Power conversion system

Abstract

The present disclosure relates to a power conversion system. The power conversion system includes a converter, a current sensor, and a motor ECU. The converter is configured to boost voltage by operating at a set carrier frequency. The current sensor detects current flowing through the converter. The motor ECU performs control to protect the converter. Furthermore, the motor ECU estimates the temperature rise of the converter based on at least one of the voltage ratio before and after the converter boost and the carrier frequency, as well as the value detected by the current sensor. If the integrated value of the temperature rise reaches a threshold, the motor ECU performs control to suppress the current flowing through the converter.

Description

Technical Field

[0001] The present disclosure relates to a power conversion system, and more particularly to a power conversion system including a converter. Background Art

[0002] Japanese Patent Application Laid-Open No. 2011-049032 discloses a control system capable of protecting a converter. The control system includes a battery, a buck-boost converter circuit, a current sensor, and a control unit. The current sensor detects the current flowing through the buck-boost converter circuit. The control unit compares the square integral of the current sensor's detection value with a threshold value for protecting the buck-boost converter circuit. If the integral is below the threshold, the control unit continues battery temperature control. If the integral is greater than the threshold, the control unit stops battery temperature control to protect the buck-boost converter circuit from overheating. Summary of the Invention

[0003] The current flowing through the converter includes a ripple component in addition to a DC component. Furthermore, even if the DC component remains constant, the converter's temperature rise increases as the ripple component increases. Current sensors, due to their detection accuracy, often cannot accurately detect the ripple component. Therefore, when estimating the converter's temperature rise based on the current sensor's detection value for the purpose of overheat protection, one approach is to estimate the converter's temperature rise under the assumption that the ripple component is always at its maximum relative to the current sensor's detection value. However, if the converter's overheat protection is implemented based on this estimated temperature rise, the converter's protection may be excessive. Japanese Patent Application Laid-Open No. 2011-049032 does not specifically address this issue.

[0004] The present disclosure provides a power conversion system including a converter, and appropriately protects the converter from overheating based on a detection value of a current sensor that detects a current flowing through the converter.

[0005] A power conversion system according to one embodiment of the present disclosure includes a converter, a current sensor, and a control device. The converter is configured to boost voltage by operating at a set carrier frequency. The current sensor detects current flowing through the converter. The control device performs control to protect the converter. The control device estimates the temperature rise of the converter based on at least one of the voltage ratio before and after the converter boost and the carrier frequency, and the value detected by the current sensor. When the integrated value of the temperature rise reaches a threshold, the control device performs control to suppress the current flowing through the converter.

[0006] In the above configuration, the converter temperature rise is estimated based not only on the current sensor's detection value but also on at least one of the converter's voltage ratio and carrier frequency, which influence the ripple component. By considering at least one of the converter's voltage ratio and carrier frequency, overheat protection of the converter can be avoided even when the ripple component is assumed to be at its maximum. Consequently, the converter can be appropriately protected from overheating.

[0007] In the above embodiment, the power conversion system may further include a storage unit that stores a detection value of the current sensor, at least one of a voltage ratio and a carrier frequency, and a predetermined relationship between the amount of temperature rise. The control device may estimate the amount of temperature rise based on the detection value of the current sensor using at least one of the voltage ratio and the carrier frequency and the predetermined relationship.

[0008] In the above configuration, the temperature rise of the converter is estimated based on the previously prepared relationship. As a result, the configuration of the power conversion system can be simplified while appropriately protecting the converter from overheating.

[0009] In the above aspect, when the integrated value reaches the threshold value, the control device may increase the carrier frequency compared to immediately before the integrated value reaches the threshold value.

[0010] In the above configuration, since the carrier frequency of the converter is higher, the ripple amplitude of the current flowing through the converter is reduced. As a result, the temperature rise of the converter is reduced, thereby protecting the converter from overheating.

[0011] In the above embodiment, the converter may be electrically connected between the power storage device and the load device. The control device may control the load device to limit the power input to and output from the power storage device to the power storage device's upper charging power limit and upper discharging power limit, respectively. Furthermore, when the integrated value reaches a threshold value, the control device may reduce the upper charging power limit and the upper discharging power limit compared to the value immediately before the integrated value reached the threshold value.

[0012] This suppresses the current flowing through the converter, thereby reducing the temperature rise of the converter, thereby protecting the converter from overheating.

[0013] According to one aspect of the present disclosure, in a power conversion system including a converter, the converter can be appropriately protected from overheating based on a detection value of a current sensor that detects a current flowing through the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals designate like elements, and in which:

[0015] Figure 1 1 is a diagram showing the overall configuration of a vehicle to which the power conversion system according to the present embodiment is applied.

[0016] Figure 2 This is a diagram showing the relationship between the ripple amplitude of the current flowing through the reactor and the voltage step-up ratio.

[0017] Figure 3 This is a diagram showing the relationship between the ripple amplitude of the current flowing through the reactor and the carrier frequency of the converter.

[0018] Figure 4 1 is a diagram showing temporal changes in converter temperature TC according to the voltage step-up ratio and the carrier frequency.

[0019] Figure 5 This is a diagram showing a map indicating the relationship between the detected value of the current flowing through the reactor and the threshold value reaching time.

[0020] Figure 6 This is a diagram showing a table indicating the relationship between the detected value of the current flowing through the reactor and the temperature rise amount of the converter.

[0021] Figure 7 This is a functional block diagram of the motor ECU.

[0022] Figure 8 This is a diagram showing an example of processing executed by the motor ECU.

[0023] Figure 9 This is a diagram for explaining the timing of executing the converter current suppression control in this embodiment.

[0024] Figure 10 This is a functional block diagram of a motor ECU in a modified example of the embodiment. DETAILED DESCRIPTION

[0025] The present embodiment is described below with reference to the accompanying drawings. It should be noted that identical or corresponding parts in the drawings are denoted by the same reference numerals, and their description will not be repeated. In the following embodiments, the structure of a vehicle is described as an example of an application of the power conversion system. However, the power conversion system disclosed herein is not limited to use in vehicles.

[0026] Figure 1 This figure shows the overall structure of a vehicle to which the power conversion system of this embodiment is applied. In this embodiment, the vehicle 10 is described as an electric vehicle, but the vehicle 10 may also be a hybrid vehicle equipped with an internal combustion engine or a fuel cell vehicle equipped with a fuel cell.

[0027] The vehicle 10 includes a battery pack 1 , a PCU (Power Control Unit) 2 , a MG (Motor Generator) 3 , and a vehicle ECU (Electronic Control Unit) 50 .

[0028] The battery pack 1 includes a battery 11 , a voltage sensor 12 , a current sensor 13 , a temperature sensor 14 , an SMR (System Main Relay) 15 , and a battery ECU 16 .

[0029] The battery 11 is a chargeable and dischargeable storage device. Battery 11 is, for example, a secondary battery such as a lithium-ion battery, a nickel-metal hydride battery, or a lead-acid battery. Alternatively, a storage device comprising a storage element such as an electric double-layer capacitor may be used in place of battery 11. Battery 11 supplies the PCU 2 with electricity used to generate driving force for the wheels (not shown) of the vehicle 10. Furthermore, battery 11 is configured to store electricity generated by the MG 3 (described later).

[0030] The voltage sensor 12 detects the voltage Vb of the battery 11. The current sensor 13 detects the current Ib input to and output from the battery 11. The temperature sensor 14 detects the temperature Tb of the battery 11. Each sensor outputs its detection value to the battery ECU 16.

[0031] The SMR 15 is provided between the battery 11 and a converter 21 (described later). The SMR 15 opens and closes in response to a command from the battery ECU 16.

[0032] The battery ECU 16 includes a processor such as a CPU (Central Processing Unit) and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory) (none of which are shown).

[0033] The battery ECU 16 monitors the state of the battery 11 and controls the SMR 15 based on signals received from various sensors and programs and maps stored in memory. For example, the battery ECU 16 calculates the battery 11's SOC (State of Charge) based on the battery 11's current Ib, voltage Vb, and temperature Tb, as well as programs and maps stored in memory. The battery ECU 16 transmits the calculated SOC to the vehicle ECU 50 (described later).

[0034] The PCU 2 includes a positive line PL1 , a negative line NL, a capacitor C1 , a converter 21 , a positive line PL2 , a capacitor C0 , voltage sensors 22 and 24 , an inverter 23 , and a motor ECU 4 .

[0035] Positive line PL1 electrically connects the positive electrode of battery 11 to a high potential terminal of converter 21 (described later). Negative line NL electrically connects the negative electrode of battery 11 to a low potential terminal of converter 21. Voltage VL is the voltage between positive line PL1 and negative line NL.

[0036] Capacitor C1 is connected between positive line PL1 and negative line NL. Capacitor C1 smoothes the voltage between positive line PL1 and negative line NL.

[0037] The voltage sensor 24 detects a voltage VL that is a voltage across the capacitor C1 , and outputs the detected value to the motor ECU 4 .

[0038] Converter 21 is a step-up chopper circuit including a reactor L1 , a current sensor 210 , switching elements Q1 , Q2 , and diodes D1 , D2 .

[0039] Reactor L1 is electrically connected between the positive electrode of battery 11 and an intermediate point (connection node) between switching element Q1 and switching element Q2 .

[0040] Current sensor 210 detects current IL flowing through reactor L1 and outputs the detected value to motor ECU 4. Current sensor 210 cannot accurately detect the ripple component of current IL. In the present embodiment, current sensor 210 outputs a value corresponding to the average of the maximum and minimum peak values ​​of the ripple component of current IL as the detected value.

[0041] Switching elements Q1 and Q2 are connected in series between positive line PL2 and negative line NL. Switching elements Q1 and Q2 are switched (turned on / off) in response to drive signals S1 and S2, respectively, from the motor ECU 4. Switching elements Q1 and Q2 are, for example, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

[0042] Diodes D1 and D2 are connected in antiparallel to switching elements Q1 and Q2 , respectively.

[0043] Converter 21 is controlled by motor ECU 4 (described later) to switch switching elements Q1 and Q2. Converter 21 is configured to boost voltage VL by operating at a set carrier frequency and output boosted voltage VH.

[0044] In converter 21, the voltage ratio (VL / VH) between voltage VH and voltage VL (i.e., the voltage ratio before and after the boost) is controlled by the on-time ratio (duty cycle) of switching elements Q1 and Q2 relative to the switching cycle (carrier cycle) of converter 21. Hereinafter, the voltage ratio (VL / VH) will be referred to as the "boost ratio." Details of converter 21 control will be described later.

[0045] The positive line PL2 electrically connects the high potential end of the converter 21 to the high potential end of the inverter 23 (described later), while the negative line NL electrically connects the low potential end of the converter 21 to the low potential end of the inverter 23 .

[0046] Capacitor C0 is connected between positive line PL2 and negative line NL to smooth the voltage between them.

[0047] The voltage sensor 22 detects a voltage VH that is a voltage across the capacitor C0 , and outputs the detected value to the motor ECU 4 .

[0048] Inverter 23 includes a U-phase arm 231, a V-phase arm 232, and a W-phase arm 233. U-phase arm 231 includes switching elements Q3 and Q4 and diodes D3 and D4 connected in antiparallel to switching elements Q3 and Q4, respectively. V-phase arm 232 includes switching elements Q5 and Q6 and diodes D5 and D6 connected in antiparallel to switching elements Q5 and Q6, respectively. W-phase arm 233 includes switching elements Q7 and Q8 and diodes D7 and D8 connected in antiparallel to switching elements Q7 and Q8, respectively.

[0049] The switching elements Q3 to Q8 are switched in accordance with drive signals S3 to S8 from the motor ECU 4 , respectively.

[0050] Inverter 23 converts DC power output from converter 21 into AC power by switching elements Q3-Q8, and outputs the converted AC power to MG3. During regenerative braking of vehicle 10, inverter 23 converts AC power generated by MG3 into DC power, and outputs this DC power to converter 21. The DC power output to converter 21 is stepped down according to converter 21's step-up ratio (VL / VH) and then stored in battery 11.

[0051] MG3 is shown as an example of a load device and is a three-phase permanent magnet synchronous motor. In MG3, one end of the three coils (U-phase, V-phase, and W-phase) is connected to the neutral point. The other ends of the coils (U-phase, V-phase, and W-phase) are connected to the midpoints of U-phase arm 231, V-phase arm 232, and W-phase arm 233, respectively. The output torque of MG3 is transmitted to the drive wheels (not shown) via a power transmission gear, thereby driving vehicle 10. Furthermore, MG3 generates electricity using the rotational force of the drive wheels during regenerative braking of vehicle 10.

[0052] Like the battery ECU 16 , the motor ECU 4 includes a processor (not shown) such as a CPU and a memory 5 including a ROM and a RAM, etc. The motor ECU 4 is configured to communicate with a vehicle ECU 50 (described later) and exchange various data and signals.

[0053] Motor ECU 4 performs pulse width modulation (PWM) control on converter 21 and inverter 23 based on signals received from various sensors and programs and maps stored in memory 5. For example, motor ECU 4 sets the carrier frequency for PWM control of converter 21 or controls voltage VH boosted by converter 21.

[0054] The vehicle ECU 50 is a higher-level ECU that controls the entire vehicle 10 based on signals output from various sensors of the vehicle 10. For example, the vehicle ECU 50 controls the upper limit of charge power Win and the upper limit of discharge power Wout of the battery 11 based on the SOC of the battery 11 transmitted from the battery ECU 16. The vehicle ECU 50 controls the torque of the MG 3 so that the input and output power (charge power and discharge power) of the battery 11 are limited to the upper limit of charge power Win and the upper limit of discharge power Wout, respectively.

[0055] The current flowing through converter 21 contains a ripple component in addition to a DC component. This ripple component is generated by the switching operation of switching elements Q1 and Q2. Even if the DC component of the current flowing through converter 21 remains constant, the temperature rise of converter 21 increases as the ripple component increases. Current sensor 210 cannot accurately detect the ripple component. Therefore, when estimating the temperature rise of converter 21 based on the detection value of current sensor 210 for the purpose of overheat protection of converter 21, it is also possible to estimate the temperature rise of converter 21 under the assumption that the ripple component is always at its maximum relative to the detection value of current sensor 210. However, if overheat protection control of converter 21 is executed based on this estimated temperature rise, the protection of converter 21 becomes excessive.

[0056] Regarding the above-mentioned problem, the inventors have focused on the fact that the amplitude of the ripple component of the current flowing through converter 21 (hereinafter also referred to as “ripple amplitude”) varies depending on the boost ratio (VL / VH) of converter 21 and the carrier frequency of PWM control of converter 21 .

[0057] Therefore, the motor ECU 4 of the present embodiment estimates the temperature rise amount of the converter 21 based on the boost ratio (VL / VH) of the converter 21, the carrier frequency of the converter 21, and the detected value of the current flowing through the converter 21. Thus, it is not necessary to overestimate the temperature rise amount under the condition that the ripple component is always maximum with respect to the detected value of the current sensor 210. Then, when the integral value of the temperature rise amount estimated as described above reaches the threshold value, control for suppressing the current flowing through the converter 21 is executed. Hereinafter, this control will also be referred to as "converter current suppression control". A specific example of the converter current suppression control will be described later.

[0058] Hereinafter, the control of the motor ECU 4 of the present embodiment will be described in further detail. In addition, in the following description, the current IL is used as an example of the current flowing through the converter 21.

[0059] It is known that the ripple amplitude ILpp (peak-to-peak value) of the current IL is a function of the voltage VL and voltage VH of the converter 21 and the carrier frequency fc of the converter 21 as shown in the following equation (1).

[0060] ILpp = (VL / L) × (1 / fc) × (VH - VL) / VH…(1)

[0061] The above equation (1) is transformed for the boost ratio (VL / VH = k) as follows.

[0062] ILpp = -(1 / L) × (1 / fc) × {(k - 1 / 2) 2 - 1 / 4} × VH (2)

[0063] Therefore, as Figure 2 shown by line 300, when the boost ratio (VL / VH = k) is 0.5, the ripple amplitude ILpp becomes maximum with respect to the boost ratio (VL / VH). In addition, in the converter 21, the boosted voltage VH is greater than or equal to the voltage VL before boosting (VL ≤ VH), so for the boost ratio VL / VH (= k), 0 < k ≤ 1 holds. When the boost ratio is 1, the ripple amplitude ILpp is minimum (value 0).

[0064] In addition, from equations (1) and (2), it can be seen that the ripple amplitude ILpp decreases as the carrier frequency fc increases. Here, when the carrier frequency fc is set between the lower limit fcmin and the upper limit fcmax, as Figure 3 shown by line 305, when the carrier frequency fc is the lower limit fcmin, the ripple amplitude ILpp becomes maximum with respect to the carrier frequency fc. On the other hand, when the carrier frequency fc is the upper limit fcmax, the ripple amplitude ILpp becomes minimum with respect to the carrier frequency fc.

[0065] As described above, regarding the voltage step-up ratio (VL / VH) and carrier frequency fc, the ripple amplitude ILpp reaches a maximum when the voltage step-up ratio (VL / VH) is 0.5 and the carrier frequency fc is fcmin. This condition is hereinafter referred to as the "maximum ripple amplitude condition."

[0066] On the other hand, regarding the voltage step-up ratio (VL / VH), the ripple amplitude ILpp becomes extremely small (ie, 0) under the condition that the voltage step-up ratio (VL / VH) is 1. This condition is hereinafter also referred to as the "extremely small ripple amplitude condition."

[0067] The temperature rise in converter 21 is related to the amount of heat generated in reactor L1, which is related to the square of current IL. Furthermore, current IL consists of a DC component and a ripple component. Therefore, even when the DC component of current IL remains constant, as the ripple amplitude ILpp representing the ripple component of current IL increases, the amount of heat generated increases, and thus the temperature rise increases. Thus, the temperature rise depends on the ripple amplitude ILpp.

[0068] As shown in equation (2), ripple amplitude ILpp is a function of the voltage step-up ratio (VL / VH) of converter 21 and the carrier frequency fc of converter 21. Therefore, the temperature rise in converter 21 depends on the voltage step-up ratio (VL / VH) of converter 21 and the carrier frequency fc of converter 21.

[0069] Reference Figure 4 , how the temperature rise pattern of converter 21 changes depending on the voltage step-up ratio of converter 21 and the carrier frequency of converter 21 will be described.

[0070] Figure 4 : is a diagram showing the temporal change of the temperature TC of the converter 21 according to the voltage step-up ratio (VL / VH) and the carrier frequency fc. Figure 4 In FIG. 5 , the horizontal axis represents the time t that has elapsed from the time when the temperature TC reaches the initial temperature T0 , and the vertical axis represents the temperature TC of the converter 21 .

[0071] Reference Figure 4 Lines 402, 410, and 420, indicated by dashed lines, respectively, represent the temporal transition of temperature TC under the maximum ripple amplitude condition, assuming that current IL continues to be at Ia, Ib, and Ic. As ripple amplitude ILpp increases, the temperature rise of converter 21 increases. Therefore, under the maximum ripple amplitude condition, the contribution of ripple amplitude ILpp to the temperature rise of converter 21 becomes the largest.

[0072] On the other hand, solid lines 405, 415, and 425 respectively represent the temporal transition of temperature TC under the extremely low ripple amplitude condition, assuming that current IL continues to be at Ia, Ib, and Ic. As ripple amplitude ILpp decreases, the temperature rise of converter 21 decreases. Therefore, under the extremely low ripple amplitude condition, the contribution of ripple amplitude ILpp to the temperature rise of converter 21 becomes extremely small.

[0073] Threshold temperature TTH is appropriately determined in advance through experiments, etc., to protect converter 21 from overheating. Threshold temperature TTH is determined based on, for example, the amount of heat generated in reactor L1 and the specific heat and usable temperature of components constituting converter 21.

[0074] Times tTH1, tTH2, and tTH3 are the times it takes for temperature TC to reach threshold temperature TH from a predetermined initial temperature T0, assuming the ripple amplitude is at its maximum when current IL remains at Ia, Ib, and Ic, respectively. Hereinafter, the time it takes for temperature TC to reach threshold temperature TH from a predetermined initial temperature T0 is referred to as the "threshold reaching time." The threshold reaching time is also the time it takes for the temperature rise from converter 21's initial temperature T0 to reach ΔTTH. Initial temperature T0 is, for example, predetermined.

[0075] Furthermore, the times tTH1 ′, tTH2 ′, and tTH3 ′ are threshold value reaching times under the extremely small ripple amplitude condition assuming that the current IL continues to be Ia, Ib, and Ic, respectively.

[0076] When the temperature TC of the converter 21 reaches the threshold temperature TH, the converter current suppression control is executed to prevent the converter 21 from overheating due to heat generation of the reactor L1 .

[0077] An example of converter current suppression control is control to reduce the battery 11's charge power upper limit Win and discharge power upper limit Wout relative to their respective values ​​immediately before the threshold reach time. For example, if discharge power upper limit Wout decreases, and the power discharged from the battery 11 to obtain the torque of MG3 in accordance with the torque command value exceeds the reduced discharge power upper limit, the motor ECU 4 controls the inverter 23 to limit the power discharged from the battery 11 and thereby the torque of MG3. This limits the power supplied to the converter 21 relative to its value immediately before the threshold reach time, thereby suppressing the current IL flowing through the converter 21. Consequently, overheating of the converter 21 is prevented.

[0078] As shown in the figure, even when the detected value of current IL is the same, the threshold reaching time varies depending on the step-up ratio (VL / VH) and the carrier frequency fc. For example, regarding lines 402 and 405, even when the detected value of current IL is the same, Ia, the step-up ratio (VL / VH) in the case of line 405 is 1 ( Figure 2 ), the step-up ratio (VL / VH) in the case of line 402 is 0.5 ( Figure 2 ). Then, the carrier frequency fc in the case of line 405 is greater than the carrier frequency fc in the case of line 402 ( Figure 3 ).

[0079] Therefore, the ripple amplitude ILpp in line 405 is smaller than the ripple amplitude ILpp in line 402. Since the smaller the ripple component, the smaller the temperature rise of converter 21, the temperature rise of converter 21 per unit time in line 405 is smaller than that in line 402. Consequently, the threshold-reaching time tTH1′ in line 405 is longer than the threshold-reaching time tTH1 in line 402.

[0080] As described above, the threshold reaching time varies depending on the ripple amplitude ILpp (specifically, the step-up ratio and the carrier frequency fc). Meanwhile, the current sensor 210 cannot accurately detect the ripple component of the current IL.

[0081] Here, if the ripple component of current IL cannot be accurately detected, estimating the temperature rise of converter 21 under the assumption that the maximum ripple amplitude condition is always satisfied will lead to overprotection of converter 21 .

[0082] For example, if the above conditions do not accurately reflect the actual ripple amplitude ILpp, converter current suppression control may be executed at an unnecessarily early timing. Specifically, "unnecessarily early timing" refers to a timing at which converter current suppression control is executed when converter 21 temperature TC has not actually risen to threshold temperature TH and execution of the control is therefore not necessary.

[0083] As part of converter current suppression control, for example, if battery 11's charge power upper limit Win and discharge power upper limit Wout are lower than immediately before the threshold reach time, MG 3's torque is often limited after the threshold reach time. In this case, the vehicle 10's driving performance deteriorates. Therefore, it is preferable to execute this control as late as possible within a range that protects converter 21 from overheating.

[0084] Therefore, in this embodiment, unlike the case where converter 21 is protected under the assumption that the maximum ripple amplitude condition is always satisfied, overheat protection control (converter current suppression control) of converter 21 is performed while taking the step-up ratio (VL / VH) and carrier frequency fc into consideration.

[0085] Reference Figure 5 , how the threshold reaching time differs between the case where the ripple amplitude ILpp is extremely large and the case where the ripple amplitude ILpp is extremely small will be described in further detail.

[0086] Figure 5 5 is a diagram showing maps 500 and 505 showing the relationship between the detected value of the current IL and the threshold reaching time. Figure 5 In the upper and lower sections, the vertical axis represents the detected value of the current IL, and the horizontal axis represents Figure 4 The threshold value reaches the time in. Maps 500 and 505 are predetermined by experiments and stored in the memory 5 ( Figure 1 ).

[0087] Reference Figure 5 In the upper part of FIG, map 500 shows the threshold reaching time when the detection value of current IL is continuously obtained under the condition of extremely large ripple amplitude. Map 500 also shows the time when the detection value of current IL is continuously obtained under the condition of extremely large ripple amplitude. Figure 4 ) are shown in association with the threshold reaching times tTH1, tTH2 and tTH3.

[0088] On the other hand, refer to Figure 5 In the lower part of FIG, map 505 shows the threshold reaching time when the detection value of current IL is continuously obtained under the condition of extremely small ripple amplitude. Map 505 also shows the time when the threshold reaching time is reached when the detection value of current IL is continuously obtained under the condition of extremely small ripple amplitude. Figure 4 ) are shown in association with the threshold reaching times tTH1', tTH2' and tTH3'.

[0089] As described above, maps 500 and 505 predefine the relationship between the detected value of current IL and the threshold-reaching time based on the boost ratio (VL / VH) and carrier frequency fc of converter 21. Memory 5 also stores a plurality of other maps (not shown) that predefine the aforementioned relationship based on other combinations of boost ratios (VL / VH) and carrier frequency fc.

[0090] By using a map prepared in advance based on experiments or the like in this manner, the configuration for converter overheat protection control can be simplified.

[0091] Motor ECU 4 selects a map corresponding to the voltage step-up ratio (VL / VH) and carrier frequency fc of converter 21 from among maps 500, 505, and the other multiple maps stored in memory 5. For example, when the voltage step-up ratio (VL / VH) is 0.5 and the carrier frequency fc is fcmin, motor ECU 4 selects map 500. Furthermore, when the voltage step-up ratio (VL / VH) is 1 and the carrier frequency fc is fcmax, motor ECU 4 selects map 505.

[0092] Next, motor ECU 4 obtains threshold-reaching time tTH corresponding to the detected value of current IL based on the selected map. For example, if the detected value is IL1 and map 505 is selected, the threshold-reaching time tTH corresponding to the continued acquisition of this detected value is assumed to be tTH1'. As described below, the threshold-reaching time tTH obtained from the selected map is used to estimate the temperature rise of converter 21.

[0093] Reference Figure 6 A method for estimating the temperature rise amount of converter 21 based on acquired threshold value reaching time tTH will be described below.

[0094] Figure 6 This diagram shows table 600 representing the relationship between the detected value of current IL and the temperature rise ΔTC of converter 21. Specifically, table 600 stores this relationship when the voltage step-up ratio (VL / VH) is VLa / VHa and the carrier frequency fc is fca. Table 600 is pre-stored in memory 5 of motor ECU 4. Table 600 includes columns 605, 610, and 615. Column 605 represents the detected value of current IL.

[0095] Column 610 indicates the threshold reaching time tTH corresponding to the detection value. The threshold reaching time is the threshold reaching time assuming that the detection value is continuously obtained. Figure 5 As described above, the threshold reaching time tTH varies depending on the voltage step-up ratio (VL / VH) and the carrier frequency fc, and is therefore a function of them.

[0096] Column 610 shows the threshold reaching time tTH in the above case when the step-up ratio (VL / VH) is VLa / VHa and the carrier frequency fc is fca. For example, when the detected value of the current IL is IL1, the threshold reaching time tTH is tTH11 if this detected value is continuously obtained. When (VLa / VHa) is 0.5 and fca is fcmin (maximum ripple amplitude condition), tTH11 is tTH1 ( Figure 4). In addition, assuming that (VLa / VHa) is 1 (ripple amplitude is extremely small condition), tTH11 is tTH1' ( Figure 4 ).

[0097] Column 615 shows the temperature rise ΔTC of converter 21 according to the threshold arrival time tTH corresponding to current IL. This temperature rise is the temperature rise of converter 21 during the sampling period from one sampling time of the detection value of current sensor 210 to the next sampling time. As described below, temperature rise ΔTC is calculated based on threshold arrival time tTH. Therefore, like threshold arrival time tTH, it is a function of the step-up ratio (VL / VH) and carrier frequency fc. Column 615 shows the estimated temperature rise ΔTC when the step-up ratio (VL / VH) is VLa / VHa and the carrier frequency fc is fca.

[0098] The detection value of current sensor 210 is acquired by motor ECU 4 at sampling period TS. The temperature TC of converter 21 increases due to heat generated by reactor L1 during the sampling period TS from the sampling time to the next sampling time. Here, the relationship between the sampling period TS and the temperature rise ΔTC of converter 21 during the sampling period TS is considered to be similar to the threshold reaching time tTH (assuming that a certain detection value of current IL is continuously obtained) and the total temperature rise ΔTTH of converter 21 after the threshold reaching time has passed ( Figure 4 ) is the same.

[0099] exist Figure 6 In the example, when the detection value of the current IL is IL1, if IL1 is continuously obtained as the detection value, the threshold reaching time tTH is tTH11. Here, it represents the temperature TC from its initial temperature T0 to the threshold temperature TTH (both Figure 4 )The rate of temperature rise is expressed as a percentage.

[0100] For example, when temperature TC has not yet risen from initial temperature T0, the temperature rise of converter 21 is 0%. Furthermore, when temperature TC rises to the average of initial temperature T0 and threshold temperature TTH, the temperature rise is 50%. Furthermore, when temperature TC rises to threshold temperature TTH, the temperature rise is 100%.

[0101] Therefore, the temperature TC rise rate during each sampling period TS is also expressed as a percentage. For example, assuming that the detected value of current IL is continuously obtained at IL1, the temperature rise rate during the time interval tTH11 is 100%. Therefore, if the detected value of current IL is IL1, the temperature rise rate during the sampling period TS from the sampling time of that detected value to the next sampling time is estimated to be (TS / tTH11) × 100 (%).

[0102] Thus, based on the total temperature increase (ΔTTH) of converter 21 from the time when temperature TC reaches initial temperature T0 to the time when the threshold value reaches time tTH ( Figure 4 ) and the aforementioned temperature rise rate, the temperature rise within sampling period TS is estimated as (TS / tTH11) × 100 × ΔTTH. When the detected value of current IL is another value (e.g., IL2 or IL3), the temperature rise ΔTC within sampling period TS is similarly estimated (column 615).

[0103] Note that, in addition to the table 600 , the memory 5 also stores tables 620 and 630 for calculating the temperature rise amount ΔTC when the voltage step-up ratio (VL / VH) and the carrier frequency fc take other combinations of values.

[0104] For example, table 620 is a table used to calculate the temperature rise ΔTC within the sampling period TS when the voltage step-up ratio (VL / VH) is VLb / VHb and the carrier frequency fc is fcb. Furthermore, table 630 is a table used to calculate the temperature rise ΔTC within the sampling period TS when the voltage step-up ratio (VL / VH) is VLc / VHc and the carrier frequency fc is fcc.

[0105] In this manner, motor ECU 4 estimates the temperature rise ΔTC during sampling period TS, from the sampling time to the next sampling time, based on the detection value of current sensor 210 at that sampling time. This temperature rise ΔTC differs from the temperature rise estimated under the assumption that the ripple amplitude maximum condition is always satisfied and reflects the actual step-up ratio (VL / VH) and carrier frequency fc of converter 21 at the sampling time.

[0106] Then, when the integrated value of the temperature increase ΔTC of converter 21 reaches the threshold value ΔTTH ( Figure 4 ), it is estimated that temperature TC of converter 21 has reached threshold temperature TH, and converter current suppression control is executed. Note that this integrated value is the integrated value of the temperature increase ΔTC from the time when temperature TC reaches initial temperature T0.

[0107] By executing converter current suppression control in this manner, the timing at which the current (current IL) flowing through converter 21 is suppressed is prevented from being unnecessarily advanced relative to the timing calculated under conditions where the ripple amplitude is extremely large. Specifically, the timing at which converter current suppression control is executed (the timing at which the driving performance of vehicle 10 degrades) can be delayed relative to the timing calculated under these conditions, within a range that protects converter 21 from overheating.

[0108] Figure 7 1 is a functional block diagram of the motor ECU 4. The motor ECU 4 includes a data selection unit 702, a temperature rise estimation unit 705, a threshold determination unit 710, a converter current suppression unit 715, a carrier frequency determination unit 717, a carrier generation unit 720, and a drive signal generation unit 725.

[0109] Data selection unit 702 receives voltage VH and voltage VL output from voltage sensor 22 and voltage sensor 24, respectively. Furthermore, data selection unit 702 receives carrier frequency fc output from carrier frequency determination unit 717. Based on the voltage step-up ratio (VL / VH) calculated from voltage VL and voltage VH and carrier frequency fc, data selection unit 702 selects data corresponding to the voltage step-up ratio and carrier frequency from temperature rise estimation data 701 stored in memory 5.

[0110] It should be noted that the temperature rise estimation data 701 is data that defines a predetermined relationship between the detected value of the current IL, the voltage step-up ratio (VL / VH), the carrier frequency fc, and the temperature rise ΔTC of the converter 21. Specifically, the temperature rise estimation data 701 is composed of a plurality of maps (e.g., Figure 5 500, 505) and multiple tables (e.g., containing Figure 6 Tables 600, 620, and 630).

[0111] For example, when the boost ratio is 0.5 and the carrier frequency fc is fcmin, the data selection unit 702 selects the map 500 ( Figure 5 ). In this case, the data selection unit 702 selects a table corresponding to the combination of the boost ratio and the carrier frequency ( Figure 6 The map and table selected by the data selection unit 702 are output to the temperature rise amount estimation unit 705 .

[0112] The temperature rise amount estimation unit 705 uses the data (map and table) selected by the data selection unit 702 to estimate the sampling period TS (from the sampling time of the detection value to the next sampling time) based on the detection value of the current IL. Figure 6 ) is used to calculate the temperature increase ΔTC of converter 21 within the device. The estimated temperature increase ΔTC is output to threshold value determination unit 710.

[0113] The threshold determination unit 710 determines whether the integrated value ΔTCS of the temperature rise ΔTC is equal to the threshold ΔTTH ( Figure 4 When integrated value ΔTCS is equal to or greater than ΔTTH, threshold value determination unit 710 outputs a request to converter current suppression unit 715 to execute converter current suppression control.

[0114] Upon receiving this request, converter current suppressing unit 715 executes control to suppress current IL to protect converter 21 from overheating. Current IL is suppressed based on charge power upper limit Win and discharge power upper limit Wout transmitted from vehicle ECU 50 as described below.

[0115] Upon receiving the request from threshold value determination unit 710 , converter current suppressing unit 715 outputs a request to vehicle ECU 50 to make charging power upper limit Win and discharging power upper limit Wout smaller than immediately before the threshold value reaching time.

[0116] Upon receiving this request, vehicle ECU 50 determines the smaller upper charge power limit Win and upper discharge power limit Wout values ​​after the threshold reach time has elapsed. These upper limits are determined based on information indicating the state of battery 11, such as the SOC and temperature Tb of battery 11, transmitted from battery ECU 16. Vehicle ECU 50 transmits the lower charge power limit Win and upper discharge power limit Wout values ​​after the threshold reach time has elapsed to converter current suppression unit 715.

[0117] When the converter current suppression unit 715 receives the smaller charging power upper limit Win and discharging power upper limit Wout after the threshold reaching time from the vehicle ECU 50, it generates a voltage command value for the inverter 23 according to these upper limits and outputs the generated voltage command value to the drive signal generation unit 725.

[0118] The drive signal generator 725 compares the voltage command value with the carrier wave CWI generated by the carrier wave generator 720. Here, the carrier wave CWI is used for PWM control of the inverter 23 and is generated based on a carrier wave frequency (not shown) for the inverter 23.

[0119] In addition, the drive signal generating unit 725 generates PWM signals whose logic states change according to the comparison results as drive signals S3 to S8. The drive signal generating unit 725 transmits the generated drive signals S3 to S8 to the switching elements Q3 to Q8 ( Figure 1 ) output.

[0120] It should be noted that the drive signal generating unit 725 also compares the carrier CWC generated by the carrier generating unit 720 based on the carrier frequency fc for the converter 21 with the command value of the voltage VH. Then, a PWM signal whose logic state changes based on the comparison result is generated as the drive signals S1 and S2. The switching elements Q1 and Q2 ( Figure 1 ) is driven according to driving signals S1 and S2.

[0121] As described above, the inverter 23 is controlled based on the charging power upper limit value Win and the discharging power upper limit value Wout. As a result, the regenerative torque of the MG3 is limited when the vehicle 10 is braking, or the power running torque of the MG3 is limited when the vehicle 10 is running. Figure 1 ) The power supplied by the inverter 21 is limited, so the current IL is suppressed. As a result, the converter 21 is protected from overheating.

[0122] Figure 8 1 is a diagram showing an example of processing executed by the motor ECU 4. This flowchart is executed in every predetermined cycle. Each sensor value is sampled in this cycle.

[0123] The motor ECU 4 obtains the detection value of the voltage VL from the voltage sensor 24 (S105) and the detection value of the voltage VH from the voltage sensor 22 (S110). Then, the motor ECU 4 selects the temperature rise estimation data 701 ( Figure 7 )(S115).

[0124] Next, the motor ECU 4 obtains the detection value of the current IL from the current sensor 210 (S120). Then, the motor ECU 4 uses the carrier frequency fc and the voltage step-up ratio (VH / VL) and the selected temperature rise estimation data 701 to estimate the sampling period TS (from the sampling time of the detection value to the next sampling time) based on the detection value of the current IL. Figure 6 ) is the temperature increase ΔTC of the converter 21 in the ?? (S125).

[0125] Next, the motor ECU 4 determines the integrated value ΔTCS ( Figure 7 ) is ΔTTH ( Figure 4 ) or more (S130). If the integrated value ΔTCS of the temperature rise ΔTC is greater than ΔTTH (YES in S130), the motor ECU 4 proceeds to step S135. Otherwise (NO in S130), the motor ECU 4 returns the process to step S105.

[0126] In step S135, the motor ECU 4 executes control to suppress the current flowing through the converter 21 as part of its protection. Specifically, the motor ECU 4 sends a request to the vehicle ECU 50 to reduce the battery 11's upper charge power limit Win and upper discharge power limit Wout relative to their values ​​immediately before the threshold reach time. This further reduces the upper charge power limit Win and upper discharge power limit Wout, resulting in suppression of the current IL. The motor ECU 4 then returns to the normal state.

[0127] Figure 9 : is a diagram for explaining the timing of executing the converter current suppression control in this embodiment. Figure 9 In, with Figure 5 Similarly, the vertical axis represents the detection value of the current IL, and the horizontal axis represents the threshold reaching time tTH. Figure 5 Mapping 500, 505.

[0128] The motor ECU of the comparative example estimates the converter temperature rise within each sampling period using map 500, which assumes that the ripple amplitude maximum condition is always satisfied. In contrast, the motor ECU 4 of the present embodiment estimates the converter 21 temperature rise ΔTC within each sampling period using map 505, which takes into account the voltage step-up ratio (VL / VH) and carrier frequency fc, which are associated with the ripple amplitude ILpp.

[0129] In the comparative example (map 500), the threshold-reaching time tTH when the detected value of current IL remains at 11a is tTHamin. tTHamin is the threshold-reaching time under conditions where the ripple amplitude is extremely large. In these conditions, it is assumed that the ripple amplitude ILpp significantly contributes to the temperature increase of converter 21. Therefore, tTHamin is the shortest possible value for threshold-reaching time tTH within the variable range of the boost ratio (VL / VH) and carrier frequency fc. As a result, converter current suppression control may be executed unnecessarily early, potentially degrading the driving performance of vehicle 10.

[0130] In contrast, in this embodiment, even when the detected value of current IL remains at Ila, threshold reaching time tTHa changes according to the step-up ratio (VL / VH) at the sampling timing of detection voltage VL and voltage VH and carrier frequency fc.

[0131] Specifically, in this embodiment, when the integrated value ΔTCS of the temperature increase ΔTC of the converter 21 reaches the threshold value ( Figure 4 Before ΔTTH), the boost ratio (VL / VH) is 0.5 ( Figure 2) or the carrier frequency fc is outside fcmin( Figure 3 ) or outside. In addition, the boost ratio (VL / VH) and the carrier frequency fc sometimes vary at each sampling time. Therefore, in the present embodiment, the threshold arrival time tTHa takes a value within the range of tTHamin < tTHa < tTHamax (described later) (within the range of the white arrow in the figure) according to the boost ratio (VL / VH) and the carrier frequency fc at the sampling time of the current IL.

[0132] Therefore, in the present embodiment, different from the comparative example where the threshold arrival time tTH is tTHamin, the converter current suppression control is not executed at an unnecessarily early time. Therefore, the driving performance of the vehicle 10 does not decrease at an unnecessarily early time. Thus, in the present embodiment, it is possible to suppress the decrease in driving performance within the range of protecting the converter 21 from overheating.

[0133] It should be noted that tTHamax is the threshold arrival time under the condition of extremely small ripple amplitude. Under this condition, the ripple amplitude ILpp is 0, so the contribution amount of the ripple amplitude ILpp to the temperature rise amount of the converter 21 is extremely small (0). Therefore, tTHamax is the longest among the values that the threshold arrival time tTH can take within the range where the boost ratio (VL / VH) and the carrier frequency fc can vary.

[0134] [Modified Example]

[0135] Refer to Figure 10 , and explain the modified example of the embodiment. Figure 10 is a functional block diagram of the motor ECU 4 in the modified example of the embodiment.

[0136] In the above embodiment, when the integrated value ΔTCS of the temperature rise amount ΔTC reaches the threshold, the converter current suppression unit 715 outputs a request to the vehicle ECU 50 to limit the upper limit value Win of the charging power and the upper limit value Wout of the discharging power.

[0137] In contrast, in the modified example of the embodiment, in the above case, the converter current suppression unit 715 outputs an instruction to the carrier frequency determination unit 717 to make the carrier frequency fc of the converter 21 higher than before the integrated value ΔTCS is about to reach the threshold. As a result, the ripple amplitude ILpp becomes smaller ( Figure 2 ), so the ripple component of the current IL decreases. As a result, the current IL is suppressed by an amount corresponding to the reduction amount of the ripple component.

[0138] When the carrier frequency fc is increased, the carrier frequency determination unit 717 determines the increased carrier frequency fc upon receiving the above instruction and outputs the increased carrier frequency fc to the data selection unit 702 and the carrier generation unit 720 .

[0139] The carrier generator 720 generates a carrier CWC for PWM control of the converter 21 based on the increased carrier frequency fc. The drive signal generator 725 generates drive signals S1 and S2 ( Figure 1 ). The converter 21 is driven according to the duty ratio based on the drive signal.

[0140] As a result, the ripple amplitude ILpp of current IL flowing through converter 21 becomes smaller than its amplitude before the carrier frequency fc was increased. Consequently, current IL is suppressed by an amount corresponding to the reduction in ripple amplitude ILpp. This reduces the amount of heat generated in reactor L1, thereby reducing the temperature rise of converter 21. Consequently, converter 21 is protected from overheating. In this manner, when the integrated value ΔTCS of the temperature rise ΔTC reaches a threshold, converter current suppression unit 715 may increase the carrier frequency fc of converter 21 compared to the value immediately before the integrated value ΔTCS reaches the threshold.

[0141] [Other modifications]

[0142] In the above embodiment, motor ECU 4 estimates converter 21 temperature increase ΔTC based on converter 21's voltage step-up ratio (VL / VH) and carrier frequency fc. Alternatively, motor ECU 4 may estimate converter 21 temperature increase ΔTC based on either the voltage step-up ratio (VL / VH) or carrier frequency fc.

[0143] In this case, temperature rise estimation data 701 defines a predetermined relationship between the detected value of current IL and temperature rise ΔTC of converter 21, based on either the voltage step-up ratio (VL / VH) or carrier frequency fc of converter 21. For example, temperature rise estimation data 701 defines the aforementioned relationship for either the voltage step-up ratio (VL / VH) of converter 21 or the carrier frequency fc.

[0144] Motor ECU 4 then selects data corresponding to either the voltage step-up ratio (VL / VH) or the carrier frequency fc from temperature rise estimation data 701. Using the selected data and the selected data, motor ECU 4 estimates temperature rise ΔTC of converter 21 within sampling period TS, from the time at which the detected value of current IL is sampled, to the next sampling time.

[0145] Furthermore, in the above embodiment, current IL is used as the current flowing through converter 21, but this is not limiting. For example, current Ib flowing through battery 11 may be used instead of current IL. In this case, current sensor 210 may not be provided, and motor ECU 4 may estimate converter 21 temperature rise ΔTC based on the detection value of current sensor 13 transmitted via battery ECU 16 and vehicle ECU 50.

[0146] Furthermore, in the above embodiment, the motor ECU 4 includes the memory 5 , but the memory 5 may be provided as a component separate from the motor ECU 4 .

[0147] In the aforementioned embodiment and its modifications, the motor ECU 4 and the vehicle ECU 50 correspond to an example of a “control device” in the present disclosure. Furthermore, the PCU 2 and the vehicle ECU 50 correspond to an example of a “power conversion system” in the present disclosure.

[0148] The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A power conversion system, comprising: a converter configured to step up the voltage by operating at a set carrier frequency; a current sensor that detects current flowing in the converter; and a control device that performs control for protecting the converter, The current detected by the current sensor and the time it takes to reach the threshold are predetermined based on the voltage ratio before and after the converter boosts the voltage and the carrier frequency. The control device estimates the threshold reaching time corresponding to the current detected by the current sensor based on the voltage ratio before and after the converter boosts the voltage and the carrier frequency, and estimates the total temperature rise based on the estimated threshold reaching time. The control device estimates the temperature rise of the converter within one sampling period based on the voltage ratio before and after the converter boosts the voltage, the carrier frequency, and the current detected by the current sensor. The control device performs control for suppressing a current flowing through the converter when an integrated value of the temperature increase reaches the total temperature increase.

2. The power conversion system according to claim 1, wherein: The power conversion system further includes a storage unit that stores a predetermined relationship among the current detected by the current sensor, the voltage ratio, the carrier frequency, and the temperature rise amount. The control device extracts data corresponding to the acquired relationship between the voltage ratio and the carrier frequency from the predetermined relationship, and estimates the temperature rise amount using the extracted data based on the current detected by the current sensor.

3. The power conversion system according to claim 1 or 2, wherein: When the integrated value reaches the total temperature rise amount, the control device increases the carrier frequency compared to immediately before the integrated value reaches the total temperature rise amount.

4. The power conversion system according to claim 1 or 2, wherein: The converter is electrically connected between the power storage device and the load device. The control device controls the load device so as to limit the power input to and output from the power storage device to a charge power upper limit value and a discharge power upper limit value of the power storage device, respectively. When the integrated value reaches the total temperature rise amount, the control device reduces the charging power upper limit value and the discharging power upper limit value compared to immediately before the integrated value reaches the total temperature rise amount.

Images