An AC / DC hybrid microgrid battery emergency power supply system

Abstract

The present invention discloses an emergency power supply system for a battery in an AC / DC hybrid microgrid, belonging to the field of power electronics technology. The system includes an AC power grid, an AC / DC converter, a bidirectional DC / DC converter, a primary battery pack, a unidirectional DC / DC converter, a first controller, a second controller, a third controller, a secondary battery bank, a DC load, and a DC bus. The primary battery pack of the system serves as a backup charging power source for the secondary battery bank, avoiding over-discharge of the secondary battery in the event of an AC power grid failure, prolonging the service life of the secondary battery, and improving the power supply reliability of the system.

Description

Technical Field

[0001] The invention discloses an emergency power supply system for a battery in an AC-DC hybrid microgrid, belonging to the field of power electronics technology and being used for an energy storage system in an AC-DC hybrid microgrid. Background Technique

[0002] The energy storage system can store energy in another form or the same form of energy, which plays a crucial role in the development of smart grids and the upgrading and transformation of traditional grids. It can be used to participate in system peak shaving, frequency modulation, voltage regulation, smoothing the power fluctuations of renewable energy sources, and realizing the voltage control of the renewable power supply terminal voltage node.

[0003] Secondary batteries can realize the secondary utilization of energy and have characteristics such as excellent power density, fast charging speed, and large specific energy. At present, most energy storage systems use secondary batteries, such as lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, single energy storage systems such as lithium-ion, as well as hybrid energy storage systems of batteries and supercapacitors, and combined systems of primary lithium batteries and secondary lithium batteries. CN109383299.B proposes an emergency power supply system for a battery, a power supply method, and a rail vehicle. The invention patent elaborates in detail on the emergency power supply method for the battery and the emergency power supply timing after an emergency occurs. CN212649184.U proposes a multi-source emergency power supply system based on an electric vehicle battery array. The utility model patent includes five power sources: a distributed electric vehicle battery array, a diesel generator, a civil air defense manual generator, a hydrogen fuel cell, and a civil air defense power supply inlet of a low-voltage distribution room. The patent details the connection method between the systems of the multi-source emergency power supply system for civil air defense projects. CN 111864889.A proposes a lead-acid battery pack open-circuit protection uninterruptible emergency power supply system and a power supply method. In the case of a power failure of the commercial power grid, the lead-acid battery pack supplies power to the load. CN112260338.A proposes a DC emergency power supply system, which adopts airborne charge and discharge control technology and a battery pack management system BMS to charge the battery pack through a charge and discharge controller, solving the problem of low floating charge efficiency of the battery pack. However, compared with primary batteries, secondary batteries have the following disadvantages: large self-discharge ability and short storage time. Summary of the Invention

[0004] The purpose of the invention is to solve the problem of emergency power supply for loads in the case of AC power grid failures or in field application scenarios, and to provide an emergency power supply system for a battery in an AC-DC hybrid microgrid.

[0005] The technical solution adopted by the present invention to solve the above problems: An AC / DC hybrid microgrid battery emergency power supply system includes an AC power grid 1, an AC / DC converter 2, a bidirectional DC / DC converter 3, a primary battery pack 4, a unidirectional DC / DC converter 5, a first controller 6, a second controller 7, a third controller 8, a secondary battery pack 9, a DC load 10, a DC load 11, and a DC bus 12:

[0006] The AC power grid 1 is connected to the input end of the AC / DC converter 2; the output end of the AC / DC converter 2 is connected to the DC bus 12; the input end of the bidirectional DC / DC converter 3 is connected to the DC bus 12; the output end of the bidirectional DC / DC converter 3 is connected to the secondary battery pack 9; the primary battery pack 4 is connected to the input end of the unidirectional DC / DC converter 5; the output end of the unidirectional DC / DC converter 5 is connected to the DC bus 12; the DC load 10 is connected to the DC bus 12; the DC load 11 is connected to the secondary battery pack 9; the output end of the first controller 6 is connected to the control end of the unidirectional DC / DC converter 5; the output end of the third controller 8 is connected to the control end of the AC / DC converter 2; the output end of the second controller 7 is connected to the control end of the bidirectional DC / DC converter 3;

[0007] The first controller 6 includes the output voltage reference value U of the unidirectional DC / DC converter 5 * o5 and the output voltage sampled value U of the unidirectional DC / DC converter 5 o5 a first comparator 13, and a first PI controller 14. The output end of the first comparator 13 is connected to the input end of the first PI controller 14;

[0008] The second controller 7 includes a charging control module 7-1 and a discharging control module 7-2, which are arranged vertically in sequence;

[0009] The charging control module 7-1 includes the voltage reference value U of the secondary battery pack 9 * o二次电池 and the voltage sampled value U of the secondary battery pack 9 o二次电池 a second comparator 15, a second PI controller 16, a third comparator 17, and a third PI controller 18. The output end of the second comparator 15 is connected to the input end of the second PI controller 16, the output end of the second PI controller 16 is connected to the input end of the third comparator 17, and the output end of the third comparator 17 is connected to the input end of the third PI controller 18; the discharging control module 7-2 includes a discharging current reference value I * 放电 and the discharging current sampled value I 放电, a fourth comparator 19 and a fourth PI controller 20, with the output terminal of the fourth comparator 19 connected to the input terminal of the fourth PI controller 20;

[0010] The third controller 8 described above includes a DC bus 12 voltage reference value U dc * , a DC bus 12 voltage sampled value U dc , a fifth comparator 21, a fifth PI controller 22, a sixth comparator 23, a sixth PI controller 24, a seventh comparator 25, and a seventh PI controller 26. The output terminal of the fifth comparator 21 is connected to the input terminal of the fifth PI controller 22, the output terminal of the fifth PI controller 22 is connected to the input terminal of the sixth comparator 23, the output terminal of the sixth comparator 23 is connected to the output terminal of the sixth PI controller 24, and the output terminal of the seventh comparator 25 is connected to the input terminal of the seventh PI controller 26.

[0011] When the AC power grid 1 is powered normally, the AC power grid 1 supplies power to the DC load 10 through the AC / DC converter 2, and supplies power to the DC load 11 through the AC / DC converter 2 and the bidirectional DC / DC converter 3; the AC power grid 1 charges the secondary battery pack 9 through the AC / DC converter 2 and the bidirectional DC / DC converter 3.

[0012] When the AC power grid 1 fails and the secondary battery pack 9 has insufficient power, the primary battery pack 4 charges the secondary battery pack 9 through the unidirectional DC / DC converter 5; the secondary battery pack 9 supplies power to the DC load 11, or supplies power to the DC load 10 through the bidirectional DC / DC converter 3; the first controller 6 is used to stabilize the voltage of the DC bus 12, and the second controller 7 is used to stabilize the voltage at the output terminal of the secondary battery pack 9.

[0013] When the AC power grid 1 fails and the secondary battery pack 9 is fully charged, the secondary battery pack 9 discharges, and the secondary battery pack 9 supplies power to the DC load 11, or supplies power to the DC load 10 through the bidirectional DC / DC converter 3.

[0014] When the AC power grid 1 is normal, the third controller 8 collects the voltage value of the DC bus 12 and the current value flowing through the AC / DC converter 2, and stabilizes the voltage of the DC bus 12 through closed-loop control of the voltage value of the DC bus 12 to ensure the power supply to the DC load 10.

[0015] When the AC power grid 1 is normal, the second controller 7 collects the voltage value at the output terminal of the secondary battery pack 9 and the current value flowing through the bidirectional DC / DC converter 3, and ensures the power supply to the DC load 11 through closed-loop control of the voltage value at the output terminal of the secondary battery pack 9.

[0016] In the case of a failure of the AC power grid 1 and the secondary battery being fully charged, the second controller 7 collects the voltage of the DC bus 12 and the current flowing through the bidirectional DC / DC converter 3, and stabilizes the voltage of the DC bus 12 by performing closed-loop control on the voltage value of the DC bus 12, ensuring the power supply to the DC loads 10 and 11.

[0017] Advantages of the present invention: In the case of a failure of the AC power grid, when the secondary battery pack has insufficient power, the primary battery pack serves as a backup power supply to continue powering the load. The switching time for the secondary battery pack to switch to primary battery power supply is in seconds, ensuring uninterrupted power supply to the system; DC / DC converters are configured on the output sides of both the primary battery pack and the secondary battery pack, and the DC bus voltage is stabilized between 600 and 750 V through the closed-loop control of the converters. Description of the Drawings

[0018] Figure 1 Block diagram of the battery emergency power supply system for the AC-DC hybrid microgrid

[0019] In the figure: 1. AC power grid, 2. AC / DC converter, 3. Bidirectional DC / DC converter, 4. Primary battery pack, 5. Unidirectional DC / DC converter, 6. First controller, 7. Second controller, 8. Third controller, 9. Secondary battery pack, 10. DC load, 11. DC load, 12. DC bus.

[0020] Figure 2 Control timing diagram of the battery emergency power supply system for the AC-DC hybrid microgrid

[0021] Figure 3 Control block diagram of the first controller

[0022] In the figure: 6. First controller, 13. First comparator, 14. First PI controller, U * o5 Output voltage reference value of the unidirectional DC / DC converter 5, U o5 Output voltage sampled value of the unidirectional DC / DC converter 5.

[0023] Figure 4 Control block diagram of the second controller

[0024] In the figure: 7. Second controller, 7-1. Charging control module, 7-2. Discharging control module, 15. Second comparator, 16. Second PI controller, 17. Third comparator, 18. Third PI controller, 19. Fourth comparator, 20. Fourth PI controller, U * o二次电池 Voltage reference value of the secondary battery pack 9, U o二次电池 Voltage sampled value of the secondary battery pack 9, I * 放电Discharge current reference value, I 放电 Sampled value of the discharge current.

[0025] Figure 5 Control block diagram of the third controller

[0026] In the figure: 8. Third controller, 21. Fifth comparator, 22. Fifth PI controller, 23. Sixth comparator, 24. Sixth PI controller, 25. Seventh comparator, 26. Seventh PI controller, U dc * DC bus 12 voltage reference value, U dc Sampled value of the DC bus 12 voltage.

[0027] Figure 6 DC bus voltage waveform diagram

[0028] In the figure: The abscissa is time, in seconds; the ordinate is the DC bus voltage, in volts. Specific implementation mode

[0029] The following further illustrates the present invention in conjunction with the drawings and embodiments.

[0030] Embodiment 1

[0031] An AC-DC hybrid microgrid battery emergency power supply system of the present invention includes an AC power grid 1, an AC / DC converter 2, a bidirectional DC / DC converter 3, a primary battery pack 4, a unidirectional DC / DC converter 5, a first controller 6, a second controller 7, a third controller 8, a secondary battery pack 9, a DC load 10, a DC load 11, and a DC bus 12.

[0032] The AC power grid 1 is connected to the input end of the AC / DC converter 2; the output end of the AC / DC converter 2 is connected to the DC bus 12; the input end of the bidirectional DC / DC converter 3 is connected to the DC bus 12; the output end of the bidirectional DC / DC converter 3 is connected to the secondary battery pack 9; the primary battery pack 4 is connected to the input end of the unidirectional DC / DC converter 5; the output end of the unidirectional DC / DC converter 5 is connected to the DC bus 12; the DC load 10 is connected to the DC bus 12; the DC load 11 is connected to the secondary battery pack 9; the output end of the first controller 6 is connected to the control end of the unidirectional DC / DC converter 5; the output end of the third controller 8 is connected to the control end of the AC / DC converter 2; the output end of the second controller 7 is connected to the control end of the bidirectional DC / DC converter 3;

[0033] The first controller 6 includes a first comparator 13 and a first PI controller 14, and the output end of the first comparator 13 is connected to the input end of the first PI controller 14;

[0034] The second controller 7 includes a charging control module 7-1 and a discharging control module 7-2, and the charging control module 7-1 and the discharging control module 7-2 are arranged vertically in sequence;

[0035] The charging control module 7-1 includes a second comparator 15, a second PI controller 16, a third comparator 17, and a third PI controller 18. The output terminal of the second comparator 15 is connected to the input terminal of the second PI controller 16. The output terminal of the second PI controller 16 is connected to the input terminal of the third comparator 17. The output terminal of the third comparator 17 is connected to the input terminal of the third PI controller 18. The discharging control module 7-2 includes a fourth comparator 19 and a fourth PI controller 20. The output terminal of the fourth comparator 19 is connected to the input terminal of the fourth PI controller 20;

[0036] The third controller 8 includes a fifth comparator 21, a fifth PI controller 22, a sixth comparator 23, a sixth PI controller 24, a seventh comparator 25, and a seventh PI controller 26. The output terminal of the fifth comparator 21 is connected to the input terminal of the fifth PI controller 22. The output terminal of the fifth PI controller 22 is connected to the input terminal of the sixth comparator 23. The output terminal of the sixth comparator 23 is connected to the output terminal of the sixth PI controller 24. The output terminal of the seventh comparator 25 is connected to the input terminal of the seventh PI controller 26.

[0037] The primary battery pack 4 is composed of 130 strings of 10 parallel lithium carbon monofluoride batteries; the unidirectional DC / DC converter 5 selects a Buck-Boost circuit with a switching frequency of 1 MHz; the AC / DC converter 2 can adopt a T-type three-level converter with a switching frequency of 20 kHz; the bidirectional DC / DC converter 3 can adopt a bidirectional Buck-Boost converter with a switching frequency of 1 MHz; the first controller 6 is responsible for data acquisition, data processing, data calculation, and voltage stabilization control of the unidirectional DC / DC converter 5. The control parameters of the first PI controller 14 in the first controller 6 are selected as 0.0547 and 8.8644; the second controller 7 is responsible for data acquisition, data processing, data calculation, and voltage stabilization control of the bidirectional DC / DC converter 3. The control parameters of the second PI controller 16 and the third PI controller 18 in the second controller 7 are both selected as 0.0547 and 8.8644, and the control parameter of the fourth PI controller 20 is selected as 1 and 0; the third controller 8 is responsible for data acquisition, data processing, data calculation, and voltage stabilization control of the AC / DC converter. The control parameter of the fifth PI controller 22 in the third controller is selected as 0.1 and 5e-6, the control parameter of the sixth PI controller 24 is selected as 1 and 20e-5, and the control parameter of the seventh PI controller 26 is selected as 1 and 20e-5.

[0038] The control timing diagram of the AC-DC hybrid microgrid battery emergency power supply system is shown in Figure 2. When the AC power grid 1 is supplying power normally, the AC power grid 1 supplies power to the DC load 10 through the AC / DC converter 2, and supplies power to the DC load 11 through the AC / DC converter 2 and the bidirectional DC / DC converter 3; the AC power grid 1 charges the secondary battery pack 9 through the AC / DC converter 2 and the bidirectional DC / DC converter 3. The structural block diagrams of the second controller 7 and the third controller 8 are shown respectively in Figure 4 and Figure 5 . When the AC power grid 1 fails and the secondary battery pack 9 has insufficient power, the primary battery pack 4 charges the secondary battery pack 9 through the unidirectional DC / DC converter 5; the secondary battery pack 9 supplies power to the DC load 11, or supplies power to the DC load 10 through the bidirectional DC / DC converter 3; the first controller 6 is used to stabilize the voltage of the DC bus 12, and the third controller 8 is used to stabilize the voltage at the output end of the secondary battery pack 9. When the AC power grid 1 fails and the secondary battery pack 9 is fully charged, the secondary battery pack 9 discharges, and the secondary battery pack 9 supplies power to the DC load 11, or supplies power to the DC load 10 through the bidirectional DC / DC converter 3. When the AC power grid 1 is normal, the third controller 8 collects the voltage value of the DC bus 12 and the current value flowing through the AC / DC converter 2, and stabilizes the voltage of the DC bus 12 by performing closed-loop control on the voltage value of the DC bus 12 to ensure the power supply of the DC load 10. When the AC power grid 1 is normal, the second controller 7 collects the voltage value at the output end of the secondary battery pack 9 and the current value flowing through the bidirectional DC / DC converter 3, and ensures the power supply of the DC load 11 by performing closed-loop control on the voltage value at the output end of the secondary battery pack 9. When the AC power grid 1 fails and the secondary battery is fully charged, the second controller 7 collects the voltage of the DC bus 12 and the current flowing through the bidirectional DC / DC converter 3, and stabilizes the voltage of the DC bus 12 by performing closed-loop control on the voltage value of the DC bus 12 to ensure the power supply of the DC load 10 and the DC load 11.

[0039] In this embodiment, when the AC power grid loses power and the secondary battery pack has insufficient power, the waveform diagram of the DC bus voltage supplied by the primary battery is shown in Figure 6 ; at 0.1 s, the power supply is switched from the secondary battery pack to the primary battery pack, and the DC bus voltage undergoes a short overcharge and stabilizes at 650 V.

Claims

1. An AC / DC hybrid microgrid battery emergency power supply system, characterized in that: The system includes an AC power grid 1, an AC / DC converter 2, a bidirectional DC / DC converter 3, a primary battery pack 4, a unidirectional DC / DC converter 5, a first controller 6, a second controller 7, a third controller 8, a secondary battery pack 9, a DC load 10, a DC load 11, and a DC bus 12: The AC power grid 1 is connected to the input end of the AC / DC converter 2; the output end of the AC / DC converter 2 is connected to the DC bus 12; the input end of the bidirectional DC / DC converter 3 is connected to the DC bus 12; the output end of the bidirectional DC / DC converter 3 is connected to the secondary battery pack 9; the primary battery pack 4 is connected to the input end of the unidirectional DC / DC converter 5; the output end of the unidirectional DC / DC converter 5 is connected to the DC bus 12; the DC load 10 is connected to the DC bus 12; the DC load 11 is connected to the secondary battery pack 9; the output end of the first controller 6 is connected to the control end of the unidirectional DC / DC converter 5; the output end of the third controller 8 is connected to the control end of the AC / DC converter 2; the output end of the second controller 7 is connected to the control end of the bidirectional DC / DC converter 3; The first controller 6 described above includes the output voltage reference value U of the unidirectional DC / DC converter 5 * o5 , the output voltage sampled value U of the unidirectional DC / DC converter 5 o5 , a first comparator 13 and a first PI controller 14. The output end of the first comparator 13 is connected to the input end of the first PI controller 14; The second controller 7 includes a charging control module 7-1 and a discharging control module 7-2, and the charging control module 7-1 and the discharging control module 7-2 are arranged vertically in sequence; The charging control module 7-1 includes the voltage reference value U of the secondary battery pack 9 * o二次电池 , the voltage sampling value U of the secondary battery pack 9 o二次电池 , a second comparator 15, a second PI controller 16, a third comparator 17, and a third PI controller 18. The output terminal of the second comparator 15 is connected to the input terminal of the second PI controller 16. The output terminal of the second PI controller 16 is connected to the input terminal of the third comparator 17. The output terminal of the third comparator 17 is connected to the input terminal of the third PI controller 18; The discharge control module 7-2 includes a discharge current reference value I * 放电 , a sampled discharge current value I 放电 , a fourth comparator 19, and a fourth PI controller 20. The output terminal of the fourth comparator 19 is connected to the input terminal of the fourth PI controller 20; The described third controller 8 includes a DC bus 12 voltage reference value U dc * , a DC bus 12 voltage sampled value U dc , a fifth comparator 21, a fifth PI controller 22, a sixth comparator 23, a sixth PI controller 24, a seventh comparator 25, and a seventh PI controller 26. The output end of the fifth comparator 21 is connected to the input end of the fifth PI controller 22, the output end of the fifth PI controller 22 is connected to the input end of the sixth comparator 23, the output end of the sixth comparator 23 is connected to the output end of the sixth PI controller 24, and the output end of the seventh comparator 25 is connected to the input end of the seventh PI controller 26.

2. The emergency power supply system for a battery in an AC / DC hybrid microgrid according to claim 1, wherein: When the AC power grid 1 is powered normally, the AC power grid 1 supplies power to the DC load 10 through the AC / DC converter 2, and supplies power to the DC load 11 through the AC / DC converter 2 and the bidirectional DC / DC converter 3; the AC power grid 1 charges the secondary battery pack 9 through the AC / DC converter 2 and the bidirectional DC / DC converter 3.

3. The emergency power supply system for a hybrid AC / DC microgrid battery according to claim 1, characterized in that: When the AC power grid 1 fails and the secondary battery pack 9 has insufficient power, the primary battery pack 4 charges the secondary battery pack 9 through the unidirectional DC / DC converter 5; the secondary battery pack 9 supplies power to the DC load 11, or supplies power to the DC load 10 through the bidirectional DC / DC converter 3; the first controller 6 stabilizes the voltage of the DC bus 12, and the second controller 7 stabilizes the voltage of the output end of the secondary battery pack 9.

4. A hybrid AC-DC microgrid battery emergency power supply system according to claim 1, characterized in that: When the AC power grid 1 fails and the secondary battery pack 9 is fully charged, the secondary battery pack 9 discharges, and the secondary battery pack 9 supplies power to the DC load 11, or supplies power to the DC load 10 through the bidirectional DC / DC converter 3.

5. The emergency power supply system for a hybrid AC / DC microgrid battery according to claim 1, characterized in that: When the AC power grid 1 is normal, the third controller 8 collects the voltage value of the DC bus 12 and the current value flowing through the AC / DC converter 2, and stabilizes the voltage of the DC bus 12 through closed-loop control of the voltage value of the DC bus 12 to ensure the power supply of the DC load 10.

6. The emergency power supply system for a hybrid AC / DC microgrid battery according to claim 1, wherein: When the AC power grid 1 is normal, the second controller 7 collects the voltage value of the output end of the secondary battery pack 9 and the current value flowing through the bidirectional DC / DC converter 3, and ensures the power supply of the DC load 11 through closed-loop control of the voltage value of the output end of the secondary battery pack 9.

7. The emergency power supply system for a hybrid AC / DC microgrid battery according to claim 1, wherein: In the case of a failure of the AC power grid 1 and the secondary battery being fully charged, the second controller 7 collects the voltage of the DC bus 12 and the current flowing through the bidirectional DC / DC converter 3, and stabilizes the voltage of the DC bus 12 by performing closed-loop control on the voltage value of the DC bus 12 to ensure the power supply to the DC loads 10 and 11.

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