Modularized multi-level energy storage system of distributed series inductors

Abstract

The invention relates to the technical field of battery energy storage, and discloses a modular multilevel energy storage system of distributed series inductors, which is connected with a three-phase power grid and comprises three phase units and an alternating current switch, and the three phase units and the alternating current switch are respectively connected to form a triangular energy storage system or a Y-shaped energy storage system; wherein the three phase units are respectively an A phase unit, a B phase unit and a C phase unit; each phase unit comprises a plurality of energy storage modules which are connected in series, and each energy storage module comprises a full-bridge unit and a battery module; a direct current port of the full-bridge unit is connected with the battery module, an alternating current port is connected with a three-phase power grid, and the full-bridge unit is used for achieving direct current and alternating current power transmission and conversion functions. By controlling the logic combination of the full-bridge semiconductor power device and the bypass switch, the adjustment of the equivalent series inductance value of the phase unit is realized, and the flexibility of the control system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery energy storage, and in particular to a modular multi-level energy storage system with distributed series inductors. Background Art

[0002] In traditional cascade energy storage solutions, energy storage modules are equipped with bypass switches S. If the bypass switch S malfunctions during system operation, the AC1\AC2 ports of the energy storage module will be directly short-circuited, and the circuit current will rise rapidly without any restrictions. This will put great pressure on the protection system, and the uncontrolled short-circuit current will cause the battery to over-discharge, overheat, or even catch fire.

[0003] In traditional cascade energy storage solutions, reactors are all centralized, with the disadvantage that the parameters are fixed values ​​and the insulation voltage is required to be the system voltage. The disadvantage of fixed inductance value is that the system power control method is relatively fixed, and there may be dead zones in some operating ranges, resulting in a reduction in the system operating range. The insulation voltage is increased to the system voltage, and the cascade type is mostly high voltage, which will increase the insulation cost of the reactor. At the same time, the electrical clearance and creepage of the layout space are also increased accordingly, increasing the layout area and leading to an increase in system cost.

[0004] The modular multi-level energy storage system is generally composed of multiple full-bridge units cascaded and connected to the grid through a centralized reactor; the centralized reactor plays a role in limiting the system short-circuit current, absorbing and compensating the grid reactive power, and limiting the closing inrush current and high-order harmonics in the grid. The full-bridge unit is generally equipped with a bypass switch at the AC port to bypass the fault module and improve the reliability of the system; however, if the bypass switch is malfunctioned during normal system operation, the full-bridge unit will be directly short-circuited, causing risks such as explosion and fire; at the same time, the number of full-bridge units in each phase of the multi-level converter will also change according to the system operation needs. If the reactor is a fixed parameter, it will limit the flexibility of the control system.

[0005] Therefore, it is an urgent problem for those skilled in the art to propose a modular multi-level energy storage system with distributed series inductors to solve the difficulties existing in the prior art. Summary of the invention

[0006] The purpose of the present invention is to provide a modular multi-level energy storage system with distributed series inductance, which can adjust the equivalent series inductance value of the phase unit by controlling the logical combination of the full-bridge semiconductor power device and the bypass switch, thereby improving the flexibility of the control system.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A modular multi-level energy storage system with distributed series inductance is connected to a three-phase power grid and includes three phase units and an AC switch. The three phase units and the AC switch are respectively connected to form a triangle energy storage system or a Y-shaped energy storage system. The three phase units are an A phase unit, a B phase unit, and a C phase unit. Each phase unit includes a plurality of series-connected energy storage modules, and the energy storage modules include a full-bridge unit and a battery module.

[0009] Full-bridge unit, the DC port is connected to the battery module, and the AC port is connected to the three-phase grid, which is used to realize DC and AC power transmission and conversion functions;

[0010] A battery module is used to exchange energy with a three-phase power grid in the form of charging and discharging;

[0011] The AC switch is used to connect the three-phase power grid with the triangle energy storage system or the Y-shaped energy storage system, and has the functions of disconnecting, connecting and protecting the energy storage system and the power grid.

[0012] Preferably, the battery module is composed of a plurality of single cells and a fuse FU connected in series.

[0013] Preferably, the full-bridge unit includes four groups of power electronic devices Q1, Q2, Q3, Q4, a DC bus capacitor C, an inductor L, a bypass switch S and a control system; wherein the control end of the power electronic device is electrically connected to the control system, the power electronic devices Q1, Q2, Q3, Q4 form two bridge arms, and the input ends of the two bridge arms are connected to the output ends of the battery module.

[0014] Preferably, the power electronic devices Q1, Q2, Q3, and Q4 are selected as MOS tubes, the source electrodes of the power electronic devices Q1 and Q3 are connected to form a DC bus DC+, the drain electrodes of the power electronic devices Q2 and Q4 are connected to form a DC bus DC-; the control system is connected to the drain electrodes of the power electronic devices Q1, Q2, Q3, and Q4;

[0015] The drain of the power electronic device Q1 is connected to the source of the power electronic device Q2, and the drain of the power electronic device Q3 is connected to the source of the power electronic device Q4; the inductor L and the bypass switch S are connected in series and connected to the drains of the power electronic devices Q1 and Q3 respectively, and the two ends of the bypass switch S are led out to form an AC port AC1 and an AC port AC2.

[0016] Preferably, the full-bridge unit also includes a current detector RT, which is arranged between the source of the power electronic devices Q1 and Q3 and the DC bus DC+. The current detector RT is electrically connected to the control system and is used to send the detected current to the control system. The control system controls the opening and closing of the four groups of power electronic devices according to preset logic.

[0017] Preferably, the connection relationship between the phase units and the phase units, and the AC switches and the phase units in the triangle energy storage system is as follows:

[0018] The AC1 port of the A phase unit is connected to the AC2 port of the B phase unit, the AC1 port of the B phase unit is connected to the AC2 port of the C phase unit, the AC1 port of the C phase unit is connected to the AC2 port of the A phase unit, the AC1 port of the A phase unit is connected to the A phase output port of the AC switch, the AC1 port of the B phase unit is connected to the B phase output port of the AC switch, and the AC1 port of the C phase unit is connected to the C phase output port of the AC switch.

[0019] Preferably, the connection relationship between the phase units and the phase units, and the AC switch and the phase units in the Y-shaped energy storage system is as follows:

[0020] The AC2 port of the A phase unit is connected to the AC2 port of the B phase unit, the AC2 port of the B phase unit is connected to the AC2 port of the C phase unit, the AC1 port of the A phase unit is connected to the A phase output port of the AC switch, the AC1 port of the B phase unit is connected to the B phase output port of the AC switch, and the AC1 port of the C phase unit is connected to the C phase output port of the AC switch.

[0021] Preferably, the connection relationship between the AC switch and the three-phase power grid in the triangle energy storage system or the Y-shaped energy storage system is as follows:

[0022] The A-phase incoming line port of the AC switch is connected to the A phase of the power grid, the B-phase incoming line port of the AC switch is connected to the B phase of the power grid, and the C-phase incoming line port of the AC switch is connected to the C phase of the power grid.

[0023] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0024] (1) The present invention designs the inductor at the AC outlet of the full-bridge unit, which can limit the rising rate of the short-circuit current of the energy storage module when the bypass switch is mistakenly closed, thereby gaining more response time for the control system protection strategy and improving the reliability of the protection system action; the inductor is designed at the AC outlet of the full-bridge unit, which can limit the rising rate of the short-circuit current when the bypass switch is mistakenly closed, thereby reducing the short-circuit current tolerance requirement of the full-bridge unit;

[0025] (2) The AC port of the full-bridge unit of the present invention is connected in series with an inductor and a bypass switch. The system adjusts the equivalent series inductance value of the phase unit by controlling the logical combination of the full-bridge semiconductor power device and the bypass switch, thereby improving the flexibility of the control system;

[0026] (3) Compared with the traditional topology, the energy storage system of the present invention eliminates the centralized reactor on the AC side, which reduces the overall footprint of the system and reduces costs. The reactor is designed at the AC port of the full-bridge unit, and compared with the centralized reactor, low-voltage inductor devices can be used to reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 A topological diagram of the energy storage module provided by the present invention;

[0029] Figure 2 A topological diagram of a modular multi-level energy storage system of distributed series inductance according to the present invention;

[0030] Among them, (a) is the topology diagram of the triangle energy storage system, and (b) is the topology diagram of the Y-shaped energy storage system. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 2 As shown, the present invention provides a distributed series inductor modular multi-level energy storage system, the whole system has a higher degree of modularization, is connected to a three-phase power grid, and includes three phase units and an AC switch, the three phase units and the AC switch are respectively connected to form a triangle energy storage system or a Y-shaped energy storage system; wherein the three phase units are respectively an A phase unit, a B phase unit, and a C phase unit; each phase unit includes a plurality of series-connected energy storage modules, and the energy storage modules include a full-bridge unit and a battery module;

[0034] Full-bridge unit, the DC port is connected to the battery module, and the AC port is connected in series with the AC end of other full-bridge units and then connected to the power grid. When working, the full-bridge unit controls the Q1~Q4 power electronic switches through PWM-pulse width modulation technology, and according to the volt-ampere equivalent principle, the DC power is chopped into equivalent AC power to achieve AC-DC conversion and power transmission functions;

[0035] Battery module, energy carrier, electrical energy is stored in the battery module, and is used to exchange energy with the three-phase power grid in the form of charging and discharging;

[0036] The AC switch is used to connect the three-phase power grid with the triangle energy storage system or the Y-shaped energy storage system, and has the functions of disconnecting, connecting and protecting the energy storage system and the three-phase power grid.

[0037] Specifically, the AC2 port of energy storage module 1 is connected to the AC1 port of energy storage module 2, and the AC2 port of energy storage module 2 is connected to the AC1 port of energy storage module 3. The AC ports of N energy storage modules are connected in series hand in hand to form a phase unit. The external interface of the phase unit is the AC1 port of energy storage module 1 and the AC2 port of energy storage module N; N depends on the system voltage.

[0038] Furthermore, the battery module is composed of a plurality of single cells and a fuse FU connected in series.

[0039] Furthermore, full-bridge units such as Figure 1 The shown embodiment includes four groups of power electronic devices Q1, Q2, Q3, Q4, a DC bus capacitor C, an inductor L, a bypass switch S and a control system; wherein the control end of the power electronic device is electrically connected to the control system, the power electronic devices Q1, Q2, Q3, Q4 form two bridge arms, and the input ends of the two bridge arms are connected to the output ends of the battery modules.

[0040] Furthermore, the power electronic devices Q1, Q2, Q3, and Q4 are selected as MOS tubes, the source electrodes of the power electronic devices Q1 and Q3 are connected to form a DC bus DC+, the drain electrodes of the power electronic devices Q2 and Q4 are connected to form a DC bus DC-; the control system is connected to the drain electrodes of the power electronic devices Q1, Q2, Q3, and Q4;

[0041] The drain of the power electronic device Q1 is connected to the source of the power electronic device Q2, and the drain of the power electronic device Q3 is connected to the source of the power electronic device Q4; the inductor L and the bypass switch S are connected in series and connected to the drains of the power electronic devices Q1 and Q3 respectively, and the two ends of the bypass switch S are led out to form an AC port AC1 and an AC port AC2.

[0042] Furthermore, the full-bridge unit also includes a current detector RT, which is arranged between the source of the power electronic devices Q1 and Q3 and the DC bus DC+. The current detector RT is electrically connected to the control system and is used to send the detected current to the control system. The control system controls the opening and closing of the four groups of power electronic devices according to preset logic.

[0043] Specifically, when the system is running, the AC1 and AC2 ports are PWM waves, and the bypass switch S is mistakenly closed when it fails, which will cause the AC1 and AC2 ports of the energy storage module to be short-circuited. RT detects the short-circuit current and sends it to the control system. The control system shuts down the Q1~Q4 power electronic devices according to the preset to achieve the short-circuit protection function. Due to the existence of L in the present invention, the rising speed of the short-circuit current is limited, the short-circuit protection cut-off current is reduced, the heat accumulation effect caused by the short-circuit current is reduced, and the short-circuit stress requirement of the device is reduced.

[0044] Furthermore, the connection relationship between the phase units and the phase units, and the AC switches and the phase units in the triangle energy storage system is as follows: Figure 2 As shown in (a):

[0045] The AC1 port of the A phase unit is connected to the AC2 port of the B phase unit, the AC1 port of the B phase unit is connected to the AC2 port of the C phase unit, the AC1 port of the C phase unit is connected to the AC2 port of the A phase unit, the AC1 port of the A phase unit is connected to the A phase output port of the AC switch, the AC1 port of the B phase unit is connected to the B phase output port of the AC switch, and the AC1 port of the C phase unit is connected to the C phase output port of the AC switch.

[0046] Furthermore, the connection relationship between the phase units and the phase units, and the AC switch and the phase units in the Y-shaped energy storage system is as follows: Figure 2 As shown in (b):

[0047] The AC2 port of the A phase unit is connected to the AC2 port of the B phase unit, the AC2 port of the B phase unit is connected to the AC2 port of the C phase unit, the AC1 port of the A phase unit is connected to the A phase output port of the AC switch, the AC1 port of the B phase unit is connected to the B phase output port of the AC switch, and the AC1 port of the C phase unit is connected to the C phase output port of the AC switch.

[0048] Furthermore, the connection relationship between the AC switch and the three-phase grid in the triangle energy storage system or the Y-shaped energy storage system is as follows:

[0049] The A-phase incoming line port of the AC switch is connected to the A phase of the power grid, the B-phase incoming line port of the AC switch is connected to the B phase of the power grid, and the C-phase incoming line port of the AC switch is connected to the C phase of the power grid.

[0050] Specifically, when the system is running, by controlling a certain energy storage module in the phase unit to be in any bypass state in Table 1, the inductance value of the AC side can be adjusted;

[0051] Table 1

[0052]

[0053] In the embodiment, during normal operation, all energy storage modules of the A-phase unit are in operation, and the A-phase AC measured inductance value is n*L, where n is the number of A-phase modules and L is the inductance value of the full-bridge unit;

[0054] When the energy storage module 1 is operated in software bypass state 1 or 2, the voltage of phase A becomes (n-1)*Vac, and the inductance of phase A remains unchanged, which is still n*L; when the energy storage module 1 is operated in hardware bypass state 1 or 2, the voltage of phase A becomes (n-1)*Vac, and the inductance of phase A becomes (n-1)*L;

[0055] By controlling the number of energy storage modules in the phase that are in the software bypass state and the hardware bypass state, the voltage and inductance in the phase can be adjusted and changed.

[0056] When the system of the present invention is in operation, it is divided into two states: charging and discharging. During charging, the AC switch is closed and the energy storage system is connected to the power grid; the full-bridge unit starts working, and the energy storage system works in the voltage source mode. The voltage phase angle of the energy storage system is adjusted to a state lagging behind the phase angle of the power grid, and the size of the phase difference is controlled to control the size of the charging power; similarly, during discharging, the voltage phase angle of the energy storage system is adjusted to a state leading the phase angle of the power grid, and the size of the phase angle difference is adjusted to achieve the adjustment of the discharge power.

[0057] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0058] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A modular multi-level energy storage system with distributed series inductance, connected to a three-phase power grid, characterized in that: It includes three phase units and an AC switch, wherein the three phase units and the AC switch are respectively connected to form a triangle energy storage system or a Y-shaped energy storage system; wherein the three phase units are respectively an A phase unit, a B phase unit, and a C phase unit; each phase unit includes a plurality of energy storage modules connected in series, and the energy storage modules include a full-bridge unit and a battery module; The full-bridge unit has a DC port connected to the battery module and an AC port connected to the three-phase power grid, and is used to realize DC and AC power transmission and conversion functions; The battery module is used to exchange energy with the three-phase power grid in the form of charging and discharging; The AC switch is used to connect the three-phase power grid and the triangle energy storage system or the Y-shaped energy storage system, and has the functions of disconnecting, connecting and protecting the energy storage system and the three-phase power grid.

2. A modular multi-level energy storage system with distributed series inductance according to claim 1, characterized in that: The battery module is composed of a plurality of single cells and a fuse FU connected in series.

3. A modular multi-level energy storage system with distributed series inductance according to claim 1, characterized in that: The full-bridge unit includes four groups of power electronic devices Q1, Q2, Q3, Q4, a DC bus capacitor C, an inductor L, a bypass switch S and a control system; wherein the control end of the power electronic device is electrically connected to the control system, the power electronic devices Q1, Q2, Q3, Q4 form two bridge arms, and the input ends of the two bridge arms are connected to the output end of the battery module.

4. A modular multi-level energy storage system with distributed series inductance according to claim 3, characterized in that: The power electronic devices Q1, Q2, Q3, and Q4 are selected as MOS tubes, the source electrodes of the power electronic devices Q1 and Q3 are connected to form a DC bus DC+, and the drain electrodes of the power electronic devices Q2 and Q4 are connected to form a DC bus DC-; the control system is connected to the drain electrodes of the power electronic devices Q1, Q2, Q3, and Q4; The drain of the power electronic device Q1 is connected to the source of the power electronic device Q2, and the drain of the power electronic device Q3 is connected to the source of the power electronic device Q4; the inductor L and the bypass switch S are connected in series and connected to the drains of the power electronic devices Q1 and Q3 respectively, and the two ends of the bypass switch S are led out to form an AC port AC1 and an AC port AC2.

5. A modular multi-level energy storage system with distributed series inductance according to claim 4, characterized in that: The full-bridge unit also includes a current detector RT, which is arranged between the source of the power electronic devices Q1 and Q3 and the DC bus DC+. The current detector RT is electrically connected to the control system and is used to send the detected current to the control system. The control system controls the opening and closing of the four groups of power electronic devices according to preset logic.

6. A modular multi-level energy storage system with distributed series inductance according to claim 1, characterized in that: In the triangle energy storage system, the connection relationship between the phase units and the AC switches and the phase units is as follows: The AC1 port of the A phase unit is connected to the AC2 port of the B phase unit, the AC1 port of the B phase unit is connected to the AC2 port of the C phase unit, the AC1 port of the C phase unit is connected to the AC2 port of the A phase unit, the AC1 port of the A phase unit is connected to the A phase outlet port of the AC switch, the AC1 port of the B phase unit is connected to the B phase outlet port of the AC switch, and the AC1 port of the C phase unit is connected to the C phase outlet port of the AC switch.

7. The method for maintaining DC balance of a high-voltage cascade energy storage system by using a grounding switch backflow according to claim 1, characterized in that: In the Y-shaped energy storage system, the connection relationship between the phase units and the phase units, and the AC switch and the phase units is as follows: The AC2 port of the A-phase unit is connected to the AC2 port of the B-phase unit, the AC2 port of the B-phase unit is connected to the AC2 port of the C-phase unit, the AC1 port of the A-phase unit is connected to the A-phase output port of the AC switch, the AC1 port of the B-phase unit is connected to the B-phase output port of the AC switch, and the AC1 port of the C-phase unit is connected to the C-phase output port of the AC switch.

8. The method for maintaining DC balance of a high-voltage cascade energy storage system by using grounding switch backflow according to claim 1, characterized in that: In the triangle energy storage system or Y-shaped energy storage system, the connection relationship between the AC switch and the three-phase power grid is as follows: The A-phase incoming line port of the AC switch is connected to the power grid A, the B-phase incoming line port of the AC switch is connected to the power grid B, and the C-phase incoming line port of the AC switch is connected to the power grid C.

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