Power balancing method and system suitable for multi-medium-voltage alternating-current port source network load storage system

Abstract

The invention discloses a power balancing method and system suitable for a multi-medium-voltage alternating-current port source network load storage system, and relates to the technical field of alternating-current power grid power flow regulation, power electronics and energy storage, and the method comprises the steps: constructing a chained battery energy storage power conversion system MACP-CHB-ESS of a plurality of medium-voltage alternating-current ports, and constructing a feeder line power flow regulation dynamic equation for the system; obtaining a fundamental frequency dynamic equation frequency domain form under the dq coordinate system; performing closed-loop control on the feeder power flow through a PI controller; and through optimal control of modulation degrees of the modules, power flow balance control of the connected feeder lines is realized. In a system of N feeder lines connected with the MACP-CHB-ESS, the power flow decoupling control of all the lines is realized, the power supply demand of the balanced lines is met, the power flow balance on the multiple feeder lines can be realized, and the problem of heavy load of a certain line and light load of a certain line in multiple parallel lines is avoided.

Description

Technical Field

[0001] The present invention relates to the fields of AC power grid flow regulation, power electronics technology and energy storage technology, and in particular to a power balancing method and system suitable for a multi-medium voltage AC port source-grid-load-storage system. Background Art

[0002] Energy storage systems can smooth out wind and solar power fluctuations, reduce peak loads and fill valleys, provide inertia and damping support for the power grid, improve the grid regulation capability, improve power quality, and provide an effective solution for the consumption of high-proportion wind and solar power. Especially with the development of power electronics technology, large-capacity energy storage systems represented by cascaded H-bridge energy storage systems (CHB-ESS) have great development potential. However, the existing CHB-ESS only has a single AC port and adopts a "one-to-one" connection with the feeder. With the large-scale access of new sources and loads, a large number of ESSs need to be distributed in the distribution network, resulting in high construction costs and large floor space, and lacking the ability to transfer loads in real time at the spatial level; on the other hand, the flexible interconnection solution uses power electronic switches to provide interconnection ports for different distribution feeders, which can realize the normalization of the "soft connection" of the distribution network and significantly enhance the flexible regulation capability of the distribution network. However, it does not have the time transfer capability of the energy storage system for loads, and when expanding the port, it is necessary to expand the full power structure, which also faces the problems of high cost and large volume.

[0003] In response to the above problems, some scholars have proposed a chain battery energy storage power conversion system (multiple-AC-ports cascaded H-bridge energy storage system, MACP-CHB-ESS) with multiple medium-voltage AC ports based on the existing single AC port CHB-ESS structure, integrating the advantages of flexible interconnection technology, and adding a low-power half-bridge module. With multiple AC feeders connected to the same CHB-ESS, it can achieve interconnection and energy storage sharing between AC power grids in different regions, which is conducive to improving the utilization rate of energy storage systems and optimizing system flow operation. Under natural conditions, the power flow distribution of the line depends on the impedance parameters of each line, and it is very easy to have uneven power flow distribution of the line, so some lines are overloaded or even overloaded, while other lines may be underloaded or underutilized. In this case, the requirements for equipment and protection devices on the heavy-loaded line are high, while the equipment on the light-loaded line is far from its carrying capacity. In extreme cases, this may cause the receiving end to lose all external power supply and the internal system to collapse due to insufficient power. Therefore, in order to ensure the stable operation of the power grid and balance the power of each line, a power balancing method suitable for a multi-medium voltage AC port source-grid-load-storage system is proposed. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the problem to be solved by the present invention is: how to solve the problem that the existing flexible interconnection structure does not have the time transfer capability of the energy storage system for the load, and when expanding the port, the full power structure needs to be expanded, which faces the problems of high cost and large volume.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a power balancing method applicable to a source-grid-load-storage system with multiple medium-voltage AC ports, comprising: constructing a chain battery energy storage power conversion system MACP-CHB-ESS with multiple medium-voltage AC ports, constructing a feeder power flow regulation dynamic equation for the system; obtaining the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system; performing closed-loop control of the feeder power flow through a PI controller; and realizing power flow balance control of the connected feeders through optimal control of the modulation degree of each module.

[0007] As a preferred solution of the power balancing method for a multi-medium voltage AC port source-grid-load-storage system according to the present invention, the feeder power flow regulation includes MACP-CHB-ESS adopting a series-parallel active interactive power flow regulation method, by adjusting the output voltage of the power flow regulation half-bridge module in PFCM, the feeder power flow is freely adjusted within the adjustment range, and under the condition of known feeder current, the calculation of the feeder power flow is expressed as,

[0008]

[0009] Among them, P j is the active power of the feeder connected to port j of MACP-CHB-ESS, Q j is the reactive power of the feeder connected to port j of MACP-CHB-ESS, v j is the feeder node voltage, i j is the feeder current, and the subscripts d and q respectively represent the d-axis component and q-axis component in the synchronous rotating coordinate system oriented with the node voltage of the balanced feeder 1. When the node voltage is determined, the feeder flow regulation is achieved by controlling the feeder current. According to Kirchhoff's voltage law, the system dynamic voltage equation is listed as:

[0010]

[0011] Where i is the feeder current, v is the feeder node voltage, k=a, b, c are the three phases A, B, and C, L is the feeder equivalent inductance, R is the resistance, and j is the jth feeder.

[0012] As a preferred solution of the power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system of the present invention, the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system includes applying the PARK transformation matrix to the system dynamic voltage equation, and the PARK transformation matrix is ​​expressed as:

[0013]

[0014] Among them, T abc / dq0 is the PARK transformation matrix; the dynamic voltage equation in the dq coordinate system is expressed as:

[0015]

[0016] Where ω is the voltage angular frequency of feeder 1.

[0017] As a preferred solution of the power balancing method for a multi-medium voltage AC port source-grid-load-storage system according to the present invention, the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system also includes Laplace transforming the dynamic voltage equation in the dq coordinate system, and obtaining the frequency domain form of the fundamental frequency dynamic equation of the MACP-CHB-ESS series equivalent regulation voltage, feeder node voltage and feeder current in the dq coordinate system is expressed as follows:

[0018]

[0019] The current of feeder j of MACP-CHB-ESS depends on the node voltage of the feeder and the equivalent output voltage of the power flow regulation half-bridge. The transfer function relationship between the series equivalent output voltage of the power flow regulation half-bridge, the feeder node voltage and the feeder current is obtained. During the regulation process, there is coupling between the d-axis and q-axis components of the feeder current, and it is affected by the feeder node voltage disturbance.

[0020] As a preferred solution of the power balancing method for a multi-medium voltage AC port source-grid-load-storage system according to the present invention, the closed-loop control includes the relationship between the feeder power and the feeder voltage and current in the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system, and the current reference value of the feeder j is calculated as follows:

[0021]

[0022] in, is the reference value of active power of feeder j, is the reference value of reactive power of feeder j, is the d-axis current reference value of feeder j, is the q-axis current reference value of feeder j; for the inner loop current controller, the controller output variable is the d-axis and q-axis components i of the j-th feeder current calculated from the current reference value of feeder j.jd and i jq , are the d-axis and q-axis components Δv of the equivalent series voltage between feeder 1 and feeder j of the control variable c1jd and Δv c1jq , v 1d 、v 1q 、v jd and v jq is a disturbance variable, and there is coupling between the d-axis and q-axis currents of the feeder; the current on feeder j (=2, 3, …, n) is closed-loop controlled using a PI controller, while considering the influence of the current coupling term between the dq axes and the feeder node voltage disturbance term.

[0023] As a preferred solution of the power balancing method for a multi-medium voltage AC port source-grid-load-storage system of the present invention, the power flow balancing control includes introducing a coupling compensation term ωL1i of the current 1q ,ωL j i jq ωL1i 1d and ωL j i jd Realize the decoupling control of current and add the voltage feedforward compensation term v 1d 、v jd 、v 1q and v jq Offset the influence of feeder node voltage disturbance and obtain the series equivalent voltage Δv in the dq coordinate system c1jd * and Δv c1jq * , the series equivalent voltage reference value in power flow regulation control is expressed as:

[0024]

[0025] Among them, k p is the proportionality coefficient, k i is the integration coefficient, is the d-axis series equivalent voltage, is the q-axis series equivalent voltage.

[0026] As a preferred solution of the power balancing method for a multi-medium voltage AC port source-grid-load-storage system described in the present invention, the power flow balancing control also includes obtaining the series equivalent voltage reference value Δv under the dq axis by the series equivalent voltage reference value formula c1jd * and Δv c1jq * Then, the Park inverse transformation is used to convert it to the voltage reference value Δv in the abc coordinate system. c1ja * , Δv c1jb *, Δv c1jb * To obtain the reference voltage of each power flow regulating half bridge in PFCM, the output reference voltage of HBSM connected to balanced feeder 1 needs to be given. It is expressed as:

[0027]

[0028] Then the output voltage of the power flow regulation half-bridge connected to each feeder is expressed as:

[0029]

[0030] in, The half-bridge output voltage is adjusted for each feeder connected power flow; and the MACP-CHB-ESS feeder power flow control strategy is obtained.

[0031] Another object of the present invention is to provide a system for a power balancing method for a multi-medium voltage AC port source-grid-load-storage system, which can solve the power balancing problem of a multi-medium voltage AC port source-grid-load-storage system by constructing a power balancing system for a multi-medium voltage AC port source-grid-load-storage system.

[0032] To solve the above technical problems, the present invention provides the following technical solutions: a power balancing system applicable to a source-grid-load-storage system with multiple medium-voltage AC ports, comprising a MACP-CHB-ESS construction module, a baseband dynamic equation module, a closed-loop control module and a power flow balancing control module; the MACP-CHB-ESS construction module is used to construct a chain battery energy storage power conversion system MACP-CHB-ESS with multiple medium-voltage AC ports, and construct a feeder power flow regulation dynamic equation for the system; the baseband dynamic equation module is used to obtain the frequency domain form of the baseband dynamic equation in the dq coordinate system; the closed-loop control module is used to perform closed-loop control of the feeder power flow through a PI controller; the power flow balancing control module is used to achieve power flow balancing control of the connected feeders through optimal control of the modulation degree of each module.

[0033] A computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system are implemented as described above.

[0034] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as described above.

[0035] The beneficial effects of the present invention are as follows: the power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided by the present invention can realize power flow decoupling control of all lines in a system of N feeders connected by MACP-CHB-ESS, and can realize power flow balance on multiple feeders while meeting the power supply demand of the balanced lines, so as to avoid the problem of heavy load on one line and light load on another line in multiple parallel lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0037] Figure 1 A flow chart of a power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system provided in the first embodiment of the present invention.

[0038] Figure 2 A schematic diagram of the topological structure of a power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided in the first embodiment of the present invention.

[0039] Figure 3 A line power balancing control strategy for a power balancing method of a multi-medium voltage AC port source-grid-load-storage system is provided in the first embodiment of the present invention.

[0040] Figure 4 A structural diagram of a power balancing system suitable for a multi-medium voltage AC port source-grid-load-storage system provided in the second embodiment of the present invention.

[0041] Figure 5 The third embodiment of the present invention provides an active power diagram of each line in the process of controlling the power balancing of parallel lines in a power balancing method for a multi-medium voltage AC port source-grid-load-storage system.

[0042] Figure 6 A reactive power diagram of each line in the process of controlling the power balancing of parallel lines in a power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided in the third embodiment of the present invention.

[0043] Figure 7 A capacitor voltage diagram of parallel CMI submodules in the process of controlling parallel line power balancing in a power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided in the third embodiment of the present invention.

[0044] Figure 8This is a current diagram of line 1 in the process of controlling the power balancing of parallel lines in a power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided in the third embodiment of the present invention.

[0045] Fig. 9 This is a current diagram of line 2 in the process of controlling the power balancing of parallel lines in a power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided in the third embodiment of the present invention.

[0046] Fig.10 This is a current diagram of line 3 in the process of controlling the power balancing of parallel lines in a power balancing method for a multi-medium voltage AC port source-grid-load-storage system provided in the third embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0048] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0049] Example 1, reference Figure 1 to Figure 3 , which is the first embodiment of the present invention, provides a power balancing method for a multi-medium voltage AC port source-grid-load-storage system, including: constructing a chain battery energy storage power conversion system MACP-CHB-ESS with multiple medium voltage AC ports, constructing a feeder power flow regulation dynamic equation for the system; obtaining the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system; performing closed-loop control of the feeder power flow through a PI controller; and realizing power flow balance control of the connected feeders through optimal control of the modulation degree of each module.

[0050] S1. Construct a chain battery energy storage power conversion system MACP-CHB-ESS with multiple medium voltage AC ports, and construct a dynamic equation for feeder power flow regulation for the system.

[0051] The present invention provides a power balancing method suitable for a multi-medium voltage AC port source-grid-load-storage system. According to the document “Multi-medium voltage AC port chain battery energy storage power conversion system”, the MACP-CHB-ESS topology is derived from a cascaded H-bridge energy storage system (cascaded H-bridge energy storage system, CHB-ESS), and a cascaded full bridge sub-module (full bridge sub-module, FBSM) is added to the CHB-ESS medium voltage AC port, which can be regarded as two half bridge sub-modules (halfbridge sub-module, HBSM) connected in parallel, one HBSM is connected to the feeder, and the other HBSM is cascaded with the second sub-module of the CHB-ESS. In order to realize the interconnection of multiple AC feeders and the sharing of energy storage, it is necessary to expand new medium voltage AC ports. Another HBSM can be connected in parallel on the DC side of the FBSM to form a MACP-CHB-ESS topology. The number of medium voltage AC ports of the MACP-CHB-ESS depends on the number of expanded HBSMs. Figure 2 shown.

[0052] The main circuit composed of the FBSM and the newly added HBSM is called the power flow control module (PFCM); the HBSM connected to the feeder is mainly used for power flow regulation between feeders and charge and discharge control of the energy storage system, which is called the power flow regulation half-bridge; the HBSM connected to the CHB-ESS is mainly used for constant control of the PFCM DC bus voltage to maintain the internal energy balance of the device, which is called the balance regulation half-bridge.

[0053] MACP-CHB-ESS adopts a series-parallel-active interactive power flow regulation method. By adjusting the output voltage of the power flow regulation half-bridge module in the PFCM, the feeder power flow can be freely adjusted within the regulation range. Under the condition of known feeder current, the calculation method of feeder power flow is:

[0054]

[0055] Among them, P j and Q j are the active power and reactive power of the feeder connected to port j of MACP-CHB-ESS, respectively, and v j and i j are the feeder node voltage and feeder current, respectively. The subscripts d and q represent the d-axis component and q-axis component in the synchronous rotating coordinate system oriented with the balanced feeder 1 node voltage. It can be seen from formula (1) that when the node voltage is determined, the feeder flow regulation can be achieved by controlling the feeder current. The feeder is connected to the port of the device, and the feeder connected to port j is feeder j.

[0056] According to Kirchhoff's voltage law, the system dynamic voltage equation can be listed:

[0057]

[0058] Where i is the feeder current, v is the feeder node voltage, k = a, b, c represents the three phases A, B, and C, L and R are the feeder equivalent inductance and resistance. j represents the jth feeder. The PARK transformation matrix in the following formula is applied to equation (2):

[0059]

[0060] Among them, T abc / dq0 is the PARK transformation matrix.

[0061] S2. Obtain the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system.

[0062] The dynamic voltage equation in the dq coordinate system can be obtained as:

[0063]

[0064] Where ω is the voltage angular frequency of feeder 1.

[0065] By performing Laplace transform on equation (4), we can obtain the frequency domain form of the fundamental frequency dynamic equation of the MACP-CHB-ESS series equivalent regulation voltage, feeder node voltage and feeder current in the dq coordinate system:

[0066]

[0067] It can be seen from formula (5) that the current of feeder j of MACP-CHB-ESS depends on the node voltage of the feeder and the equivalent output voltage of the power flow regulation half bridge. According to formula (5), the transfer function relationship between the series equivalent output voltage of the power flow regulation half bridge, the feeder node voltage and the feeder current can be obtained. It can be seen that there is coupling between the d-axis and q-axis components of the feeder current during the regulation process, and it will be affected by the feeder node voltage disturbance.

[0068] S3. Perform closed-loop control of the feeder power flow through a PI controller.

[0069] According to the relationship between feeder power and feeder voltage and current described in equation (5), the reference values ​​of active power and reactive power of feeder j are recorded, and the current reference value of feeder j can be calculated as:

[0070]

[0071] in, is the reference value of active power of feeder j, is the reference value of reactive power of feeder j, is the d-axis current reference value of feeder j, is the q-axis current reference value of feeder j.

[0072] For the inner loop current controller, from (6), the controller output variable is the d-axis and q-axis components i of the j-th feeder current. jd and i jq , are the d-axis and q-axis components Δv of the equivalent series voltage between feeder 1 and feeder j of the control variable c1jd and Δv c1jq , v 1d 、v 1q 、v jd and v jq Then it is a disturbance variable, and there is coupling between the d-axis and q-axis currents of the feeder. The PI controller is used to perform closed-loop control on the current on feeder j (=2, 3, …, n), while considering the influence of the current coupling term between the dq axes and the feeder node voltage disturbance term. The coupling compensation term ωL1i of the current is introduced 1q ,ωL j i jq ωL1i 1d and ωL j i jd To achieve current decoupling control, and add the voltage feedforward compensation term v 1d 、v jd 、v 1q and v jq To offset the influence of the voltage disturbance at the feeder node, the series equivalent voltage Δv in the dq coordinate system is obtained. c1jd * and Δv c1jq * Therefore, the series equivalent voltage reference value in power flow regulation control can be expressed as:

[0073]

[0074] Among them, k p is the proportionality coefficient, k i is the integration coefficient, is the d-axis series equivalent voltage, is the q-axis series equivalent voltage.

[0075] S4. Through optimal control of the modulation degree of each module, the power flow balance control of the connected feeders is achieved.

[0076] The series equivalent voltage reference value Δv under the dq axis is obtained by formula (7): c1jd * and Δv c1jq *After that, the Park inverse transformation can be used to convert it to the voltage reference value Δv in the abc coordinate system. c1ja * , Δv c1jb * , Δv c1jb * To further obtain the reference voltage of each power flow regulating half bridge in the PFCM, the output reference voltage of the HBSM connected to the balanced feeder 1 must also be given. In order to fully utilize the regulation capability of each submodule, the maximum value of the reference voltage amplitude of all power flow regulation half-bridges should be as small as possible, that is:

[0077]

[0078] Then the output voltage of the power flow regulation half-bridge connected to each feeder can be expressed as:

[0079]

[0080] Based on the above analysis, the MACP-CHB-ESS feeder power flow control strategy can be obtained. Figure 2 shown.

[0081] The following describes the design of the reactive power control strategy for MACP-CHB-ESS charging and discharging power and balanced feeder 1. The reactive power control of MACP-CHB-ESS charging and discharging power and balanced feeder 1 can be achieved by controlling the active and reactive components of the balanced feeder current. According to Kirchhoff's voltage law, the dynamic voltage equation between v1 and vp can be listed as:

[0082]

[0083] By performing PARK transformation on equation (10), we can obtain the dynamic voltage equation between v1 and vp in the dq coordinate system:

[0084]

[0085] Similar to the design of feeder power flow control strategy, by performing Laplace transform on equation (11), the frequency domain form of the fundamental frequency dynamic equation of MACP-CHB-ESS series equivalent regulation voltage, feeder node voltage and feeder current in the dq coordinate system can be obtained:

[0086]

[0087] To achieve the charging and discharging power control of CHB-ESS, the active power command value of feeder 1 is determined by the CHB-ESS energy storage and the active power commands of other feeders:

[0088]

[0089] In the dq coordinate system oriented by the voltage of the feeder 1 node, the power flow command value expression of feeder 1 can be obtained from equation (6):

[0090]

[0091] According to Kirchhoff's current law, the q-axis component of the current in feeder 1 satisfies:

[0092]

[0093] When the currents of other feeders follow the system instructions without static error, it can be seen from equation (15) that the q-axis component of the current of feeder 1 is determined by the q-axis component of the current of CHB. Therefore, by controlling the q-axis component of the current of CHB, the reactive power of feeder 1 can be effectively controlled.

[0094] Based on the above analysis, consistent with the design method of power flow decoupling control strategy, the MACP-CHB-ESS charging and discharging power control and the reactive power control of the balanced feeder can be further designed.

[0095] According to the above power balancing method, in the system of N feeders connected by MACP-CHB-ESS, the power flow decoupling control of all lines can be realized. While meeting the power supply demand of balanced lines, the power flow balance on multiple feeders can be achieved, so as to avoid the problem of heavy load on one line and light load on another line in multiple parallel lines.

[0096] Example 2, reference Figure 4 , which is the second embodiment of the present invention, which is different from the previous embodiment in that it provides a power balancing system suitable for a multi-medium voltage AC port source-grid-load-storage system, including: a MACP-CHB-ESS building module 100, a baseband dynamic equation module 200, a closed-loop control module 300 and a power flow balancing control module 400;

[0097] The MACP-CHB-ESS building module 100 is used to build a chain battery energy storage power conversion system MACP-CHB-ESS of multiple medium voltage AC ports, and to build a feeder power flow regulation dynamic equation for the system;

[0098] The fundamental frequency dynamic equation module 200 is used to obtain the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system;

[0099] The closed-loop control module 300 is used to perform closed-loop control on the feeder power flow through a PI controller;

[0100] The power flow balance control module 400 is used to achieve power flow balance control of the connected feeders through optimal control of the modulation degree of each module.

[0101] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0102] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0103] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0104] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0105] Example 3, reference Figures 5 to 10 , which is the third embodiment of the present invention, and which is different from the first two embodiments in that it is used to verify and illustrate the technical effects adopted in the present invention, so as to verify the real effects of this method.

[0106] In this embodiment, MACP-CHB-ESS connects three feeders, of which feeder 2 and feeder 3 are parallel lines. Taking the power balance of the two lines as an example, it is assumed that line 1 is a balanced line. Feeder 2 and feeder 3 are parallel double-circuit lines, but due to the difference in impedance parameters of the two lines, the power flow distribution of the two lines is uneven, one line is heavily loaded and the other line is lightly loaded. Through the power balancing method proposed in the present invention, the power flow balance of the two lines is achieved.

[0107] The following is a further explanation of the application of the above structure and method in conjunction with a specific simulation example; in conjunction with the above embodiment, MATLAB / Simulink software is used to simulate and verify the system, and the simulation parameters are shown in Table 1. The simulation sequence is as follows: at t=0s, the parameters of the three lines are asymmetric, resulting in unbalanced line power flow; at t=0.4s, MACP-CHB-ESS controls the power balance of the three lines;

[0108] Table 1 Simulation parameters

[0109]

[0110]

[0111] Figure 5 and Figure 6 The waveforms are the active power and reactive power waveforms of each line after the MACP-CHB-ESS is put into use. From the simulation results, it can be seen that the proposed control can effectively balance the power of each line and ensure that the line will not be overloaded. Figures 7 to 10 They are: feeder 1 current waveform, feeder 2 current waveform, feeder 3 current waveform, and line 1 port voltage.

[0112] The simulation results show that when the power flow of parallel lines is unevenly distributed, the proposed control strategy can be used to achieve power balance of parallel lines by connecting to MACP-CHB-ESS, breaking through the bottleneck of feeder lines due to uneven power flow distribution and improving power supply efficiency. The results verify that the proposed parallel line power balance method based on MACP-CHB-ESS can achieve power flow balance of multiple parallel lines.

[0113] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system, characterized by: include, Construct a chain battery energy storage power conversion system MACP-CHB-ESS with multiple medium voltage AC ports, and construct a dynamic equation for feeder power flow regulation for the system; The frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system is obtained; Closed-loop control of feeder power flow is performed through PI controller; Through optimal control of the modulation degree of each module, the power flow balance control of the connected feeders can be achieved.

2. The power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as claimed in claim 1, characterized in that: The feeder power flow regulation includes MACP-CHB-ESS, which adopts a series-parallel active interactive power flow regulation method. By adjusting the output voltage of the power flow regulation half-bridge module in the PFCM, the feeder power flow is freely adjusted within the regulation range. Under the condition of known feeder current, the calculation of the feeder power flow is expressed as: Among them, P j is the active power of the feeder connected to port j of MACP-CHB-ESS, Q j is the reactive power of the feeder connected to port j of MACP-CHB-ESS, v j is the feeder node voltage, i j is the feeder current, the subscripts d and q represent the d-axis component and q-axis component, respectively, in the synchronous rotating coordinate system oriented with the balanced feeder 1 node voltage; When the node voltage is determined, feeder power flow regulation is achieved by controlling the feeder current; According to Kirchhoff's voltage law, the system dynamic voltage equation is expressed as: Where i is the feeder current, v is the feeder node voltage, k=a, b, c are the three phases A, B, and C, L is the feeder equivalent inductance, R is the resistance, and j is the jth feeder.

3. The power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as claimed in claim 2, characterized in that: The frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system includes applying the PARK transformation matrix to the system dynamic voltage equation. The PARK transformation matrix is ​​expressed as: Among them, T abc / dq0 is the PARK transformation matrix; The dynamic voltage equation in the dq coordinate system is expressed as: Where ω is the voltage angular frequency of feeder 1.

4. The power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as claimed in claim 3, characterized in that: The frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system also includes performing Laplace transform on the dynamic voltage equation in the dq coordinate system, and obtaining the frequency domain form of the fundamental frequency dynamic equation of the MACP-CHB-ESS series equivalent regulation voltage, feeder node voltage and feeder current in the dq coordinate system, which is expressed as follows: The current of feeder j of MACP-CHB-ESS depends on the node voltage of the feeder and the equivalent output voltage of the power flow regulation half-bridge. The transfer function relationship between the series equivalent output voltage of the power flow regulation half-bridge, the feeder node voltage and the feeder current is obtained. During the regulation process, there is coupling between the d-axis and q-axis components of the feeder current, and it is affected by the feeder node voltage disturbance.

5. The power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as claimed in claim 4, characterized in that: The closed-loop control includes the relationship between the feeder power and the feeder voltage and current in the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system. The current reference value of feeder j is calculated as: in, is the reference value of active power of feeder j, is the reference value of reactive power of feeder j, is the d-axis current reference value of feeder j, is the q-axis current reference value of feeder j; For the inner loop current controller, the controller output variable is the d-axis and q-axis components i of the jth feeder current, calculated from the current reference value of feeder j. jd and i jq , are the d-axis and q-axis components Δv of the equivalent series voltage between feeder 1 and feeder j of the control variable c1jd and Δv c1jq , v 1d 、v 1q 、v jd and v jq Then it is a disturbance variable, and there is coupling between the d-axis and q-axis currents of the feeder; The PI controller is used to perform closed-loop control on the current on feeder j (=2, 3, ..., n), while considering the influence of the current coupling term between the dq axes and the voltage disturbance term of the feeder node.

6. The power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as claimed in claim 5, characterized in that: The power flow balancing control includes introducing the current coupling compensation term ωL1i 1q ,ωL j i jq ωL1i 1d and ωL j i jd Realize the decoupling control of current and add the voltage feedforward compensation term v 1d 、v jd 、v 1q and v jq Offset the influence of feeder node voltage disturbance and obtain the series equivalent voltage Δv in the dq coordinate system c1jd * and Δv c1jq * , the series equivalent voltage reference value in power flow regulation control is expressed as, Among them, k p is the proportionality coefficient, k i is the integration coefficient, is the d-axis series equivalent voltage, is the q-axis series equivalent voltage.

7. The power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system as claimed in claim 6, characterized in that: The power flow balancing control also includes obtaining a series equivalent voltage reference value Δv under the dq axis by using a series equivalent voltage reference value formula c1jd * and Δv c1jq * Then, the Park inverse transformation is used to convert it to the voltage reference value Δv in the abc coordinate system. c1ja * , Δv c1jb * , Δv c1jb * To obtain the reference voltage of each power flow regulating half bridge in PFCM, the output reference voltage of HBSM connected to balanced feeder 1 needs to be given. It is expressed as, Then the output voltage of the power flow regulation half-bridge connected to each feeder is expressed as: in, Regulate the half-bridge output voltage for each feeder connected to the power flow; The MACP-CHB-ESS feeder power flow control strategy is obtained.

8. A system using the power balancing method for a multi-medium voltage AC port source-grid-load-storage system as claimed in any one of claims 1 to 7, characterized in that: It includes a MACP-CHB-ESS construction module (100), a baseband dynamic equation module (200), a closed-loop control module (300) and a power flow balance control module (400); The MACP-CHB-ESS construction module (100) is used to construct a chain battery energy storage power conversion system MACP-CHB-ESS with multiple medium voltage AC ports, and to construct a feeder power flow regulation dynamic equation for the system; The fundamental frequency dynamic equation module (200) is used to obtain the frequency domain form of the fundamental frequency dynamic equation in the dq coordinate system; The closed-loop control module (300) is used to perform closed-loop control on the feeder power flow through a PI controller; The power flow balancing control module (400) is used to achieve power flow balancing control of the connected feeders through optimal control of the modulation degree of each module.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the power balancing method applicable to a multi-medium voltage AC port source-grid-load-storage system according to any one of claims 1 to 7 are implemented.

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