Cascade H-bridge battery energy storage system with independent active and reactive capacity and control method

Abstract

The present invention relates to a cascaded H-bridge battery energy storage system with independent active and reactive capacities and a control method. The system connects a grid-connected inductor L, a plurality of submodules equipped with capacitors and a plurality of submodules equipped with batteries in series in the A, B and C phases of a three-phase power grid, respectively, and the three phases are connected in star connection or delta connection. The control method of the system is as follows: a modulation wave of a submodule is obtained according to a given active and reactive value, thereby controlling the energy storage system; a coordinate system is established with the direction of the power grid voltage vector Us as the positive direction of the x-axis, and the system is divided into four categories according to the different active and reactive exchange conditions between the energy storage system and the power grid: (1) the energy storage battery is charged, and the system outputs capacitive reactive power; (2) the energy storage battery is charged, and the system outputs inductive reactive power; (3) the energy storage battery is discharged, and the system outputs inductive reactive power; (4) the energy storage battery is discharged, and the system outputs capacitive reactive power, and the control is performed separately. The system and the control method are conducive to reducing the waste of active capacity and reducing the application cost of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery energy storage, and in particular relates to a cascaded H-bridge battery energy storage system with independent active and reactive capacities and a control method. Background Art

[0002] Battery energy storage systems mainly store and release energy, and can effectively solve the power quality problems caused by renewable energy generation such as wind and solar energy, and maintain the power balance of the power grid. With the expansion of renewable energy generation, larger capacity battery energy storage systems are needed. Among large-capacity battery energy storage systems, the cascade H-bridge energy storage system has broad application prospects due to its strong scalability, large capacity, high voltage, and low output voltage and current harmonic content.

[0003] The research and application of cascaded H-bridge battery energy storage systems started relatively early in China. A series of studies have been conducted on its topological structure to improve different performances. The most commonly used topological structure is the one in which each submodule is equipped with a storage battery. Starting from the earliest demonstration application of 10kV / 2MW direct hanging at the Baoqing Battery Energy Storage Station in Shenzhen in 2004, the cascaded H-bridge battery energy storage system has now entered the commercial application stage and has commercial products. Conventional cascaded H-bridge battery energy storage systems, in which energy storage batteries are configured in each submodule, each submodule provides active and reactive power, has a large number of output levels, and has a small output voltage harmonic content, and are widely used in large-capacity systems.

[0004] At present, there are some shortcomings in the design and application of cascade H-bridge battery energy storage systems. The cascade H-bridge battery energy storage system is suitable for direct access to the 6-35kV power grid. Each phase requires 8-42 energy storage sub-modules, and three phases require 24-126 energy storage sub-modules. The rated current of the cascade H-bridge battery energy storage system generally reaches hundreds to several hundred amperes, and the capacity specifications of the energy storage battery monomer are generally large. Each submodule is equipped with an energy storage battery monomer, which enables the entire cascade H-bridge battery energy storage system to achieve large charging and discharging power and capacity.

[0005] However, for some occasions that require direct access to 6-35kV but have a small demand for active power and a large demand for reactive power, if all energy storage submodules are equipped with energy storage batteries, the system cost will be greatly increased, and objectively, the energy storage batteries will be seriously wasted. This in turn restricts the promotion and application of cascaded H-bridge battery energy storage systems.

[0006] Although there are literatures that study cascaded H-bridge battery energy storage systems and realize the cascade utilization of batteries and even the mixed use of different batteries, they are all based on the situation where all submodules are energy storage submodules. From the perspective of energy output and exchange, the active power and reactive power capacities of these cascaded H-bridge battery energy storage systems are the same. Therefore, in situations where the active power demand is small and the reactive power demand is large, active capacity will be wasted. Summary of the invention

[0007] The object of the present invention is to provide a cascaded H-bridge battery energy storage system with independent active and reactive capacities and a control method, which are conducive to reducing active capacity waste and lowering system application costs.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is: a cascaded H-bridge battery energy storage system with independent active and reactive capacity, in which a grid-connected inductor L, a plurality of sub-modules equipped with capacitors and a plurality of sub-modules equipped with batteries are respectively connected in series in the A, B and C phases of the three-phase power grid, and the three phases are connected in star connection or delta connection.

[0009] Furthermore, the number of submodules equipped with capacitors for the three phases A, B and C is the same.

[0010] Furthermore, the submodules equipped with capacitors for the three phases A, B, and C adopt a single-phase H-bridge topology, and the parameters of capacitor capacity and voltage level are exactly the same.

[0011] Furthermore, the number of submodules equipped with batteries for the three phases A, B and C is the same.

[0012] Furthermore, the submodules equipped with batteries for the three phases A, B, and C adopt a single-phase H-bridge topology, and the battery capacity and voltage level parameters are exactly the same.

[0013] The present invention also provides a control method for the cascaded H-bridge battery energy storage system with independent active and reactive capacities, wherein the modulation wave of the submodule is obtained according to the given active and reactive reference values, and then the energy storage system is controlled; the grid voltage vector U S A coordinate system is established with the direction of the x-axis as the positive direction of the x-axis. According to the different active and reactive exchange conditions between the energy storage system and the power grid, it is divided into four categories: (1) the energy storage battery is charged and the system outputs capacitive reactive power; (2) the energy storage battery is charged and the system outputs inductive reactive power; (3) the energy storage battery is discharged and the system outputs inductive reactive power; (4) the energy storage battery is discharged and the system outputs capacitive reactive power, and they are controlled separately.

[0014] Furthermore, for the charging of energy storage batteries, the system outputs capacitive reactive power:

[0015] Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e. discharging the energy storage battery; P<0 means outputting active power to the grid, i.e. charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid. At this time, P<0, Q<0, the output voltage falls in the first quadrant, i.e. the upper right quadrant of the coordinate system; α1 is the difference between U0 and -U L The angle between U S The angle between U0 and U1;

[0016] First, according to Calculate the effective value of the energy storage system output voltage U0, and then according to Calculate θ;

[0017] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is α1+θ-π / 2, and the effective value is U s sin(α1+θ);

[0018] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is α1+θ, and the effective value is U s cos(α1+θ)+U L .

[0019] Furthermore, for the charging of energy storage batteries, the system outputs inductive reactive power:

[0020] Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e. discharging the energy storage battery; P<0 means outputting active power to the grid, i.e. charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid; at this time, P<0, Q>0, the output voltage falls in the second quadrant, i.e. the upper left quadrant of the coordinate system; α2 is U S and U L The angle of

[0021] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is π / 2-α2, and the effective value is U s sinα2;

[0022] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is -α2, and the effective value is U s cosα2-U L .

[0023] Furthermore, for the case where the energy storage battery discharges and the system outputs inductive reactive power:

[0024] Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e., discharging the energy storage battery; P<0 means outputting active power to the grid, i.e., charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid; at this time, P>0, Q>0, the output voltage falls in the third quadrant, i.e., the lower left quadrant of the coordinate system; α2 is U S and U L The angle of

[0025] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is α2-π / 2, and the effective value is U s sinα2;

[0026] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is α2, the effective value is U s cosα2-U L .

[0027] Furthermore, for the case where the energy storage battery discharges and the system outputs capacitive reactive power:

[0028] Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e. discharging the energy storage battery; P<0 means outputting active power to the grid, i.e. charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid. At this time, P>0, Q<0, the output voltage falls in the fourth quadrant, i.e. the lower right quadrant of the coordinate system; α1 is the difference between U0 and -U L The angle between U S The angle between U0 and U1;

[0029] First, according to Calculate the effective value of the energy storage system output voltage U0, and then according to Calculate θ;

[0030] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is π / 2-α1-θ, and the effective value is U s sin(α1+θ);

[0031] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is -α1-θ, and the effective value is U s cos(α1+θ)+U L .

[0032] Compared with the prior art, the present invention has the following beneficial effects: by connecting a grid-connected inductor L, a plurality of submodules equipped with capacitors, and a plurality of submodules equipped with batteries in series in the A, B, and C phases of the three-phase power grid, respectively, the design flexibility of the cascaded H-bridge battery energy storage system is improved, so as to reduce the waste of active capacity in different application scenarios and reduce the system application cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of system topology according to an embodiment of the present invention.

[0034] Figure 2 It is a schematic diagram of the energy storage battery charging and the system outputting capacitive reactive power in an embodiment of the present invention.

[0035] Figure 3 It is a schematic diagram of the energy storage battery charging and the system outputting inductive reactive power in an embodiment of the present invention.

[0036] Figure 4 It is a schematic diagram of the energy storage battery discharging and the system outputting inductive reactive power in an embodiment of the present invention.

[0037] Figure 5 It is a schematic diagram of the energy storage battery discharging and the system outputting capacitive reactive power in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0039] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] This embodiment provides a cascaded H-bridge battery energy storage system with independent active and reactive capacities, in which a grid-connected inductor L, a plurality of sub-modules equipped with capacitors, and a plurality of sub-modules equipped with batteries are respectively connected in series in the A, B, and C phases of a three-phase power grid, and the three phases are connected in star connection or delta connection.

[0042] The topology of the cascaded H-bridge battery energy storage system with independent active and reactive capacities in this embodiment is as follows Figure 1As shown. Where Usn (n = a, b, c) is the three-phase grid voltage, L is the grid inductance, U SMCn The total output voltage of the submodules equipped with capacitors in series, U SMBn Output total voltage for submodules equipped with batteries connected in series.

[0043] In this embodiment, the number of submodules equipped with capacitors for the three phases A, B, and C is the same. The submodules equipped with capacitors for the three phases A, B, and C adopt a single-phase H-bridge topology, and the parameters such as the capacitor capacity and the voltage level are exactly the same. The number of submodules equipped with batteries for the three phases A, B, and C is the same. The submodules equipped with batteries for the three phases A, B, and C adopt a single-phase H-bridge topology, and the parameters such as the battery capacity and the voltage level are exactly the same. Both the submodules equipped with capacitors and the submodules equipped with batteries adopt PWM modulation.

[0044] In other embodiments of the present invention, according to the needs of actual applications, the number of sub-modules equipped with capacitors for the three phases A, B, and C may be different, and the number of sub-modules equipped with batteries for the three phases A, B, and C may also be different.

[0045] This embodiment also provides a control method for the above-mentioned cascade H-bridge battery energy storage system with independent active and reactive capacities, which obtains the modulation wave of the submodule according to the given active and reactive reference values, and then controls the energy storage system. S A coordinate system is established with the direction of the x-axis as the positive direction of the x-axis. According to the different active and reactive exchange conditions between the energy storage system and the power grid, it is divided into four categories: (1) the energy storage battery is charged and the system outputs capacitive reactive power; (2) the energy storage battery is charged and the system outputs inductive reactive power; (3) the energy storage battery is discharged and the system outputs inductive reactive power; (4) the energy storage battery is discharged and the system outputs capacitive reactive power, and they are controlled separately.

[0046] For this energy storage system, P and Q are defined as given active and reactive reference values. P>0 means outputting active power to the grid, i.e. discharging the energy storage battery; P<0 means outputting active power to the grid, i.e. charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid.

[0047] α x (x=1,2)=arctan|P| / |Q|

[0048] I L =|P| / (U s sinα x )

[0049] U L =ωLI L

[0050] Among them, U L ,I Lis the effective value of the inductor voltage and current.

[0051] (1) For energy storage battery charging, the system outputs capacitive reactive power

[0052] At this time, if Figure 2 As shown, P<0, Q<0, the output voltage falls in the first quadrant, that is, the upper right quadrant of the coordinate system; α1 is U0 and -U L The angle between U S and the angle between U0.

[0053] First, according to Calculate the effective value of the energy storage system output voltage U0, and then according to θ is calculated.

[0054] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is α1+θ-π / 2 (relative to the grid voltage), and the effective value is U s sin(α1+θ).

[0055] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is α1+θ, and the effective value is U s cos(α1+θ)+U L .

[0056] (2) When charging the energy storage battery, the system outputs inductive reactive power

[0057] At this time, if Figure 3 As shown, P<0, Q>0, the output voltage falls in the second quadrant, that is, the upper left quadrant of the coordinate system; α2 is U S and U L Angle.

[0058] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is π / 2-α2, and the effective value is U s sinα2.

[0059] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is -α2, and the effective value is U s cosα2-U L .

[0060] (3) When the energy storage battery discharges and the system outputs inductive reactive power

[0061] At this time, if Figure 4 As shown, P>0, Q>0, the output voltage falls in the third quadrant, that is, the lower left quadrant of the coordinate system; α2 is U S and U LAngle.

[0062] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is α2-π / 2, and the effective value is U s sinα2.

[0063] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is α2, the effective value is U s cosα2-U L .

[0064] (4) When the energy storage battery is discharged and the system outputs capacitive reactive power

[0065] At this time, if Figure 5 As shown, P>0, Q<0, the output voltage falls in the fourth quadrant, that is, the lower right quadrant of the coordinate system; α1 is U0 and -U L The angle between U S and the angle between U0.

[0066] First, according to Calculate the effective value of the energy storage system output voltage U0, and then according to θ is calculated.

[0067] The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is π / 2-α1-θ, and the effective value is U s sin(α1+θ).

[0068] The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is -α1-θ, and the effective value is U s cos(α1+θ)+U L .

[0069] In this way, full operating condition operation and control in four quadrants can be achieved.

[0070] In this embodiment, a 10kV / 5MVA / 1MW*1h cascade H-bridge battery energy storage system is designed.

[0071] According to the grid-connected voltage requirements, the energy storage system is designed with 20 units per phase, and the rated voltage of the DC side of each unit is 768V. Among them, the battery energy storage active unit is 20*20%=4, the energy storage battery cluster is composed of 240 LFP batteries connected in series, and there are 16 capacitor reactive units.

[0072] The active and reactive power control of this embodiment is as follows (assuming that the inductor voltage drop is 10% of the phase voltage):

[0073] (1) Charging of energy storage batteries, and output of capacitive reactive power by the system

[0074] P=-1MW, Q=-4MVar, the output voltage falls in the first quadrant.

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081] The output voltage phase angle of the battery energy storage active unit is -74.6°, and the total output voltage effective value is U SMB =1533.19V

[0082] The phase angle of the output voltage of the capacitor reactive unit is 15.4°, and the total output voltage effective value is U SMC =6143.56V

[0083] (2) Energy storage battery charging, system output inductive reactive power

[0084] P=-1MW, Q=4MVar, the output voltage falls in the second quadrant.

[0085]

[0086]

[0087]

[0088] The output voltage phase angle of the battery energy storage active unit is 76°, and the total output voltage effective value is U SMB =1396.74V

[0089] The output voltage phase angle of the capacitor reactive unit is -14°, and the total output voltage effective value is U SMC =5024.65V

[0090] (3) The energy storage battery discharges and the system outputs inductive reactive power

[0091] P = 1MW, Q = 4MVar, the output voltage falls in the third quadrant

[0092]

[0093]

[0094]

[0095] The output voltage phase angle of the battery energy storage active unit is -76°, and the total output voltage effective value is U SMB =1396.74V

[0096] The output voltage phase angle of the capacitor reactive unit is 14°, and the total output voltage effective value is U SMC =5024.65V

[0097] (4) The energy storage battery discharges and the system outputs capacitive reactive power

[0098] P=1MW, Q=-4MVar, the output voltage falls in the fourth quadrant.

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] The output voltage phase angle of the battery energy storage active unit is 74.6°, and the total output voltage effective value is U SMB =1533.19V

[0105] The output voltage phase angle of the capacitor reactive unit is -15.4°, and the total output voltage effective value is U SMC =6143.56V

[0106] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A control method for a cascaded H-bridge battery energy storage system with independent active and reactive capacities, characterized in that: The cascaded H-bridge battery energy storage system with independent active and reactive capacity respectively connects a grid-connected inductor L, a plurality of submodules equipped with capacitors, and a plurality of submodules equipped with batteries in series on the three phases A, B, and C of the three-phase power grid, and the three phases adopt star connection or delta connection; The control method of the cascaded H-bridge battery energy storage system with independent active and reactive capacities obtains the modulation wave of the submodule according to the given active and reactive reference values, and then controls the energy storage system; a coordinate system is established with the direction of the grid voltage vector Us as the positive direction of the x-axis, and is divided into four categories according to the different active and reactive exchange conditions between the energy storage system and the grid: (1) charging of the energy storage battery, the system outputs capacitive reactive power; (2) charging of the energy storage battery, the system outputs inductive reactive power; (3) discharging of the energy storage battery, the system outputs inductive reactive power; (4) discharging of the energy storage battery, the system outputs capacitive reactive power, and the control is performed separately; For energy storage battery charging, the system outputs capacitive reactive power: Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e. discharging the energy storage battery; P<0 means outputting active power to the grid, i.e. charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid; at this time, P<0, Q<0, the output voltage falls in the first quadrant, i.e. the upper right quadrant of the coordinate system; α1 is the difference between U0 and -U L The angle between U S The angle between U0 and U1; First, according to Calculate the effective value of the energy storage system output voltage U0, and then according to Calculate θ; The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is α1+θ-π / 2, and the effective value is U s sin(α1+θ); The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is α1+θ, and the effective value is U s cos(α1+θ)+U L ; For energy storage battery charging, the system outputs inductive reactive power: Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e., discharging the energy storage battery; P<0 means outputting active power to the grid, i.e., charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid; at this time, P<0, Q>0, the output voltage falls in the second quadrant, i.e., the upper left quadrant of the coordinate system; α2 is the difference between Us and U L The angle of The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is π / 2-α2, and the effective value is U s sinα2; The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is -α2, and the effective value is U s cosα2-U L ; When the energy storage battery discharges and the system outputs inductive reactive power: Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e., discharging the energy storage battery; P<0 means outputting active power to the grid, i.e., charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid. At this time, P>0, Q>0, the output voltage falls in the third quadrant, i.e., the lower left quadrant of the coordinate system; α2 is the difference between Us and U L The angle of The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is α2-π / 2, and the effective value is U s sinα2; The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is α2, the effective value is U s cosα2-U L ; When the energy storage battery discharges and the system outputs capacitive reactive power: Define P and Q as given active and reactive reference values. P>0 means outputting active power to the grid, i.e., discharging the energy storage battery; P<0 means outputting active power to the grid, i.e., charging the energy storage battery; Q>0 means outputting inductive reactive power to the grid; Q<0 means outputting capacitive reactive power to the grid. At this time, P>0, Q<0, the output voltage falls in the fourth quadrant, i.e., the lower right quadrant of the coordinate system; α1 is the difference between U0 and -U L The angle between U S The angle between U0 and U1; First, according to Calculate the effective value of the energy storage system output voltage U0, and then according to Calculate θ; The voltage U provided by the submodule equipped with a battery SMB The control strategy is: the phase angle is π / 2-α1-θ, and the effective value is U s sin(α1+θ); The voltage U provided by the submodule equipped with capacitors SMC The control strategy is: the phase angle is -α1-θ, and the effective value is U s cos(α1+θ)+U L .

2. The control method of the cascaded H-bridge battery energy storage system with independent active and reactive capacities according to claim 1, characterized in that: The number of submodules equipped with capacitors for phases A, B, and C is the same.

3. The control method of the cascaded H-bridge battery energy storage system with independent active and reactive capacities according to claim 1, characterized in that: The submodules equipped with capacitors for phases A, B, and C adopt a single-phase H-bridge topology, and the parameters of capacitor capacity and voltage level are exactly the same.

4. The control method of the cascaded H-bridge battery energy storage system with independent active and reactive capacities according to claim 1, characterized in that: The number of submodules equipped with batteries for phases A, B, and C is the same.

5. The control method of the cascaded H-bridge battery energy storage system with independent active and reactive capacities according to claim 1, characterized in that: The submodules equipped with batteries for the three phases A, B, and C adopt a single-phase H-bridge topology, and the battery capacity and voltage level parameters are exactly the same.

Images