CN103199630A - High-capacity medium voltage battery energy storage system - Google Patents

Abstract

The invention discloses a large-capacity medium-voltage battery energy storage system, wherein: the output end of the energy storage battery unit is connected to the input end of a pre-charging circuit to transmit a DC voltage, and the output end of the pre-charging circuit is connected to the DC voltage of a single-phase H-bridge converter. The terminals are connected to transmit DC voltage, and the output terminals of the single-phase H-bridge converter are connected in series with reactance, thus forming an energy storage unit. Multiple energy storage units are connected in series on the AC side and then connected in series with an inductor to form a branch circuit. The three branches are connected end to end. A delta connection is formed, and the three endpoints of the triangle are connected to the medium-voltage grid in three phases. The grid-connected inductance of the present invention is composed of the inductances of each energy storage unit in series, and the failure of a single inductance has little influence on the system and has high reliability. Under the same power, high voltage, low current, small current harmonics, low requirements on battery capacity; redundancy can be realized through bypass, high reliability; it has the function of balancing the battery. Compared with the star-connected medium-voltage energy storage system on the primary side, the control is simpler and the reliability is higher.

Description

A large-capacity medium-voltage battery energy storage system

technical field

The invention relates to a large-capacity medium-voltage energy storage system, in particular to a modular AC cascaded structure energy storage system, which is used for large-capacity battery energy storage applications. It belongs to the field of electric energy storage.

Background technique

The use of battery energy storage systems to smooth wind power and photovoltaic power generation is an effective way to solve the problem of new energy grid connection and wind power "abandonment". The application of large-capacity electric energy storage in the power grid has changed the history that electric energy can only be transmitted but not stored, has brought a revolutionary impact on the production and operation of the power grid, and greatly promoted the development of my country's smart grid.

The battery energy storage system uses a DC/AC bidirectional power converter to realize the bidirectional flow of power between the battery and the grid. The power converter is the core of the energy control of the energy storage system. In most energy storage applications, the power converter adopts a low-voltage solution, the AC side voltage is generally ≤ AC690V, and the power capacity of a single unit is generally several hundred kW, and a larger capacity needs to be achieved by paralleling multiple power converters on the AC side. ABB's individual models of power converters use IGCT power devices, the DC side voltage can reach 3-5kV, and the AC side voltage can reach 2kV.

The capacity of a single power converter in the low-voltage solution is limited. When it is applied in a large-capacity application, it is necessary to expand the capacity through multiple parallel connections and use a step-up transformer to boost the voltage. At present, the power converters used in battery energy storage mainly have two structural forms: DC/AC single-stage structure and DC/DC+DC/AC two-stage structure. Considering that the efficiency of single-stage power converter is <98%, the efficiency of two-stage power converter is <96%, the loss of transformer is 2%, and the total efficiency of energy storage system is <96% and <94%, respectively, the system efficiency is low.

The voltage on the DC side of the power converter of ABB's energy storage system is too high, which requires an extremely large number of batteries to be used in series. The short-circuit effect of the battery is significant, and the existing battery balancing technology cannot guarantee its long-term stable operation.

In the published Chinese invention patent "A Modularized Medium Voltage Energy Storage System" (publication number: CN102355065), the primary side is connected in a star connection, and functions such as charging, discharging and balancing are realized by controlling the three phase voltages. Its shortcoming is that the amplitude and phase of the three-phase voltage need to be properly controlled when the energy storage system performs phase-to-phase balance and fault redundancy control, but the control of the three-phase voltage is mutually coupled, and the control is difficult, which is not conducive to It works stably.

In a device similar to a chain structure, the primary side grid connection adopts a centralized connection reactance. Due to the structural layout, considering the possible short circuit between the lower end of the reactance directly to the ground/phase to phase, the connection reactance needs to be in accordance with the direct short circuit resistance. Power design, high cost, large volume, high anti-saturation requirements.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention proposes a large-capacity medium-voltage energy storage system. The three-phase structure adopts a cascaded structure of modularized energy storage units. Finally, a triangle connection is adopted, and the three vertices of the triangle are connected to the three wires of the medium voltage grid. The current control of the three branches is decoupled from each other, the control is simple, the reliability is high, and the balancing function of the battery can be realized.

In order to achieve the above purpose, the present invention provides a large-capacity medium-voltage battery energy storage system, including an energy storage battery unit, a pre-charging circuit, a single-phase H-bridge bidirectional converter and a connecting reactance, wherein: the output of the energy storage battery unit The terminal is connected to the input terminal of the pre-charging circuit to transmit the DC voltage, the output terminal of the pre-charging circuit is connected to the DC terminal of the single-phase H-bridge converter to transmit the DC voltage, and the output terminal of the single-phase H-bridge converter is connected in series with the connecting reactance, so To form an energy storage unit, a plurality of energy storage units are connected in series on the AC side to form a branch, and the three branches are connected end to end to form a triangle connection, and the three endpoints of the triangle are connected to the medium voltage grid in three phases. The system adopts a three-phase The triangular H-bridge cascade structure, each line branch is composed of multiple energy storage units in series, and the energy storage unit adopts a single-phase H-bridge converter to realize AC/DC bidirectional conversion of electric energy.

The energy storage battery unit is composed of rechargeable batteries connected in series and parallel.

The pre-charging circuit includes: a resistor and a contactor, wherein: the resistor and the contactor are connected in parallel.

The single-phase H-bridge converter includes 4 power electronic switching devices and DC capacitors, the 4 switching devices are connected in a single-phase H-bridge structure, the DC capacitors are connected in parallel on the DC side, and the output of the single-phase H-bridge converter is connected to the inductance in series.

The connecting reactance can be either an air-core reactor or a reactor with an iron core.

In the present invention, the energy balance of different energy storage units on the same line voltage branch can be realized by controlling the mutual ratio of output voltage amplitudes of each energy storage unit.

In the present invention, the total energy balance of the energy storage units on different line branches can be realized by controlling the current ratios of the three line voltage branches.

Compared with the prior art, the beneficial effects of the present invention are: under the same power, high voltage, low current, small current harmonics, low requirements on battery cell capacity; redundancy can be realized through bypass; Function. The cost of the MW-level large capacity is lower than that of the high-voltage energy storage solution. Compared with the star-connected medium-voltage energy storage system on the primary side, the control is simpler and the reliability is higher. The energy storage unit has its own connection reactor, and the single connection reactor only needs to be designed according to the voltage level of the H-bridge converter, and the withstand voltage requirement is low. Since there is no need for an additional series-connected centralized reactor, it is more suitable for modular arrangement as a whole, with better maintainability and reduced floor space and cost. Under the same power, the current is lower than that of the three-phase star connection, and the requirement for the capacity of the battery cell is lower.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

FIG. 1 is a schematic diagram of an energy storage unit according to an embodiment of the present invention.

Fig. 2 is an overall structural diagram of a large-capacity medium-voltage energy storage system according to an embodiment of the present invention.

FIG. 3 is a circuit schematic diagram of an embodiment of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

As shown in Figure 1-2, the large-capacity medium-voltage battery energy storage system provided by the present invention includes: 3N energy storage battery units, 3N pre-charging circuits, 3N single-phase H-bridge converters, and 3N connection reactances. Among them: the output terminals of 3N energy storage batteries are respectively connected to the input terminals of 3N pre-charging circuits to transmit DC voltage, and the output terminals of 3N pre-charging circuits are respectively connected to the DC terminals of 3N single-phase H-bridge converters to transmit DC Voltage, 3N H-bridge converter output terminals are connected in series with 3N connected reactances, thus forming 3N energy storage units AB1, AB2...ABN, BC1, BC2...BCN, CA1, CA2...CAN with the same structure. The line voltage UAB branch is composed of N energy storage units AB1, AB2...ABN in series on the AC side; the line voltage UBC branch is composed of N energy storage units BC1, BC2...BCN in series on the AC side; the line voltage UCA branch is composed of N storage units The energy units CA1, CA2...CAN are connected in series on the AC side; the three branches are connected end to end to form a delta connection, and the three ends of the triangle are connected to the medium voltage grid in three phases.

Example

This embodiment is a 2MW*2h battery energy storage system with a rated voltage of 10kV.

As shown in FIG. 3 , the energy storage unit of this embodiment includes: 1 battery pack, 1 resistor, 1 contactor, 1 set of capacitors, 4 IGBTs and 1 connection reactance. A, B, and C phases each have 20 energy storage units connected as shown in Figure 2 to form the entire medium-voltage energy storage system.

In this embodiment, the rated voltage of one storage battery unit is 960V, and the nominal capacity is 200Ah.

In this embodiment, the pre-charging circuit is composed of a resistor R1 and a contactor K1. Among them: Resistor R1 and contactor K1 are connected in parallel. One end of the resistor R1 and the contactor K1 is connected to the positive pole of the battery pack, which is the input end of the pre-charging circuit; the other end of the resistor R1 and the contactor K1 is the output end of the pre-charging circuit. The resistance value of R1 is 200 ohms, the rated voltage of K1 is 1200VDC, and the rated current is 100A.

In this embodiment, the single-phase H-bridge converter is composed of a group of capacitors C1, IGBT devices V1, V2, V3, V4 and connection reactance L. Among them: V1 and V2 are connected in series to form a branch circuit, V3 and V4 are connected in series to form a branch circuit, the above two branches and the capacitor bank C1 are connected in parallel, and the output of the H-bridge converter is connected in series with the inductance L. Capacitor bank C1 has a rated voltage of 1400VDC and a capacity of 4000uF. IGBT devices V1, V2, V3, V4 rated voltage 1700V, rated current 200A. The connection reactance L inductance of the H-bridge converter is 1mH, the rated voltage is 800V, and the rated current is 200A. This makes the total inductance of a single line branch 20mH.

The working process of this embodiment is as follows:

1. Keep the switching devices V1, V2, V3, and V4 of the single-phase H-bridge converter of each energy storage unit in an off state.

2. A battery unit with a rated voltage of 960V and a nominal capacity of 200Ah will be formed by connecting 20 lithium iron phosphate battery modules with a nominal voltage of 48V/200Ah in series. The battery unit on the left side of each energy storage unit inputs direct current, and since the voltage of the battery unit changes with its electric quantity, its voltage fluctuation range is 800-1200VDC.

3. First, charge the capacitor bank C1 through the resistor R1. The initial charging current for the capacitor bank C1 is 15-20A. After 3s, the voltage on the capacitor bank C1 rises to close to the DC input voltage. Closing K1 bypasses the resistor R1, and the voltage of the capacitor bank C1 is exactly equal to the voltage of the battery pack.

4. When charging the energy storage system from the grid, control the H-bridge converter of the energy storage unit in the three branches of UAB, UBC, and UCA to make the phase difference between the current Iab, Ibc, and Ica flowing into the energy storage system and Uab, Ubc, and Uca At the same time, the phases of the three branch output voltages Uvab, Uvbc, and Uvca are slightly ahead of the grid line voltages Usab, Usbc, and Usca by a certain electrical angle. The charging power can be adjusted by adjusting the phase angle difference between the two.

5. When discharging from the energy storage system to the grid, control the H-bridge converter of the energy storage unit in the three branches of UAB, UBC, and UCA to make the phase difference between the current Iab, Ibc, and Ica flowing into the energy storage system and Uab, Ubc, and Uca At the same time, the phases of the output voltages Uvab, Uvbc, and Uvca of the three branches lag slightly behind the grid voltages Usab, Usbc, and Usca by a certain electrical angle. The magnitude of the discharge power can be adjusted by adjusting the phase angle difference between the two.

6. When the energy storage system is discharged, when the energy stored in the 20 energy storage units of the UAB branch is not equal, the output voltage of the single-phase H-bridge converter of each energy storage unit is controlled according to the ratio of the energy stored in each energy storage unit The amplitude can make the output active power of each energy storage unit on the UAB branch proportional to its stored energy. In this way, the energy balance between the various energy storage units on the UAB branch and the purpose of preventing over-discharge are achieved.

7. With the same operation, when the energy storage system is discharged, the energy between the energy storage units of the UBC branch and UCA branch can be balanced to prevent over-discharge.

8. When the energy storage system is charging, when the energy stored in the 20 energy storage units of the UAB branch is not equal, the output of the single-phase H-bridge converter of each energy storage unit is controlled according to the proportion of the energy that can be charged by each energy storage unit The voltage amplitude can make the input active power of each energy storage unit on the UAB branch proportional to its rechargeable energy. In this way, the energy balance among the energy storage units on the UAB branch and the purpose of preventing overcharging are achieved.

9. With the same operation, when the energy storage system is discharged, the energy between the energy storage units of the UBC branch and UCA branch can be balanced to prevent overcharging.

10. When the energy storage system is discharged, such as the total energy stored by the 20 energy storage units of the UAB branch of the energy storage system, the total energy stored by the 20 energy storage units of the UBC branch, and the total energy stored by the 20 energy storage units of the UCA branch The three are not equal, control the H-bridge converter of the energy storage unit of the three branches of UAB, UBC, and UCA, so that the ratio of the total output voltage Uvab, Uvbc, and Uvca of the branch is equal to the total energy stored in the energy storage unit on the three branches. Compare. Thus, the discharge energy balance among the three branches of UAB, UBC and UCA can be realized.

11. When the energy storage system is charging, such as the total energy stored by the 20 energy storage units of the UAB branch of the energy storage system, the total energy stored by the 20 energy storage units of the UBC branch, and the total energy stored by the 20 energy storage units of the UCA branch The three are not equal, control the H-bridge converter of the energy storage unit of the three branches of UAB, UBC, and UCA, so that the ratio of the total output voltage Uvab, Uvbc, and Uvca of the branch is equal to the total chargeable energy of the energy storage unit on the three branches Ratio. Thus, the charging energy balance among the three branches of UAB, UBC and UCA can be realized.

The advantage of this embodiment is that 10kV is directly connected to the power grid, no transformer, large capacity and high efficiency of a single unit; the cost is lower than that of the high-voltage solution with the same capacity at the MW level; under the same capacity, the lower-voltage solution of this embodiment has high voltage, low current, and The current harmonic is small, and the requirement for the capacity of the battery cell is low; it can realize the balance function of the battery. When a certain energy storage unit fails, the faulty energy storage unit can be bypassed by controlling the switching device of its H-bridge converter, so as to realize the fault redundant operation of the energy storage system.

Compared with the star-connected medium-voltage energy storage system on the primary side, it has more energy storage units with the same capacity, so the power and current of the energy storage units required are smaller, and the battery capacity is lower. When a certain energy storage unit fails, its impact is limited to the branch where the faulty energy storage unit is located, and has no impact on other branches at all, and there is no impact on the other two phases that exists in the star structure on the primary side. When the balance of the three branches is realized, the voltage control is also completely decoupled, and there is no need to coordinate the amplitude and phase of the three-phase voltages in the primary side star structure. Therefore, the control is simpler and the reliability is higher.

Since each energy storage unit has its own connection reactor, the connection reactance inside the energy storage unit on each branch jointly plays the role of smoothing, and the inductance requirement of a single reactor is small, and the withstand voltage requirement is low. Since there is no need for external series centralized connection reactors, the overall structure is more modular, which is convenient for maintenance and replacement, while reducing the footprint and cost.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (5)

1. A large-capacity medium-voltage battery energy storage system, characterized in that it includes an energy storage battery unit, a pre-charging circuit, a single-phase H-bridge converter and a connecting inductor, wherein: the output terminal of the energy storage battery unit is connected to the pre-charging circuit The input terminal is connected to transmit DC voltage, the output terminal of the pre-charging circuit is connected to the DC terminal of the single-phase H-bridge converter to transmit DC voltage, and the output terminal of the single-phase H-bridge converter is connected in series with the connection reactance, thus forming an energy storage unit. The AC side of each energy storage unit is connected in series to form a branch, and the three branches are connected end to end to form a delta connection, and the three endpoints of the triangle are connected to the medium voltage grid in three phases. The system adopts a three-phase delta H-bridge cascade connection Structure, each line branch is composed of multiple energy storage units in series, and the energy storage unit adopts a single-phase H-bridge converter to realize AC/DC bidirectional conversion of electric energy. 2. The large-capacity medium-voltage battery energy storage system according to claim 1, characterized in that: by controlling the mutual ratio of the output voltage amplitudes of each of the energy storage units, the energy of different energy storage units on the same line voltage branch is realized. balanced. 3. The large-capacity medium-voltage battery energy storage system according to claim 1, characterized in that: the total energy balance of the energy storage units on different line voltage branches is realized by controlling the current amplitude ratio of the three line voltage branches . 4. The modularized medium-voltage energy storage system according to any one of claims 1-3, wherein the energy storage battery unit is composed of series-parallel connection of rechargeable batteries. 5. The large-capacity medium-voltage battery energy storage system according to any one of claims 1-3, wherein the single-phase H-bridge converter includes 4 power electronic switching devices and DC capacitors, and 4 switches The device is connected as a single-phase H-bridge structure, the DC capacitor is connected in parallel on the DC side, and the output of the single-phase H-bridge converter is connected in series with the connected inductor.

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