JP7643364B2 - Control device - Google Patents

Description

The present invention relates to a control device for a voltage converter.

For example, Patent Document 1 describes a DC-DC converter that has a reactor and a switching element as a voltage converter. In this DC-DC converter, the reactor current flowing through the reactor is controlled by switching control of the switching element, and the input voltage is converted into an output voltage.

JP 2010-279151 A

In the above switching control, the duty ratio of the switching element is feedback controlled so that the average value of the reactor current becomes a target value. One possible method for calculating the average value of the reactor current is to detect the reactor current at a predetermined time interval and calculate the average value of the reactor current using the maximum and minimum values of the current detection value. In this case, depending on the time interval for detecting the current value, it may not be possible to obtain the maximum value of the reactor current as the current detection value. If the maximum value of the current detection value and the maximum value of the reactor current do not match, there is a concern that the accuracy of calculating the average value of the reactor current will decrease.

The present invention has been made in consideration of the above problems, and aims to provide a control device that can properly calculate the average value of the reactor current in a voltage converter having a reactor and a switching element.

A first invention for solving the above problem is a control device applied to a voltage converter having a reactor and a switching element that, when turned on, gradually increases the reactor current flowing from a power source to the reactor and, when turned off, gradually decreases the reactor current, and that transforms and outputs an input voltage by controlling the switching of the switching element, and is equipped with a current acquisition unit that acquires the reactor current at a predetermined time interval, a classification unit that classifies the multiple current values acquired by the current acquisition unit into multiple groups including a current value increase group that is a collection of current values acquired during an increase period of the reactor current and a current value decrease group that is a collection of current values acquired during a decrease period of the reactor current based on the time rate of change of the current value, and a calculation unit that calculates an approximation line that linearly approximates the relationship between the current value and the acquisition timing of the current value for each group, calculates the current value at the intersection of the approximation line calculated in the current value increase group and the current value decrease group that are successive in a chronological order as the maximum value of the reactor current, and calculates an average value of the reactor current using the calculated maximum value of the reactor current.

In a voltage converter having a reactor and a switching element, the reactor current is controlled so that it repeats a gradual increase and decrease by switching control of the switching element. The time change rate of the reactor current during the increase period and the decrease period of the reactor current are different from each other. Therefore, by acquiring the reactor current at a predetermined time interval and classifying the acquired multiple current values based on the time change rate of the current value, it is possible to classify into a current value increase group, which is a set of current values acquired during the increase period of the reactor current, and a current value decrease group, which is a set of current values acquired during the decrease period of the reactor current. In this case, the current value increase group and the current value decrease group appear alternately in a chronological order. Therefore, an approximation line that linearly approximates the relationship between the current value and the timing of acquiring the current value for each group is calculated, and the current value at the intersection of the approximation lines calculated in the current value increase group and the current value decrease group that are successive in the chronological order can be calculated as the maximum value of the reactor current. As a result, even if the maximum value of the reactor current cannot be acquired as the current detection value, the maximum value of the reactor current can be calculated, and the average value of the reactor current can be calculated with high accuracy.

FIG. 1 is a diagram showing the configuration of a voltage conversion system. 4 is a flowchart showing a processing procedure of a control process according to the first embodiment. 5 is a flowchart showing the processing procedure of classification processing according to the first embodiment. 4 is a timing chart showing a transition of a reactor current. 4 is a timing chart showing a transition of a current detection value according to the first embodiment. 4 is a timing chart showing an approximation line of a reactor current. 10 is a timing chart showing a transition of a current detection value according to the second embodiment. 10 is a flowchart showing a processing procedure of a control process according to a second embodiment. 13 is a flowchart showing the processing procedure of a classification process according to the second embodiment. FIG. 13 is a configuration diagram of a voltage conversion system according to another embodiment.

First Embodiment
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a control device according to the present invention will now be described with reference to the drawings. The control device of the present embodiment is mounted on a vehicle equipped with a traction motor, such as a hybrid vehicle or an electric vehicle.

As shown in FIG. 1, the voltage conversion system includes a power source 10, a power supply target 11, and a voltage converter 20.

The power source 10 supplies power to the power supply target 11 via a voltage converter 20. The power source 10 is a rechargeable secondary battery, for example a lithium ion battery. The positive terminal of the power source 10 is connected to the high potential side terminal of the power supply target 11 via a high potential side wiring LH. The negative terminal of the power source 10 is connected to the low potential side terminal of the power supply target 11 via a low potential side wiring LL.

The voltage converter 20 is a DC-DC converter that boosts the power supply voltage VB input from the power supply 10 and applies it to the power supply target 11. The voltage converter 20 includes a switching element 21, a reactor 22, and a diode 23.

In this embodiment, the switching element 21 is an N-channel MOSFET. The drain of the switching element 21 is connected to the high potential side wiring LH, and the source of the switching element 21 is connected to the low potential side wiring LL. A parasitic diode DA is connected in parallel to the switching element 21. The anode of the parasitic diode DA is connected to the source of the switching element 21, and the cathode of the parasitic diode DA is connected to the drain of the switching element 21.

The reactor 22 and the diode 23 are provided on the high potential side wiring LH. The reactor 22 is provided on the high potential side wiring LH closer to the power source 10 than the connection point PA between the high potential side wiring LH and the drain of the switching element 21, and the diode 23 is provided on the high potential side wiring LH closer to the power supply target 11 than the connection point PA. The diode 23 is oriented such that the anode is on the connection point PA side and the cathode is on the power supply target 11 side.

The voltage conversion system includes a first voltage sensor 30, a current sensor 31, and a second voltage sensor 32. The first voltage sensor 30 detects the power supply voltage VB of the power supply 10. The current sensor 31 detects the reactor current IL flowing through the reactor 22. The second voltage sensor 32 detects the output voltage VT applied to the power supply target 11. The input voltage detection value Vind, which is the detected power supply voltage VB, the current detection value Iind, which is the detected reactor current IL, and the output voltage detection value Voutd, which is the detected output voltage VT, are input to a control device 40 provided in the voltage converter 20.

The control device 40 is a device equipped with a well-known microcomputer consisting of a CPU, ROM, RAM, flash memory, etc. The control device 40 acquires each of the detection values Vind, Iind, and Voutd, and executes various controls based on the acquired information. Specifically, the control device 40 outputs a gate voltage VG to the gate of the switching element 21 based on each of the detection values Vind, Iind, and Voutd, and executes switching control of the switching element 21. The control device 40 is equipped with a memory unit 41. The memory unit 41 is composed of a memory such as a RAM or a flash memory (specifically, a non-volatile memory).

In this embodiment, the control device 40 executes continuous current mode control, which controls the switching element 21 so that the reactor current IL does not become zero. In the continuous current mode control, the switching element 21 is periodically controlled to be turned on and off, and the reactor current IL alternately increases and decreases linearly in response to the on-off control of the switching element 21. Specifically, the reactor current IL gradually increases during the on-period of the switching element 21 and gradually decreases during the off-period of the switching element 21. The control device 40 calculates the average value Iav of the reactor current IL, and controls the duty ratio of the switching element 21 to feedback control the average value Iav of the reactor current IL to a target value. The duty ratio is the ratio (Ton/TF) of the on-time Ton in one switching period TF of the switching element 21.

As a method of calculating the average value Iav of the reactor current IL, a method is considered in which the current detection value Iind is acquired at a time interval TX using the current sensor 31, and the median value of the maximum and minimum values of the acquired current detection value Iind is calculated as the average value Iav of the reactor current IL. In this case, depending on the time interval TX for acquiring the current detection value Iind, it may not be possible to acquire the maximum value Imax and minimum value Imin of the reactor current IL as the current detection value Iind. In addition, depending on the control device 40, it may be difficult to adjust the time interval TX so that the maximum value Imax and minimum value Imin of the reactor current IL can be acquired as the current detection value Iind due to low specifications, etc. As a result, if the maximum value of the current detection value Iind does not match the maximum value Imax of the reactor current IL, there is a concern that the calculation accuracy of the average value Iav (= (Imax + Imin) / 2) of the reactor current IL will decrease.

Therefore, in this embodiment, the time rate of change DI of the current detection value Iind is calculated, and the current detection value Iind is classified into a plurality of groups that are successive in a chronological order based on this time rate of change DI. Here, the time rate of change DI is the unit time change amount in two current detection values Iind that are successive in a chronological order. The time rates of change of the reactor current IL in the increase period and decrease period of the reactor current IL are different from each other. Therefore, by classifying the current detection value Iind based on the time rate of change DI, the current detection value Iind can be classified into a current value increase group (hereinafter, increase group) GA, which is a set of current detection values Iind obtained during the increase period, and a current value decrease group (hereinafter, decrease group) GB, which is a set of current detection values Iind obtained during the decrease period. In this case, the increase group GA and the decrease group GB appear alternately in a chronological order. Therefore, an approximate straight line LK is calculated for each group by linearly approximating the relationship between the current detection value Iind and the timing of obtaining the current detection value Iind, and the current values at the intersections of the approximate straight lines LK calculated for the groups GA and GB that are successive in time series can be calculated as the maximum value Imax and minimum value Imin of the reactor current IL. This makes it possible to accurately calculate the average value Iav of the reactor current IL even if the maximum value Imax and minimum value Imin of the reactor current IL cannot be obtained as the current detection value Iind.

Figure 2 shows the procedure of the control process performed by the control device 40. The control process is performed repeatedly, for example, during the operation period of the voltage converter 20.

In step S10, the duty ratio of the switching element 21 is set. The duty ratio is set based on the target value of the average value Iav of the reactor current IL.

In step S11, the detection values Vind, Iind, and Voutd are acquired. The detection values Vind, Iind, and Voutd are acquired at time intervals TX. In this embodiment, the process of step S11 corresponds to the "current acquisition unit."

In step S12, the first range HA and the second range HB are calculated. Here, the first range HA is the range of the time increase rate (speed of increase) of the reactor current IL during the increase period of the reactor current IL, and is set based on the first slope KA. The first slope KA is the theoretical increase rate of the reactor current IL during the increase period of the reactor current IL, and is expressed as the following (Equation 1) using the power supply voltage VB and the inductance value LA of the reactor 22.

KA=VB/LA...(Formula 1)
The first range HA is a range of width W (KA±W/2) centered on the first gradient KA. Here, the width W is set based on the fluctuation range ΔLA of the inductance value LA accompanying the temperature change of the reactor 22, and is stored in the storage unit 41 together with the inductance value LA. Specifically, the reactor 22 has a usable temperature range ΔYA set in advance, and based on this temperature range ΔYA, a fluctuation range ΔLA of the inductance value LA is set with the inductance value LA corresponding to the minimum temperature Ymin of the temperature range ΔYA as the lower limit value and the inductance value LA corresponding to the maximum temperature Ymax of the temperature range ΔYA as the upper limit value. The storage unit 41 stores the width W set based on this fluctuation range ΔLA. The control device 40 calculates the first range HA using the input voltage detection value Vind acquired in step S11 and the inductance value LA and width W stored in the storage unit 41.

The second range HB is the range of the time decrease rate (decrease speed) of the reactor current IL during the decrease period of the reactor current IL, and is set based on the second slope KB. The second slope KB is the theoretical decrease rate of the reactor current IL during the decrease period of the reactor current IL, and is expressed as the following (Equation 2) using the power supply voltage VB, the output voltage VT, and the inductance value LA of the reactor 22.

KB=-(VT-VB)/LA...(Formula 2)
The second range HB is a range of width W (KB±W/2) centered on the second slope KB. The control device 40 calculates the second range HB using the input voltage detection value Vind and the output voltage detection value Voutd acquired in step S11, and the inductance value LA and width W stored in the storage unit 41.

In step S13, a classification process is performed to classify the current detection value Iind acquired in step S11 into groups GA and GB based on the time rate of change DI. The procedure for the classification process is shown in FIG. 3. In this embodiment, the process of step S13 corresponds to the "classification unit."

In step S30, a first current value IA and a second current value IB are selected from the current detection value Iind acquired in step S11. The first current value IA and the second current value IB are current values used to calculate the time change rate DI, and are selected so as to satisfy the following three conditions: (1) The first current value IA and the second current value IB are two current detection values Iind that are successive in time series, that is, acquired with a time interval TX between them. (2) The first current value IA is the current detection value Iind acquired earlier than the second current value IB. (3) The first current value IA is selected in order from the current detection value Iind that was acquired earliest among the multiple current detection values Iind that are successive in time series.

In step S31, the time rate of change DI of the two current values IA and IB selected in step S30 is calculated. The time rate of change DI is expressed as shown in the following (Equation 3) using the difference value ΔI obtained by subtracting the first current value IA from the second current value IB and the time interval TX.

DI=ΔI/TX...(Formula 3)
In step S32, it is determined whether the time rate of change DI calculated in step S31 is within the first range HA. If the determination in step S32 is affirmative, it is determined in step S33 that the two current values IA and IB used in the calculation of the time rate of change DI belong to the increase group GA, and the process proceeds to step S37.

If the determination in step S32 is negative, then in step S34 it is determined whether the time rate of change DI calculated in step S31 is included in the second range HB. If the determination in step S34 is positive, then in step S35 it is determined that the two current detection values Iind used to calculate the time rate of change DI belong to the decrease group GB, and the process proceeds to step S37.

On the other hand, if the result of step S34 is negative, then in step S36, the process performs a process of excluding the second current value IB from each of the groups GA and GB among the two current values IA and IB used in the calculation of the time change rate DI, and proceeds to step S37. A negative determination is made in step S34, for example, when the time change rate DI falls outside the first range HA during the increase period of the reactor current IL due to noise being mixed into the detection value of the current sensor 31, or when the time change rate DI falls outside the second range HB during the decrease period of the reactor current IL. This process of exclusion can prevent the second current value IB that falls outside the ranges HA and HB from being used in the calculation of the average value Iav, thereby improving the calculation accuracy of the average value Iav.

In step S37, it is determined whether classification into the increase group GA or the decrease group GB in one switching cycle TF has been completed. For example, it may be determined that classification into the increase group GA has been completed when it is determined that the switching element 21 has been switched off after the switching element 21 has been switched on. It may be determined that classification into the decrease group GB has been completed when it is determined that the switching element 21 has been switched on after the switching element 21 has been switched off. If a positive determination is made in step S37, the process returns to step S30. Each time a positive determination is made in step S37, the increase group GA and the decrease group GB are generated alternately. On the other hand, if a positive determination is made in step S37, the classification process is terminated.

Returning to FIG. 2, in step S14, for each group GA, GB classified in step S13, an approximate line LK is calculated using the current detection values Iind contained in each group GA, GB. The approximate line LK is calculated, for example, by the least squares method. For example, if the most recently generated group is the decrease group GB, the approximate line LK calculated using the multiple current detection values Iind contained in the decrease group GB is a monotonically decreasing line. On the other hand, if the most recently generated group is the increase group GA, the approximate line LK calculated using the multiple current detection values Iind contained in the increase group GA is a monotonically increasing line. Note that when calculating the approximate line LK, all the current detection values Iind contained in the group may be used, or a portion and multiple current detection values Iind of the current detection values Iind contained in the group may be used.

In step S15, the current value at the intersection of the approximate straight lines LK calculated in step S14 for the groups that are adjacent in time series is calculated as the maximum value Imax and minimum value Imin of the reactor current IL. For example, if the most recently generated group is the decrease group GB, the current value at the intersection of the approximate straight line LK based on the decrease group GB and the approximate straight line LK based on the increase group GA generated immediately before the decrease group GB is calculated as the maximum value Imax. On the other hand, if the most recently generated group is the increase group GA, the current value at the intersection of the approximate straight line LK based on the increase group GA and the approximate straight line LK based on the decrease group GB generated immediately before the increase group GA is calculated as the minimum value Imin.

In step S16, the median value of the maximum value Imax and the minimum value Imin of the reactor current IL calculated in step S15 is calculated as the average value Iav of the reactor current IL. Note that in this embodiment, the processes in steps S14 to S16 correspond to the "calculation unit."

In step S17, the inductance value LA stored in the memory unit 41 is corrected based on the average value Iav of the reactor current IL calculated in step S16. Specifically, if the average value Iav of the reactor current IL increases, the inductance value LA is corrected to increase, and if the average value Iav of the reactor current IL decreases, the inductance value LA is corrected to decrease. As a result, in the next control process, the first range HA and the second range HB can be calculated using the inductance value LA corrected based on the average value Iav of the reactor current IL.

In step S18, the duty ratio of the switching element 21 is corrected in order to feedback control the average value Iav of the reactor current IL calculated in step S16 to the target value. Specifically, if the average value Iav of the reactor current IL is smaller than the target value, the duty ratio of the switching element 21 is increased, and if the average value Iav of the reactor current IL is larger than the target value, the duty ratio of the switching element 21 is decreased. This makes it possible to control the average value Iav of the reactor current IL to the target value. In this embodiment, the process of step S18 corresponds to a "control unit."

Next, the procedure for calculating the maximum value Imax and minimum value Imin of the reactor current IL will be explained using Figures 4 to 6.

As shown by the dashed line in FIG. 4, the reactor current IL alternately increases and decreases linearly in response to the on/off control of the switching element 21. In this embodiment, due to the parasitic capacitance of the switching element 21 and control delays, the reactor current IL reaches a minimum value Imin after a first delay time TA has elapsed from timing t1, t3 when the switching element 21 is switched to the on state, and reaches a maximum value Imax after a second delay time TB has elapsed from timing t2 when the switching element 21 is switched to the off state. Therefore, the on period of the switching element 21 is different from the increase period of the reactor current IL, and the off period of the switching element 21 is different from the decrease period of the reactor current IL.

In addition, in this embodiment, the first delay time TA and the second delay time TB are different, and the first delay time TA is longer than the second delay time TB. Therefore, even if the start timings t1, t3 and the end timing t2 of the on-period of the switching element 21 are delayed by the first delay time TA, the on-period of the switching element 21 does not coincide with the increase period of the reactor current IL, and even if the start timings t1, t3 and the end timing t2 of the off-period of the switching element 21 are delayed by the second delay time TB, the on-period of the switching element 21 does not coincide with the decrease period of the reactor current IL.

Next, as shown in FIG. 5, the reactor current IL is detected at time intervals TX, and the current detection value Iind is obtained. In the example shown in FIG. 5, the maximum value Imax and minimum value Imin of the reactor current IL are not obtained as the current detection value Iind. Therefore, the maximum value of the current detection value Iind does not match the maximum value Imax of the reactor current IL, and the minimum value of the current detection value Iind does not match the minimum value Imin of the reactor current IL.

The current detection value Iind is classified into groups GA and GB based on the time rate of change DI. As surrounded by a dashed line in FIG. 5, a set of current detection values Iind obtained during an increase period of the reactor current IL and that are continuous in time series is classified as an increase group GA, and a set of current detection values Iind obtained during a decrease period of the reactor current IL and that are continuous in time series is classified as a decrease group GB. Then, the increase group GA and the decrease group GB appear alternately in time series according to the increase or decrease of the reactor current IL.

Next, as shown by the straight lines in FIG. 6, an approximate straight line LK is calculated for each group GA, GB, and the maximum value Imax and minimum value Imin of the reactor current IL are calculated from the intersection of the approximate straight lines LK calculated for the groups that are adjacent in time series. Specifically, the current value at the intersection of the approximate straight lines LK calculated for the increase group GA and the decrease group GB that follows the increase group GA is calculated as the maximum value Imax. In addition, the current value at the intersection of the approximate straight lines LK calculated for the decrease group GB and the increase group GA that follows the decrease group GB is calculated as the minimum value Imin.

When the maximum value Imax and the minimum value Imin of the reactor current IL are calculated, the average value Iav of the reactor current IL is calculated, and the inductance value LA and the duty ratio of the switching element 21 stored in the memory unit 41 are corrected based on this average value Iav. In this embodiment, as shown in FIG. 6, the minimum value Imin is calculated for the first decrease group GB1 and the first increase group GA1 following the first decrease group GB1, and when the maximum value Imax is calculated for the first increase group GA1 and the second decrease group GB2 following the first increase group GA1, the average value Iav of the reactor current IL is calculated, and the inductance value LA and the duty ratio of the switching element 21 stored in the memory unit 41 are corrected based on this average value Iav. Then, the corrected inductance value LA and duty ratio are used to obtain the current detection value Iind of the second increase group GA2 following the second decrease group GB2.

The present embodiment described above provides the following advantages:

In this embodiment, the first slope KA and the second slope KB are used to classify the current detection value Iind into groups GA and GB. In a voltage converter 20 having a reactor 22 and a switching element 21, it is known that the theoretical increase rate of the reactor current IL during the increase period of the reactor current IL is the first slope KA, and that the theoretical decrease rate of the reactor current IL during the decrease period of the reactor current IL is the second slope KB. Therefore, by using the first slope KA and the second slope KB, the current detection value Iind can be accurately classified into groups GA and GB.

Specifically, a first range HA is set using a first slope KA, and a second range HB is set using a second slope KB, and the current detection value Iind is classified into groups GA and GB using these ranges HA and HB. In this case, the width W of the first range HA and the second range HB is set based on the fluctuation range ΔLA of the inductance value LA associated with temperature changes in the reactor 22.

The temperature of the reactor 22 changes depending on the temperature around the reactor 22 and the current passing through the reactor 22. When the temperature of the reactor 22 changes, the inductance value LA of the reactor 22 changes. That is, the inductance value LA of the reactor 22 changes with the temperature change of the reactor 22, and the first slope KA and the second slope KB change. In this embodiment, the width W is set based on the fluctuation range ΔLA of the inductance value LA with the temperature change of the reactor 22. Therefore, even if the temperature of the reactor 22 changes due to the current passing through the reactor 22 and the first slope KA and the second slope KB change, the first slope KA and the second slope KB are prevented from fluctuating beyond the first range HA and the second range HB. This allows the current detection value Iind to be classified into groups GA and GB, taking into account the change in the inductance value LA of the reactor 22 with the current passing through.

In this embodiment, the inductance value LA stored in the memory unit 41 is corrected based on the average value Iav of the reactor current IL. The inductance value LA of the reactor 22 and the average value Iav of the reactor current IL are correlated, and the inductance value LA of the reactor 22 changes based on the average value Iav of the reactor current IL. Therefore, by correcting the inductance value LA of the reactor 22 based on the average value Iav of the reactor current IL, the current detection value Iind can be appropriately classified into groups GA and GB using the first range HA and second range HB calculated using the corrected inductance value LA.

In this embodiment, there is no need to detect the temperature of the inductance value LA in order to correct the inductance value LA. Therefore, there is no need to provide a temperature sensor in the voltage conversion system to detect the temperature of the inductance value LA, and the system configuration can be simplified.

As a method of acquiring the average value Iav of the reactor current IL, a method of acquiring the reactor current IL at the center timing of the on-period or off-period of the switching element 21 as the average value Iav of the reactor current IL can be considered. However, as in this embodiment, when there is a delay time TA or TB between the switching timing t1 to t3 of the switching element 21 and the timing at which the reactor current IL becomes the maximum value Imax or the minimum value Imin, the reactor current IL at the center timing of the on-period or off-period of the switching element 21 does not become the average value Iav of the reactor current IL. Also, as in this embodiment, when the first delay time TA and the second delay time TB are different, for example, even if the reactor current IL is acquired at a timing shifted by the first delay time TA from the center timing of the on-period of the switching element 21, the average value Iav of the reactor current IL cannot be acquired.

In this embodiment, when obtaining the average value Iav of the reactor current IL, the switching timings t1 to t3 of the switching element 21 are not used, and the average value Iav of the reactor current IL is calculated using the approximate straight line LK of each group calculated by detecting the reactor current IL. Therefore, even if there is a delay time TA or TB between the switching timings t1 to t3 of the switching element 21 and the timing at which the reactor current IL reaches its maximum value Imax or minimum value Imin, the average value Iav of the reactor current IL can be calculated with high accuracy.

(Modification of the first embodiment)
The control device 40 may calculate the approximate straight line LK by using the current detection values Iind included in each group GA, GB, excluding the specific current value IT. Here, the specific current value IT is the current detection value Iind obtained in each group GA, GB at the timing closest to the switching timings t1 to t3 of the switching element 21, as shown in FIG. 5.

In the voltage converter 20, the reactor current IL increases and decreases as the switching element 21 switches between on and off states, so that the reactor current IL is likely to become unstable near switching times t1 to t3 of the switching element 21 due to noise and the like that accompanies the switching of the reactor current IL. In this modified example, when calculating the approximate straight line LK, the current detection value Iind excluding the specific current value IT is used to calculate the approximate straight line LK, thereby suppressing the instability of the inductance value LA that accompanies the switching of the switching element 21, and the approximate straight line LK can be calculated appropriately.

Second Embodiment
The second embodiment will be described below with reference to FIGS. 7 to 9, focusing on the differences from the first embodiment.

As shown in FIG. 7, in this embodiment, the control device 40 executes discontinuous current mode control to control the switching element 21 so that the reactor current IL becomes zero, which is different from the first embodiment. In continuous current mode control, a zero period in which the reactor current IL becomes zero exists in one switching period TF of the switching element 21, and the reactor current IL flows intermittently through the reactor 22. In this case, although the maximum value Imax of the reactor current IL exists, the minimum value Imin of the reactor current IL does not exist. In this embodiment, the maximum value Imax of the reactor current IL is calculated using the approximate straight line LK, and the start timing TS and end timing TE of the zero period are calculated, and the average value Iav of the reactor current IL is calculated using these. Here, the start timing TS is the timing when the reactor current IL becomes zero and the zero period begins, and the end timing TE is the timing when the zero period ends and the reactor current IL begins to flow.

Figure 8 shows a flowchart of the control process in this embodiment. For convenience, the same steps in Figure 8 as those shown in Figure 2 above are given the same step numbers and will not be described.

In the control process of this embodiment, in step S13, a classification process is performed to classify the current detection value Iind acquired in step S11 into an increase group GA, a decrease group GB, and a zero group GC based on the time rate of change DI of the current detection value Iind. Here, the zero group GC is a set of current detection values Iind acquired during a zero period. Figure 9 shows the procedure for the classification process of this embodiment. For convenience, the same steps in Figure 9 as those shown in Figure 3 above are given the same step numbers and will not be described.

In the classification process of this embodiment, if a negative judgment is made in step S34, then in step S50 it is judged whether the time rate of change DI calculated in step S31 is zero. If a positive judgment is made in step S50, then it is judged in step S51 that the two current detection values Iind used to calculate the time rate of change DI belong to the zero group GC, and the process proceeds to step S37. On the other hand, if a negative judgment is made in step S50, then the process proceeds to step S36.

Returning to FIG. 8, once the approximate line LK is calculated in step S14, the process proceeds to step S40. In step S40, the maximum value Imax of the reactor current IL, the start timing TS, and the end timing TE are calculated using the approximate line LK calculated in step S14. Specifically, the start timing TS is calculated as the timing at which the current value of the approximate line LK calculated in the decrease group GB becomes zero. The end timing TE is calculated as the timing at which the current value of the approximate line LK calculated in the increase group GA becomes zero.

In step S16, the average value Iav of the reactor current IL is calculated from the maximum value Imax of the reactor current IL calculated in step S40, the start timing TS, and the end timing TE, and the process proceeds to step S16. The average value Iav of the reactor current IL can be calculated as shown in Equation 4 below using the maximum value Imax of the reactor current IL, the end timing TE calculated using the approximation straight line LK of the increase group GA, the start timing TS calculated using the approximation straight line LK of the decrease group GB following the increase group GA, and one switching period TF of the switching element 21.

Iav=(TS-TE)×Imax/(TF×2)...(Formula 4)
According to the present embodiment described above in detail, even if the reactor current IL flows intermittently through the reactor 22 and there is no minimum value Imin of the reactor current IL, the maximum value Imax of the reactor current IL is calculated using the approximate straight line LK, and the average value Iav of the reactor current IL can be calculated by calculating the start timing TS and the end timing TE.

<Other embodiments>
Each of the above embodiments may be modified as follows.

The configuration of the voltage converter 20 is not limited to the boost chopper circuit shown in the above embodiment, and may be, for example, a step-down chopper circuit or a step-up/step-down chopper circuit. An example of a step-down chopper circuit is shown in FIG. 10. Note that the components shown in FIG. 10 that correspond to the components shown in FIG. 1 above are given the same reference numerals. In the case of a step-down chopper circuit, the first slope KA is expressed as the following (Equation 5) using the power supply voltage VB, the output voltage VT, and the inductance value LA of the reactor 22. Therefore, the control device 40 calculates the first range HA using the input voltage detection value Vind and the output voltage detection value Voutd, and the inductance value LA and width W stored in the memory unit 41.

KA=(VB-VT)/LA...(Formula 5)
On the other hand, the second slope KB is expressed as the following (Equation 6) using the output voltage VT and the inductance value LA of the reactor 22. For this reason, the control device 40 calculates the second range HB using the output voltage detection value Voutd and the inductance value LA and width W stored in the storage unit 41.

KB=-VT/LA...(Formula 6)
The control device 40 may determine whether the continuous current mode control or the discontinuous current mode control is being executed based on the calculated minimum value Imin of the reactor current IL. Specifically, if the minimum value Imin is a positive value, it may be determined that the continuous current mode control is being executed, and if the minimum value Imin is zero or a negative value, it may be determined that the discontinuous current mode control is being executed. This makes it possible to properly determine whether the continuous current mode control or the discontinuous current mode control is being executed, and to accurately calculate the average value Iav of the reactor current IL in accordance with the control being executed.

- The method of classifying the current detection value Iind into groups based on the time rate of change DI is not limited to the method using the first range HA and the second range HB, and may be classified based on whether the time rate of change DI is positive or negative. In this case, for example, for the current detection value Iind acquired at the end of the increase period, the time rate of change DI calculated using the current detection value Iind as the second current value IB may be positive, and the time rate of change DI calculated using the current detection value Iind as the first current value IA may be negative. In this way, when the time rate of change DI calculated using a certain current detection value Iind is different between positive and negative, the current detection value Iind may be determined to not belong to any group.

The specific current value IT is not limited to being determined based on the switching timings t1 to t3 of the switching element 21 as shown in the above embodiment, but may also be determined based on the switching timing between the increase period and the decrease period. Specifically, when the switching timing between the increase period and the decrease period is estimated based on the delay times TA and TB, the current detection value Iind obtained within a predetermined period centered on that switching timing may be set as the specific current value IT.

- The power source 10 may be, for example, a fuel cell. A fuel cell is a battery that generates electricity using an electrochemical reaction.

- The method for calculating the approximate line LK is not limited to the least squares method. Any method can be used as long as it calculates the deviation between the current detection value Iind and the approximate line LK and determines the approximate line LK so that this deviation is minimized.

The control device and the method thereof described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control device and the method thereof described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control device and the method thereof described in the present disclosure may be realized by one or more dedicated computers configured by combining a processor and memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by the computer.

10...power supply, 20...voltage converter, 21...switching element, 22...reactor, 40...control device.

Claims (7)

A reactor (22);
A control device (40) for use in a voltage converter (20) that transforms an input voltage by controlling switching of the switching element, the control device (40) comprising: a switching element (21) that, when turned on, gradually increases a reactor current flowing from a power source (10) to the reactor and that, when turned off, gradually decreases the reactor current;
a current acquisition unit that acquires the reactor current at a predetermined time interval;
a classification unit that classifies the multiple current values acquired by the current acquisition unit into multiple groups including a current value increase group that is a set of current values acquired during an increase period of the reactor current and a current value decrease group that is a set of current values acquired during a decrease period of the reactor current based on a time rate of change of the current values;
a calculation unit that calculates an approximation line that linearly approximates the relationship between the current value and the timing of acquiring the current value for each group, calculates the current value at an intersection of the approximation lines calculated for the current value increase group and the current value decrease group that are successive in time series as a maximum value of the reactor current, and calculates an average value of the reactor current using the calculated maximum value of the reactor current. The control device according to claim 1, wherein in a continuous current mode in which switching control of the switching element is performed so that the reactor current does not become zero, the calculation unit calculates the current values at the intersections of the approximation lines calculated in the current value increase group and the current value decrease group, which are successive in a time series, as the maximum and minimum values of the reactor current, and calculates the median of the maximum and minimum values of the reactor current as the average value. The classification unit includes:
calculating a first slope which is a time rate of increase of the reactor current during an increase period of the reactor current, and when the time rate of change of the current value is included in a first range which is a range of the time rate of increase of the reactor current including the first slope, the current value used for calculating the time rate of change is set to the current value acquired during the increase period, and classifying a set of the current values acquired during the increase period as the current value increase group;
3. The control device according to claim 1, further comprising: a second slope which is a time rate of decrease of the reactor current during a period in which the reactor current decreases; and when the time rate of change of the current value is included in a second range which is a range of the time rate of decrease of the reactor current that includes the second slope, the current value used in calculating the time rate of change is the current value acquired during the decrease period; and a set of the current values acquired during the decrease period is classified as the current value decrease group. The classification unit calculates the first gradient and the second gradient by using an inductance value of the reactor;
The control device according to claim 3 , wherein the first range and the second range are set based on a range of fluctuation of the inductance value associated with a temperature change of the reactor. The control device according to claim 4, wherein the classification unit corrects the inductance value based on the average value calculated by the calculation unit. The control device according to any one of claims 1 to 5, wherein the calculation unit calculates the approximation line using the current values excluding a specific current value, which is the current value acquired at the timing closest to the timing of switching the on/off state of the switching element, in each group. a control unit that controls a duty ratio of the switching element so as to control the average value calculated by the calculation unit to a target value,
The control device according to any one of claims 1 to 6, wherein the control unit increases the duty ratio when the average value is smaller than the target value, and decreases the duty ratio when the average value is larger than the target value.

Images