Power System

Abstract

To provide a power system which allows load sharing in a state without voltage deviation of a DC line.SOLUTION: A power system comprises: a plurality of DC / DC converters 10 connected in parallel with a DC bus line; and a plurality of DC / DC converter controllers 22 which performs proportional plus integral control for each of the DC / DC converters, and in which an integrated value of difference between voltage V_bus of an actual DC bus line and a voltage target value V_ref of the DC bus line is shared so as to arbitrarily control load sharing of the plurality of DC / DC converters 10.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a power system using multiple batteries. [Background technology]

[0002] Methods for controlling the balance of current and power in an autonomous and decentralized manner in a DC bus line to which multiple batteries are connected have been disclosed (Patent Document 1 and Patent Document 2). Specifically, in a closed-loop control system that does not have an element for integrating the difference between a command value of a control target state quantity and a feedback value of the state quantity, droop control is applied in which the command value is larger than the feedback value by a certain amount and is settled in a state where the difference remains. Droop control has the characteristic that the operating point fluctuates when there is a fluctuation in the characteristics or load of the controlled object, thereby stabilizing the control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-141761 A [Patent Document 2] JP 2020-22331 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, because droop control generates a steady voltage deviation, it was not possible to achieve steady-state operation under conditions that maximize the power conversion efficiency of the DC / DC converter. Furthermore, conventional droop control is restricted by the need to maintain upper and lower voltage limits, including overshoot and undershoot voltages, in addition to stability, and to have a voltage deviation above a detectable level, which makes the design of the control system complicated. [Means for solving the problem]

[0005] One aspect of the present invention is a power system comprising a plurality of DC / DC converters connected in parallel to a DC bus line, and a plurality of DC / DC converter controllers that perform proportional-integral control of each of the DC / DC converters, wherein the plurality of DC / DC converter controllers share an integral value of the difference between an actual DC bus line voltage V_bus and a DC bus line voltage target value V_ref, thereby arbitrarily controlling the load sharing of the plurality of DC / DC converters.

[0006] Here, it is preferable to provide an analog signal bus line for sharing the integral value.

[0007] It is also preferable to provide a single integral value calculator shared by a plurality of the DC / DC converter controllers, the integral value calculator determining the integral value and outputting the integral value to the analog signal bus line.

[0008] It is also preferable that the multiple DC / DC converter controllers each include an integrator, share an average integral value obtained by averaging the integral values ​​via the analog signal bus line, and perform integral error correction processing using the average integral value.

[0009] It is also preferable to provide a wired or wireless communication line for sharing the integral value.

[0010] It is also preferable that the device includes an integral value averaging calculator which calculates an average integral value by averaging the integral values ​​calculated by a plurality of the DC / DC converter controllers and outputs the average integral value to the communication line, and that the plurality of DC / DC converter controllers each include an integrator, share the average integral value via the communication line, and perform integral error correction processing using the average integral value.

[0011] It is also preferable to provide a first control means that shares an average integral value obtained by averaging the integral values ​​using an analog signal bus line and performs integral error correction processing using the average integral value, and a second control means that shares an average integral value obtained by averaging the integral values ​​using a communication line and performs integral error correction processing using the average integral value, and if either the first control means or the second control means fails, control is performed by the other.

[0012] Furthermore, if the function of sharing the integral value fails, it is preferable to stop integral control in the plurality of DC / DC converter controllers. Effect of the Invention

[0013] According to the power system of the present invention, load sharing is possible in a state where there is no voltage deviation in the DC line, and the power conversion efficiency of the DC / DC converter is improved. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a typical power system. [Diagram 2] FIG. 1 is a diagram showing a simulation result for a typical power system. [Diagram 3] 1 is a diagram showing a basic configuration of a power system according to a first embodiment. [Figure 4] FIG. 2 is a diagram illustrating a specific configuration example of a power system according to the first embodiment. [Diagram 5] FIG. 2 is a diagram showing a configuration for simulating a power system in the first embodiment. [Figure 6] FIG. 4 is a diagram showing a result of a simulation of the power system in the first embodiment. [Figure 7] FIG. 11 is a diagram illustrating a specific configuration example of a power system according to a second embodiment. [Figure 8] FIG. 11 is a diagram showing a configuration for simulating a power system in a second embodiment. [Figure 9]FIG. 11 is a diagram illustrating a result of a simulation of the power system in the second embodiment. [Figure 10] FIG. 13 is a diagram illustrating a specific configuration example of a power system according to a third embodiment. [Figure 11] FIG. 13 is a diagram illustrating a configuration for simulating a power system according to a third embodiment. [Figure 12] FIG. 13 is a diagram illustrating a result of a simulation of the power system in the third embodiment. [Figure 13] FIG. 13 is a diagram showing a modified example of the configuration for correcting an integral value to an average integral value in the embodiment of the present invention. [Figure 14] 4 is a flowchart showing an example of control of the power system in the embodiment of the present invention. [Figure 15] FIG. 13 is a diagram showing the results of a simulation in the case where integral control is stopped and only proportional control is performed in the power system in the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [General power system configuration] Fig. 1 shows a power system 100 connected to two DC / DC converters that perform general PI control and a photovoltaic power generator (PV) as a distributed power source. The power system 100 includes a DC / DC converter 10 (10a, 10b), a DC / DC converter controller 12 (12a, 12b), a PV 14, and a DC / DC converter 16 with maximum power point tracking (MPPT).

[0016] The DC / DC converter 10 converts the voltage of a connected DC power supply and supplies it to a DC bus line. The DC / DC converter controller 12 includes a proportional-integral controller (PI controller) that senses the voltage V_bus of the DC bus line and controls the current output I_DC / DC (I_DC / DC1, I_DC / DC2) of each DC / DC converter 10 (10a, 10b) in order to bring the voltage of the DC bus line closer to a target value V_ref. That is, the current output I_DC / DC of the DC / DC converter 10 is controlled by adding a proportional output of a gain K and an integral output of a gain K' to the difference between the actual DC bus line voltage V_bus and the DC bus line voltage target value V_ref.

[0017] Ideally, in the power system 100, the voltage V_bus of the DC bus line is steady and constant, and a desired current load sharing is realized in each DC / DC converter 10. However, in reality, a bias in the load sharing occurs due to a measurement error of the voltage V_bus of the DC bus line in each DC / DC converter 10.

[0018] 2 shows the simulation results of the output voltage and output current of each DC / DC converter 10 when a voltage measurement error V_error occurs in the DC / DC converter 10b. In the simulation, -0.2V was given as the voltage measurement error V_error. As other parameters, the proportional control gains of the DC / DC converter controller 12 were set to K_1=0.5 and K_2=1.0, and the integral control gains were set to K'_1=1.0 and K'_2=2.0. The initial voltage of the power system 100 was set to 360V.

[0019] As the simulated current for PV14, a current I_PV was given that linearly rises from 0 A at time t = 5.0 seconds, reaches a maximum value at time t = 5.5 seconds, begins to decrease linearly at time t = 9.5 seconds, and reaches 0 A at time t = 10.0 seconds.

[0020] As shown in FIG. 2, in the integral calculation block of the DC / DC converter controller 12 provided for each DC / DC converter 10, the measured voltage of the DC bus line including the voltage measurement error V_error is integrated with the target value V_ref, causing the current of the DC / DC converter 10 to diverge, and the desired current distribution ratio could not be achieved.

[0021] [First embodiment] As shown in FIG. 3, a power system 200 in the first embodiment is configured to provide a common integral value calculator 20 for a plurality of DC / DC converters 10 and input the integral value to each of the DC / DC converter controllers 22 (22a, 22b, . . . 22n).

[0022] The integral value calculator 20 outputs an integral value obtained by time-integrating the difference between the actual DC bus line voltage V_bus and the DC bus line voltage target value V_ref over a predetermined period of time. The DC / DC converter controller 22 proportionally processes the integral value received from the integral value calculator 20 with a gain K', and proportionally processes the difference between the actual DC bus line voltage V_bus and the DC bus line voltage target value V_ref with a gain K, and adds these values ​​to control the current output I_DC / DC of the DC / DC converter 10.

[0023] In this way, by using a common integral value to perform proportional-integral control (PI control) on the multiple DC / DC converters 10 by the DC / DC converter controller 22, any load sharing can be realized. The current distribution ratio in the steady state is the gain ratio K_1':K_2':...:K_n' set in each DC / DC converter controller 22 (22a, 22b...22n). Also, the current distribution ratio in the transient state in which the voltage fluctuates is the gain ratio K_1:K_2:...:K_n set in each DC / DC converter controller 22 (22a, 22b...22n). Therefore, the current distribution ratio in the steady state and the transient state of each DC / DC converter 10 can be set arbitrarily.

[0024] For example, when using a low-capacity, high-output storage battery (such as a lithium-ion battery), setting the integral control gain low and the proportional control gain high makes it possible to reduce the steady-state charging and discharging power and increase the load sharing during transients. Conversely, when using a high-capacity, low-output battery (such as a NAS battery), setting the integral control gain high and the proportional control gain small makes it possible to increase the steady-state charging and discharging power and reduce the load sharing during transients.

[0025] It should be noted that a higher-level controller (not shown) may be provided, and the higher-level controller may set the load sharing rate and the current offset value for the DC / DC converter controller 22. The same applies to the other embodiments and modified examples described below.

[0026] 4 shows a specific example of the configuration of the power system 200 in the first embodiment. The power system 200 includes DC / DC converters 10 (10a, 10b, . . . 10n), an integral value calculator 20, DC / DC converter controllers 22 (22a, 22b, . . . 22n), a PV 14, a DC / DC converter 16 with MPPT, an AC power source (commercial power source) 24, and an AC / DC converter 26. In the power system 200, a plurality of DC / DC converters 10 are connected to a common DC bus line, and a load such as a storage battery or an EV is connected to the other end of the DC / DC converter 10. In addition, the power system 200 may be connected to the AC power source 24 via the AC / DC converter 26, or a distributed power source such as the PV 14 may be connected.

[0027] In the power system 200, in order to eliminate errors in the integral value due to measurement errors of the voltage sensor, a signal bus line is provided for sharing a common integral value calculated by the integral value calculator 20 among multiple DC / DC converter controllers 22. The signal bus may be an analog signal bus line or a communication bus line.

[0028] As shown in Fig. 5, a simulation was performed using a model of a power system 200 composed of two DC / DC converters 10, a DC / DC converter controller 22, and a distributed power source simulating the PV 14. The voltage measurement error V_error in the DC / DC converter 10b, the gain in each DC / DC converter controller 22, and the current I_PV of the PV 14 were set to the same conditions as in the simulation for the power system 100 shown in Fig. 1.

[0029] Fig. 6 shows the results of a simulation for the power system 200. Although the voltage V_bus of the DC bus line changes with the change in the current I_PV of the PV 14, it was possible to restore the original voltage by integral control using the common integral value calculator 20. In addition, the steady-state current distribution ratio I_DC / DC1:I_DC / DC2 of the output of the DC / DC converter 10 (10a, 10b) became equal to the gain K_1:K_2 of the integral control of the DC / DC converter controller 22 (22a, 22b).

[0030] Thus, according to the power system 200 of the first embodiment, in a state where there is no voltage deviation in the DC bus lines, the load can be shared at a distribution ratio set in the multiple DC / DC converters 10. This improves the power conversion efficiency of the DC / DC converters 10. In addition, the design of the control system for the DC bus lines becomes easier.

[0031] [Second embodiment] In the power system 200 in the first embodiment, one integral calculator 20 is used to calculate the integral, but there is a problem that a failure of the integral calculator 20 may cause the system to stop.

[0032] As shown in FIG. 7, a power system 202 in the second embodiment does not use a standalone integral value calculator 20, but instead employs a configuration in which an analog signal line is used to calculate the integral value of the difference between a target value V_ref of the DC bus line voltage and an actual DC bus line voltage V_bus.

[0033] The power system 202 includes DC / DC converter controllers 28 (28a, 28b, 28n) for each of the DC / DC converters 10 (10a, 10b, 10n). Each DC / DC converter controller 28 calculates an integral value ΔV / s of a difference ΔV between a target value V_ref of the voltage of the DC bus line and an actual voltage V_bus of the DC bus line, and outputs the integral value ΔV / s to an analog signal bus line via a resistor R. As a result, the voltage value of the analog signal bus line becomes equal to an average value ΔVave / s of an integral value of a difference between the target value V_ref of the voltage of the DC bus line and an actual voltage V_bus of the DC bus line calculated by each DC / DC converter controller 28. The difference value between the integral value ΔV / s of each DC / DC converter controller 28 and the average integral value ΔVave / s is proportionally processed by a gain Kp and then fed back to the integrator of the DC / DC converter controller 28. As a result, the integral value ΔV / s calculated by each DC / DC converter controller 28 is corrected so as to approach the average integral value ΔVave / s.

[0034] The DC / DC converter controller 28 proportionally processes the integral value ΔV / s with a gain K', and also proportionally processes the difference ΔV between the actual DC bus line voltage V_bus and the target value V_ref of the DC bus line voltage with a gain K, and adds these values ​​together to control the current output I_DC / DC of the DC / DC converter 10.

[0035] In this way, the integral values ​​ΔV / s of all DC / DC converter controllers 28 are approximately equal when the correction errors are ignored. Therefore, power system 202 can achieve the same operation as power system 200 as a distributed system.

[0036] As shown in Fig. 8, a simulation was performed using a model of a power system 202 consisting of two DC / DC converters 10, a DC / DC converter controller 28, and a distributed power source simulating the PV 14. The voltage measurement error V_error in the DC / DC converter 10b, the gain in each DC / DC converter controller 28, and the current I_PV of the PV 14 were set to the same conditions as in the simulation for the power system 100 shown in Fig. 1. The gains K_p1 and K_p2 for feedback were set to 1.

[0037] 9 shows the results of a simulation of the power system 202. It was confirmed that the voltage V_bus of the DC bus line changes with the change in the current I_PV, but returns to the original voltage by integral control in the DC / DC converter controller 28. In addition, the steady-state current distribution ratio I_DC / DC1:I_DC / DC2 became equal to the gain ratio K'_1:K'_2 of the integral control of each DC / DC converter controller 28. In this way, it was confirmed that the power system 202 performed the desired operation.

[0038] In particular, it is possible to suppress a delay in feedback of the integral value of the difference between the target value V_ref of the DC bus line voltage and the actual DC bus line voltage V_bus by distributing the processing in each DC / DC converter controller 28 without providing a common integral value calculator 20. Therefore, the control becomes smoother and more stable over time than when a common integral value calculator 20 is used.

[0039] [Third embodiment] As shown in Fig. 10, a power system 204 in the third embodiment does not use a single integral value calculator 20, but employs a configuration in which a communication line is used to calculate an integral value of a difference between a target value V_ref of a DC bus line voltage and an actual voltage V_bus of the DC bus line. The power system 204 includes a DC / DC converter controller 30 (30a, 30b, . . . 30n) for each of the DC / DC converters 10 (10a, 10b, . . . 10n). The power system 204 also includes an integral value average calculator 32 for calculating an average value ΔVave / s of integral values ​​ΔV / s of differences between the target value V_ref of a DC bus line voltage calculated by each DC / DC converter controller 30 and the actual voltage V_bus of the DC bus line.

[0040] Each DC / DC converter controller 30 calculates an integral value ΔV / s of the difference ΔV between the target value V_ref of the DC bus line voltage and the actual DC bus line voltage V_bus, and outputs the integral value ΔV / s to the communication line. The integral value average calculator 32 receives the integral values ​​ΔV / s calculated in each DC / DC converter controller 30 from the communication line, calculates their average value ΔVave / s, and outputs it to the communication line. The difference value between the integral value ΔV / s of each DC / DC converter controller 30 and the average integral value ΔVave / s is proportionally processed by a gain Kp, and then fed back to the integrator of the DC / DC converter controller 30. As a result, the integral value ΔV / s calculated in each DC / DC converter controller 30 is corrected so as to approach the average integral value ΔVave / s.

[0041] The DC / DC converter controller 30 proportionally processes the integral value ΔV / s with a gain K', and also proportionally processes the difference ΔV between the actual DC bus line voltage V_bus and the DC bus line voltage target value V_ref with a gain K, and adds these values ​​together to control the current output I_DC / DC of the DC / DC converter 10.

[0042] In this way, ignoring the correction error, the integral values ​​ΔV / s of all the DC / DC converter controllers 30 are approximately equal. Therefore, the power system 204 can achieve the same operation as the power system 200 as a distributed system.

[0043] As shown in Fig. 11, a simulation was performed using a model of a power system 204 composed of two DC / DC converters 10, a DC / DC converter controller 30, and a distributed power source simulating a PV 14. The voltage measurement error V_error in the DC / DC converter 10b, the gain in each DC / DC converter controller 30, and the current I_PV of the PV 14 were set to the same conditions as in the simulation for the power system 100 shown in Fig. 1. The feedback gains K_p1 and K_p2 were set to 1. In addition, the average value ΔVave / s of the integral value calculated by the integral value average calculator 32 was shared every 0.5 seconds to correct the integral error.

[0044] 12 shows the results of a simulation of the power system 204. It was confirmed that the voltage V_bus of the DC bus line changes with the change in the current I_PV, but returns to the original voltage by integral control in the DC / DC converter controller 30. In addition, the steady-state current distribution ratio I_DC / DC1:I_DC / DC2 became equal to the gain ratio K'_1:K'_2 of the integral control of each DC / DC converter controller 30. In this way, it was confirmed that the power system 204 performed the desired operation.

[0045] In particular, it is possible to suppress a delay in feedback of the integral value of the difference between the target value V_ref of the DC bus line voltage and the actual DC bus line voltage V_bus by distributing the processing in each DC / DC converter controller 30 without providing a common integral value calculator 20. Therefore, the control becomes smoother and more stable over time than when a common integral value calculator 20 is used.

[0046] In the present embodiment, an example in which the communication line is a wired system has been shown, but the communication line may be a wireless system.

[0047] [Other variations] Fig. 13 shows a modified example of the configuration for correcting the integral value to the average integral value. In the configuration of Fig. 13(a), proportional control of the gain Kp is performed according to the difference between the average integral value ΔVave / s and the calculated integral value ΔV / s, similar to the power system 202 of Fig. 7 and the power system 204 of Fig. 10. In this case, a steady-state deviation occurs. In the configuration of Fig. 13(b), proportional control of the gain Kp and integral control of the gain Ki are performed according to the difference between the average integral value ΔVave / s and the calculated integral value V / s. In this case, a steady-state deviation does not occur.

[0048] Moreover, in the configuration of FIG. 13(c), a general controller C is applied to the difference between the average integral value ΔVave / s and the calculated integral value ΔV / s. The controller C may be any controller that performs a calculation to reduce the difference between the average integral value ΔVave / s and the calculated integral value ΔV / s. Moreover, in the configuration of FIG. 13(d), a refresh process is performed so that the integral value ΔV / s becomes the average integral value ΔVave / s. The cycle of the refresh process may be appropriately set to a time period that allows the power system to operate stably.

[0049] Also, a configuration may be adopted that includes both an analog signal bus line like power system 202 and a communication line like power system 204. In this manner, in a system that includes a plurality of integral value sharing means, even if one of the sharing means breaks down, charging and discharging can be performed stably by using the other sharing means.

[0050] Fig. 14 is a flowchart of an example of control in a system having a plurality of integral value sharing means. In the example of Fig. 14, the control by the analog signal bus line is prioritized over the control by the digital communication line.

[0051] First, it is determined whether the integral control using the analog signal bus line is sound (step S10). If the integral control using the analog signal bus line is sound ("Yes" in step S10), control is performed by sharing an integral value using the analog signal bus line (step S12). If the integral control using the analog signal bus line is not sound ("No" in step S10), it is determined whether the integral control using the communication line is sound (step S14). If the integral control using the communication line is sound ("Yes" in step S14), control is performed by sharing an integral value using the communication line (step S16). If the integral control using the communication line is not sound ("No" in step S14), the integral control is stopped and only proportional control is performed (step S18).

[0052] In this way, the means for sharing the integral value are prioritized, and if the highest-ranked means fails, the system switches to a lower-ranked means. If all means fail, the integral control is stopped, and any load sharing is performed using only proportional control. This makes it possible to continue operating the entire power system even if it becomes impossible to share the integral value.

[0053] FIG. 15 shows the simulation results for a power system consisting of two DC / DC converters, a DC / DC converter controller, and a distributed power source simulating a PV system, in which only proportional control is performed based on the difference between the measured DC bus line voltage V_bus and the target value V_ref when it becomes impossible to share the integral value.

[0054] The voltage measurement error V_error, the gain in each DC / DC converter controller, and the PV current I_PV were set to the same conditions as in the simulation for the power system 100 shown in Fig. 1. Although there was a slight difference in the current distribution ratio because one of the bus line voltages of the DC / DC converters contained an error, the current distribution ratio I_DC / DC1:I_DC / DC2 of the two DC / DC converters was approximately the gain ratio K_1:K_2. In this way, it was confirmed that the desired current distribution ratio could be realized.

[0055] As described above, by multiplying the shared integral value by the gain of each DC / DC converter controller to obtain a current output, the gain ratio can be made to match the current ratio of each DC / DC converter, making it possible to share the load even when there is no voltage deviation on the DC bus line.

[0056] In addition, since the voltage with high power efficiency of the DC / DC converter can be matched with the voltage of the DC bus line, the power conversion efficiency of the DC / DC converter can be improved.

[0057] In addition, in conventional DC droop control, the design of the control system was complicated due to constraints such as maintaining upper and lower voltage limits including overshoot and undershoot voltages in addition to stability, and the need for a voltage deviation above a detectable level. In contrast, in the present invention, it is only necessary to guarantee stability and transient characteristics, making it easier to design the control system for the DC bus line.

[0058] By providing double redundancy using an analog signal bus line and a wired or wireless communication line, it is possible to stabilize control in the power system. Furthermore, even if integral control is stopped, it is possible to maintain power balance by proportional control based only on the voltage deviation. [Explanation of symbols]

[0059] 10 DC / DC converter, 12 DC / DC converter controller, 14 PV, 16 DC / DC converter with MPPT, 20 integral value calculator, 22 DC / DC converter controller, 24 AC power supply (commercial power supply), 26 AC / DC converter, 28 DC / DC converter controller, 30 DC / DC converter controller, 32 integral value average calculator, 100, 200, 202, 204 Power system.

Claims

1. a plurality of DC / DC converters connected in parallel to a DC bus line; and a plurality of DC / DC converter controllers that perform proportional-integral control of each of the DC / DC converters, In the plurality of DC / DC converter controllers, an integral value of a difference between an actual DC bus line voltage V_bus and a DC bus line voltage target value V_ref is shared, thereby arbitrarily controlling load sharing of the plurality of DC / DC converters; an analog signal bus line for sharing the integral value; A power system characterized in that each of the multiple DC / DC converter controllers is equipped with an integrator, shares an average integral value obtained by averaging the integral values ​​via the analog signal bus line, and performs an integration error correction process using the average integral value.

2. A power supply system comprising: a plurality of DC / DC converters connected in parallel to a DC bus line; and a plurality of DC / DC converter controllers that perform proportional-integral control of each of the DC / DC converters; In the plurality of DC / DC converter controllers, an integral value of a difference between an actual DC bus line voltage V_bus and a DC bus line voltage target value V_ref is shared, thereby arbitrarily controlling load sharing of the plurality of DC / DC converters; a wired or wireless communication line for sharing the integral value; an integral value average calculator that averages the integral values ​​calculated by a plurality of the DC / DC converter controllers to calculate an average integral value and outputs the average integral value to the communication line; A power system, characterized in that each of the plurality of DC / DC converter controllers is equipped with an integrator, the average integral value is shared via the communication line, and an integral error correction process is performed using the average integral value.

3. A power supply system comprising: a plurality of DC / DC converters connected in parallel to a DC bus line; and a plurality of DC / DC converter controllers that perform proportional-integral control of each of the DC / DC converters; In the plurality of DC / DC converter controllers, an integral value of a difference between an actual DC bus line voltage V_bus and a DC bus line voltage target value V_ref is shared, thereby arbitrarily controlling load sharing of the plurality of DC / DC converters; a first control means for sharing an average integral value obtained by averaging the integral values ​​using an analog signal bus line and performing an integration error correction process using the average integral value; a second control means for sharing an average integral value obtained by averaging the integral values ​​using a communication line and performing an integration error correction process using the average integral value; Equipped with 2. A power system comprising: a power supply means for supplying power to a power source in a power grid; a power supply means for supplying power to a power source in a power grid;

4. A power supply system comprising: a plurality of DC / DC converters connected in parallel to a DC bus line; and a plurality of DC / DC converter controllers for proportional-integral control of each of the DC / DC converters; In the plurality of DC / DC converter controllers, an integral value of a difference between an actual DC bus line voltage V_bus and a DC bus line voltage target value V_ref is shared, thereby arbitrarily controlling load sharing of the plurality of DC / DC converters; When the function of sharing the integral value fails, integral control in the plurality of DC / DC converter controllers is stopped.

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