Energy storage system and negative sequence current phase-to-phase soc equalization control device and method thereof
By setting the initial phase and ratio of the negative sequence current in the high-voltage energy storage system and using d- and q-axis decoupling control to adjust the three-phase SOC, the problem of large computational load and complexity in the existing technology is solved, and balanced control of phase SOC is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HENAN XUJI POWER ELECTRONICS CO LTD
- Filing Date
- 2023-09-27
- Publication Date
- 2026-04-14
AI Technical Summary
Existing negative sequence current injection phase-to-phase SOC equalization strategies are computationally intensive and complex in high-voltage energy storage systems, making them inconvenient for software implementation.
By comparing the three-phase SOC deviation values of the energy storage system, the term with the largest deviation is determined, and the initial phase and ratio of the negative sequence current are set according to the deviation. The three-phase SOC is adjusted by using d-axis and q-axis decoupling control to achieve phase-to-phase SOC balance.
It simplifies the calculation process, has clear logic, and makes it easy to achieve phase-to-phase SOC balancing, thus reducing the amount of computation and system complexity.
Smart Images
Figure CN117477618B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of energy storage system technology, specifically relating to energy storage systems and their negative sequence current phase-to-phase SOC equalization control devices and methods. Background Technology
[0002] With the development of smart grids, energy storage technology has become an important part of the development process because it can solve problems such as the intermittency and volatility of renewable energy power generation. Among them, battery energy storage systems have developed rapidly due to their advantages such as high power density, fast response speed, small footprint, and no special requirements for installation location.
[0003] Currently, most battery energy storage systems are designed based on low-voltage power grids, especially for low-power energy storage systems. For high-power applications, both DC / AC single-stage and DC / DC+DC / AC bipolar energy storage converters require large-capacity power frequency transformers for voltage step-up before connection to the medium- or high-voltage grid. H-bridge cascaded energy storage converter systems, however, have large capacity, do not include primary equipment such as combiner cabinets and power frequency transformers, have low system losses and costs, and good redundancy, making them widely used in energy storage conversion systems. Their battery packs can be distributed across the DC side of each module in the cascaded H-bridge, allowing the battery modules to be low-voltage modules, thus enabling current battery technology to meet the requirements of high-voltage, high-capacity battery energy storage conversion systems. However, module inconsistencies and grid voltage imbalances can lead to imbalances in the state of charge (SOC) between phases, severely affecting the system's charging and discharging capacity and reducing economic efficiency.
[0004] Interphase SOC balancing strategies include hardware and software strategies. Hardware strategies balance interphase SOC by adding balancing circuits, which increases system cost and complexity, and is therefore less commonly used. Software strategies achieve interphase SOC balancing by injecting negative-sequence current. While this does not increase system cost, existing negative-sequence current injection interphase SOC balancing strategies are relatively complex, computationally intensive, and not easily implemented in software. Summary of the Invention
[0005] The purpose of this invention is to provide an energy storage system and its negative sequence current phase-to-phase SOC equalization control device and method, which solves the problems of complex and computationally intensive existing negative sequence current injection phase-to-phase SOC equalization strategies.
[0006] To address the aforementioned technical problems, this invention provides a method for interphase SOC balancing control of negative-sequence current in an energy storage system. The energy storage system is a high-voltage energy storage system. First, the three-phase SOC deviations of the energy storage system are compared to determine the largest deviation term. When the absolute value of the largest deviation term is less than or equal to a set dead zone value, the negative-sequence current setpoint is set to 0. When the absolute value of the largest deviation term is greater than the set dead zone value, an initial phase of the negative-sequence current is set according to the different deviation conditions. Based on the ratio of the initial phase to the set negative-sequence current, the d-axis and q-axis component setpoints of the negative-sequence current are obtained. Based on the obtained negative-sequence current setpoints, d-axis and q-axis decoupling control is performed to obtain the negative-sequence control component, which is then added to the obtained positive-sequence control component to obtain the modulation wave of the converter in the energy storage system, thereby adjusting the three-phase SOC and achieving SOC balancing of the energy storage system.
[0007] The beneficial effects of the above technical solution are as follows: This invention discovers that when the phase-to-phase SOC imbalance occurs in a high-voltage energy storage system, the phase-to-phase SOC balance can be achieved by adjusting the phase-to-phase power interaction between the three-phase grid-connected negative-sequence current and the three-phase grid positive-sequence voltage through setting the initial phase and current ratio of the negative-sequence current. Therefore, this invention sets the initial phase of the corresponding negative-sequence current according to different three-phase SOC deviations, and then obtains the d-axis and q-axis component setpoints of the negative-sequence current according to the ratio of the initial phase and the set current. Based on the obtained negative-sequence current setpoints, d-axis and q-axis decoupling control is performed to obtain the negative-sequence control component, which is added to the obtained positive-sequence control component to obtain the modulation wave of the converter in the energy storage system. Compared with the prior art, the computational load is small, the strategy and method are simple, the logic is clear, and it is easy to implement.
[0008] Furthermore, in step 1), the initial phase of the negative sequence current is set according to different deviation conditions:
[0009] If the SOC deviation of phase A is positive and the absolute value of the SOC deviation of phase A is the largest, the initial phase of the corresponding negative sequence current is set to 0.
[0010] If the SOC deviation of phase A is negative and the absolute value of the SOC deviation of phase A is the largest, the initial phase of the corresponding negative sequence current is set to... ;
[0011] If the SOC deviation of phase B is positive and the absolute value of the SOC deviation of phase B is the largest, the initial phase of the corresponding negative sequence current is set as follows: ;
[0012] If the SOC deviation of phase B is negative and the absolute value of the SOC deviation of phase B is the largest, the initial phase of the corresponding negative sequence current is set as follows: ;
[0013] If the SOC deviation of phase C is positive and the absolute value of the SOC deviation of phase C is the largest, the initial phase of the corresponding negative sequence current is set to... ;
[0014] If the SOC deviation of phase C is negative and the absolute value of the SOC deviation of phase C is the largest, the initial phase of the corresponding negative sequence current is set as follows: .
[0015] The beneficial effects of the above technical solution are: the initial phase setting value can be accurately obtained according to different deviation conditions, there is a clear correspondence, the method is simple, the logic is clear, the amount of calculation is small, and it is easy to implement.
[0016] Further, the three-phase SOC deviation value mentioned in step 1) is calculated as follows: obtain the SOC value of each phase of the energy storage converter and calculate the average value of all phase SOC values. The deviation value of each phase SOC value from the average value is taken as the corresponding phase SOC deviation value; the corresponding largest deviation term is the term with the largest absolute value of the three-phase SOC deviation value.
[0017] The advantages of the above technical solution are: it accurately obtains the term with the largest deviation and the calculation method is simple.
[0018] Furthermore, in step 1), the ratio of the negative sequence current is set to k times the rated current, where k is 0. <k≤1。
[0019] The beneficial effects of the above technical solution are: it accurately obtains the proportion of negative sequence current, and the method is simple and the logic is clear.
[0020] Furthermore, the given values for the d and q components of the negative sequence current in step 4) are respectively , ;in The given value of the d-axis component of the negative sequence current For rated current, For the initial phase, It is the given value of the q-axis component of the negative sequence current.
[0021] The beneficial effects of the above technical solution are as follows: when the phase and ratio of the negative sequence current are known, the d-axis and q-axis components of the negative sequence current can be directly derived. Compared with the existing method, which directly calculates and adds the positive sequence control component after coordinate transformation, the logic is simple and the amount of calculation is small.
[0022] To address the aforementioned technical problems, this invention also provides a negative sequence current phase-to-phase SOC equalization control device for an energy storage system, comprising a memory and a processor. The processor executes computer program instructions stored in the memory to implement the negative sequence current phase-to-phase SOC equalization control method for the energy storage system described in the above steps.
[0023] The beneficial effects of the above technical solution are as follows: This device ensures the effective and reliable execution of the negative sequence current phase-to-phase SOC equalization control method of the energy storage system of the present invention through software strategy. The beneficial effects of the negative sequence current phase-to-phase SOC equalization control method of the energy storage system have been discussed in the above steps and will not be repeated here.
[0024] To address the aforementioned technical problems, the present invention also provides an energy storage system, including a negative sequence current phase-to-phase SOC equalization control device for the energy storage system.
[0025] The beneficial effects of the above technical solution are as follows: This system includes a negative sequence current phase-to-phase SOC equalization control device for energy storage systems. The beneficial effects of the negative sequence current phase-to-phase SOC equalization control method for energy storage systems included in the negative sequence current phase-to-phase SOC equalization control device for energy storage systems have been described in detail in the section on negative sequence current phase-to-phase SOC equalization control method for energy storage systems, and will not be repeated here. Attached Figure Description
[0026] Figure 1 This is the main circuit system of the H-bridge cascaded energy storage system of the present invention;
[0027] Figure 2 This is a control block diagram of the H-bridge cascaded energy storage converter of the present invention;
[0028] Figure 3 This is a flowchart illustrating the implementation of the negative sequence current injection phase-to-phase SOC equalization strategy of the present invention. Detailed Implementation
[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.
[0030] Example of a method for interphase SOC equalization control of negative sequence current in energy storage systems:
[0031] The high-voltage energy storage system addressed in this embodiment is as follows: Figure 1 As shown, each phase includes N cascaded H-bridge converters and battery banks, and each phase is connected to the high-voltage grid through corresponding filter inductors and circuit breakers (QF-A, QF-B and QF-C).
[0032] According to circuit principles, the active power generated by the positive-sequence voltage and the negative-sequence current flowing into the three-phase grid, as well as the positive-sequence voltage and the positive-sequence current flowing into the three-phase grid, only flows between phases, with the total three-phase power flowing into the grid being zero. Since the grid is usually in a balanced state, the active power generated by the negative-sequence voltage and the positive-sequence current flowing into the three-phase grid can be approximated as zero. Therefore, the principle of interphase power interaction between the positive-sequence voltage and the negative-sequence current flowing into the three-phase grid can be used to achieve interphase SOC balance.
[0033] For example, let the positive sequence voltage of phase A of the power grid be... The cascaded energy storage converter supplies negative sequence current to the power grid. Then the positive sequence voltage and negative sequence current generate power. Then the positive sequence voltage of phase B of the power grid. The cascaded energy storage converter supplies negative sequence current to the power grid. Positive sequence voltage and negative sequence current generate power C-phase grid positive sequence voltage The cascaded energy storage converter supplies negative sequence current to the power grid. Positive sequence voltage and negative sequence current generate power Therefore, the power interaction between phases A, B, and C can be adjusted by adjusting the initial phase φ.
[0034] Let the three phases have SOCs of respectively. , , The average SOC is The three-phase SOC difference is , , Assuming at this time If the absolute value of the current is the largest and the sign is positive, then let the initial phase φ of the negative sequence current of phase A be 0. , , This achieves the effect of phase A releasing power and phases B and C absorbing energy; conversely, if at this time... The absolute value of φ is the largest and the sign is negative. Let φ = π, thus achieving the effect of phase A absorbing energy and phases B and C releasing energy. Phases B and C also satisfy this law.
[0035] Based on the above patterns, it is known that only real-time monitoring of the three phases is needed. , , By comparing the values, selecting the term with the largest absolute value, and then determining the sign of the term with the largest absolute value, the initial phase of the negative sequence current flowing into the power grid can be obtained. This allows for real-time adjustment of the three-phase SOC, ultimately achieving a balanced SOC state.
[0036] Therefore, based on the above principles, the flowchart of the negative sequence current injection phase-to-phase SOC equalization strategy for the energy storage system of the present invention is as follows: Figure 3 As shown, the details are as follows:
[0037] 1) Compare the three-phase SOC deviation values of the energy storage system and determine the item with the largest deviation.
[0038] Obtain the SOC value of each phase of the energy storage converter and calculate the average SOC value of all phases. Take the deviation of each phase's SOC value from the average as the corresponding phase SOC deviation value. Compare the three-phase SOC deviation values of the energy storage system. The item with the largest deviation is the one with the largest absolute value of the three-phase SOC deviation value.
[0039] 2) Compare the absolute value of the term with the maximum deviation with the set dead zone value, and set different given values for the negative sequence current based on the results.
[0040] When the absolute value of the deviation of the largest deviation term is less than or equal to the set dead zone value (e.g., it can be set to 5), the negative sequence current is given as 0. When the absolute value of the deviation of the largest deviation term is greater than the set dead zone value (e.g., it can be set to 5), depending on the different deviation situations, assuming the current direction is towards the power grid, the formulas for the positive sequence voltage and negative sequence current of the three-phase power grid are as follows:
[0041] , Then the positive-sequence voltage and negative-sequence current in the three-phase power are respectively , , .
[0042] Therefore, according to the power formula, if the SOC deviation of phase A is positive and the absolute value of the SOC deviation of phase A is the largest, that is, phase A needs to be discharged and phases B and C need to be charged, the initial phase of the corresponding negative sequence current is set to 0.
[0043] If the SOC deviation of phase A is negative and the absolute value of the SOC deviation of phase A is the largest, that is, phase A needs to be charged and phases B and C need to be discharged, the initial phase of the corresponding negative sequence current is set to π.
[0044] If the SOC deviation of phase B is positive and the absolute value of the SOC deviation of phase B is the largest, that is, phase B needs to be discharged and phases A and C need to be charged, the initial phase of the corresponding negative sequence current is set to 2π / 3.
[0045] If the SOC deviation of phase B is negative and the absolute value of the SOC deviation of phase B is the largest, that is, phase B needs to be charged and phases A and C need to be discharged, the initial phase of the corresponding negative sequence current is set to -π / 3.
[0046] If the SOC deviation of phase C is positive and the absolute value of the SOC deviation of phase C is the largest, that is, phase C needs to be discharged and phases A and B need to be charged, the initial phase of the corresponding negative sequence current is set to -2π / 3.
[0047] If the SOC deviation of phase C is negative and the absolute value of the SOC deviation of phase C is the largest, that is, phase C needs to be charged and phases A and B need to be discharged, the initial phase of the corresponding negative sequence current is set to π / 3.
[0048] 3) Based on the initial phase and the set ratio of the negative sequence current, the given values of the d-axis and q-axis components of the negative sequence current are obtained, and then the modulation wave of the converter in the energy storage system is obtained to achieve phase-to-phase SOC balance.
[0049] Set the negative sequence current injection ratio to k times the rated current. Due to the existence of grid impedance, the introduction of negative sequence current will generate negative sequence voltage in the grid, causing grid voltage imbalance. The national standard stipulates that the negative sequence voltage imbalance of the grid should be less than 2%. Therefore, the allowable value of negative sequence voltage imbalance can generally be calculated as the corresponding negative sequence current by converting according to the normal minimum short-circuit capacity at the connection point. The approximate calculation formula for negative sequence voltage imbalance is , and the calculation formula for k is . Where is the grid line voltage,[[]] is the short-circuit capacity at the common connection point,[[]] is the negative sequence current. So the value of k is 0 < k ≤ 1. At this time, after the transformation from the three-phase stationary coordinate system to the rotating coordinate system when the initial phase is known, we get , . Where is the given value of the d-axis component of the negative sequence current,[[]] is the rated current,[[]] is the initial phase,[[]] is the given value of the q-axis component of the negative sequence current. As Figure 2 shown, according to the obtained given value of the negative sequence current, perform d, q-axis decoupling control of the negative sequence control component, and add it to the obtained positive sequence control component to obtain the modulation wave of the converter in the energy storage system, so as to adjust the three-phase SOC and achieve the inter-phase SOC balance of the energy storage system.[[]]
[0050] An embodiment of a device for controlling the inter-phase SOC balance of negative sequence current in an energy storage system:
[0051] In the embodiment of the device for controlling the inter-phase SOC balance of negative sequence current in the energy storage system of the present invention, it includes a memory, a processor and an internal bus. The processor and the memory complete mutual communication and data interaction through the internal bus. The memory includes at least one software function module stored in the memory. The processor executes various functional applications and data processing by running the software programs and modules stored in the memory, and realizes the method for controlling the inter-phase SOC balance of negative sequence current in the energy storage system introduced in the method embodiment of the present invention. Among them, the processor can be a microprocessor MCU, a programmable logic device FPGA and other processing devices. The memory can be various memories that store information in the form of electric energy, such as RAM, ROM, etc.[[]]
[0052] An embodiment of an energy storage system:
[0053] In an embodiment of an energy storage system of the present invention, the circuit topology of the energy storage system is as Figure 1As shown, the system includes a phase-to-phase SOC balancing control device for negative-sequence current in an energy storage system (e.g., a controller for a converter in the energy storage system). This device is consistent with the phase-to-phase SOC balancing control device for negative-sequence current in an energy storage system described in the embodiment. The essence of the method implemented by this phase-to-phase SOC balancing control device is that the phase-to-phase SOC balancing can be achieved by adjusting the phase-to-phase power interaction between the three-phase grid-connected negative-sequence current and the three-phase grid positive-sequence voltage through setting the initial phase and current ratio of the negative-sequence current. This device sets the initial phase of the corresponding negative-sequence current according to the different three-phase SOC deviations. Compared with the prior art, it has a smaller computational load, a simpler strategy, clearer logic, and is easier to implement.
Claims
1. A method for phase-to-phase SOC equalization control of negative sequence current in an energy storage system, wherein the energy storage system is a high-voltage energy storage system, characterized in that, include: 1) Compare the three-phase SOC deviation values of the energy storage system to determine the term with the largest deviation; 2) When the absolute value of the deviation of the largest deviation item is less than or equal to the set dead zone value, the negative sequence current setpoint is set to 0; When the absolute value of the deviation of the largest deviation term is greater than the set dead zone value, the initial phase of the negative sequence current is set in the following manner; If the SOC deviation of phase A is positive and the absolute value of the SOC deviation of phase A is the largest, then the initial phase of the negative sequence current is set to 0. If the SOC deviation of phase A is negative and the absolute value of the SOC deviation of phase A is the largest, then the initial phase of the negative sequence current is set to π. If the SOC deviation of phase B is positive and the absolute value of the SOC deviation of phase B is the largest, then the initial phase of the negative sequence current is set to 2π / 3. If the SOC deviation of phase B is negative and the absolute value of the SOC deviation of phase B is the largest, then the initial phase of the negative sequence current is set to -π / 3. If the SOC deviation of phase C is positive and the absolute value of the SOC deviation of phase C is the largest, then the initial phase of the negative sequence current is set to -2π / 3. If the SOC deviation of phase C is negative and the absolute value of the SOC deviation of phase C is the largest, then the initial phase of the negative sequence current is set to π / 3. Based on the set initial phase and the set ratio of the negative sequence current, the given values of the d-axis and q-axis components of the negative sequence current are obtained; The set ratio of negative sequence current ensures that the imbalance of the negative sequence voltage in the power grid meets the imbalance requirements. 3) Based on the obtained negative sequence current setpoint, the d-axis and q-axis decoupling control is performed to obtain the negative sequence control component, which is then added to the obtained positive sequence control component to obtain the modulation wave of the converter in the energy storage system, so as to adjust the three-phase SOC and realize the SOC balance of the energy storage system.
2. The method for phase-to-phase SOC equalization control of negative sequence current in an energy storage system according to claim 1, characterized in that: The set dead zone value is 5.
3. The method for phase-to-phase SOC equalization control of negative sequence current in an energy storage system according to claim 1, characterized in that: In step 1), the three-phase SOC deviation value is calculated as follows: obtain the SOC value of each phase of the energy storage converter and calculate the average value of all phase SOC values. The deviation value of each phase SOC value from the average value is taken as the corresponding phase SOC deviation value; the corresponding largest deviation term is the term with the largest absolute value of the three-phase SOC deviation value.
4. The method for phase-to-phase SOC equalization control of negative sequence current in an energy storage system according to claim 1, characterized in that: The set negative sequence current ratio is k times the rated current, where k is 0. <k≤1。 5. The method for phase-to-phase SOC equalization control of negative sequence current in an energy storage system according to claim 4, characterized in that: The given values for the d and q components of the negative sequence current are respectively , ;in It is the given value of the d-axis component of the negative sequence current. For rated current, For the initial phase, It is the given value of the q-axis component of the negative sequence current.
6. A negative sequence current phase-to-phase SOC equalization control device for an energy storage system, comprising a memory and a processor, characterized in that: The processor is used to execute computer program instructions stored in the memory to implement the negative sequence current phase-to-phase SOC equalization control method for energy storage systems as described in any one of claims 1 to 5.
7. An energy storage system, characterized in that: Includes the negative sequence current phase-to-phase SOC equalization control device for energy storage systems as described in claim 6.