Three-phase four-wire topological optimization method and system applied to energy storage converter system

Abstract

The invention discloses a three-phase four-wire topological optimization method and system applied to an energy storage conversion system, and the method comprises the steps: enabling a converter to be connected with an energy storage battery system, and carrying out the structure topology; and after connection is completed, balance control is performed on the battery cluster through adjustment of a control algorithm. A three-phase four-wire system topology can be transformed after a current transformer of an existing three-phase three-wire system topological structure is added and connected with a direct-current midpoint, the requirement for the ripple current endurance capacity of a direct-current bus capacitor of the current transformer is small, the direct-current midpoint is clamped by a direct-current midpoint of a battery system, the midpoint fluctuation is small, the unbalanced loading capacity is high, and the selection range of a control algorithm is wider.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage conversion systems, and in particular to a three-phase four-wire topology optimization method and system applied to energy storage conversion systems. Background Art

[0002] The application of energy storage systems in grid voltage and frequency regulation, reducing peak-to-valley differences, smoothing fluctuations, and improving local consumption of new renewable energy can solve the problems brought about by the development of new energy. It has been widely studied and has achieved a large number of technical results.

[0003] In the industrial and commercial energy storage application field and AC / DC microgrid system on the distribution network side, most of the distribution loads are single-phase loads. Therefore, the energy storage inverter is required to have the ability to carry single-phase loads. Under grid-connected conditions, it is also required to have the ability to compensate for the imbalance of the three-phase active power of the power grid. Therefore, the demand for the three-phase four-wire output method of the inverter is becoming increasingly urgent. Summary of the invention

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

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a three-phase four-wire topology optimization method applied to an energy storage converter system, comprising:

[0006] Connect the converter to the energy storage battery system and perform the structural topology;

[0007] After the connection is completed, the battery cluster is balanced and controlled by adjusting the control algorithm.

[0008] As a preferred solution of the three-phase four-wire topology optimization method applied to the energy storage converter system described in the present invention, wherein: the connecting the converter to the energy storage battery system includes connecting the energy storage battery system and the converter using a three-phase four-wire topology circuit;

[0009] The three-phase four-wire topology circuit has one end connected to the grid side or load of the energy storage conversion system, and the other end connected to the battery side of the energy storage conversion system;

[0010] The DC positive pole of the energy storage battery is connected to the positive pole of the converter, the negative pole of the energy storage battery is connected to the negative pole of the converter, and the midpoint of the energy storage battery is connected to the midpoint of the DC side of the converter.

[0011] As a preferred solution of the three-phase four-wire topology optimization method applied to the energy storage converter system described in the present invention, wherein: after the midpoint of the energy storage battery is connected to the DC midpoint of the converter, when the number of battery clusters is greater than 1, one of the two execution schemes is randomly executed; the two execution schemes include connecting the current midpoint connection line to one or more clusters and the DC midpoint of the converter separately; connecting the midpoints of all battery clusters to the DC midpoint of the converter;

[0012] When the number of converters is greater than 1, one of two execution schemes is randomly executed; the two execution schemes include connecting the midpoint connection line of the energy storage battery to the DC midpoint of one or more converters individually; connecting the midpoint of the battery cluster to the DC midpoint of all converters.

[0013] As a preferred solution of the three-phase four-wire topology optimization method applied to the energy storage conversion system described in the present invention, the connection between the midpoint of the energy storage battery and the DC midpoint of the converter includes: a direct midpoint electrical connection, a midpoint electrical connection after a switch device, a midpoint electrical connection after a series inductor and resistor, and a midpoint electrical connection after a combination of multiple switches and components are connected in series.

[0014] As a preferred solution of the three-phase four-wire topology optimization method applied to the energy storage converter system described in the present invention, wherein: the structural topology includes that the midpoint of the energy storage battery and the DC midpoint of the converter are connected and then led out as the AC N line;

[0015] After the cells of the energy storage battery are connected in series, the number of cells on the upper and lower busbars is equal;

[0016] The energy storage battery is used by directly connecting the battery cells in series or by connecting an even number of battery packs in series.

[0017] As a preferred solution of the three-phase four-wire topology optimization method applied to the energy storage conversion system described in the present invention, wherein: the conversion topology structure of the converter is other converter topologies whose DC midpoint is led out and connected to the DC midpoint of the energy storage system, including but not limited to the font three-level, T-type three-level, and ANPC.

[0018] As a preferred solution of the three-phase four-wire topology optimization method applied to the energy storage conversion system described in the present invention, the control algorithm includes subdividing the balanced control of the battery cluster into 0.5 cluster control as the control target, and realizing different power charging and discharging strategies for the upper bus and the lower bus of the energy storage battery system through the adjustment of the control algorithm.

[0019] A three-phase four-wire topology optimization system for an energy storage converter system using the method of the present invention is characterized in that:

[0020] A topology unit connects the converter to the energy storage battery system and performs structural topology;

[0021] After the control unit completes the connection, it controls the balancing of the battery cluster by adjusting the control algorithm.

[0022] A computer device comprises: a memory and a processor; the memory stores a computer program, wherein: the processor implements the steps of any one of the methods of the present invention when executing the computer program.

[0023] A computer-readable storage medium stores a computer program, wherein: when the computer program is executed by a processor, the steps of any one of the methods of the present invention are implemented.

[0024] Beneficial effects of the present invention: The three-phase four-wire topology optimization method for energy storage conversion system provided by the present invention can be transformed into a three-phase four-wire topology after adding a converter of the existing three-phase three-wire topology structure and connecting the DC midpoint. The ripple current tolerance capability of the converter DC bus capacitor is small, the DC midpoint is clamped by the DC midpoint of the battery system, the midpoint fluctuation is small, the unbalanced load capacity is strong, and the control algorithm has a wider range of choices. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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 work.

[0026] Figure 1 An overall flow chart of a three-phase four-wire topology optimization method applied to an energy storage converter system provided by the first embodiment of the present invention;

[0027] Figure 2 A schematic diagram of a three-phase four-wire topology with a three-phase three-bridge midpoint lead in a three-phase four-wire topology optimization method for an energy storage converter system provided in the first embodiment of the present invention;

[0028] Figure 3 A three-phase four-bridge arm three-phase four-wire topology principle diagram in a three-phase four-wire topology optimization method for an energy storage converter system provided by the first embodiment of the present invention;

[0029] Figure 4 A schematic diagram of a three-phase four-wire topology with a three-phase three-bridge midpoint lead in a three-phase four-wire topology optimization method for an energy storage converter system provided in the first embodiment of the present invention;

[0030] Figure 5 A topology change diagram from NPC to ANPC in a three-phase four-wire topology optimization method for an energy storage converter system provided in the first embodiment of the present invention;

[0031] Figure 6A topology change diagram from NPC1 to NPC2 in a three-phase four-wire topology optimization method for an energy storage converter system provided in a first embodiment of the present invention;

[0032] Figure 7 A topological principle diagram of a midpoint-to-midpoint connection of three-phase three-bridge arms in a three-phase four-wire topology optimization method for an energy storage converter system provided in a second embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned purposes, 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 drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0034] Example 1, reference Figure 1-6 , which is an embodiment of the present invention, provides a three-phase four-wire topology optimization method applied to an energy storage converter system, comprising:

[0035] It should be said that there are currently two main solutions for three-phase four-wire converter topology. The first solution is Figure 2 The three-phase three-bridge midpoint lead-out three-phase four-wire topology shown in the figure, in this topology, the midpoint of the DC side capacitor of the converter is connected to the AC point N after being led out, as the AC side output N line, the disadvantage of the scheme is that in order to adapt to the unbalanced load application conditions, the selection range of the modulation algorithm is small, and the DC bus voltage utilization rate is low. Because a large current flows through the N line, the ability of the DC capacitor to withstand ripple current is put to a greater test. At the same time, the AC and DC side parallel operation control method of the converter is relatively complicated. The second scheme is as follows Figure 3 The three-phase four-bridge midpoint shown in the figure leads to a three-phase four-wire topology. This solution adds an N-wire input bridge arm. The disadvantage is that the increase in the number of components leads to increased costs and increased system control complexity. For the current fiercely competitive market, the advantages are not obvious.

[0036] S1: Connect the converter to the energy storage battery system and perform the structural topology.

[0037] Furthermore, the energy storage battery system and its converter system, and the power connection between the energy storage battery and the converter. Figure 4 As shown, the AC side output of the converter is a three-phase four-wire system. When the converter is connected to the grid, the AC side is connected to the grid. When the converter is off-grid, the AC side is connected to the load.

[0038] like Figure 4As shown, the DC side of the converter is connected to the energy storage system, the DC positive pole of the converter is connected to the positive pole of the energy storage system, the DC negative pole of the converter is connected to the negative pole of the energy storage system, and the DC midpoint output of the converter is connected to the midpoint of the energy storage battery system. The connection between the midpoint of the converter and the midpoint of the energy storage battery is the key point of this embodiment. After the midpoint of the energy storage battery and the DC midpoint of the converter are connected, they are led out as the AC N line. However, it may not be led out in special circumstances. The energy storage battery can be a different battery energy storage system such as a lithium-ion battery, a liquid flow battery, or a lead-acid battery. After the cells of the energy storage battery are connected in series, the number of cells in the upper and lower busbars is equal. In unconventional circumstances, the number of cells in the DC upper and lower busbars can also be configured with different numbers. The energy storage battery can be a cell directly connected in series, or an even number of battery packs can be used in series.

[0039] When the number of energy storage battery clusters in the system is greater than 1 or the number of converters is greater than 1, the midpoint connection between the converter and the energy storage battery can be connected to the DC midpoint of some battery clusters or to the DC midpoints of all battery clusters. It can be connected to the DC midpoint of some converters or to the DC midpoints of all converters, and can be flexibly configured according to the system application scenario.

[0040] The three-phase four-wire topology structure is as follows: Figure 4 As shown, Figure 2 The difference between the conventional topology structures shown in the figure is that the midpoint of the energy storage battery system is brought out and connected to the DC midpoint of the converter. The advantage of connecting the two midpoints is that the existing three-phase three-wire topology converter can be transformed into a three-phase four-wire topology after adding and connecting the DC midpoint. The ripple current tolerance requirement for the converter DC bus capacitor is small, the DC midpoint is clamped by the DC midpoint of the battery system, the midpoint fluctuation is small, and the unbalanced load capacity is strong. At the same time, more refined balanced control of the battery cluster can be achieved, and the control algorithm can be selected from a wider range.

[0041] The conversion topology of the converter is other converter topologies in which the DC midpoint is led out and connected to the DC midpoint of the energy storage system, including but not limited to the three-level type, the T-type three-level, and the ANPC.

[0042] Figure 5 It is a change from the straight NPC to the ANPC topology. Figure 6 It is a change to T-type three-level. For this type of topology with DC midpoint lead-out, the conditions for connecting the DC midpoint of the converter to the DC side of the energy storage battery system are met.

[0043] S2: After the connection is completed, the battery cluster is balanced by adjusting the control algorithm.

[0044] Specifically, the control algorithm is adjusted to realize the charging and discharging strategies of different powers for the upper bus and the lower bus of the energy storage battery system, thereby subdividing the balancing control of the battery cluster into 0.5 cluster control.

[0045] On the other hand, this embodiment also provides a three-phase four-wire topology optimization system applied to an energy storage converter system, which includes:

[0046] The topology unit connects the converter to the energy storage battery system and performs structural topology.

[0047] After the control unit is connected, it can adjust the control algorithm to balance the battery cluster.

[0048] If the above 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 method 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 and other media that can store program codes.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Example 2, reference Figure 7 , which is an embodiment of the present invention, provides a three-phase four-wire topology optimization method applied to an energy storage conversion system. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0053] Figure 7 It is a variation of the topology proposed in this patent, that is, it is used in scenarios where the N line does not need to be led out. In this scenario, the connection between the midpoint of the energy storage battery and the midpoint of the converter is conducive to the balanced control of the battery and the midpoint balance control of the converter. At the same time, the midpoint connection line can be a direct midpoint electrical connection, a midpoint electrical connection after connecting mechanical switches (circuit breakers, disconnectors, contactors, relays, etc.) and semiconductor switches (IGBT, IGCT, MOSFET, SICMOSFET, GaN, etc.) in series, a midpoint electrical connection after connecting inductors and resistors in series, or a midpoint electrical connection after connecting a combination of the above switches and components in series.

[0054] 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 three-phase four-wire topology optimization method applied to an energy storage converter system, characterized in that: include: Connect the converter to the energy storage battery system and perform the structural topology; After the connection is completed, the battery cluster is balanced and controlled by adjusting the control algorithm.

2. The three-phase four-wire topology optimization method for energy storage conversion system according to claim 1, characterized in that: Connecting the converter to the energy storage battery system includes connecting the energy storage battery system and the converter using a three-phase four-wire topology circuit; The three-phase four-wire topology circuit has one end connected to the grid side or load of the energy storage conversion system, and the other end connected to the battery side of the energy storage conversion system; The DC positive pole of the energy storage battery is connected to the positive pole of the converter, the negative pole of the energy storage battery is connected to the negative pole of the converter, and the midpoint of the energy storage battery is connected to the midpoint of the DC side of the converter.

3. The three-phase four-wire topology optimization method for energy storage conversion system according to claim 2, characterized in that: After the energy storage battery midpoint and the converter DC midpoint are connected, when the number of battery clusters is greater than 1, one of the two execution schemes is randomly executed; the two execution schemes include connecting one or more clusters of the current midpoint connection line to the converter DC midpoint; connecting all the midpoints of the battery clusters to the converter DC midpoint; When the number of converters is greater than 1, one of two execution schemes is randomly executed; the two execution schemes include connecting the midpoint connection line of the energy storage battery to the DC midpoint of one or more converters individually; connecting the midpoint of the battery cluster to the DC midpoints of all converters.

4. The three-phase four-wire topology optimization method for energy storage conversion system according to claim 3, characterized in that: The connection between the energy storage battery midpoint and the converter DC midpoint includes: direct midpoint electrical connection, midpoint electrical connection after the switch device, midpoint electrical connection after the series inductor and resistor, and midpoint electrical connection after the series connection of multiple switches and components.

5. The three-phase four-wire topology optimization method for energy storage conversion system according to claim 4, characterized in that: The structural topology includes that the midpoint of the energy storage battery and the DC midpoint of the converter are connected and then led out as an AC N line; After the cells of the energy storage battery are connected in series, the number of cells on the upper and lower busbars is equal; The energy storage battery is used by directly connecting the battery cells in series or by connecting an even number of battery packs in series.

6. The three-phase four-wire topology optimization method for energy storage conversion system according to claim 5, characterized in that: The conversion topology of the converter is other converter topologies in which the DC midpoint is led out and connected to the DC midpoint of the energy storage system, including but not limited to the three-level type, the T-type three-level, and the ANPC.

7. The three-phase four-wire topology optimization method for energy storage conversion system according to claim 6, characterized in that: The control algorithm includes subdividing the balanced control of the battery cluster into 0.5 cluster control as a control target, and realizing different power charging and discharging strategies for the upper bus and the lower bus of the energy storage battery system through adjustment of the control algorithm.

8. A three-phase four-wire topology optimization system for an energy storage converter system using the method according to any one of claims 1 to 7, characterized in that: A topology unit connects the converter to the energy storage battery system and performs structural topology; After the control unit completes the connection, it controls the balancing of the battery cluster by adjusting the control algorithm.

9. A computer device comprising: A memory and a processor; the memory stores a computer program, wherein the processor implements the steps of any method as claimed in claim 1 when executing the computer program.

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 method according to any one of claims 1 to 7 are implemented.

Images