A fault-tolerant control method and device for a multi-level battery energy storage system

Abstract

The present invention discloses a fault-tolerant control method and device for a multi-level battery energy storage system. The method includes: establishing a mathematical model after a submodule failure of a cascaded battery energy storage system, locating the fault phase, and obtaining the number of faulty submodules; dividing the operating conditions when the system fails into three intervals, calculating the power factor angle and power factor based on the voltage and current sampling values, and determining the operating interval when the system fails; injecting the corresponding fundamental frequency zero-sequence voltage and negative sequence current according to the interval in which the system fails; controlling the fundamental frequency zero-sequence voltage and negative sequence current to obtain a control signal for the cascaded battery energy storage system, and performing fault-tolerant control on the cascaded battery energy storage system. The device includes: a fault diagnosis module, a fault-tolerant control module, an AC power control module, a current control module, and a modulation module. The fault-tolerant control method and device for a multi-level battery energy storage system disclosed by the present invention can avoid power reverse, effectively reduce the risk of overcharge and over-discharge, and improve the safety of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of control of battery energy storage systems, and in particular to a fault-tolerant control method and device for a multi-level battery energy storage system. Background Art

[0002] The cascaded battery energy storage system distributes battery packs to the direct side of the cascaded H-bridge converter submodules. By cascading multiple submodules, it can be connected to the medium and high voltage power grid without a transformer. It has the ability to regulate both active and reactive power, and has the advantages of modularity, easy management, high voltage, and high power. It has broad prospects in large-scale battery energy storage systems.

[0003] Cascaded battery energy storage systems contain numerous power devices, presenting a high risk of failure. When a submodule failure occurs in one phase of a cascaded battery energy storage system, the faulty submodule must be removed and fault tolerance measures implemented to ensure uninterrupted and continuous system operation.

[0004] Fault tolerance methods are categorized into hardware and software. Hardware methods primarily increase system reliability through submodule redundancy, but this requires additional hardware investment and is costly. Software methods utilize fault-tolerant control methods to alter system control instructions and achieve stable control of each phase.

[0005] Existing cascaded battery energy storage systems often use a fault-tolerant control strategy of cascaded H-bridge converters, employing zero-sequence constant-voltage injection or special modulation techniques. This can cause three-phase power imbalance. In low-power-factor scenarios, the power of one phase can be opposite to its power command, i.e., power reversal. This creates the risk of overcharging or over-discharging, endangering the safe operation of the battery energy storage system.

[0006] To this end, it is necessary to develop a fault-tolerant control method suitable for the safe operation of the cascade battery energy storage system based on the operating characteristics of the cascade battery energy storage system, so as to achieve safe and uninterrupted operation of the cascade battery energy storage system. Summary of the Invention

[0007] The present invention provides a fault-tolerant control method and device for a multi-level battery energy storage system. This method can solve the power reverse problem that occurs during submodule fault control in a cascaded battery energy storage system, ensuring the safe and uninterrupted operation of the cascaded battery energy storage system. Details are described below:

[0008] In a first aspect, a fault-tolerant control method for a multi-level battery energy storage system is provided, the method comprising:

[0009] Establish a mathematical model for submodule failure in a cascaded battery energy storage system, locate the faulty phase, and obtain the number of faulty submodules;

[0010] The operating conditions during a system fault are divided into three intervals. The power factor angle and power factor are calculated based on the voltage and current sampling values ​​to determine the operating interval during a system fault.

[0011] According to the interval where the system is located when the fault occurs, the corresponding fundamental frequency zero-sequence voltage and negative-sequence current are injected;

[0012] The fundamental frequency zero-sequence voltage and negative-sequence current are controlled to obtain a control signal of the cascade battery energy storage system, and the cascade battery energy storage system is subjected to fault-tolerant control.

[0013] The steps of establishing a mathematical model of a cascaded battery energy storage system submodule after a failure, locating the faulty phase, and obtaining the number of faulty submodules are as follows:

[0014] For a three-phase cascade battery energy storage system, the phase where the submodule fails is defined as the fault phase, the phase whose phase voltage lags the fault phase voltage by 120 degrees is defined as the lagging phase, and the phase whose phase voltage leads the fault phase voltage by 120 degrees is defined as the leading phase.

[0015] After the submodule fails, the fundamental frequency zero sequence voltage needs to be injected to avoid overmodulation. The output phase voltage V j (v f 、v z 、v h’ ), the expression of {j=f, z, h} is as follows:

[0016]

[0017] Where V f 、V z and V h are the amplitudes of the output voltages of the fault phase, lagging phase, and leading phase respectively, ω is the grid angular frequency (rad / s), and It is the initial phase of the fault phase voltage, lagging phase voltage and leading phase voltage.

[0018] Phase current I j (i f 、i z 、i h )The expression is as follows:

[0019]

[0020] Where, I f , I z and I h are the amplitudes of the output currents of the fault phase, lagging phase, and leading phase respectively, is the initial phase of the fault phase voltage, is the power factor angle.

[0021] After the submodule fails, the fundamental frequency zero-sequence voltage is injected, and its expression is as follows:

[0022] v0=V0cos(ωt+δ)

[0023] Where V0 and δ are the fundamental frequency zero-sequence voltage amplitude and initial phase.

[0024] After the submodule fails, the output phase voltage of the system is equal to the sum of the grid voltage of each phase and the fundamental frequency zero sequence voltage, V f 、V z and V h The value of V0, δ and Determined by express.

[0025] After a submodule fails, the maximum number of submodules in the fault phase becomes NN f , N is the number of bridge arm modules, N f is the number of faulty submodules.

[0026] The operating conditions during a system failure are divided into three intervals, and the power factor angle and power factor are calculated based on the voltage and current sampling values. The operating interval during a system failure is determined as follows:

[0027] According to the power factor from high to low, the operating conditions of the cascade battery energy storage system are divided into three intervals, namely interval one, interval two, and interval three.

[0028] Power factor PF is equal to

[0029] PF1 is the critical threshold between interval 1 and interval 2, and PF2 is the critical threshold between interval 1 and interval 2.

[0030] PF1 solves get, It is the power factor angle corresponding to when the power factor PF is equal to PF1.

[0031] when For the positive time, Obtained by solving the following equation:

[0032]

[0033] when When it is negative, Obtained by solving the following equation:

[0034]

[0035] Where V m and I m are the grid voltage and the output current amplitude of the cascaded battery energy storage system, V0c The calculation formula is as follows:

[0036] V 0c =(mN-N+N f )v dc

[0037] Where m is the modulation ratio, v dc is the DC side voltage of the submodule.

[0038] PF2 is obtained by solving the following equation:

[0039]

[0040] Where, The power factor angle corresponding to the power factor PF equal to PF2, its value is equal to the set Equal to the empty set of The maximum value of Defined as a given power factor angle Under the condition, the intersection of the set of (V0,δ) that satisfies the first constraint and the set of (V0,δ) that satisfies the second constraint is expressed as follows:

[0041]

[0042] The first constraint is that the amplitude of each phase voltage after a fault is less than the product of the maximum number of sub-modules in each phase multiplied by the DC voltage of the sub-module, which can be expressed as:

[0043]

[0044] The second constraint is that the positive and negative signs of the power of each phase after the fault are consistent with those before the fault, which can be expressed as:

[0045]

[0046] Where V is the phase voltage phasor value after the fault, is the conjugate of the phase current phasor value after the fault, is the phasor V and the phasor The real part of the dot product result, Indicates the sign of the power reference value of each phase.

[0047] The sampling device is used to obtain the output voltage and output current sampling values ​​of the cascaded battery energy storage system when the fault occurs, that is, the grid voltage and output current before the fault are recorded as v j and i j ; Get v through the phase-locked loop j and i j The phase value of i j With vj The phase difference between them, the value of which is used as

[0048] Calculate the power factor PF, and the calculation expression is as follows:

[0049]

[0050] Judge the operating range during system faults according to the PF value.

[0051] If PF>PF1, the system is in Range 1;

[0052] If PF1>PF>PF2, the system is in Range 2;

[0053] If PF<PF2, the system is in Range 3.

[0054] Among them, according to the range where the system fails, injecting the corresponding fundamental frequency zero-sequence voltage and negative-sequence current specifically means:

[0055] If the system fails in Range 1, inject the fundamental frequency zero-sequence voltage, the amplitude V0 of which is equal to V 0c , and the initial phase δ is δ 0c , and its expression is as follows:

[0056]

[0057] The injected negative-sequence current is 0;

[0058] If the system fails in Range 2, inject the fundamental frequency zero-sequence voltage, the amplitude V0 and the initial phase δ of which are elements in the set , and the injected negative-sequence current is 0;

[0059] If the system fails in Range 3, inject the fundamental frequency zero-sequence voltage, the amplitude V0 of which is equal to V 0c , and the initial phase δ is δ [[ID=4[7]] 0c , and inject the negative-sequence current to make the second constraint condition hold.

[0060] Among them, controlling the fundamental frequency zero-sequence voltage and negative-sequence current to obtain the control signal of the cascaded battery energy storage system and performing fault-tolerant control on the cascaded battery energy storage system specifically means:

[0061] Obtain the positive-sequence current reference value of the cascaded battery energy storage system through the power control command and the AC power control link;

[0062] Use the current control link to control the positive-sequence current and negative-sequence current to make them track their respective reference values;

[0063] Add the control signal obtained by the current control link and the required fundamental frequency zero-sequence voltage reference value, and perform per-unit processing to obtain the modulation signal;

[0064] The control signal of each power device of the cascaded battery energy storage system is obtained through modulation technology, and the power devices are controlled to achieve fault-tolerant control of the cascaded battery energy storage system.

[0065] In a second aspect, a fault-tolerant control device for a multi-level battery energy storage system is provided, the device comprising:

[0066] Fault diagnosis module, used to locate the fault phase and obtain fault information such as the number of faulty modules;

[0067] A fault-tolerant control module is used to calculate the power factor and power factor angle, determine the operating range of the system, and calculate the fundamental frequency zero-sequence voltage and negative-sequence current reference values ​​for fault-tolerant control based on the operating range of the system;

[0068] AC power control module, used to instruct energy storage power control instructions and obtain positive sequence current reference value;

[0069] A current control module for controlling the positive-sequence current and negative-sequence current of the cascaded battery energy storage system;

[0070] The modulation module generates a modulation signal from the control signal obtained by the current control module and the fundamental frequency zero-sequence voltage, and uses a modulation algorithm to obtain the actual switching signal of each power device in the cascaded battery energy storage system.

[0071] The beneficial effects of the technical solution provided by the present invention are:

[0072] 1. The fault-tolerant control method and device for a multi-level battery energy storage system proposed in the present invention can avoid overmodulation in each phase, ensuring uninterrupted and continuous operation of the cascaded battery energy storage system.

[0073] 2. The fault-tolerant control method and device for a multi-level battery energy storage system proposed in the present invention can prevent power reversal in each phase, ensuring that the charge and discharge states of the battery pack are consistent with its power command. This avoids the risk of overcharging or over-discharging the battery pack due to power reversal, thereby improving the safety of the battery pack.

[0074] 3. The fault-tolerant control method and device for a multi-level battery energy storage system proposed in the present invention do not require the addition of additional hardware circuits, thereby reducing the complexity of the cascaded battery energy storage system and improving the reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is the topology diagram of the cascade battery energy storage system;

[0076] Figure 2 is the set of intervals in polar coordinates

[0077] Figure 3is the set of interval 2 in polar coordinates

[0078] Figure 4 is the set of interval three in polar coordinates

[0079] Figure 5 This is a fault-tolerant control block diagram;

[0080] Figure 6 It is the overall control block diagram;

[0081] Figure 7 This is a prototype diagram of a three-phase cascade battery energy storage system;

[0082] Figure 8 This is the experimental waveform of the cascade battery energy storage system;

[0083] Among them, Figure (a) shows the a-phase grid voltage and three-phase output current, Figure (b) shows the three-phase phase voltage, Figure (c) shows the three-phase line voltage, Figure (d) shows the three-phase modulation reference value and fundamental frequency zero-sequence voltage, Figure (e) shows the three-phase power, and Figure (f) shows the negative-sequence current reference value and actual value. DETAILED DESCRIPTION

[0084] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0085] To address the problems in the background technology, prevent power reverse during fault-tolerant control of a cascaded battery energy storage system, achieve uninterrupted operation of the cascaded battery energy storage system, and improve the safety of the cascaded battery energy storage system, the present invention provides a fault-tolerant control method for a cascaded battery energy storage system, taking a three-phase cascaded battery energy storage system as the research object.

[0086] Example 1

[0087] A fault-tolerant control method for a multi-level battery energy storage system, the method comprising the following steps:

[0088] Step 101: Establish a mathematical model for a cascaded battery energy storage system submodule failure, locate the faulty phase, and obtain the number of faulty submodules.

[0089] Step 102: Divide the operating conditions of the system during a fault into three intervals, calculate the power factor angle and power factor based on the voltage and current sampling values, and determine the operating interval during the fault.

[0090] Step 103: injecting corresponding fundamental frequency zero-sequence voltage and negative-sequence current according to the interval where the system is located at the time of the fault;

[0091] Step 104: Control the fundamental frequency zero-sequence voltage and negative-sequence current to obtain a control signal for the cascaded battery energy storage system, and perform fault-tolerant control on the cascaded battery energy storage system;

[0092] Step 105: Experimental testing verifies the effectiveness of the proposed fault-tolerant control method for the cascaded battery energy storage system;

[0093] Example 2

[0094] The solution in Example 1 is further introduced below with reference to specific calculation formulas, drawings, and examples.

[0095] Step 201: Establish a mathematical model for a cascaded battery energy storage system submodule failure, locate the faulty phase, and obtain the number of faulty submodules;

[0096] Cascade battery energy storage system topology Figure 1 As shown, it includes three phase units, each of which includes N cascaded H-bridge submodules and a filter inductor L. Each H-bridge submodule contains four power devices, four anti-parallel diodes, and a capacitor. The DC side of each H-bridge module is connected to a battery unit. Each battery unit includes two power devices, two anti-parallel diodes, an inductor, and a battery pack. The three-phase grid voltage in the figure is v si , i is the phase sequence, i={a, b, c}, the output current is i i , the output phase voltage is v i , the AC side output voltage of each submodule is u ik , k is the serial number of each submodule in each phase, k = {1, 2, ..., N}.

[0097] Before a submodule fails, the voltage drop on the filter inductor can be ignored, and the output voltage of each phase is equal to the grid voltage.

[0098]

[0099] Where ω is the grid angular frequency (rad / s), m is the modulation ratio, N is the number of bridge arm modules, and v dc is the DC side voltage of the submodule.

[0100] For a three-phase cascade battery energy storage system, the phase where the submodule fails is defined as the fault phase, the phase whose phase voltage lags the fault phase voltage by 120 degrees is defined as the lagging phase, and the phase whose phase voltage leads the fault phase voltage by 120 degrees is defined as the leading phase.

[0101] If the first submodule of phase a fails, phase a becomes the fault phase f, phase b becomes the lagging phase z, and phase c becomes the leading phase h.

[0102] After a submodule fails, a fundamental frequency zero-sequence voltage needs to be injected to avoid overmodulation. Figure 1 The reference direction and Kirchhoff's voltage / current law give the output phase voltage V of the system. j (v f 、v z 、v h’ ), the expression of {j=f, z, h} is as follows:

[0103]

[0104] Where V f 、V z and V h are the amplitudes of the output voltages of the fault phase, lagging phase, and leading phase respectively, and It is the initial phase of the fault phase voltage, lagging phase voltage and leading phase voltage.

[0105] Phase current I j (i f 、i z 、i h )The expression is as follows:

[0106]

[0107] Where, I f , I z and I h are the amplitudes of the output currents of the fault phase, lagging phase, and leading phase respectively, is the initial phase of the fault phase voltage, is the power factor angle. If no negative sequence current is injected, only positive sequence current exists, and the output current amplitude of each phase is the same, recorded as I m .

[0108] After the submodule fails, the fundamental frequency zero-sequence voltage is injected, and its expression is as follows:

[0109] v0=V0cos(ωt+δ) (4)

[0110] Where V0 and δ are the fundamental frequency zero-sequence voltage amplitude and initial phase.

[0111] After the submodule fails, the output phase voltage of the system is equal to the sum of the grid voltage of each phase and the fundamental frequency zero sequence voltage, V f 、V z and V h The value of V0, δ and Determined by express.

[0112] After a submodule fails, the maximum number of submodules in the fault phase becomes NN f , N f is the number of faulty submodules.

[0113] Step 202: Divide the operating conditions of the system during a fault into three intervals, calculate the power factor angle and power factor based on the voltage and current sampling values, and determine the operating interval during the fault.

[0114] According to the power factor from high to low, the operating conditions of the cascade battery energy storage system are divided into three intervals, namely interval one, interval two, and interval three.

[0115] Power factor PF is equal to

[0116] PF1 is the critical threshold between interval 1 and interval 2, and PF2 is the critical threshold between interval 1 and interval 2.

[0117] PF1 solves get, It is the power factor angle corresponding to when the power factor PF is equal to PF1.

[0118] when For the positive time, Obtained by solving the following equation:

[0119]

[0120] when When it is negative, Obtained by solving the following equation:

[0121]

[0122] Where V m and I m are the grid voltage and the output current amplitude of the cascaded battery energy storage system, V 0c The calculation formula is as follows:

[0123] V 0c =(mN-N+N f )v dc (7)

[0124] PF2 is obtained by solving the following equation:

[0125]

[0126] Where, The power factor angle corresponding to the power factor PF equal to PF2, its value is equal to the set Equal to the empty set of The maximum value of Defined as a given power factor angle Under the condition, the intersection of the set of (V0,δ) that satisfies the first constraint and the set of (V0,δ) that satisfies the second constraint is expressed as follows:

[0127]

[0128] The first constraint condition is that the amplitude of each phase voltage after the fault is less than the product of the maximum number of sub-modules in each phase and the DC voltage of the sub-module, which is expressed as

[0129]

[0130] The second constraint is that the positive and negative signs of the power of each phase after the fault are consistent with those before the fault, which can be expressed as:

[0131]

[0132] Where V is the phase voltage phasor value after the fault, is the conjugate of the phase current phasor value after the fault, is the phasor V and the phasor The real part of the dot product result, Indicates the sign of the power reference value of each phase. Positive power indicates battery discharge, and negative power indicates battery charging.

[0133] The sampling device is used to obtain the output voltage and output current sampling values ​​of the cascaded battery energy storage system when the fault occurs, that is, the grid voltage and output current before the fault are recorded as v j and i j ; Get v through the phase-locked loop j and i j The phase value of i j With v j The phase difference between

[0134] Calculate the power factor PF, the calculation expression is as follows:

[0135]

[0136] Determine the operating range when the system fails based on the PF value.

[0137] If PF>PF1, the system is in interval 1, with PF=0.1, For example, the set of interval 1 in polar coordinate system is like Figure 2 As shown, the points in the polar coordinate system are the set The elements (V0,δ) in .

[0138] If PF1>PF>PF2, the system is in interval 2, with PF=0.08, For example, the set of interval two in the polar coordinate system In the polar coordinate system, as Figure 3 shown, the points in the polar coordinate system are the elements (V0, δ) of the set ;

[0139] If PF < PF2, the system is in interval three. Taking PF = 0.05, for example, the set of interval three in the polar coordinate system is an empty set, as Figure 4 shown.

[0140] Step 203: Inject the corresponding fundamental zero-sequence voltage and negative-sequence current according to the interval where the system fails;

[0141] The fault-tolerant control block diagram after the fault is as Figure 5 shown.

[0142] When the system fails, if PF > PF1, the system is in interval one, and the injected fundamental zero-sequence voltage V0 is V 0c , and its amplitude V0 is equal to V 0c , and the initial phase δ is δ 0c , and its expression is as follows:

[0143]

[0144] The injected negative-sequence current is 0.

[0145] Otherwise, if PF > PF2, the system is in interval two, and the parameters of the injected fundamental zero-sequence voltage V0 are the elements of the set . By solving the set to inject the fundamental zero-sequence voltage, its amplitude V0 and initial phase δ are the elements in the set where V0 takes the maximum value, and the injected negative-sequence current is 0.

[0146] Otherwise, the system is in interval three, and the injected fundamental zero-sequence voltage V0 is V 0c , and its amplitude V0 is equal to V 0c , and the initial phase δ is δ 0c . Inject the negative-sequence current to make the second constraint condition hold. Taking a single sub-module fault in phase a and PF = 0.05, and the active power of each phase > 0 as an example. At this time, only inject the fundamental zero-sequence voltage V 0c , then the power of phase b is less than 0, and the power of phase b at this time is recorded as the reverse power P r , and the expression is as follows:

[0147]

[0148] The injection of negative sequence current makes the second constraint condition valid, so that the power of phase b is 0 after the injection of negative sequence current, and the power of phase b is compensated by phase c, and the unbalanced power generated by the interaction between the injected negative sequence current and the output voltage is The expression is as follows:

[0149]

[0150] Will Convert to the αβ coordinate system and get the power component in the αβ coordinate system and The expression is as follows:

[0151]

[0152] Then the reference value of negative sequence current in dq coordinate system is obtained and The expression is as follows:

[0153]

[0154] Where V sd and V sq is the component of the grid voltage under the d and q axes, k is the coefficient, and the expression is as follows:

[0155]

[0156] Then the injected fundamental frequency zero sequence voltage reference value V0 and negative sequence current reference value are obtained. and

[0157] Step 204: Control the fundamental frequency zero-sequence voltage and negative-sequence current to obtain a control signal for the cascaded battery energy storage system, and perform fault-tolerant control on the cascaded battery energy storage system;

[0158] The overall control block diagram of the system is as follows: Figure 6 As shown, it consists of AC power control link, current control link, modulation and fault-tolerant control, wherein the current control link includes positive sequence current control and negative sequence current control.

[0159] Through the power control instruction P ac * and Q ac * The dq axis components of the positive sequence current reference value of the cascaded battery energy storage system are obtained through calculation with the AC power control link.

[0160] The current control link is used to control the positive sequence current and the negative sequence current so that they track their respective reference values.

[0161] The control signal obtained by the current control link and the required injected fundamental frequency zero-sequence voltage reference value are added to obtain the reference value of each phase voltage, and the modulation signal v is obtained after standardization. j * .

[0162] Through modulation technology, carrier stacking modulation technology plus a sorting algorithm can be used to obtain the control signals of each power device in the cascaded battery energy storage system, that is, the switching signals of the 12N sub-module power devices, to control the power devices of the sub-modules. For the power devices in the battery unit, a separate constant voltage control strategy can be used to maintain the constant DC side voltage of the sub-module, thereby realizing fault-tolerant control of the cascaded battery energy storage system.

[0163] Step 205: Experimental testing verifies the effectiveness of the proposed fault-tolerant control method for the cascaded battery energy storage system;

[0164] In order to further verify the effectiveness of the proposed fault-tolerant control method, we use Figure 7 The three-phase cascade battery energy storage system experimental platform shown in FIG was experimentally verified, and its main circuit parameters are listed in Table 1.

[0165] Table 1 Experimental parameters

[0166]

[0167] The experimental results of the cascade battery energy storage system under the proposed fault-tolerant control method are as follows: Figure 8 As shown in the figure. In the experiment, the first submodule of phase a of the cascaded battery energy storage system fails, and the proposed fault-tolerant control method is adopted to perform fault-tolerant control on the cascaded battery energy storage system. Phase a is the faulty phase f, phase b is the lagging phase z, and phase c is the leading phase h. The number of faulty submodules N f 1. The grid voltage and three-phase output current of phase a before and after the submodule failure are as follows Figure 8 As shown in (a), under the experimental working conditions, the AC grid phase voltage amplitude is 192V, the modulation ratio is 0.8, the current amplitude is 5A, the system outputs active power and capacitive reactive power, the battery is in the discharge state, PF = 0.05, at this time the cascaded battery energy storage system is in interval 3, and the corresponding fundamental frequency zero sequence voltage and negative sequence current need to be injected; the three-phase phase voltage is as follows Figure 8 As shown in (b), the three-phase line voltage is Figure 8 As shown in (c), after a submodule failure, the maximum number of submodules in phase a changes from 3 to 2, the number of phase voltage levels changes from 3 to 2, the number of levels of the other phase voltages remains unchanged, and the three-phase line voltage remains unchanged, which can ensure the uninterrupted and continuous operation of the cascaded battery energy storage system; the three-phase modulation reference value and the fundamental frequency zero-sequence voltage are as follows Figure 8 As shown in (d), the amplitude of the fundamental frequency zero-sequence voltage is 32V, and the initial phase is the initial phase of the fault phase voltage plus π / 2; the three-phase power is as follows Figure 8As shown in (e), after the submodule fails, the three-phase power is all positive, with the same sign as the power instruction before the fault, avoiding power reverse; the negative sequence current reference value and the actual value are as follows Figure 8 As shown in Figure (f), the d-axis component of the negative-sequence current is 0, and the q-axis component is -0.45 A. By adopting the proposed fault-tolerant control method and injecting specific fundamental frequency zero-sequence voltage and negative-sequence current, it is possible to ensure that each phase voltage is not overmodulated, ensuring uninterrupted and continuous system operation, while also avoiding three-phase power reverse, ensuring the safe and stable operation of the cascaded battery energy storage system.

[0168] In summary, the advantages of this multi-level battery energy storage system fault-tolerant control method are as follows:

[0169] 1. The fault-tolerant control method for a multi-level battery energy storage system proposed in this invention can avoid overmodulation in each phase, ensuring uninterrupted and continuous operation of the cascaded battery energy storage system.

[0170] 2. The fault-tolerant control method and device for a multi-level battery energy storage system proposed in the present invention can prevent power reversal in each phase, ensuring that the charge and discharge states of the battery pack are consistent with its power command. This avoids the risk of overcharging or over-discharging the battery pack due to power reversal, thereby improving the safety of the battery pack.

[0171] 3. The fault-tolerant control method for a multi-level battery energy storage system proposed in the present invention does not require the addition of additional hardware circuits, can reduce the complexity of the cascade battery energy storage system, and improve the reliability of the system.

[0172] A multi-level battery energy storage system fault tolerance control device, the device comprising:

[0173] Fault diagnosis module, used to locate the fault phase and obtain fault information such as the number of faulty modules;

[0174] A fault-tolerant control module is used to calculate the power factor and power factor angle, determine the operating range of the system, and calculate the fundamental frequency zero-sequence voltage and negative-sequence current reference values ​​for fault-tolerant control based on the operating range of the system;

[0175] AC power control module, used to obtain a positive sequence current reference value according to the energy storage power control instruction;

[0176] A current control module for controlling the positive-sequence current and negative-sequence current of the cascaded battery energy storage system;

[0177] The modulation module generates a modulation signal from the control signal obtained by the current control module and the fundamental frequency zero-sequence voltage, and uses a modulation algorithm to obtain the actual switching signal of each power device in the cascaded battery energy storage system.

[0178] The execution entities of the above modules and units can be devices with computing functions such as computers, single-chip microcomputers, and microcontrollers. In specific implementation, the embodiments of the present invention do not limit the execution entities and they can be selected according to the needs of actual applications.

[0179] Unless otherwise specified, the embodiments of the present invention do not limit the models of the components. Any component that can perform the above functions may be used.

[0180] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0181] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fault-tolerant control method for a multi-level battery energy storage system, characterized in that: The method includes: Establish a mathematical model after a sub-module fault in the cascaded battery energy storage system, locate the fault phase, and obtain the number of faulty sub-modules; Divide the operating conditions of the system during a fault into three intervals, calculate the power factor angle and power factor based on the voltage and current sampling values, and determine the operating interval of the system during a fault; Inject the corresponding fundamental zero-sequence voltage and negative-sequence current according to the interval where the system is during a fault; Control the fundamental zero-sequence voltage and negative-sequence current to obtain the control signal of the cascaded battery energy storage system, and perform fault-tolerant control on the cascaded battery energy storage system.

2. A fault-tolerant control method for a multi-level battery energy storage system according to claim 1, characterized in that: The establishment of the mathematical model after a sub-module fault in the cascaded battery energy storage system, the location of the fault phase, and the obtaining of the number of faulty sub-modules are specifically as follows: For a three-phase cascaded battery energy storage system, the phase in which a sub-module fails is defined as the fault phase, the phase whose phase voltage lags the fault-phase voltage by 120 degrees is defined as the lagging phase, and the phase whose phase voltage leads the fault-phase voltage by 120 degrees is defined as the leading phase; After a submodule fails, a fundamental frequency zero-sequence voltage needs to be injected to avoid overmodulation. The output phase voltage of the system V j ( v f 、 v z 、 v h’ ), { j =f, z, h}The expression is as follows: Where, V f 、 V z and V h are the amplitudes of the output voltages of the fault phase, lagging phase, and leading phase respectively, ω is the grid angular frequency (rad / s), 、 and is the initial phase of the fault phase voltage, lagging phase voltage, and leading phase voltage; Phase current I j ( i f 、 i z 、 i h )The expression is as follows: Where, I f 、 I z and I h are the amplitudes of the output currents of the fault phase, lagging phase, and leading phase respectively, is the initial phase of the fault phase voltage, is the power factor angle; After a sub-module fault, inject a fundamental zero-sequence voltage, and its expression is as follows: Where, V 0 and is the fundamental frequency zero-sequence voltage amplitude and initial phase; After a submodule fails, the system's output phase voltage is equal to the sum of each phase grid voltage and the fundamental frequency zero-sequence voltage. V f 、 V z and V h The value of V 0. and Determined by express; After a submodule fails, the maximum number of submodules that can be put into operation in the fault phase becomes , Number of bridge arm modules, is the number of faulty submodules; The division of the operating conditions of the system during a fault into three intervals, the calculation of the power factor angle and power factor based on the voltage and current sampling values, and the determination of the operating interval of the system during a fault are specifically as follows: Divide the operating conditions of the cascaded battery energy storage system into three intervals from high to low according to the power factor, namely Interval 1, Interval 2, and Interval 3; Power factor PF is equal to ; PF1 is the critical threshold between Interval 1 and Interval 2, and PF2 is the critical threshold between Interval 1 and Interval 2; PF1 solves get, is the power factor angle corresponding to when the power factor PF is equal to PF1; when For the positive time, Obtained by solving the following equation: when When it is negative, Obtained by solving the following equation: Where, V m and I m are the amplitudes of the grid voltage and the output current of the cascaded battery energy storage system, V 0c The calculation formula is as follows: Where, m is the modulation ratio, v dc is the DC side voltage of the submodule; PF2 is obtained by solving the following equation: Where, The power factor angle corresponding to the power factor PF equal to PF2, its value is equal to the set Equal to the empty set of The maximum value of Defined as a given power factor angle Under the condition, the first constraint is satisfied The set of the second constraint The intersection of the sets of is expressed as follows: The first constraint condition is that the amplitude of each phase voltage after a fault is less than the product of the maximum number of inserted sub-modules per phase and the DC voltage of the sub-module, which is expressed as: The second constraint condition is that the positive and negative of the power of each phase after a fault are the same as those of the power of each phase before the fault, which is specifically expressed as: Where, V is the phase voltage phasor value after the fault, is the conjugate of the phase current phasor value after the fault, is a phasor V and phasor The real part of the dot product result, The symbol representing the power reference value of each phase; The sampling device is used to obtain the output voltage and output current sampling values ​​of the cascaded battery energy storage system when the fault occurs, that is, the grid voltage and output current before the fault are recorded as v j and i j ; Obtained through the phase-locked loop v j and i j The phase value of i j and v j The phase difference between ; Calculate the power factor PF, and its calculation expression is as follows: Judge the operating interval of the system during a fault according to the PF value; If PF>PF1, the system is in Interval 1; If PF1>PF>PF2, the system is in Interval 2; If PF<PF2, the system is in Interval 3; The injection of the corresponding fundamental zero-sequence voltage and negative-sequence current according to the interval where the system is during a fault is specifically as follows: If the system is in interval 1 when fault occurs, the fundamental frequency zero sequence voltage is injected, and its amplitude is V 0 is equal to V 0c , initial phase for , which is expressed as follows: The injected negative-sequence current is 0; If the system is in interval 2 when the fault occurs, the fundamental frequency zero sequence voltage is injected, and its amplitude is V 0 and initial phase For collection The elements in, the injected negative sequence current is 0; If the system is in interval 3 when fault occurs, the fundamental frequency zero sequence voltage is injected, and its amplitude is V 0 is equal to V 0c , initial phase for , injecting negative sequence current makes the second constraint condition meet.

3. A fault-tolerant control method for a multi-level battery energy storage system according to claim 1, characterized in that: The control of the fundamental zero-sequence voltage and negative-sequence current to obtain the control signal of the cascaded battery energy storage system and perform fault-tolerant control on the cascaded battery energy storage system are specifically as follows: Obtain the positive-sequence current reference value of the cascaded battery energy storage system through the power control command and the AC power control link; Use the current control link to control the positive-sequence current and negative-sequence current to make them track their respective reference values; Add the control signal obtained by the current control link and the required fundamental zero-sequence voltage reference value, and obtain the modulation signal after per-unit processing; Obtain the control signals of each power device of the cascaded battery energy storage system through modulation technology, control the power devices, and realize the fault-tolerant control of the cascaded battery energy storage system.

4. A fault-tolerant control device for a multi-level battery energy storage system, characterized in that: The device includes: A fault diagnosis module for locating the fault phase and obtaining the fault information of the number of faulty modules; A fault-tolerant control module is used to calculate the power factor and power factor angle, determine the operating range of the system, and calculate the fundamental frequency zero-sequence voltage and negative-sequence current reference values ​​for fault-tolerant control based on the operating range of the system; AC power control module, used to obtain a positive sequence current reference value according to the energy storage power control instruction; A current control module for controlling the positive-sequence current and negative-sequence current of the cascaded battery energy storage system; The modulation module generates a modulation signal from the control signal obtained by the current control module and the fundamental frequency zero-sequence voltage, and uses a modulation algorithm to obtain the actual switching signal of each power device in the cascaded battery energy storage system.

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