Energy storage converter and control method thereof

Abstract

The application discloses an energy storage converter and a control method thereof, which comprises multiple cascaded level boosting circuits to realize multi-level output, improve the overall output voltage level of the energy storage converter, meet the demand of the direct current micro-grid for high power, reduce the output voltage of each level boosting circuit, further reduce the hardware pressure of the switching device in each level boosting circuit, reduce the step of the output voltage of each level boosting circuit, and improve the stability of the system; each level boosting circuit comprises multiple power units and multiple circulating current detection and suppression circuits; one circulating current detection and suppression circuit is connected between the midpoints of any two power units in the same level boosting circuit, circulating current between any two power units can be detected in real time, and the circulating current is suppressed in time, so that the energy storage converter can provide high-power output for the direct current micro-grid while ensuring stable operation of the energy storage converter.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electric energy transmission, in particular to a kind of energy storage converter and control method thereof. BACKGROUND

[0002] In network type direct current off-network power system, usually adopt energy storage converter to carry out electric energy transmission, energy storage converter as a kind of bidirectional DC / DC (Direct Current / Direct Current, direct current / direct current) conversion circuit, can carry out voltage conversion to the direct current of battery output, to provide stable voltage support for direct current microgrid, to enhance the stability of direct current microgrid.

[0003] The energy storage converter in prior art usually includes a level boost circuit that can realize bidirectional step-up and step-down function, can carry out voltage conversion to the direct current of battery output to provide power for direct current microgrid, can also take power from direct current microgrid, and carry out voltage conversion to charge battery, but single level boost circuit structure is difficult to meet the application demand of high-power direct current microgrid, and voltage step is large in working process, there are many harmonics in output waveform, which can easily lead to system voltage fluctuation, affect power quality. SUMMARY

[0004] The purpose of the present application is to provide an energy storage converter and control method thereof, including a plurality of cascaded level boost circuits to realize multi-level output, improve the output voltage level of the overall energy storage converter, to meet the demand of direct current microgrid for high power, while reducing the output voltage of each level boost circuit, thereby reducing the hardware pressure of switching devices in each level boost circuit, reducing the step of output voltage of each level boost circuit, improving the stability of the system;Each level boost circuit includes a plurality of power units and a plurality of circulating current detection suppression circuits, by connecting a circulating current detection suppression circuit between the midpoint of any two power units in the same level boost circuit, whether circulating current appears between any two power units can be detected in real time, and circulating current is suppressed in time, so that the energy storage converter can provide high-power output for direct current microgrid while ensuring stable operation of the energy storage converter.

[0005] To solve the above technical problems, the application provides a kind of energy storage converter, multiple cascaded level boost circuits, each of the level boost circuit includes: multiple power units, the first end of each power unit is connected with corresponding energy storage unit respectively, the second end of each power unit is connected with DC microgrid after being connected with each other, for voltage conversion between corresponding energy storage unit and DC microgrid;Multiple circulating current detection suppression circuits, each of the circulating current detection suppression circuit is connected between the midpoint of any two power units in the same level boost circuit, for detecting the circulating current of the corresponding two power units, and the circulating current is inhibited.

[0006] Preferably, the circulating current detection suppression circuit includes a current sensor, a circulating current suppression control circuit and a virtual resistance module;The first end of the current sensor is connected with the midpoint of the corresponding first power unit, and the current sensor is used to collect the circulating current between the corresponding two power units;The second end of the current sensor is connected with the first end of the virtual resistance module, and the second end of the virtual resistance module is connected with the midpoint of the corresponding second power unit;The input end of the circulating current suppression control circuit is connected with the output end of the current sensor, and the output end of the circulating current suppression control circuit is connected with the control end of the virtual resistance module, for adjusting the parameters of the virtual resistance module based on the circulating current, to suppress the circulating current.

[0007] Preferably, the circulating current suppression control circuit includes a signal amplifier, a filter, an analog-to-digital conversion module and a control unit;The input end of the signal amplifier is connected with the output end of the current sensor, and the signal amplifier is used to amplify the circulating current output by the current sensor;The first end of the filter is connected with the output end of the signal amplifier, and the filter is used to filter the amplified circulating current;The input end of the analog-to-digital conversion module is connected with the second end of the filter, for converting the filtered circulating current into analog-to-digital conversion;The input end of the control unit is connected with the output end of the analog-to-digital conversion module, and the output end of the control unit is connected with the control end of the virtual resistance module, for adjusting the parameters of the virtual resistance module based on the digital circulating current, to suppress the circulating current.

[0008] To solve the above technical problems, the application provides a control method of an energy storage converter, which is applied to the energy storage converter described above, and the method comprises the following steps: determining the optimal phase shift angle corresponding to each power unit in each level-boosting circuit in the energy storage converter, respectively, and generating a PWM modulation wave corresponding to each power unit based on the optimal phase shift angle corresponding to each power unit, so as to control each power unit through each PWM modulation wave; obtaining the circulating current between each two power units in the same level-boosting circuit detected by each circulating current detection and suppression circuit; determining two power units with a circulating current greater than a preset circulating current threshold as to-be-adjusted power units; adjusting the actual phase shift angle of each to-be-adjusted power unit based on the optimal phase shift angle corresponding to each to-be-adjusted power unit, respectively, and generating a post-adjustment PWM modulation wave corresponding to each to-be-adjusted power unit based on the actual phase shift angle of each to-be-adjusted power unit, so as to control each to-be-adjusted power unit through the post-adjustment PWM modulation wave corresponding to each to-be-adjusted power unit.

[0009] Preferably, the step of determining two power units with a circulating current greater than a preset circulating current threshold as to-be-adjusted power units comprises the following steps: determining a power unit with a maximum midpoint voltage in the two power units with a circulating current greater than the preset circulating current threshold as a first to-be-adjusted power unit, and determining a power unit with a minimum midpoint voltage as a second to-be-adjusted power unit; the step of adjusting the actual phase shift angle of each to-be-adjusted power unit based on the optimal phase shift angle corresponding to each to-be-adjusted power unit, respectively, and generating a post-adjustment PWM modulation wave corresponding to each to-be-adjusted power unit based on the actual phase shift angle of each to-be-adjusted power unit, so as to control each to-be-adjusted power unit through the post-adjustment PWM modulation wave corresponding to each to-be-adjusted power unit comprises the following steps: performing hysteresis adjustment on the actual phase shift angle corresponding to the first to-be-adjusted power unit based on the optimal phase shift angle corresponding to the first to-be-adjusted power unit, and generating a first post-adjustment PWM modulation wave corresponding to the first to-be-adjusted power unit, and / or, performing advance adjustment on the actual phase shift angle corresponding to the second to-be-adjusted power unit based on the optimal phase shift angle corresponding to the second to-be-adjusted power unit, and generating a second post-adjustment PWM modulation wave corresponding to the second to-be-adjusted power unit, so that the phase of the first post-adjustment PWM modulation wave lags behind the phase of the second post-adjustment PWM modulation wave; controlling the first to-be-adjusted power unit through the first post-adjustment PWM modulation wave, and / or, controlling the second to-be-adjusted power unit through the second post-adjustment PWM modulation wave.

[0010] Preferably, after determining the optimal phase shift angle corresponding to each power unit in each level-boosting circuit in the energy storage converter respectively and generating the PWM modulation wave corresponding to each power unit based on the optimal phase shift angle corresponding to each power unit respectively to control each power unit through the PWM modulation wave respectively, the method further comprises: for each power unit, determining a midpoint voltage, and adjusting the actual phase shift angle corresponding to the power unit based on the optimal phase shift angle as a reference according to the midpoint voltage and a voltage phase correspondence relationship; the voltage phase correspondence relationship is that, based on a preset overvoltage threshold, in a case where the midpoint voltage is greater than the preset overvoltage threshold, the actual phase shift angle corresponding to the power unit is adjusted based on the optimal phase shift angle as a reference in a lagging mode; and in a case where the midpoint voltage is less than the preset overvoltage threshold, the actual phase shift angle corresponding to the power unit is adjusted based on the optimal phase shift angle as a reference in an advancing mode.

[0011] Preferably, each power unit in the energy storage converter is configured to perform voltage conversion on direct current output by a corresponding energy storage unit and transmit the direct current to a direct current micro-grid; after determining the optimal phase shift angle corresponding to each power unit in each level-boosting circuit in the energy storage converter respectively and generating the PWM modulation wave corresponding to each power unit based on the optimal phase shift angle corresponding to each power unit respectively to control each power unit through the PWM modulation wave respectively, the method further comprises: obtaining a current residual capacity of each energy storage unit; based on the current residual capacity of each energy storage unit, adjusting the actual phase shift angle of each power unit based on the optimal phase shift angle of each power unit respectively, and generating the actual PWM modulation wave corresponding to each power unit respectively to control each power unit through the actual PWM modulation wave respectively to adjust the output current of each power unit; the output current of each power unit is positively correlated with the current residual capacity of the corresponding energy storage unit.

[0012] Preferably, the method further comprises: controlling the power unit corresponding to the energy storage unit with the current remaining power not greater than the preset minimum power to perform voltage conversion on the direct current of the direct current micro-grid to charge the energy storage unit; if a charging instruction is received, controlling the power unit corresponding to the energy storage unit with the current remaining power greater than the preset minimum power but not greater than the preset maximum power to perform voltage conversion on the direct current of the direct current micro-grid to charge the energy storage unit; the charging current of each power unit when charging the corresponding energy storage unit is negatively correlated with the current remaining power of the energy storage unit; after charging the energy storage unit to the current remaining power not less than the preset maximum power, entering the step of adjusting the actual phase shift angle of each power unit based on the current remaining power of each energy storage unit and taking the optimal phase shift angle of each power unit as a reference.

[0013] Preferably, before controlling the power unit corresponding to the energy storage unit with the current remaining power not greater than the preset minimum power to perform voltage conversion on the direct current of the direct current micro-grid to charge the energy storage unit, the method further comprises: obtaining the cumulative running time of each energy storage unit and the charge-discharge cycle number of each energy storage unit; determining the power unit corresponding to the energy storage unit with the cumulative running time greater than a preset cumulative time and / or the charge-discharge cycle number not less than a preset cycle number as a sixth to-be-adjusted power unit; controlling the sixth to-be-adjusted power unit to perform voltage conversion on the direct current of the direct current micro-grid and charge the energy storage unit to a full power state based on a preset charging current.

[0014] Preferably, each power unit in the energy storage converter is used to perform voltage conversion on the direct current output by the corresponding energy storage unit and transmit the direct current to the direct current micro-grid; the method further comprises: obtaining the current state parameter of each energy storage unit; performing state analysis on the current state parameter of each energy storage unit based on calling a random forest model to determine the health state grade of each energy storage unit; controlling the power unit corresponding to the energy storage unit with the health state grade lower than a preset state grade to be shut down and performing fault maintenance on the energy storage unit with the health state grade lower than the preset state grade.

[0015] The application provides a kind of energy storage converter and its control method, including multiple cascaded level boost circuits, to realize multi-level output, improve the output voltage level of energy storage converter as a whole, to meet the demand of high power of direct current microgrid, while reducing the output voltage of each level boost circuit, in turn, reduce the hardware pressure of switching device in each level boost circuit, reduce the step of the output voltage of each level boost circuit, improve the stability of system;Each level boost circuit includes multiple power units and multiple circulating current detection suppression circuits, by connecting one circulating current detection suppression circuit between the midpoint of any two power units in the same level boost circuit, whether circulating current appears between any two power units can be detected in real time, and circulating current is inhibited in time, so that energy storage converter can provide high-power output for direct current microgrid while ensuring the stable operation of energy storage converter. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0017] Figure 1 A structural schematic diagram of the energy storage converter provided by the present application is provided.

[0018] Figure 2 A structural schematic diagram of the power unit provided by the present application is provided.

[0019] Figure 3 A structural schematic diagram of the circulating current detection suppression circuit provided by the present application is provided.

[0020] Figure 4 A flowchart of the control method of the energy storage converter provided by the present application is provided. DETAILED DESCRIPTION

[0021] The core of the present application is to provide a kind of energy storage converter and control method thereof, including multiple cascaded level boost circuits, to realize multi-level output, improve the output voltage level of energy storage converter as a whole, to meet the demand of high power of direct current microgrid, while reducing the output voltage of each level boost circuit, in turn, reduce the hardware pressure of switching device in each level boost circuit, reduce the step of the output voltage of each level boost circuit, improve the stability of system;Each level boost circuit includes multiple power units and multiple circulating current detection suppression circuits, by connecting one circulating current detection suppression circuit between the midpoint of any two power units in the same level boost circuit, whether circulating current appears between any two power units can be detected in real time, and circulating current is inhibited in time, so that energy storage converter can provide high-power output for direct current microgrid while ensuring the stable operation of energy storage converter.

[0022] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0023] Please refer to Figure 1 , Figure 1 A structural schematic diagram of an energy storage converter is provided for the present application, and the energy storage converter includes multiple cascaded level boost circuits 1, each of the level boost circuits 1 includes:

[0024] A plurality of power units 11, the first end of each power unit 11 is connected to the corresponding energy storage unit, the second end of each power unit 11 is connected to the direct current microgrid after being connected to each other, for voltage conversion between the corresponding energy storage unit and the direct current microgrid;

[0025] A plurality of circulating current detection suppression circuits 12, each circulating current detection suppression circuit 12 is connected between the midpoint of any two power units 11 in the same level boost circuit, for detecting the circulating current of the corresponding two power units 11, and suppressing the circulating current.

[0026] In the network type direct current off-grid power system, the importance of energy storage converter is increasingly prominent. As an efficient, reliable and clean power supply system, direct current micro-grid is gradually becoming an important carrier to promote the development of new quality productivity. Under the background of rapid development of renewable energy and diversification of electricity load, the traditional alternating current power grid is facing more and more challenges. Direct current micro-grid has become an effective way to solve this problem with its advantages of efficient transmission, flexible configuration and easy integration of renewable energy.

[0027] The energy storage converter is the core equipment to realize the efficient and stable operation of the direct current micro-grid under this background. It is mainly used to realize the efficient conversion between different voltage levels of direct current, provide stable voltage support for the direct current micro-grid, and enhance the stability of the power grid. In addition, the energy storage converter also has the functions of rapid voltage regulation and suppression of wide frequency oscillation, which can significantly improve the stability and reliability of the direct current power system. The energy storage converter in the prior art usually includes a level boosting circuit 1 connected between the energy storage unit and the direct current micro-grid, which can convert the energy of the energy storage unit to the direct current micro-grid, or use the energy of the direct current micro-grid to charge the energy storage unit. In the charging process, the energy storage unit absorbs the energy of the external power supply and stores it in the battery; in the discharging process, the energy storage unit releases the stored energy to provide power for the external load. The level boosting circuit 1 realizes the step-up or step-down conversion of the input voltage by controlling the conduction and shutdown of the switching device. The high voltage bus on the output side transmits the direct current output by the level boosting circuit 1 to the external load. The control module uses control algorithm to realize accurate control and management of the level boosting circuit 1 according to the data provided by the monitoring module, to ensure stable operation and safety protection of the system. However, since there is only one level boosting circuit 1, if the required power of the direct current micro-grid is large, the level boosting circuit 1 needs to output large power, and the output voltage of the level boosting circuit 1 is large, which leads to large voltage step of the output of the level boosting circuit 1, easily causing the increase of output harmonics, affecting the stability of the voltage of the direct current micro-grid, and also easily leading to large voltage difference borne by each device in the level boosting circuit 1, and further causing overvoltage damage of the internal devices of the level boosting circuit 1.

[0028] Based on this, multiple level boosting circuits 1 are arranged in the energy storage converter in the present application, please refer to Figure 1 , Figure 1For example, in the prior art, in the energy storage converter with only one level-boosting circuit 1, in order to avoid overvoltage damage of the elements in the level-boosting circuit 1, the maximum output voltage of the energy storage converter is limited, such as only 2kV, but it cannot be applied to a DC microgrid with a voltage demand of 10kV. In the present application, multiple level-boosting circuits 1 are provided for multi-level output, such as three level-boosting circuits 1 for three-level output and five level-boosting circuits 1 for five-level output. Each level-boosting circuit 1 can output a voltage of 2kV, and after cascading, the energy storage converter can output a voltage of 10kV, thereby ensuring the normal operation of the level-boosting circuit 1 and supplying power to a DC microgrid with a higher voltage level.

[0029] In addition, through the cascading connection of multiple level-boosting circuits 1, the system is more flexible, easy to expand, maintain and upgrade, and therefore, the energy storage converter can also realize redundant design, and increase additional level-boosting circuits 1 to improve the reliability and availability of the system. The cascading design can reduce the voltage stress of the switching devices in the level-boosting circuit 1, improve the reliability and life of the devices, and thereby improve the overall efficiency of the system, reduce energy loss, and meet the demand for high-power, high-voltage, high-power quality and high-reliability power supply of different loads.

[0030] For example, in the prior art, in the energy storage converter with only one level-boosting circuit 1, in order to avoid overvoltage damage of the elements in the level-boosting circuit 1, the maximum output voltage of the energy storage converter is limited, such as only 2kV, but it cannot be applied to a DC microgrid with a voltage demand of 10kV. In the present application, multiple level-boosting circuits 1 are provided for multi-level output, such as three level-boosting circuits 1 for three-level output and five level-boosting circuits 1 for five-level output. Each level-boosting circuit 1 can output a voltage of 2kV, and after cascading, the energy storage converter can output a voltage of 10kV, thereby ensuring the normal operation of the level-boosting circuit 1 and supplying power to a DC microgrid with a higher voltage level.

[0031] The design of cascading multiple level-boost circuits 1 can not only improve the voltage utilization rate of the input side to increase the output voltage level, but also simplify the filter design of each output side due to the reduction of the output voltage of each level-boost circuit 1, thereby reducing the capacity of the filter inductance and filter capacitance, reducing the volume, cost and loss of the filter at the output side of the level-boost circuit 1, and improving the stability of the output voltage and power quality.

[0032] In addition, in order to reduce the voltage stress of the switching device in each level-boost circuit 1, a plurality of power units 11 are also provided in each level-boost circuit 1, the first end of each power unit 11 is connected with the corresponding energy storage unit, the second ends of the power units 11 are connected with each other and serve as one end of the level-boost circuit 1 connected with the DC microgrid, and the plurality of power units 11 realize smoother voltage waveform output through complementary or phase-shift modulation, reduce output ripple and harmonic components, thereby simplifying the filter design and improving system reliability. At the same time, this structure has higher control freedom and redundancy capability, supports soft switching, bidirectional power flow and degraded operation after failure, and is particularly suitable for complex application scenarios such as high-performance energy storage and grid interface. Due to the electrical coupling between the DC bus bars of each power unit 11, one or more closed electrical loops are naturally formed. Due to the limitations of different battery parameters of different energy storage units, such as the difference in DC bus capacitance value, the different on-state voltage drops of switching tubes and the driving delay, the output voltages of the power units 11 cannot be completely accurate and consistent, and circulating current may occur between different power units 11. The circulating current flows through the power switching device and the freewheeling diode, which will generate additional conduction loss and switching loss, reduce system efficiency, and even affect the stable operation of the system. Therefore, circulating current detection and suppression circuits 12 are provided between any two power units 11 in the same level-boost circuit 1 in the present application, so as to detect and suppress the circulating current between any two power units 11, to ensure the normal operation of each power unit 11.

[0033] Please refer to Figure 2 , Figure 2 A structure diagram of a power unit is provided in the present application, taking two power units 11 provided in each level-boost circuit 1 as an example. Each power unit 11 includes multiple power switching devices such as IGBT (Insulated Gate Bipolar Transistor) and inductors, capacitors and other elements, which realize efficient power conversion and management through reasonable configuration and control.

[0034] In summary, the application includes multiple cascaded level boosting circuits 1 to achieve multi-level output, improve the overall output voltage level of the energy storage converter, meet the demand of high power of the DC microgrid, reduce the output voltage of each level boosting circuit 1, thereby reducing the hardware pressure of the switching device in each level boosting circuit 1, reducing the step of the output voltage of each level boosting circuit 1, and improving the stability of the system; each level boosting circuit 1 includes multiple power units 11 and multiple circulating current detection and suppression circuits 12, by connecting one circulating current detection and suppression circuit 12 between the midpoints of any two power units 11 in the same level boosting circuit 1, the presence of circulating current between any two power units 11 can be detected in real time, and the circulating current is suppressed in time, so that the energy storage converter can provide high-power output for the DC microgrid while ensuring stable operation of the energy storage converter.

[0035] Based on the above embodiments:

[0036] As a preferred embodiment, the circulating current detection and suppression circuit 12 includes a current sensor 21, a circulating current suppression control circuit, and a virtual resistance module 26; the first end of the current sensor 21 is connected to the midpoint of the corresponding first power unit 11, and the current sensor 21 is used to collect the circulating current between the corresponding two power units 11; the second end of the current sensor 21 is connected to the first end of the virtual resistance module 26, and the second end of the virtual resistance module 26 is connected to the midpoint of the corresponding second power unit 11; the input end of the circulating current suppression control circuit is connected to the output end of the current sensor 21, and the output end of the circulating current suppression control circuit is connected to the control end of the virtual resistance module 26, which is used to adjust the parameters of the virtual resistance module 26 based on the circulating current to suppress the circulating current.

[0037] The current sensor 21 is connected between the midpoints of the corresponding two power units 11, which can detect the circulating current between the midpoints of the corresponding two power units 11 and transmit it to the circulating current suppression circuit, and a virtual resistance module 26 is provided between the two power units 11, and the circulating current suppression control circuit adjusts the parameters of the virtual resistance module 26 according to the circulating current detected by the current sensor 21 to suppress the circulating current.

[0038] Compared with suppressing the circulating current by setting an actual resistance, the resistance of the virtual resistance module 26 is an adjustment parameter that is actively set to suppress the currently detected circulating current, and there is a negative feedback regulation relationship between the resistance and the circulating current, and the suppression of the circulating current can be achieved without consuming electrical energy, thereby reducing system power loss.

[0039] It should be noted that the current sensor 21 can detect the bidirectional circulating current between the corresponding two power units 11, and suppress the bidirectional circulating current through the virtual resistance module 26, so as to avoid the influence of the bidirectional circulating current between the two power units 11 on the normal operation of the two power units 11.

[0040] The current sensor 21 can be a Hall effect current sensor 21, a current transformer TA, a Rogowski coil, or a current detection device composed of a precision shunt resistor and an isolation amplifier, which is not limited in the present application.

[0041] As a preferred embodiment, the circulating current suppression control circuit includes a signal amplifier 22, a filter 23, an analog-to-digital conversion module 24, and a control unit 25; the input end of the signal amplifier 22 is connected with the output end of the current sensor 21, and the signal amplifier 22 is used for amplifying the circulating current output by the current sensor 21; the first end of the filter 23 is connected with the output end of the signal amplifier 22, and the filter 23 is used for filtering the amplified circulating current; the input end of the analog-to-digital conversion module 24 is connected with the second end of the filter 23, and is used for converting the filtered circulating current into an analog-to-digital conversion; the input end of the control unit 25 is connected with the output end of the analog-to-digital conversion module 24, and the output end of the control unit 25 is connected with the control end of the virtual resistance module 26, and the control unit 25 is used for adjusting the parameters of the virtual resistance module 26 based on the digital circulating current, so as to suppress the circulating current.

[0042] Specifically, considering that the signal output by the current sensor 21 (such as a Hall sensor or a shunt resistor) is usually a weak voltage signal, and the standard operating voltage of the control unit 25 is usually 0~3.3V, 0~5V or ±10V. The signal amplifier 22 in the circulating current suppression control circuit can amplify the circulating current detected by the current sensor 21, so as to be able to drive the filter 23 and the analog-to-digital conversion module 24 in the rear stage, and thus improve the precision of the control unit 25 in adjusting the parameters of the virtual resistance module 26 based on the circulating current.

[0043] In addition, due to the existence of strong switching noise, electromagnetic interference (EMI) and conducted interference in the power unit 11, these noises will be superimposed on the weak circulating current detection signal, that is, on the circulating current output by the current sensor 21. Therefore, the signal amplifier 22 is usually connected at the output end of the current sensor 21, and the effective signal output by the current sensor 21 is amplified at the same time, and the front-end noise is also amplified. The high-frequency noise component in the amplified circulating current is filtered out through the filter 23, so that the effective circulating current output by the current sensor 21 is less likely to be overwhelmed by noise in the subsequent transmission and processing process, and the measurement accuracy and reliability are improved.

[0044] Because the circulating current is essentially an analog quantity, and the control unit 25 is a digital processor that can only process discrete digital signals, the filtered circulating current is converted into a digital quantity by the analog-digital conversion module 24, so that the control unit 25 can identify the size and dynamic characteristics of the circulating current. In addition, the digital circulating current is transmitted to the control unit 25 through differential transmission or optical fiber isolation, which has strong anti-common-mode noise capability, so as to improve the data processing accuracy of the control unit 25.

[0045] Based on this, please refer to Figure 3 , Figure 3 A structural diagram of a circulating current detection and suppression circuit provided by the present application is shown in the figure. The current sensor 21 is used to collect the circulating current between the two power units 11 in real time. After being amplified by the signal amplifier 22, the circulating current is filtered by the filter 23 to remove high-frequency noise and ensure signal quality. The filtered circulating current is an analog signal, which is converted into a digital quantity by the analog-digital conversion module 24 and analyzed digitally by the control unit 25 to determine whether there is circulating current. According to the analysis result, the parameters of the virtual resistance module 26 are dynamically adjusted to control the impedance between the power units 11 and suppress the generation of circulating current. Based on this, the circulating current detection and suppression circuit 12 in the present application has high detection sensitivity, fast response and flexible control, and is suitable for effective detection and dynamic suppression of circulating current in a multi-power unit interconnection system.

[0046] The circulating current detection and suppression circuit 12 has multiple functions such as reducing circulating current, assisting voltage equalization, filtering, and current limiting protection in a multi-power unit interconnection system. Due to factors such as control error, voltage deviation, or parameter inconsistency, circulating current is easily generated between the power units 11, affecting the stability and power quality of the system. The circulating current detection and suppression circuit 12 can effectively suppress the circulating current between the power units 11 by monitoring the current state between the power units 11 in real time and introducing impedance or adjusting means, thereby improving the overall system performance. At the same time, the circulating current detection and suppression circuit 12 can also assist in realizing voltage equalization control to ensure that the output voltages of the power units 11 are reasonably distributed, avoiding the problem of uneven power or system efficiency reduction caused by inconsistent output voltages. In addition, the circulating current detection and suppression circuit 12 can also form an RC filter network with resistors, capacitors, and other devices to effectively filter out high-frequency noise and harmonics in the output voltage of the power units 11, suppress voltage ripple caused by switching frequency, and improve the smoothness of the output voltage. In addition, in the case of system startup or sudden overload, the circulating current detection and suppression circuit 12 can also provide current limiting protection to prevent excessive current from damaging key devices in the system, thereby ensuring the safe and reliable operation of the entire system.

[0047] The control unit can be, but is not limited to, an MCU (Microcontroller Unit).

[0048] Please refer to Figure 4 , Figure 4 A flowchart of a control method of an energy storage converter is provided in the present application, the method is applied to the energy storage converter as described above, and the method comprises: S41: determining the optimal phase shift angle corresponding to each power unit in each level-boosting circuit in the energy storage converter, and generating a PWM modulation wave corresponding to each power unit based on the optimal phase shift angle corresponding to each power unit 11, so as to control each power unit through the respective PWM modulation wave.

[0049] The generation of circulating current between the power units 11 is usually related to the mismatch of parameters between the power units 11 and the setting of the phase shift angle. Therefore, the circulating current detection and suppression circuit 12 in the present application can quickly identify abnormal current fluctuations or circulating currents by monitoring the current changes between the power units 11 in real time. Once an abnormality is detected, the circulating current detection and suppression circuit 12 will immediately take measures such as adjusting the control parameters or introducing a virtual impedance to reduce or eliminate the impact of circulating current. Through accurate control algorithms and fast-response hardware design, the circulating current can be effectively suppressed, thereby improving the efficiency and reliability of the system. Based on this, in addition to suppressing the circulating current through the circulating current detection and suppression circuit 12, the phase shift angle for controlling each power unit 11 can also be adjusted to avoid the generation of circulating current.

[0050] When controlling each power unit 11 in the energy storage converter, the optimal phase shift angle corresponding to each power unit 11 needs to be determined, so as to generate a PWM (Pulse Width Modulation) modulation wave for controlling each switch tube in each power unit 11 according to the optimal phase shift angle, thereby controlling each power unit 11 to output a corresponding voltage.

[0051] Specifically, the phases of multiple triangular carriers are offset based on the optimal phase shift angle corresponding to each power unit 11, and compared with the same sinusoidal modulation wave to generate a PWM modulation wave corresponding to each power unit 11. In actual application, n triangular carriers with the same amplitude and frequency but different phases are compared with the same sinusoidal modulation wave to generate a PWM modulation wave corresponding to each power unit 11. The phases of the PWM modulation waves of each power unit 11 are different, thereby realizing carrier phase shift. The use of carrier phase shift modulation technology can reduce the ripple of inductance current in the power unit 11 to 1 / N^2 (N is the number of cascaded power units 11) of the carrier layering technology.

[0052] In an embodiment, when solving the optimal phase-shifting angle, the harmonic order to be suppressed is determined by analyzing the harmonic components in the inductor current. For a topology of N power units 11 in cascade, the number of suppressible harmonics is (N-1) / 2 (when N is odd) or (N-2) / 2 (when N is even). For example, for a three-power-unit cascade system, the suppressible harmonic orders are 1st and 2nd. According to the harmonic analysis results, a system of equations is established to solve the optimal phase-shifting angle. In order to suppress the nth harmonic, the optimal phase-shifting angle needs to satisfy the following conditions:

[0053] ; .

[0054] wherein, is the nth harmonic coefficient of the jth power unit 11, j is the summation variable, is the optimal phase-shifting angle of the jth power unit 11, based on which the optimal phase-shifting angles of the N power units 11 can be determined. The two formulas respectively constrain the sum of the sine and cosine components of the nth harmonic to be zero, so that the nth harmonic (sine and cosine components) of the system output cancels each other out, and finally only the fundamental wave (or the desired harmonic) is left, thereby achieving specific harmonic elimination, improving power quality, and optimizing electromagnetic characteristics.

[0055] S42: Obtain the circulating current between each two power units in the same level-boost circuit detected by the circulating current detection and suppression circuit.

[0056] In order to reduce the circulating current between the power units 11, the phase of the PWM modulation wave of each power unit 11 is adjusted in this embodiment. Specifically, the real-time circulating current between each two power units 11 is obtained by obtaining the circulating current between each two power units 11 detected by the circulating current detection and suppression circuit 12 in the energy storage converter, so as to adjust the phase-shifting angle of the PWM modulation wave of the corresponding power unit 11 according to the circulating current, thereby reducing the circulating current.

[0057] S43: Determine the two power units with circulating current greater than the preset circulating current threshold as the power units to be adjusted.

[0058] After obtaining the circulating current between each two power units 11, it is determined whether the circulating current between each two power units 11 is greater than the preset circulating current threshold. If none of them is greater than the preset circulating current threshold, the power units 11 can be controlled according to the PWM modulation wave generated by the optimal phase-shifting angle corresponding to each power unit 11. However, if the circulating current between two power units 11 is greater than the preset circulating current threshold, the circulating current between the two power units 11 needs to be suppressed, and the two power units 11 are determined as the power units to be adjusted 11.

[0059] It should be noted that if the circulating current between multiple groups of power units 11 in the same level boosting circuit 1 is greater than the preset circulating current threshold, the corresponding two power units 11 can be respectively set as the power units 11 to be adjusted, and the phase shift angle adjustment can be performed respectively. For example, when four power units 11 are arranged in the same level boosting circuit 1, the circulating current between the first power unit 11 and the second power unit 11 is greater than the preset circulating current threshold, and the circulating current between the third power unit 11 and the fourth power unit 11 is also greater than the preset circulating current threshold, the first power unit 11 and the second power unit 11 can be determined as a group of power units 11 to be adjusted, and the phase shift angle of the first power unit 11 and the second power unit 11 is adjusted; the third power unit 11 and the fourth power unit 11 can be determined as another group of power units 11 to be adjusted, and the phase shift angle of the third power unit 11 and the fourth power unit 11 is adjusted. The adjustment of the phase shift angle of the first power unit 11 and the second power unit 11 is independent of and does not conflict with the adjustment of the phase shift angle of the third power unit 11 and the fourth power unit 11. Of course, since there may be circulating current between the first power unit 11 and the third power unit 11, the phase shift angle of the other several power units 11 can be considered for reference adjustment when adjusting the phase shift angle, so as to avoid the circulating current between the other power units 11 after the phase shift angle adjustment.

[0060] S44: Adjust the actual phase shift angle of each power unit to be adjusted based on the optimal phase shift angle corresponding to each power unit to be adjusted, and generate a corresponding adjusted PWM modulation wave based on the actual phase shift angle of each power unit to be adjusted, to control each power unit to be adjusted by the corresponding adjusted PWM modulation wave.

[0061] After the power units to be adjusted are determined, the actual phase shift angle is adjusted based on the optimal phase shift angle of the power units to be adjusted, so as to generate an adjusted PWM modulation wave according to the adjusted actual phase shift angle, and control the power units to be adjusted according to the adjusted PWM modulation wave, so as to reduce the circulating current between the two power units to be adjusted.

[0062] It should be noted that the circulating current only occurs between the power units 11 in the same level boosting circuit 1, and the power units 11 in different level boosting circuits 1 are not connected to each other, and there is no circulating current.

[0063] As a preferred embodiment, the two power units 11 with the circulating current greater than the preset circulating current threshold are determined as the power units to be adjusted, including: determining the power unit 11 with the maximum midpoint voltage among the two power units 11 with the circulating current greater than the preset circulating current threshold as the first power unit to be adjusted, and determining the power unit 11 with the minimum midpoint voltage as the second power unit to be adjusted; adjusting the actual phase shift angle of each power unit to be adjusted based on the optimal phase shift angle corresponding to the power unit to be adjusted, and generating the corresponding adjusted PWM modulation wave based on the actual phase shift angle of each power unit to be adjusted, so as to control each power unit to be adjusted through the corresponding adjusted PWM modulation wave, including: adjusting the actual phase shift angle of the first power unit to be adjusted based on the corresponding optimal phase shift angle, and generating the corresponding first adjusted PWM modulation wave, and / or, adjusting the actual phase shift angle of the second power unit to be adjusted based on the corresponding optimal phase shift angle, and generating the corresponding second adjusted PWM modulation wave, so that the phase of the first adjusted PWM modulation wave lags behind the phase of the second adjusted PWM modulation wave; controlling the first power unit to be adjusted through the first adjusted PWM modulation wave, and / or, controlling the second power unit to be adjusted through the second adjusted PWM modulation wave.

[0064] Specifically, since the second end of each power unit 11 is connected to the DC microgrid in series, a voltage drop occurs between the power unit 11 with the larger midpoint voltage and the power unit 11 with the smaller midpoint voltage, and the power unit 11 with the larger midpoint voltage transmits current to the power unit 11 with the smaller midpoint voltage, thereby generating circulating current between the two power units 11. Therefore, in the embodiment, the first power unit to be adjusted and the second power unit to be adjusted are distinguished according to the sizes of the midpoint voltages of the two power units 11 with the circulating current greater than the preset circulating current threshold, and the actual phase shift angle of the first power unit to be adjusted is adjusted to lag, so that the switching time of the first power unit to be adjusted and the second power unit to be adjusted deviates from the coincidence area, thereby reducing the probability of synchronous step of the midpoint voltages of the first power unit to be adjusted and the second power unit to be adjusted, and reducing the circulating current between the first power unit to be adjusted and the second power unit to be adjusted.

[0065] In addition, the actual phase shift angle of the second power unit to be adjusted can also be adjusted to lead, so that the switching time of the first power unit to be adjusted and the second power unit to be adjusted deviates from the coincidence area, and the circulating current is suppressed.

[0066] The hysteresis adjustment based on the optimal phase-shifting angle refers to starting from the optimal phase-shifting angle, for example, the optimal phase-shifting angle is 90 degrees, and the actual phase-shifting angle after hysteresis adjustment is 100 degrees. The advance adjustment based on the optimal phase-shifting angle refers to starting from the optimal phase-shifting angle, for example, the optimal phase-shifting angle is 90 degrees, and the actual phase-shifting angle after hysteresis adjustment is 80 degrees. Of course, the application is not limited in this regard, and the adjustment range is set based on the size of the circulating current.

[0067] It should be further noted that when the actual phase-shifting angle of the power unit 11 is adjusted based on the circulating current, the greater the circulating current between the two power units 11, the greater the hysteresis adjustment range of the actual phase-shifting angle of the first power unit 11 to be adjusted among the two power units 11, and the greater the advance adjustment range of the actual phase-shifting angle of the second power unit to be adjusted. Of course, the application is not limited in this regard, and several ranges can also be divided according to the actual size of the circulating current, and the adjustment range of the actual phase-shifting angle in different ranges is different.

[0068] As a preferred embodiment, the optimal phase-shifting angle corresponding to each power unit 11 in each level-boosting circuit in the energy storage converter is determined respectively, and the PWM modulation wave corresponding to each power unit 11 is generated based on the optimal phase-shifting angle corresponding to each power unit 11, so as to control each power unit 11 through each PWM modulation wave. After that, it further comprises: determining the midpoint voltage for each power unit, adjusting the actual phase-shifting angle of the power unit based on the corresponding optimal phase-shifting angle according to the midpoint voltage and voltage phase correspondence. The voltage phase correspondence is that, based on a preset overvoltage threshold, in the case that the midpoint voltage is greater than the preset overvoltage threshold, the actual phase-shifting angle of the power unit is adjusted based on the corresponding optimal phase-shifting angle. Hysteresis; in the case that the midpoint voltage is less than the preset overvoltage threshold, the actual phase-shifting angle of the power unit is adjusted based on the corresponding optimal phase-shifting angle. After the optimal phase-shifting angle of each power unit 11 is determined and the PWM modulation wave is generated based on the optimal phase-shifting angle, the power unit 11 is controlled, and during the operation of the power unit 11, the actual phase-shifting angle of each power unit 11 can be adjusted according to the midpoint voltage of each power unit 11 before the circulating current appears between the power units 11, thereby avoiding the generation of circulating current in advance.

[0069] Specifically, the actual phase shift angle of the power unit 11 whose midpoint voltage is greater than the preset overvoltage threshold is hysteresis adjusted, and the greater the midpoint voltage, the greater the degree of hysteresis adjustment; the actual phase shift angle of the power unit 11 whose midpoint voltage is less than the preset overvoltage threshold is advanced adjusted, and the smaller the midpoint voltage, the greater the degree of advance adjustment, so as to avoid that the power unit 11 with a larger midpoint voltage transmits voltage to the power unit 11 with a smaller midpoint voltage, thereby generating circulating current. Based on this, the pre-judgment before the generation of circulating current is performed, and the actual phase shift angle of each power unit 11 is adjusted before the generation of circulating current, so as to avoid the generation of circulating current in advance.

[0070] Therefore, in each PWM modulation period, the actual phase shift angle of each power unit 11 is dynamically adjusted according to the real-time monitored midpoint voltage of each power unit 11, and a feedback control system can also be used to monitor the operating state of each power unit 11 in real time, and the actual phase shift angle is adjusted according to the feedback information to adapt to the change of system parameters. The carrier phase shift modulation strategy of optimizing the phase shift angle effectively suppresses the current ripple by real-time calculation and adjustment of the actual phase shift angle, improves the performance and efficiency of the system, and can also effectively suppress the current ripple under unbalanced working conditions.

[0071] As a preferred embodiment, each power unit 11 in the energy storage converter is used to convert the direct current output by the corresponding energy storage unit into voltage and transmit it to the direct current micro-grid; the best phase shift angle corresponding to each power unit 11 in each power unit 11 in the energy storage converter is determined respectively, and the PWM modulation wave corresponding to each power unit 11 is generated based on the best phase shift angle corresponding to each power unit 11, so as to control each power unit 11 through each PWM modulation wave. After that, it further comprises: acquiring the current residual capacity of each energy storage unit; based on the current residual capacity of each energy storage unit, adjusting the actual phase shift angle of each power unit 11 based on the best phase shift angle of each power unit 11, and generating the actual PWM modulation wave corresponding to each power unit 11 respectively, so as to control each power unit 11 through each actual PWM modulation wave to adjust the output current of each power unit 11; the output current of each power unit 11 is positively correlated with the current residual capacity of the corresponding energy storage unit.

[0072] In this embodiment, the SOC (State of Charge) of each energy storage unit is monitored in real time to determine the current remaining power of each energy storage unit. The system can adjust the actual phase shift angle of the corresponding power unit 11 according to the current remaining power of each energy storage unit, and then adjust the output current of the power unit 11. For example, when the SOC of the energy storage unit is large, that is, the current remaining power is large, the output current of the power unit 11 in the corresponding level boost circuit 1 can be increased accordingly. At this time, the actual phase shift angle of the corresponding power unit 11 can be adjusted in advance to increase the output current of the corresponding power unit 11, fully utilize the power of the energy storage unit, and then provide sufficient power for the DC microgrid. When the SOC of the energy storage unit is small, that is, the current remaining power is small, the output current of the power unit 11 in the corresponding level boost circuit 1 can be reduced accordingly. At this time, the actual phase shift angle of the corresponding power unit 11 can be adjusted to reduce the output current of the corresponding power unit 11, and then avoid over-discharge of the energy storage unit.

[0073] Of course, the more the current remaining power of the energy storage unit, the greater the phase shift angle of the corresponding power unit 11 can be adjusted in advance, and then the greater the output current of the corresponding power unit 11. The less the current remaining power of the energy storage unit, the greater the phase shift angle of the corresponding power unit 11 can be adjusted in advance, and then the smaller the output current of the corresponding power unit 11.

[0074] As a preferred embodiment, it further includes: controlling the power unit 11 corresponding to the energy storage unit with a current remaining power not greater than a preset minimum power to convert the DC voltage of the DC microgrid to charge the energy storage unit; if a charging instruction is received, controlling the power unit 11 corresponding to the energy storage unit with a current remaining power greater than the preset minimum power but not greater than a preset maximum power to convert the DC voltage of the DC microgrid to charge the energy storage unit; the charging current of each power unit 11 when charging the corresponding energy storage unit is negatively related to the current remaining power of the energy storage unit; after charging the energy storage unit to a current remaining power not less than the preset maximum power, entering the step of adjusting the actual phase shift angle of each power unit 11 based on the current remaining power of each energy storage unit and taking the optimal phase shift angle of each power unit 11 as a reference.

[0075] When the remaining current of the energy storage unit is not greater than the preset minimum power, the energy storage battery needs to be charged to avoid over-discharge. At this time, the corresponding power unit 11 can perform reverse charging transmission on the DC power of the DC microgrid to charge the energy storage unit. In addition, the energy storage unit can also be connected to an external power source to charge the energy storage unit with a current remaining power not greater than the preset minimum power. The present application does not limit this.

[0076] If the remaining power of the energy storage unit is greater than the preset minimum power, but at this time the charging instruction is received, the corresponding power unit 11 can also be controlled to reverse and charge the energy storage unit, to ensure the sufficiency of the power of the energy storage unit.

[0077] The above processes are steps executed in the process of normal operation of each power unit 11, that is, the current remaining power of each energy storage unit is determined in the working process of the power unit 11, so as to perform corresponding charging processing.

[0078] After the current remaining power of the energy storage unit is charged to not less than the preset maximum power, the actual phase shift angle of each power unit 11 can be adjusted according to the current remaining power of the energy storage unit, so that the power unit 11 can continue to work normally.

[0079] It should be noted that when charging the energy storage unit, the output current of the power unit 11 when charging the energy storage unit can be dynamically adjusted according to the size of the SOC of the energy storage unit. When the SOC of the energy storage unit to be charged is high, the actual phase shift angle of the corresponding power unit 11 can be adjusted in advance when the corresponding power unit 11 is reversed to output to charge the energy storage unit, so as to appropriately increase the output current; when the SOC of the energy storage unit to be charged is low, the actual phase shift angle of the power unit 11 can be adjusted in lag when the corresponding power unit 11 is reversed to output to charge the energy storage unit, so as to appropriately reduce the output current, to avoid that the charging current is too large to affect the normal work of the energy storage unit. The constant current output adjustment strategy based on dynamic monitoring of the SOC ensures the stable operation and efficient energy utilization of the energy storage system.

[0080] In the system, when the current remaining power of the energy storage unit is between the preset minimum power and the preset maximum power, the power unit 11 normally takes power from the energy storage unit and outputs, for example, the preset minimum power is 20% of the total power, and the preset maximum power is 80% of the total power. Therefore, 80% of the energy storage unit is used for power fast consumption and output, and only 20% of the total power is used for daily charging and discharging, to ensure that the system can respond quickly in the event of sudden power demand or excess power, and realize fast power output or consumption. When the SOC is lower than 20%, the energy storage unit is preferentially charged; when the SOC is between 20% and 80%, the energy storage unit is charged according to the charging instruction until the current remaining power is maintained above 80% of the total power.

[0081] This strategy not only significantly reduces the deep charge and discharge times of the energy storage units, effectively extending the life of the energy storage units, but also optimizes the system's operating efficiency under different operating conditions by dynamically adjusting the use of reserved capacity, while improving the system's stability and reliability, providing strong support for the rapid power regulation of the DC microgrid. By monitoring the battery status and power demand in real time, the system can intelligently switch between reserved capacity and actual use capacity, ensuring that the grid's fast response requirements are met while maximizing the protection of the battery health of the energy storage units, achieving efficient, stable and long-term operation of the energy storage units.

[0082] As a preferred embodiment, the power unit 11 corresponding to the energy storage unit with a current remaining power not greater than a preset minimum power is controlled to convert the DC power of the DC microgrid to voltage to charge the energy storage unit, further comprising: obtaining the cumulative running time of each energy storage unit and the charge and discharge cycle number of each energy storage unit; determining the power unit 11 corresponding to the energy storage unit with a cumulative running time greater than a preset cumulative time and / or a charge and discharge cycle number not less than a preset cycle number as a sixth to-be-adjusted power unit; controlling the sixth to-be-adjusted power unit to convert the DC power of the DC microgrid to voltage and charge the energy storage unit to a full power state based on a preset charging current.

[0083] In order to correct the SOC of the energy storage unit, the energy storage battery is also periodically charged in this embodiment. When the cumulative running time of the energy storage unit is greater than the preset cumulative time, the energy storage unit is charged to a full power state, or when the charge and discharge cycle number of the energy storage unit is not less than the preset cycle number, the energy storage unit is charged to a full power state. The periodic full charging strategy is based on the pre-positioned voltage limiting control strategy of the charge and discharge curve, which adjusts the charging parameters of the energy storage unit in advance by analyzing the key points of the charge and discharge curve, such as voltage and current changes, to ensure that the energy storage unit operates within a safe range. Within the SOC range of 80% or more, experimental data or model-based prediction methods are used to fit and optimize the charge and discharge curve, accurately obtaining the charge and discharge current corresponding to each SOC percentage, so as to charge each energy storage unit based on the corresponding charging current.

[0084] The voltage control keeps the voltage of the energy storage unit stable, and the current limiting control prevents overcharging or overdischarging caused by excessive current. This strategy not only corrects the SOC value of the battery management system of the energy storage unit to ensure its accuracy, but also maintains the battery capacity and performance of the energy storage unit through periodic full charging, prolongs the life of the energy storage unit, and improves the stability and reliability of the system, providing strong support for the rapid power regulation of the DC microgrid.

[0085] It should be noted that when charging the energy storage unit, not only can power be taken from the DC microgrid in reverse, but the specific charging method can be dynamically adjusted according to the current operating condition and the SOC of the energy storage unit, and the energy from the upper DC bus (such as the rectified high-voltage DC bus or photovoltaic string bus), the AC grid side (through AC / DC conversion) or the local distributed power source (such as PV (Photovoltaic), wind power, fuel cell, etc.) guided by the controller is used to charge the energy storage unit in reverse.

[0086] As a preferred embodiment, each power unit 11 in the energy storage converter is used to convert and transmit the DC power output by the corresponding energy storage unit to the DC microgrid; the method further comprises: obtaining the current state parameters of each energy storage unit; based on calling the random forest model, the current state parameters of each energy storage unit are analyzed to determine the health state level of each energy storage unit; the power unit 11 corresponding to the energy storage unit with a health state level lower than the preset state level is shut down, and the energy storage unit with a health state level lower than the preset state level is maintained.

[0087] In the actual operation process of the energy storage system, the system not only needs to monitor the state of charge SOC of the energy storage unit in real time, but also must continuously track and dynamically evaluate the health state SOH of the energy storage unit. SOH is a key parameter for measuring the degree of battery performance degradation and remaining life, and is of great significance to the long-term stable operation of the system and the development of maintenance strategies. The system uses a multi-parameter fusion method to realize dynamic monitoring of SOH, and comprehensively considers the changes of key electrical parameters in the operation process of the energy storage unit, such as terminal voltage, working current, working temperature and the most critical battery internal resistance. Among them, the change of the battery internal resistance of the energy storage unit is considered as one of the most sensitive indicators reflecting the battery aging and performance degradation. With the increase of the number of battery cycles, the recession of active substances and the deterioration of the electrode / electrolyte interface state will cause the internal resistance to gradually increase, thereby affecting the charge and discharge efficiency and power response capability.

[0088] To achieve high-precision SOH estimation, the system introduces an online monitoring mechanism based on Electrochemical Impedance Spectroscopy (EIS) technology. This method extracts state parameters in the equivalent circuit model by applying small signal excitation and obtaining electrochemical response data at different frequencies, and then quantifies the resistance change trend and aging characteristics of the battery. In addition, combined with historical operation data and battery degradation model, the system can predict trends and estimate Remaining Useful Life (RUL), thereby providing decision support for subsequent scheduling optimization, capacity compensation and fault warning.

[0089] Through the above SOH dynamic monitoring mechanism, the intelligent management level of the energy storage converter is improved, and the safety, reliability and economy of the system under complex operating conditions are significantly enhanced.

[0090] Specifically, to achieve comprehensive perception and intelligent management of the operating state of the energy storage converter, a real-time monitoring system with multi-dimensional acquisition capability and intelligent analysis function is constructed. The system takes the energy storage unit as the monitoring object and obtains its current state parameters in real time, including SOC, SOH, working temperature, terminal voltage and working current, etc. Through continuous and high-frequency monitoring mechanism, the system provides basic data support for the energy storage converter, realizes accurate evaluation and fault warning of the system state.

[0091] At the data analysis level, the system introduces an intelligent analysis method based on machine learning to model and mine the large amount of historical operation data and real-time monitoring data of the energy storage unit. The system uses Random Forest algorithm as the core data mining tool, which integrates multiple decision tree models to improve the stability and generalization ability of classification. This method first performs Bootstrap sampling on the current state parameters of the energy storage unit, constructs multiple training subsets, and randomly selects some features in the splitting process of each tree, thereby avoiding model overfitting and enhancing anti-interference ability.

[0092] The system inputs the collected current state parameters into the Random Forest model, which divides the feature space by constructing several weak classifiers (i.e. decision trees), and each leaf node corresponds to a specific operating state category. During operation, the current state parameters are input into the model, and each classifier makes a judgment, and the final classification result is determined through a voting mechanism to determine the health state level of each energy storage unit, such as normal, slight fault, abnormal and serious fault. This method not only has high classification accuracy and robustness, but also can effectively identify the potential abnormal operating mode and fault characteristics of the energy storage unit, providing theoretical basis and decision support for predictive maintenance of the system.

[0093] If the health state level of the energy storage unit is poor and lower than the preset state level, for example, the preset state level is a slight failure, and the health state level of the current energy storage unit is abnormal or serious failure, the health state level of the energy storage unit is lower than the preset state level, and the power unit 11 corresponding to the energy storage unit needs to be shut down to troubleshoot and maintain the energy storage unit, so as to avoid the abnormality of the energy storage unit affecting the normal work of the entire energy storage converter.

[0094] In addition, after shutting down the power unit corresponding to the energy storage unit with a poor health state level, the actual phase shift angle of each remaining power unit needs to be adjusted according to the current remaining power of the energy storage unit connected by each remaining power unit and the required power of the DC microgrid, that is, due to the shutdown of part of the power units, the output voltage of the remaining normally working power units needs to be appropriately increased to meet the demand of the DC microgrid, thereby meeting the load demand.

[0095] Through the cooperative application of the multi-dimensional real-time monitoring system and the machine learning algorithm, the sensing sensitivity and fault response capability of the energy storage system to the change of the operating state are significantly improved, which provides an important guarantee for building a safe, stable and efficient energy management system.

[0096] It should also be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another, without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element preceded by "comprises a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0097] The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An energy storage converter, characterized in that, This includes multiple cascaded level boosting circuits, each of which includes: Multiple power units, each with its first end connected to a corresponding energy storage unit, and its second end interconnected with each other and connected to a DC microgrid, are used for voltage conversion between the corresponding energy storage unit and the DC microgrid. Multiple circulating current detection and suppression circuits are provided, each of which is connected between the midpoints of any two power units in the same level boost circuit, for detecting the circulating current of the corresponding two power units and suppressing the circulating current. The circulating current detection and suppression circuit includes a current sensor, a circulating current suppression control circuit, and a virtual resistor module; The first end of the current sensor is connected to the midpoint of the corresponding first power unit, and the current sensor is used to collect the circulating current between the corresponding two power units. The second end of the current sensor is connected to the first end of the virtual resistor module, and the second end of the virtual resistor module is connected to the midpoint of the corresponding second power unit. The input terminal of the circulating current suppression control circuit is connected to the output terminal of the current sensor, and the output terminal of the circulating current suppression control circuit is connected to the control terminal of the virtual resistor module. It is used to adjust the parameters of the virtual resistor module based on the circulating current in order to suppress the circulating current. The circulating current suppression control circuit includes a signal amplifier, a filter, an analog-to-digital converter module, and a control unit; The input terminal of the signal amplifier is connected to the output terminal of the current sensor, and the signal amplifier is used to amplify the circulating current output by the current sensor. The first end of the filter is connected to the output end of the signal amplifier, and the filter is used to filter the amplified circulating current. The input terminal of the analog-to-digital converter module is connected to the second terminal of the filter, and is used to convert the filtered circulating current into an analog-to-digital converter. The input terminal of the control unit is connected to the output terminal of the analog-to-digital converter module, and the output terminal of the control unit is connected to the control terminal of the virtual resistor module. The control unit is used to adjust the parameters of the virtual resistor module based on the circulating current in digital form, so as to suppress the circulating current.

2. A control method for an energy storage converter, characterized in that, The method, applied to the energy storage converter as described in claim 1, includes: The optimal phase shift angle for each power unit in each level boost circuit of the energy storage converter is determined respectively, and a PWM modulation wave corresponding to each power unit is generated based on the optimal phase shift angle of each power unit, so as to control each power unit through each PWM modulation wave. The circulating current between every two power units in the same level boost circuit is obtained from the circulating current detection and suppression circuits. Two power units whose circulating current is greater than a preset circulating current threshold are identified as power units to be adjusted. Using the optimal phase shift angle corresponding to each of the power units to be adjusted as a reference, the actual phase shift angle of each power unit to be adjusted is adjusted, and a corresponding adjusted PWM modulation wave is generated based on the actual phase shift angle of each power unit to be adjusted, so as to control each power unit to be adjusted through the corresponding adjusted PWM modulation wave.

3. The control method for the energy storage converter as described in claim 2, characterized in that, Two power units whose circulating current is greater than a preset circulating current threshold are identified as power units to be adjusted, including: The power unit with the largest midpoint voltage among the two power units whose circulating current is greater than the preset circulating current threshold is determined as the first power unit to be adjusted, and the power unit with the smallest midpoint voltage is determined as the second power unit to be adjusted. Using the optimal phase shift angle corresponding to each of the power units to be adjusted as a reference, the actual phase shift angle of each power unit to be adjusted is adjusted, and a corresponding adjusted PWM modulation wave is generated based on the actual phase shift angle of each power unit to be adjusted, so as to control each power unit to be adjusted through the corresponding adjusted PWM modulation wave, including: The actual phase shift angle corresponding to the first power unit to be adjusted is hysterically adjusted based on the corresponding optimal phase shift angle, and a corresponding first adjusted PWM modulation wave is generated. And / or, the actual phase shift angle corresponding to the second power unit to be adjusted is advanced based on the corresponding optimal phase shift angle, and a corresponding second adjusted PWM modulation wave is generated, so that the phase of the first adjusted PWM modulation wave lags behind the phase of the second adjusted PWM modulation wave. The first power unit to be adjusted is controlled by the first adjusted PWM modulation wave, and / or the second power unit to be adjusted is controlled by the second adjusted PWM modulation wave.

4. The control method for the energy storage converter as described in claim 2, characterized in that, The optimal phase shift angle for each power unit in each boost circuit of the energy storage converter is determined, and a PWM modulation wave corresponding to each power unit is generated based on the optimal phase shift angle. After controlling each power unit through the PWM modulation wave, the process further includes: For each power unit, the midpoint voltage is determined, and based on the correspondence between the midpoint voltage and the voltage phase, the actual phase shift angle corresponding to the power unit is adjusted with the corresponding optimal phase shift angle as a reference. The voltage phase correspondence is as follows: with a preset overvoltage threshold as a reference, when the midpoint voltage is greater than the preset overvoltage threshold, the actual phase shift angle corresponding to the power unit is adjusted with hysteresis based on the corresponding optimal phase shift angle; when the midpoint voltage is less than the preset overvoltage threshold, the actual phase shift angle corresponding to the power unit is adjusted with lead based on the corresponding optimal phase shift angle.

5. The control method for the energy storage converter as described in claim 2, characterized in that, Each power unit in the energy storage converter is used to convert the DC power output from the corresponding energy storage unit into voltage and transmit it to the DC microgrid. The optimal phase shift angle for each power unit in each boost circuit of the energy storage converter is determined, and a PWM modulation wave corresponding to each power unit is generated based on the optimal phase shift angle. After controlling each power unit through the PWM modulation wave, the process further includes: Obtain the current remaining power of each of the energy storage units; Based on the current remaining power of each energy storage unit, the actual phase shift angle of each power unit is adjusted according to the optimal phase shift angle of each power unit, and an actual PWM modulation wave corresponding to each power unit is generated. The power unit is controlled by the actual PWM modulation wave to adjust the output current of each power unit. The output current of each power unit is positively correlated with the current remaining power of the corresponding energy storage unit.

6. The control method for the energy storage converter as described in claim 5, characterized in that, Also includes: The power unit corresponding to the energy storage unit whose current remaining power is not greater than the preset minimum power is controlled to perform voltage conversion on the DC power of the DC microgrid to charge the energy storage unit; If a charging command is received, the power unit corresponding to the energy storage unit whose current remaining power is greater than the preset minimum power but not greater than the preset maximum power will be controlled to perform voltage conversion on the DC power of the DC microgrid to charge the energy storage unit. The magnitude of the charging current when each power unit charges the corresponding energy storage unit is negatively correlated with the current remaining power of the energy storage unit. After charging the energy storage unit to a current remaining power level not less than the preset maximum power level, the process proceeds to the step of adjusting the actual phase shift angle of each power unit based on the current remaining power level of each energy storage unit and using the optimal phase shift angle of each power unit as a reference.

7. The control method for the energy storage converter as described in claim 6, characterized in that, Before controlling the power unit corresponding to the energy storage unit whose current remaining power is not greater than a preset minimum power to perform voltage conversion on the DC power of the DC microgrid to charge the energy storage unit, the method further includes: Obtain the cumulative operating time of each energy storage unit and the number of charge-discharge cycles of each energy storage unit; The power unit corresponding to the energy storage unit whose cumulative operating time is greater than the preset cumulative time and / or whose charge-discharge cycle number is not less than the preset cycle number is determined as the sixth power unit to be adjusted. The sixth power unit to be regulated is controlled to perform voltage conversion on the DC power of the DC microgrid, and the energy storage unit is charged to full capacity based on a preset charging current.

8. The control method for the energy storage converter as described in any one of claims 2-7, characterized in that, Each power unit in the energy storage converter is used to convert the DC power output from the corresponding energy storage unit into voltage and transmit it to the DC microgrid. The method further includes: Obtain the current state parameters of each of the energy storage units; Based on the use of a random forest model to analyze the current state parameters of each energy storage unit, the health status level of each energy storage unit is determined. The power units corresponding to the energy storage units whose health status level is lower than the preset status level are shut down, and fault maintenance is performed on the energy storage units whose health status level is lower than the preset status level.

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