Active harmonic suppression control method for photovoltaic system based on hybrid energy storage

Abstract

The invention discloses a hybrid energy storage-based active harmonic suppression control method for a photovoltaic system, and the method comprises the following steps: S1, converting a three-phase power grid voltage and current signal from a three-phase static coordinate system to a two-phase rotating coordinate system, separating a fundamental component through a low-pass filter, and carrying out the inverse transformation to obtain a three-phase harmonic current component; s2, calculating the power needing to be absorbed or released by the hybrid energy storage system according to the power of the photovoltaic system, and dynamically adjusting the power distribution proportion between the lithium battery pack and the super capacitor bank by adopting an algorithm according to the charge states and the power change rates of the lithium battery pack and the super capacitor bank; and S3, calculating a compensation current reference value needing to be output by the inverter, and comparing the compensation current reference value with the actual output current of the inverter by adopting a composite control strategy based on combination of proportional-integral control and fuzzy logic control, and the duty ratio of the pulse width modulation signal is controlled through the proportional integral controller and the fuzzy logic controller.

Description

Technical Field

[0001] This invention relates to the field of harmonic suppression and control, and more specifically to a method for active harmonic suppression and control of photovoltaic systems based on hybrid energy storage. Background Technology

[0002] With the rapid development of photovoltaic power generation technology, photovoltaic systems are accounting for an increasing proportion of electricity supply. However, due to the use of a large number of power electronic devices in photovoltaic systems, such as inverters, a large number of harmonics are generated during the photovoltaic grid connection process. These harmonics can seriously affect the power quality of the power grid, reduce the stability and reliability of the grid, and interfere with the normal operation of other electrical equipment.

[0003] Traditional harmonic suppression methods primarily employ passive filters, but these suffer from drawbacks such as susceptibility to grid parameter variations, limitation to specific frequency harmonics, and large size and weight. While active filters can dynamically track and compensate for harmonics, their high cost and limited capacity when used alone are problematic. Furthermore, the intermittent and fluctuating output power of photovoltaic systems further exacerbates the complexity of harmonic issues. Therefore, developing a device and control method that can effectively suppress harmonics generated by grid-connected photovoltaic systems while also incorporating energy storage capabilities to address fluctuations in photovoltaic output power is of significant practical importance. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for active harmonic suppression control of a photovoltaic system based on hybrid energy storage, comprising the following steps: Step S1, using a method based on instantaneous reactive power theory detection, phase information of the grid voltage is obtained through a phase-locked loop, and the three-phase grid voltage and current signals are transformed from a three-phase stationary coordinate system to a two-phase rotating coordinate system. The fundamental component is separated by a low-pass filter, and the three-phase harmonic current components are obtained through inverse transformation; Step S2, based on the output power of the photovoltaic system, the load power, and the grid power, the power that the hybrid energy storage system needs to absorb or release is calculated. Based on the state of charge and power change rate of the lithium battery pack and the supercapacitor pack, a fuzzy logic control algorithm is used to dynamically adjust the power distribution ratio between them; Step S3, based on the obtained harmonic current components and the compensation target set by the controller, the reference value of the compensation current that the inverter needs to output is calculated. A composite control strategy based on proportional-integral control and fuzzy logic control is used to compare the reference value of the compensation current with the actual output current of the inverter. The duty cycle of the pulse width modulation signal is controlled by the proportional-integral controller and the fuzzy logic controller.

[0005] Furthermore, step S1 also includes the following steps: Step S11, using a phase-locked loop to accurately track the phase of the grid voltage, converting the three-phase grid voltage and the photovoltaic system output current to the Clark coordinate system through a Clark transformation to obtain the first voltage component and the first current component; Step S12, then using a Park transformation to convert the first voltage component and the first current component in the Clark coordinate system to the Park coordinate system to obtain the second voltage component and the second current component; Step S13, using a low-pass filter to filter the second current component and separate the fundamental component; Step S14, using an inverse transformation to obtain the three-phase harmonic current components from the fundamental component.

[0006] Furthermore, in step S2, the calculated power that the hybrid energy storage system needs to absorb or release is Pbat + Psc = Pl - Ppv + Pg, where PI is the load power, Ppv is the output power of the photovoltaic system, and Pg is the grid power.

[0007] Furthermore, in step S2, when the output power of the photovoltaic system is greater than the load power and the grid power is within the allowable range, the lithium battery is charged first. If the state of charge of the lithium battery reaches the upper limit, the excess power is stored in the supercapacitor. When the output power of the photovoltaic system is less than the load power, the supercapacitor first releases power to make up for the power deficit. If the state of charge of the supercapacitor is lower than the lower limit, the lithium battery begins to discharge to meet the load demand.

[0008] Furthermore, in step S3, when the actual output current deviates slightly from the reference value, it is mainly adjusted by the proportional-integral controller; when the deviation is large or the system operating conditions change abruptly, it is adjusted by the fuzzy logic controller based on the deviation and the rate of change of the deviation.

[0009] Furthermore, in step S4, during the control process, the digital signal processing chip monitors the changes in grid voltage and current in real time, as well as the status of the hybrid energy storage module. If the grid voltage fluctuates or a fault occurs, or if the voltage, current, or state of charge of the hybrid energy storage module exceeds the normal range, the controller will automatically adjust the control strategy and take corresponding protection measures.

[0010] Furthermore, in step S4, a high-precision Hall sensor is used to collect and monitor changes in grid voltage and current. After digital-to-analog conversion, the data is transmitted to a digital signal processing chip. A moving average filtering algorithm is used to remove high-frequency noise, ensuring that the data signal-to-noise ratio is greater than or equal to 60dB. The lithium battery pack uploads its state of charge, individual cell voltage, and temperature in real time through the battery management system. The supercapacitor pack collects terminal voltage through a dedicated voltage sensor and calculates its equivalent state of charge.

[0011] Furthermore, in step S4, when one of the following conditions is met: the grid voltage drops below 80% of the rated value or rises sharply to above 120%, the inverter output current exceeds 150% of the rated value, or the DC bus voltage deviates from the reference value by ±20%, the digital signal processing chip immediately cuts off the fuzzy logic control and forces a switch to proportional-integral control. At the same time, it triggers the rapid discharge or charging protection of the hybrid energy storage module through a hardware interrupt: the supercapacitor releases instantaneous power within 200 microseconds to stabilize the DC bus voltage.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This application employs hybrid energy storage technology, combining the advantages of lithium batteries and supercapacitors. This effectively mitigates fluctuations in the output power of photovoltaic (PV) systems, improving their stability and reliability while reducing the impact on energy storage equipment and extending its lifespan. Furthermore, the detection method based on instantaneous reactive power theory can more quickly and accurately detect harmonic currents generated by PV grid connection, providing a reliable data foundation for active harmonic suppression. Finally, the inverter utilizes a three-phase full-bridge topology combined with filters, effectively injecting compensation current into the grid to offset harmonic currents and improve power quality. Simultaneously, a composite control strategy enables precise control of the inverter, enhancing the device's dynamic response and control accuracy.

[0013] Additional aspects and advantages of the invention will be set forth in the description which follows, and in some respects will be obvious from the description or may be learned by practice of the invention. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is an overall flowchart of the intelligent power distribution network adaptive energy-saving control method based on dynamic load forecasting of the present invention; Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The present invention will now be described in more detail. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected to" another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them.

[0018] In the description of this invention, it should be noted that directional terms such as "front," "rear," "up," "down," "left," "right," "horizontal," "vertical," "horizontal," and "top," "bottom," etc., indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner or outer contours of each component itself. In the description of this invention, it should be noted that the use of terms such as "first" and "second" to define components is merely for the convenience of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0019] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0020] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0021] The preferred embodiments of the present invention will now be further described with reference to the accompanying drawings, such as... Figure 1As shown, a method for active harmonic suppression control of a photovoltaic system based on hybrid energy storage includes the following steps: Step S1, using a phase-locked loop to obtain the phase information of the grid voltage based on instantaneous reactive power theory detection, transforming the three-phase grid voltage and current signals from a three-phase stationary coordinate system to a two-phase rotating coordinate system, separating the fundamental component through a low-pass filter, and then obtaining the three-phase harmonic current components through inverse transformation; Step S2, calculating the power that the hybrid energy storage system needs to absorb or release based on the output power of the photovoltaic system, the load power, and the grid power, and dynamically adjusting the power distribution ratio between the lithium battery pack and the supercapacitor pack according to their state of charge and power change rate using a fuzzy logic control algorithm; Step S3, calculating the reference value of the compensation current that the inverter needs to output based on the obtained harmonic current components and the compensation target set by the controller, and comparing the reference value of the compensation current with the actual output current of the inverter using a composite control strategy based on proportional-integral control and fuzzy logic control, and controlling the duty cycle of the pulse width modulation signal through the proportional-integral controller and the fuzzy logic controller.

[0022] This application pertains to harmonic suppression methods, primarily applied in photovoltaic systems based on hybrid energy storage. The hybrid energy storage typically consists of lithium-ion battery packs and supercapacitor banks. The specific workflow of this application is as follows: Real-time acquisition of the grid voltage signals ua, ub, uc and the photovoltaic system output current signals ia, ib, ic are performed. These analog signals are converted to digital signals by a digital-to-analog converter and input into a digital signal processing chip. Then, the phase harmonic current components iah, ibh, and ich are calculated. For example, at a certain moment, the acquired three-phase grid voltages are ua = 220sin(ωt) V, ub = 220sin(ωt - 120°) V, uc = 220sin(ωt + 120°) V, and the photovoltaic system output currents are ia = 50sin(ωt + 30°) + 10sin(3ωt + 45°) + 5sin(5ωt + 60°) A, ib = 50sin(ωt - 90°) + 10sin(ωt + 90°) + 10sin(ωt + 120°) A. (3ωt - 75°) + 5sin (5ωt - 60°) A, ic = 50sin (ωt + 150°) + 10sin (3ωt + 165°) + 5sin (5ωt + 120°) A. After processing by the above harmonic detection algorithm, the harmonic current components are obtained as follows: iah = 10sin (3ωt + 45°) + 5sin (5ωt + 60°) A, ibh = 10sin (3ωt - 75°) + 5sin (5ωt - 60°) A, ich = 10sin (3ωt + 165°) + 5sin (5ωt + 120°) A; Then, based on the output power of the photovoltaic system, the load power, and the grid power, the power that the hybrid energy storage system needs to absorb or release is calculated. Based on the state of charge and power change rate of the lithium battery pack and the supercapacitor pack, a fuzzy logic control algorithm is used to dynamically adjust the power distribution ratio between them. This is to optimize the performance and lifespan of the hybrid energy storage system. Finally, by using the obtained harmonic current components and combining them with the compensation target set by the controller, the reference value of the compensation current that the inverter needs to output is calculated. The reference value of the compensation current is compared with the actual output current of the inverter, and the duty cycle of the pulse width modulation signal is adjusted so that the compensation current output by the inverter can quickly and accurately track the reference value, thereby achieving effective compensation for harmonic current.

[0023] Compared to existing technologies, this application employs hybrid energy storage technology, combining the advantages of lithium batteries and supercapacitors. This effectively mitigates fluctuations in the output power of photovoltaic systems, improving their stability and reliability while reducing the impact on energy storage equipment and extending its lifespan. Furthermore, the detection method based on instantaneous reactive power theory can more quickly and accurately detect harmonic currents generated by photovoltaic grid connection, providing a reliable data foundation for active harmonic suppression. Finally, the inverter utilizes a three-phase full-bridge topology combined with filters, effectively injecting compensation current into the grid to offset harmonic currents and improve grid power quality. Simultaneously, a composite control strategy enables precise control of the inverter, enhancing the device's dynamic response and control accuracy.

[0024] Further, based on the above embodiment, step S1 also includes the following steps: Step S11, using a phase-locked loop to accurately track the phase of the grid voltage, converting the three-phase grid voltage and the photovoltaic system output current to the Clark coordinate system through Clark transformation to obtain the first voltage component and the first current component; Step S12, then using Park transformation to convert the first voltage component and the first current component in the Clark coordinate system to the Park coordinate system to obtain the second voltage component and the second current component; Step S13, using a low-pass filter to filter the second current component and separate the fundamental component; Step S14, using an inverse transformation to obtain the three-phase harmonic current components from the fundamental component.

[0025] Further, based on the above embodiments, in step S2, the power Pbat + Psc = Pl - Ppv + Pg that the hybrid energy storage system needs to absorb or release is calculated, where PI is the load power, Ppv is the output power of the photovoltaic system, and Pg is the grid power.

[0026] Further, based on the above embodiments, in step S2, when the output power of the photovoltaic system is greater than the load power and the grid power is within the allowable range, the lithium battery is charged first. If the state of charge of the lithium battery reaches the upper limit, the excess power is stored in the supercapacitor. When the output power of the photovoltaic system is less than the load power, the supercapacitor first releases power to make up for the power shortage. If the state of charge of the supercapacitor is lower than the lower limit, the lithium battery begins to discharge to meet the load demand. For example, when the output power of the photovoltaic system is greater than the load power and the grid power is within the allowable range, if the state of charge of the lithium battery is 60% (lower than the upper limit of 80%), the excess power is preferentially stored in the lithium battery at a larger proportion (e.g., 70%), and the remaining 30% is stored in the supercapacitor. If the state of charge of the lithium battery reaches 80%, all the excess power is stored in the supercapacitor. When the output power of the photovoltaic system is less than the load power, if the state of charge of the supercapacitor is 30% (higher than the lower limit of 20%), the supercapacitor will first release power at a larger proportion (such as 60%) to make up for the power shortage, and the remaining part will be provided by the lithium battery; if the state of charge of the supercapacitor is lower than 20%, the lithium battery will start to discharge at full capacity to meet the load demand.

[0027] Furthermore, in step S3, when the actual output current deviates slightly from the reference value, it is mainly adjusted by the proportional-integral controller; when the deviation is large or the system operating conditions change abruptly, the fuzzy logic controller adjusts the parameters based on the deviation and the rate of change of the deviation, thereby enabling rapid adjustment of the control parameters so that the compensation current output by the inverter can quickly and accurately track the reference value and achieve effective compensation for harmonic current.

[0028] Building upon the above embodiments, step S4 further includes the following: During the control process, the digital signal processing chip monitors changes in grid voltage and current, as well as the status of the hybrid energy storage module, in real time. If the grid voltage fluctuates or a fault occurs, or if the voltage, current, or state of charge of the hybrid energy storage module exceeds the normal range, the controller will automatically adjust the control strategy and take corresponding protective measures. This ensures that the device operates stably and efficiently under different operating conditions. For example, when the grid voltage drops, the controller can adjust the output power of the inverter to enable the photovoltaic system to ride through low voltage, while simultaneously controlling the charging and discharging of the hybrid energy storage module to maintain the system's power balance; when the lithium battery's state of charge (SOC) is too low, the controller can limit the lithium battery's discharge current to protect the lithium battery's safety.

[0029] Furthermore, in step S4, a high-precision Hall sensor is used to collect and monitor changes in grid voltage and current. After digital-to-analog conversion, the data is transmitted to a digital signal processing chip, where a moving average filtering algorithm is used to remove high-frequency noise, ensuring that the data signal-to-noise ratio is greater than or equal to 60dB. The lithium battery pack uploads its state of charge, individual cell voltage, and temperature in real time through the battery management system. The supercapacitor pack collects its terminal voltage through a dedicated voltage sensor and calculates its equivalent state of charge.

[0030] Further, in step S4, if any of the following conditions are met: the grid voltage drops below 80% of the rated value or rises sharply above 120%, the inverter output current exceeds 150% of the rated value, or the DC bus voltage deviates from the reference value by ±20%, the digital signal processing chip immediately cuts off the fuzzy logic control and forces a switch to proportional-integral control. At the same time, it triggers the rapid discharge or charging protection of the hybrid energy storage module through a hardware interrupt: the supercapacitor releases instantaneous power within 200 microseconds to stabilize the DC bus voltage.

[0031] The details of the exemplary embodiments described above are provided, and the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention.

Claims

1. A method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage, characterized in that, The steps include: Step S1, using the instantaneous reactive power theory detection method, the phase information of the grid voltage is obtained through the phase-locked loop, the three-phase grid voltage and current signals are transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system, the fundamental component is separated by the low-pass filter, and the three-phase harmonic current components are obtained by the inverse transformation. Step S2: Calculate the power that the hybrid energy storage system needs to absorb or release based on the output power of the photovoltaic system, the load power, and the grid power. Then, dynamically adjust the power distribution ratio between the lithium battery pack and the supercapacitor pack based on their state of charge and power change rate using a fuzzy logic control algorithm. Step S3: Based on the obtained harmonic current components and the compensation target set by the controller, calculate the reference value of the compensation current that the inverter needs to output. Use a composite control strategy based on proportional-integral control and fuzzy logic control to compare the reference value of the compensation current with the actual output current of the inverter. Control the duty cycle of the pulse width modulation signal through the proportional-integral controller and the fuzzy logic controller.

2. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 1, characterized in that, In step S1, the following steps are also included: Step S11, using a phase-locked loop to accurately track the phase of the grid voltage, the three-phase grid voltage and the output current of the photovoltaic system are converted to the Clark coordinate system through Clark transformation to obtain the first voltage component and the first current component. Step S12: Then, the first voltage component and the first current component in the Clark coordinate system are transformed to the Park coordinate system through the Park transformation to obtain the second voltage component and the second current component. Step S13: Use a low-pass filter to filter the second current component and separate the fundamental component; Step S14: Use an inverse transform to obtain the three-phase harmonic current components from the fundamental component.

3. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 1, characterized in that, In step S2, the calculated power that the hybrid energy storage system needs to absorb or release is Pbat + Psc = Pl - Ppv + Pg, where PI is the load power, Ppv is the output power of the photovoltaic system, and Pg is the grid power.

4. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 1, characterized in that, In step S2, when the output power of the photovoltaic system is greater than the load power and the grid power is within the allowable range, the lithium battery is charged first. If the state of charge of the lithium battery reaches the upper limit, the excess power is stored in the supercapacitor. When the output power of the photovoltaic system is less than the load power, the supercapacitor first releases power to make up for the power deficit. If the state of charge of the supercapacitor is lower than the lower limit, the lithium battery starts to discharge to meet the load demand.

5. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 1, characterized in that, In step S3, when the actual output current deviates from the reference value by a small amount, it is mainly adjusted by the proportional-integral controller; when the deviation is large or the system operating conditions change abruptly, it is adjusted by the fuzzy logic controller based on the deviation and the rate of change of the deviation.

6. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 1, characterized in that, In step S4, during the control process, the digital signal processing chip monitors the changes in grid voltage and current, as well as the status of the hybrid energy storage module, in real time. If the grid voltage fluctuates or a fault occurs, or if the voltage, current, or state of charge of the hybrid energy storage module exceeds the normal range, the controller will automatically adjust the control strategy and take corresponding protection measures.

7. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 6, characterized in that, In step S4, a high-precision Hall sensor is used to collect and monitor changes in grid voltage and current. After digital-to-analog conversion, the data is transmitted to a digital signal processing chip. A moving average filtering algorithm is used to remove high-frequency noise, ensuring that the data signal-to-noise ratio is greater than or equal to 60dB. The lithium battery pack uploads its state of charge, cell voltage, and temperature in real time through the battery management system; the supercapacitor pack collects terminal voltage through a dedicated voltage sensor and calculates its equivalent state of charge.

8. The method for active harmonic suppression and control of a photovoltaic system based on hybrid energy storage according to claim 6, characterized in that, In step S4, if any of the following conditions are met: the grid voltage drops below 80% of the rated value or rises sharply to above 120%, the inverter output current exceeds 150% of the rated value, or the DC bus voltage deviates from the reference value by ±20%, the digital signal processing chip immediately cuts off the fuzzy logic control and forces a switch to proportional-integral control. At the same time, it triggers the rapid discharge or charging protection of the hybrid energy storage module through a hardware interrupt: the supercapacitor releases instantaneous power within 200 microseconds to stabilize the DC bus voltage.

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