Photovoltaic voltage amplitude active regulation and harmonic voltage treatment fusion method and system

Abstract

The application discloses a kind of photovoltaic voltage amplitude active regulation and harmonic voltage management fusion method and system, obtain the intermediate stage direct current voltage of photovoltaic converter in no energy storage island microgrid;According to the amplitude of direct current link voltage, the power output mode of forestage direct current converter is selected;For the post-stage inverter circuit, construct the adaptive voltage amplitude active regulation control loop of fusion direct current voltage feedforward;Based on direct current link voltage real-time regulation net side fundamental voltage amplitude instruction;And in combination with the current operating state of forestage direct current converter and the real-time residual capacity of the post-stage inverter, adaptive power quality collaborative control is executed.The application cooperates and controls photovoltaic power generation state, net side fundamental voltage amplitude instruction and the priority allocation limit of non-full harmonic by the state feedback of direct current link voltage, solves the problem of photovoltaic voltage amplitude active regulation and harmonic voltage management of traditional island photovoltaic system under the working condition of no energy storage.

Description

Technical Field

[0001] This invention relates to the field of microgrid control and power electronics technology, specifically to a method and system for integrating active regulation of photovoltaic voltage amplitude and harmonic voltage control. Background Technology

[0002] With the increasing application of distributed photovoltaic (PV) systems in microgrids, especially in islanded operation scenarios, PV inverters need to have the ability to actively regulate voltage amplitude to maintain the stability of the system's base voltage. Meanwhile, to improve the overall utilization rate of inverter equipment, existing technologies typically integrate the power quality management function of active power filters (APFs) into the voltage control loop, enabling them to output harmonic compensation current while supporting the microgrid's fundamental voltage.

[0003] However, the existing technology has the following technical defects:

[0004] First, existing composite control schemes rely excessively on stable power support on the DC side (such as configuring large-capacity energy storage devices). In isolated photovoltaic microgrid scenarios without energy storage, when faced with sudden drops in sunlight or sudden increases in load, the maximum power output of the photovoltaic array may not be able to meet the load demand on the AC side. At this time, if the inverter still forcibly maintains the rated fundamental voltage amplitude and simultaneously injects full harmonic compensation current, it will lead to a severe imbalance of energy on the DC bus side, causing a significant drop or even collapse of the DC link voltage, thereby causing the isolated microgrid system to shut down.

[0005] Second, existing harmonic mitigation strategies do not fully consider the inverter's underlying physical current-carrying capacity. Under heavy load conditions, the fundamental current output by the inverter to maintain the fundamental voltage often approaches the maximum permissible current-carrying limit of its semiconductor switching devices. If full harmonic compensation commands are still applied at this time, the inverter's overcurrent protection mechanism is easily triggered, causing equipment shutdown or damage.

[0006] In summary, existing technologies are generally based on the ideal assumptions of ample DC-side energy or stable system operation. In isolated scenarios without energy storage, photovoltaic inverters face the dual challenges of high energy fluctuations and source-load imbalance. Existing control schemes typically maintain the rated fundamental voltage and perform full harmonic compensation when photovoltaic output is insufficient, leading to power imbalance and system collapse. Existing solutions cannot effectively handle constant-voltage regulation and comprehensive management modes when photovoltaic output is sufficient, nor do they possess MPPT-coordinated step-down regulation and hierarchical management modes when photovoltaic output is insufficient, making it difficult to guarantee the continuous and stable operation of the microgrid and optimal power quality distribution under extreme conditions. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method and system for integrating active photovoltaic voltage amplitude regulation and harmonic voltage mitigation. This invention solves the problems of active photovoltaic voltage amplitude regulation and harmonic voltage mitigation in traditional isolated photovoltaic systems operating without energy storage by coordinating the regulation of photovoltaic power generation status, grid-side fundamental voltage amplitude commands, and priority allocation restrictions for non-full harmonics through DC link voltage state feedback.

[0008] This invention relates to a method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control. The method includes the following steps:

[0009] Step S1: Obtain the intermediate stage DC voltage of the photovoltaic converter in the isolated microgrid without energy storage, and extract the AC harmonic components of the common coupling point (PCC) voltage on the AC side.

[0010] Step S2: Select the power output mode of the front-end DC converter based on the comparison result between the magnitude of the DC link voltage and the safety boundary;

[0011] Step S3: For the downstream inverter circuit, construct an adaptive voltage amplitude active regulation control loop that integrates DC voltage feedforward; use the deviation of the DC link voltage from its steady-state reference value to adjust the amplitude command of the grid-side fundamental voltage in real time, so that when the photovoltaic system energy supply is insufficient, the reference amplitude of the grid-side output voltage can be automatically reduced.

[0012] Step S4: While maintaining the operation of the active voltage amplitude regulation control loop, the load harmonic characteristic quantity is separated from the grid-side output current, and combined with the current operating status of the front-end DC converter and the real-time remaining capacity of the back-end inverter, a harmonic compensation voltage command and a comprehensive voltage reference command are generated to execute adaptive power quality collaborative control.

[0013] Further, in step S2, when the DC link voltage Based on the set low-voltage safety boundary With the set DC link voltage reference value During this period, the preceding DC converter is operated in maximum power point tracking (MPPT) mode; when the DC link voltage... Between the DC link voltage reference value With respect to the established high-voltage safety boundary When in between, switch it to DC voltage clamping mode and actively reduce the output power of the photovoltaic side according to preset rules. At this time, it is in photovoltaic power reduction mode.

[0014] Furthermore, the specific method for selecting the power output mode of the front-end DC converter is as follows:

[0015] Establish photovoltaic output power With the DC link voltage Negative correlation between linear power reserve adjustment model:

[0016]

[0017]

[0018] in, To reduce the photovoltaic reference output power, This represents the maximum theoretical output power of photovoltaic power under current environmental conditions. The minimum output power of photovoltaics is set by humans. This is the reference value for the DC link voltage. This is the low-pressure safety boundary. This is the high-voltage safety boundary. This is the DC voltage adaptive power limiting proportional coefficient.

[0019] Further, in step S3, the adaptive voltage amplitude active regulation control loop includes grid-side frequency control and grid-side voltage control. The grid-side frequency control is based on the actual reactive power output of the photovoltaic converter and the reactive power reference value, combined with the output frequency reference value to calculate the output frequency of the photovoltaic converter. The grid-side voltage control is based on the DC link voltage and the output voltage amplitude reference value, combined with the output voltage amplitude reference value to calculate the output voltage amplitude of the photovoltaic converter.

[0020] Furthermore, in step S4, the method for calculating the remaining capacity of the converter is as follows:

[0021] The fundamental frequency of the grid-side output current is extracted to obtain the amplitude of the current fundamental frequency output from the grid side. ;

[0022] Read the maximum current carrying capacity allowed by the hardware topology of the subsequent inverter circuit. ;

[0023] Based on the fundamental current amplitude and the ultimate current-carrying threshold, the real-time residual current margin of the converter is calculated according to the principle of square difference. That is, the remaining capacity; satisfying the analytical expression:

[0024] .

[0025] Furthermore, the priority-weighted limiting scheduling logic further includes: constructing an order weight vector for the target harmonic compensation, allocating the real-time remaining current margin to the corresponding order current tracking controller according to the order weight vector, as the saturation limiting boundary of the corresponding order harmonic compensation command; when the vector sum of the detected ideal harmonic compensation commands of each order exceeds the real-time remaining current margin, performing truncation or proportional attenuation operations on the higher-order harmonic compensation commands in order of weight from low to high, so that the total output combined current is strictly constrained within the limit current threshold range.

[0026] Furthermore, in step S4, the adaptive power quality cooperative control specifically includes:

[0027] If in the DC voltage clamping mode, a wideband harmonic suppression command is generated based on the real-time remaining capacity, and full power quality compensation is performed.

[0028] If the network is in MPPT mode and the amplitude command of the grid-side fundamental voltage is controlled to decrease, the separated harmonic characteristic quantities are subjected to amplitude limiting scheduling based on priority weight according to the calculated real-time remaining capacity, so as to give priority to ensuring the compensation current output of characteristic low-order harmonics.

[0029] Furthermore, the generation process of the harmonic compensation voltage command and the comprehensive voltage reference command is as follows:

[0030] Let the h-th harmonic component of the PCC voltage extracted without delay be... Since the desired high-order harmonic voltage at the PCC point is zero in the islanded microgrid mode, the gain of the corresponding h-th harmonic voltage closed-loop feedback controller is set to... Considering dynamic harmonic compensation coefficient The generated total harmonic compensation voltage command A negative feedback term is introduced into the total harmonic compensation voltage command to forcibly eliminate the voltage distortion at the PCC point, and the compensation depth is constrained by the dynamic harmonic compensation coefficient; the fundamental voltage reference command is generated based on the active voltage amplitude control algorithm to obtain the comprehensive voltage reference command.

[0031] Furthermore, the specific rule for generating the dynamic harmonic compensation coefficient is as follows: A DC voltage threshold corresponding to full harmonic compensation is set as... ,in ;

[0032] Set the dynamic harmonic compensation coefficient For the current active power margin The piecewise continuous nonlinear function driven by the function has the following analytical expression:

[0033]

[0034] Among them, when At that time, the photovoltaic inverter actively and completely abandons the closed-loop compensation for PCC voltage harmonics to avoid the DC side collapse of the photovoltaic system caused by instantaneous high-frequency power throughput.

[0035] Furthermore, the method also includes an extreme low-voltage crash protection mechanism:

[0036] The output voltage amplitude of the photovoltaic converter is monitored in real time. When the output voltage amplitude drops to the preset minimum safe voltage threshold of the power grid, the harmonic compensation current command of the power quality collaborative management is forcibly set to zero, and the entire current capacity of the photovoltaic converter is used to maintain the fundamental voltage and voltage amplitude active support.

[0037] On the other hand, the present invention also provides a photovoltaic voltage amplitude active regulation and harmonic voltage control integrated system, the system comprising:

[0038] A multi-dimensional electrical quantity sensing module is used to extract the DC link voltage, grid-side output voltage, and grid-side output current in real time during the operation of the system.

[0039] The mode switching and DC control module is configured in the DC / DC converter stage. It is used to operate in MPPT tracking mode when the intermediate stage DC voltage is lower than the set low voltage safety boundary, and switch to constant voltage mode to limit power output when the intermediate stage DC voltage is between the low voltage safety boundary and the set high voltage safety boundary.

[0040] An adaptive droop control module, configured in the DC / AC converter stage, is used to adjust the amplitude of the AC side fundamental voltage in real time by using the deviation of the intermediate stage DC voltage.

[0041] The dynamic harmonic allocation and mitigation module is used to generate harmonic compensation voltage commands and comprehensive voltage reference commands based on the mode switching and DC control module status and the remaining available current margin of the inverter. It performs full harmonic mitigation in the constant voltage mode and dynamically increases the amplitude of the harmonic compensation commands in the MPPT mode and AC fundamental voltage reduction mode.

[0042] The beneficial effects of this invention are:

[0043] 1. Improved system survivability under extreme conditions: This invention does not rely on energy storage devices. It only uses real-time sensing of DC link voltage to actively reduce the active power consumed by the load under heavy load or low light conditions by actively lowering the grid-side voltage amplitude, thereby achieving power self-balancing and avoiding the collapse of isolated microgrids. Under light load or sufficient sunlight conditions, it avoids system power imbalance by limiting photovoltaic output power.

[0044] 2. Achieves efficient and safe utilization of inverter capacity: Overcomes the overcurrent risk caused by blindly mitigating harmonics under heavy loads in existing technologies. This invention calculates current margin in real time and prioritizes the mitigation of lower-order harmonics with greater harm when current capacity is tight, achieving adaptive optimal allocation of inverter capacity.

[0045] 3. Highly integrated control logic: Front-end power control, active AC voltage amplitude regulation and power quality management are uniformly coupled to DC link voltage feedback, with smooth and seamless logic, reducing the complexity of the system. Attached Figure Description

[0046] 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.

[0047] Figure 1 This is a schematic diagram of the overall topology and control architecture of the photovoltaic voltage amplitude active regulation and harmonic voltage control integrated system provided in an embodiment of the present invention;

[0048] Figure 2 A flowchart of the dual-mode control logic for a front-end DC / DC converter provided in an embodiment of the present invention;

[0049] Figure 3 This is a block diagram illustrating the adaptive voltage amplitude active regulation control principle of the downstream DC / AC inverter provided in an embodiment of the present invention.

[0050] Figure 4 A flowchart of the harmonic dynamic allocation algorithm under remaining capacity provided in an embodiment of the present invention;

[0051] Figure 5 The above are simulation waveforms of the system response under different operating conditions without harmonic mitigation in the embodiments of the present invention.

[0052] Figure 6 This is a schematic diagram illustrating the harmonic mitigation process performed by the network under stable operating conditions according to an embodiment of the present invention.

[0053] Figure 7 This is an FFT analysis diagram of power quality management before and after grid operation under stable conditions according to an embodiment of the present invention;

[0054] Figure 8 This is a schematic diagram illustrating the harmonic mitigation process performed by the network under different operating conditions according to an embodiment of the present invention.

[0055] Figure 9This is an FFT analysis diagram of the system during normal operation and when power quality management is not enabled, as shown in this embodiment of the invention.

[0056] Figure 10 This is an FFT analysis diagram of the system in MPPT mode and power quality management not enabled in an embodiment of the present invention.

[0057] Figure 11 This is an FFT analysis diagram of the system in MPPT mode and power quality management enabled according to an embodiment of the present invention.

[0058] Figure 12 This is a schematic diagram of a device for integrating active regulation of photovoltaic voltage amplitude and harmonic voltage control provided by the present invention. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0060] This invention relates to a method for integrating active regulation of photovoltaic voltage amplitude and harmonic voltage control, the method comprising the following steps:

[0061] Step S1: Obtain the DC link voltage of the photovoltaic converter in the energy storage-free islanded microgrid. The electrical parameters of the common coupling point (PCC) on the AC side are extracted without delay to obtain the AC harmonic components of the PCC voltage;

[0062] Step S2: Select the power output mode of the front-end DC converter based on the amplitude of the DC link voltage:

[0063] When the DC link voltage Between the low-pressure safety boundary With the set DC link voltage reference value During this period, the preceding DC converter is operated in maximum power point tracking (MPPT) mode;

[0064] When the DC link voltage Between the DC link voltage reference value With respect to the established high-voltage safety boundary During this period, it is switched to DC voltage clamping mode and the output power of the photovoltaic side is actively reduced according to preset rules. At this time, it is in photovoltaic power reduction mode; the power output mode selection diagram is shown in Figure 1. Figure 2 As shown.

[0065] The specific method for selecting the power output mode of the front-stage DC converter is as follows:

[0066] Establish photovoltaic output power With the DC link voltage Negative correlation between linear power reserve adjustment model:

[0067]

[0068]

[0069] in, To reduce the photovoltaic reference output power, This represents the maximum theoretical output power of photovoltaic power under current environmental conditions. The minimum output power of photovoltaics is set by humans. This is the reference value for the DC link voltage. This is the low-pressure safety boundary. This is the high-voltage safety boundary. This is the DC voltage adaptive power limiting proportional coefficient.

[0070] Step S3: For the downstream inverter circuit, construct an adaptive voltage amplitude active control loop that integrates DC voltage feedforward; utilize the DC link voltage relative to the DC link voltage reference value. The deviation amount is used to adjust the amplitude command of the grid-side fundamental voltage in real time, so that when the energy supply of the photovoltaic system is insufficient, the reference amplitude of the grid-side output voltage can be automatically reduced.

[0071] The mathematical model of the adaptive voltage amplitude active regulation control loop is expressed as follows:

[0072] Grid-side frequency control equations:

[0073] ;

[0074] Grid-side voltage control equations:

[0075] ;

[0076]

[0077] in, This is the frequency droop factor. This is the amplitude compensation coefficient. This refers to the actual reactive power output of the photovoltaic converter. This is a reference value for reactive power. and These represent the output voltage amplitude and output frequency of the photovoltaic converter, respectively. and These are the output voltage amplitude reference value and the output frequency reference value, respectively. This is a manually set minimum grid-side voltage value. The specific adaptive voltage amplitude active control block diagram is shown below. Figure 3 As shown.

[0078] Step S4: While maintaining the operation of the adaptive voltage amplitude active regulation control loop, the load harmonic characteristic quantity is separated from the grid-side output current, and combined with the current operating status of the front-end DC converter and the real-time remaining capacity of the back-end inverter, the harmonic compensation voltage command and the comprehensive voltage reference command are generated to execute adaptive power quality collaborative control.

[0079] If in the DC voltage clamping mode, a wideband harmonic suppression command is generated based on the real-time remaining capacity, and full power quality compensation is performed.

[0080] If the network is in MPPT mode and the amplitude command of the grid-side fundamental voltage is controlled to decrease, the separated harmonic characteristic quantities are subjected to amplitude limiting scheduling based on priority weight according to the calculated real-time remaining capacity, so as to give priority to ensuring the compensation current output of characteristic low-order harmonics.

[0081] The specific method for calculating the remaining capacity of the converter is as follows:

[0082] Existing research on the extraction of harmonic current and harmonic voltage is already quite mature, so this invention will not elaborate on this method.

[0083] The fundamental frequency of the grid-side output current is extracted to obtain the amplitude of the current grid-side output fundamental frequency current. ;

[0084] Read the maximum current carrying capacity allowed by the hardware topology of the subsequent inverter circuit. ;

[0085] The real-time residual current margin of the converter is calculated based on the principle of square difference. It satisfies the analytical expression:

[0086] .

[0087] The priority-weighted amplitude limiting scheduling logic further includes: constructing an order weight vector for the target harmonic compensation, and incorporating the real-time remaining current margin... The weight vectors are assigned to the corresponding order current tracking controllers as saturation limiting boundaries for the corresponding order harmonic compensation commands; when the vector sum of the ideal harmonic compensation commands of each order detected by the system exceeds the real-time residual current margin... At that time, the higher harmonic compensation commands are truncated or proportionally attenuated in order of weight from low to high, so that the total output combined current is strictly constrained to the limiting current carrying threshold. Within the range.

[0088] The specific mathematical model for generating the harmonic compensation voltage command and the comprehensive voltage reference command is as follows:

[0089] Let the h-th harmonic component of the PCC voltage extracted without delay be... Since the desired high-order harmonic voltage at the PCC point is zero in the islanded microgrid mode, the gain of the corresponding h-th harmonic voltage closed-loop feedback controller is set to... ;

[0090] Considering dynamic harmonic compensation coefficient The generated total harmonic compensation voltage command The expression is:

[0091]

[0092] The fundamental voltage reference command generated by the adaptive voltage amplitude active regulation control loop is denoted as... The integrated voltage reference command The expression is:

[0093]

[0094] By introducing negative feedback terms Forcefully eliminate voltage distortion at PCC point, and utilize The compensation depth is dynamically constrained.

[0095] The dynamic harmonic compensation coefficient The specific generation rules are as follows:

[0096] Set the DC voltage threshold corresponding to full harmonic compensation as follows: ,in ;

[0097] Set the dynamic harmonic compensation coefficient For the current active power margin The piecewise continuous nonlinear function driven by the function has the following analytical expression:

[0098]

[0099] Among them, when At this time, the photovoltaic inverter actively and completely abandons closed-loop compensation for PCC voltage harmonics to avoid DC-side collapse of the photovoltaic system caused by instantaneous high-frequency power throughput. The flowchart of the harmonic dynamic allocation algorithm is as follows: Figure 4 As shown.

[0100] Furthermore, the present invention also includes an extreme low-voltage anti-collapse protection mechanism:

[0101] The output voltage amplitude V of the photovoltaic converter is monitored in real time. When the output voltage amplitude V drops to the preset minimum safe voltage threshold of the power grid, the harmonic compensation current command of the power quality collaborative management is forcibly set to zero, and the entire current capacity of the photovoltaic converter is used to maintain the fundamental voltage and voltage amplitude active support.

[0102] Example:

[0103] To demonstrate the effectiveness of the proposed control strategy, an islanded microgrid system with a photovoltaic inverter without energy storage and a local nonlinear load was built in MATLAB / Simulink 2024b. The overall system structure is as follows: Figure 1 As shown. The rated maximum power of the photovoltaic array is set to P. max =35kW, the minimum output power of photovoltaic power set by the user. The rated reference value for DC bus voltage is Low-voltage safety boundary High-voltage safety boundary The maximum safe current allowed by the inverter is I. limit It is 35A.

[0104] Example 1: The system operates under different working conditions without harmonic mitigation;

[0105] The system's operation and testing process under different operating conditions is as follows:

[0106] From t=0 to t=0.6s, the system is in normal operation (i.e., under light load conditions with sufficient sunlight), and the upstream converter is in DC voltage clamping mode. For example... Figure 5 (a) Figure 5 As shown in (b) above, the DC link voltage at this time The voltage is stable at 750V, and the AC fundamental frequency is in a normal, undiminished state.

[0107] At t=0.6s, the system load increases, and the power required by the system load exceeds the maximum output power that the photovoltaic system can provide. Even with the photovoltaic converter operating at full capacity, the demand cannot be met. Figure 5 As shown in (a), DC voltage The voltage drops rapidly below 750V, and the upstream converter switches to MPPT mode. For example... Figure 5 As shown in (b), due to the feedforward compensation term As a result, the fundamental voltage V on the AC side smoothly decreased from 1.0 pu to 0.88 pu, indicating that the AC side effectively stepped down the voltage.

[0108] At t=1s, the light intensity increases, and the maximum output power that the photovoltaic system can provide exceeds the power required by the system load. At this point, the upstream converter enters DC voltage clamping mode. For example... Figure 5 (a) Figure 5 As shown in (b) above, the DC voltage at this time When the voltage rises above 750V, the AC fundamental voltage returns to its normal value.

[0109] Example 2: The system operates under stable conditions, performing harmonic mitigation.

[0110] In this embodiment, the light intensity is sufficient, meaning the maximum output power provided by the photovoltaic system exceeds the power required by the system load. At this time, the system is in DC voltage clamping mode, and power quality management begins at t=0.6s. Figure 6 (a) and Figure 6 As shown in (b) above, the DC link voltage before and after power quality management... Maintaining a stable voltage around 750V, the AC side voltage remained stable, and a significant improvement in the voltage waveform was clearly observed. The FFT analysis graphs before and after power quality improvement are shown below. Figure 7 (a) and Figure 7 As shown in (b) in the figure, Figure 7 (a) in the figure is the FFT analysis diagram before the power quality management was started. Figure 7 (b) is the FFT analysis diagram after the power quality management was enabled. As can be seen from the diagram, the system THD decreased from 12.28% to 3.29% after the power quality management was enabled, and the power quality was effectively improved.

[0111] Example 3: The system operates under different conditions to perform harmonic mitigation.

[0112] Between t=0.2 and t=0.6s, the system is in normal operation (i.e., under light load conditions with sufficient sunlight), and the upstream converter is in DC voltage clamping mode. For example... Figure 8 (a) Figure 8 As shown in (b) above, the DC link voltage at this time The voltage is stable at 750V, and the AC fundamental frequency is in a normal, undiminished state.

[0113] At t=0.6s, the system load increases, and the power required by the system load exceeds the maximum output power that the photovoltaic system can provide. Even with the photovoltaic converter operating at full capacity, the demand cannot be met. Figure 8 As shown in (a), DC voltage The voltage quickly drops below 750V, and the upstream converter switches to MPPT mode. For example... Figure 8As shown in (b), the AC fundamental voltage V smoothly decreased from 1.0 pu to 0.88 pu, indicating that the AC side effectively stepped down.

[0114] Power quality management begins at t=1.0s, such as... Figure 8 (a) and Figure 8 As shown in (b) above, the DC link voltage before and after power quality management... Maintaining a stable voltage around 750V, the AC side voltage remained stable, and a significant improvement in the voltage waveform was clearly observed. The FFT analysis graphs before and after power quality improvement are shown below. Figures 9-11 As shown, Figure 9 This is an FFT analysis diagram of the system under normal operation and when power quality management is not enabled. Figure 10 This is an FFT analysis diagram when the system is in MPPT mode and power quality management is not enabled. Figure 11 This is an FFT analysis graph showing the system in MPPT mode with power quality management enabled. The graph shows that the system THD was 12.27% and 10.70% before power quality management was enabled. After enabling power quality management, the system THD decreased to 2.72%, indicating an effective improvement in power quality.

[0115] The above application examples demonstrate that the present invention can maintain the normal operation of the power grid in the case of isolated photovoltaic systems without energy storage, while at the same time it can perform power quality management and improve the power quality of the system.

[0116] Corresponding to the aforementioned embodiment of the method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control, the present invention also provides an embodiment of a device for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control.

[0117] See Figure 12 The present invention provides a photovoltaic voltage amplitude active regulation and harmonic voltage control fusion device, including a memory and one or more processors. The memory stores executable code, and when the processor executes the executable code, it is used to implement a photovoltaic voltage amplitude active regulation and harmonic voltage control fusion method in the above embodiment.

[0118] The embodiment of the photovoltaic voltage amplitude active regulation and harmonic voltage control integrated device provided by this invention can be applied to any device with data processing capabilities, such as a computer. The device embodiment can be implemented through software, hardware, or a combination of both. Taking software implementation as an example, as a logical device, it is formed by the processor of any data processing device loading the corresponding computer program instructions from non-volatile memory into memory for execution. From a hardware perspective, such as... Figure 12 The diagram shown is a hardware structure diagram of any device with data processing capabilities, which is an integrated device for active regulation of photovoltaic voltage amplitude and harmonic voltage control provided by the present invention. (Except for...) Figure 12 In addition to the processor, memory, network interface, and non-volatile memory shown, any data processing device in the embodiment may also include other hardware depending on the actual function of the data processing device, which will not be described in detail here.

[0119] The specific implementation process of the functions and roles of each unit in the above device can be found in the implementation process of the corresponding steps in the above method, and will not be repeated here.

[0120] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to in the description of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of the present invention according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0121] This invention also provides a computer-readable storage medium storing a program thereon, which, when executed by a processor, implements a method for integrating active regulation of photovoltaic voltage amplitude and harmonic voltage control as described in the above embodiments.

[0122] The computer-readable storage medium can be an internal storage unit of any data processing device described in any of the foregoing embodiments, such as a hard disk or memory. The computer-readable storage medium can also be an external storage device of any data processing device, such as a plug-in hard disk, smart media card (SMC), SD card, flash card, etc., equipped on the device. Furthermore, the computer-readable storage medium can include both internal storage units and external storage devices of any data processing device. The computer-readable storage medium is used to store the computer program and other programs and data required by the data processing device, and can also be used to temporarily store data that has been output or will be output.

[0123] The present invention also provides a computer program product, including a computer program, which, when executed by a processor, implements the aforementioned method for integrating active regulation of photovoltaic voltage amplitude and harmonic voltage control.

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control, characterized in that, The method includes the following steps: Step S1: Obtain the intermediate stage DC voltage of the photovoltaic converter in the isolated microgrid without energy storage, and extract the AC harmonic components of the common coupling point (PCC) voltage on the AC side. Step S2: Select the power output mode of the front-end DC converter based on the comparison result between the magnitude of the DC link voltage and the safety boundary; Step S3: For the downstream inverter circuit, construct an adaptive voltage amplitude active regulation control loop that integrates DC voltage feedforward; use the deviation of the DC link voltage from its steady-state reference value to adjust the amplitude command of the grid-side fundamental voltage in real time, so that when the photovoltaic system energy supply is insufficient, the reference amplitude of the grid-side output voltage can be automatically reduced. Step S4: While maintaining the operation of the active voltage amplitude regulation control loop, the load harmonic characteristic quantity is separated from the grid-side output current, and combined with the current operating status of the front-end DC converter and the real-time remaining capacity of the back-end inverter, a harmonic compensation voltage command and a comprehensive voltage reference command are generated to execute adaptive power quality collaborative control.

2. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 1, characterized in that, In step S2, when the DC link voltage is between the set low-voltage safety boundary and the set DC link voltage reference value, the front-end DC converter is operated in maximum power point tracking (MPPT) mode; when the DC link voltage is between the DC link voltage reference value and the set high-voltage safety boundary, it is switched to DC voltage clamping mode, and the output power of the photovoltaic side is actively reduced according to preset rules, at which time it is in photovoltaic power reduction mode.

3. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 1, characterized in that, In step S3, the adaptive voltage amplitude active regulation control loop includes grid-side frequency control and grid-side voltage control. The grid-side frequency control is based on the actual reactive power output of the photovoltaic converter and the reactive power reference value, combined with the output frequency reference value to calculate the output frequency of the photovoltaic converter. The grid-side voltage control is based on the DC link voltage and the output voltage amplitude reference value, combined with the output voltage amplitude reference value to calculate the output voltage amplitude of the photovoltaic converter.

4. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 1, characterized in that, In step S4, the method for calculating the real-time remaining capacity of the downstream inverter is as follows: The fundamental frequency of the grid-side output current is extracted to obtain the amplitude of the current fundamental frequency output by the grid side. Read the maximum current carrying capacity allowed by the hardware topology of the subsequent inverter circuit; Based on the fundamental current amplitude and the ultimate current carrying capacity threshold, the real-time remaining current carrying capacity of the downstream inverter is calculated according to the principle of square difference.

5. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 4, characterized in that, The priority-weighted limiting scheduling logic further includes: constructing an order weight vector for the target harmonic compensation, allocating the real-time remaining current margin to the corresponding order current tracking controller according to the order weight vector, as the saturation limiting boundary of the corresponding order harmonic compensation command; when the vector sum of the detected ideal harmonic compensation commands of each order exceeds the real-time remaining current margin, performing truncation or proportional attenuation operations on the higher-order harmonic compensation commands in order of weight from low to high, so that the total output combined current is strictly constrained within the limit current threshold range.

6. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 2, characterized in that, In step S4, the adaptive power quality cooperative control specifically includes: If in the DC voltage clamping mode, a wideband harmonic suppression command is generated based on the real-time remaining capacity, and full power quality compensation is performed. If in MPPT mode and the amplitude command of the grid-side fundamental voltage is reduced in a controlled manner, the separated harmonic characteristic quantities are subjected to amplitude limiting scheduling based on priority weights according to the calculated real-time remaining capacity, so as to give priority to ensuring the compensation current output of characteristic low-order harmonics.

7. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 1, characterized in that, The specific process for generating harmonic compensation voltage commands and integrated voltage reference commands is as follows: Assume the harmonic components of the PCC voltage extracted without delay and the gain of the harmonic voltage closed-loop feedback controller; considering the dynamic harmonic compensation coefficient, generate the total harmonic compensation voltage command; introduce a negative feedback term to the total harmonic compensation voltage command to forcibly eliminate the voltage distortion at the PCC point, and use the dynamic harmonic compensation coefficient to constrain its compensation depth; generate the fundamental voltage reference command based on the voltage amplitude active regulation control algorithm to obtain the comprehensive voltage reference command.

8. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 7, characterized in that, The specific rules for generating the dynamic harmonic compensation coefficient are as follows: a DC voltage threshold corresponding to full harmonic compensation is set, and the current active power margin is calculated based on the DC link voltage. The dynamic harmonic compensation coefficient is a piecewise continuous nonlinear function driven by the current active power margin.

9. The method for integrating active photovoltaic voltage amplitude regulation and harmonic voltage control according to claim 1, characterized in that, The method also includes an extreme low-pressure crash protection mechanism: The output voltage amplitude of the photovoltaic converter is monitored in real time. When the output voltage amplitude drops to the preset minimum safe voltage threshold of the power grid, the harmonic compensation current command for power quality collaborative management is forcibly set to zero, and the entire current capacity of the photovoltaic converter is used to maintain the fundamental voltage and voltage amplitude active support.

10. A photovoltaic voltage amplitude active regulation and harmonic voltage control integrated system for implementing the method of any one of claims 1-9, characterized in that, include: A multi-dimensional electrical quantity sensing module is used to extract the DC link voltage, grid-side output voltage, and grid-side output current in real time during the operation of the system. The mode switching and DC control module is configured in the DC / DC converter stage. It is used to operate in MPPT mode when the intermediate stage DC voltage is lower than the set low voltage safety boundary, and switch to constant voltage mode to limit power output when the intermediate stage DC voltage is between the low voltage safety boundary and the set high voltage safety boundary. An adaptive droop control module, configured in the DC / AC converter stage, is used to adjust the amplitude of the AC side fundamental voltage in real time by using the deviation of the intermediate stage DC voltage. The dynamic harmonic allocation and mitigation module is used to generate harmonic compensation voltage commands and comprehensive voltage reference commands based on the mode switching and DC control module status and the remaining available current margin of the inverter. It performs full harmonic mitigation in the constant voltage mode and dynamically increases the amplitude of the harmonic compensation commands in the MPPT mode and AC fundamental voltage reduction mode.

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