Energy storage converter for sodium ion battery energy storage system and control method thereof

Abstract

The present invention discloses an energy storage converter for a sodium ion battery energy storage system and a control method thereof. The energy storage converter is a PPP converter, which is a DC-DC converter with different connection structures, including a type-one structure with parallel input and series output and a type-two structure with series input and parallel output. During the charging and discharging process of the sodium ion battery energy storage system, the output voltage of the sodium ion battery cluster is judged, and the PPP converter is controlled to bypass the DC-DC converter in the PPP converter, or a square wave driving signal with a lagging phase angle is applied to the two H bridges on the primary and secondary sides of the converter, and the DC-DC converter in the PPP converter is controlled to boost the voltage. The present invention can make the converter run normally and be smoothly connected to the grid, and improve the reliability, utilization rate and overall energy conversion efficiency of the converter.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery energy storage, and in particular to an energy storage converter for a sodium ion battery energy storage system and a control method thereof. Background Art

[0002] In recent years, energy storage technology has developed rapidly due to its functions of peak shaving, backup energy, and grid connection with renewable energy. Among them, sodium-ion batteries are increasingly being used in the field of energy storage due to their excellent performance and low cost. A converter is set up in the energy storage system to achieve bidirectional energy transmission between the energy storage battery and the subsequent inverter, and to boost the DC battery to provide a normal and stable input voltage for the subsequent inverter, thereby ensuring the stability and reliability of the entire energy storage system.

[0003] However, with the continuous increase in energy storage capacity and power, traditional energy storage systems face the challenge of designing converters with larger capacity and higher withstand voltage values, which not only puts higher requirements on cost, volume and components, but also because the operating voltage range of sodium-ion batteries (1.5-3.9V) is wider than that of lithium-ion batteries (2.5-3.65V), the converter connected to sodium-ion batteries needs to have a wider input voltage range. This requirement is more demanding on the design of the converter. When the sodium-ion battery operates at a lower or higher operating voltage, the existing converter may not be suitable for the operating voltage, which makes the converter unable to operate in the best state, thereby reducing the reliability and utilization of the converter and the overall energy conversion efficiency of the system. Therefore, it is of great significance and value to study the structure of energy storage converters for sodium-ion batteries. Summary of the invention

[0004] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides an energy storage converter for a sodium ion battery energy storage system and a control method thereof, designs a converter structure based on partial power processing (PPP), namely, a PPP converter, and designs a corresponding control method according to the PPP converter, so that the converter can perform a voltage boosting action in coordination with the input voltage of the energy storage battery, thereby enabling the subsequently connected DC-AC converter to operate normally and be smoothly connected to the grid, thereby ensuring the stability of the energy storage system; at the same time, the converter has a smaller size, cost and capacity, effectively improving the reliability, utilization rate and overall energy conversion efficiency of the converter.

[0005] In a first aspect, the present invention provides an energy storage converter for a sodium ion battery energy storage system.

[0006] An energy storage converter for a sodium ion battery energy storage system, the energy storage converter is a PPP converter, the PPP converter is a DC-DC converter using different connection structures, the connection structure includes a type one structure of input parallel output series and a type two structure of input series output parallel;

[0007] The input side of the PPP converter is connected to a sodium ion battery cluster, the output side of the PPP converter is connected to a DC end of a bidirectional DC-AC converter, and the AC end of the bidirectional DC-AC converter is connected to a power grid.

[0008] In a second aspect, the present invention also provides a control method for an energy storage converter.

[0009] A control method for an energy storage converter, comprising:

[0010] During the charging and discharging process of the sodium ion battery cluster, when the voltage of the sodium ion battery cluster is higher than the set threshold voltage, the PPP converter is controlled to bypass the DC-DC converter in the PPP converter. At this time, the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter and is regulated and connected to the grid through the bidirectional DC-AC converter.

[0011] When the voltage of the sodium ion battery cluster is lower than the set threshold voltage, the DC-DC converter in the PPP converter is controlled to boost the voltage, and the boosted voltage is then adjusted by the bidirectional DC-AC converter and connected to the power grid.

[0012] One or more of the above technical solutions have the following beneficial effects:

[0013] 1. The present invention provides an energy storage converter for a sodium ion battery energy storage system and a control method thereof. A converter structure based on partial power processing with high efficiency and high power density is designed, and a corresponding control method is designed according to the converter structure, so that the converter can perform a voltage boosting action in coordination with the input voltage of the energy storage battery, thereby enabling the subsequently connected DC-AC converter to operate normally and be smoothly connected to the grid, thereby ensuring the stability of the energy storage system.

[0014] 2. The sodium-ion battery energy storage converter and control method thereof provided by the present invention can greatly reduce the volume, cost and capacity of the converter in the lithium-ion battery energy storage system, and effectively improve the reliability, utilization rate and overall energy conversion efficiency of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0016] Figure 1This is a schematic diagram of the structure of a sodium ion battery energy storage system in an embodiment of the present invention;

[0017] Figure 2 Schematic diagram of two PPP converter structures and energy flow during forward boost and reverse buck in the embodiment of the present invention;

[0018] Figure 3 Schematic diagram of the structure of a type (IPOS) PPP converter based on a DAB converter in an embodiment of the present invention;

[0019] Figure 4 It is a working flow chart of a type (IPOS) PPP converter structure based on a DAB converter in an embodiment of the present invention;

[0020] Figure 5 Schematic diagram of the structure of a type II (ISOP) PPP converter based on a DAB converter in an embodiment of the present invention;

[0021] Figure 6 1 is a flowchart of the working process of the type II (ISOP) PPP converter structure based on the DAB converter in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] It should be noted that the following detailed descriptions are exemplary only, are intended to describe specific embodiments, are intended to provide further explanation of the present invention, and are not intended to limit exemplary embodiments according to the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] Embodiment 1

[0024] This embodiment provides an energy storage converter for a sodium ion battery energy storage system. The energy storage converter is a converter structure based on partial power processing (PPP), hereinafter referred to as a PPP converter. Figure 1 As shown in FIG. 1 , the sodium-ion battery energy storage system includes four parts: a sodium-ion battery cluster, a PPP converter, a bidirectional DC-AC converter, and a power grid. The input side of the PPP converter is connected to the sodium-ion battery cluster, the output side of the PPP converter is connected to the DC end of the bidirectional DC-AC converter, and the AC end of the bidirectional DC-AC converter is connected to the power grid. Among them, the PPP converter is a DC-DC converter with different connection structures. The typical connection structures are input parallel output series (IPOS, Input Parallel Output Series) type structures, such as Figure 2 (a) and (c) show the second type of structure, which is input series output parallel (ISOP, Input Series Output Parallel). Figure 2 As shown in (b) and (d).

[0025] In this embodiment, the DC-DC converter adopts a DAB converter as an example, that is, a type I (IPOS) PPP converter and a type II (ISOP) PPP converter based on a DAB (Dual Active Bridge) converter are taken as examples for further detailed introduction.

[0026] Among them, the topology of a type of PPP converter based on DAB converter is as follows: Figure 3 As shown, the topological structure of the DAB converter includes two H bridges and a transformer; each H bridge is composed of two bridge arms connected in parallel, and each bridge arm is composed of an upper switch and a lower switch connected in series; one of the H bridges (i.e. Figure 3 The left H bridge in the middle) is connected in parallel with the input circuit as the primary side of the transformer, and the other H bridge (i.e. Figure 3 The H bridge on the right side of the transformer is connected in series with the output circuit as the secondary side of the transformer. The input circuit includes a parallel input voltage source (i.e., input voltage V in ) and a first DC capacitor, the output circuit includes an output voltage source (i.e., output voltage V0) and a second DC capacitor connected in parallel. In addition, the primary side of the transformer is connected to the midpoint of the two bridge arms of the H bridge in the primary circuit after being connected to the inductor, and the secondary side of the transformer is connected to the midpoint of the two bridge arms of the H bridge in the secondary circuit.

[0027] Furthermore, the H bridge in the primary circuit includes a first switch Q l , a second switch Q2, a third switch Q3 and a fourth switch Q4, wherein the first switch Q1 and the second switch Q2 constitute a first bridge arm of the H-bridge, and the third switch Q3 and the fourth switch Q4 constitute a second bridge arm of the H-bridge. Similarly, the H-bridge in the secondary circuit comprises a fifth switch Q5, a sixth switch Q6, a seventh switch Q7 and an eighth switch Q8, wherein the fifth switch Q5 and the sixth switch Q6 constitute a first bridge arm of the H-bridge, and the seventh switch Q7 and the eighth switch Q8 constitute a second bridge arm of the H-bridge.

[0028] Similarly, among them, the topology of the type II PPP converter based on the DAB converter, such as Figure 5As shown, the topological structure of the DAB converter includes two H-bridges and a transformer; each H-bridge is formed by two bridge arms connected in parallel, and each bridge arm is formed by two upper and lower switches connected in series; one of the H-bridges is connected in series with the input circuit as the primary side of the transformer, and the other H-bridge is connected in parallel with the output circuit as the secondary side of the transformer, the input circuit includes a parallel input voltage source and a first DC capacitor, and the output circuit includes a parallel output voltage source and a second DC capacitor. In addition, the primary side of the transformer is connected to the midpoint of the two bridge arms of the H-bridge in the primary circuit after being connected to the inductor, and the secondary side of the transformer is connected to the midpoint of the two bridge arms of the H-bridge in the secondary circuit.

[0029] Embodiment 2

[0030] This embodiment provides a control method for an energy storage converter, which is used to control the energy storage converter for a sodium ion battery energy storage system proposed in Embodiment 1. The control method includes:

[0031] During the charging and discharging process of the sodium ion battery cluster, when the voltage of the sodium ion battery cluster is higher than the set threshold voltage, the PPP converter is controlled to bypass the DC-DC converter in the PPP converter. At this time, the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter and is regulated and connected to the grid through the bidirectional DC-AC converter; when the voltage of the sodium ion battery cluster is lower than the set threshold voltage, the DC-DC converter in the PPP converter is controlled to boost the voltage, and the boosted voltage is then regulated and connected to the grid through the bidirectional DC-AC converter.

[0032] Specifically, the sodium-ion battery energy storage system can be divided into the battery charging process and the battery discharging process, and each process can be divided into two stages. During the battery discharging process (the energy flow direction is specified as forward at this time), when the voltage of the sodium-ion battery cluster is higher than the set threshold voltage, the DC-DC converter in the PPP converter is bypassed, and the sodium-ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter, and then connected to the grid after being inverted by the bidirectional DC-AC converter. The energy flow of the PPP converter is as follows: Figure 2 As shown in the dotted line loop in (a) and (b); when the voltage of the sodium ion battery cluster is lower than the set threshold voltage, the DC-DC converter in the PPP converter is activated and cooperates with the battery voltage V in The voltage is boosted to enable the bidirectional DC-AC converter to operate normally and connect to the grid smoothly. The energy flow is as follows Figure 2 As shown by the arrows in (a) and (b). During the battery charging process (the energy flow direction is specified to be reverse at this time), the AC end of the bidirectional DC-AC converter is connected to the grid, and the battery is charged after being rectified by the bidirectional DC-AC converter. When the voltage of the sodium ion battery cluster is higher than the set threshold voltage, the DC-DC converter in the PPP converter is bypassed, and the DC end of the bidirectional DC-AC converter is directly connected to the sodium ion battery cluster. The energy flow of the PPP converter is shown in Figure 1. Figure 2 As shown in the dotted loops in (c) and (d); when the voltage of the sodium ion battery cluster is lower than the set threshold voltage, the bidirectional DC-AC converter cannot rectify the grid voltage to such a low voltage, so the DC-DC converter in the PPP converter is controlled to act and achieve reverse voltage reduction. At this time, the sodium ion battery can be charged normally, and the energy flow is shown in Figure 2 As indicated by the arrows in (c) and (d).

[0033] Taking the IPOS PPP converter and the ISOP PPP converter based on the DAB (Dual Active Bridge) converter proposed in the first embodiment as examples, the control methods thereof are further introduced. In this embodiment, the nominal voltage of the sodium ion battery cluster is 1500V (the voltage of the single cell is 3V), the output voltage range of the sodium ion battery cluster is 750-1950V (the voltage range of the single cell is 1.5-3.9V), the threshold voltage is set to 1350V, and the rated charge and discharge current of the battery is I r In this embodiment, the control method adopts phase shift control, that is, a 50% duty cycle square wave driving signal is applied to the same upper and lower complementary tubes of the primary and secondary H-bridge diagonal tubes of the DAB, and the phase angle of the primary side leading the secondary side is controlled. ( Also called the phase shift angle, ), realize the control of converter energy flow, set the rated operating

[0034] (1) Type I (IPOS) PPP converter

[0035] The working process of a type (IPOS) PPP converter based on DAB converter is as follows Figure 4 As shown, first, it is determined whether the sodium-ion battery energy storage system is in a charging state or a discharging state, and the hysteresis phase angle applied by the two H bridges of the primary and secondary sides of the DC-DC converter is set according to the different charging and discharging states. The set lag phase angle is the set phase shift angle. If it is in the discharge state, the set phase shift angle And the phase shift angle during the whole discharge process If it is in charging state, set the phase shift angle And the phase shift angle during the entire charging process

[0036] Then, it is determined whether the battery voltage of the sodium ion battery cluster during the charging and discharging process is within the rated voltage range of the battery cluster. If it is within the range, it is determined whether the voltage exceeds the set threshold voltage. If it exceeds, the seventh switch and the eighth switch of the H-bridge arm of the secondary side of the converter are closed to bypass the DC-DC converter, so that the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter. If it does not exceed, a square wave driving signal with a set lagging phase angle is applied to the two H-bridges of the primary and secondary sides of the converter to control the converter switch action, and the lagging phase angle is adjusted according to the output current of the converter, that is, the shift phase is adjusted until the output current reaches the rated current value, and then connected to the grid for charging and discharging.

[0037] Specifically, it is determined whether the battery can work normally according to the battery voltage. If not, an undervoltage or saturation warning is issued and the system does not start running; if yes, the system continues to work.

[0038] When the system is in the discharge state, if the battery voltage is greater than 1350V, the switch tubes Q7 and Q8 are closed to bypass the DAB converter. The sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter and then connected to the grid through the bidirectional DC-AC converter. The energy transmission does not pass through the DC-DC converter, avoiding the additional energy loss caused by the current flowing through the switches, transformers, and wires of the converter, thereby improving the energy conversion efficiency of the system. The energy flow is shown in the figure. Figure 2 (a) is shown as the dotted line loop. If the battery voltage is less than 1350V, the DAB converter switch tube will operate to form a voltage V C , V C Then with the battery voltage V in The voltage V is obtained by connecting in series o (i.e. V o =V in +V C ), achieving a boost effect, allowing the bidirectional DC-AC converter to be smoothly connected to the grid. The energy flow is as follows Figure 2 As shown by the arrow in (a). Since only part of the power flows to the grid through the DC-DC converter in this process, the required converter capacity is reduced, the converter cost is reduced, the converter volume is reduced, and the system energy conversion efficiency is improved. Figure 3 , the formula can be obtained from the DAB converter topology:

[0039]

[0040] Where n is the transformer T r Transformation ratio, D is the displacement ratio f s is the frequency of the driving signal, L k is the DAB inductance value. From formula (1), we can see that when the battery voltage V inWhen the current I changes, the shift phase D can be adjusted to maintain the current I o stability, and because V o =I o R o (R o is the PPP converter output equivalent resistance) to maintain the voltage V o In addition, V in I in =V o I o , then we can get the formula:

[0041]

[0042] From the above formula, we can know that the battery charge and discharge current I can be controlled by adjusting the shift phase D. in When in the discharge state, if the converter output current I in Greater than the rated current I r , which can reduce the phase shift angle Then the current I in Reduce to rated current I r On the contrary, the phase shift angle can be increased Then the current I in Rise to rated current I r .

[0043] When the system is in charging state, if the battery voltage is greater than 1350V, the switch tubes Q7 and Q8 are closed to bypass the DAB converter. The grid energy is rectified by the bidirectional DC-AC converter and directly charges the battery. The energy transmission does not pass through the DC-DC converter, which improves the energy conversion efficiency of the system. The energy flow is as follows: Figure 2 (c) is shown as the dotted line loop; if the battery voltage is less than 1350V, the bidirectional DC-AC converter cannot rectify the grid voltage to such a low voltage, and a square wave drive signal with a set lag phase angle is applied to the two H bridges on the primary and secondary sides of the converter to control the DAB converter switch to form a voltage V C , thereby reducing the charging voltage to achieve a voltage reduction effect, the charging voltage V in =V o -V C , the energy flow is as follows Figure 2 As shown by the arrow in (c). From formula (1), we can see that at voltage V in When the current I changes, the system stability can still be maintained by adjusting the phase shift D. From formula (2), it can be seen that when the current I in Greater than current-I r (The current is negative, indicating that its direction is the same as Figure 3 The direction is opposite to that in the calibration), which can be reduced by Make the current I inDrop to current -I r (i.e. battery charging current |I in |Rise to rated current I r ); On the contrary, the phase shift angle can be increased Then the current I in Rise to current -I r (i.e. battery charging current |I in | Reduce to rated current I r ).

[0044] (2) Type II (ISOP) PPP Converter

[0045] The working process of the second type (ISOP) PPP converter based on DAB converter is as follows Figure 6 As shown, first, it is determined whether the sodium-ion battery energy storage system is in a charging state or a discharging state, and the hysteresis phase angle applied by the two H bridges of the primary and secondary sides of the DC-DC converter is set according to the different charging and discharging states. The set lag phase angle is the set phase shift angle. If it is in the discharge state, the set phase shift angle is 0 and the phase shift angle during the entire discharge process If it is in charging state, set the phase shift angle for And the phase shift angle during the entire charging process

[0046] Then, it is determined whether the battery voltage of the sodium ion battery cluster during the charging and discharging process is within the rated voltage range of the battery cluster. If it is within the range, it is determined whether the voltage exceeds the set threshold voltage. If it exceeds, the first switch and the second switch of the H-bridge arm of the secondary side of the converter are closed to bypass the DC-DC converter, so that the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter. If it does not exceed, a square wave driving signal with a set lagging phase angle is applied to the two H-bridges of the primary and secondary sides of the converter to control the converter switch action, and the lagging phase angle is adjusted according to the output current of the converter, that is, the shift phase is adjusted until the output current reaches the rated current value, and then connected to the grid for charging and discharging.

[0047] Specifically, it is determined whether the battery can work normally according to the battery voltage. If not, an undervoltage or saturation warning is issued and the system does not start running; if yes, the system continues to work.

[0048] When the system is in the discharge state, if the battery voltage is greater than 1350V, the switch tubes Q1 and Q2 are closed to bypass the DAB converter. The sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter and then connected to the grid through the bidirectional DC-AC converter. The energy transmission does not pass through the DC-DC converter, which improves the energy conversion efficiency of the system. The energy flow is as follows: Figure 2(b) is shown as the dotted line loop. If the battery voltage is less than 1350V, the DAB converter switch tube will be activated, feeding the energy on the output side back to the input side to form a voltage V C , V C Then with the battery voltage V in The voltage V is obtained by connecting in series o (i.e. V o =V in +V C ), achieving a boost effect, allowing the bidirectional DC-AC converter to be smoothly connected to the grid. The energy flow is as follows Figure 2 As shown by the arrow in (b). C <V in When (V o <2V in ), the power processed by the DC-DC converter is less than the total power transmitted by the PPP converter, reducing the capacity, volume and cost of the required converter; but on the contrary, the power processed increases instead, losing the advantages of the PPP structure, so the second type (ISOP) PPP converter only has V o <2V in Used when Figure 5 , based on the DAB converter topology and the formula V in I in =V o I o We can get:

[0049]

[0050] Where n is the transformer T r Transformation ratio, D is the displacement ratio f s is the frequency of the driving signal, L k is the DAB inductance value. From formula (3), we can see that when the battery voltage V in When the current I changes, the shift phase D can be adjusted to maintain the current I o stability, and because V o =I o R o (R o is the PPP converter output equivalent resistance) to maintain the voltage V o In addition, the formula can be obtained from the DAB converter:

[0051]

[0052] From the above formula, we can know that the battery charge and discharge current I can be controlled by adjusting the shift phase D. in . When in discharge state, if the current I in Greater than the rated current I r , which can increase the phase shift angle Then the current I in Reduce to rated current I r On the contrary, the phase shift angle can be reduced Then the current I in Rise to rated current I r .

[0053] When the system is in charging state, if the battery voltage is greater than 1350V, the switch tubes Q1 and Q2 are closed to bypass the DAB converter. The grid energy is rectified by the bidirectional DC-AC converter and directly charges the battery. The energy transmission does not pass through the DC-DC converter, which improves the system energy conversion efficiency. The energy flow is as follows: Figure 2 (d) is shown as the dotted line loop; if the battery voltage is less than 1350V, the bidirectional DC-AC converter cannot rectify the grid voltage to such a low voltage, and a square wave drive signal with a set lag phase angle is applied to the two H bridges on the primary and secondary sides of the converter to control the DAB converter switch to form a voltage V C , thereby reducing the charging voltage to achieve a voltage reduction effect. At this time, the charging voltage V in =V o -V C , the energy flow is as follows Figure 2 As shown by the arrow in (d). From formula (3), we can see that at voltage V in When the current I changes, the system stability can still be maintained by adjusting the phase shift D. From formula (4), it can be obtained that when the current I in Greater than current-I r When the phase shift angle is increased Then the current I in Drop to current -I r (i.e. battery charging current |I in |Rise to rated current I r ); On the contrary, the phase shift angle can be reduced Then the current I in Rise to current -I r (i.e. battery charging current |I in | Reduce to rated current I r ).

[0054] In this embodiment, when the battery voltage is relatively large, the DC-DC converter can be bypassed, and energy transmission does not pass through the DC-DC converter, which improves the energy conversion efficiency of the system; when the battery voltage is relatively small, the DC-DC converter only needs to process part of the power to achieve the transmission of all the power. The processed energy is less than the actual transmitted energy, which greatly reduces the volume, cost and capacity of the sodium ion energy storage converter, and effectively improves the reliability, utilization rate and overall energy conversion efficiency of the converter.

[0055] The above description is only a preferred embodiment of the present invention. Although the specific implementation mode of the present invention is described in conjunction with the accompanying drawings, it is not a limitation of the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the protection scope of the present invention.

Claims

1. A control method for an energy storage converter for a sodium ion battery energy storage system, characterized in that: The energy storage converter is a PPP converter, and the PPP converter is a DC-DC converter using different connection structures, and the connection structure includes a type 1 structure in which the input is parallel and the output is series, and a type 2 structure in which the input is series and the output is parallel; The input side of the PPP converter is connected to the sodium ion battery cluster, the output side of the PPP converter is connected to the DC end of the bidirectional DC-AC converter, and the AC end of the bidirectional DC-AC converter is connected to the power grid; During the charging and discharging process of the sodium ion battery cluster, when the voltage of the sodium ion battery cluster is higher than the set threshold voltage, the PPP converter is controlled to bypass the DC-DC converter in the PPP converter. At this time, the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter and is regulated and connected to the grid through the bidirectional DC-AC converter. When the voltage of the sodium ion battery cluster is lower than the set threshold voltage, the DC-DC converter in the PPP converter is controlled to step up the voltage, and the voltage is then adjusted by the bidirectional DC-AC converter and connected to the grid. The DC-DC converter adopts a DAB converter, and the topological structure of a type PPP converter based on the DAB converter is: The topological structure of the DAB converter includes two H-bridges and a transformer; each H-bridge is formed by two bridge arms connected in parallel, and each bridge arm is formed by two upper and lower switches connected in series; one of the H-bridges is connected in parallel with an input circuit as a primary side of the transformer, and the other H-bridge is connected in series with an output circuit as a secondary side of the transformer, the input circuit includes an input voltage source and a first DC capacitor connected in parallel, and the output circuit includes an output voltage source and a second DC capacitor connected in parallel; Determine whether the sodium-ion battery energy storage system is in a charging state or a discharging state, and set the hysteresis phase angle applied by the two H bridges on the primary and secondary sides of the DC-DC converter according to the different charging and discharging states. Determine whether the battery voltage of the sodium ion battery cluster during the charge and discharge process is within the rated voltage range of the battery cluster. If it is within the range, determine whether the voltage exceeds the set threshold voltage. If it exceeds, the seventh switch and the eighth switch of the H-bridge arm of the secondary side of the converter are closed to bypass the DC-DC converter, so that the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter; If it does not exceed the limit, a square wave drive signal with a set lagging phase angle is applied to the two H-bridges on the primary and secondary sides of the converter to control the switching action of the converter, and the lagging phase angle is adjusted according to the output current of the converter, that is, the shift phase is adjusted until the output current reaches the rated current value, and then connected to the grid for charging and discharging.

2. The control method of the energy storage converter according to claim 1, characterized in that: The set lag phase angle is the set phase shift angle. If it is in the discharge state, the set phase shift angle is 0 and the phase shift angle during the entire discharge process If it is in charging state, set the phase shift angle for And the phase shift angle during the entire charging process 3. The control method of the energy storage converter according to claim 1, characterized in that: If the converter output current is greater than the rated current value, the lagging phase angle is reduced, otherwise the lagging phase angle is increased until the output current reaches the rated current value.

4. A control method for an energy storage converter for a sodium ion battery energy storage system, characterized in that: The energy storage converter is a PPP converter, and the PPP converter is a DC-DC converter using different connection structures, and the connection structure includes a type 1 structure in which the input is parallel and the output is series, and a type 2 structure in which the input is series and the output is parallel; The input side of the PPP converter is connected to the sodium ion battery cluster, the output side of the PPP converter is connected to the DC end of the bidirectional DC-AC converter, and the AC end of the bidirectional DC-AC converter is connected to the power grid; During the charging and discharging process of the sodium ion battery cluster, when the voltage of the sodium ion battery cluster is higher than the set threshold voltage, the PPP converter is controlled to bypass the DC-DC converter in the PPP converter. At this time, the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter and is regulated and connected to the grid through the bidirectional DC-AC converter. When the voltage of the sodium ion battery cluster is lower than the set threshold voltage, the DC-DC converter in the PPP converter is controlled to step up the voltage, and the voltage is then adjusted by the bidirectional DC-AC converter and connected to the grid. The DC-DC converter adopts a DAB converter, and the topological structure of the second-type PPP converter based on the DAB converter is: The topological structure of the DAB converter includes two H-bridges and a transformer; each H-bridge is formed by two bridge arms connected in parallel, and each bridge arm is formed by two upper and lower switches connected in series; one of the H-bridges is connected in series with an input circuit as a primary side of the transformer, and the other H-bridge is connected in parallel with an output circuit as a secondary side of the transformer, the input circuit includes an input voltage source and a first DC capacitor connected in parallel, and the output circuit includes an output voltage source and a second DC capacitor connected in parallel; Determine whether the sodium-ion battery energy storage system is in a charging state or a discharging state, and set the lag phase angle applied by the two H-bridges on the primary and secondary sides of the DC-DC converter according to the different charging and discharging states; Determine whether the battery voltage of the sodium ion battery cluster during the charge and discharge process is within the rated voltage range of the battery cluster. If it is within the range, determine whether the voltage exceeds the set threshold voltage. If it exceeds, the first switch and the second switch of the H-bridge arm of the primary side of the converter are closed to bypass the DC-DC converter, so that the sodium ion battery cluster is directly connected to the DC end of the bidirectional DC-AC converter; If it does not exceed the limit, a square wave drive signal with a set lagging phase angle is applied to the two H-bridges on the primary and secondary sides of the converter to control the switching action of the converter, and the lagging phase angle is adjusted according to the output current of the converter, that is, the shift phase is adjusted until the output current reaches the rated current value, and then connected to the grid for charging and discharging.

5. The control method of the energy storage converter according to claim 4, characterized in that the transformer The primary side of the transformer is connected to the inductor and then connected to the midpoint of the two bridge arms of the H bridge in the primary circuit, and the secondary side of the transformer is connected to the midpoint of the two bridge arms of the H bridge in the secondary circuit.

6. The control method of the energy storage converter according to claim 4, characterized in that: The set lag phase angle is the set phase shift angle. If it is in the discharge state, the set phase shift angle is 0 and the phase shift angle during the entire discharge process If it is in charging state, set the phase shift angle for And the phase shift angle during the entire charging process 7. The control method of the energy storage converter according to claim 4, characterized in that: If the converter output current is greater than the rated current value, the lagging phase angle is increased, otherwise the lagging phase angle is reduced until the output current reaches the rated current value.

Images