.5|.

[0088] Here, D DM * corresponds to the first control voltage command value V output from the current controller 12. DM The duty cycle value, and by passing the first control voltage command value V DM Divide by the output voltage V DC And thus obtained. In this article, this is referred to as the first control duty cycle.

[0089] According to Equation 6, based on the first control duty cycle D DM *Duty cycle D fc Able to be Figure 9 This indicates that the first control duty cycle D DM *Corresponds to passing the first control voltage command value V DM Divide by the output voltage V DC The value obtained.

[0090] Figure 9 To illustrate the ratio of the conduction range of the flying capacitor according to the first control duty cycle, the first control duty cycle corresponds to the ratio of the first control voltage command value to... Figure 1 The value obtained by the output voltage of the DC-DC converter shown.

[0091] Typically, the temperature of a capacitor depends on its cooling performance and the amount of heat generated based on the ambient temperature and temperature coefficient. The amount of heat generated is known to vary depending on the root mean square (RMS) value of the current flowing through the capacitor. That is, various known techniques exist for calculating the amount of heat generated by the capacitor based on the RMS value of the current flowing through it.

[0092] like Figure 7 and Figure 8 As shown, the RMS value in the form of a bipolar pulse train can be calculated using Equation 7.

[0093] [Equation 7]

[0094]

[0095] When the definition of the duty ratio D fc in Equation 6 is applied to Equation 7, the RMS value I FC of the current flowing through the flying capacitor C ft,rms may be expressed as Equation 8.

[0096] [Equation 8]

[0097]

[0098] In Equation 8, the RMS determination coefficient a fc of the current of the flying capacitor can be expressed as a function of the first control duty ratio D DM *as shown in Equation 9. Figure 10

[0099] Figure 10 To show a graph of the RMS determination coefficient of the current of the flying capacitor according to the first control duty ratio, which corresponds to a value obtained by dividing the first control voltage command value by the output voltage of the DC-DC converter as shown in Equation 10. Figure 1

[0100] As described above, the RMS value of the current of the flying capacitor is determined by the first control duty ratio D DM *and the inductor current I L . According to one embodiment of the present application, the controller further includes a capacitor protector 150. The capacitor protector 150 includes a divider 151, a current calculator 152, a temperature estimator 153, an output determiner 154; the divider 151 divides the first control voltage command value V DM * determined by the current controller 12 by the output voltage V DC to derive the first control duty ratio D DM *; the current calculator 152 receives the first control duty ratio D DM *and the detected current I L of the inductor L, and derives the RMS value of the current of the flying capacitor C FC using Equation 8; the temperature estimator 153 estimates the temperature of the flying capacitor C FC based on the RMS value of the current of the flying capacitor; and the output determiner 154 determines whether to derate the output voltage by comparing the estimated temperature with a preset reference temperature.

[0101] Here, the temperature estimator 153 can require information such as a coolant temperature (or an outdoor air temperature) to estimate the temperature of the capacitor, and can perform a calculation for temperature estimation using various models or techniques known in the art.

[0102] ​​In addition, when the output determiner 154 has determined that derating is required, a derating request is sent to a higher-level controller that generates the voltage command value of the DC-DC converter. The higher-level controller or the like generates a new voltage command value for derating, and provides the voltage command value to the voltage controller 11. In general, the term "derating" refers to a control technique in which a controller forcibly reduces the performance of a device. In the present application, the term "derating" refers to the voltage controller 11 forcibly reducing the output voltage of the converter.

[0103] In order for the controller 10 itself to derate the output voltage, the capacitor protector 150 further includes a limiter 155 that limits the current command value I L * applies a limit. The limiter 155 limits the output voltage of the DC-DC converter by limiting the current command value provided to the current controller 12 to a predetermined level or less.

[0104] The foregoing operations / functions performed by the controller can be implemented as computer-readable codes / algorithms / software stored on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store data that can be subsequently read by a computer or a processor / microprocessor. Examples of the computer-readable recording medium include a hard disk drive (HDD), a solid state drive (SSD), a silicon disk drive (SDD), a read-only memory (ROM), a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, etc.

[0105] The foregoing controller can include one or more processors / microprocessors. The controller can be implemented with a circuit. The controller can perform the foregoing operations / functions by executing computer-readable codes / algorithms / software stored on a computer-readable recording medium.

[0106] Although the present application has been described with reference to preferred embodiments, the preferred embodiments are presented for the purpose of describing the technical spirit of the present application only, and those skilled in the art will understand that various modifications and changes can be made without departing from the scope and spirit of the present application. Therefore, it should be understood that the scope of protection of the present application is defined by the appended claims, not the description presented above.

Claims

1. A DC-DC converter comprising: a first capacitor; a first switch, a second switch, a third switch, and a fourth switch connected in series between a first electrode and a second electrode of the first capacitor; a second capacitor whose first electrode is connected to a connection node of the first switch and the second switch, and whose second electrode is connected to a connection node of the third switch and the fourth switch; an inductor whose first terminal is connected to a connection node of the second switch and the third switch; and a controller that determines control duty ratios of the first switch to the fourth switch, estimates a temperature of the second capacitor based on the control duty ratios and a detection current that is an actually measured inductor current, and determines whether to perform derating in accordance with the estimated temperature of the second capacitor; wherein the controller includes: a voltage controller that generates a current command value that is a target current to be flowed through the inductor, based on a difference between a first detection voltage and an output voltage command value; a current controller that generates a first control voltage command value based on a difference between the current command value and the detection current; a flying capacitor voltage controller that generates a second control voltage command value based on a difference between a second detection voltage and a second voltage command value; and a capacitor protector that calculates a root mean square current of the second capacitor based on the detection current and a control duty ratio obtained by dividing the first control voltage command value by the output voltage, estimates a temperature of the second capacitor based on the calculated root mean square current, and determines whether to perform derating in accordance with the estimated temperature of the second capacitor. the controller generates a current command value that is a target inductor current to be flowed through the inductor, based on a comparison result between a first detection voltage that is a measured output voltage of the DC-DC converter and an output voltage command value that is a target voltage to be output from the DC-DC converter, determines control duty ratios of the first switch to the fourth switch based on a comparison result between the detection current and the current command value, calculates a root mean square current of the second capacitor based on the control duty ratios and the detection current, and estimates a temperature of the second capacitor based on the calculated root mean square current; 2. The DC-DC converter according to claim 1, wherein, wherein the output voltage is a voltage between the first electrode and the second electrode of the first capacitor or a voltage between a second terminal of the inductor and a connection node of the first capacitor and the fourth switch.

3. The DC-DC converter according to claim 2, further comprising a voltage sensor for obtaining the measured output voltage. the controller performs derating by imposing a limit on the current command value when the estimated temperature of the second capacitor is higher than a predetermined reference temperature.

4. The DC-DC converter of claim 1, wherein, the controller outputs a result of the decision on whether to perform derating to a higher-level controller that generates the output voltage command value.

5. The DC-DC converter of claim 1, wherein, the capacitor protector includes:

6. The DC-DC converter of claim 2, wherein, The controller utilizes the equation computes the root-mean-square current of the second capacitor, where I ft，rms is the root-mean-square current of the second capacitor, I L is the detection current, is the control duty cycle.

7. The DC-DC converter of claim 1, wherein, a divider that calculates the control duty ratio by dividing the first control voltage command value by the output voltage; a current calculator that calculates the root mean square current of the second capacitor based on the control duty ratio and the detection current; a temperature estimator that estimates the temperature of the second capacitor in accordance with the root mean square current of the second capacitor calculated by the current calculator; and ​ an output determiner that determines whether to perform derating in accordance with a comparison result between the temperature of the second capacitor estimated by the temperature estimator and a predetermined reference temperature.

8. The DC-DC converter of claim 7, wherein, When the output determiner determines to perform derating, the capacitor protector further includes a limiter that imposes a limit on a current command value output from the voltage controller and provides the limited current command value to the current controller.

9. The DC-DC converter of claim 7, wherein, The output determiner outputs a result of the decision on whether to perform derating to a higher-level controller that generates an output voltage command value.

10. The DC-DC converter of claim 7, wherein, The current calculator calculates the root mean square current of the second capacitor using the equation I2 = I1 * D ft，rms I2 = I1 * D L I2 = I1 * D D = control duty cycle 11. The DC-DC converter of claim 1, further comprising a current sensor for obtaining an actual measured inductor current.

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