Energy storage converter and inter-phase charge state balance control method thereof

Abstract

The embodiment of the invention discloses an energy storage converter and an inter-phase charge state balance control method thereof, and the method comprises the steps: determining a target amplitude of an injected zero-sequence voltage according to an inter-phase imbalance degree, a target balance coefficient corresponding to the inter-phase imbalance degree, and a phase current of the energy storage converter; determining a target phase angle according to the inter-phase imbalance degree and the initial phase angle of the phase current of the energy storage converter, enabling the determined target amplitude of the zero-sequence voltage and the target phase angle to be related to the inter-phase imbalance degree, and finally injecting the zero-sequence voltage into a modulation wave controlled by the energy storage converter according to the target amplitude and the target phase angle. The inter-phase charge state of the energy storage converter is balanced, the charge state of each phase battery pack of the energy storage converter can be dynamically balanced according to the real-time working condition of the energy storage converter, the charge and discharge efficiency of the battery pack is improved, the service life of the battery pack is prolonged, and the system reliability is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of energy storage technology, and in particular to an energy storage converter and a method for controlling the phase-to-phase charge state balancing thereof. Background Art

[0002] With the transformation of the global energy structure and the vigorous development of clean energy, the energy storage system industry has gradually become an important link in the new energy industry chain. Energy storage technology is a key technology for achieving efficient energy utilization and optimizing energy structure. It is also the core support for promoting the development of smart grids, distributed energy, electric vehicles and other fields. Against the background of the in-depth promotion of carbon peak and carbon neutrality, building a new power system has become a huge change in the system development model in the energy field. As an important regulating resource, energy storage has maintained a high-speed development trend in recent years. Since energy storage can effectively improve the reliability and economy of the distribution network, it has been widely used in the distribution network.

[0003] In energy storage systems, the balance of the battery's state of charge (SOC) is crucial to ensuring the operating life and efficiency of the energy storage system. Due to production processes and usage, battery energy storage systems, such as energy storage inverters, have differences in SOC of each phase battery pack, which is difficult to eliminate during the charging and discharging process, affecting the charging and discharging efficiency of the battery pack, accelerating the aging and damage of the battery pack, affecting the overall efficiency of the energy storage system, and reducing reliability. Summary of the invention

[0004] The present invention provides an energy storage converter and a method for controlling the charge state balance between phases thereof, so as to dynamically balance the charge state of each phase battery pack of the energy storage converter, extend the service life of the battery pack, and improve the system reliability.

[0005] In a first aspect, an embodiment of the present invention provides a method for controlling the inter-phase charge state balancing of an energy storage converter, comprising:

[0006] Obtaining the state of charge of each phase battery group of the energy storage converter, and determining the phase imbalance degree according to the state of charge of each phase battery group; wherein the phase imbalance degree includes the imbalance degree of the state of charge of each phase battery group;

[0007] Under the condition of meeting the balancing condition, determining the target amplitude of the injected zero-sequence voltage according to the phase imbalance, the target balancing coefficient corresponding to the phase imbalance and the phase current of the energy storage converter, and determining the target phase angle according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter;

[0008] According to the target amplitude and the target phase angle, the zero-sequence voltage is injected into the modulation wave controlled by the energy storage converter to balance the charge state between the phases of the energy storage converter.

[0009] Optionally, when the balancing condition is met, the target amplitude of the injected zero-sequence voltage is determined according to the inter-phase imbalance, the target balancing coefficient corresponding to the inter-phase imbalance, and the phase current of the energy storage converter, including:

[0010] When the balancing conditions are met, the target balancing coefficient is determined according to the preset interval to which the maximum imbalance degree among the phase imbalance degrees belongs and the charge and discharge state of the energy storage converter, wherein the preset intervals include at least two, and the absolute values ​​of the target balancing coefficients corresponding to different preset intervals are different; the maximum imbalance degree is equal to the maximum value of the absolute values ​​of the imbalance degrees of the charge states of the battery groups of each phase;

[0011] The target amplitude is determined according to the root mean square of the imbalance degree of the charge state of each phase battery group in the phase imbalance degree, the effective value of the phase current and the target balancing coefficient.

[0012] Optionally, when the balancing condition is met, the target balancing coefficient is determined according to the preset interval to which the maximum imbalance degree among the inter-phase imbalance degrees belongs and the charging and discharging state of the energy storage converter, including:

[0013] When the balancing condition is met, the absolute value of the target balancing coefficient is determined according to the preset interval to which the maximum imbalance degree belongs;

[0014] The positive or negative value of the target balancing coefficient is determined according to the charging and discharging state of the energy storage converter.

[0015] Optionally, the preset interval includes a first preset interval, a second preset interval and a third preset interval; the minimum value in the first preset interval is greater than the maximum value in the second preset interval, and the minimum value in the second preset interval is greater than the maximum value in the third preset interval;

[0016] When the balancing condition is met, the absolute value of the target balancing coefficient is determined according to the preset interval to which the maximum imbalance degree belongs, including:

[0017] When the maximum imbalance degree is within a first preset interval, determining a preset first equalization coefficient as an absolute value of a target equalization coefficient;

[0018] When the maximum imbalance degree is within a third preset interval, determining the preset second equalization coefficient as the absolute value of the target equalization coefficient;

[0019] When the maximum imbalance is within the second preset interval, the absolute value of the target balancing coefficient is determined within the set range according to the maximum imbalance, and the absolute value of the target balancing coefficient is positively correlated with the maximum imbalance;

[0020] The maximum value of the setting range is smaller than the first balancing coefficient, and the minimum value of the setting range is larger than the second balancing coefficient.

[0021] Optionally, the target amplitude is determined according to the root mean square of the imbalance degree of the charge state of each phase battery group in the inter-phase imbalance degree, the effective value of the phase current and the target balancing coefficient, including determining the target amplitude according to the following formula:

[0022]

[0023] Among them, U0 represents the target amplitude, λ represents the target equalization coefficient, ΔSOC a Indicates the imbalance of the charge state of the a-phase battery pack, ΔSOC b Indicates the imbalance of the charge state of the b-phase battery pack, ΔSOC c It represents the imbalance of the charge state of the c-phase battery pack, and I represents the effective value of the phase current.

[0024] Optionally, determining the target phase angle according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter includes:

[0025] Perform Clarke transformation on the inter-phase imbalance degree, convert the inter-phase imbalance degree from the three-phase coordinate system to the two-phase coordinate system, and obtain the first imbalance component and the second imbalance component;

[0026] Determine, according to the first unbalanced component and the second unbalanced component, a vector angle between a synthetic vector of interphase unbalance and the first unbalanced component;

[0027] The target phase angle is determined based on the sum of the vector angle and the initial phase angle.

[0028] Optionally, performing Clarke transformation on the inter-phase imbalance degree, converting the inter-phase imbalance degree from a three-phase coordinate system to a two-phase coordinate system, and obtaining a first imbalance component and a second imbalance component, includes:

[0029] The coordinate axis corresponding to the first unbalanced component in the two-phase coordinate system and one of the coordinate axes in the three-phase coordinate system are determined to be in the same direction, and coordinate transformation is performed to obtain the first unbalanced component and the second unbalanced component;

[0030] Determining the vector angle between the synthetic vector of the interphase imbalance degree and the first unbalanced component according to the first unbalanced component includes calculating the vector angle using the following formula, including:

[0031]

[0032] Where θ represents the vector angle, ΔSOC α Represents the first unbalanced component, ΔSOC β Represents the second unbalanced component.

[0033] Optionally, when the balancing condition is met, before determining the target amplitude and target direction of the injected zero-sequence voltage according to the phase imbalance degree and the relationship between the phase imbalance and the regulated power, the method further includes:

[0034] Determine whether the balance condition is met according to the magnitude relationship between the maximum balance degree among the phase imbalance degrees and the preset judgment threshold;

[0035] If so, then, when the balancing condition is met, the target amplitude of the injected zero-sequence voltage is determined according to the phase imbalance, the target balancing coefficient corresponding to the phase imbalance, and the phase current of the energy storage converter, and the target phase angle is determined according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter;

[0036] If not, no zero-sequence voltage is injected into the modulation wave controlled by the energy storage converter.

[0037] Optionally, obtaining the charge state of each phase battery group of the energy storage converter, and determining the phase imbalance degree according to the charge state of each phase battery group includes:

[0038] Obtaining the state of charge of the battery module in each submodule of each phase of the energy storage converter, and determining the state of charge of the battery pack of each phase according to the state of charge of the battery module in each submodule; wherein the submodule includes a battery module and a drive circuit;

[0039] Determine the average state of charge between phases according to the state of charge of each phase battery group;

[0040] The phase imbalance is determined based on the difference between the state of charge of each phase battery group and the average state of charge between the phases.

[0041] In a second aspect, an embodiment of the present invention further provides an energy storage converter, which uses the energy storage converter phase-to-phase charge state balancing control method of any embodiment of the present invention to perform balancing control.

[0042] The energy storage converter and the inter-phase state of charge balancing control method thereof of the present embodiment determine the inter-phase imbalance degree according to the state of charge of each phase battery group, determine the target amplitude of the injected zero-sequence voltage according to the inter-phase imbalance degree, the target balancing coefficient corresponding to the inter-phase imbalance degree and the phase current of the energy storage converter, and determine the target phase angle according to the inter-phase imbalance degree and the initial phase angle of the phase current of the energy storage converter, so that the determined target amplitude and target phase angle of the zero-sequence voltage are related to the inter-phase imbalance degree, and finally inject the zero-sequence voltage into the modulation wave controlled by the energy storage converter according to the target amplitude and target phase angle, balance the inter-phase state of charge of the energy storage converter, so that the target amplitude and target phase angle of the injected zero-sequence voltage match the actual operating condition of the energy storage converter, that is, the state of charge of the battery groups of each phase of the energy storage converter can be dynamically balanced according to the real-time operating condition of the energy storage converter, which is beneficial to improving the charging and discharging efficiency of the battery group, extending the service life of the battery group, and improving the system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a structural schematic diagram of a cascade type energy storage converter in the related art;

[0044] Figure 2 It is a flow chart of a method for controlling the inter-phase charge state balancing of an energy storage converter provided by an embodiment of the present invention;

[0045] Figure 3 It is a flow chart of another method for controlling the inter-phase charge state balancing of an energy storage converter provided by an embodiment of the present invention;

[0046] Figure 4 It is a vector diagram of the imbalance of the state of charge of each phase battery pack;

[0047] Figure 5 It is a detailed flow chart for determining the target phase angle according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter;

[0048] Figure 6 It is another vector diagram of the imbalance of the state of charge of each phase battery pack;

[0049] Figure 7 It is a control block diagram of a method for controlling a phase-to-phase charge state balancing of an energy storage converter provided by an embodiment of the present invention;

[0050] Figure 8 It is a simulation diagram of the energy storage converter in the charging state under the first initial working condition;

[0051] Fig. 9 It is a simulation diagram of the energy storage converter under the second initial working condition in the charging state;

[0052] Fig.10It is a simulation diagram of the energy storage converter under the second initial working condition in the charging state;

[0053] Fig.11 It is a simulation diagram of the energy storage converter under an initial working condition in the discharge state. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0055] An embodiment of the present invention provides a method for balancing the state of charge between phases of an energy storage converter. The balancing control method can be used to balance the state of charge between phases of an energy storage converter. For example, the balancing control method can be used to balance the state of charge between phases of a cascaded energy storage converter, so that the state of charge of battery groups in different phases is more balanced. Figure 1 This is a schematic diagram of the structure of the cascade energy storage converter in the related technology. Figure 1 , the cascaded energy storage converter can be a three-phase energy storage converter ( Figure 1 a, b, c three phases), for example, a three-phase three-wire topology, wherein each phase includes multiple submodules, each submodule includes a battery module 10 and a drive circuit 20, the drive circuit 20 can be an H-bridge circuit, and multiple submodules are connected through the H-bridge circuit. Figure 2 is a flow chart of a method for controlling the phase-to-phase charge state balance of an energy storage converter provided by an embodiment of the present invention, with reference to Figure 2 The energy storage converter interphase charge state balancing control method comprises:

[0056] S110, acquiring the state of charge of each phase battery group of the energy storage converter, and determining the phase imbalance degree according to the state of charge of each phase battery group.

[0057] The phase imbalance includes the imbalance of the state of charge of each phase battery group.

[0058] Specifically, obtaining the state of charge of each phase battery pack of the energy storage converter may include obtaining the state of charge of each battery module in each phase battery pack. Exemplarily, the energy storage converter is a three-phase energy storage converter, and the state of charge of each phase battery pack can be calculated based on the state of charge of each battery module in the phase. Optionally, the state of charge of each phase battery pack is equal to the average of the state of charge of each battery module in the phase. After the state of charge of each phase battery pack is determined, the phase imbalance can be calculated based on the state of charge of each phase battery pack. For the calculation method of the phase imbalance, in some embodiments, the state of charge of one phase battery pack can be used as a reference, and the imbalance of the phase used as a reference is determined to be 0. In the state of charge of other phase battery packs, the imbalance corresponding to the state of charge of each phase battery pack can be equal to the difference between the state of charge of the phase battery pack and the state of charge of the one phase battery pack used as a reference. For example, taking the charge state of the battery pack of phase b as a reference, the imbalance degree of the charge state of the battery pack of phase b is 0, and the imbalance degree corresponding to the charge state of the battery pack of phase a can be equal to the difference between the charge state of the battery pack of phase a and the charge state of the battery pack of phase b. In other embodiments, the imbalance degree of the charge state of any phase battery pack can be obtained based on the difference between the charge state of the battery pack of that phase and the average charge state of the battery packs of each phase.

[0059] S120. When the balancing conditions are met, the target amplitude of the injected zero-sequence voltage is determined according to the phase imbalance, the target balancing coefficient corresponding to the phase imbalance, and the phase current of the energy storage converter, and the target phase angle is determined according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter.

[0060] Among them, the equilibrium condition can be set in advance. In some embodiments, it can be determined whether the equilibrium condition is met based on the maximum imbalance among the phase imbalances. In other embodiments, it can also be determined whether the equilibrium condition is met based on the difference between the maximum imbalance and the minimum imbalance among the phase imbalances. For example, when the difference between the maximum imbalance and the minimum imbalance among the phase imbalances is greater than a preset value, it is determined that the equilibrium condition is met.

[0061] In this step, when the balancing condition is met, the corresponding target balancing coefficient can be determined according to the phase imbalance. Optionally, the corresponding relationship between the phase imbalance and the target balancing coefficient is preset. In some embodiments, the corresponding relationship between the phase imbalance and the absolute value of the target balancing coefficient can be preset, and then the absolute value of the target balancing coefficient is determined according to the preset corresponding relationship. In which, the positive and negative of the corresponding target balancing coefficient of the energy storage inverter are opposite in the charging state and the discharging state.

[0062] After the interphase imbalance and the target balancing coefficient corresponding to the interphase imbalance are determined, the target amplitude of the zero-sequence voltage is calculated in combination with the acquired phase current of the energy storage converter. Optionally, a first calculation rule is pre-set based on the interphase imbalance, the target balancing coefficient corresponding to the interphase imbalance, and the phase current of the energy storage converter and the target amplitude of the zero-sequence voltage, and then the target amplitude of the zero-sequence voltage is determined according to the pre-set first calculation rule.

[0063] In this step, not only the target amplitude of the injected zero-sequence voltage is determined, but also the target phase angle of the zero-sequence voltage is determined. Optionally, a second calculation rule between the phase imbalance, the initial phase angle of the phase current and the target phase angle of the zero-sequence voltage is pre-set, and then the calculated phase imbalance and the obtained initial phase angle of the phase current are substituted into the second calculation rule to obtain the target phase angle of the zero-sequence voltage.

[0064] S130, injecting zero-sequence voltage into the modulation wave controlled by the energy storage converter according to the target amplitude and the target phase angle, so as to balance the charge state between phases of the energy storage converter.

[0065] Specifically, in this step, a zero-sequence voltage with a target amplitude and a target phase angle can be injected into the modulation wave that controls the energy storage converter. For example, the zero-sequence voltage can be injected into the original modulation wave that controls the energy storage converter. The target amplitude and target phase angle of the zero-sequence voltage are both related to the phase-to-phase imbalance. In this way, the target amplitude and target phase angle of the zero-sequence voltage under the corresponding phase-to-phase imbalance can be obtained according to the different actual operating conditions of the energy storage converter, so that the target amplitude and target phase angle of the injected zero-sequence voltage match the actual operating conditions of the energy storage converter.

[0066] The phase-to-phase state of charge balancing control method of the energy storage converter of the present embodiment determines the phase imbalance according to the state of charge of each phase battery group, determines the target amplitude of the injected zero-sequence voltage according to the phase imbalance, the target balancing coefficient corresponding to the phase imbalance, and the phase current of the energy storage converter, and determines the target phase angle according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter, so that the determined target amplitude and target phase angle of the zero-sequence voltage are related to the phase imbalance, and finally injects the zero-sequence voltage into the modulation wave controlled by the energy storage converter according to the target amplitude and the target phase angle, balances the phase state of charge of the energy storage converter, so that the target amplitude and target phase angle of the injected zero-sequence voltage match the actual operating condition of the energy storage converter, that is, the charge state of each phase battery group of the energy storage converter can be dynamically balanced according to the real-time operating condition of the energy storage converter, which is beneficial to improving the charging and discharging efficiency of the battery group, extending the service life of the battery group, and improving the system reliability.

[0067] Figure 3is a flowchart of another method for controlling the phase-to-phase charge state balancing of an energy storage converter provided by an embodiment of the present invention, with reference to Figure 3 The energy storage converter interphase charge state balancing control method comprises:

[0068] S210, acquiring the state of charge of each phase battery group of the energy storage converter, and determining the phase imbalance degree according to the state of charge of each phase battery group.

[0069] The phase imbalance includes the imbalance of the state of charge of each phase battery group.

[0070] In some embodiments, S210 includes: obtaining the state of charge of the battery module in each submodule of each phase of the energy storage converter, and determining the state of charge of each phase battery group according to the state of charge of the battery module in each submodule; determining the average state of charge between phases according to the state of charge of each phase battery group; determining the phase imbalance according to the difference between the state of charge of each phase battery group and the average state of charge between phases. Figure 1 , wherein the submodule includes a battery module and a driving circuit.

[0071] In some embodiments, the state of charge of the battery pack of each phase is determined by taking the average state of charge of the battery modules in each submodule of each phase. Specifically, the average state of charge of the battery modules in each submodule of one phase can be expressed by the following formula:

[0072]

[0073] Wherein, x = a, b, c; N is the total number of submodules in phase x; represents the average state of charge of the battery modules in each submodule of phase x, Can be used as the x-phase battery pack state of charge, SOC xn Indicates the state of charge of the battery module in the nth submodule of phase x.

[0074] The mean state of charge between phases can be calculated using the following formula:

[0075]

[0076] Among them, SOC avg Indicates the average state of charge between phases, SOC 总 Indicates the total state of charge of each phase battery pack, SOC a Indicates the state of charge of the a-phase battery pack, SOC b Indicates the state of charge of the b-phase battery pack, SOC c Indicates the charge state of the C-phase battery pack.

[0077] The phase imbalance can be calculated using the following formula:

[0078]

[0079] Among them, ΔSOC represents the phase imbalance, ΔSOC a Indicates the imbalance of the charge state of the a-phase battery pack, ΔSOC b Indicates the imbalance of the charge state of the b-phase battery pack, ΔSOC c Indicates the imbalance of the charge state of the C-phase battery pack.

[0080] S220: When the balancing condition is met, determine the target balancing coefficient according to the preset interval to which the maximum imbalance degree among the inter-phase imbalance degrees belongs and the charging and discharging state of the energy storage converter.

[0081] Among them, the preset intervals include at least two, and the absolute values ​​of the target balancing coefficients corresponding to different preset intervals are different; the maximum imbalance degree is equal to the maximum value of the absolute values ​​of the imbalance degrees of the charge states of the battery packs of each phase.

[0082] After the interphase imbalance is determined, the charge state of the battery pack of one phase with the largest absolute value among the interphase imbalance can be determined according to the charge state of each phase battery pack, and the absolute value of the charge state of the battery pack of this phase is used as the corresponding maximum imbalance. Then, when the balancing condition is met, the absolute value of the target balancing coefficient is determined according to the preset interval to which the maximum imbalance belongs, and the positive and negative values ​​of the target balancing coefficient are determined according to the charge and discharge state of the energy storage inverter. In this way, it can be ensured that the determined target balancing coefficient is adapted to the current working condition of the energy storage inverter, for example, it is adapted to the interphase imbalance of the energy storage inverter under the current charge and discharge state, thereby ensuring that after interphase balancing is performed according to the determined target balancing coefficient, a better balancing effect is achieved. In some embodiments, the charge and discharge state of the energy storage inverter can be determined according to the phase current direction of the energy storage inverter, thereby determining the positive and negative values ​​of the target balancing coefficient.

[0083] Specifically, the unbalanced state of charge of any phase battery group is proportional to the regulated power generated by the injected zero-sequence voltage. The relationship between the two can be expressed by the following formula:

[0084] λΔSOC x =ΔP x (4);

[0085] Where λ represents the target balance coefficient, ΔSOC x Indicates the imbalance of the x-phase battery charge state, ΔP xIt represents the regulated power generated by the injected zero-sequence voltage in the x-phase, x = a, b, c. When the battery pack in the energy storage converter is in the charging state, λ is a negative value; when the battery pack in the energy storage converter is in the discharging state, λ is a positive value. It can be seen that the absolute value of the regulated power generated by the injected zero-sequence voltage in the x-phase is positively correlated with the absolute value of the imbalance degree of the charge state of the x-phase battery pack.

[0086] In some embodiments, the preset interval includes a first preset interval, a second preset interval, and a third preset interval; the minimum value in the first preset interval is greater than the maximum value in the second preset interval, and the minimum value in the second preset interval is greater than the maximum value in the third preset interval. When the balancing condition is met, the absolute value of the target balancing coefficient is determined according to the preset interval to which the maximum imbalance belongs, including: when the maximum imbalance is within the first preset interval, the preset first balancing coefficient is determined as the absolute value of the target balancing coefficient; when the maximum imbalance is within the third preset interval, the preset second balancing coefficient is determined as the absolute value of the target balancing coefficient; when the maximum imbalance is within the second preset interval, the absolute value of the target balancing coefficient is determined within a set range according to the maximum imbalance, and the absolute value of the target balancing coefficient is positively correlated with the maximum imbalance; wherein the maximum value of the set range is less than the first balancing coefficient, and the minimum value of the set range is greater than the second balancing coefficient.

[0087] Specifically, when the maximum imbalance is in the first preset interval, it means that the maximum imbalance is large. At this time, a target balancing coefficient with a larger absolute value is used for phase balancing, so that the absolute value of the regulating power generated by the injected zero-sequence voltage will also be larger, which is beneficial to improving the balancing speed when the phase imbalance of the energy storage converter is more serious.

[0088] When the maximum imbalance is in the third preset interval, it means that the maximum imbalance is small. At this time, a target balancing coefficient with a smaller absolute value is used for phase balancing, so that the absolute value of the regulated power generated by the injected zero-sequence voltage will also be smaller, preventing the injected zero-sequence voltage from being too large and unable to reach a balanced state.

[0089] When the maximum imbalance is in the second preset interval, it means that the maximum imbalance is moderate. In this case, the absolute value of the target balancing coefficient is determined within the set range according to the maximum imbalance. The absolute value of the target balancing coefficient is positively correlated with the maximum imbalance. The maximum value of the set range is less than the first balancing coefficient, and the minimum value of the set range is greater than the second balancing coefficient. In this way, when the relative imbalance is relatively moderate, different absolute values ​​of target balancing coefficients are determined according to different maximum imbalances, thereby achieving the purpose of rapid balancing.

[0090] S230, determining a target amplitude according to the root mean square of the imbalance degree of the charge state of each phase battery group in the inter-phase imbalance degree, the effective value of the phase current and the target balancing coefficient.

[0091] Optionally, before S230, the process further includes determining a calculation formula for determining a target amplitude based on the root mean square of the imbalance degree of the charge state of each phase battery pack in the inter-phase imbalance degree, the effective value of the phase current, and the target balancing coefficient.

[0092] Specifically, the calculation formula for calculating the target amplitude can be derived based on the proportional relationship between the imbalance of the state of charge of any phase battery group and the regulating power generated by injecting zero-sequence voltage (that is, formula (4)). In the proportional relationship between the imbalance of the state of charge of any phase battery group and the regulating power generated by injecting zero-sequence voltage, the proportional coefficient is the target balancing coefficient. The imbalance of the state of charge of each phase battery group in formula (4) has been obtained above. For the calculation formula of the regulating power, the zero-sequence voltage can be superimposed on the original output voltage of the energy storage inverter, and determined in combination with the output current of the energy storage inverter. In an embodiment of the present invention, the topological structure of the energy storage inverter is a three-phase three-wire system. This structure does not generate zero-sequence current through zero-sequence voltage injection.

[0093] Assume the injected zero-sequence voltage u0 is:

[0094] u0=U0sin(ωt+θ0) (5)

[0095] U0 is the amplitude of the injected zero-sequence voltage, θ0 is the target phase angle of the injected zero-sequence voltage, and ω is the grid angular frequency.

[0096] The injected zero-sequence voltage is superimposed on the original output voltage of the energy storage converter. After superposition, the output voltage of each phase is:

[0097]

[0098] u a Indicates the output voltage of phase a of the energy storage converter, u b represents the output voltage of phase b of the energy storage converter, u c represents the C-phase output voltage of the energy storage converter, and U represents the voltage amplitude of the grid connected to the energy storage converter.

[0099] Assume that the output current of the energy storage converter is

[0100]

[0101] In the formula, i a represents the output current of phase a of the energy storage converter, i b represents the output current of phase b of the energy storage converter, i crepresents the output current of phase c of the energy storage converter, I is the effective value of each phase current, Initial phase angle of the phase current.

[0102] It can be concluded that the three-phase output power of the energy storage converter is:

[0103]

[0104] Where P a Represents the output power of phase a of the energy storage converter, P b Represents the output power of phase b of the energy storage converter, P c represents the c-phase output power of the energy storage converter, P represents the original output power of the energy storage converter, ΔP a is the regulating power generated by the injected zero-sequence voltage in phase a, ΔP b is the regulating power generated by the injected zero-sequence voltage in phase b, ΔP c It is the regulating power generated by injecting zero-sequence voltage into phase c.

[0105] According to formula (8) and formula (4), we can get:

[0106]

[0107] in,

[0108] Figure 4 It is a vector diagram of the imbalance of the state of charge of each phase battery pack. According to the vector diagram, the following relationship can be obtained:

[0109]

[0110] Among them, ΔSOC 合 The resultant vector representing the imbalance of each phase.

[0111] according to Figure 4 It can be seen that

[0112]

[0113] In the formula, ΔSOC α represents the first equilibrium component in the two-phase coordinate system, ΔSOC β Represents the second equilibrium component in the two-phase coordinate system.

[0114] According to formulas (4), (9), and (10), we can obtain:

[0115]

[0116] Therefore, optionally, S230 includes: determining the target amplitude according to the following formula:

[0117]

[0118] Among them, U0 represents the target amplitude, λ represents the target equalization coefficient, ΔSOC a Indicates the imbalance of the charge state of the a-phase battery pack, θSOC b Indicates the imbalance of the charge state of the b-phase battery pack, ΔSOC c represents the imbalance of the charge state of the c-phase battery group, and I represents the effective value of the phase current. According to formula (13), in the embodiment of the present invention, according to the different charging and discharging states of the energy storage converter, the target balance coefficient has different positive and negative values, and the corresponding target amplitude of the zero-sequence voltage also has positive and negative values. For example, when the energy storage converter is in the charging state, the target amplitude of the zero-sequence voltage is a negative value; when the energy storage converter is in the charging state, the target amplitude of the zero-sequence voltage is a positive value.

[0119] S240: Determine a target phase angle according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter.

[0120] S250, injecting zero-sequence voltage into the modulation wave controlled by the energy storage converter according to the target amplitude and the target phase angle, so as to balance the charge state between phases of the energy storage converter.

[0121] Figure 5 This is a detailed flow chart for determining the target phase angle based on the phase imbalance and the initial phase angle of the energy storage converter phase current. Figure 5 Optionally, S120 determines the target phase angle according to the phase imbalance and the initial phase angle of the phase current of the energy storage converter, or S240 includes:

[0122] S241 . Perform Clarke transformation on the inter-phase imbalance degree, and convert the inter-phase imbalance degree from a three-phase coordinate system to a two-phase coordinate system to obtain a first imbalance component and a second imbalance component.

[0123] Due to the injection of zero-sequence voltage, the regulated power ΔP generated in each phase a , ΔP b , ΔP c It is a vector and is linearly related to the unbalanced state of charge of the corresponding phase battery pack. Therefore, the phase angle of the injected zero-sequence voltage cannot be accurately locked in the control. It is necessary to introduce Clarke transformation to transform the three-phase vector into a synthetic vector in the αβ axis of the rotating two-phase coordinate system through coordinate transformation. Figure 4 The vector diagram shown, ΔSOC α represents the first equilibrium component of the α-axis, ΔSOC β represents the second equilibrium component of the β axis.

[0124] like Figure 4As shown, optionally, the coordinate axis corresponding to the first unbalanced component in the two-phase coordinate system and one of the coordinate axes in the three-phase coordinate system are determined to be in the same direction, and coordinate transformation is performed to obtain the first unbalanced component and the second unbalanced component.

[0125] S242: Determine, according to the first unbalanced component and the second unbalanced component, an angle between a synthetic vector of the inter-phase imbalance and the vector of the first unbalanced component.

[0126] Combination Figure 4 , when the component of the second unbalanced component on the β axis is greater than 0, the vector angle θ is positive. Specifically, Figure 4 In the case shown, the vector angle θ can be expressed by the following formula:

[0127]

[0128] Considering that the range of arccos is [0, π], the range needs to be expanded in the entire coordinate system. The above calculation is in the positive half plane of the β axis, that is, the rotation angle θ is in the range of [0, π]. Figure 6 Another vector diagram of the imbalance of the state of charge of each phase battery pack is shown in Figure 2. Figure 6 , when the rotation vector is in the negative half plane of the β axis, the vector angle θ is in the range of [π, 2π]. In this case, the vector angle θ can be expressed by the following formula:

[0129]

[0130] According to this, in S242, determining the vector angle between the synthetic vector of the inter-phase imbalance degree and the first imbalance component according to the first imbalance component and the second imbalance component includes:

[0131]

[0132] Where θ represents the vector angle, ΔSOC α Represents the first unbalanced component, ΔSOC β Represents the second unbalanced component.

[0133] S243. Determine the target phase angle according to the sum of the vector angle and the initial phase angle.

[0134] Specifically, in this step, the sum of the vector angle and the initial phase angle is determined as the target phase angle of the zero-sequence voltage.

[0135] On the basis of the above embodiments, S130, according to the target amplitude and the target phase angle, injects a zero-sequence voltage into the modulation wave controlled by the energy storage converter to balance the interphase charge state of the energy storage converter, including: injecting a zero-sequence voltage with a target amplitude and a target phase angle into the modulation wave controlled by the energy storage converter, and limiting the modulation wave after superimposing the zero-sequence voltage when it exceeds the preset amplitude, so as to balance the interphase charge state of the energy storage converter. In this way, by limiting the modulation wave, it is ensured that the total modulation index does not reach the saturation state. In some embodiments, the limiting of the modulation wave is applied in the above embodiments, when the target balancing coefficient is in the first preset interval and the second preset interval.

[0136] Figure 7 is a control block diagram of a method for controlling the phase-to-phase charge state balancing of an energy storage converter provided by an embodiment of the present invention, with reference to Figure 7 First, the root mean square of the state of charge of each phase battery pack is determined according to the state of charge of each phase battery pack in the phase imbalance, and then the target amplitude of the injected zero-sequence voltage is obtained by the root mean square and the target balancing coefficient corresponding to the phase imbalance. The first imbalance component ΔSOC is obtained by transforming the phase imbalance from the three-phase coordinate system to the two-phase rotating coordinate system α and the second unbalanced component ΔSOC β After that, according to the first unbalanced component ΔSOC α and the second unbalanced component ΔSOC β Determine the initial formula for calculating the vector angle θ In this process, the second unbalanced component ΔSOC is considered β The positive and negative of ΔSOC β When ΔSOC is greater than or equal to 0, multiply the initial formula by 1. β When it is less than 0, multiply the initial formula by -1 to obtain the vector angle. Then the sum of the vector angle and the initial phase angle of the phase current is determined as the target phase angle of the zero-sequence voltage. Finally, the injected zero-sequence voltage is obtained according to the target amplitude and the target phase angle, and the voltages injected into phase a, phase b, and phase c are obtained according to the zero-sequence voltage, which are ΔU a-相间 , ΔU b-相间 and ΔU c-相间 .

[0137] In some embodiments, before S120, the process includes: determining whether a balance condition is met according to a magnitude relationship between a maximum balance degree among the inter-phase imbalance degrees and a preset judgment threshold.

[0138] Optionally, when the maximum balance degree among the phase imbalance degrees is greater than a preset judgment threshold, it is determined that the balance condition is met. The preset judgment threshold can be set according to actual conditions. When the balance condition is met, S120 is executed; when the balance condition is not met, the zero-sequence voltage is not injected into the modulation wave controlled by the energy storage converter.

[0139] The following are simulation diagrams of balanced control performed using the phase-to-phase charge state balanced control method of the energy storage converter according to an embodiment of the present invention under several actual working conditions. Figure 8-Figure 11 This is a simulation diagram of the energy storage converter under four different working conditions, where the horizontal axis is time and the vertical axis is the SOC value.

[0140] Figure 8 This is a simulation diagram of the energy storage converter in the charging state under the first initial working condition. Figure 8 , in the first initial condition, SOC a =24, SOC b =20, SOC c =16, according to Figure 8 It can be seen that after a certain period of time, the charge state of the three-phase battery pack is balanced and consistent.

[0141] Fig. 9 This is a simulation diagram of the energy storage converter under the second initial working condition when it is in the charging state. Fig. 9 , under the second initial condition, SOC a =30, SOC b =20, SOC c =10, according to Fig. 9 It can be seen that after a certain period of time, the charge state of the three-phase battery pack is balanced and consistent.

[0142] Fig.10 This is a simulation diagram of the energy storage converter under the second initial working condition when it is in the charging state. Fig.10 , under the third initial condition, SOC a =10, SOC b =30, SOC c =20, according to Fig. 9 It can be seen that after a certain period of time, the charge state of the three-phase battery pack also reaches a balanced consistency.

[0143] Fig.11 This is a simulation diagram of the energy storage converter under an initial operating condition in the discharge state. Fig.11 , in the initial condition of the discharge state, SOC a =80, SOC b =84, SOC c =76, according to Fig.11It can be seen that after a certain period of time, the charge state of the three-phase battery pack also reaches a balanced consistency.

[0144] An embodiment of the present invention further provides an energy storage converter, which can be balanced controlled by using the energy storage converter inter-phase charge state balancing control method of any of the above embodiments of the present invention.

[0145] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for controlling the interphase charge state balance of an energy storage converter, characterized in that: include: Obtaining the state of charge of each phase battery group of the energy storage converter, and determining the phase imbalance degree according to the state of charge of each phase battery group; wherein the phase imbalance degree includes the imbalance degree of the state of charge of each phase battery group; Under the condition that the balancing condition is met, the target amplitude of the injected zero-sequence voltage is determined according to the inter-phase imbalance, the target balancing coefficient corresponding to the inter-phase imbalance, and the phase current of the energy storage converter, and the target phase angle is determined according to the inter-phase imbalance and the initial phase angle of the phase current of the energy storage converter; A zero-sequence voltage is injected into the modulation wave controlled by the energy storage converter according to the target amplitude and the target phase angle, so as to balance the charge state between phases of the energy storage converter.

2. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 1, characterized in that: The method of determining a target amplitude of the injected zero-sequence voltage according to the inter-phase imbalance, a target balancing coefficient corresponding to the inter-phase imbalance, and a phase current of the energy storage converter when the balancing condition is met includes: When the balancing condition is met, the target balancing coefficient is determined according to the preset interval to which the maximum imbalance degree among the phase imbalance degrees belongs and the charge and discharge state of the energy storage converter, wherein the preset intervals include at least two, and the absolute values ​​of the target balancing coefficients corresponding to different preset intervals are different; the maximum imbalance degree is equal to the maximum value of the absolute values ​​of the imbalance degrees of the charge states of the battery groups of each phase; The target amplitude is determined according to the root mean square of the imbalance degree of the charge state of each phase battery group in the inter-phase imbalance degree, the effective value of the phase current and the target balancing coefficient.

3. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 2, characterized in that: In the case where the balancing condition is met, determining the target balancing coefficient according to the preset interval to which the maximum imbalance degree among the inter-phase imbalance degrees belongs and the charging and discharging state of the energy storage converter comprises: When the balancing condition is met, determining the absolute value of the target balancing coefficient according to the preset interval to which the maximum imbalance degree belongs; The positive or negative value of the target balancing coefficient is determined according to the charging and discharging state of the energy storage converter.

4. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 3, characterized in that: The preset interval includes a first preset interval, a second preset interval and a third preset interval; the minimum value in the first preset interval is greater than the maximum value in the second preset interval, and the minimum value in the second preset interval is greater than the maximum value in the third preset interval; The step of determining the absolute value of the target equalization coefficient according to the preset interval to which the maximum imbalance degree belongs when the equalization condition is met includes: When the maximum imbalance degree is within the first preset interval, determining a preset first equalization coefficient as an absolute value of a target equalization coefficient; When the maximum imbalance degree is within the third preset interval, determining the preset second equalization coefficient as the absolute value of the target equalization coefficient; When the maximum imbalance is within the second preset interval, determining an absolute value of a target balancing coefficient within a set range according to the maximum imbalance, wherein the absolute value of the target balancing coefficient is positively correlated with the maximum imbalance; The maximum value of the setting range is smaller than the first balancing coefficient, and the minimum value of the setting range is larger than the second balancing coefficient.

5. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 2, characterized in that: The determining the target amplitude according to the root mean square of the imbalance degree of the charge state of each phase battery group in the inter-phase imbalance degree, the effective value of the phase current and the target balancing coefficient includes determining the target amplitude according to the following formula: Wherein, U0 represents the target amplitude, λ represents the target equalization coefficient, ΔSOC a Indicates the imbalance of the charge state of the a-phase battery pack, ΔSOC b Indicates the imbalance of the charge state of the b-phase battery pack, ΔSOC c represents the imbalance of the charge state of the c-phase battery group, and I represents the effective value of the phase current.

6. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 1, characterized in that: The step of determining a target phase angle according to the inter-phase imbalance and the initial phase angle of the phase current of the energy storage converter comprises: Performing Clarke transformation on the inter-phase imbalance degree, converting the inter-phase imbalance degree from a three-phase coordinate system to a two-phase coordinate system, and obtaining a first imbalance component and a second imbalance component; Determining, according to the first unbalanced component and the second unbalanced component, an angle between a synthetic vector of the inter-phase imbalance degree and a vector of the first unbalanced component; The target phase angle is determined according to the sum of the vector angle and the initial phase angle.

7. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 6, characterized in that: The Clarke transformation is performed on the inter-phase imbalance degree to convert the inter-phase imbalance degree from a three-phase coordinate system to a two-phase coordinate system to obtain a first imbalance component and a second imbalance component, including: The coordinate axis corresponding to the first unbalanced component in the two-phase coordinate system and one of the coordinate axes in the three-phase coordinate system are determined to be in the same direction, and coordinate transformation is performed to obtain the first unbalanced component and the second unbalanced component; Determining the vector angle between the synthetic vector of the inter-phase imbalance degree and the first unbalanced component according to the first unbalanced component and the second unbalanced component includes calculating the vector angle using the following formula: Wherein, θ represents the vector angle, ΔSOC α represents the first unbalanced component, ΔSOC β represents the second unbalanced component.

8. The method for controlling the interphase charge state balancing of the energy storage converter according to claim 1, characterized in that: Before determining the target amplitude and target direction of the injected zero-sequence voltage according to the phase imbalance degree and the relationship between the phase imbalance and the regulated power when the balancing condition is met, the method further includes: Determining whether the balance condition is met according to the magnitude relationship between the maximum balance degree among the phase imbalance degrees and a preset judgment threshold; If so, then, under the condition that the balancing condition is met, the target amplitude of the injected zero-sequence voltage is determined according to the inter-phase imbalance, the target balancing coefficient corresponding to the inter-phase imbalance, and the phase current of the energy storage converter, and the target phase angle is determined according to the inter-phase imbalance and the initial phase angle of the phase current of the energy storage converter; If not, the zero-sequence voltage is not injected into the modulation wave controlled by the energy storage converter.

9. The method for controlling the phase-to-phase charge state balancing of the energy storage converter according to claim 1, characterized in that: The acquiring the state of charge of each phase battery group of the energy storage converter and determining the phase imbalance degree according to the state of charge of each phase battery group includes: Obtaining the state of charge of the battery module in each submodule of each phase of the energy storage converter, and determining the state of charge of the battery pack of each phase according to the state of charge of the battery module in each submodule; wherein the submodule includes a battery module and a drive circuit; Determine the inter-phase state of charge average according to the state of charge of each phase battery pack; The inter-phase imbalance degree is determined according to the difference between the state of charge of the battery group of each phase and the average state of charge of the phases.

10. An energy storage converter, characterized in that: The energy storage converter phase-to-phase charge state balancing control method described in any one of claims 1 to 9 is used for balancing control.

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