Control device for DC-DC converter, and program

Abstract

A control device (50) is applied to a DC-DC converter (10, 110) provided with a switch (31, 131) and a reactor (30, 130), the control device performing switching control of the switch so as to control an electric current flowing in the reactor to a command electric current value. The control device comprises: a voltage acquisition unit that acquires a first detection value of a first detection unit that detects a low-voltage-side voltage of the DC-DC converter, and a second detection value of a second detection unit that detects a high-voltage-side voltage of the DC-DC converter; a duty ratio calculation unit that, on the basis of a voltage ratio that is the ratio of the first detection value to the second detection value, calculates a duty ratio that is the proportion of an on period of the switch in one switching cycle; an estimation unit that estimates an error in the voltage ratio; a correction unit that corrects the duty ratio on the basis of the error in the voltage ratio estimated by the estimation unit; and a control unit that performs switching control on the basis of the duty ratio corrected by the correction unit.

Description

Control device and program for DC-DC converter CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-143880, filed on September 5, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a control device and a program for a DC-DC converter.

[0003] Conventionally, a DC-DC converter including a switch and a reactor has been known. A known control device for a DC-DC converter performs switching control of a switch to control a current flowing through the reactor to a command current value. In the switching control, the control device calculates a duty ratio, which is the ratio of an on-period of the switch in one switching cycle, and performs switching control based on the calculated duty ratio. An example of such a technique is disclosed in Patent Document 1.

[0004] Japanese Patent Application Laid-Open No. 2014-212587

[0005] There is a concern that the controllability of the current flowing through the reactor may be reduced due to an inappropriate calculation of the duty ratio of the switch.

[0006] A main object of the present disclosure is to provide a control device and program for a DC-DC converter that can improve the controllability of a current flowing through a reactor.

[0007] The present disclosure is applicable to a DC-DC converter including a switch and a reactor, and a control device for the DC-DC converter that performs switching control of the switch to control a current flowing through the reactor to a command current value, the control device comprising: a voltage acquisition unit that acquires a first detection value from a first detection unit that detects a low-voltage side voltage of the DC-DC converter and a second detection value from a second detection unit that detects a high-voltage side voltage of the DC-DC converter; a duty ratio calculation unit that calculates a duty ratio that is a ratio of an on-period of the switch in one switching cycle based on a voltage ratio that is a ratio of the first detection value to the second detection value; an estimation unit that estimates an error in the voltage ratio; a correction unit that corrects the duty ratio based on the error in the voltage ratio estimated by the estimator; and a control unit that performs the switching control based on the duty ratio corrected by the correction unit.

[0008] The duty ratio of the switch is calculated based on the first detection value of the first detector and the second detection value of the second detector. In this case, there is a concern that the duty ratio may not be calculated appropriately due to an error in the first detection value and the second detection value, and the current flowing through the reactor may deviate from the command current value. Here, the duty ratio of the switch is calculated based on a voltage ratio, which is the ratio of the first detection value to the second detection value.

[0009] Therefore, in the present disclosure, an error in the voltage ratio used to calculate the duty ratio is estimated, and the duty ratio is corrected based on the error in the estimated voltage ratio. This makes it possible to appropriately calculate the duty ratio taking into account the error in the first detection value and the second detection value. Then, by performing switching control based on the corrected duty ratio, it is possible to improve the controllability of the current flowing through the reactor.

[0010] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is an overall configuration diagram of a control system including a DC-DC converter according to a first embodiment, Fig. 2 is a time chart showing switching behavior and transitions of a reactor current value in a first current mode, Fig. 3 is a time chart showing switching behavior and transitions of a reactor current value in a current criticality mode, Fig. 4 is a time chart showing switching behavior and transitions of a reactor current value in a second current mode, Fig. 5 is a diagram showing transitions of an average reactor current value when switching from the first current mode to the second current mode is slow, and Fig. 6 is a diagram showing transitions of an average reactor current value when switching from the first current mode to the second current mode is slow. 8 is a time chart for explaining the process of estimating the voltage ratio error; FIG. 9 is a flowchart showing the control process executed by the control device; FIG. 10 is a time chart showing an example of control; FIG. 11 is an overall configuration diagram of a control system including a DC-DC converter according to a second embodiment; FIG. 12 is a flowchart showing the control process according to another embodiment; and FIG. 13 is an overall configuration diagram of a control system according to another embodiment.

[0011] Several embodiments will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding and / or associated parts may be designated by the same reference numerals or reference numerals that differ in the hundredth or more digit. For corresponding and / or associated parts, reference may be made to the descriptions of other embodiments.

[0012] First Embodiment A first embodiment of a control device according to the present disclosure will now be described with reference to the drawings.

[0013] As shown in FIG. 1 , the control system includes a DC-DC converter 10 , a DC power supply 20 , and a storage battery 21 .

[0014] The DC-DC converter 10 is a non-insulated boost converter that boosts a voltage input from a high-side input terminal THi and a low-side input terminal TLi and outputs the boosted voltage from a high-side output terminal THo and a low-side output terminal TLo. In this embodiment, a positive terminal of a DC power supply 20 is connected to the high-side input terminal THi, and a negative terminal of the DC power supply 20 is connected to the low-side input terminal TLi. The DC power supply 20 is a storage battery, a fuel cell, or the like. A positive terminal of a storage battery 21 is electrically connected to the high-side output terminal THo, and a negative terminal of the storage battery 21 is electrically connected to the low-side output terminal TLo. The storage battery 21 is a rechargeable secondary battery, such as a lithium-ion storage battery or a nickel-metal hydride storage battery. The voltage (e.g., rated voltage) of the storage battery 21 is higher than the voltage (e.g., rated voltage) of the DC power supply 20.

[0015] The DC-DC converter 10 includes a reactor 30, a switch 31, a diode 32, an input-side capacitor 33, and an output-side capacitor 34. In this embodiment, the switch 31 is an N-channel MOSFET. Note that the switch 31 is not limited to an N-channel MOSFET, and may be, for example, an IGBT to which a freewheeling diode is connected in antiparallel.

[0016] A first end of the reactor 30 is connected to a first end of the input capacitor 33 and the high potential side input terminal THi. A second end of the reactor 30 is connected to the drain of the switch 31 and the anode of the diode 32. A source of the switch 31 is connected to the low potential side input terminal TLi and the low potential side output terminal TLo.

[0017] A first end of the output capacitor 34 and the high potential side output terminal THo are connected to the cathode of the diode 32. A source of the switch 31, a low potential side input terminal TLi, and a low potential side output terminal TLo are connected to second ends of the capacitors 33 and 34.

[0018] The DC-DC converter 10 includes an input voltage sensor 40, an output voltage sensor 41, and a current sensor 42. The input voltage sensor 40 detects the voltage of the input-side capacitor 33. The output voltage sensor 41 detects the voltage of the output-side capacitor 34. The current sensor 42 detects the current flowing through the reactor 30. The detected values ​​of the sensors 40 to 42 are input to a control device 50 included in the DC-DC converter 10. In this embodiment, the input voltage sensor 40 corresponds to a "first detection unit," and the output voltage sensor 41 corresponds to a "second detection unit."

[0019] The control device 50 is primarily composed of a microcomputer 51, which includes a CPU. The functions provided by the microcomputer 51 can be provided by software stored in a physical memory device and a computer executing the software, software alone, hardware alone, or a combination thereof. For example, if the microcomputer 51 is provided by a hardware electronic circuit, the function can be provided by a digital circuit including multiple logic circuits or an analog circuit. For example, the microcomputer 51 executes a program stored in a non-transitory tangible storage medium serving as a storage unit of the microcomputer 51. The program includes, for example, programs for the processes shown in Figures 7, 9, and 12 (described below). Execution of the program results in the execution of a method corresponding to the program. The storage unit is, for example, a non-volatile memory. The program stored in the storage unit can be updated via a communication network such as the Internet, for example, via OTA (Over the Air).

[0020] The control device 50 performs switching control of the switch 31 to control the current flowing through the reactor 30 to a command current value. In the switching control, the control device 50 calculates a duty ratio D of the switch 31. The duty ratio D is a value that determines the ratio of the on-period Ton of the switch 31 in one switching period Ts (Ton / Ts=D). The control device 50 turns on the switch 31 for a period of "D×Ts" and turns off the switch 31 for a period of "(1−D)×Ts" in one switching period Ts.

[0021] The DC-DC converter 10 includes a drive circuit 52. The control device 50 generates a drive command Sg based on the calculated duty ratio D and outputs the drive command Sg to the drive circuit 52. Specifically, the drive command Sg is a PWM signal. The drive circuit 52 turns the switch 31 on and off based on the drive command Sg.

[0022] The control device 50 uses different methods for calculating the duty ratio D used for switching control depending on the state of the current flowing through the reactor 30. Here, a first current mode (i.e., discontinuous mode) in which the current flowing through the reactor 30 intermittently becomes zero in one switching period, and a second current mode (i.e., continuous mode) in which the current continues to flow through the reactor 30 in one switching period will be described.

[0023] 2 , in one switching period Ts of the switch 31, there occurs a period in which the value of the current flowing through the reactor 30 becomes zero. Specifically, during the on period of the switch 31, the value of the current flowing through the reactor 30 gradually increases, and magnetic energy is accumulated in the reactor 30. During the off period of the switch 31, the magnetic energy accumulated in the reactor 30 is released, and the value of the current flowing through the reactor 30 decreases and becomes zero. In this case, the time transition waveform of the value of the current flowing through the reactor 30 during one switching period Ts ideally becomes a triangular waveform and then becomes a waveform that is maintained at zero.

[0024] The control device 50 calculates a feedforward term DffA (corresponding to the "first duty ratio") for the first current mode in the process of calculating the duty ratio D. In the present embodiment, the control device 50 calculates the feedforward term DffA for the first current mode based on the following equation (eq1):

[0025] In the above equation (eq1), VL is the low-voltage side voltage of the DC-DC converter 10, and VH is the high-voltage side voltage of the DC-DC converter 10. Furthermore, Ls indicates the assumed inductance value of the reactor 30, and fsw indicates the switching frequency (=1 / Ts) of the switch 31. Iref indicates a command current value of the current flowing through the reactor 30. For example, the command current value Iref is set as a time average value of the current flowing through the reactor 30 over one switching period Ts. The command current value Iref input to the control device 50 is updated, for example, every one switching period Ts.

[0026] In the second current mode, as shown in FIG. 4, a current continues to flow from the first terminal to the second terminal of the reactor 30 during one switching period Ts of the switch 31.

[0027] The control device 50 calculates a feedforward term DffB (corresponding to the "second duty ratio") for the second current mode in the process of calculating the duty ratio D. In the present embodiment, the control device 50 calculates the feedforward term DffB for the second current mode based on the following equation (eq2):

[0028] In this embodiment, when calculating the feedforward terms DffA and DffB, the control device 50 uses the detected voltage VLr (corresponding to the first detected value) of the input voltage sensor 40 in the current switching cycle as the low-voltage side voltage VL. The control device 50 also uses the detected voltage VHr (corresponding to the second detected value) of the output voltage sensor 41 in the current switching cycle as the high-voltage side voltage VH. The control device 50 can use predetermined values ​​for the switching frequency fsw of the switch 31 and the assumed inductance value Ls of the reactor 30, for example.

[0029] For example, the control device 50 calculates the feedforward term DffA based on map information or formula information that correlates the feedforward term DffA for the first current mode with the detected voltages VHr, VLr, the switching frequency fsw, and the assumed inductance value Ls. Also, for example, the control device 50 calculates the feedforward term DffB for the second current mode based on map information or formula information that correlates the feedforward term DffB for the second current mode with the detected voltages VHr, VLr.

[0030] The boundary between the first current mode and the second current mode is the critical current mode shown in Fig. 3. In the critical current mode, the switch 31 is turned on when the value of the current flowing through the reactor 30 decreases to zero.

[0031] The control device 50 determines whether the current current mode is the first current mode or the second current mode based on a comparison of the feedforward terms DffA and DffB. Specifically, if the control device 50 determines that the feedforward term DffA for the first current mode is smaller than the feedforward term DffB for the second current mode, it determines that the current current mode is the first current mode. In this case, the control device 50 controls the switching of the switch 31 based on the feedforward term DffA for the first current mode. On the other hand, if the control device 50 determines that the feedforward term DffA for the first current mode is equal to or greater than the feedforward term DffB for the second current mode, it determines that the current current mode is the second current mode. In this case, the control device 50 controls the switching of the switch 31 based on the feedforward term DffB for the second current mode.

[0032] In order to prevent a decrease in the controllability of the current flowing through the reactor 30, it is necessary to appropriately calculate the duty ratio D used for the switching control of the switch 31.

[0033] Specifically, in order to suppress a decrease in the controllability of the current flowing through the reactor 30, it is necessary to reduce the difference between the timing of switching the current mode and the timing of switching the calculation method of the duty ratio D. This difference will be explained using calculation examples in FIGS. 5 and 6. The calculation examples shown in FIGS. 5 and 6 show the transition of the average current value flowing through the reactor 30 when the command current value Iref is gradually increased at a constant speed. The average current value is the average value of the current flowing through the reactor 30 over one switching period Ts. In addition, in FIGS. 5 and 6, DffA shows the transition of the feedforward term calculated based on the above equation (eq1), and DffB shows the transition of the feedforward term calculated based on the above equation (eq2).

[0034] 5 shows an example of calculation when the timing of switching from DffA to DffB is delayed relative to the timing of switching from the first current mode to the second current mode. In this example, the feedforward term DffA (>DffB) for the first current mode is used to calculate the duty ratio D in a situation where the feedforward term DffB for the second current mode should be used, so the average current value temporarily becomes excessively large relative to the command current value Iref.

[0035] 6 shows a calculation example in which the timing of switching from DffA to DffB is earlier than the timing of switching from the first current mode to the second current mode. In this example, the feedforward term DffB (<DffA) for the second current mode is used to calculate the duty ratio D when the feedforward term DffA for the first current mode should be used, so the average current value temporarily drops excessively relative to the command current value Iref.

[0036] In this way, if there is a large difference between the timing of switching the current mode and the timing of switching the calculation method of the duty ratio D, there is a concern that the average current value flowing through the reactor 30 will deviate significantly from the command current value Iref.

[0037] In this embodiment, the timing for switching the calculation method for duty ratio D is determined based on a comparison between a feedforward term DffA for the first current mode and a feedforward term DffB for the second current mode. In this case, there is a concern that a deviation may occur between the timing for switching the current mode and the timing for switching the calculation method for duty ratio D due to the inclusion of errors such as a detection error of the detected voltage VLr of the input voltage sensor 40 and a detection error of the detected voltage VHr of the output voltage sensor 41. Here, each of the feedforward terms DffA and DffB is calculated based on a voltage ratio VL / VH, which is the ratio of the low-voltage side voltage VL to the high-voltage side voltage VH.

[0038] Therefore, the control device 50 performs error estimation control to estimate the error Verr of the voltage ratio VL / VH. Fig. 7 shows a processing procedure performed by the control device 50 in the error estimation control.

[0039] In step S10, an estimation duty ratio Ds, which is a duty ratio set for estimating an error in the voltage ratio VL / VH, is set to an initial value. The initial value of the estimation duty ratio Ds is, for example, 0. In this case, switching control of the switch 31 is performed based on the set estimation duty ratio Ds.

[0040] In step S11, it is determined whether the current mode has switched from the first current mode to the second current mode based on the current flowing through the reactor 30 during switching control. If a negative determination is made in step S11, the process proceeds to step S12. In step S12, the estimation duty ratio Ds is updated. In this case, switching control of the switch 31 is performed based on the updated estimation duty ratio Ds. Then, the process of step S11 is performed again. If a positive determination is made in step S11, the process proceeds to step S13. In other words, the processes of steps S11 and S12 are repeatedly performed during the period in which it is determined that the current current mode is the first current mode. In this embodiment, the process of step S11 corresponds to a "switching determination unit."

[0041] The processes of steps S11 and S12 will be described in detail below with reference to FIG.

[0042] 8 shows the transition of the PWM signal supplied to the gate of the switch 31, the transition of the current flowing through the reactor 30, and the transition of the estimation duty ratio Ds. When the logic of the PWM signal is H, the switch 31 is turned on, and when the logic of the PWM signal is L, the switch 31 is turned off.

[0043] The control device 50 samples the current detection value of the current sensor 42 at the same timing in each switching period Ts. Fig. 8 shows an example in which the current value is detected at the end timing of each switching period Ts. Taking the switching period Ts from time t1 to t2 as an example, the control device 50 detects the current value I1 as the current flowing through the reactor 30 when switching control is performed using the estimation duty ratio Ds1.

[0044] The control device 50 increases the estimation duty ratio Ds in the current switching period Ts by an increase amount δ compared to the estimation duty ratio Ds in the previous switching period Ts. That is, the control device 50 sets the estimation duty ratio Ds to be increased by the increase amount δ every predetermined period. Here, the predetermined period is one switching period Ts. For example, the estimation duty ratio Ds2 in one switching period Ts from time t2 to time t3 is the sum of the estimation duty ratio Ds1 in one switching period Ts from time t1 to time t2 and the increase amount δ (i.e., Ds1 + δ). Note that the predetermined period may be the total period of multiple switching periods Ts. In this embodiment, the processes of steps S10 and S12 correspond to the "setting unit."

[0045] The control device 50 calculates a difference ΔI between the current value detected in the current switching period Ts and the current value detected in the previous switching period Ts. If the control device 50 determines that the current value difference ΔI is equal to or smaller than a predetermined current threshold Ith, it determines that the current mode in the current switching period Ts is the first current mode. On the other hand, if the control device 50 determines that the current value difference ΔI is greater than the current threshold Ith, it determines that the current mode in the current switching period Ts is the second current mode.

[0046] 8, the difference ΔI between the current value detected in the current switching cycle Ts and the current value detected in the previous switching cycle Ts is equal to or less than the current threshold value Ith. In this case, during the period from time t1 to t4, the control device 50 determines that the current current mode is the first current mode.

[0047] The difference ΔI between the current value I4 detected in the switching period Ts from time t4 to time t5 and the current value I3 detected in the switching period Ts from time t3 to time t4 becomes larger than the current threshold value Ith. In this case, the control device 50 determines that the current mode has switched from the first current mode to the second current mode in the switching period Ts from time t4 to time t5.

[0048] 7 , in step S13, the estimation duty ratio Dsk set in the switching period Ts at which it is determined that the first current mode has been switched to the second current mode is acquired. The low-voltage side voltage VLk and the high-voltage side voltage VHk at the switching period Ts at which it is determined that the first current mode has been switched to the second current mode are also acquired. The low-voltage side voltage VLk is acquired as the detected voltage VLr of the input voltage sensor 40, and the high-voltage side voltage VHk is acquired as the detected voltage VHr of the output voltage sensor 41.

[0049] 8, the control device 50 acquires Ds4 as the estimation duty ratio Dsk. The control device 50 acquires the detected voltages VLr and VHr in the switching period Ts from time t4 to time t5 as the voltages VLk and VHk.

[0050] In step S14, an error Verr in the voltage ratio VL / VH is estimated based on the obtained estimation duty ratio Dsk, low-voltage side voltage VLk, and high-voltage side voltage VHk. In this embodiment, the processes of steps S10 to S14 correspond to an "estimation unit," and the process of step S14 corresponds to an "error estimation unit."

[0051] The error estimation of the voltage ratio VL / VH is performed based on the relational expression between the duty ratio, the low-side voltage VL, and the high-side voltage VH in the second current mode. Here, the voltage ratio VLr / VHr, which is the ratio of the detected voltages VLr and VHr of the voltage sensors 40 and 41, includes an error Verr with respect to the voltage ratio VLT / VHT, which is the ratio of the true value VLT of the low-side voltage to the true value VHT of the high-side voltage. In this case, the duty ratio Da of the switch 31 in the second current mode is expressed as in the following equation (eq3). Equation (eq3) can be modified to obtain equation (eq4).

[0052] The above equation (eq4) is obtained by calculating the error Verr in the voltage ratio VL / VH from the left and right sides of the above equation (eq3). In the above equation (eq4), the control device 50 estimates the error Verr in the voltage ratio VL / VH by substituting Da for the acquired estimation duty ratio Dsk, VLr for the acquired low-voltage side voltage VLk, and VHr for the acquired high-voltage side voltage VHk.

[0053] In the error estimation control described above, the estimation duty ratio Ds is set to increase by an increase amount δ every predetermined period, and it is determined every predetermined period whether the current mode during switching control has switched from the first current mode to the second current mode. In this case, by setting the increase amount δ of the estimation duty ratio Ds to a value that is as small as possible within the processing performance range of the microcomputer 51, it is possible to accurately determine the timing when the current mode switched from the first current mode to the second current mode. This makes it possible to realize a configuration suitable for obtaining the estimation duty ratio Dsk, the low-voltage side voltage VLk, and the high-voltage side voltage VHk at the timing when the current mode switched from the first current mode to the second current mode in the process of step S13. As a result, the estimation accuracy of the error Verr of the voltage ratio VL / VH can be improved.

[0054] For example, assuming that the estimation duty ratio Ds is 100% when the switch 31 is kept on during one switching period Ts, the increase δ (>0) of the estimation duty ratio Ds may be set to 0.1% or less, preferably 0.05% or less, and more preferably 0.01% or less. For example, the increase δ may be set to a value equivalent to the minimum resolution of the microcomputer 51 (e.g., 1 bit). In this case, in the process of step S11, the current current mode can be determined for each finely divided estimation duty ratio Ds. This makes it possible to realize a configuration suitable for accurately determining the timing when the current mode switches from the first current mode to the second current mode.

[0055] In this embodiment, the control device 50 performs error estimation control during an error estimation period that is separate from the actual use period of the DCDC converter 10. For example, the error estimation period is a period established during operation confirmation in the manufacturing process of the DCDC converter 10. By performing error estimation control during the error estimation period, it is possible to set an estimation duty ratio Ds that is more suitable for estimating the error Verr in the voltage ratio VL / VH than during the actual use period of the DCDC converter 10. For example, it is possible to set the estimation duty ratio Ds using a smaller increase width δ than during actual use of the DCDC converter 10. This makes it possible to realize a configuration that is suitable for improving the estimation accuracy of the error Verr in the voltage ratio VL / VH.

[0056] The control device 50 corrects the feedforward term DffA for the first current mode and the feedforward term DffB for the second current mode based on the error Verr of the estimated voltage ratio VL / VH.

[0057] Specifically, the control device 50 calculates corrected feedforward terms DffA and DffB in each current mode based on the following equations (eq5) and (eq6).

[0058] Here, the control device 50 uses, as Verr, the value estimated in step S14 of Fig. 7. The control device 50 performs switching control of the switch 31 based on the corrected feedforward terms DffA and DffB in each corrected current mode.

[0059] 9 shows a control procedure executed by the control device 50. This control is executed, for example, when a drive command for the DC-DC converter 10 is output from a higher-level control device to the control device 50. In this embodiment, the current flowing through the reactor 30 is controlled in the switching control.

[0060] In step S20, the command current value Iref and the reactor current IL in the current switching period Ts are acquired. For example, the command current value Iref can be acquired from a higher-level control device than the control device 50. The detection value of the current sensor 42 can be used as the reactor current IL.

[0061] In step S21, the detected voltage VLr of the input voltage sensor 40 in the current switching period Ts and the detected voltage VHr of the output voltage sensor 41 in the current switching period Ts are acquired. In this embodiment, the process of step S21 corresponds to a "voltage acquisition unit."

[0062] In step S22, it is determined whether the error Verr in the voltage ratio VL / VH has already been estimated. If the determination in step S22 is negative, the process proceeds to step S23. In step S23, the feedforward terms DffA and DffB for each current mode are calculated without using the error Verr in the voltage ratio VL / VH. In this case, the feedforward term DffA for the first current mode can be calculated based on the above equation (eq1). Also, the feedforward term DffB for the second current mode can be calculated based on the above equation (eq2).

[0063] On the other hand, if the determination in step S22 is affirmative, the process proceeds to step S24. In step S24, the feedforward terms DffA and DffB are calculated by correcting them using the error Verr in the voltage ratio VL / VH. In this case, the feedforward term DffA for the first current mode can be calculated based on the above equation (eq5). Also, the feedforward term DffB for the second current mode can be calculated based on the above equation (eq6).

[0064] In the processing of steps S23 and S24, the acquired detected voltage VLr of the input voltage sensor 40 is used as the low-voltage-side voltage VL, and the acquired detected voltage VHr of the output voltage sensor 41 is used as the high-voltage-side voltage VH. In the processing of step S25 and subsequent steps, if a positive determination is made in step S22, the feedforward terms DffA and DffB calculated in the processing of step S24 are used. In the processing of step S25 and subsequent steps, if a negative determination is made in step S22, the feedforward terms DffA and DffB calculated in the processing of step S23 are used. In this embodiment, the processing of steps S23 and S24 corresponds to a "duty ratio calculation unit," and the processing of step S24 corresponds to a "correction unit."

[0065] In step S25, it is determined whether the current current mode is the first current mode. Here, it is determined whether the feedforward term DffA for the first current mode is smaller than the feedforward term DffB for the second current mode. If the determination in step S25 is affirmative, the process proceeds to step S26. On the other hand, if the determination in step S25 is negative, the process proceeds to step S27. In this embodiment, the process in step S25 corresponds to a "mode determination unit."

[0066] In step S26, the feedforward term DffA for the first current mode is used as the feedforward term Dff used to set the duty ratio D of the switch 31. In step S27, the feedforward term DffB for the second current mode is used as the feedforward term Dff used to set the duty ratio D of the switch 31.

[0067] In step S28, a feedback term Dfb of the duty ratio D is calculated. Here, the feedback term Dfb is calculated as a manipulated variable for controlling the acquired reactor current IL to the command current value Iref. The feedback control used to calculate the feedback term Dfb may be, for example, proportional-integral control.

[0068] In step S29, the duty ratio D of the switch 31 is set to the sum of the feedforward term Dff and the feedback term Dfb. In step S30, switching control of the switch 31 is performed. Here, a drive command Sg is calculated based on the set duty ratio D, and the calculated drive command Sg is output to the drive circuit 52. In this embodiment, the process of step S30 corresponds to the "control unit."

[0069] In step S31, it is determined whether or not to stop driving the DC-DC converter 10. If the determination in step S31 is affirmative, the control ends. If the determination in step S31 is negative, the control returns to step S20 and continues.

[0070] 10 shows an example of a case where the feedforward terms DffA and DffB are corrected based on the error Verr in the voltage ratio VL / VH during switching control. In this case, a deviation between the timing of switching the current mode and the timing of switching the method of calculating the duty ratio D is suppressed. Therefore, the deviation of the average current value flowing through the reactor 30 from the command current value Iref is suppressed.

[0071] According to the present embodiment described above in detail, the following effects can be obtained.

[0072] An error Verr in the voltage ratio VL / VH used to calculate the duty ratio D is estimated, and the duty ratio D is corrected based on the estimated error Verr in the voltage ratio VL / VH. Specifically, the feedforward term Dff is corrected based on the error Verr in the estimated voltage ratio VL / VH. This makes it possible to appropriately calculate the duty ratio D, taking into account the fact that the detected voltages VLr and VHr of the voltage sensors 40 and 41 contain errors. Therefore, by performing switching control based on the corrected duty ratio D, it is possible to improve the controllability of the current flowing through the reactor 30.

[0073] Feedforward terms DffA and DffB are calculated using different calculation methods corresponding to the respective current modes. A duty ratio D of the switch 31 is calculated based on one of the feedforward terms DffA and DffB. Switching control is then performed based on the calculated duty ratio D. Here, the feedforward terms DffA and DffB used to calculate the duty ratio D are corrected based on the error Verr in the voltage ratio VL / VH. This makes it possible to reduce the error in the feedforward terms DffA and DffB. Therefore, in a configuration in which different calculation methods for the duty ratio D are used depending on the current mode, a configuration suitable for improving the controllability of the current flowing through the reactor 30 can be realized.

[0074] The duty ratio Da of the switch 31 in the second current mode reflects the voltage ratio VLT / VHT, which is the ratio between the true value VLT of the low-voltage side voltage and the true value VHT of the high-voltage side voltage. Therefore, in this embodiment, the error Verr of the voltage ratio VL / VH is estimated by determining whether the current mode during switching control has switched from the first current mode to the second current mode. Then, an estimation duty ratio Dsk is acquired when it is determined that the current mode during switching control has switched from the first current mode to the second current mode. The error Verr of the voltage ratio VL / VH is estimated based on the acquired estimation duty ratio Dsk. In this case, the error Verr of the voltage ratio VL / VH can be accurately estimated from the estimation duty ratio Dsk, which reflects the true value VLT of the low-voltage side voltage and the true value VHT of the high-voltage side voltage. Therefore, by correcting the feedforward terms DffA and DffB using the estimated error Verr, the controllability of the current flowing through the reactor 30 can be improved accurately.

[0075] Based on a comparison of the feedforward terms DffA and DffB, it is determined whether the current current mode is the first current mode or the second current mode. Switching control is performed based on the feedforward terms calculated using a calculation method corresponding to the determined current mode. Here, the feedforward terms DffA and DffB are corrected by the error Verr in the voltage ratio VL / VH when switching from the first current mode to the second current mode. This synchronizes the timing of switching the calculation method for the feedforward terms with the timing of switching from the first current mode to the second current mode. This prevents a discrepancy between the actual current mode switching timing and the timing of switching the calculation method for the duty ratio D, thereby preventing switching control from being performed using a duty ratio that does not correspond to the current mode. As a result, it is possible to accurately prevent the average current value flowing through the reactor 30 from deviating from the command current value Iref around the timing of switching the current mode, thereby accurately improving the controllability of the current flowing through the reactor 30.

[0076] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, the DC-DC converter is a step-down converter instead of a step-up converter.

[0077] As shown in Fig. 11 , the DC-DC converter 110 is a non-insulated step-down converter that steps down a voltage input from a high-potential side input terminal THi and a low-potential side input terminal TLi and outputs the voltage from a high-potential side output terminal THo and a low-potential side output terminal TLo. In this embodiment, a DC power supply 120 is connected to the high-potential side input terminal THi and the low-potential side input terminal TLi. A storage battery 121 is connected to the high-potential side output terminal THo and the low-potential side output terminal TLo. The voltage of the storage battery 121 (e.g., rated voltage) is lower than the voltage of the DC power supply 120 (e.g., rated voltage). Note that in Fig. 11 , the same components as those shown in Fig. 1 are denoted by the same reference numerals for convenience.

[0078] The DC-DC converter 110 includes a reactor 130, a switch 131, and a diode 132. In this embodiment, the switch 131 is an N-channel MOSFET. Note that the switch 131 is not limited to an N-channel MOSFET, and may be, for example, an IGBT to which a freewheeling diode is connected in antiparallel.

[0079] The drain of the switch 131 is electrically connected to a first end of the input capacitor 33 and the high-potential side input terminal THi. The source of the switch 131 is connected to a cathode of the diode 132 and a first end of the reactor 130. The anode of the diode 132 is connected to the low-potential side input terminal TLi and the low-potential side output terminal TLo. The second end of the reactor 130 is connected to a first end of the output capacitor 34 and the high-potential side output terminal THo.

[0080] In this embodiment, the current sensor 42 detects the current flowing through the reactor 130. The control device 50 performs switching control of the switch 131 to control the current flowing through the reactor 130 to a command current value Iref. In the switching control, the control device 50 calculates a duty ratio D of the switch 131. The control device 50 generates a drive command Sg based on the calculated duty ratio D and outputs it to the drive circuit 52. The drive circuit 52 turns the switch 131 on and off based on the drive command Sg.

[0081] In the switching control of the switch 131, the control device 50 uses a different calculation method for the duty ratio D depending on whether the current mode of the current flowing through the reactor 130 is the first current mode or the second current mode, as in the first embodiment.

[0082] The control device 50 calculates the feedforward terms DffA and DffB in the process of calculating the duty ratio D. The control device 50 calculates the feedforward term DffA for the first current mode based on the following equation (eq7). The control device 50 calculates the feedforward term DffB for the second current mode based on the following equation (eq8).

[0083] As shown in the above equations (eq7) and (eq8), the feedforward terms DffA and DffB are calculated based on the voltage ratio VL / VH, which is the ratio of the low-voltage side voltage VL to the high-voltage side voltage VH. In this embodiment, when calculating the feedforward terms DffA and DffB, the control device 50 uses the detected voltage VLr of the output voltage sensor 41 in the current switching period Ts as the low-voltage side voltage VL. The control device 50 also uses the detected voltage VHr of the input voltage sensor 40 in the current switching period Ts as the high-voltage side voltage VH. In this embodiment, the output voltage sensor 41 corresponds to the "first detection unit," and the detected voltage VHr corresponds to the "first detected value." The input voltage sensor 40 corresponds to the "second detection unit," and the detected voltage VLr corresponds to the "second detected value."

[0084] The control device 50 performs the error estimation control described above with reference to Fig. 7. Here, the process performed by the control device 50 in step S14 will be described.

[0085] The error estimation of the voltage ratio VL / VH is performed based on the relational expression between the duty ratio, the low-voltage side voltage VL, and the high-voltage side voltage VH in the second current mode. Here, the voltage ratio VLr / VHr, which is the ratio of the detected voltages VHr and VLr of the voltage sensors 40 and 41, contains an error Verr with respect to the voltage ratio VLT / VHT, which is the ratio of the true value VLT of the low-voltage side voltage to the true value VHT of the high-voltage side voltage. In this case, the duty ratio Da of the switch 31 in the second current mode is expressed as in the following equation (eq9). Equation (eq9) can be modified to obtain equation (eq10).

[0086] The above equation (eq10) is obtained by calculating the error Verr in the voltage ratio VL / VH from the left and right sides of the above equation (eq9). In the above equation (eq10), the control device 50 estimates the error Verr in the voltage ratio VL / VH by substituting Da for the acquired estimation duty ratio Dsk, VLr for the acquired low-voltage side voltage VLk, and VHr for the acquired high-voltage side voltage VHk.

[0087] The control device 50 corrects the feedforward terms DffA and DffB based on the error Verr of the estimated voltage ratio VL / VH. Specifically, the control device 50 calculates the corrected feedforward terms DffA and DffB in each current mode based on the following equations (eq11) and (eq12).

[0088] The control device 50 performs switching control in the same manner as in the first embodiment. In this case, in step S23 of Fig. 9 , the feedforward term DffA for the first current mode can be calculated based on the above equation (eq7), and the feedforward term DffB for the second current mode can be calculated based on the above equation (eq8). In step S24, the feedforward term DffA for the first current mode can be calculated based on the above equation (eq11), and the feedforward term DffB for the second current mode can be calculated based on the above equation (eq12).

[0089] Other Embodiments The above-described embodiments may be modified as follows.

[0090] When the DCDC converter is mounted on a vehicle such as an electric vehicle, a fuel cell vehicle, or a hybrid vehicle, the error estimation period may be the period from when the vehicle ignition switch is turned on until the start of actual use of the DCDC converter 10. Even in this case, error estimation control can be performed during a period separate from the actual use period of the DCDC converter 10. This makes it possible to realize a configuration suitable for improving the estimation accuracy of the error Verr in the voltage ratio VL / VH.

[0091] The control device 50 may repeatedly execute the error estimation control shown in Fig. 7 at a predetermined cycle, for example, during actual use of the DC-DC converter 10. In this case, the processes of steps S10 and S12 may not be performed. In step S13, instead of the estimation duty ratio Dsk, the control device 50 may acquire a feedforward term DffB for the second current mode in the switching cycle Ts in which the first current mode is switched to the second current mode.

[0092] When the control device 50 estimates the error Verr of the voltage ratio VL / VH multiple times, the latest value or the average value of each estimated error Verr can be used to correct each feedforward term DffA, DffB.

[0093] To improve the accuracy of estimating the voltage ratio VL / VH error Verr, it is desirable to minimize the influence of the deviation between the actual duty ratio DT at the timing of switching from the first current mode to the second current mode and the estimation duty ratio Dsk obtained by the processing in step S13. Here, to estimate the influence of the deviation of the estimation duty ratio Dsk on the estimation of the error Verr, the actual duty ratio DT at the timing of switching from the first current mode to the second current mode and a duty ratio that deviates from the actual duty ratio DT by α are considered. In a boost converter, the actual duty ratio DT at the switching timing is DT = 1 - VLT / VHT, where VLT is the true value of the low-voltage side voltage and VHT is the true value of the high-voltage side voltage. In a buck converter, the actual duty ratio DT at the switching timing is DT = VLT / VHT.

[0094] The ratio between the error VerrT in the voltage ratio VL / VH calculated from the actual duty ratio DT at the timing of switching from the first current mode to the second current mode and the error VerrM in the voltage ratio VL / VH calculated from the duty ratio including the deviation α from the actual duty ratio DT is expressed by the following equation (eq13) in the case of a boost converter and by (eq14) in the case of a buck converter.

[0095] According to the above equations (eq13) and (eq14), the larger the voltage ratio VL / VH, the closer the error ratio VerrM / VerrT becomes to 1, and the smaller the influence of the deviation α becomes.

[0096] Therefore, in this embodiment, the control device 50 performs error estimation control shown in Fig. 12. This control is repeatedly executed at a predetermined cycle, for example, during actual use of the DC-DC converter 10. Note that this control may also be executed during an error estimation period.

[0097] In step S40, it is determined whether the voltage ratio VLr / VHr of the detected voltages VLr and VHr is greater than a predetermined value A. The predetermined value A is a value in the range of 0.85 to 0.95, for example, 0.9. If the determination in step S40 is affirmative, the process proceeds to step S10. On the other hand, if the determination in step S40 is negative, the process ends.

[0098] According to this embodiment, the error estimation process of steps S10 to S14 can be performed in a situation suitable for estimating the error Verr of the voltage ratio VL / VH.

[0099] 1 and 11 , an electric load may be connected to the output terminals THo and TLo instead of the storage batteries 21 and 121. In this case, instead of a current-controlled DC-DC converter, the DC-DC converter may be a voltage-controlled DC-DC converter to which current minor loop control is added in the current control of the control device 50. In this case, in step S20 of FIG. 9 , a command current value Iref is obtained to control the voltage of the electric load to the target voltage.

[0100] The control system is not limited to the configuration shown in FIG. 1 , and may be, for example, the configuration shown in FIG. 13 . The configuration shown in FIG. 13 is a motor drive system for an electric vehicle equipped with a fuel cell 220. This system includes a boost converter 200, a storage battery 221, an inverter 230, and a motor 231. The boost converter 200 boosts the output voltage of the fuel cell 220 and supplies the boosted voltage to the inverter 230. The inverter 230 converts DC power supplied from at least one of the boost converter 200 or the storage battery 221 into AC power and supplies the AC power to the armature winding of the motor 231. In this configuration, the present disclosure may be applied to current control of the boost converter 200.

[0101] The DC-DC converter to which the present disclosure is applied is not limited to a non-isolated type, but may be an isolated type including a transformer. The transformer has a primary reactor on the input side and a secondary reactor on the output side. The isolated DC-DC converter is, for example, a flyback converter, a forward converter, a push-pull converter, or a full-bridge converter, and includes a switch on the primary side.

[0102] For example, in the case of a forward converter, a reactor (hereinafter referred to as a specific reactor) separate from the secondary-side reactor of the transformer is provided on the secondary side. In the forward converter, during the on-period of the primary-side switch, the value of the current flowing through the specific reactor on the secondary side gradually increases, and magnetic energy is accumulated in the specific reactor. Furthermore, during the off-period of the primary-side switch, the value of the current flowing through the specific reactor gradually decreases to zero. As a result, during one switching period Ts, the time transition waveform of the current flowing through the specific reactor becomes a triangular waveform and then becomes a waveform that is maintained at zero.

[0103] For example, in the case of a flyback converter, during an on-period of a primary switch, the current flowing through a primary reactor constituting a transformer gradually increases, and magnetic energy is accumulated in the primary reactor and the core of the transformer. During an off-period of the primary switch, the accumulated energy is released, and the current flowing through the primary reactor gradually decreases to zero. As a result, during one switching period Ts, the time transition waveform of the current flowing through the primary reactor becomes a triangular waveform and then remains at zero.

[0104] The control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium.

[0105] The following describes characteristic configurations extracted from the above-described embodiments. [Configuration 1] A control device (50) for a DC-DC converter (10, 110) including a switch (31, 131) and a reactor (30, 130), the control device performing switching control of the switch to control a current flowing through the reactor to a command current value, the control device for a DC-DC converter comprising: a voltage acquisition unit acquiring a first detection value from a first detection unit that detects a low-voltage side voltage of the DC-DC converter and a second detection value from a second detection unit that detects a high-voltage side voltage of the DC-DC converter, a duty ratio calculation unit that calculates a duty ratio that is a ratio of an on-period of the switch in one switching cycle based on a voltage ratio that is a ratio of the first detection value to the second detection value, an estimator that estimates an error in the voltage ratio, a corrector that corrects the duty ratio based on the error in the voltage ratio estimated by the estimator, and a control unit that performs the switching control based on the duty ratio corrected by the corrector. and an error estimator configured to estimate an error in the voltage ratio based on the duty ratio when the switching determination unit determines that the current mode has switched from the first current mode to the second current mode.[Configuration 4] The DC-DC converter control device according to Configuration 3, wherein the estimator includes a setting unit that sets an estimation duty ratio for estimating an error in the voltage ratio so as to increase it by an increase amount every predetermined period, and the switch determination unit determines, every predetermined period, whether the current mode during which the switching control is being performed has switched from the first current mode to the second current mode. [Configuration 5] The DC-DC converter control device according to Configuration 4, wherein the increase amount is a value of 0.1% or less, where the estimation duty ratio when the switch is maintained on in one switching cycle is 100%. [Configuration 6] The DC-DC converter control device according to any one of Configurations 3 to 5, further includes a mode determination unit that determines whether the current mode is the first current mode or the second current mode based on a comparison of the first duty ratio and the second duty ratio corrected by the correction unit, and the control unit performs the switching control based on the duty ratio in the current mode determined by the mode determination unit, of the first duty ratio and the second duty ratio. [Configuration 7] The DC-DC converter control device according to any one of Configurations 1 to 6, wherein the estimation unit estimates an error in the voltage ratio when a condition that the voltage ratio is greater than a predetermined value is satisfied. [Configuration 8] The DC-DC converter control device according to any one of Configurations 1 to 7, wherein the estimation unit estimates the error in the voltage ratio during a period separate from a period of actual use of the DC-DC converter.

[0106] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A control device (50) for a DC-DC converter applied to a DC-DC converter (10, 110) having a switch (31, 131) and a reactor (30, 130), which performs switching control of the switch to control a current flowing through the reactor to a command current value, the control device for a DC-DC converter comprising: a voltage acquisition unit which acquires a first detection value from a first detection unit which detects a low-voltage side voltage of the DC-DC converter and a second detection value from a second detection unit which detects a high-voltage side voltage of the DC-DC converter; a duty ratio calculation unit which calculates a duty ratio which is the ratio of an on-period of the switch in one switching period based on a voltage ratio which is the ratio of the first detection value to the second detection value; an estimation unit which estimates an error in the voltage ratio; a correction unit which corrects the duty ratio based on the error in the voltage ratio estimated by the estimation unit; and a control unit which performs the switching control based on the duty ratio corrected by the correction unit.

2. The control device for a DC-DC converter as described in claim 1, wherein the duty ratio calculation unit calculates, as the duty ratio, a first duty ratio in a first current mode in which the current flowing through the reactor during the one switching period is intermittently zero, and a second duty ratio in a second current mode in which current continues to flow through the reactor during the one switching period; the correction unit corrects the first duty ratio and the second duty ratio based on an error in the voltage ratio estimated by the estimator; and the control unit performs the switching control based on one of the first duty ratio and the second duty ratio corrected by the correction unit.

3. The control device for a DC-DC converter as described in claim 2, wherein the estimation unit has: a switching determination unit that determines whether the current mode during execution of the switching control has switched from the first current mode to the second current mode; and an error estimation unit that estimates an error in the voltage ratio based on the duty ratio when it is determined by the switching determination unit that the current mode has been switched.

4. The control device for a DC-DC converter as described in claim 3, wherein the estimation unit has a setting unit that sets an estimation duty ratio for estimating an error in the voltage ratio so as to increase the estimation duty ratio by an increase amount every predetermined period, and the switching determination unit determines, every predetermined period, whether the current mode during which the switching control is being performed has switched from the first current mode to the second current mode.

5. The control device for a DC-DC converter according to claim 4, wherein the estimation duty ratio when the switch is maintained on during one switching period is taken as 100%, and the increase range is a value of 0.1% or less.

6. A control device for a DC-DC converter as described in any one of claims 3 to 5, further comprising a mode determination unit that determines whether a current mode is the first current mode or the second current mode based on a comparison of the first duty ratio and the second duty ratio corrected by the correction unit, and the control unit performs the switching control based on the duty ratio in the current mode determined by the mode determination unit, out of the first duty ratio and the second duty ratio.

7. A control device for a DC-DC converter according to any one of claims 1 to 5, wherein the estimation unit estimates an error in the voltage ratio when a condition is established that the voltage ratio is greater than a predetermined value.

8. A control device for a DC-DC converter according to any one of claims 1 to 5, wherein the estimation unit estimates the error in the voltage ratio during a period other than a period during which the DC-DC converter is actually used.

9. A program applied to a DC-DC converter (10, 110) having a switch (31, 131) and a reactor (30, 130), causing a computer (50) to execute switching control of the switch to control a current flowing through the reactor to a command current value, the program causing the computer to execute the following: a voltage acquisition process for acquiring a first detection value of a first detection unit that detects a low-voltage side voltage of the DC-DC converter and a second detection value of a second detection unit that detects a high-voltage side voltage of the DC-DC converter; a duty ratio calculation process for calculating a duty ratio that is a ratio of an on-period of the switch in one switching cycle based on a voltage ratio that is a ratio of the first detection value to the second detection value; an estimation process for estimating an error in the voltage ratio; a correction process for correcting the duty ratio based on the error in the voltage ratio estimated by the estimation process; and a control process for performing the switching control based on the duty ratio corrected by the correction process.

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