MMC battery energy storage system and state of charge estimation method thereof

Abstract

The invention relates to the technical field of energy storage systems, and discloses an MMC battery energy storage system and a charge state estimation method thereof, in the system, each battery bridge arm is connected in series with a bridge arm current sampling sensor; the state of charge estimation method comprises the following steps: defining a corresponding relation among the switching state, the working mode and the switching function of each full-control semiconductor device; determining a switching function based on the corresponding relation and the switching state of the current full-control semiconductor device; based on the Kirchhoff's current law, deriving the current of the battery PACK according to the multiplication of the switching function and the bridge arm current; and carrying out current integration on the battery PACK based on an ampere-hour integration method to obtain the state of charge of the battery PACK. According to the invention, the current of the battery branch can be collected with high precision, the current of each battery pack is calculated by combining the control mode of each PACK controller, and then the SOC is estimated, so that the complexity of the system can be effectively reduced, the cost of the system is reduced, the loss of the system is reduced, and the reliability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and particularly to a MMC battery energy storage system and a method for estimating its state of charge. Background Art

[0002] In traditional battery energy storage systems, the method for estimating the SOC of a battery pack is based on the assumption that the current flowing through each battery pack is the same. The SOC of all battery packs on this branch can be calculated using the current of this branch. However, in a MMC battery energy storage system, a controller is connected in series in the battery pack loop. Different working states of the controller will result in different currents flowing into the battery packs. The currents flowing into or out of the battery packs in the same branch are not consistent. Therefore, it is impossible to directly estimate the SOC of each battery pack using the branch current. The current solution is to measure the current of each battery pack and then estimate the SOC of each battery pack. This solution generally adds a current sampling circuit to each controller, calculates the average current, and then estimates the power of the battery pack.

[0003] The current sampling circuit generally uses a shunt or a Hall sensor. A shunt is an instrument for measuring direct current. It is made based on the principle that a voltage is generated across a resistor when current passes through it. A shunt can be equivalent to a resistor, and the loss of the shunt is proportional to the magnitude of the current flowing through it. If there is a shunt inside each controller, it will increase the loss of the entire system; the accuracy requirement for the Hall sensor used for SOC estimation is 2‰, and the cost is relatively high. Configuring a Hall sensor inside each controller will increase the overall cost of the machine. In addition, the current sampling circuit will also increase the complexity of the system and reduce the reliability of the system. Moreover, since the current is in the form of pulses, high-speed sampling is required, and the accuracy requirement is also relatively high, which brings problems that are difficult to solve. Therefore, it is urgent to further improve the state-of-charge estimation scheme of the MMC battery energy storage system. Summary of the Invention

[0004] The object of the present invention is to provide a MMC battery energy storage system and a method for estimating its state of charge, which can accurately collect the current of the battery branch, combine the control mode of each PACK controller, calculate the current of each battery pack, and then estimate the SOC, effectively reducing the complexity of the system, reducing the system cost, reducing the system loss, and improving the system reliability.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] An MMC battery energy storage system includes three phase units, which are respectively connected to a three-phase AC power grid. Each phase unit includes at least two battery bridge arms arranged in parallel, and a reactor is connected in series to each battery bridge arm. Each battery bridge arm includes a plurality of battery PACKs connected in series, and each battery PACK is connected to a PACK controller;

[0007] A bridge arm current sampling sensor is connected in series to each battery bridge arm. The bridge arm current sampling sensor is used to collect the bridge arm current. The PACK controller adopts a full-bridge control circuit or a half-bridge control circuit. The full-bridge control circuit includes four fully controlled semiconductor devices, and the half-bridge control circuit includes two fully controlled semiconductor devices;

[0008] A bridge arm controller is provided for each battery bridge arm. The PACK controller is communicatively connected to the bridge arm controller of its corresponding battery bridge arm, and the bridge arm controller is communicatively connected to the system controller;

[0009] The PACK controller obtains the current of the battery PACK based on the switching states of the fully controlled semiconductor devices inside it and the bridge arm current, and estimates the state of charge of the battery PACK based on the current of the battery PACK.

[0010] Furthermore, the fully controlled semiconductor device adopts a MOSFET or an IGBT.

[0011] Furthermore, the bridge arm current sampling sensor adopts a Hall sensor.

[0012] The present invention also provides a method for estimating the state of charge of an MMC battery energy storage system, which is applied to the above-mentioned MMC battery energy storage system, and includes:

[0013] Define the corresponding relationships among the switching states, working modes, and switching functions of the fully controlled semiconductor devices;

[0014] Based on the corresponding relationships and the current switching states of the fully controlled semiconductor devices, determine the switching function;

[0015] Based on Kirchhoff's current law, deduce the current of the battery PACK according to the switching function and the bridge arm current:

[0016] I bat =I arm* S AB

[0017] where, I bat represents the current of the battery PACK, I arm represents the bridge arm current, and S AB represents the switching function;

[0018] Integrate the current of the battery PACK based on the ampere-hour integration method to obtain the state of charge of the battery PACK.

[0019] Further, when the PACK controller adopts a full-bridge control circuit, and the four fully-controlled semiconductor devices are represented by Q1, Q2, Q3, and Q4 respectively, then the corresponding relationships defining the switching states, operating modes, and switching functions of each fully-controlled semiconductor device specifically include:

[0020] When Q1 and Q3 are turned on and Q2 and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current cannot flow into the battery PACK either. The operating mode of the PACK controller is bypass, and the switching function is 0;

[0021] When Q2 and Q4 are turned on and Q1 and Q3 are turned off, the forward current cannot flow into the battery PACK, and the reverse current cannot flow into the battery PACK either. The operating mode of the PACK controller is bypass, and the switching function is 0;

[0022] When Q1 and Q4 are turned on and Q2 and Q3 are turned off, the forward current charges the battery PACK, and the reverse current discharges the battery PACK. The operating mode of the PACK controller is series forward, and the switching function is 1;

[0023] When Q2 and Q3 are turned on and Q1 and Q4 are turned off, the forward current discharges the battery PACK, and the reverse current charges the battery PACK. The operating mode of the PACK controller is series reverse, and the switching function is -1;

[0024] When Q1 is turned on and Q2, Q3, and Q4 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The operating mode of the PACK controller is charge forward and zero reverse, and the switching function is sgn(I arm );

[0025] When Q2 is turned on and Q1, Q3, and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current charges the battery PACK. The operating mode of the PACK controller is charge reverse and zero forward, and the switching function is -sgn(-I arm );

[0026] When Q3 is turned on and Q1, Q2, and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current charges the battery PACK. The operating mode of the PACK controller is charge forward and zero reverse, and the switching function is sgn(I arm );

[0027] When Q4 is turned on and Q1, Q2, and Q3 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The operating mode of the PACK controller is charge reverse and zero forward, and the switching function is -sgn(-I arm );

[0028] When Q1, Q2, Q3, and Q4 are all turned off, the forward current charges the battery PACK, and the reverse current charges the battery PACK. The working mode of the PACK controller is uncontrolled rectification, and the switching function is sgn(I arm ) - sgn(-I arm ).

[0029] Furthermore, when the PACK controller adopts a half-bridge control circuit, the two fully controlled semiconductor devices are represented by Q1 and Q2 respectively. Then, the corresponding relationships defining the switching states, working modes, and switching functions of each fully controlled semiconductor device specifically include:

[0030] When Q2 is turned on and Q1 is turned off, neither the forward current nor the reverse current can flow into the battery PACK. The working mode of the PACK controller is bypass, and the switching function is 0;

[0031] When Q1 is turned on and Q2 is turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The working mode of the PACK controller is series positive, and the switching function is 1;

[0032] When Q1 and Q2 are both turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The working mode of the PACK controller is uncontrolled rectification, and the switching function is sgn(I arm ).

[0033] Furthermore, the sign function sgn(x) = {0, x <= 0; 1, x > 0}. When x is greater than 0, the output is 1, and when x is less than or equal to 0, the output is 0, where x represents I arm or -I arm , and the result of this function is denoted as S AB .

[0034] According to the specific embodiments provided by the present invention, the MMC battery energy storage system and its state of charge estimation method provided by the present invention disclose the following technical effects:

[0035] The present invention does not require installing current sensors for each battery pack, reducing the complexity of hardware wiring and signal processing. Only one bridge-arm current sampling sensor needs to be connected in series to each battery bridge arm to collect the bridge-arm current. By simplifying the system structure, the system installation cost is greatly reduced. A PACK controller is connected to both the positive and negative ends of each battery PACK. The PACK controller can adopt a full-bridge, half-bridge, or other controllable power electronic controllers. The PACK controller includes multiple fully controlled semiconductor devices. By analyzing the switching states of the fully controlled semiconductor devices and the influence of the switching states of the PACK controller on the battery pack current, the operating states of each controller are comprehensively calculated with the current of the current bridge arm to obtain the current of each battery pack, and then the power of each battery pack is estimated. This method realizes the indirect calculation of the battery pack current, effectively reducing the system complexity, system cost, system loss, and improving system reliability. In addition, the state-of-charge estimation method of the present invention has wide applicability and can be applied to any scenario where the controller is used to control the battery pack and causes inconsistent battery pack currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 It is a hardware topology diagram of the MMC battery energy storage system according to an embodiment of the present invention;

[0038] Figure 2 It is a control system architecture of the MMC battery energy storage system according to an embodiment of the present invention;

[0039] Figure 3 It is a schematic structural diagram of the PACK controller according to an embodiment of the present invention, where (a) is a full-bridge control circuit and (b) is a half-bridge control circuit;

[0040] Figure 4 It is a schematic diagram of the relationship between the bridge-arm current and the battery current in the full-bridge control circuit according to an embodiment of the present invention;

[0041] Figure 5 It is a schematic diagram of current sampling in the full-bridge control circuit according to an embodiment of the present invention under different switching states;

[0042] Figure 6 It is a schematic diagram of the working state when Q1 and Q3 are turned on and Q2 and Q4 are turned off in the full-bridge control circuit, where (a) is a schematic diagram of the forward current and (b) is a schematic diagram of the reverse current;

[0043] Figure 7 Schematic diagram of the working state when Q2 and Q4 are turned on and Q1 and Q3 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0044] Figure 8 Schematic diagram of the working state when Q1 and Q4 are turned on and Q2 and Q3 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0045] Figure 9 Schematic diagram of the working state when Q2 and Q3 are turned on and Q1 and Q4 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0046] Figure 10 Schematic diagram of the working state when Q1 is turned on and Q2, Q3, and Q4 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0047] Figure 11 Schematic diagram of the working state when Q2 is turned on and Q1, Q3, and Q4 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0048] Figure 12 Schematic diagram of the working state when Q3 is turned on and Q1, Q2, and Q4 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0049] Figure 13 Schematic diagram of the working state when Q4 is turned on and Q1, Q2, and Q3 are turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0050] Figure 14 Schematic diagram of the working state when Q1, Q2, Q3, and Q4 are all turned off in the full-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0051] Figure 15 Schematic diagram of the working state when Q1 is turned on and Q2 is turned off in the half-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0052] Figure 16 Schematic diagram of the working state when Q2 is turned on and Q1 is turned off in the half-bridge control circuit. Among them, (a) is the schematic diagram of the forward current, and (b) is the schematic diagram of the reverse current;

[0053] Figure 17It is a schematic diagram of the working state when Q1 and Q2 in the half-bridge control circuit are turned off. Among them, (a) is a schematic diagram of the forward current, and (b) is a schematic diagram of the reverse current;

[0054] Figure 18 It is an energy storage system with a common DC bus;

[0055] Among them, the reference numerals are explained as follows: 1. Bridge arm current sampling sensor; 2. Cluster current sampling sensor. Specific embodiments

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0057] The purpose of the present invention is to provide an MMC battery energy storage system and its state of charge estimation method, which can accurately collect the current of the battery branch, and then combine the control modes of each PACK controller to calculate the current of each battery pack, and then estimate the SOC, which can effectively reduce the system complexity, reduce the system cost, reduce the system loss, and improve the system reliability.

[0058] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] As Figures 1 - 3 shown, the MMC battery energy storage system provided by the present invention includes three phase units, and the three phase units are respectively connected to a three-phase AC power grid. Each phase unit includes at least two battery bridge arms arranged in parallel. Each battery bridge arm is connected in series with a reactor. The battery bridge arm includes a plurality of battery PACKs connected in series. A PACK controller is connected to both the positive and negative ends of each battery PACK;

[0060] Each battery bridge arm is connected in series with a bridge arm current sampling sensor 1, and the bridge arm current sampling sensor 1 is used to collect the bridge arm current. The PACK controller adopts a full-bridge control circuit or a half-bridge control circuit. As Figure 3 shown in (a) in Figure 3 the full-bridge control circuit includes four fully controlled semiconductor devices. As shown in (b) in

[0061] A bridge arm controller is set for each battery bridge arm. The PACK controller is communicatively connected to the bridge arm controller of the battery bridge arm where it is located, and the bridge arm controller is communicatively connected to the system controller; each PACK controller is communicatively connected to the bridge arm controller through point-to-point communication, and each bridge arm controller is communicatively connected to the system controller through point-to-point communication.

[0062] The PACK controller obtains the current of the battery PACK based on the switching states of all the fully controlled semiconductor devices inside it and the bridge arm current, and estimates the state of charge of the battery PACK based on the current of the battery PACK.

[0063] Among them, the fully controlled semiconductor device uses MOSFET or IGBT. The bridge arm current sampling sensor uses a Hall sensor.

[0064] As Figure 4 shown, essentially to obtain the SOC of the battery, it is necessary to integrate the current I flowing through the battery pack to obtain the ampere-hour of electricity flowing through the battery. Considering the relationship between the battery pack current, the bridge arm current, and the switching state of the PACK controller, the battery pack current I bat theoretically can be indirectly calculated through the bridge arm current I bat . Considering that all the battery PACKs in a single bridge arm are connected in series and the bridge arm current is the same, only 1 bridge arm current sampling sensor is needed for a single bridge arm, and the overall cost can be greatly reduced. arm

[0065] The present invention also provides a method for estimating the state of charge of an MMC battery energy storage system, which is applied to the above MMC battery energy storage system, including:

[0066] Defining the corresponding relationship between the switching states, working modes, and switching functions of all the fully controlled semiconductor devices;

[0067] Based on the corresponding relationship and the current switching states of the fully controlled semiconductor devices, determining the switching function;

[0068] Based on Kirchhoff's current law, deriving the current of the battery PACK according to the switching function and the bridge arm current:

[0069] I bat = I arm* S AB

[0070] Among them, I bat represents the current of the battery PACK, I arm represents the bridge arm current, and S AB represents the switching function;

[0071] Based on the ampere-hour integration method, integrating the current of the battery PACK to obtain the state of charge of the battery PACK.

[0072] Among them, as Figure 3 shown in (a) below, when the PACK controller adopts a full-bridge control circuit, the four fully-controlled semiconductor devices are represented by Q1, Q2, Q3, and Q4 respectively. Then, the corresponding relationships defining the switching states, operating modes, and switching functions of each fully-controlled semiconductor device specifically include:

[0073] Each arm of a single-phase voltage source full-bridge has 3 switching methods (except for direct conduction), and there are a total of 9 switching states for the left and right arms. Through the analysis of the switching states, the corresponding relationships are shown in Table 1:

[0074] Table 1 Relationship between Switching States and Switching Functions of Full-Bridge Control Circuit

[0075]

[0076]

[0077] Among them, the sign function sgn(x) = {0, x <= 0; 1, x > 0}. When x is greater than 0, the output is 1, and when x is less than or equal to 0, the output is 0. Denote the result of this function as S AB . For example, if I arm is -100 A, then substituting it into the function sgn(x) gives a calculation result of 0; if I arm is 100 A, then the result of the function sgn(x) is 1.

[0078] According to KCL (Kirchhoff's Current Law), it can be known that I bat = I arm * S AB . The integral of I bat can be changed to the integral of I arm * S AB .

[0079] According to the above switching states of the PACK controller, multiplying the received arm current by the switching function and performing an averaging process gives the current flowing into the battery pack, and the SOC of this battery pack can be estimated through this current.

[0080] In order to improve the current calculation accuracy, it is necessary to increase the sampling frequency of the switching states of the fully-controlled semiconductor devices. The higher the sampling frequency, the higher the sampling accuracy. Generally, the sampling frequency is not lower than 1 MHz. Figure 5 Figure is a schematic diagram of sampling the switching states of fully-controlled semiconductor devices. Figure 5 In it, I arm is the arm current, Q1 - Q4 are fully-controlled semiconductor devices, high level means on, and low level means off; T S1 is the average period, generally 10 ms, T S2is the sampling period of the switch tube state, generally 1 us; I arm (t0) and I arm (t1) are the instantaneous values of the arm current at times t0 and t1 respectively; S 1 、S 2 ……S N is the sampling period of the switch tube. Figure 4 In Figure 4 , the current flows in from M+ and out from M-, which is the forward current; otherwise, it is the reverse current.

[0081] When the PACK controller adopts a full-bridge control circuit, the corresponding relationships between the switching states, working modes, and switching functions of each fully controlled semiconductor device are as follows:

[0082] When Q1 and Q3 are turned on and Q2 and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current cannot flow into the battery PACK either. The working mode of the PACK controller is bypass, the switching function is 0, and the battery pack current is 0, as Figure 6 shown;

[0083] When Q2 and Q4 are turned on and Q1 and Q3 are turned off, the forward current cannot flow into the battery PACK, and the reverse current cannot flow into the battery PACK either. The working mode of the PACK controller is bypass, the switching function is 0, and the battery pack current is 0, as Figure 7 shown;

[0084] When Q1 and Q4 are turned on and Q2 and Q3 are turned off, the forward current charges the battery PACK, and the reverse current discharges the battery PACK, as Figure 8 shown. The working mode of the PACK controller is series positive, and the switching function is 1;

[0085] When Q2 and Q3 are turned on and Q1 and Q4 are turned off, the forward current discharges the battery PACK, and the reverse current charges the battery PACK, as Figure 9 shown. The working mode of the PACK controller is series negative, and the switching function is -1;

[0086] When Q1 is turned on and Q2, Q3, and Q4 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK, as Figure 10 shown. The working mode of the PACK controller is charge positive and discharge zero, and the switching function is sgn(I arm );

[0087] When Q2 is turned on and Q1, Q3, and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current charges the battery PACK, as Figure 11 shown. The working mode of the PACK controller is charge negative and discharge zero, and the switching function is -sgn(-I arm );

[0088] When Q3 is turned on and Q1, Q2, and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current charges the battery PACK. As Figure 12 shown, the working mode of the PACK controller is positive charge and reverse zero, and the switching function is sgn(I arm );

[0089] When Q4 is turned on and Q1, Q2, and Q3 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. As Figure 13 shown, the working mode of the PACK controller is reverse charge and positive zero, and the switching function is -sgn(-I arm );

[0090] When Q1, Q2, Q3, and Q4 are all turned off, the forward current charges the battery PACK, and the reverse current charges the battery PACK. As Figure 14 shown, the working mode of the PACK controller is uncontrolled rectification, and the switching function is sgn(I arm ) - sgn(-I arm );

[0091] As Figure 3 shown in (b), when the PACK controller adopts a half-bridge control circuit, the two fully controlled semiconductor devices are represented by Q1 and Q2 respectively. Then, the corresponding relationships defining the switching states, working modes, and switching functions of each fully controlled semiconductor device are specifically as follows:

[0092] Each arm of each side of the single-phase voltage source type half-bridge has 3 switching methods (except for through connection), and there are a total of 3 switching states. Through the analysis of the switching states, the corresponding relationships are defined in Table 2:

[0093] Table 2 Relationship table between switching states and switching functions of half-bridge control circuit

[0094] Serial number Switch state Operating mode <![CDATA[Switching function S AB > 1 (Q1 = 0, Q2 = 1) Bypass 0 2 (Q1 = 1, Q2 = 0) Series connection 1 3 (Q1 = 0, Q2 = 0) Uncontrolled rectification <![CDATA[sgn(I arm )]]>

[0095] When the PACK controller adopts a half-bridge control circuit, the corresponding relationships of the switching states, working modes, and switching functions of each fully controlled semiconductor device are described as follows:

[0096] When Q1 is turned on and Q2 is turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK either. As Figure 15 shown, the working mode of the PACK controller is positive series connection, and the switching function is 1;

[0097] When Q2 is turned on and Q1 is turned off, neither the forward current nor the reverse current can flow into the battery PACK. As Figure 16 shown, the working mode of the PACK controller is bypass, and the switching function is 0;

[0098] When both Q1 and Q2 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK either. As Figure 17 shown, the working mode of the PACK controller is uncontrolled rectification, and the switching function is sgn(I arm ).

[0099] In the state of charge estimation method of the MMC battery energy storage system, the current of the battery PACK is integrated based on the ampere-hour integration method to obtain the state of charge of the battery PACK. Specifically, it includes:

[0100] The battery pack current is obtained based on the following formula:

[0101] I bat = I arm* S AB

[0102] The value obtained by multiplying the arm current by the switching function is smoothed and filtered to facilitate subsequent use at a low calculation frequency. If the subsequent calculation is not limited by the calculation frequency, averaging may not be necessary, and the integration operation can be directly performed; the low calculation frequency refers to the number of operations per second being less than 1 MHz, because the switching state sampling frequency needs to be greater than or equal to 1 MHz to ensure calculation accuracy. If the calculation period of the subsequent calculation module is large, it will lead to a decrease in calculation accuracy;

[0103] Based on the battery pack current, the commonly used SOC estimation method is the ampere-hour integration method combined with the open-circuit voltage method. The ampere-hour integration method is also simply referred to as the ampere-hour method (Ampere Hour, AH), which is the most commonly used SOC estimation method. If the initial state of the battery SOC is defined as SOC(0), the SOC of the battery pack at time t is:

[0104]

[0105] Among them, C n is the battery capacity parameter; i is the average value of I arm *S AB mentioned above; τ is the time.

[0106] All scenarios where the controller is used to control the battery pack resulting in inconsistent battery pack currents are applicable. For example, as Figure 18 shown in the energy storage system with a common DC bus, it is also possible to only set the cluster current sampling sensor 2 in the branch of the battery cluster, and then the state of charge estimation method of the MMC battery energy storage system described in the present invention can be applied.

[0107] In this article, specific examples are used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and application scope. In summary, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An MMC battery energy storage system, comprising three phase units, the three phase units are respectively connected to a three-phase AC power grid, each phase unit comprises at least two battery bridge arms arranged in parallel, each battery bridge arm is connected in series with a reactor, the battery bridge arm comprises a plurality of battery PACKs arranged in series, each of the battery PACKs is connected to a PACK controller, characterized in that: Each battery bridge arm is connected in series with a bridge arm current sampling sensor, the bridge arm current sampling sensor is used to collect the bridge arm current, the PACK controller adopts a full-bridge control circuit or a half-bridge control circuit, the full-bridge control circuit includes four fully-controlled semiconductor devices, and the half-bridge control circuit includes two fully-controlled semiconductor devices; Each battery bridge arm is provided with a bridge arm controller, the PACK controller is communicatively connected to the bridge arm controller of the battery bridge arm where it is located, and the bridge arm controller is communicatively connected to the system controller; The PACK controller obtains the current of the battery PACK according to the switch states of each fully-controlled semiconductor device inside the PACK controller and the bridge arm current, and estimates the state of charge of the battery PACK based on the current of the battery PACK.

2. The MMC battery energy storage system according to claim 1, characterized in that: The fully controlled semiconductor device adopts MOSFET or IGBT.

3. The MMC battery energy storage system according to claim 1, characterized in that: The bridge arm current sampling sensor adopts a Hall sensor.

4. A method for estimating the state of charge of an MMC battery energy storage system, applied to the MMC battery energy storage system according to any one of claims 1 to 3, characterized in that: include: Define the corresponding relationship between the switching state, working mode and switching function of each fully controlled semiconductor device; Determining a switching function based on the corresponding relationship and the current switching state of the fully-controlled semiconductor device; Based on Kirchhoff's current law, the current of the battery PACK is derived according to the switching function and the bridge arm current: I bat =I arm* S AB Among them, I bat Indicates the current of the battery PACK, I arm Represents the bridge arm current, S AB represents the switch function; The current of the battery PACK is integrated based on the ampere-hour integration method to obtain the charge state of the battery PACK.

5. The method for estimating the state of charge of the MMC battery energy storage system according to claim 4, characterized in that: When the PACK controller adopts a full-bridge control circuit, the four fully-controlled semiconductor devices are represented by Q1, Q2, Q3, and Q4 respectively, and the corresponding relationship between the switch state, working mode, and switch function of each fully-controlled semiconductor device is defined, specifically including: When Q1 and Q3 are turned on and Q2 and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current cannot flow into the battery PACK. The working mode of the PACK controller is bypass, and the switching function is 0; When Q2 and Q4 are turned on and Q1 and Q3 are turned off, the forward current cannot flow into the battery PACK, and the reverse current cannot flow into the battery PACK. The working mode of the PACK controller is bypass, and the switching function is 0; When Q1 and Q4 are turned on and Q2 and Q3 are turned off, the forward current charges the battery PACK and the reverse current discharges the battery PACK. The working mode of the PACK controller is positive series and the switching function is 1. When Q2 and Q3 are turned on and Q1 and Q4 are turned off, the forward current discharges the battery PACK and the reverse current charges the battery PACK. The working mode of the PACK controller is reverse series and the switching function is -1. When Q1 is turned on and Q2, Q3, and Q4 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The working mode of the PACK controller is positive charge and reverse zero, and the switching function is sgn(I arm ); When Q2 is turned on and Q1, Q3, and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current charges the battery PACK. The PACK controller works in reverse charging mode, and the switching function is -sgn(-I arm ); When Q3 is turned on and Q1, Q2, and Q4 are turned off, the forward current cannot flow into the battery PACK, and the reverse current charges the battery PACK. The PACK controller works in the forward charging and reverse zeroing mode, and the switching function is sgn(I arm ); When Q4 is turned on and Q1, Q2, and Q3 are turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The working mode of the PACK controller is reverse charging to zero, and the switching function is -sgn(-I arm ); When Q1, Q2, Q3, and Q4 are all turned off, the forward current charges the battery PACK, and the reverse current charges the battery PACK. The PACK controller works in uncontrolled rectification mode, and the switching function is sgn(I arm )-sgn(-I arm ).

6. The method for estimating the state of charge of the MMC battery energy storage system according to claim 4, characterized in that: When the PACK controller adopts a half-bridge control circuit, the two fully-controlled semiconductor devices are represented by Q1 and Q2 respectively, and the corresponding relationship between the switch state, working mode and switch function of each fully-controlled semiconductor device is defined, specifically including: When Q2 is turned on and Q1 is turned off, neither the forward current nor the reverse current can flow into the battery PACK, the PACK controller works in bypass mode, and the switch function is 0; When Q1 is turned on and Q2 is turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The PACK controller works in the forward series mode, and the switching function is 1; When Q1 and Q2 are both turned off, the forward current charges the battery PACK, and the reverse current cannot flow into the battery PACK. The PACK controller works in uncontrolled rectification mode, and the switching function is sgn(I arm ).

7. The method for estimating the state of charge of the MMC battery energy storage system according to claim 5 or 6, characterized in that: The sign function sgn(x) = {0, x <= 0; 1, x > 0}, when x is greater than 0, the output is 1, when x is less than or equal to 0, the output is 0, where x represents I arm or -I arm , the result of this function is recorded as S AB .

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