DC / DC Conversion System, Energy Storage System, and Control Method for DC / DC Converter

Abstract

A DC / DC conversion system is provided between a plurality of DC power supplies and a common DC bus. The DC / DC conversion system correspondingly has a DC / DC converter provided between the DC power supply and the DC bus and a control unit for controlling the DC / DC converter for each of the plurality of DC power supplies. The control unit corrects the voltage detection value of the DC bus by introducing the voltage detection deviation of the DC bus related to each DC / DC converter observed from the overall view of the plurality of parallel DC / DC converters, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power. The DC / DC conversion system as described above can operate multiple DC / DC converters in parallel to equalize the output without the need for high-speed communication.

Description

Technical Field

[0001] The present invention relates to a DC / DC conversion system, a power storage system, and a control method for a DC / DC converter.

[0002] This application claims priority based on Japanese Application No. 2019-213013 filed on November 26, 2019, and incorporates by reference all the descriptions recorded in the above-mentioned Japanese application. Background Art

[0003] There has been proposed a large-capacity (e.g., several megawatt class) power storage system (e.g., see Patent Document 1) using a large number of battery cells with high energy density such as lithium-ion batteries. Since the voltage of one battery cell is about 4V, it is necessary to form a battery string in which many battery cells are connected in series to increase the voltage. In addition, in order to obtain a large capacity, it is necessary to further connect a plurality of battery strings in parallel. The SOC (State of Charge) of each of the battery strings connected in parallel becomes different due to charge and discharge. Therefore, in order to adjust the distribution of power of the parallel-connected battery string group, a structure is adopted in which it is connected to a common bus via a power conversion device.

[0004] In addition, there has also been proposed a structure in which different types of distributed power sources such as solar power generation panels, storage batteries, and fuel cells are respectively connected to a common DC bus via power conversion devices (e.g., see Patent Document 2).

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-171335

[0006] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2015-122885 Summary of the Invention

[0007] The present invention includes the following technical solutions. However, the present invention is defined by the claims.

[0008] The present invention is a DC / DC conversion system provided between a plurality of DC power sources and a common DC bus,

[0009] The DC / DC conversion system correspondingly has, for each of the plurality of DC power sources:

[0010] a DC / DC converter provided between the DC power source and the DC bus; and

[0011] a control unit that controls the DC / DC converter,

[0012] The control unit corrects the voltage detection value of the DC bus by introducing the voltage detection deviation of the DC bus related to each of the DC / DC converters observed from the whole of the plurality of parallel DC / DC converters, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power.

[0013] Furthermore, the present invention is a power storage system having a plurality of DC power supplies connected to a common DC bus.

[0014] This power storage system correspondingly has, for each of the plurality of DC power supplies:

[0015] a DC / DC converter provided between the DC power supply and the DC bus; and

[0016] a control unit that controls the DC / DC converter.

[0017] The control unit corrects the voltage detection value of the DC bus by introducing the voltage detection deviation of the DC bus related to each of the DC / DC converters observed from the whole of the plurality of parallel DC / DC converters, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power.

[0018] Furthermore, the present invention is a method for controlling a DC / DC converter, which is a method for controlling a plurality of DC / DC converters provided in parallel between a plurality of DC power supplies and a common DC bus.

[0019] In this method for controlling a DC / DC converter,

[0020] the voltage detection value of the DC bus is corrected by introducing the voltage detection deviation of the DC bus related to each of the DC / DC converters observed from the whole of the plurality of DC / DC converters.

[0021] The DC / DC converter is controlled according to a voltage command value having a droop characteristic with respect to the output power. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a single-line connection diagram of a power supply system including a power storage system.

[0023] Figure 2 is, as an example, a circuit diagram in which two sets of DC power supply devices are connected to a DC bus.

[0024] Figure 3 is a diagram showing an equivalent model of a DC / DC converter.

[0025] Figure 4 It is a figure graphically representing Equation (4).

[0026] Figure 5 It is an example of the control block diagram of a DC / DC converter.

[0027] Figure 6 It is a figure showing the state of an energy storage system in which two DC / DC converters are connected in parallel and operated without droop control for comparison. As conditions, the difference in the voltage detection values of the two DC / DC converters is set to 0, and the difference in the wiring impedance of the circuit is set to 0.

[0028] Figure 7 It is a figure showing the state of an energy storage system in which two DC / DC converters are connected in parallel and operated without droop control for comparison. As conditions, the difference in the voltage detection values of the two DC / DC converters is set to 0.1%, and the difference in the wiring impedance is set to 0.

[0029] Figure 8 It is a figure representing the state of an energy storage system in which two DC / DC converters are connected in parallel and operated with droop control. As conditions, the difference in the DC bus voltage detection values is set to 0.1%, and the difference in the wiring impedance is set to 0.

[0030] Figure 9 It is a figure representing the state of an energy storage system in which two DC / DC converters are connected in parallel and operated with droop control. As conditions, the difference in the DC bus voltage detection values is increased to 1%, and the difference in the wiring impedance is set to 0.

[0031] Figure 10 It is a figure representing the state of an energy storage system in which two DC / DC converters are connected in parallel and operated with droop control. As conditions, the proportionality constant of the droop control is set to 2 times 0.005, i.e., 0.01, the difference in the DC bus voltage detection values is set to 1%, and the difference in the wiring impedance is set to 0.

[0032] Figure 11 It is a figure representing the state of an energy storage system in which two DC / DC converters are connected in parallel and operated with droop control. As conditions, the proportionality constant of the droop control is set to 0.01, the difference in the DC bus voltage detection values is set to 1%, and moreover, the difference in the wiring impedance is not 0, and one is set to be 2 times the other.

[0033] Figure 12 It is a figure showing the relationship between the output deviation and the voltage detection deviation.

[0034] Figure 13It is a graph showing the state of a power storage system that performs correction based on droop control and operates with two DC / DC converters connected in parallel. As a condition, the proportionality constant f of the droop control is 0.005, the difference in the detected DC bus voltage values is set to 1%, and the difference in the wiring impedance is set to 0.

[0035] Figure 14 It is a graph showing the state of a power storage system that performs correction based on droop control and operates with two DC / DC converters connected in parallel. On the basis of Figure 13 the same conditions and corrections, the resistive load connected between the lines on the AC side of the DC / AC converter is replaced from 10 Ω to 2 Ω.

[0036] Figure 15 It is a graph showing the state of a power storage system that performs correction based on droop control and operates with two DC / DC converters connected in parallel after imposing severe conditions on the load connection.

[0037] Figure 16 It is a graph showing the relationship between the output deviation and the DC bus voltage detection deviation.

[0038] Figure 17 It is a graph showing the state of a power storage system that performs correction based on droop control and operates with three DC / DC converters connected in parallel.

[0039] Figure 18 It is a graph showing the relationship between the output deviation before correction and the output deviation after the first correction.

[0040] Figure 19 It is an example of a flowchart showing the processing operation of DC bus voltage detection correction. Detailed implementation mode

[0041] [Problems to be solved by the present invention]

[0042] In a power storage system, when controlling the currents of a plurality of battery strings connected in parallel to each other, it is necessary to interpose a DC / DC converter between the DC bus and each battery string. By using the DC / DC converter, voltage fluctuations caused by the SOC of the battery string can be absorbed, and the DC bus voltage can be maintained at an optimal value. By setting it to the optimal value, the power conversion loss of the DC / AC converter connected to the DC bus can be minimized.

[0043] The control unit of the DC / DC converter communicates with a battery management system (BMS) that monitors the state of the battery string, and controls charging and discharging according to the state of the battery string. For example, CAN (Controller Area Network) or RS-485 is used during this communication.

[0044] In the case of a power storage system in which systems are interconnected via a DC / AC converter from a DC bus, for example, charge and discharge are performed by each DC / DC converter according to a power command value transmitted from a power control unit included in the power storage system, and the DC / AC converter controls the power so that the DC bus voltage is always constant. The power control unit determines the power command values for the charge and discharge of each DC / DC converter so that the total output of the DC / DC converters matches the power command value.

[0045] As described above, in an existing power storage system, a communication unit for transmitting a power command value from a power control unit to each DC / DC converter is indispensable. This communication requires real-time performance for keeping the control delay constant. In addition, it is required to be able to transmit command values from one power control unit to many DC / DC converters, and high reliability including tolerance to noise generated by on / off is also required. Therefore, for example, RS-485 communication related to a bus-type network is used. The control cycle varies according to the requirements of the power storage system, but in order to be faster than the operation condition of the reverse power protection relay required by the system interconnection regulation, that is, 0.5 seconds, and to eliminate transient reverse power generated by load changes, the control delay needs to be set to 100 milliseconds or less, and the communication speed that always meets this requirement is pursued.

[0046] On the other hand, in a power storage system that operates autonomously, the DC / AC converter performs AC voltage control, and the output power is determined by the load. At this time, the DC bus voltage cannot be controlled to the optimum value by the DC / AC converter, so multiple DC / DC converters perform feedback control to keep the DC bus voltage constant. The power control unit compares the detected value of the DC bus voltage with the target value and determines the overall power command value for charge and discharge, and transmits the allocated power command value to the control unit of each DC / DC converter. In order to converge the fluctuation range of the DC bus voltage within a specified range, the delay time from the voltage detection of the DC bus to the control, for example, must be within 1.2 milliseconds, that is, about one percent of the delay time required for system interconnection operation. When the delay time becomes longer, in order to suppress the voltage fluctuation range, it is necessary to increase the capacitance of the smoothing capacitor, which leads to an increase in cost.

[0047] As described above, in a large-capacity power storage system using lithium-ion batteries, many DC / DC converters are required to connect each battery string in parallel to the DC bus. Moreover, in order to send charge / discharge power command values from the power control unit to each DC / DC converter, a communication unit with high reliability and short delay time must be provided. Especially during autonomous operation, the control delay must be at least within a few milliseconds. However, the larger the capacity of the power storage system and the greater the number of parallel-connected battery strings, the more the number of objects to which the command value is transmitted from the power control unit increases, and it becomes difficult to keep the control delay within a few milliseconds. If a faster real-time communication can be applied through future innovations in communication technology, it may be possible to solve this problem, but currently it is difficult.

[0048] Therefore, an object of the present invention is to enable parallel operation of multiple DC / DC converters and equalize the outputs without requiring high-speed communication.

[0049] [Effects of the present invention]

[0050] According to the present invention, it is possible to equalize the outputs among multiple DC / DC converters without requiring high-speed communication.

[0051] [Description of embodiments of the present invention]

[0052] The embodiments of the present invention mainly include at least the following.

[0053] (1) The present invention is a DC / DC conversion system provided between multiple DC power supplies and a common DC bus. The DC / DC conversion system includes, corresponding to each of the multiple DC power supplies: a DC / DC converter provided between the DC power supply and the DC bus; and a control unit that controls the DC / DC converter. The control unit corrects the voltage detection value of the DC bus by introducing the voltage detection deviation of the DC bus related to each DC / DC converter observed from the whole of the multiple parallel-existing DC / DC converters, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power.

[0054] In the DC / DC conversion system as described above, according to the droop characteristic of the voltage command value with respect to the output power, it is possible to achieve control such that the outputs of the multiple parallel-connected DC / DC converters are in the same direction. In addition, in order to suppress the output inconsistency of the multiple DC / DC converters caused by errors in the voltage detection of the DC bus, the voltage detection deviation of the DC bus is introduced to correct the voltage detection value of the DC bus. In this way, it is possible to equalize the outputs among the multiple DC / DC converters without relying on high-speed communication.

[0055] (2) In the DC / DC conversion system of (1) above, it may be configured to have a management control unit that determines the voltage detection deviation corresponding to the output deviation related to each DC / DC converter observed from the whole of the plurality of DC / DC converters, and gives a correction value for suppressing the voltage detection deviation to the control unit of each of the plurality of DC / DC converters.

[0056] In this case, the management control unit determines the voltage detection deviation regarding the whole of the plurality of DC / DC converters at any time, and can notify the correction value for suppressing the voltage detection deviation to each control unit. Each control unit can use the notified correction value to equalize the outputs of the plurality of DC / DC converters. In addition, communication is used at the time of this notification, but high-speed communication is not required.

[0057] (3) In the DC / DC conversion system of (2) above, the management control unit may vary the correction value corresponding to the number of parallel-connected DC / DC converters.

[0058] In this case, based on the understanding that an appropriate correction value changes according to the number of parallel-connected DC / DC converters, an appropriate correction value corresponding to the number of parallel connections can be given to each control unit.

[0059] (4) In the DC / DC conversion system of (2) or (3) above, if the correction value is set as the first correction value, each control unit uses the first correction value, and then the management control unit determines again the voltage detection deviation corresponding to the output deviation related to each DC / DC converter observed from the whole of the plurality of DC / DC converters, and gives a second correction value for suppressing the voltage detection deviation to the control unit of each of the plurality of DC / DC converters.

[0060] In this case, even if the first correction value is a provisional value, the outputs of the plurality of DC / DC converters can be equalized by the second correction value.

[0061] (5) In the DC / DC conversion system of (2) or (3) above, the management control unit may update the correction value regularly and give it to the control unit of each of the plurality of DC / DC converters.

[0062] In this case, even if the voltage detection deviation changes over time, an appropriate correction value can be provided regularly.

[0063] (6) In the DC / DC conversion system according to any one of (1) to (5) above, the DC power supply is a storage battery, and the control unit can also limit the current flowing in the DC power supply based on the charge state of the DC power supply.

[0064] In this case, the DC / DC converter corresponding to the fully charged or discharged-to-the-limit storage battery can be excluded from the object of output normalization.

[0065] (7) Further, the present invention disclosed herein is an electricity storage system including a plurality of DC power sources and a common DC bus, and the electricity storage system includes, corresponding to each of the plurality of DC power sources: a DC / DC converter provided between the DC power source and the DC bus; and a control unit that controls the DC / DC converter. The control unit corrects the voltage detection value of the DC bus by introducing a voltage detection deviation of the DC bus related to each of the DC / DC converters observed from the whole of the plurality of parallel DC / DC converters, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power.

[0066] In the electricity storage system as described above, according to the droop characteristic of the voltage command value with respect to the output power, control can be achieved such that the outputs of the plurality of parallel DC / DC converters are directed in the same direction. Further, in order to suppress the output inconsistency of the plurality of DC / DC converters caused by an error in the voltage detection of the DC bus, the voltage detection deviation of the DC bus is introduced to correct the voltage detection value of the DC bus. Thus, between the plurality of DC / DC converters, an electricity storage system that equalizes the output can be provided without relying on high-speed communication.

[0067] (8) The electricity storage system of (7) above may have the following system configuration, that is, it has a DC / AC converter provided between the DC bus and an AC circuit, and the DC / AC converter changes its output according to the state of a commercial power system or a load connected to the AC circuit.

[0068] In an existing electricity storage system, the command value of the charge / discharge power is received by the control unit of the DC / DC converter, and the DC / AC converter controls to keep the DC bus voltage that changes according to the output of the DC / DC converter constant. Therefore, the control delay when controlling the charge / discharge power becomes long. In contrast, in the electricity storage system described above, the DC / AC converter directly receives the charge / discharge command value, so the control delay is short.

[0069] (9) In the electricity storage system of (7) above, the DC / DC converter may perform current control for the corresponding DC power source.

[0070] In this case, a power storage system can be configured in which a DC power supply is connected in parallel with a DC bus via a DC / DC converter that controls current. The DC power supply is, for example, a power generation device such as solar power generation or a fuel cell, in addition to a storage battery that needs to limit the charge and discharge current according to its state such as the SOC.

[0071] (10) From the perspective of a method, it is a control method for a DC / DC converter, which is a control method for a plurality of DC / DC converters arranged in parallel between a plurality of DC power supplies and a common DC bus. In this DC / DC converter control method, a voltage detection deviation of the DC bus related to each of the DC / DC converters observed from the overall view of the plurality of DC / DC converters is introduced to correct the voltage detection value of the DC bus, and the DC / DC converter is controlled according to a voltage command value having a droop characteristic with respect to the output power.

[0072] According to the above-described DC / DC converter control method, through the droop characteristic of the voltage command value with respect to the output power, it is possible to achieve control such that the outputs of a plurality of DC / DC converters arranged in parallel are directed in the same direction. In addition, in order to suppress the output inconsistency of the plurality of DC / DC converters caused by errors in the voltage detection of the DC bus, the voltage detection deviation of the DC bus is introduced to correct the DC bus voltage detection value. In this way, the outputs can be equalized among the plurality of DC / DC converters without relying on high-speed communication.

[0073] [Details of Embodiments of the Present Invention]

[0074] Next, a specific example of the DC / DC conversion system of the present invention, a power storage system including the DC / DC conversion system, and a control method for the DC / DC converter will be described with reference to the drawings.

[0075] 《Overall Structure of Power Storage System》

[0076] Figure 1 It is a single-line connection diagram of a power supply system including a power storage system 1. In the figure, the power storage system 1 is connected to an AC circuit L AC connected. The solar power generation system 2 is also connected to the AC circuit L AC connected. The three-phase commercial power system 3 is connected to the AC circuit L via a transformer 4 AC connected. A CT (Current Transformer) 5 for detecting the AC current is provided between the secondary side of the transformer 4 and the AC circuit L AC connected. A load 6 is connected to the AC circuit L AC connected.

[0077] The power storage system 1 has a DC power supply system 11 and a DC / AC converter 12. The DC / AC converter 12 is controlled by a control unit 13. Information on the current value detected by the CT 5 is sent to the control unit 13.

[0078] The DC power supply system 11 is composed of n (n is a natural number of 2 or more) sets of DC power supply devices 11_1, 11_2, ···, 11 - n connected in parallel to a common DC bus L. DC The DC power supply device 11_1 has a series string of a plurality of battery cells, i.e., a storage battery 14, a battery management system 15 provided along with the storage battery 14, a DC / DC converter 16 connected to the storage battery 14, and a control unit 17 for controlling the DC / DC converter. The other DC power supply devices 11_2, ···, 11 - n also have the same internal circuit. The battery management system 15 obtains SOC and other information related to the storage battery 14 and sends the information to the control unit 17.

[0079] The solar power generation system 2 has an array 21A formed by further connecting in parallel a series string of solar cells 21 and a DC / AC converter 22. The output of the array 21A is converted into AC power by the DC / AC converter 22 and supplied to an AC circuit L. AC The solar power generation system 2 can supply power to the AC circuit L as a distributed power source. AC Supply power.

[0080] The power storage system 1 can charge the power supplied to the AC circuit L. AC And can supply power to the AC circuit L through discharging. AC Power is supplied from the AC circuit L. AC To the load 6. In autonomous operation without system interconnection, the power output by the solar power generation system 2 is supplied to the load 6, and in addition, the power storage system 1 can be charged. When the power required by the load 6 is large or solar power generation stops, power can be supplied to the load 6 from the power storage system 1.

[0081] In addition, as the DC power supply of the DC power supply system 11, for example, in addition to a storage battery that needs to limit the charge and discharge current according to the state such as SOC, power generation devices such as solar power generation and fuel cells can also be used.

[0082] 《Detailed circuit structure》

[0083] Figure 2 As an example, two sets of DC power supply devices 11_1 and 11_2 are connected to the DC bus L. DCThe circuit diagram. In the figure, the labels of two groups of DC / DC converters are set as 16_1 and 16_2 respectively. The labels of two groups of control units are set as 17_1 and 17_2 respectively. The battery 14 and BMS 15 on the DC power supply device 11_1 side are connected to the DC / DC converter 16_1. The battery 14 and BMS 15 on the DC power supply device 11_2 side are connected to the DC / DC converter 16_2.

[0084] The DC / DC converter 16_1 has a smoothing capacitor 161, a DC reactor 162, a switching element Q on the low potential side L , a switching element Q on the high potential side H and a smoothing capacitor 163 on the DC bus L DC side, and they are connected as shown in the figure. In addition, as measuring instruments, a voltage sensor 165 for detecting the voltage on the low voltage side of the DC / DC converter 16_1, a current sensor 166 for detecting the current flowing through the DC reactor 162, and a voltage sensor 167 for detecting the voltage between two lines of the DC bus L DC are provided. The information of the BMS 15 and the signals of the detection values output by each sensor are sent to the control unit 17_1.

[0085] The internal circuit structure of the DC / DC converter 16_2 is the same, so the same labels are used and the description is omitted.

[0086] The structure related to multiple groups of DC / DC conversion, that is, in this example, the DC / DC converter 16_1 and its control unit 17_1, and the DC / DC converter 16_2 and its control unit 17_2, if generalized, constitute a DC / DC conversion system 100 provided between multiple DC power supplies (14) and a common DC bus (L DC ).

[0087] The DC / AC converter 12 has: a smoothing capacitor 121; an AC reactor 122, which is respectively arranged in three branches, a full-bridge switching element Q1, Q2, Q3, Q4, Q5, Q6, and an AC side three-circuit; and a capacitor 123, which forms an LC circuit with the AC reactor 122, and they are connected as shown in the figure. In addition, as measuring instruments, there are a voltage sensor 124 for detecting the voltage between two lines of the DC bus L DC , voltage sensors 124, 125, 126 for detecting the voltage between three AC lines, and current sensors 127, 128, 129 for detecting the current flowing through the three AC circuits. The signals of the detection values output by each sensor are sent to the control unit 13.

[0088] In addition, as the switching element Q L , QH , Q1, Q2, Q3, Q4, Q5, Q6 can use, for example, the illustrated IGBT (Insulated Gate Bipolar Transistor), but MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor) can also be used instead.

[0089] The control units 17_1, 17_2 and the control unit 13 can communicate with the management control unit 18 (either wired or wireless). The control units 13, 17_1, 17_2 and the management control unit 18 include, for example, a computer, and the required control functions are realized by executing software (computer program) by the computer. The software is stored in the storage devices (not shown) of the control units 13, 17_1, 17_2 and the management control unit 18.

[0090] In Figure 1 , Figure 2 , with respect to the DC bus L DC A plurality of DC / DC converters 16 (16_1, 16_2) connected in parallel with each other are independently controlled by the control described later by the control units 17 (17_1, 17_2) so that the DC bus voltage becomes constant. Therefore, the DC / AC converter 12 does not need to control the DC bus voltage to be constant not only during autonomous operation but also during system interconnection operation, and only needs to control the output power according to the command value of the control unit 13.

[0091] That is, a communication unit for sending power command values to the plurality of DC / DC converters in real time is not required. Only the control unit 13 of the DC / AC converter 12 needs to know the AC power command value.

[0092] "Regarding droop characteristics"

[0093] Figure 3 is a diagram showing an equivalent model of the DC / DC converter. If the output voltage (DC bus voltage) of the DC / DC converter is set to E, the line impedance between the DC / DC converter and the load (if it is the Figure 1 and Figure 2 circuit structure, it is the DC / AC converter 12) is set to Z, and the voltage supplied to the load is set to V, then the output current I of the DC / DC converter is obtained by the following formula (1).

[0094] I = (E - V) / Z ··· (1)

[0095] If Z in formula (1) is assumed to be a pure resistance R, the power P output by the DC / DC converter is expressed by the following formula (2).

[0096] P = VI = (EV - V 2 ) / R ··· (2)

[0097] If Equation (2) is transformed, the following Equation (3) is obtained.

[0098] E = (R / V)P + V ··· (3)

[0099] According to Equation (3), the output voltage E is proportional to the output power P. Therefore, the characteristic of the voltage command value E ＊ is expressed as a function of negative feedback with a proportionality coefficient f with respect to the output power P, as shown in the following Equation (4).

[0100] E ＊ = E ref - f(P - P ref ) ··· (4)

[0101] Here, E ref and P ref respectively represent the reference values of the output voltage (DC bus voltage) and output power of the DC / DC converter. The control units 17 (17_1, 17_2) of all the DC / DC converters 16 (16_1, 16_2) independently perform the operation of Equation (4) repeatedly, for example, at 20 kHz.

[0102] Figure 4 is a diagram showing Equation (4) graphically. In Figure 4 , the voltage command value E ＊ has a droop characteristic with a slope (-f) based on the proportionality coefficient f with respect to the output power P. At P = P ref , E ＊ = E ref . For example, if one of the two DC / DC converters (e.g., DC / DC converter 16_1) is at the coordinate point (P 1 , E ＊1 ) on the droop characteristic, and the other (DC / DC converter 16_2) is at (P 2 , E ＊2 ), then relatively, the voltage target value of the one with the smaller output power becomes higher, and the voltage target value of the one with the larger output power becomes lower. As a result, the DC / DC converter 16_1 attempts to increase the output power, and the DC / DC converter 16_2 attempts to decrease the output power. In this way, the two DC / DC converters 16_1 and 16_2 converge towards the direction of consistent output power.

[0103] "Control Block Diagram of DC / DC Converter"

[0104] Figure 5This is an example of the control block diagram of a DC / DC converter. In Figure 5 In (a), the product of the low-side voltage vL1 and current i1 of the DC / DC converter is set as the power P1. Next, in (b), the proportionality coefficient f of Equation (4) for the droop characteristic with respect to the power P1 is set to 0.005, and the reference value E of the DC bus voltage ref is generated as the voltage command value E1 as 400 [V] ＊ . Next, in (c), the difference between the voltage command value E1 ＊ and the actual high-side voltage vH1 is subjected to proportional-integral and limiting processing to obtain the current command value i1 ＊ . Thereafter, similar to the control of a normal DC / DC converter, in (d), a voltage reference value v1r is generated. Moreover, in (e), the voltage reference value v1r is superimposed on a triangular wave (20 kHz), and the high-potential-side gate drive signal gdH1 and the low-potential-side gate drive signal gdL1 having a relationship of reversing it can be obtained.

[0105] Verification

[0106] (Effect of droop control)

[0107] Figure 6 and Figure 7 are graphs showing the state of a power storage system in which two DC / DC converters are connected in parallel and operated without performing control with a droop characteristic (hereinafter referred to as droop control) for comparison. The horizontal axis is time. In Figure 6 , Figure 7 in each figure, the upper graph shows the three-phase AC output voltage of the DC / AC converter and the DC bus voltage higher than their peaks. The middle graph shows the two battery currents corresponding to the two DC / DC converters. The lower graph shows the output power of the two DC / DC converters.

[0108] In Figure 6 , as a condition, it is assumed that the difference in the voltage detection values of the two DC / DC converters is 0 and the difference in the wiring impedance of the circuit is 0. In this case, there are fine fluctuations in the two battery currents due to pulsations, but they are approximately the same and become like one thick line. The output powers (lower part) of the two DC / DC converters are the same, which is 2024 W. However, it is difficult to achieve the above ideal state in reality. Regarding the DC bus voltage detection value, even if the detection circuit is accurately calibrated, a difference of about ±1 V will occur in the voltage detection values of the two due to the bias variation of the amplifier associated with temperature changes, etc., which is inevitable. Even if the wiring impedance is designed to be as consistent as possible, it is difficult to set the error below 10%.

[0109] InFigure 7 Among them, as a condition, the difference in the voltage detection values of the two DC / DC converters is set to 0.1%, and the difference in the wiring impedance is set to 0. In this case, for one DC / DC converter, the battery current reaches the current upper limit value of 30 A, and the power is 7408 W for discharging. For the other DC / DC converter, the battery current is -13 A, and the power is 3281 W for charging. As described above, it can be seen that the DC bus voltage detection values of the two DC / DC converters only differ by 0.1%, which is a small difference, but the outputs deviate greatly.

[0110] Next, the state of the energy storage system in the case of droop control is described.

[0111] In the control of the DC / DC converter, the sign of the power when discharging the battery and outputting to the DC bus is set to positive. In addition, the reference value E of the DC bus voltage in Equation (4) ref is set to 400 V, the reference value P of the output power of the DC / DC converter ref is set to 0 W, and the proportionality constant f is set to 0.005. In this case, the DC bus voltage command value E of the DC / DC converter ＊ becomes 350 V when the output power is 10 kW (discharging), and becomes 450 V when it is -10 kW (charging). The proportional gain of the DC bus voltage control oscillates at the same value as when droop control is not performed, which is 10, and thus drops to 0.2.

[0112] Figures 8 to 11 is a graph showing the state of the energy storage system in which droop control is performed and two DC / DC converters are connected in parallel and operated. The horizontal axis is time. In each graph, the upper graph shows the three-phase AC output voltage of the DC / AC converter and the DC bus voltage higher than their peaks. The middle graph shows the two battery currents corresponding to the two DC / DC converters. The lower graph shows the output powers of the two DC / DC converters.

[0113] In Figure 8 Among them, as a condition, the difference in the DC bus voltage detection values is set to 0.1%, and the difference in the wiring impedance is set to 0. As a result, the output powers of the two DC / DC converters become 2063 W and 1985 W, and the deviation from their average value of 2024 W becomes ±1.9%. That is, although the powers of the two DC / DC converters are not the same, they become close values.

[0114] In Figure 9 Among them, as a condition, the difference in the DC bus voltage detection values is increased to 1%, and the difference in the wiring impedance is set to 0. As a result, the output powers of the two DC / DC converters become 2410 W and 1638 W, and the deviation from their average value increases to ±19%.

[0115] In Figure 10 , as a condition, the proportional constant of droop control is set to 0.01 which is twice of 0.005, the difference in the detected values of the DC bus voltage is set to 1%, and the difference in the wiring impedance is set to 0. As a result, the output powers of the two DC / DC converters become 2212 W and 1836 W, and the deviation from the average value of the two becomes ±9%.

[0116] In Figure 11 , as a condition, the proportional constant of droop control is set to 0.01, the difference in the detected values of the DC bus voltage is set to 1%, and furthermore, the difference in the wiring impedance is set not to be 0, with one being twice the other. As a result, the output powers of the two DC / DC converters become 2215 W and 1833 W. Compared with Figure 10 the result of

[0117] there is almost no change. That is, it can be understood that the difference in the wiring impedance does not have a significant impact on the result. ＊ According to the above results, it can be seen that compared with the wiring impedance, the difference in the detected values of the DC bus voltage has a greater impact on the output fluctuations of the DC / DC converter. In addition, the following effect is known, that is, the larger the proportional constant f of droop control is, the more the output fluctuations caused by the difference in the DC bus voltage value can be suppressed. However, even when the proportional constant f is set to 0.01, the deviation of the output powers of the two DC / DC converters from the average value is still ±9%. In addition, at this time, the DC bus voltage command value E

[0118] drops to 300 V when the output power of the DC / DC converter is -10 kW (charging). This voltage value is not a sufficient value for conversion to AC 200 V through a DC / AC converter. ＊ When the output power of the DC / DC converter is 10 kW (discharging), the DC bus voltage command value E

[0119] becomes 500 V. It is a sufficient value for conversion to AC 200 V, but it is too high as the DC bus voltage, so the power loss of the DC / AC converter becomes large. In order not to make the variation range of the DC bus voltage too large, it is necessary to study the following method, that is, the proportional constant f of droop control hardly increases, but the fluctuations of the output of the DC / DC converter become smaller.

[0120] Figure 12It is a graph showing the relationship between the output deviation and the voltage detection deviation. This graph plots the deviation (output deviation (ratio)) of the output of the DC / DC converter from the average value when the proportionality constant f of the droop control is set to 0.005 as described above and the respective deviations (voltage detection deviations) observed from the average value (overall) of the DC bus voltage, and is obtained as their approximate straight line. From this graph, it can be seen that the output deviation and the voltage detection deviation are in a proportional relationship with each other.

[0121] Therefore, the voltage detection value can be corrected based on the output deviation. For example, when the output deviation is +19%, if the approximate straight line is applied, the deviation of the DC bus voltage detection value is -0.494%. Thus, if the voltage detection value is divided by (1 - 0.00494), that is, 0.99506, the voltage detection value can be corrected. In fact, at the site where the energy storage system is installed, after the system is constructed, it is run at about 20% of the rated output, and it is only necessary to determine the correction coefficient of the DC bus voltage detection value of each DC / DC converter according to the output deviation. The DC bus voltage detection values of two DC / DC converters were corrected using the correction coefficient as described above.

[0122] Figure 13 and Figure 14 is a graph showing the state of the energy storage system in which the above correction is performed on the basis of droop control and two DC / DC converters are connected in parallel and operated. The horizontal axis is time. In each graph, the upper graph shows the three-phase AC output voltage of the DC / AC converter and the DC bus voltage higher than their peak values. The middle graph shows the two battery currents corresponding to the two DC / DC converters. The lower graph shows the output powers of the two DC / DC converters.

[0123] In Figure 13 as a condition, the proportionality constant f of the droop control is 0.005, the difference in the DC bus voltage detection values is set to 1%, and the difference in the wiring impedance is set to 0. This condition is the same as Figure 9 Moreover, the DC bus voltage detection values of two DC / DC converters were corrected using the correction coefficient obtained by applying the output deviation of Figure 9 to the approximate straight line of Figure 12 As a result, the output powers of the two DC / DC converters became 2024W and 2019W, which were roughly the same. The deviation from the average value of the two became smaller, becoming ±0.135%. On the graph of Figure 13 the output powers of the two DC / DC converters overlapped with each other and looked like one line.

[0124] In Figure 14 in, in Figure 13On the basis of the same conditions and calibration, the resistive load connected between each line on the AC side of the DC / AC converter was replaced from 10 Ω to 2 Ω. In this case, the output powers of the respective DC / DC converters became 10.330 kW and 10.325 kW, which were roughly the same. The deviation from the average value of the two was only ±0.02%. On Figure 14 In the graph of, the output powers of the two DC / DC converters overlapped with each other and appeared as one line. The DC bus voltage was also stable at around 350 V.

[0125] Figure 15 It is a graph of the state of a power storage system in which, after imposing severe conditions on the load connection, calibration is performed on the basis of droop control, and two DC / DC converters are connected in parallel and operated. The horizontal axis is time. The graph of the first layer from the top shows the three-phase AC output voltage of the DC / AC converter. The graph of the second layer shows the three-phase AC output current of the DC / AC converter. The graph of the third layer shows the DC bus voltage. The graph of the fourth layer shows the two battery currents corresponding to the two DC / DC converters. The graph of the fifth layer shows the output powers of the two DC / DC converters.

[0126] In Figure 15 as a condition, the proportionality constant f of the droop control was 0.005, the difference in the detected values of the DC bus voltage was set to 1%, and the difference in the wiring impedance was set to 0. This condition was the same as Figure 9 Moreover, a correction coefficient obtained by applying the output deviation of Figure 9 to the approximate straight line of Figure 12 was used to correct the detected values of the DC bus voltage of the two DC / DC converters. In addition, in Figure 15 in order to impose severe conditions, it was set that 2 Ω × 3 resistive loads were repeatedly connected / disconnected at a cycle of 0.2 seconds. As a result, the output voltage of the DC / AC converter was disturbed immediately after the load was disconnected, but other than that, the AC voltage stably output 200 V between lines. The DC bus voltage became a steady state at 350 V when the load was connected and became a steady state at 400 V when the load was disconnected, but it was stable including the intermediate voltage state of the two during the transition. The output powers of the two DC / DC converters were also the same in the steady state and the transition state.

[0127] Summary So Far

[0128] As described above, droop characteristics are added in which the DC bus voltage command value of each DC / DC converter changes in a way that is negatively feedback-controlled by the output power, and a mechanism for correcting the detected value of the DC bus voltage by the deviation of the output power from the average value is also used. As a result, it was confirmed that, without relying on communication, multiple DC / DC converters can control to keep the DC bus voltage at a constant value.

[0129] Parallel Operation of Three or More DC / DC Converters

[0130] Next, consider the parallel operation of three or more DC / DC converters. That is, consider the case where the Figure 1 , Figure 2 DC power supply devices are operated in parallel as three units: 11_1, 11_2, and 11_3.

[0131] First, perform a simulation for obtaining the correction coefficient of the DC bus voltage detector. Set the error rates of the DC bus voltage detectors of the three DC / DC converters to +1%, ±0%, and -1% respectively, and connect a 10 Ω resistive load between each line on the AC side. Set all the correction coefficients to 1. If the output deviation δ i is defined by the following formula (5), then the δ i of the three DC / DC converters becomes -0.580, 0, and +0.580.

[0132] In addition, different types of fonts for notations and arithmetic expressions are mixed in the specification, but the differences in fonts have no meaning, and the same characters represent the same physical quantities.

[0133]

[0134] Also, set the error rates of the DC bus voltage detectors of the three DC / DC converters to +0.5%, ±0%, and -0.5% respectively, and connect a 10 Ω resistive load between each line on the AC side. In this case, the δ i of the three DC / DC converters becomes -0.290, 0, and +0.290.

[0135] Based on these results, the graph showing the relationship between the output deviation δ i and the DC bus voltage detection deviation is Figure 16 . The straight line representing the relationship passes through the origin, showing a proportional relationship with a negative slope. From this relationship, the correction coefficient G i for minimizing the output deviation δ i of the DC bus voltage detection value can be obtained by the following formula (6). When calculating the DC bus voltage detection value through the software of the control unit of the DC / DC converter, it is returned as G i , thereby correcting the deviation of the detection value and minimizing the output deviation.

[0136] G i = 1 + hδ i , h = -0.01725 ··· (6)

[0137] In addition, Figure 16The slope h (=-0.01725) is approximately 2 / 3 compared to -0.0260 of the two parallel DC / DC converters shown in Figure 12 That is, the slope changes according to the number of parallel units. Defining δ i and applying Equation (5) that defines it to Equation (6) gives the following Equation (7). Equation (7) shows that the product of h and the number of parallel DC / DC converters n is constant.

[0138]

[0139] Therefore, if redefined as H = nh, Equation (6) can be generalized to an equation including the number of parallel DC / DC converters n through the following Equation (8).

[0140] G i = 1 + (H / n)·δ i , H = -0.05175 ··· (8)

[0141] 《Correction Regarding Output Deviation》

[0142] Regarding the three DC / DC converters, the error rates of DC bus voltage detection are set to +0.8%, +0.3%, and -0.9% respectively, and a 10 Ω resistive load is connected between each line on the AC side. The results before correction of the DC bus voltage detection values at this time show that the outputs of the three DC / DC converters are on average 1350 W, and the deviation becomes δ 1 : -0.4249, δ 2 : -0.1352, δ 3 : +0.5601 and fluctuates. Therefore, if the above output deviation is applied to Equation (8), the correction coefficients of the DC bus voltage detection values become G 1 : 1.00733, G 2 : 1.00233, G 3 : 0.990. The DC bus voltage detection values are corrected using these correction coefficients.

[0143] Figure 17 is a graph showing the state of the power storage system in which the above correction is performed on the basis of droop control and three DC / DC converters are connected in parallel and operated. The horizontal axis is time. In the figure, the upper graph shows the three-phase AC output voltages of the DC / AC converter and the DC bus voltage higher than their peaks. The middle graph shows the three battery currents corresponding to the three DC / DC converters. The lower graph shows the output powers of the three DC / DC converters.

[0144] As a result, the outputs of the three DC / DC converters are roughly the same, and the output deviation is δ 1 : 0.00673, δ2 : 0.00653, δ 3 : becomes extremely small due to -0.0132.

[0145] In addition, the AC-side load resistance is changed to 1.5 Ω. In this case, the outputs of the three DC / DC converters are also roughly the same, and the output deviation from the average value of 9213.6 W is δ 1 : 0.000888, δ 2 : 0.000861, δ 3 : and further decreases to -0.00175.

[0146] Next, the error rates of the DC bus voltage detection are changed to +1.2%, -0.5%, -1.2%, and 10 Ω resistive loads are connected between the lines on the AC side. As a result, the outputs of the three DC / DC converters become an average of 1344 W, and the deviation becomes δ 1 : -0.7972, δ 2 : +0.1944, δ 3 : +0.6027. If this output deviation is applied to Equation (8), the correction coefficient of the DC bus voltage detection value becomes G 1 : 1.01375, G 2 : 0.9966, G 3 : 0.9896. The DC bus voltage detection value is corrected using this correction coefficient.

[0147] As a result, the outputs of the three DC / DC converters are roughly the same, and the output deviation is δ 1 : 0.00445, δ 2 : -0.00254, δ 3 : and becomes smaller to -0.00191.

[0148] And the AC-side load resistance is changed to 1.5 Ω. In this case, the outputs of the three DC / DC converters are also roughly the same, and the output deviation from the average value of 9213.8 W is δ 1 : 0.000586, δ 2 : -0.000337, δ 3 : and further decreases to -0.000249.

[0149] Next, the number of parallel DC / DC converters is increased to 5. The error rates of the DC bus voltage detection are set to +1.2%, -0.5%, -1.2%, +0.8%, -0.8% respectively, and 10 Ω resistive loads are connected between the lines on the AC side. As a result, the output of the DC / DC converter becomes an average of 803.6 W, and the deviation becomes δ 1 : -1.276, δ 2: 0.3926, δ 3 : 1.07979, δ 4 : -0.88349, δ 5 : 0.68712. If this output deviation is applied to Equation (8), the correction coefficient of the DC bus voltage detection value becomes G 1 : 1.0132, G 2 : 0.9959, G 3 : 0.9888, G 4 : 1.00914, G 5 : 0.99289. The DC bus voltage detection value was corrected using this correction coefficient.

[0150] As a result, the outputs of the five DC / DC converters were roughly the same, becoming an average of 810.61 W, and the output deviation became δ 1 : 0.0194, δ 2 : -0.00787, δ 3 : -0.0171, δ 4 : 0.0141, δ 5 : -0.00859.

[0151] And the AC side load resistance was changed to 0.9 Ω. In this case, the outputs of the five DC / DC converters were also roughly the same, and the output deviation with respect to the average value of 9325.3 W was δ 1 : 0.00150, δ 2 : -0.000612, δ 3 : -0.00132, δ 4 : 0.00109, δ 5 : -0.000663 and further decreased.

[0152] In addition, the following situation was confirmed, that is, the case where five were connected in parallel and the error rate of the DC bus voltage detection only shifted to the positive side. As an example, the error rates were set to +2.0%, +1.5%, +1.0%, +0.5%, 0%. As a result in this case, the outputs of the DC / DC converters could also be equalized.

[0153] In addition, the situation that the voltage of the DC power supply connected to each DC / DC converter is different is also confirmed. Specifically, the voltage of each DC power supply is set to 200V, 225V, 250V, 275V, and 300V. As a result, the output of only one DC / DC converter is constrained by the upper limit of the output current 45A, so it becomes smaller, but the other four become uniform. According to this result, it can be seen that the voltage of the DC power supply does not affect the output sharing of the DC / DC converter. When any DC / DC converter is constrained by the upper limit value of the current, the other DC / DC converters automatically distribute the insufficient amount of load power consumption equally.

[0154] That is, even if the output of a particular storage battery is restricted according to the remaining capacity or the degree of degradation, the storage system operates as expected. The DC / DC converters corresponding to the storage battery that has reached the discharge limit or has reached full charge can be excluded from the output uniformization. In addition, if the upper limit of the output current is increased to 50A, the output constraint of one DC / DC converter is released, and the outputs of the five DC / DC converters become uniform.

[0155] 《Correction of proportionality factor H》

[0156] So far, the correction of the DC bus voltage detection value related to the output deviation has shown the research results based on the premise of accurately obtaining the proportional coefficient H relative to the output deviation included in the formula (8) for calculating the correction coefficient. However, in fact, this premise may not be established. The reason is that even if the coefficient H is predicted by simulation that models each condition of the actual machine as faithfully as possible, it is impossible to make the simulation and the actual machine completely consistent, and it is inevitable that a certain degree of error is included compared with the H of the actual machine. Therefore, when H contains an error, it is considered to further correct it and make the output uniform.

[0157] If the study is conducted only by simulation, there will be no error in H, but it is assumed that H is obtained in advance for the simulation. ＊ The correction factor is G, which is half of the actual value, that is, -0.025875. 1 ＊ :1.00502530059405、G 2 ＊ :1.0025130560483, G 3 ＊ :0.999999866085955, G 4 ＊ :0.99748727259746, G 5 ＊: 0.994974504674805. Set the correction of the DC bus voltage detection performed using these correction factors as the first correction, and obtain the result after the first correction. Obtain the relationship between the output deviation before correction and the output deviation after the first correction.

[0158] Figure 18 is a graph showing the relationship between the output deviation before correction and the output deviation after the first correction. The two are in a proportional relationship, and the output deviation after the first correction is reduced to 0.4904 times the value before correction. This output deviation is due to the error of H ＊ used in the first correction. Therefore, H ＊ can be corrected based on the change in the deviation before and after this correction. The relationship between the output deviation δ i and the DC bus voltage detection deviation Δ i can be expressed by Equation (9). Here, v i is the DC bus voltage detection value, and v o is the DC bus voltage without deviation.

[0159]

[0160] When using H ＊ to correct v i , the relationship between the DC bus voltage detection deviation Δ i ＊ and the output deviation δ i ＊ becomes Equation (10).

[0161]

[0162] Through the above Equation (9) and Equation (10), the following Equation (11) and Equation (12) are obtained.

[0163]

[0164]

[0165] Transform Equation (12) and use the equation of the correction factor G i in Equation (8) to obtain the following Equation (13) and (14).

[0166]

[0167]

[0168] Obtain the correction factor G i from Equation (14) based on the results before the first correction and after the first correction. In Equation (14), (δ i＊ ) / δ i Used Figure 18 The slope is 0.4904. At this time, it becomes G 1 :1.009909185、G 2 :1.004943384、G 3 :0.999999737, G 4 :0.99508111, G 5 : 0.990185816, and the correction coefficient is substantially consistent with the correction coefficient obtained by using the original H. The correction of the DC bus voltage detection value using this correction coefficient is referred to as secondary correction.

[0169] The output deviations of the five DC / DC converters after secondary calibration are as follows when the load is 10Ω.

[0170] P 1 :808.72111W、δ 1 : -0.0015630963095791

[0171] P 2 :807.53344W、δ 2 : -0.0030293787433416

[0172] P 3 :808.11476W、δ 3 : -0.0023116883879441

[0173] P 4 :810.58379W、δ 4 :0.00073654497438117

[0174] P 5 :814.98289W、δ 5 :0.0061676184664834

[0175] Average: 809.987198W

[0176] In addition, the output deviation after the secondary correction becomes as follows when the load is 0.9Ω.

[0177] P 1 :9322.7666W、δ 1 : -0.0001225987849281

[0178] P 2 :9321.6954W、δ 2: -0.00023748621246296

[0179] P 3 : 9322.2296W, δ 3 : -0.00018019265029986

[0180] P 4 : 9324.4640W, δ 4 : 5.9449310196535E - 005

[0181] P 5 : 9328.3929W, δ 5 : 0.00048082833749458

[0182] Average: 9323.9097W

[0183] As shown above, even when the coefficient H cannot be accurately predicted, according to the method of obtaining the correction coefficient in two stages, the output can be equalized.

[0184] "Flowchart"

[0185] Figure 19 is an example of a flowchart showing the processing actions for DC bus voltage detection and correction. The execution entity of this flowchart is the management control unit 18. By starting the DC bus voltage detection and correction, the management control unit 18 makes the energy storage system operate at a constant output (step S1). The control unit 17 of the DC / DC converter 16 detects its own output (output power) and sends it to the management control unit 18. The management control unit 18 receives the output information sent from the control unit 17 (step S2). The management control unit 18 calculates the output deviation of each DC / DC converter 16 based on the output information (step S3).

[0186] Next, the management control unit 18 calculates the correction coefficient using Equation (8) and notifies each DC / DC converter 16 of the correction coefficient (step S4). On the side of the DC / DC converter 16, the notified correction coefficient is introduced to calculate the output, which is sent to the management control unit 18. The management control unit 18 that has received the information output from each DC / DC converter 16 recalculates the output deviation of each DC / DC converter 16 (step S6).

[0187] Next, the management control unit 18 determines whether the output deviation is less than a specified value (step S7). If it is less than the specified value, the DC bus voltage detection correction is ended. If it is not less than the specified value, the management control unit 18 recalculates the correction coefficient using Equation (14) (step S8). After that, the management control unit 18 executes steps S5, S6, and S7 again. In step S7, if the output deviation becomes less than the specified value, the DC bus voltage detection correction is ended. Usually, it is considered that the output deviation becomes less than the specified value at this stage. However, in case it does not become smaller, the correction coefficient can be recalculated further and the same process can be repeated.

[0188] As described above, the management control unit 18 determines the voltage detection deviation corresponding to each output deviation observed from the overall view of the multiple DC / DC converters, and gives the correction value (correction coefficient) for suppressing the voltage detection deviation to the control units of the multiple DC / DC converters respectively. Each control unit can equalize the outputs of the multiple DC / DC converters using the notified correction value. In addition, communication is used at the time of this notification, but high-speed communication is not required.

[0189] In addition, the management control unit 18 changes the correction value corresponding to the number of parallel-connected DC / DC converters. That is, based on the understanding that the appropriate correction value changes according to the number of parallel-connected DC / DC converters, the appropriate correction value corresponding to the number of parallel connections is given to each control unit.

[0190] If the correction value (correction coefficient) in step S4 is set as the first correction value, each control unit uses the first correction value, and then the management control unit 18 determines again the voltage detection deviation corresponding to the output deviation related to each DC / DC converter observed from the overall view of the multiple DC / DC converters, and gives the second correction value (correction coefficient) for suppressing the voltage detection deviation to the control units of the multiple DC / DC converters respectively (step S8). In this way, even if the first correction value is a provisional value, the outputs of the multiple DC / DC converters can be equalized by the second correction value.

[0191] Summary of the Invention

[0192] As described in detail above, in the DC / DC conversion system 100 provided between the multiple storage batteries 14 and the common DC bus L DC correspondingly to each of the multiple storage batteries 14, there are provided DC / DC converters 16 provided between the storage battery 14 and the DC bus L DC and control units 17 for controlling the DC / DC converters 16. Moreover, the control unit 17 is related to the DC bus L regarding each DC / DC converter observed from the overall view of the multiple DC / DC converters 16 existing in parallel DCThe voltage detection deviation is introduced to correct the DC bus voltage detection value, and the DC / DC converter 16 is controlled according to the voltage command value that becomes a droop characteristic with respect to the output power.

[0193] As a control method for the power storage system 1 and the DC / DC converter, the gist is the same.

[0194] In the DC / DC conversion system 100 as described above, according to the droop characteristic of the voltage command value with respect to the output power, control is achieved such that the outputs of the plurality of DC / DC converters 16 arranged in parallel are directed in the same direction. In addition, in order to suppress the output inconsistency of the plurality of DC / DC converters caused by the error of the voltage detection of the DC bus L DC the voltage detection deviation of the DC bus L DC is introduced to correct the DC bus voltage detection value. In this way, between the plurality of DC / DC converters 16, the output can be equalized without relying on high-speed communication.

[0195] In order to notify each DC / DC converter of the voltage detection deviation related to each observed from the whole, a function such as a management control unit that observes the whole is required. However, the communication for this notification does not need to be performed in real time, and it is sufficient if it is low-speed and can be updated periodically. By performing periodic updates, even if the voltage detection deviation changes over time, an appropriate correction value (correction coefficient) can be provided.

[0196] The above output equalization control is performed, in other words, the DC bus voltage decentralized control, so that the DC bus voltages of the plurality of DC / DC converters connected in parallel to the DC bus become constant independently. Since the DC bus voltage is controlled by the DC / DC converter so as to always converge within a certain range, the DC / AC converter does not need to control the DC bus voltage to be constant not only during autonomous operation but also during system interconnection operation, and only needs to control the output power specifically.

[0197] "Comparison with Central Control"

[0198] During system interconnection operation, the responsiveness of the existing "central control" that hypothetically uses high-speed communication to send output command values and the responsiveness of the DC bus voltage decentralized control were compared through simulation.

[0199] For example, in the case of autonomous operation, if the communication delay associated with the transmission of the power command value from the central control unit to each DC / DC converter under central control becomes about 10 milliseconds, the DC bus voltage drops when the load changes suddenly, and the output voltage of the DC / AC converter cannot maintain a sine wave. On the other hand, in the DC bus voltage decentralized control, the command value transmission implemented through communication is not performed, and the control units of the respective DC / DC converters independently control the DC bus voltage. Therefore, the response is fast, and even when the load changes suddenly, the DC bus voltage is maintained within an appropriate range, and the output voltage of the DC / AC converter does not become disordered.

[0200] In addition, in the case of system interconnection operation, under central control, it is not affected by the communication delay and the follow-up delay of the DC bus voltage control through the DC / AC converter. When the communication delay is 10 milliseconds, the response time after the power command value is changed becomes about 30 milliseconds. In contrast, in the DC bus voltage decentralized control, if the power command value is updated, the output current command value of the DC / AC converter is immediately updated. Therefore, the response time becomes one-tenth of that of the central control, that is, 3 milliseconds. As described above, in the system interconnection operation, for applications that also require timely responsiveness such as load following, smoothing of renewable energy power generation, and frequency control, the DC bus voltage decentralized control becomes effective.

[0201] Supplementary Note

[0202] In addition, it should be considered that the embodiments disclosed this time are illustrative in all aspects and are not restrictive. The scope of the present invention is represented by the claims, including meanings equivalent to the claims and all changes within the scope.

[0203] Description of Reference Numerals

[0204] 1 Energy Storage System

[0205] 2 Solar Power Generation System

[0206] 3 Commercial Power System

[0207] 4 Transformer

[0208] 5 CT

[0209] 6 Load

[0210] 11 DC Power Supply System

[0211] 11_1, 11_2, 11_n DC Power Supply Device

[0212] 12 DC / AC Converter

[0213] 13 Control Unit

[0214] 14 Battery

[0215] 15 Battery Management System

[0216] 16, 16_1, 16_2 DC / DC Converter

[0217] 17, 17_1, 17_2 Control Unit

[0218] 18 Management and Control Unit

[0219] 21 Solar Cell

[0220] 21A Array

[0221] 22 DC / AC Converter

[0222] 100 DC / DC Conversion System

[0223] 121 Smoothing Capacitor

[0224] 122 AC Reactor

[0225] 123 Capacitor

[0226] 124, 125, 126 Voltage Sensor

[0227] 127, 128, 129 Current Sensor

[0228] 161 Smoothing Capacitor

[0229] 162 DC Reactor

[0230] 163 Smoothing Capacitor

[0231] 165 Voltage Sensor

[0232] 166 Current Sensor

[0233] 167 Voltage Sensor

[0234] L AC AC Circuit

[0235] L DC DC Bus

[0236] Q H , Q L Switching Element

[0237] Q1, Q2, Q3, Q4, Q5, Q6 Switching Element

Claims

1. A DC / DC conversion system is provided between a plurality of DC power supplies and a common DC bus. The DC / DC conversion system correspondingly has, for each of the plurality of DC power supplies: a DC / DC converter provided between the DC power supply and the DC bus; a control unit that controls the DC / DC converter; and a management control unit that determines a voltage detection deviation of the DC bus corresponding to an output deviation related to each DC / DC converter observed from the overall of the plurality of DC / DC converters, and gives a correction value for suppressing the voltage detection deviation to the control unit of each of the plurality of DC / DC converters. The control unit corrects the voltage detection value of the DC bus based on the correction value, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power.

2. The DC / DC conversion system according to claim 1, wherein the management control unit varies the correction value corresponding to the number of parallel-connected DC / DC converters.

3. The DC / DC conversion system according to claim 1 or 2, wherein if the correction value is set as a first correction value, each control unit uses the first correction value, and then the management control unit determines again a voltage detection deviation corresponding to an output deviation related to each DC / DC converter observed from the overall of the plurality of DC / DC converters, and gives a second correction value for suppressing the voltage detection deviation to the control unit of each of the plurality of DC / DC converters.

4. The DC / DC conversion system according to claim 1 or 2, wherein the management control unit periodically updates the correction value and gives it to the control unit of each of the plurality of DC / DC converters.

5. The DC / DC conversion system according to claim 1 or 2, wherein the DC power supply is a storage battery, and the control unit restricts the current flowing through the DC power supply based on the charge state of the DC power supply.

6. A power storage system includes a plurality of DC power supplies and a common DC bus, and the power storage system correspondingly has, for each of the plurality of DC power supplies: a DC / DC converter provided between the DC power supply and the DC bus; a control unit that controls the DC / DC converter; and a management control unit that determines a voltage detection deviation of the DC bus corresponding to an output deviation related to each DC / DC converter observed from the overall of the plurality of DC / DC converters, and gives a correction value for suppressing the voltage detection deviation to the control unit of each of the plurality of DC / DC converters. The control unit corrects the voltage detection value of the DC bus based on the correction value, and controls the DC / DC converter according to a voltage command value having a droop characteristic with respect to the output power.

7. The power storage system according to claim 6, wherein it has a DC / AC converter provided between the DC bus and an AC circuit. The DC / AC converter varies the output according to the conditions of a commercial power system or a load connected to the AC circuit.

8. The power storage system according to claim 6, wherein, the DC / DC converter performs current control for the corresponding DC power supply.

9. A control method for a DC / DC converter, which is a control method for a plurality of DC / DC converters arranged in parallel between a plurality of DC power supplies and a common DC bus, in this control method for the DC / DC converter, a voltage detection deviation of the DC bus corresponding to an output deviation related to each of the DC / DC converters observed from the whole of the plurality of DC / DC converters is determined, and a correction value for suppressing the voltage detection deviation is determined, the voltage detection value of the DC bus is corrected based on the correction value, and the DC / DC converter is controlled according to a voltage command value having a droop characteristic with respect to the output power.

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