Virtual synchronous power generation system in which distributed power supply and plurality of storage batteries are connected on DC side

Abstract

To provide a virtual synchronous generator, a virtual synchronous power generation system, and a power supply method for stabilizing power output to a power system of a renewable energy power generation system.SOLUTION: A virtual synchronous generator system (VSG) includes a secondary battery and a capacitor each including a DC-DC converter, and a controller that controls the DC-DC converter. The VSG is connected to a DC side in a power system into which a distributed generator (DG) is introduced via a system interconnection inverter that converts DC into AC. The power system is a power transmission system in which power output from the DG (DG output power) is converted from direct current to alternating current by a system interconnection inverter, and the power is supplied to a grid of a city, a residence, or the like.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a virtual synchronous generator that provides inertia and synchronizing force to a distributed power source in order to stabilize the power output to a power grid of a renewable energy power generation system, and more particularly to an output stabilization device that stabilizes the power output to a power grid by cooperatively utilizing a controller for simulating the dynamic characteristics of a renewable energy power generation device and a synchronous generator, and multiple power storage devices. [Background technology]

[0002] In recent years, renewable energy power generation such as solar and wind power has been attracting global attention because it does not use fossil fuels and does not emit greenhouse gases. Analysis has shown that by 2050, 70% of the world's energy supply will be supplied by solar and wind power. In Japan, the government has declared its aim to achieve carbon neutrality, which means reducing greenhouse gas emissions to zero overall, and the introduction of renewable energy power generation is expected to expand. As a result, it is predicted that the proportion of renewable energy power generation, which is a distributed power source, will increase as an alternative to thermal and hydroelectric power generation.

[0003] Renewable energy generation, which is a distributed power source, is connected to the power grid via a grid-connected inverter. However, grid-connected inverters do not have the synchronizing power and inertia of synchronous generators, so as the proportion of distributed power sources increases, the burden on the grid's synchronous generators increases. Furthermore, since the amount of power generated by renewable energy generation fluctuates depending on natural conditions such as weather, situations can arise where the amount of power generated does not match the amount of power consumed. When this mismatch occurs, it may become impossible to maintain the grid frequency, and there are concerns that the expansion of distributed power sources will lead to grid instability.

[0004] For this reason, a virtual synchronous generator (VSG) equipped with inertia and synchronizing force has been proposed to promote the stabilization of the power system. A VSG consists of a controller that simulates the dynamic characteristics of a synchronous generator and an energy storage system (ESS), and is thought to enable the expansion of the introduction of distributed power sources without reducing the inertia of the power system.

[0005] However, previous research has focused on parallel operation of VSGs and synchronous generators and controller design, and has not addressed ESS control or output fluctuations of distributed power sources. Because controller design is affected by the type and capacity of the storage battery used in the ESS, a design that includes the ESS is necessary to put VSGs into practical use.

[0006] An ESS is composed of power converters such as storage batteries and DC-DC converters, and the VSG simulates inertia by charging and discharging the difference between the energy generated by the distributed power sources and the output to the grid. Therefore, as mentioned above, the type and capacity of the storage batteries used in the ESS affect the VSG controller design, so they must be carefully considered when introducing them. When selecting a storage battery, it is desirable to have both high power density and energy density. However, power density and energy density vary depending on the type of storage battery, and their lifespans also differ, so these characteristics and costs must be taken into consideration when selecting a storage battery.

[0007] Generally, storage batteries used in VSGs include lithium-ion batteries (LiBs) and electric double layer capacitors (EDLCs). LiBs have a high energy density but a low power density, making them suitable for situations with small fluctuations in power generation and for compensating for power demand during normal times, but they may not be able to compensate for sudden fluctuations in power generation or peak power demand. On the other hand, EDLCs have a high power density but a low energy density, which is the opposite of LiBs.

[0008] For these reasons, if a single battery is used, the battery capacity must be increased to meet both the power and energy specifications. However, the larger the battery capacity, the higher the installation cost, which may lead to an increase in the installation cost of the VSG. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] J. Fang, Y. Tang, H. Li and X. Li, “A Battery / Ultracapacitor Hybrid Energy Storage System for Implementing the Power Management of Virtual Synchronous Generators,” in IEEE Transactions on Power Electronics, vol. 33, no. 4, pp. 2820-2824, April 2018 [Non-patent document 2]

[17] C. Sun, SQ Ali, G. Joos and F. Bouffard, “Design of Hybrid-Storage-Based Virtual Synchronous Machine With Energy Recovery Control Considering Energy Consumed in Inertial and Damping Support,” in IEEE Transactions on Power Electronics, vol. 37, no. 3, pp. 2648-2666, March 2022 Summary of the Invention [Problem to be solved by the invention]

[0010] Distributed generators (DGs), such as conventional renewable energy generation, are introduced into the power grid via inverters. However, grid-connected inverters lack the synchronizing power and inertia of synchronous generators, and increasing the proportion of distributed generators places a greater burden on synchronous generators in the grid. Furthermore, renewable energy generation is subject to natural conditions such as weather, which can lead to mismatches between power generation and consumption in the grid. This mismatch can lead to grid frequency instability, and the expansion of DG deployment can lead to grid instability. To address this issue, virtual synchronous generators (VSGs), which incorporate inertia and synchronizing power into DGs, have been proposed to stabilize the power grid. However, when using a single storage battery, the battery's capacity must be increased to meet both power and energy specifications. However, since the cost increases with increasing battery capacity, there is still room for further consideration regarding the introduction cost of VSGs. [Means for solving the problem]

[0011] As a result of careful consideration by the inventors to solve the above problems, they discovered that by connecting a converter to each of the two storage batteries, the LiB and the EDLC, which have opposing characteristics, and enabling bidirectional exchange of power, the capacity of the storage batteries can be reduced, and that the amount of electricity generated by the DG, which fluctuates due to weather changes, can be smoothed out by the storage batteries, leading to stabilization of the system, and they were able to complete the present invention. [Effects of the Invention]

[0012] The configuration of the VSG proposed in this invention is shown in Figure 3.3. The DG, LiB, and EDLC are connected in parallel on the DC side, and one VSG system uses one inverter. A DC-DC converter is connected to the LiB and EDLC to allow bidirectional power exchange. The DC-DC converter allows flexibility in the power distribution of the storage battery, which is expected to lead to the miniaturization of the storage battery. Furthermore, although the amount of power generated by the DG fluctuates due to weather, the fluctuations can be compensated for and smoothed out by the ESS, leading to grid stabilization. [Brief explanation of the drawings]

[0013] [Figure 3.3] 1 is a diagram showing an example of the configuration of a virtual synchronous power generation system in which a distributed power source and a storage battery are connected on the DC side in an embodiment of the present invention. [Figure 3.4] FIG. 2 is a diagram illustrating a VSG controller that is a grid-connected inverter control system according to an embodiment of the present invention. [Figure 3.5] FIG. 2 is a diagram illustrating an EDLC controller that is a grid-connected inverter control system according to an embodiment of the present invention. [Figure 3.6] FIG. 2 is a diagram illustrating a Lib controller that is a grid-connected inverter control system according to an embodiment of the present invention. [Figure 3.7] FIG. 2 is a diagram showing a circuit relating to an EDLC that is a grid-connected inverter control system in an embodiment of the present invention. [Figure 3.8] FIG. 2 is a diagram showing an EDLC block diagram of a grid-connected inverter control system according to an embodiment of the present invention. [Figure 3.9] FIG. 2 is a diagram showing a circuit related to Lib, which is a grid-connected inverter control system in an embodiment of the present invention. [Figure 3.10] FIG. 1 shows a block diagram 1 of Lib, which is the control system of Lib. [Figure 3.11] This is a diagram showing a block diagram 2 of Lib, which is the control system of Lib. [Figure 3.12] This is a diagram showing a block diagram 3 of Lib, which is the control system of Lib. [Figure 3.13]FIG. 4 is a block diagram 4 of Lib, which is the control system of Lib. [Figure 3.14] FIG. 5 is a block diagram 5 of Lib, which is the control system of Lib. [Figure 3.15] FIG. 1 is a diagram showing a Bode diagram relating to a simulation of an EDLC control system. [Figure 3.16] FIG. 1 is a diagram showing a Bode diagram relating to an EDLC control system simulation. [Figure 3.17] FIG. 1 is a diagram showing a Bode diagram relating to an EDLC control system simulation. [Figure 3.18] FIG. 1 is a diagram showing a Bode diagram relating to an EDLC control system simulation. [Figure 3.19] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 3.20] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 3.21] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 3.22] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 3.23] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 3.24] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 3.25] FIG. 10 is a diagram showing a Bode diagram relating to a Lib control system simulation. [Figure 4.1] FIG. 10 is a diagram showing a configuration for performing a system response simulation when a load fluctuation occurs on the system side. [Figure 4.2] FIG. 10 is a diagram showing a VSG output simulation. [Figure 4.3] FIG. 10 is a diagram showing a VSG1 output. [Figure 4.4] FIG. 10 is a diagram showing an ESS output simulation. [Figure 4.5] FIG. 10 is a diagram showing Lib output. [Figure 4.6] FIG. 2 is a diagram illustrating the voltage of a distributed power source. [Figure 4.7] FIG. 2 is a diagram illustrating the frequency of a power transmission and distribution system. [Figure 4.8] FIG. 2 is a diagram illustrating the output of a distributed power source. [Figure 4.9] FIG. 10 is a diagram showing a simulation of the VSG1 output. [Figure 4.10] FIG. 10 is a diagram showing an ESS output simulation. [Figure 4.11] FIG. 10 is a diagram showing the charging rate of an EDLC. [Figure 4.12] FIG. 10 is a diagram showing the charging rate of Lib. [Figure 4.13] FIG. 10 is a diagram showing the output of Lib. [Figure 4.14] FIG. 2 is a diagram illustrating the voltage of a distributed power source. [Figure 4.15] FIG. 2 is a diagram illustrating the frequency of a power transmission and distribution system. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes embodiments of the present invention. The scope of the present invention is not limited to these descriptions, and other than the following examples, the present invention can be implemented with appropriate modifications within the scope that does not depart from the spirit of the present invention.

[0015] The configuration of the virtual synchronous generation system (VSG) of the present invention is shown in Figure 3.3. The VSG has a secondary battery and a capacitor, each equipped with a DC-DC converter, and a controller (also referred to as "control means") that controls the DC-DC converter. The VSG is also connected to the DC side of a power system that has distributed generation (DG) via a grid-connected inverter that converts DC to AC. This power system is a power transmission system in which the power output from the DG (hereinafter referred to as "DG output power") is converted from DC to AC by the grid-connected inverter and supplied to the grid of a city, residence, etc.

[0016] Figure 3.3 shows an example of a VSG connected in parallel to the DC side of a power grid. In this invention, the DC side to which the VSG is connected refers to the power grid on the side of the grid-connected inverter that supplies DC input power to the inverter, and the AC side refers to the power grid on the side where the inverter outputs AC power to the grid.

[0017] Figure 3.3 also shows a configuration in which a lithium-ion battery (LiB) is used as the secondary battery and an electric double-layer capacitor (EDLC) is used as the capacitor. The secondary battery is not limited to lithium-ion batteries; other applicable batteries include lead-acid batteries, nickel-cadmium batteries, metallic lithium batteries, and sodium-ion batteries. The capacitor is also not limited to electrolytic double-layer capacitors; various other types of capacitors are also applicable, including electrolytic capacitors and film capacitors.

[0018] With the VSG of this invention, by connecting it to the DC side of the power grid, only one inverter outputs power to the AC side. While conventional systems required the installation of multiple inverters, the VSG of this invention makes it possible to significantly simplify power grids using distributed power sources. A DC-DC converter is also connected to the LiB and EDLC to allow for bidirectional power exchange. The DC-DC converter allows for flexibility in the power distribution of the storage battery, which leads to the miniaturization of the storage battery. Furthermore, while the amount of power generated by the DG fluctuates due to weather conditions, the ESS can compensate for and smooth out these fluctuations, stabilizing the grid.

[0019] This section describes the proposed control system for the VSG with HESS. The roles of each controller in this system are as follows: The grid-connected inverter controls the VSG controller and the LiB SoC. The EDLC control system controls the high frequency components of the generated power, the surplus or shortage of power during load fluctuations, and the voltage of the EDLC itself. The LiB control system controls the DC link voltage.

[0020] Regarding the role of the VSG of the present invention, by arranging the VSG on the DC side, it can be used more effectively for power supply than the AC side, which is often seen in conventional technology. Typically, in power systems with distributed generators (DGs), DC link capacitors are arranged to maintain the DC link voltage in order to stabilize the output voltage of the distributed generators. They are also used for distributed generators such as renewable energy power generation to respond to load fluctuations due to natural environments, etc. However, in conventional VSG AC side arrangements that compensate for the stability of the power system using this DC link capacitor, although the VSG has a capacitor, it is difficult to directly respond to fluctuations in the DC link voltage that occur on the DC side, and there is room for further consideration in maintaining stable output power.

[0021] Through extensive research by the inventors of the present invention, it has been discovered that by arranging the VSG on the DC side of the power system, like the DG, the secondary batteries and capacitors of the VSG, which are conventionally arranged on the AC side, can be made to act effectively against fluctuations in the DC link voltage.

[0022] The control means for the secondary battery of the VSG placed on the DC side controls the operation of the secondary battery to compensate for load fluctuations in the DG output power based on the DC link voltage value of the DC link capacitor connected to the power grid. This configuration makes it possible to respond directly to changes in the DC power grid, and by making it possible to use secondary batteries with high energy density, it is possible to improve responsiveness to load fluctuations and the ability to absorb power fluctuations.

[0023] The controller of the grid-connected inverter (hereinafter also referred to as the "VSG controller") controls the output voltage to the AC power grid based on the remaining capacity of the secondary battery. In this configuration, by installing the secondary battery on the DC side, the remaining capacity is efficiently managed while taking into account the secondary battery's response to the DC link voltage, providing a more stable power supply in response to load fluctuations.

[0024] In addition, a low-pass filter (LPF) can be installed in the power grid, and a portion of the output from the DG can be passed through the LPF and controlled by the controller of the grid-connected inverter as the DG output power. This configuration enables control in the low-frequency range, where load fluctuations are more gradual than in the high-frequency range, and also allows for a more stable power supply because power is compensated for by secondary batteries with high energy density.

[0025] The capacitor control means controls the capacitor output based on the capacitor's own output voltage to compensate for the output power from the grid-connected inverter to the AC side. As mentioned above, capacitors are generally used as DC link capacitors in power systems. However, there is room for improvement in effectively utilizing the performance of capacitors, which generally have high power density. Taking this into consideration, the present invention provides a configuration in which a capacitor is installed on the DC side where power is generated to address the impact of load fluctuations on power generation and to more efficiently handle and store surplus power, such as power generated during high power generation or power consumption. This configuration allows for more effective utilization of the capacitor's performance without considering power loss during power transmission, compared to conventional configurations in which the capacitor is installed on the AC side. Furthermore, in addition to the compensation of the DG output power using the secondary battery described above, effective compensation by the capacitor allows for a stable power supply.

[0026] It is also possible to provide a high-pass filter (HPF) in the power grid and use a capacitor control unit to control a portion of the DG's output power, passing it through the HPF. In this case, the capacitor can share power control in the high-frequency range, where load fluctuations cause subtle fluctuations, contributing to greater power stabilization. Furthermore, by using the low-pass filter in combination with the above-mentioned low-pass filter, the performance role of the grid-connected inverter can be shared, and by linking with the grid-connected inverter, more effective and efficient power control is possible across the entire frequency range, from low to high. Each control system will be described in detail below.

[0027] First, we will describe the control system of the grid-connected inverter. Figure 3.4 shows the proposed VSG controller. Unlike the conventional VSG controller shown in equation 2.10, the grid-connected inverter in the proposed system uses a VSG controller based on equation 3.3.

number

number

number

[0028] Finally, the control system for the LiB is shown in Figure 3.6. In Figure 3.6, v2, i2, and V2 are the DC link voltage, the current flowing from the LiB, and the reference operating point of the DC link voltage, respectively. The controlled object and controller are the DC-DC converter and PI controller connected to the LiB, as with the EDLC. The LiB is controlled to maintain the DC link voltage. In addition, as described in Section 3.3.2, the damping coefficient can be virtually changed by current feedback, thereby suppressing oscillations in the DC link voltage. The SoC is controlled by a VSG controller.

[0029] A model is derived to design the controller for each ESS. Figure 3.7 shows the circuit related to the EDLC. The state equation is derived by applying the state averaging method

[16] to this circuit. Note that S1 and S2 represent switches that operate in a complementary manner, and R1 represents the internal resistance of inductor L1. Also, although a capacitor is usually connected to the output stage, we assume that the voltage is properly controlled and treat it as a constant value. Regarding Figure 3.7, the equation of state for state I (S1 on, S2 off) is

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

[0030] Find the state equation for the circuit shown in Figure 3.9 in the same way as before. Let R2 be the internal resistance of inductor L2, and Po be the energy flowing out of capacitor C2. Regarding Figure 3.9, the equation of state for state I (S1 on, S2 off) is

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

[0031] In this section, we design the parameters of the proposed control system. The design procedure is as follows: 1. Determine the capacitance of the EDLC, LiB, and DC link capacitor. 2. Determine the time constant T1 of the LPF used in the VSG controller. 3. EDLC controller parameter Kp1 ,K i1 ,K u ,Determine the time constant T2 of the HPF 4. Controller parameter K of LiB p2 ,K i2 ,K † and K of the VSG controller e Determine. 5. A simulation was performed when the load on the grid side fluctuated, and the DC link voltage V dc Check the decreasing value of and increase the capacitance of the DC link capacitor if the inverter is operating in overmodulation mode. 6. Conduct simulations of power generation fluctuations, and if the EDLC or LiB capacity is insufficient, redesign from scratch. Follow the steps above to actually design the parameters.

[0032] To determine the parameters of the control system, it is first necessary to determine the capacity of the storage battery. The reference power is set to 0.5 MW, and the rated output of the inverter is set to 0.3 pu. The capacity of the EDLC is determined by the capacitance and rated voltage, so the capacitance is set to 200 F and the rated voltage to 300 V. Furthermore, from equation 3.2, the rated capacity of the LiB is determined by the C rate and the rated output of the LiB, so the C rate is set to 3, the rated output is set to 0.143 pu, and the capacitance of the DC link capacitor is set to 3000 μF and V dc is 1500 V.

[0033] Next, T1 is determined. The LPF is connected to smooth out fluctuations in the generated power, so it must be designed in accordance with the technical requirements for grid connection. However, in this invention, we do not consider these technical requirements and set T1 = 100. As shown in

[22] , the fluctuation smoothing controller has a significant effect on the rated capacity of the battery, so further study is required.

[0034] After determining the capacitance of the EDLC, LiB, and DC link capacitor, and the time constant of the LPF, the EDLC controller parameters are determined. The switching frequency of the DC-DC converter is set to 5 kHz. As stated in Section 3.2.2, the EDLC is controlled to compensate for high-frequency components. Therefore, the parameters are determined so that the high-frequency range of the frequency response of G5(s) in equation 3.31 is wide. However, if the high-frequency range is made too wide, the switching frequency will be included in the output as noise, so the gain is set to -3 dB at about 1 / 5 of the switching frequency. K i1 = 1,K u = 1 and K p1 Figure 3.15 shows the frequency response when the proportional gain K p1 By increasing K, the high frequency range can be widened. p1 = 10. Next, K p1 = 10,K u = 1 and K i1 The frequency response when is changed is shown in Figure 3.16. i1 By changing the frequency, both the gain and phase change slightly in the range from 10 Hz to 103 Hz. i1 Increasing increases the gain resonance. K p1 = 10,K i1 = 100 for T2 and K u First, we will explain why an HPF is connected to the EDLC controller. From Figure 3.5 and equation 3.23, P pu dg From v pu The transfer function up to 1 is T2 = 100.

number

number

[0035] Next, we determine the parameters of LiB. † As mentioned above, K † The damping coefficient of the controlled object can be virtually changed by using the following formula.

number

number

number

number

number

[0036] The parameters are designed as described above, and simulations are performed to confirm whether the design is appropriate. The results of simulations using the designed parameters are shown in the next chapter. The designed parameters are shown in Table 3.1. [Table 3.1] [Example]

[0037] In this chapter, we verify the proposed system designed in the previous chapter when the power generation amount of the load-varying DG changes. We also perform a similar verification on a conventional system that uses only LiBs as the ESS storage battery, and compare it with the proposed method. In this invention, simulations were performed using MATLAB (registered trademark) / Simulink 2022a.

[0038] In this section, we verify the case where a load fluctuation occurs on the grid side. A load of 0.075 MW is applied at 100 s, and the system response is confirmed. Figure 4.1 shows the configuration for the simulation. f1 ,L f2 ,C f1 ,C f2 are the inductance and capacitance of the filter, respectively, and L g1 ,L g2 is the inductance of the transmission line. VSG1 is the VSG using the proposed method or the conventional method, VSG2 is connected to an ideal DC power source, and the DG power generation power of VSG1 is constant at 0.15 MW (0.3 pu). The parameters used are shown in Tables 3.1 and 4.1. The simulation results are shown in Figure 4.2 and subsequent figures. [Table 4.1] The parameters for VSG1 and VSG2 in the proposed method were the same as those in the conventional method. Therefore, as shown in Figures 4.3 and 4.7, there was little difference in VSG output and system frequency. On the other hand, as shown in Figure 4.6, the DC link voltage decreased relatively significantly during load fluctuations in the conventional method. This is because when power at frequencies higher than the LiB's bandwidth is output from the VSG, the DC link voltage decreases, compensating for this. In contrast, the proposed method uses EDLCs to compensate for the high-frequency power that the LiB cannot compensate for, resulting in a smaller decrease in DC link voltage. As shown in Figures 4.4 and 4.5, in the proposed method, the high-frequency component of the power shortage due to load fluctuations is compensated for by the EDLC. In contrast, in the conventional method, the LiB compensates for all of the power, resulting in higher output during fluctuations. The maximum LiB power in the proposed method and conventional method is 0.0285 pu and 0.111 pu, respectively. The maximum LiB power in the proposed method is 25.7% of that in the conventional method.

[0039] In this section, we verify the case where the generated power fluctuates. The simulation configuration is shown in Figure 4.1, and the 0.075 MW load is left disconnected. We will confirm the system response when the DG generated power of VSG1 fluctuates as shown in Figure 4.8. As in the previous section, the parameters are shown in Tables 3.1 and 4.1. Figure 4.9 and subsequent figures show the simulation results. Figure 4.10 confirms that the EDLC compensates for the high-frequency components of the generated power fluctuations, and the LiB compensates for the low-frequency components. Figures 4.11 and 4.12 show the SoC of the EDLC and LiB. Figure 4.12 confirms that the LiB SoC fluctuates more in the proposed method. This is thought to be because the rated output of the LiB is different between the proposed method and the conventional method, but Ke is the same value. Figure 4.15 also shows that the grid frequency fluctuates more in the proposed method, which is thought to be affected by the LiB SoC. As for the link voltage, as shown in Figure 4.14, the proposed method has smaller fluctuations. Finally, Figure 4.1 compares the maximum power consumption of the LiB between the proposed method and the conventional method. The maximum power consumption of the LiB in the proposed method was 0.144 pu, while that in the conventional method was 0.221 pu. Therefore, the maximum power consumption of the LiB in the proposed method is 65.2% of that in the conventional method. [Industrial Applicability]

[0040] We provide a virtual synchronous generator for stabilizing the power output to the power grid of a renewable energy power generation system. This invention proposes an output stabilization device that mimics the dynamic characteristics of a renewable energy power generation device and a synchronous generator, and stabilizes the output by cooperatively using a controller and multiple power storage devices. Specifically, two storage batteries, an LiB and an EDLC, are used as a hybrid ESS, and their opposing characteristics are utilized to reduce the storage battery capacity and reduce the introduction cost of the VSG.

Claims

1. A virtual synchronous power generation system comprising a secondary battery and a capacitor, each of which includes a DC / DC converter and a control means, and wherein the secondary battery and the capacitor are connected to the DC side of an electric power system to which a distributed power source is introduced via a grid-connected inverter.

2. 2. The virtual synchronous power generation system according to claim 1, wherein the grid-connected inverter has a control means, and the control means controls the output power of the distributed power sources based on the remaining capacity of the secondary battery, and compensates for and stabilizes the power in a low frequency range of the output power.

3. 3. The virtual synchronous power generation system according to claim 1, wherein the control means for the capacitor controls the output voltage in a high frequency range of the output power from the grid interconnection inverter to be compensated and stabilized based on the remaining capacity of the secondary battery and the voltage value of the capacitor itself.

4. 3. The virtual synchronous power generation system according to claim 1, wherein the control means for the secondary battery controls the secondary battery to maintain a DC link voltage value based on a DC link voltage value in the power grid.

5. 4. The virtual synchronous power generation system according to claim 3, wherein the control means for the secondary battery controls the secondary battery to maintain the DC link voltage value based on the DC link voltage value in the power grid.

6. A power supply method using a virtual synchronous power generation system, comprising a secondary battery and a capacitor, each of which includes a DC / DC converter and a control means, said secondary battery and capacitor being connected to the DC side of an electric power system to which a distributed power source is introduced via a grid-connected inverter, and wherein the control means of said capacitor controls to compensate and stabilize the voltage in the high frequency range of the output power from said grid-connected inverter based on the remaining capacity of said secondary battery and the voltage value of said capacitor itself.

7. 7. The power supply method using a virtual synchronous power generation system according to claim 6, wherein the control means of the grid-connected inverter controls the output power of the distributed power source based on the remaining capacity of the secondary battery, and compensates for power in a low frequency range of the output power to output it stably.

8. 8. The power supply method using a virtual synchronous power generation system according to claim 6 or 7, wherein the control means for the capacitor controls to compensate and stabilize the output voltage in a high frequency range of the output power from the grid-connected inverter based on the remaining capacity of the secondary battery and the voltage value of the capacitor itself.

9. 8. The power supply method using a virtual synchronous generation system according to claim 6, wherein the control means for the secondary battery controls the secondary battery to maintain a DC link voltage value based on a DC link voltage value in the power grid.

10. 9. The power supply method using a virtual synchronous power generation system according to claim 8, wherein the control means for the secondary battery controls the secondary battery to maintain a DC link voltage value based on a DC link voltage value in the power grid.

Images