A Bidirectional Virtual Inertia Control Method, Device and Medium for a Power Distribution System

Abstract

The present invention provides a method, device and medium for bidirectional virtual inertia control of a distribution system. The method includes: obtaining key data of the distribution system and selecting the magnitudes of virtual capacitance and virtual inertia parameters; determining the power flow direction between the AC subnet and the DC subnet in the AC-DC hybrid distributed power grid-connected distribution system; selecting a corresponding inertial support energy calculation formula according to the determined power flow direction, and using the obtained key data of the distribution system and the selected virtual capacitance and virtual inertia to calculate the power data for auxiliary inertia support; combining the auxiliary inertia support power command and the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and realizing bidirectional virtual inertia control of the AC-DC hybrid distributed power grid-connected distribution system by tracking this reference value. The present invention is beneficial to improving the inertial support ability of the AC-DC hybrid distribution system and ensuring the stable operation of the system.

Description

Technical Field

[0001] The present invention relates to the field of power system inertia support, and particularly to a bidirectional virtual inertia control method, device and medium for a distribution system. Background Art

[0002] In recent years, with the depletion of traditional fossil energy and the aggravation of environmental pollution, the energy problem has become a severe challenge for the current economic and social development. Distributed generation such as photovoltaic and wind power, as clean and environmentally friendly flexible power generation technologies, has become the focus of attention of governments, industries and academia around the world. Distributed generation has the advantages of local consumption, low construction cost, economic and environmental protection, etc., and the grid connection voltage level of the unit is generally below 10 kV. Flexibly integrating distributed generation with an energy storage system to form an AC / DC hybrid distribution system is conducive to maximizing the utilization efficiency of clean and renewable energy and is an important measure to achieve green power generation and energy conservation and emission reduction.

[0003] Due to the intermittency and uncertainty of distributed generation in the AC / DC hybrid distribution system, power fluctuation has become the main problem affecting the stable operation of the system. At the same time, the inertial performance of the hybrid distribution system dominated by multiple converters is relatively low, making it impossible for distributed generation to improve the transient characteristics of frequency and voltage like traditional synchronous generators when the system faces external power fluctuations. Especially when the superior power grid is unable to provide any inertial support, both the AC grid and the DC grid are affected by external power source disturbances. To improve the inertial support ability, existing research has proposed the concept of virtual inertia by simulating the electromagnetic and mechanical equations of synchronous generators. When the system power fluctuates, its transient response can be similar to that of a synchronous generator. However, for an AC / DC hybrid distribution system, using virtual inertia control for distributed generation connected in parallel within the same bus may cause power oscillation problems. Therefore, the bidirectional AC / DC converter between the AC and DC sub-grids plays a crucial role in improving the inertial support ability of the distribution system and ensuring the stable operation of the distribution system, but existing research generally ignores the bidirectional inertial support ability and demand between the AC and DC sub-grids. Therefore, how to achieve bidirectional virtual inertia control of the AC / DC hybrid distributed power grid-connected distribution system is a technical difficulty in the future field of new energy active support. Summary of the Invention

[0004] In view of this, the present invention proposes a bidirectional virtual inertia control method and device for a power distribution system. Based on the dynamic power balance of a bidirectional AC / DC converter, a bidirectional virtual inertia control method, device and medium based on virtual capacitance and virtual inertia are proposed. By judging the power flow direction between the AC subnet and the DC subnet in an AC / DC hybrid distributed power grid-connected power distribution system, the magnitude of the power data for auxiliary inertia support is calculated, and this power command is combined with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet. By tracking this reference value, bidirectional virtual inertia control of the AC / DC hybrid distributed power grid-connected power distribution system is achieved.

[0005] A bidirectional virtual inertia control method for a power distribution system includes the following steps:

[0006] Obtain key data of the power distribution system and select the magnitudes of virtual capacitance and virtual inertia parameters;

[0007] Judge the power flow direction between the AC subnet and the DC subnet in the AC / DC hybrid distributed power grid-connected power distribution system;

[0008] According to the judged power flow direction, select the corresponding inertia support energy calculation formula, and use the obtained key data of the power distribution system and the selected virtual capacitance and virtual inertia to calculate the power data for auxiliary inertia support;

[0009] Combine the obtained power data for auxiliary inertia support with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and use a PI controller to make the actual bidirectional power between the AC subnet and the DC subnet track the bidirectional power reference value, so as to achieve bidirectional virtual inertia control of the AC / DC hybrid distributed power grid-connected power distribution system.

[0010] Further, the key data of the power distribution system includes the DC capacitor C of the bidirectional AC / DC converter dc , the frequency f of all AC subnets ac , and the DC subnet voltage U dc .

[0011] Further, the judgment of the power flow direction between the AC subnet and the DC subnet in the AC / DC hybrid distributed power grid-connected power distribution system specifically includes: when P bi_con is positive, it is determined that the power is transmitted from the AC subnet to the DC subnet; when P bi_con is negative, it is determined that the power is transmitted from the DC subnet to the AC subnet; where P bi_con is the power transmitted from the AC subnet to the DC subnet.

[0012] Further, the inertia support energy calculation formula is:

[0013]

[0014] In the formula, is the inertia support energy; when P bi_con is positive, virtual inertia energy is simulated according to the deviation of the DC voltage to support the voltage recovery; when P bi_con is negative, virtual inertia energy is simulated according to the frequency deviation to support the AC frequency recovery.

[0015] Furthermore, according to Equation (1), the power data P w for auxiliary inertia support is obtained as:

[0016]

[0017] A bidirectional virtual inertia control device for a distribution system, comprising:

[0018] A data acquisition module, configured to acquire key data of the distribution system and select the magnitudes of virtual capacitance and virtual moment of inertia parameters;

[0019] A power flow direction judgment module, configured to judge the power flow direction between the AC subnet and the DC subnet in an AC / DC hybrid distributed power grid-connected distribution system;

[0020] A power command calculation module, configured to select a corresponding inertia support energy calculation formula according to the judged power flow direction, and calculate the power data for auxiliary inertia support by using the key data of the distribution system and the selected virtual capacitance and virtual moment of inertia;

[0021] A bidirectional virtual inertia control module, configured to combine the obtained power data for auxiliary inertia support with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and make the actual bidirectional power between the AC subnet and the DC subnet track the bidirectional power reference value through a PI controller, so as to realize the bidirectional virtual inertia control of the AC / DC hybrid distributed power grid-connected distribution system

[0022] Furthermore, the key data of the distribution system includes the DC capacitance C dc of the bidirectional AC / DC converter, the frequency f ac of all AC subnets, and the DC subnet voltage U dc .

[0023] Furthermore, the power flow direction judgment module judges the power flow direction between the AC subnet and the DC subnet in the AC / DC hybrid distributed power grid-connected distribution system, specifically including: when P bi_con is positive, it is determined that the power is transmitted from the AC subnet to the DC subnet; when P bi_conWhen it is negative, it is determined that the power is transmitted from the DC subnet to the AC subnet; where P bi_con is the power transmitted from the AC subnet to the DC subnet.

[0024] Furthermore, the formula for calculating the inertia support energy is:

[0025]

[0026] In the formula is the inertia support energy; when P bi_con is positive, the virtual inertia energy is simulated according to the deviation of the DC voltage to support the voltage recovery; when P bi_con is negative, the virtual inertia energy is simulated according to the frequency deviation to support the recovery of the AC frequency.

[0027] Furthermore, according to Equation (1), the power command P w for the auxiliary inertia support is:

[0028]

[0029] A non-transitory computer-readable storage medium stores a computer program, which, when executed by a processor, implements the two-way virtual inertia control method for the distribution system described above.

[0030] When a disturbance occurs in the system, the present invention can utilize the power support capability of the sub-microgrid on the side of the bidirectional AC / DC converter to provide support for the rapid recovery of the system, enhance the inertia interaction support capability of the hybrid distribution system, and improve the stable operation capability of the system to cope with faults and disturbances. On the PSCAD / EMTDC platform, a simulation model of the AC-DC distribution system is built to verify the effectiveness of the proposed control scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of an AC-DC hybrid distributed power grid-connected distribution system according to an embodiment of the present invention;

[0032] Figure 2 is an overall two-way virtual inertia control block diagram of a bidirectional AC / DC converter according to an embodiment of the present invention;

[0033] Figure 3 is a system frequency response diagram under different controls according to an embodiment of the present invention;

[0034] Figure 4 is a system DC voltage response diagram under different controls according to an embodiment of the present invention;

[0035] Figure 5 is a system DC voltage response diagram under different controls according to an embodiment of the present invention;

[0036] Figure 6 It is the system DC voltage response diagram under different controls in the embodiments of the present invention. Detailed implementation manners

[0037] The following further describes the present application in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present application.

[0038] The first aspect of the present invention provides a two-way virtual inertia control method for a distribution system, including the following steps:

[0039] Step 1: Obtain the key data of the distribution system and select the magnitudes of the virtual capacitance and virtual moment of inertia parameters. Specifically, select the AC / DC hybrid distributed power grid-connected distribution system as the research object. The network topology structure of the system is as Figure 1 shown. Obtain the key parameters of the system, including the DC capacitance C dc of the bidirectional AC / DC converter, the frequency f ac of all AC subnets, and the DC subnet voltage U dc , and select the key control parameters, the virtual capacitance C vir and the virtual moment of inertia J vir .

[0040] Step 2: Judge the power flow direction between the AC subnet and the DC subnet in the AC / DC hybrid distributed power grid-connected distribution system. Here, define P bi_con as the power transmitted from the AC subnet to the DC subnet. When the power is transmitted from the AC subnet to the DC subnet, P bi_con is positive; when the power is transmitted from the DC subnet to the AC subnet, P bi_con is negative.

[0041] Step 3: Select the corresponding inertia support energy calculation formula according to the power flow direction judged in Step 2, and use the key data of the distribution system obtained in Step 1 and the selected virtual capacitance C vir and virtual moment of inertia J vir to calculate the power data P w for auxiliary inertia support.

[0042] The system inertia support energy can be obtained from the corresponding AC and DC subnets through the bidirectional AC / DC converter. For example, when a disturbance occurs in the DC subnet and causes DC voltage fluctuations, the bidirectional AC / DC converter should transmit more transient power from the AC subnet according to the deviation of the DC voltage. Conversely, when a disturbance occurs in the AC subnet, the bidirectional AC / DC converter can also provide inertia power support for the AC subnet from the DC subnet according to the fluctuation deviation of the frequency. Therefore, define the inertia support energy calculation formula as:

[0043]

[0044] wherein is the inertia support energy; when P bi_con is positive, virtual inertia energy is simulated according to the deviation of the DC voltage to support the voltage recovery; when P bi_con is negative, virtual inertia energy is simulated according to the deviation of the frequency to support the AC frequency recovery. Therefore, by introducing the virtual capacitor C vir or the moment of inertia J vir , the DC voltage or frequency support during the transient process can be achieved.

[0045] Furthermore, according to Equation (1), the power data P w for the auxiliary inertia support is obtained as

[0046]

[0047] After introducing the virtual capacitor C vir or the moment of inertia J vir , the equivalent inertia of the system is enhanced to prevent sudden changes in the DC voltage or frequency. For example, when the transmission power is from the DC subnet to the AC subnet, due to external power interference, the AC frequency decreases, and a frequency regulation signal is generated according to J vir f ac df ac / dt. Therefore, more transient power is transmitted from the DC subnet to the AC subnet for frequency inertia recovery. When the transmission power is from the DC subnet to the AC subnet, DC voltage inertia support can also be performed.

[0048] Step 4: Combine the power data of the auxiliary inertia support obtained in Step 3 with the power reference value of the bidirectional AC / DC converter, for example, by adding them, to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and use a PI controller to make the actual bidirectional power between the AC subnet and the DC subnet track its reference value, so as to achieve the bidirectional virtual inertia control of the AC-DC hybrid distributed power grid-connected distribution system. The overall bidirectional virtual inertia control block diagram is as shown in Figure 2 shown.

[0049] The specific implementation process is as follows: First, determine the magnitudes of the virtual capacitor and virtual moment of inertia parameters, and then judge the power flow direction between the AC subnet and the DC subnet in the AC-DC hybrid distributed power grid-connected distribution system. Subsequently, calculate the magnitude of the power data of the auxiliary inertia support according to the virtual capacitor and virtual moment of inertia. Combine the auxiliary inertia support power command with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and achieve the bidirectional virtual inertia control of the AC-DC hybrid distributed power grid-connected distribution system by tracking this reference value.

[0050] To verify the effectiveness of the proposed control method, an AC-DC hybrid distributed power grid-connected distribution system was established on the PSCAD platform. The AC sub-network includes two DGs with a rated capacity of 40 kW, and the DC sub-network also includes two DGs with a rated capacity of 40 kW. The rated AC frequency is 50 Hz, and the DC voltage is 700 V. A bidirectional AC / DC converter is set between the AC and DC sub-grids. The initial active load of the AC sub-network is 80 kW, and the initial active load of the DC sub-network is also 80 kW. When it is the 4th second, the load power of the DC sub-network drops to 60 kW. When the bidirectional virtual inertia control method of the distribution system provided by the present invention is adopted and not adopted, the simulation results are as Figures 3 - 6 shown. From Figure 3 and Figure 4 the simulation results, it can be seen that during the load power fluctuation, when the proposed bidirectional inertia control method of the present invention is adopted, the changes in frequency and DC voltage are smaller. Under the conventional control without inertia support ability, the frequency and DC voltage are impacted during the transient process and show a large overshoot. The bidirectional inertia control can enable the DC sub-network to provide inertia support to the AC sub-network, thereby slowing down the frequency change and improving the transient response of the system. During the improved transient process, the change in DC voltage can also be alleviated. From Figure 5 and Figure 6 it can be seen that as the virtual inertia parameter increases, the transient process is better improved. Therefore, by selecting appropriate virtual inertia parameters, the proposed bidirectional inertia control method can significantly improve the inertia support ability of the hybrid distribution system.

[0051] In summary, the present invention provides a bidirectional virtual inertia control method for a distribution system. Based on the dynamic power balance of the bidirectional AC / DC converter, a bidirectional virtual inertia control method based on virtual capacitance and virtual moment of inertia is proposed, which enhances the inertia interaction support ability of the hybrid distribution system. On the PSCAD / EMTDC platform, a simulation model of the AC-DC distribution system was built to verify the effectiveness of the proposed control scheme.

[0052] On the other hand, the present invention provides a bidirectional virtual inertia control device for a distribution system, including:

[0053] A data acquisition module, configured to acquire key data of the distribution system and select the magnitudes of virtual capacitance and virtual moment of inertia parameters;

[0054] A power flow direction judgment module, configured to judge the power flow direction between the AC sub-network and the DC sub-network in the AC-DC hybrid distributed power grid-connected distribution system;

[0055] A power command calculation module is used to select a corresponding inertial support energy calculation formula according to the judged power flow direction, and calculate the power data for auxiliary inertia support by using the key data of the distribution system obtained and the selected virtual capacitance and virtual inertia.

[0056] A bidirectional virtual inertia control module is used to combine the obtained power data for auxiliary inertia support with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC sub-network and the DC sub-network, and make the actual bidirectional power between the AC sub-network and the DC sub-network track the bidirectional power reference value through a PI controller, so as to realize the bidirectional virtual inertia control of the AC-DC hybrid distributed power grid-connected distribution system.

[0057] On the other hand, the present invention provides a bidirectional virtual inertia control system for a distribution system, including: a computer-readable storage medium and a processor;

[0058] The computer-readable storage medium is used to store executable instructions;

[0059] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the bidirectional virtual inertia control method for the distribution system described in the first aspect.

[0060] On the other hand, the present invention provides a non-transitory computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the bidirectional virtual inertia control method for the distribution system described in the first aspect is realized.

[0061] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0062] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate for realizing in the process Figure 1 one process or multiple processes and / or blocks Figure 1a device for the functions specified in one or more boxes.

[0063] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device that implements the functions specified in one Figure 1 process or more processes and / or boxes Figure 1 a box or more boxes.

[0064] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are performed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one Figure 1 process or more processes and / or boxes Figure 1 a box or more boxes.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific implementation manners of the present invention, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A two-way virtual inertia control method for a power distribution system, characterized in that, it includes the following steps: Obtain the key data of the power distribution system and select the magnitudes of the virtual capacitance and virtual moment of inertia parameters; Judge the power flow direction between the AC subnet and the DC subnet in the AC-DC hybrid distributed power grid-connected power distribution system; Select the corresponding inertial support energy calculation formula according to the judged power flow direction, and use the obtained key data of the power distribution system and the selected virtual capacitance and virtual moment of inertia to calculate the power data of the auxiliary inertia support; Combine the obtained power data of the auxiliary inertia support with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and make the actual bidirectional power between the AC subnet and the DC subnet track the bidirectional power reference value through a PI controller to achieve the two-way virtual inertia control of the AC-DC hybrid distributed power grid-connected power distribution system; The inertial support energy calculation formula is: (1)； In the formula, is the inertia support energy; when P bi_con is positive, virtual inertia energy is simulated according to the deviation of the DC voltage to support the voltage recovery; when P bi_con is negative, virtual inertia energy is simulated according to the deviation of the frequency to support the AC frequency recovery; According to Equation (1), the power data P of the auxiliary inertia support is obtained w as follows: (2)。 2. The two-way virtual inertia control method for a power distribution system according to claim 1, characterized in that, The key data of the distribution system include the DC capacitor C of the bidirectional AC / DC converter dc , the frequency f of all AC subnets ac , and the DC subnet voltage U dc .

3. The two-way virtual inertia control method for a power distribution system according to claim 2, characterized in that, Judging the power flow direction between the AC subnet and the DC subnet in the AC-DC hybrid distributed power grid-connected distribution system specifically includes: when P bi_con is positive, it is determined that the power is transmitted from the AC subnet to the DC subnet; when P bi_con is negative, it is determined that the power is transmitted from the DC subnet to the AC subnet; where P bi_con is the power transmitted from the AC subnet to the DC subnet.

4. A two-way virtual inertia control device for a power distribution system, characterized in that, it includes: A data acquisition module for obtaining the key data of the power distribution system and selecting the magnitudes of the virtual capacitance and virtual moment of inertia parameters; A power flow direction judgment module for judging the power flow direction between the AC subnet and the DC subnet in the AC-DC hybrid distributed power grid-connected power distribution system; A power command calculation module for selecting the corresponding inertial support energy calculation formula according to the judged power flow direction, and using the obtained key data of the power distribution system and the selected virtual capacitance and virtual moment of inertia to calculate the power data of the auxiliary inertia support; A two-way virtual inertia control module for combining the obtained power data of the auxiliary inertia support with the power reference value of the bidirectional AC / DC converter to obtain the actual bidirectional power reference value between the AC subnet and the DC subnet, and making the actual bidirectional power between the AC subnet and the DC subnet track the bidirectional power reference value through a PI controller to achieve the two-way virtual inertia control of the AC-DC hybrid distributed power grid-connected power distribution system; The inertial support energy calculation formula is: (1)； In the formula, is the inertia support energy; when P bi_con is positive, virtual inertia energy is simulated according to the deviation of the DC voltage to support the voltage recovery; when P bi_con is negative, virtual inertia energy is simulated according to the deviation of the frequency to support the AC frequency recovery; According to Equation (1), the power data P of the auxiliary inertia support is obtained w as follows: (2)。 5. The two-way virtual inertia control device for a power distribution system according to claim 4, characterized in that, The key data of the distribution system include the DC capacitor C of the bidirectional AC / DC converter dc , the frequency f of all AC subnets ac , and the DC subnet voltage U dc .

6. The two-way virtual inertia control device for a power distribution system according to claim 5, characterized in that, The power flow direction judgment module judges the power flow direction between the AC subnet and the DC subnet in the AC-DC hybrid distributed power grid-connected distribution system, specifically including: when P bi_con is positive, it is determined that the power is transmitted from the AC subnet to the DC subnet; when P bi_con is negative, it is determined that the power is transmitted from the DC subnet to the AC subnet; where P bi_con is the power transmitted from the AC subnet to the DC subnet.

7. A non-transitory computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the two-way virtual inertia control method for a power distribution system according to any one of claims 1-3.

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