Distributed photovoltaic access voltage treatment method based on micro energy storage

Abstract

The invention relates to the technical field of voltage treatment, in particular to a distributed photovoltaic access voltage treatment method based on micro energy storage. According to the technical scheme, the distributed photovoltaic access voltage treatment method based on micro energy storage comprises the following steps that S1, a voltage signal U monitored by micro energy storage pcs serves as input to be compared with threshold voltage U1; s2, when the monitored voltage U is greater than the threshold voltage U1, stopping voltage monitoring, and entering a high-voltage closed-loop PI control process; and S3, when the monitored voltage U is less than or equal to the threshold voltage U1, continuing voltage monitoring and executing a segmented fuzzy control process. The micro energy storage equipment is accessed to a power grid nearby, a control algorithm is upgraded, and an energy storage system is energized, so that the micro energy storage equipment has the closed-loop treatment capability of the distributed photovoltaic large-area access to the power grid on the influence of the local power supply quality of the power grid, the application scene of the micro energy storage equipment is expanded, and the construction of a novel power system is assisted.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage management, and in particular to a distributed photovoltaic access voltage management method based on micro energy storage. Background Art

[0002] Distributed photovoltaic development has ushered in new opportunities, and the installed capacity will maintain a rapid growth trend. However, the randomness and volatility of photovoltaic power generation are obvious, and the growing scale of new energy power generation has put forward higher requirements for its large-scale optimization configuration and power system flexibility.

[0004] When large-scale, high-proportion photovoltaic power generation is connected to the low-voltage distribution network system, it will most likely cause power flow reversal, leading to large fluctuations in node voltage within the substation area and increased system losses, and even asymmetric operation of the power grid.

[0005] Therefore, it is necessary to study the local power quality problems caused by the access of distributed photovoltaic power to the power grid and effectively manage them, so as to maximize the local consumption and flexible and friendly grid connection of distributed photovoltaic power, and improve the reliability and economy of the substation operation.

[0006] In the prior art, there are devices that achieve corresponding power quality management through hierarchical regulation. They rely on responsible systematic equipment such as regulation platforms to improve power quality, but their ability to improve local voltage rise is insufficient, and the system consists of many devices and is complex, which is essentially different from the solution of the present invention.

[0007] The patent with publication number CN119231632A discloses a micro-energy storage type low voltage control device in conjunction with a rural power grid photovoltaic absorption control method. The micro-energy storage type low voltage control device is combined with the rural power grid photovoltaic absorption control method to obtain the real-time monitoring voltage and current data of the rural power grid and the power generation of photovoltaic modules, and respectively calculate the voltage fluctuation value to determine whether the rural power grid voltage is stable, calculate the power within the rural power grid cycle, and calculate the net load of the rural power grid by combining the power within the rural power grid cycle and the power generation of photovoltaic modules. The net load of the rural power grid and the voltage fluctuation are combined to determine whether it is necessary to connect the electric energy generated by the photovoltaic modules to the grid or store the electric energy generated by the photovoltaic modules.

[0008] The patent with publication number CN215120144U discloses a multifunctional multiplexed power-type micro energy storage device, including a solid-state switch, a pulse transformer, a rectifier inverter module and a power-type energy storage body. The solid-state switch is arranged between the power grid and the sensitive power user, the input end of the pulse transformer is connected between the solid-state switch and the sensitive power user, the output end of the pulse transformer is connected to the rectifier inverter module, the rectifier inverter module is connected to the power-type energy storage body, the solid-state switch is used to prevent the inverter output voltage from returning to the power grid, the rectifier inverter module is used to convert DC energy storage into three-phase AC power and provide bidirectional energy flow, and the power-type energy storage body is used to store and release energy.

[0009] However, the above two patents do not make improvements to the problem of large fluctuations in node voltage and increased system losses in the substation area caused by large-scale, high-proportion photovoltaic power generation connected to the low-voltage distribution network system. Summary of the invention

[0010] The present invention proposes a distributed photovoltaic access voltage management method based on micro-energy storage, which solves the problem in the prior art that after large-scale and high-proportion photovoltaic power generation is connected to the low-voltage distribution network system, it will greatly cause power flow reverse, resulting in large fluctuations in node voltage in the substation area and increased system losses, resulting in asymmetric operation of the power grid.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0012] A distributed photovoltaic access voltage management method based on micro energy storage includes the following steps:

[0013] S1, the voltage signal U monitored by the micro energy storage pcs is used as input and compared with the threshold voltage U1;

[0014] S2: When the monitored voltage U is greater than the threshold voltage U1, the voltage monitoring is stopped and the high voltage closed-loop PI control process is entered;

[0015] S3. When the monitored voltage U is less than or equal to the threshold voltage U1, the voltage monitoring is continued and the segmented fuzzy control process is executed.

[0016] Furthermore, in step S1 , the voltage signal U is used as an input signal, and the voltage U is processed using a first-order filter transfer function, and the transfer function formula is G(s)=1 / (Ts+1).

[0017] Furthermore, in step S2, when the monitoring voltage U is greater than the threshold voltage U1, the high voltage closed-loop PI control process is entered, and the specific steps are as follows:

[0018] Record the energy storage power P1 at the time of entry;

[0019] With voltage as input, incremental PI control is performed, and the output is the energy storage given power increment ΔPout 1;

[0020] ΔPout 1=Kp.(e(t)-e(t-1))+Ki.e(t);

[0021] The energy storage given power is: Pout2 = ΔPout1 + P1;

[0022] The power limit condition for energy storage is: Pout2 = max(Pout2, Pret), where Pret is the rated power of the micro energy storage PCS.

[0023] Furthermore, if Soc>0.9, Pout2=0, and Soc is the current energy storage percentage of the energy storage battery.

[0024] Furthermore, if the energy storage management power is less than the tolerance value Pr, and the voltage deviation from the target value is less than the tolerance value Ur, the high voltage closed-loop PI control process is exited and voltage monitoring is restarted, otherwise step S2 is continued.

[0025] Furthermore, in the segmented fuzzy control process in step S3, 24 hours a day are divided into three states according to the load size: over-generation state, balanced state, and over-use state.

[0026] Furthermore, energy storage charging is set in the over-generation state, and energy storage rest is set in the balanced state. No charging or discharging is performed, and only the voltage is monitored. Energy storage discharging is set in the over-use state.

[0027] Furthermore, the segmented fuzzy control process in the over-issuance state is as follows:

[0028] Input fuzzification, taking voltage as input, the voltage from 210V to 235V is divided into five levels: negative large, negative small, medium, positive small, and positive large;

[0029] The inference engine and rule base correspond the monitored voltage to five levels: negative large, negative small, medium, positive small, and positive large according to the linear relationship;

[0030] Determine the reasonable charging power of fuzzy inputs: negative large, negative small, medium, positive small, and positive large;

[0031] Defuzzification: the reasonable input power is also planned into 5 levels, and the output takes one of these 5 values;

[0032] The output power is used as the command value to guide the energy storage charging.

[0033] Furthermore, in the over-use state, the battery is discharged. The segmented fuzzy control process in the over-use state has the same logic as the process in the over-generation state. The charged capacity in the over-generation state needs to be discharged within one cycle day.

[0034] Furthermore, in the over-discharge state, check that Soc is greater than 90% and stop charging; in the over-use state, check that Soc is less than 10% and stop discharging.

[0035] The positive effects of the present invention are:

[0036] 1. Micro energy storage devices are connected to the nearest power grid to upgrade the control algorithm, empowering the energy storage system so that it has the closed-loop management capability to deal with the impact of large-scale distributed photovoltaic access to the power grid on the local power supply quality of the power grid, expand the application scenarios of micro energy storage devices, and assist in the construction of new power systems.

[0037] 2. The process of distributed photovoltaic voltage rise is indirectly smoothed by energy storage, which can also prevent the positive and negative overload of the substation. It can extend the transformation time of the substation, increase the use time of equipment in the substation, and indirectly improve the economic benefits of energy storage.

[0038] 3. In the process of voltage raising, it avoids the aggravation of overload and reverse overload in the substation area, and at the same time has the effect of preventing overload and reverse overload in the substation area. The direct effect of the governance process is to achieve the time and space shift and matching between photovoltaic power generation and load power consumption, complete the on-site consumption of photovoltaic power, and maximize the effect of energy storage power quality governance.

[0039] 4. During the instruction issuance process, the energy storage works under fuzzy control logic under normal circumstances. The classic PI controller is used for high voltage management to achieve closed-loop automatic adjustment control, which facilitates the joint access and control of multiple micro energy storages in the system. The adaptability and convenience of this solution are reflected.

[0040] 5. Use micro energy storage to complete the peak-valley shift of distributed photovoltaic power generation, add new capabilities of micro energy storage, use energy storage to improve the power quality of local power systems, and achieve the purpose of helping new power systems to operate stably; through simple energy storage function empowerment, without adding metering equipment and relying on platform information interaction, through energy storage self-testing and self-control, reliable closed-loop regulation is achieved, and distributed photovoltaic power generation is completed. Local peak-valley smoothing and local voltage rise management is achieved. The effect of preventing heavy overloads in the forward and reverse directions of the substation area and improving the power quality of the power supply is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flowchart of the distributed photovoltaic access voltage management method based on micro energy storage of the present invention;

[0042] Figure 2 It is a flow chart of high voltage closed-loop PI control in the present invention;

[0043] Figure 3 It is a line graph of the real load collection value of a certain area in the embodiment of the present invention;

[0044] Figure 4 For the present invention Figure 3 The corresponding voltage fluctuation line chart;

[0045] Figure 5 It is a block diagram of the segmented fuzzy control process in the present invention; DETAILED DESCRIPTION

[0046] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] In the prior art, micro energy storage PCS (energy storage converter) is the core component that realizes the bidirectional flow of electric energy between the energy storage system and the power grid or microgrid. It is mainly used to control the charging and discharging process of the battery and perform AC / DC conversion. In the absence of a power grid, PCS can directly power the AC load.

[0048] This micro-energy storage is mainly used to stabilize the local voltage rise near the distributed photovoltaic access point; the trigger condition is based on the maximum supply voltage of the residential power supply standard (which can be set, the base voltage 220V is 7% higher as an example)

[0049] Example 1

[0050] A distributed photovoltaic access voltage management method based on micro energy storage, in which the hardware carrier of the logic algorithm is a micro energy storage device, and the operation carrier of the algorithm is a fusion control board of the micro device, that is, embedded in the energy storage PCS control board.

[0051] Micro energy storage equipment is a quick-access energy storage device with convenient location migration function and rapid access to the power grid. As long as the power line is connected to the power grid, it can be adjusted and controlled according to its own closed-loop control logic.

[0052] Specifically, the device can be used as an existing micro energy storage cabinet, and the software program of the PCS control version inside the original micro energy storage can be directly updated, and the connection can be directly connected to the photovoltaic residential grid point, which greatly improves the convenience of application.

[0053] Combination Figure 1 As shown, a distributed photovoltaic access voltage management method based on micro energy storage includes the following steps:

[0054] S1, the voltage signal U monitored by the micro energy storage pcs is used as input and compared with the threshold voltage U1;

[0055] S2: When the monitored voltage U is greater than the threshold voltage U1, the voltage monitoring is stopped and the high voltage closed-loop PI control process is entered;

[0056] S3. When the monitored voltage U is less than or equal to the threshold voltage U1, the voltage monitoring is continued and the segmented fuzzy control process is executed.

[0057] Combination Figure 1-2 As shown, in step S1, the voltage signal U is used as the input signal, and the voltage U is processed by a first-order filter transfer function, and the transfer function formula is G(s)=1 / (Ts+1). In this embodiment, the time constant T can be taken as 60s;

[0058] By processing the voltage signal U through a first-order filter transfer function, high-frequency noise can be effectively filtered out and the signal can be smoothed. The processing process includes Laplace transform, filtering and inverse Laplace transform. The specific effect depends on the value of the time constant T, thereby obtaining a smoother, more stable and accurate voltage signal U.

[0059] In step S2, when the monitoring voltage U is greater than the threshold voltage U1, the high voltage closed-loop PI control process is entered. The specific steps are as follows:

[0060] Record the energy storage power P1 at the time of entry;

[0061] With voltage as input, incremental PI control is performed, and the output is the energy storage given power increment ΔPout 1;

[0062] ΔPout 1=Kp.(e(t)-e(t-1))+Ki.e(t);

[0063] Where e(t) is the current error (the difference between the expected value and the actual value), and e(t-1) is the previous error.

[0064] In incremental PI control, Kp and Ki represent the proportional coefficient and the integral coefficient, respectively. They are two key parameters of the PI controller and are used to determine how the controller responds to errors.

[0065] Kp determines the intensity of the controller's direct response to the current error. In incremental PI control, Kp is multiplied by the current error (i.e., the difference between the expected value and the actual value) to calculate the proportional term. The role of the proportional term is to quickly reduce the error and increase the response speed of the system. The larger the Kp, the greater the impact of the proportional term on the control output and the faster the system responds to the error. However, too large a Kp may cause the system to over-oscillate and affect stability.

[0066] Ki determines the intensity of the controller's response to the accumulated error. In incremental PI control, Ki is multiplied by the accumulated sum of the error (i.e., the integral term) to calculate the integral term.

[0067] The function of the integral term is to eliminate steady-state errors and improve the accuracy of the system. The larger the Ki is, the greater the impact of the integral term on the control output and the stronger the system's ability to eliminate steady-state errors. However, an excessively large Ki may cause the system to respond more slowly or even cause oscillations.

[0068] By adjusting the values ​​of Kp and Ki, the performance of the control system can be optimized, including response speed, accuracy and stability. In this embodiment, Kp is 0.6 and Ki is 0.4. These values ​​can be selected and adjusted according to the characteristics and requirements of the actual system.

[0069] The energy storage given power is: Pout2 = ΔPout1 + P1;

[0070] The power limit condition for energy storage is: Pout2 = max (Pout2, Pret), where Pret is the rated power of the micro energy storage PCS;

[0071] Through this calculation process, when Pout2 is less than the rated power Pret, Pout2 is updated to Pret to ensure that the output power of the energy storage system will not be lower than the rated power;

[0072] When Pout2 is greater than or equal to the rated power Pret, Pout2 is kept unchanged.

[0073] In this way, it can be ensured that the energy storage system will not operate below its rated power under any circumstances, thus ensuring the stability and reliability of the system.

[0074] If Soc>0.9, Pout2=0, Soc is the current energy storage percentage of the energy storage battery. When the power of the energy storage system reaches 90%, energy storage is stopped to protect the energy storage battery.

[0075] If the energy storage management power is less than the tolerance value Pr, and the voltage deviation from the target value is less than the tolerance value Ur, then exit the high voltage closed-loop PI control process and restart voltage monitoring, otherwise continue to execute step S2.

[0076] In this embodiment, the tolerance Pr is related to the energy storage capacity. For example, if the rated capacity of the energy storage is 15kw / 30kwh, the value of Pr can be 2.5kw, and the value of Ur can be 5V. Therefore, when the current power and voltage of the energy storage system are close to the target value (within the tolerance range), it is considered that the system is stable, and the high-voltage closed-loop PI control process can be exited and voltage monitoring can be restarted; otherwise, the control process continues to be executed to further adjust the system state.

[0077] Example 2

[0078] Combination Figure 3-5 As shown, the difference between this embodiment and embodiment 1 is that:

[0079] When the voltage does not exceed the threshold, the time-divided fuzzy control process is executed. During the execution of this process, the high voltage monitoring process runs in parallel and is ready to enter high voltage management at any time.

[0080] In step S3, the segmented fuzzy control process divides 24 hours a day into three states according to the load size: over-generation state, balanced state, and over-use state;

[0081] A. Over-issuance status: attached Figure 3 10:00 to 16:00, the voltage is higher during this period, see attached Figure 4 The voltage collection value is easy to exceed the voltage limit and enter the closed-loop PI control. In this stage, energy storage charging is set, and the charging power size executes the fuzzy control process.

[0082] B. Balance state: Figure 3 The voltage is normal during the two periods from 8:00 to 10:00 and 16:00 to 18:00. Figure 4 The voltage collection value is set at this stage. The energy storage is set to rest, without charging or discharging, and only the voltage is monitored.

[0083] C. Overuse status: attached Figure 3 The remaining period is mainly for electricity consumption, and the voltage is relatively low. Figure 4 The voltage collection value is set at this stage, and the energy storage discharge is set, and the discharge power size executes the fuzzy control process.

[0084] The charging and discharging plan takes 8:00 as the starting time of the day. The power charged in the over-generation state and the power discharged in the over-usage state must be equal. That is, at the time node of 8:00, the energy storage SOC just returns to the state of 10%, forming a cycle.

[0085] In the over-generation state, the energy storage is set to charge; in the balanced state, the energy storage is set to rest, without charging or discharging, only monitoring the voltage; in the over-use state, the energy storage is set to discharge.

[0086] The segmented fuzzy control process in the over-issuance state is as follows:

[0087] Input fuzzification, taking voltage as input, the voltage from 210V to 235V is divided into five levels: negative large, negative small, medium, positive small, and positive large;

[0088] The inference engine and rule base correspond the monitored voltage to five levels: negative large, negative small, medium, positive small, and positive large according to the linear relationship;

[0089] According to the attached Figure 3 The reverse power and the attached Figure 4 The size of the output voltage determines the reasonable charging power of the fuzzy input of large negative, small negative, medium, small positive, and large positive.

[0090] Defuzzification is performed and the reasonable input power is also planned into 5 levels, such as 1KW, 4KW, 7KW, 10KW, and 15KW. The output only takes one of these 5 values. The output of charging under the negative voltage state is the largest, so as to consume photovoltaic power generation on site.

[0091] The output power is used as the command value to guide the energy storage charging.

[0092] In the over-use state, the charging is discharged. The segmented fuzzy control process in the over-use state is the same as the process logic in the over-discharge state. The charging capacity in the over-discharge state needs to be discharged within one cycle day. Figure 5 shown.

[0093] In the over-generation state, check that Soc is greater than 90% and stop charging; in the over-use state, check that Soc is less than 10% and stop discharging, thereby protecting the energy storage system.

[0094] When the voltage does not cross the threshold, the time-divided fuzzy control process is executed. During the execution of this process, the high voltage monitoring process runs in parallel and is ready to enter high voltage management at any time. The fuzzy control system is highly robust and can maintain stable performance in the event of system parameter changes and external interference.

[0095] Time-division fuzzy control can flexibly adjust the control strategy according to different time periods and load conditions to better adapt to different operating conditions. For example, different control rules can be used during peak hours and off-peak hours to optimize system performance.

[0096] The combination of time-segment fuzzy control and high voltage monitoring not only improves the system's adaptability and robustness, but also ensures real-time performance and safety, thereby optimizing voltage management and improving system stability.

[0097] The above-mentioned embodiments describe in detail and concretely, and express the preferred embodiments of the present invention. They are only used to illustrate the technical ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. However, they are not limited to the present invention alone, and the patent scope of the present invention cannot be limited only by this embodiment. That is, any equivalent changes or modifications made to the spirit disclosed by the present invention, for researchers or technicians in the field, without departing from the structure of the present invention, local improvements within the system and changes and conversions between subsystems, etc., are still within the patent scope of the present invention.

Claims

1. A distributed photovoltaic access voltage management method based on micro energy storage, characterized in that: The following steps are involved: S1, the voltage signal U monitored by the micro energy storage pcs is used as input and compared with the threshold voltage U1; S2: When the monitored voltage U is greater than the threshold voltage U1, the voltage monitoring is stopped and the high voltage closed-loop PI control process is entered; S3. When the monitored voltage U is less than or equal to the threshold voltage U1, the voltage monitoring is continued and the segmented fuzzy control process is executed.

2. According to a method for voltage management of distributed photovoltaic access based on micro energy storage according to claim 1, it is characterized in that: In step S1 , the voltage signal U is used as an input signal, and the voltage U is processed by a first-order filter transfer function, and the transfer function formula is G(s)=1 / (Ts+1).

3. According to a method for voltage management of distributed photovoltaic access based on micro energy storage according to claim 1, it is characterized in that: In step S2, when the monitoring voltage U is greater than the threshold voltage U1, the high voltage closed-loop PI control process is entered. The specific steps are as follows: Record the energy storage power P1 at the time of entry; With voltage as input, incremental PI control is performed, and the output is the energy storage given power increment ΔPout1; ΔPout1=Kp.(e(t)-e(t-1))+Ki.e(t); The energy storage given power is: Pout2 = ΔPout1 + P1; The power limit condition for energy storage is: Pout2 = max(Pout2, Pret), where Pret is the rated power of the micro energy storage PCS.

4. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 3, characterized in that: If Soc>0.9, Pout2=0, and Soc is the current energy storage percentage of the energy storage battery.

5. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 4, characterized in that: If the energy storage management power is less than the tolerance value Pr, and the voltage deviation from the target value is less than the tolerance value Ur, then exit the high voltage closed-loop PI control process and restart voltage monitoring, otherwise continue to execute step S2.

6. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 5, characterized in that: In step S3, the segmented fuzzy control process divides 24 hours a day into three states according to the load size: over-generation state, balanced state, and over-use state.

7. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 6, characterized in that: In the over-generation state, the energy storage is set to charge; in the balanced state, the energy storage is set to rest, without charging or discharging, only monitoring the voltage; in the over-use state, the energy storage is set to discharge.

8. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 7, characterized in that: The segmented fuzzy control process in the over-issuance state is as follows: Input fuzzification, taking voltage as input, the voltage from 210V to 235V is divided into five levels: negative large, negative small, medium, positive small, and positive large; The inference engine and rule base correspond the monitored voltage to five levels: negative large, negative small, medium, positive small, and positive large according to the linear relationship; Determine the reasonable charging power of fuzzy inputs: negative large, negative small, medium, positive small, and positive large; Defuzzification: the reasonable input power is also planned into 5 levels, and the output takes one of these 5 values; The output power is used as the command value to guide the energy storage charging.

9. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 8, characterized in that: In the over-use state, it is discharging. The segmented fuzzy control process in the over-use state has the same logic as the process in the over-generation state. The charged capacity in the over-generation state needs to be discharged within one cycle day.

10. A distributed photovoltaic access voltage management method based on micro energy storage according to claim 9, characterized in that: In the over-discharge state, check that Soc is greater than 90% and stop charging; in the over-use state, check that Soc is less than 10% and stop discharging.

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