DC load device

Abstract

To realize ripples of a low current, a high efficiency and high response of current in a DC load device connected with a plurality of DC loads.SOLUTION: A DC load device comprises: an ACDC converter 1 which rectifies an AC voltage to a DC voltage and adjusts a voltage; and a plurality of units Unit_1 to Unit_m connected in parallel at an output side of the ACDC converter 1. The units Unit_1 to Unit_m respectively have: a DCDC converter 2 controlling a current of a DC load 4; a filter 3 connected with at an output side of the DCDC converter 2; and the DC load 4 connected with the filter 3. An output voltage command value of the ACDC converter 1 is set based on a voltage of the DC load 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a DC load device to which a plurality of DC loads (for example, large-capacity batteries) are connected. [Background technology]

[0002] A DC power supply that charges and discharges batteries (DC loads) is called a charge / discharge device. When charging and discharging multiple large-capacity batteries, there are problems such as an increase in the number of devices or a longer test time.

[0003] Therefore, in Patent Document 1, the AC / DC converter is shared and DC / DC converters are connected according to the number of batteries, thereby constructing a charging / discharging device without increasing the number of devices.

[0004] However, with this method, batteries of different voltages may be mixed, and if the output voltage of the ACDC converter is made common, some DCDC converters may not be able to operate at the optimal step-up / step-down ratio as designed. This results in reduced efficiency and increased charging current ripple. The reduced efficiency leads to larger cooling equipment, and the increased charging current ripple causes problems such as battery degradation.

[0005] Therefore, in Patent Document 2, the switching frequency of the DC-DC converter is increased to enable a reduction in the charging current ripple. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-244742 [Patent Document 2] Japanese Patent Application Publication No. 7-115730 [Non-patent literature]

[0007] [Non-Patent Document 1] Tatsuya Yamagishi, Yasufumi Akagi, Shinichi Kinouchi, Yuji Miyazaki, Masato Koyama, "750V, 100kW, 20kHz Bidirectional Isolated DC / DC Converter Using SiC-MOSFET / SBD Modules," IEEJ Transactions on Power Electronics, Vol. 134, No. 5, pp. 544-553 (2014) [Non-patent document 2] B. Zhao Q. Song W. Liu and Y. Sun, “Overview of Dual-Active-Bridge Isolated Bidirectional DC-DC Converter for High-Frequency-Link Power-Conversion System” in IEEE Transactions on Power Electronics, vol.29, no.8, pp.4091-4106 Summary of the Invention [Problem to be solved by the invention]

[0008] However, switching losses in switching regulators increase in proportion to the switching frequency. Also, while there is a method to reduce current ripple by inserting a filter between the charging / discharging device and the battery, this results in an increase in the size of the device.

[0009] As shown above, the challenges for DC load devices with multiple DC loads connected are to achieve low current ripple, high efficiency, and high current response. [Means for solving the problem]

[0010] The present invention was devised in view of the above-mentioned problems of the conventional art, and one aspect of the present invention is a DC load device including an AC / DC converter that rectifies AC voltage to DC voltage and adjusts the voltage, and a plurality of units connected in parallel to the output side of the ACDC converter, wherein each of the units has a DC / DC converter that controls the current of the DC load, a filter connected to the output side of the DC / DC converter, and the DC load connected to the filter, and the output voltage command value of the ACDC converter is set based on the voltage of the DC load.

[0011] In one aspect, the output voltage command value is an average voltage value of the DC load of the unit being driven.

[0012] In another aspect, the output voltage command value is set to the voltage of the DC load of the unit having the largest charge / discharge current of the DC load.

[0013] In one aspect, an insulating DC-DC converter is connected between the AC-DC converter and the connection point between the units.

[0014] In another aspect, each of the units has an isolated DC-DC converter connected between the DC-DC converter and a connection point between the units. [Effects of the Invention]

[0015] According to the present invention, it is possible to achieve low current ripple, high efficiency, and high current response in a DC load device in which a plurality of DC loads are connected. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a system configuration of a charge / discharge device according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing a control block of the first embodiment. [Figure 3]FIG. 2 is a diagram showing a voltage command value generating unit according to the first embodiment. [Figure 4] FIG. 10 is a diagram showing the system configuration of a charging / discharging device according to a second embodiment. [Figure 5] FIG. 10 is a diagram showing a control block according to the second embodiment. [Figure 6] FIG. 10 is a diagram showing the system configuration of a charging / discharging device according to a third embodiment. [Figure 7] FIG. 10 is a diagram showing a control block according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] First to third embodiments of the DC load device of the present invention will be described in detail below with reference to Figures 1 to 7. In the first to third embodiments, a charge / discharge device will be described as an example of the DC load device.

[0018] [Embodiment 1] Fig. 1 shows the system configuration of the charge / discharge device in this embodiment 1. As shown in Fig. 1, the charge / discharge device in this embodiment 1 has an AC / DC converter 1 to which the output voltage of an AC system AC is input, and m (m = an integer of 2 or more) units Unit_1 to Unit_m connected in parallel on the output side of the AC / DC converter 1.

[0019] Each of the units Unit_1 to Unit_m includes a DC-DC converter 2, a filter 3 connected to the output side of the DC-DC converter 2, and a DC load 4 (for example, a battery, hereinafter referred to as the battery) connected to the filter 3.

[0020] Figures 2 and 3 show control block diagrams of this embodiment 1. In contrast to the system configuration of Figure 1, there is a control system block of the AC-DC converter 1 shown in Figure 2(a), a control system block of the DC-DC converter 2 shown in Figure 2(b), and a block (output voltage command value generator) that generates an output voltage command value for the AC-DC converter 1 shown in Figure 3.

[0021] The control block of the AC / DC converter 1 shown in FIG. 2(a) includes a first differentiator 5 that calculates the difference between the output voltage command value Vdc_ref of the AC / DC converter 1 and the output voltage detection value Vdc, a first PI control unit (or P control unit) 6 that outputs a grid current command value based on the output of the first differentiator 5, a second differentiator 7 that calculates the difference between the grid current command value and the grid current detector, a second PI control unit (or P control unit) 8 that outputs a gate generation command value based on the output of the second differentiator 7, and a first gate generator 9 that outputs a gate signal for the AC / DC converter 1 based on the output of the second PI control unit 8.

[0022] The control block of the DC-DC converter shown in Figure 2(b) has a third differentiator 10 that takes the difference between the battery current command value ibat_ref_m of the mth unit and the battery current detection value ibat_m of the mth unit, a third PI control unit (or P control unit) 11 that outputs a command value for the second gate generator based on the output of the third differentiator 10, and a second gate generator 12 that outputs a gate signal for the DC-DC converter 2 based on the output of the third PI control unit 11.

[0023] Although Figure 2(b) shows the control block of the DC-DC converter 2 of the mth unit, other units may have a similar configuration. However, the battery current command value and battery current detection value are changed to the values ​​of that unit. For example, for the first unit, Unit_1, the battery current command value is ibat_ref_1 and the battery current detection value is ibat_1.

[0024] FIG. 3 shows an output voltage command value generating unit that generates an output voltage command value Vdc_ref for the AC / DC converter 1 based on the voltage of the battery 4.

[0025] In FIG. 3(a), the average voltage of the battery 4 in the drive unit is set as the output voltage command value Vdc_ref.

[0026] Specifically, multiplier 13 multiplies the battery voltages Vbat_1 to Vbat_m of each unit by the unit drive state (drive: 1, stop: 0). Then, average value calculation section 14 adds up the outputs of multipliers 13 and divides by the number of units that are being driven to calculate the average battery voltage value of the drive units, and this value is used as the output voltage command value Vdc_ref.

[0027] In FIG. 3(b), the voltage of the battery 4 of the unit having the largest charge / discharge current (current command value) of the battery 4 is set as the output voltage command value Vdc_ref of the AC / DC converter 1.

[0028] Specifically, maximum value detection unit 15 detects the unit with the largest current command value based on the current command values ​​ibat_ref_1 to ibat_ref_m of each unit. Multiplexer 16 inputs the battery voltages Vbat_1 to Vbat_m of each unit and sets the battery voltage of the unit with the largest current command value as the output voltage command value Vdc_ref.

[0029] With the configuration shown in Figure 1, the input AC voltage (single-phase or three-phase) is rectified (converted) to DC voltage by the ACDC converter 1, and the voltage is adjusted and output. There are three-phase inverter and single-phase inverter types for the ACDC converter 1.

[0030] Furthermore, the current of the battery 4 is controlled by the DCDC converter 2. Also, since the current output by the DCDC converter 2 has ripples, the current ripples of the battery 4 are reduced via a filter 3 consisting of an inductor and a capacitor.

[0031] Patent Document 1 focuses on shortening test time and reducing component costs, and does not consider the increase in loss and current ripple caused by deviations in the step-up / step-down ratio. However, when the battery voltage changes due to charging / discharging, the step-up / step-down ratio of the DC-DC converter 2 deviates from the optimal 1:1, which significantly increases the battery current ripple and loss in the DC-DC converter 2.

[0032] Therefore, the output voltage of the AC / DC converter 1 is controlled by the control shown in Fig. 2. As shown in Fig. 3(a), by setting the average battery voltage of the driven unit as the output voltage command value Vdc_ref, the drive unit can be driven at an optimum step-up / step-down ratio of around 1:1, thereby reducing losses and current ripple in the entire system.

[0033] Furthermore, by setting the voltage value of battery 4 of the unit with the largest charge / discharge current to the output voltage command value Vdc_ref as shown in Figure 3(b), the unit with the largest charge / discharge current can be driven at an optimal step-up / step-down ratio of approximately 1:1, thereby reducing the loss of the unit with the largest current.

[0034] In this first embodiment, the loss can be reduced when the DC-DC converter 2 has a constant switching frequency. The DC-DC converter 2 can increase the switching frequency by the amount of the loss reduction, so the charging current ripple can be reduced. Furthermore, since the charging current ripple can be reduced, the filter 3 for reducing the charging current ripple can be made smaller. Furthermore, since the switching frequency can be increased, high response can be achieved.

[0035] As described above, according to the first embodiment, by adopting a parallel configuration in a charge / discharge device (DC load device) equipped with multiple DC loads (e.g., large-capacity batteries), it is possible to achieve a reduction in test time and circuit costs.

[0036] Furthermore, current ripple can be reduced and efficiency can be improved by controlling the input voltage so that the step-up / step-down ratio of the DC / DC converter 2 of the majority of units or the unit with the greatest load is 1:1 using the AC / DC converter 1. This makes it possible to increase the switching frequency, achieving both high efficiency and fast response.

[0037] This makes it possible to apply the present invention not only to charge / discharge devices but also to impedance measurement for diagnosing battery deterioration.

[0038] [Embodiment 2] Figure 4 shows the system configuration of the charging / discharging device of this embodiment 2. Compared to embodiment 1, a bidirectional isolated DC-DC converter 17 is provided between the connection point of the AC-DC converter 1 and the units Unit_1 to Unit_m. The input / output voltage ratio of this isolated DC-DC converter 17 is the winding ratio of the high-frequency transformer inside the converter.

[0039] FIG. 5 shows a control block diagram added in this second embodiment. FIG. 5 is a block diagram showing an output voltage command value generation unit that generates an output voltage command value Vdc_ref for the AC-DC converter 1. First, as in the first embodiment (FIG. 3), a multiplier 13 and an average value calculation unit 14 calculate the average voltage of the battery 4 of the drive unit. Then, a turns ratio multiplication unit 18 multiplies the average voltage of the battery 4 of the drive unit by the turns ratio (gain) of the isolated DC-DC converter 17, and this value is used as the output voltage command value Vdc_ref. Alternatively, the output of FIG. 3(b) may be multiplied by the turns ratio of the isolated DC-DC converter 17.

[0040] In the configuration of FIG. 4, an isolated DC-DC converter 17 employing a Dual Active Bridge system or a resonant system as shown in Non-Patent Documents 1 and 2 is connected to the output of the AC-DC converter 1.

[0041] With this configuration, the isolated DC-DC converter 17 can be driven with high efficiency even at a high step-up / step-down ratio using the high-frequency transformer. As a specific control method, the output voltage command value Vdc_ref of the AC-DC converter 1 is set to the value obtained by multiplying the average battery voltage of the driven unit by the turns ratio of the high-frequency transformer using the control shown in Figure 5.

[0042] As a result, the step-up / step-down ratio between the voltage of the battery 4 and the input voltage becomes approximately 1:1, so that the DC / DC converter 2 can be driven with high efficiency and low current ripple.

[0043] In the first embodiment, if there is a large difference between the AC voltage and the voltage value of the battery 4, there is a risk of large losses in the AC-DC converter 1. In the second embodiment, the AC voltage and the output voltage of the AC-DC converter 1 can be made to be approximately the same voltage, so the problem of large losses in the AC-DC converter 1 can be solved.

[0044] Furthermore, the addition of the isolated DC-DC converter 17 ensures insulation between the AC voltage and the battery 4. Since an insulating transformer is not required within the DC-DC converter 1, the AC-DC converter 1 can be made smaller.

[0045] [Embodiment 3] Fig. 6 shows the system configuration of the charging / discharging device in the third embodiment. Compared to the first embodiment, a bidirectional isolated DC-DC converter 19 is added to each unit. That is, in each unit, an isolated DC-DC converter 19 is provided between the connection point of the units Unit_1 to Unit_m and the DC-DC converter 2. The other configurations are the same as those in the first embodiment.

[0046] Fig. 7 shows a control block diagram added in the third embodiment. Fig. 7 is a control block diagram of the isolated DC-DC converter 19 of the third embodiment.

[0047] A fourth differentiator 20 calculates the difference between the unit voltage command value Vdc_ref_m and the unit voltage detection value Vdc_m of the isolated DC-DC converter 19 in the mth unit. A fourth PI control unit (P control unit) 21 outputs a command value for a third gate generator 22 based on the output of the fourth differentiator 20. The third gate generator 22 generates a gate signal for the isolated DC-DC converter 19 based on the output of the fourth PI control unit 21.

[0048] Although Figure 7 shows the control block of the isolated DC-DC converter 19 of the mth unit, other units may have a similar configuration. However, the unit voltage command value and unit voltage detection value are changed to the values ​​of that unit. For example, for the first unit Unit_1, the unit voltage command value is Vdc_ref_1 and the unit voltage detection value is Vdc_1.

[0049] The difference between the third embodiment and the second embodiment is that the insulating DC-DC converter 19 has a voltage control function.

[0050] 6, in the method of the third embodiment, the output voltage command value Vdc_ref of the AC-DC converter 1 is determined in the same manner as in the second embodiment. That is, the outputs of FIGS. 3(a) and 3(b) are multiplied by the turns ratio of the isolated DC-DC converter 19.

[0051] A feature of the third embodiment is that the output voltage of the isolated DC-DC converter 19 is controlled to be equal to the voltage of the battery 4 by the control shown in Fig. 7. This allows the DC-DC converters 2 of all units to be driven at a step-up / step-down ratio of 1:1, which is a voltage condition that results in high efficiency and low current ripple. The third embodiment is advantageous in a charging / discharging device with a large number of units and in which the AC voltage and the voltage value of the battery 4 differ greatly.

[0052] As described above, in comparison with the second embodiment, the third embodiment is able to drive the DC-DC converters 2 of all units at a step-up / step-down ratio of 1:1 by connecting an isolated DC-DC converter 19 to each unit, thereby further improving the efficiency of the DC-DC converters 2 and reducing the current ripple.

[0053] In each embodiment, if it is known from a prior loss calculation or the like that loss can be reduced more when the step-up / step-down ratio of the DC-DC converter 2 is other than 1:1, the voltage command value may be corrected according to the step-up / step-down ratio at which the loss is minimized.

[0054] Furthermore, the present invention may be applied to a system with a DC load (such as a capacitor) other than a battery.

[0055] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0056] AC…Alternating current system 1...ACDC converter Unit_1~Unit_m... Unit 2...DCDC converter 3...Filter 4...Battery (DC load) 5...First differentiator 6...First PI control unit (P control unit) 7…Second differentiator 8…Second PI control section (P control section) 9...First gate generator 10…Third differentiator 11...Third PI control unit (P control unit) 12...Second gate generator 13...Multiplier 14...Average value calculation section 15...Maximum value detection section 16...Multiplexer 17...Isolated DC / DC converter 18...Turns ratio calculation section 19...Isolated DC / DC converter 20…4th differentiator 21...Fourth PI control unit (P control unit) 22...Third gate generation unit

Claims

1. an AC-DC converter that rectifies AC voltage to DC voltage and adjusts the voltage; A DC load device comprising a plurality of units connected in parallel to an output side of the AC-DC converter, Each of the units comprises: a DC-DC converter for controlling a current of a DC load; a filter connected to an output side of the DC-DC converter; the DC load connected to the filter; and A DC load device, characterized in that an output voltage command value of the AC-DC converter is set based on the voltage of the DC load.

2. The output voltage command value is 2. The DC load device according to claim 1, wherein the voltage is an average voltage of the DC load of the unit being driven.

3. The output voltage command value is 2. The DC load device according to claim 1, wherein the voltage of the DC load of the unit having the largest charge / discharge current is set as the voltage of the DC load.

4. 2. The DC load device according to claim 1, wherein an insulating DC / DC converter is connected between the AC / DC converter and a connection point between the units.

5. Each of the units comprises:

2. The DC load device according to claim 1, wherein an insulating DC-DC converter is connected between the connection point between the units and the DC-DC converter.

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