Photovoltaic power station output adaptive adjustment method based on PMU measurement data

Abstract

According to the photovoltaic power station output adaptive adjustment method based on PMU measurement data, active and real-time management is carried out on each photovoltaic power station by using a PMU, the impedance between a grid-connected point of the photovoltaic power station and a secondary side of a power distribution station is accurately measured, the optimal power generation amount of the photovoltaic power station is measured and calculated by using the impedance, and the optimal power generation amount of the photovoltaic power station is calculated. Therefore, the power loss is minimized when the load of the power grid dynamically changes, and the photovoltaic access capacity and the voltage offset level of the power distribution network are improved. The method has the advantages of being low in calculation complexity, real-time and rapid, the equivalent impedance of the power distribution network can be measured through a simple and convenient method, and then the impedance obtained through calculation is used for optimal dispatching of the photovoltaic power station.

Description

Technical Field

[0001] The present invention relates to the field of intelligent power distribution systems, and in particular to a photovoltaic power station output adaptive regulation method based on PMU measurement data. Background Art

[0002] As the last link in the power system structure, the distribution system undertakes the important task of receiving electricity from the high-voltage transmission system and then transmitting electricity to users at low voltage. When a photovoltaic power station is connected to the distribution system, it may affect the steady-state and transient characteristics of the power grid. Appropriate control and regulation measures need to be taken to ensure the safe connection of the photovoltaic power station to the distribution network.

[0003] Adaptive regulation of photovoltaic power stations in power distribution systems refers to the use of smart grid technology to accurately adjust the power generated by photovoltaic power stations to keep the supply and demand relationship with the power grid balanced. This technology is mainly used in the field of distributed photovoltaic power generation, aiming to solve problems such as grid stability and voltage quality.

[0004] With the continuous increase of photovoltaic power generation equipment, the fluctuation of photovoltaic power generation under various weather conditions has led to some safety hazards and voltage stability problems in the power grid. In order to solve these problems, the adaptive regulation technology of photovoltaic power stations in the distribution system has emerged. This technology can automatically monitor the voltage, frequency and load of the power grid, and adjust the power generation of the photovoltaic power station according to real-time data. If the power grid is overloaded, the photovoltaic power station will automatically reduce the power generation to ensure the balance of the power grid; if the power grid is lightly loaded, the photovoltaic power station will automatically increase the power generation to improve energy efficiency.

[0005] In addition, the adaptive regulation technology of photovoltaic power stations in the distribution system can also achieve remote monitoring and management through intelligent control systems, improve the reliability and safety of the power system, and reduce the maintenance and operating costs of the power grid.

[0006] Therefore, the application of adaptive regulation technology of photovoltaic power stations in distribution systems is of great significance. It can effectively solve the problems existing in the field of photovoltaic power generation and promote the development and utilization of clean energy. Summary of the invention

[0007] The present invention proposes a photovoltaic power station output adaptive adjustment method based on PMU measurement data, which has low calculation complexity and has the characteristics of real-time and rapidity. By using this method, the equivalent impedance of the distribution network can be measured in a simple way, and the calculated impedance can be used for the optimal scheduling of the photovoltaic power station.

[0008] The present invention adopts the following technical solutions.

[0009] A method for adaptively regulating the output of a photovoltaic power station based on PMU measurement data. The method uses a phasor measurement unit (PMU) to actively and real-time manage each photovoltaic power station, accurately measures the impedance between the grid connection point of the photovoltaic power station and the secondary side of the distribution station, and uses the impedance to calculate the optimal power generation of the photovoltaic power station, so as to minimize the power loss when the grid load changes dynamically, and improve the photovoltaic access capacity of the distribution network and the voltage offset level of the distribution network.

[0010] The method comprises the following steps:

[0011] Step S1: Determine the PMU installation and deployment location, use the PMU to monitor the electrical quantities at two nodes, the photovoltaic power station and the distribution transformer station of the distribution station in real time, and set the threshold value of the photovoltaic power station output fluctuation;

[0012] Step S2: start the photovoltaic power station output adaptive adjustment at a fixed time, determine whether the photovoltaic power station output fluctuation exceeds the set threshold, and when the output fluctuation is greater than the set threshold, perform real-time control of the photovoltaic power station output;

[0013] Step S3: Calculate the impedance between the grid connection point of the photovoltaic power station and the secondary side of the distribution station, and then calculate the optimal active and reactive power generation of the photovoltaic power station, and then adjust its output;

[0014] Step S4: read the PMU measurement value again to determine whether the voltage change amplitude exceeds the threshold. If it exceeds the threshold, update the optimal power generation of the photovoltaic power station and recalculate whether the voltage meets the threshold requirement.

[0015] The specific implementation process of determining the PMU installation and deployment location as described in step S1 is as follows: a PMU device is installed on the secondary side of the distribution station, and another PMU device is installed at the photovoltaic power station to provide measurement data with high time resolution and time stamp; a GPS is configured for the entire station to synchronize the time of the measurement device, and then calculate and extract the electrical quantities of the two nodes on the secondary side of the photovoltaic power station and the distribution station.

[0016] In step S1, the calculation formula for setting the threshold value of the photovoltaic power station output fluctuation is:

[0017] S t -S t-1 |≥S N *α%

[0018] Where S t is the current output power of the photovoltaic power station, S t-1 is the output power of the photovoltaic power station at the previous moment, S N is the rated output power of the photovoltaic power station, and α is an adjustable variable.

[0019] The timed start of the adaptive adjustment of the photovoltaic power station output described in step S2 is specifically: the photovoltaic power station output is monitored every t minutes. When the amplitude of the output fluctuation at the photovoltaic power station does not meet the threshold requirement, the power of the photovoltaic power station is adjusted according to the real-time output data of the photovoltaic power station with high sampling rate and high refresh rate obtained by the PMU; if the requirements are met, the power adjustment is not performed.

[0020] The specific implementation steps of measuring the impedance between the photovoltaic power station grid connection point and the secondary side of the distribution station described in step S3 are:

[0021] S3A, re-read the measured values ​​of the PMU, based on the Thevenin equivalent theorem, ignore the specific conditions of each branch, perform line equivalence and network simplification on the distribution system, define the node voltage on the secondary side of the distribution station as the reference voltage, and the system equivalent resistance and inductance are equal to the sum of the resistance and inductance between the secondary side of the distribution station and the photovoltaic power station;

[0022] S3B. The relationship between the actual active power and reactive power in the circuit at the current moment is expressed in a matrix as follows:

[0023] Where V t ,δ t They represent the voltage amplitude and phase angle of the photovoltaic power station node at the current moment, P t ,Q t They respectively represent the active and reactive power output by the photovoltaic power station at the current moment;

[0024] Similarly, the relationship between the actual active power and reactive power in the circuit at the previous moment is expressed in a matrix as follows:

[0025] Where V t-1 ,δ t-1 They represent the voltage amplitude and phase angle of the photovoltaic power station node at the last moment, P t-1 ,Q t-1 They respectively represent the active and reactive power output by the photovoltaic power station at the current moment;

[0026] Compare the actual active and reactive power relationship in the circuit at the current moment with that at the previous moment to obtain the system equivalent impedance, which can be expressed as:

[0027]

[0028] Where: ΔP represents the difference between the active power of the photovoltaic power station at the current moment and the previous moment, and ΔQ represents the difference between the reactive power of the photovoltaic power station at the current moment and the previous moment.

[0029] In step S3, the optimal active and reactive power generation of the photovoltaic power station is calculated, and the specific implementation process is: assuming that in order to make the line power loss zero, the power injected into the photovoltaic power station node is all provided by the photovoltaic power station, then the optimal active and reactive output of the photovoltaic power station at the next moment is:

[0030]

[0031] Where P ref.t+1 Indicates the active output reference value of the photovoltaic power station at the next moment, Q ref.t+1 Indicates the reactive power output reference value of the photovoltaic power station at the next moment, V t+1 ,δ t+1 They respectively represent the voltage amplitude and phase angle of the photovoltaic power station node at the next moment.

[0032] The updating of the active and reactive output of the photovoltaic power station in step S4 is specifically implemented as follows: reading the measured value of the PMU again, and if the node voltage of the photovoltaic power station changes, determining whether the grid topology has changed, if so, updating the equivalent impedance of the distribution network, otherwise the active and reactive output of the photovoltaic power station needs to be recalculated.

[0033] The specific steps to determine whether the distribution network topology has changed are:

[0034] S4A, define a threshold value of the power ratio change on both sides caused by the topology change as the switch change coefficient λ, and the selection of this coefficient is determined by the maximum load and the minimum load carried by the node;

[0035] S4B. Assume that the switch state change of the branch will cause the fluctuation of the power ratio between the secondary side of the distribution station and the photovoltaic power station. Therefore, calculate the power ratio η between the secondary side of the distribution station and the photovoltaic power station measured by the PMU:

[0036]

[0037] Where P0 is the power value measured by the PMU at the secondary side of the distribution station, and P1 is the power value measured by the PMU at the node of the photovoltaic power station. When compared with the switch change coefficient λ, if the relationship between the two changes, it is determined that the topology of the distribution network has changed; if the relationship between the two remains unchanged, it is determined that the topology has not changed.

[0038] The recalculation of the photovoltaic power station node voltage in step S4 is specifically implemented as follows: recalculating the corrected photovoltaic power station node voltage, determining whether the photovoltaic power station node voltage meets the threshold condition, and minimizing the target node voltage deviation and active and reactive power regulation;

[0039] In the method, the photovoltaic power station reduces network transmission costs and operating computing power by spontaneously performing regulation operations.

[0040] The present invention is beneficial to improving the photovoltaic access capacity of the distribution network and the voltage deviation level of the distribution network, and can maximize the power generation efficiency of the photovoltaic power station under the premise of ensuring the stable operation of the power grid; at the same time, the photovoltaic power station can be spontaneously regulated, reducing network transmission costs and operating computing power.

[0041] The method of the present invention can automatically monitor the voltage, frequency and load of the power grid, and adjust the power generation of the photovoltaic power station according to the real-time data. If the power grid is overloaded, the photovoltaic power station will automatically reduce the power generation to ensure the balance of the power grid; if the power grid is lightly loaded, the photovoltaic power station will automatically increase the power generation to improve energy utilization efficiency.

[0042] In the present invention, the adaptive regulation technology of the photovoltaic power station of the power distribution system can also realize remote monitoring and management through an intelligent control system, thereby improving the reliability and safety of the power system and reducing the maintenance cost and operation cost of the power grid.

[0043] In the present invention, the application of the adaptive regulation technology of the photovoltaic power station in the power distribution system is of great significance, and can effectively solve the problems existing in the field of photovoltaic power generation and promote the development and utilization of clean energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0045] Attached Figure 1 It is a flow chart of a method for adaptively adjusting the output of a photovoltaic power station based on PMU;

[0046] Attached Figure 2 It is a schematic diagram of the power distribution system model and its simplified model. DETAILED DESCRIPTION

[0047] As shown in the figure, a method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data is provided. The method uses a phasor measurement unit (PMU) to actively and in real time manage each photovoltaic power station. The impedance between the grid connection point and the secondary side of the distribution station of the photovoltaic power station is accurately measured, and the optimal power generation of the photovoltaic power station is calculated using the impedance to minimize the power loss when the grid load changes dynamically, thereby improving the photovoltaic access capacity of the distribution network and the voltage offset level of the distribution network.

[0048] The method comprises the following steps:

[0049] Step S1: Determine the PMU installation and deployment location, use the PMU to monitor the electrical quantities at two nodes, the photovoltaic power station and the distribution transformer station of the distribution station in real time, and set the threshold value of the photovoltaic power station output fluctuation;

[0050] Step S2: start the photovoltaic power station output adaptive adjustment at a fixed time, determine whether the photovoltaic power station output fluctuation exceeds the set threshold, and when the output fluctuation is greater than the set threshold, perform real-time control of the photovoltaic power station output;

[0051] Step S3: Calculate the impedance between the grid connection point of the photovoltaic power station and the secondary side of the distribution station, and then calculate the optimal active and reactive power generation of the photovoltaic power station, and then adjust its output;

[0052] Step S4: read the PMU measurement value again to determine whether the voltage change amplitude exceeds the threshold. If it exceeds the threshold, update the optimal power generation of the photovoltaic power station and recalculate whether the voltage meets the threshold requirement.

[0053] The specific implementation process of determining the PMU installation and deployment location as described in step S1 is as follows: a PMU device is installed on the secondary side of the distribution station, and another PMU device is installed at the photovoltaic power station to provide measurement data with high time resolution and time stamp; a GPS is configured for the entire station to synchronize the time of the measurement device, and then calculate and extract the electrical quantities of the two nodes on the secondary side of the photovoltaic power station and the distribution station.

[0054] In step S1, the calculation formula for setting the threshold value of the photovoltaic power station output fluctuation is:

[0055] S t -S t-1 |≥S N *α%

[0056] Where S t is the current output power of the photovoltaic power station, S t-1 is the output power of the photovoltaic power station at the previous moment, S N is the rated output power of the photovoltaic power station, and α is an adjustable variable.

[0057] The timed start of the adaptive adjustment of the photovoltaic power station output described in step S2 is specifically: the photovoltaic power station output is monitored every t minutes. When the amplitude of the output fluctuation at the photovoltaic power station does not meet the threshold requirement, the power of the photovoltaic power station is adjusted according to the real-time output data of the photovoltaic power station with high sampling rate and high refresh rate obtained by the PMU; if the requirements are met, the power adjustment is not performed.

[0058] The specific implementation steps of measuring the impedance between the photovoltaic power station grid connection point and the secondary side of the distribution station described in step S3 are:

[0059] S3A, re-read the measured values ​​of the PMU, based on the Thevenin equivalent theorem, ignore the specific conditions of each branch, perform line equivalence and network simplification on the distribution system, define the node voltage on the secondary side of the distribution station as the reference voltage, and the system equivalent resistance and inductance are equal to the sum of the resistance and inductance between the secondary side of the distribution station and the photovoltaic power station;

[0060] S3B. The relationship between the actual active power and reactive power in the circuit at the current moment is expressed in a matrix as follows:

[0061] Where V t ,δ t They represent the voltage amplitude and phase angle of the photovoltaic power station node at the current moment, P t ,Q t They respectively represent the active and reactive power output by the photovoltaic power station at the current moment;

[0062] Similarly, the relationship between the actual active power and reactive power in the circuit at the previous moment is expressed in a matrix as follows:

[0063] Where V t-1 ,δ t-1 They represent the voltage amplitude and phase angle of the photovoltaic power station node at the last moment, P t-1 ,Q t-1 They respectively represent the active and reactive power output by the photovoltaic power station at the current moment;

[0064] Compare the actual active and reactive power relationship in the circuit at the current moment with that at the previous moment to obtain the system equivalent impedance, which can be expressed as:

[0065]

[0066] Where: ΔP represents the difference between the active power of the photovoltaic power station at the current moment and the previous moment, and ΔQ represents the difference between the reactive power of the photovoltaic power station at the current moment and the previous moment.

[0067] In step S3, the optimal active and reactive power generation of the photovoltaic power station is calculated, and the specific implementation process is: assuming that in order to make the line power loss zero, the power injected into the photovoltaic power station node is all provided by the photovoltaic power station, then the optimal active and reactive output of the photovoltaic power station at the next moment is:

[0068]

[0069] Where P ref.t+1 Indicates the active output reference value of the photovoltaic power station at the next moment, Q ref.t+1 Indicates the reactive power output reference value of the photovoltaic power station at the next moment, V t+1 ,δ t+1 They respectively represent the voltage amplitude and phase angle of the photovoltaic power station node at the next moment.

[0070] The updating of the active and reactive output of the photovoltaic power station in step S4 is specifically implemented as follows: reading the measured value of the PMU again, and if the node voltage of the photovoltaic power station changes, determining whether the grid topology has changed, if so, updating the equivalent impedance of the distribution network, otherwise the active and reactive output of the photovoltaic power station needs to be recalculated.

[0071] The specific steps to determine whether the distribution network topology has changed are:

[0072] S4A, define a threshold value of the power ratio change on both sides caused by the topology change as the switch change coefficient λ, and the selection of this coefficient is determined by the maximum load and the minimum load carried by the node;

[0073] S4B. Assume that the switch state change of the branch will cause the fluctuation of the power ratio between the secondary side of the distribution station and the photovoltaic power station. Therefore, calculate the power ratio η between the secondary side of the distribution station and the photovoltaic power station measured by the PMU:

[0074]

[0075] Where P0 is the power value measured by the PMU at the secondary side of the distribution station, and P1 is the power value measured by the PMU at the node of the photovoltaic power station. When compared with the switch change coefficient λ, if the relationship between the two changes, it is determined that the topology of the distribution network has changed; if the relationship between the two remains unchanged, it is determined that the topology has not changed.

[0076] The recalculation of the photovoltaic power station node voltage in step S4 is specifically implemented as follows: recalculating the corrected photovoltaic power station node voltage, determining whether the photovoltaic power station node voltage meets the threshold condition, and minimizing the target node voltage deviation and active and reactive power regulation;

[0077] In the method, the photovoltaic power station reduces network transmission costs and operating computing power by spontaneously performing regulation operations.

Claims

1. A method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data, characterized in that: The method uses a phasor measurement unit (PMU) to manage each photovoltaic power station, accurately measures the impedance between the grid connection point of the photovoltaic power station and the secondary side of the distribution station, and uses the impedance to calculate the optimal power generation of the photovoltaic power station, so as to minimize the power loss when the grid load changes dynamically, and improve the photovoltaic access capacity of the distribution network and the voltage offset level of the distribution network.

2. A method for adaptively adjusting output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: The method comprises the following steps: Step S1: Determine the PMU installation and deployment location, use the PMU to monitor the electrical quantities at two nodes, the photovoltaic power station and the distribution transformer station of the distribution station in real time, and set the threshold value of the photovoltaic power station output fluctuation; Step S2: start the photovoltaic power station output adaptive adjustment at a fixed time, determine whether the photovoltaic power station output fluctuation exceeds the set threshold, and when the output fluctuation is greater than the set threshold, perform real-time control of the photovoltaic power station output; Step S3: Calculate the impedance between the grid connection point of the photovoltaic power station and the secondary side of the distribution station, and then calculate the optimal active and reactive power generation of the photovoltaic power station, and then adjust its output; Step S4: Read the PMU measurement value again to determine whether the voltage change amplitude exceeds the threshold. If it exceeds the threshold, update the optimal power generation of the photovoltaic power station and recalculate whether the voltage meets the threshold requirement.

3. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: The specific implementation process of determining the PMU installation and deployment location as described in step S1 is as follows: a PMU device is installed on the secondary side of the distribution station, and another PMU device is installed at the photovoltaic power station to provide measurement data with high time resolution and time stamp; a GPS is configured for the entire station to synchronize the time of the measurement device, and then calculate and extract the electrical quantities of the two nodes on the secondary side of the photovoltaic power station and the distribution station.

4. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: In step S1, the calculation formula for setting the threshold value of the photovoltaic power station output fluctuation is: S t -S t-1 |≥S N *a% Where S t is the current output power of the photovoltaic power station, S t-1 is the output power of the photovoltaic power station at the previous moment, S N is the rated output power of the photovoltaic power station, and α is an adjustable variable.

5. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: The timed start of the adaptive adjustment of the photovoltaic power station output described in step S2 is specifically: the photovoltaic power station output is monitored every t minutes. When the amplitude of the output fluctuation at the photovoltaic power station does not meet the threshold requirement, the power of the photovoltaic power station is adjusted according to the real-time output data of the photovoltaic power station with high sampling rate and high refresh rate obtained by the PMU; if the requirements are met, the power adjustment is not performed.

6. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: The specific implementation steps of calculating the impedance between the photovoltaic power station grid connection point and the secondary side of the distribution station in step S3 are as follows: S3A, re-read the measured values ​​of the PMU, based on the Thevenin equivalent theorem, ignore the specific conditions of each branch, perform line equivalence and network simplification on the distribution system, define the node voltage on the secondary side of the distribution station as the reference voltage, and the system equivalent resistance and inductance are equal to the sum of the resistance and inductance between the secondary side of the distribution station and the photovoltaic power station; S3B. The relationship between the actual active power and reactive power in the circuit at the current moment is expressed in a matrix as follows: Where V t ,δ t They represent the voltage amplitude and phase angle of the photovoltaic power station node at the current moment, P t ,Q t They respectively represent the active and reactive power output by the photovoltaic power station at the current moment; Similarly, the relationship between the actual active power and reactive power in the circuit at the previous moment is expressed in a matrix as follows: Where V t-1 ,δ t-1 They represent the voltage amplitude and phase angle of the photovoltaic power station node at the last moment, P t-1 ,Q t-1 They respectively represent the active and reactive power output by the photovoltaic power station at the current moment; Compare the actual active and reactive power relationship in the circuit at the current moment with that at the previous moment to obtain the system equivalent impedance, which can be expressed as: Where: ΔP represents the difference between the active power of the photovoltaic power station at the current moment and the previous moment, and ΔQ represents the difference between the reactive power of the photovoltaic power station at the current moment and the previous moment.

7. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: In step S3, the optimal active and reactive power generation of the photovoltaic power station is calculated, and the specific implementation process is: assuming that in order to make the line power loss zero, the power injected into the photovoltaic power station node is all provided by the photovoltaic power station, then the optimal active and reactive output of the photovoltaic power station at the next moment is: Where P ref.t+1 Indicates the active output reference value of the photovoltaic power station at the next moment, Q ref.t+1 Indicates the reactive power output reference value of the photovoltaic power station at the next moment, V t+1 ,δ t+1 They respectively represent the voltage amplitude and phase angle of the photovoltaic power station node at the next moment.

8. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: The updating of the active and reactive output of the photovoltaic power station in step S4 is specifically implemented as follows: reading the measured value of the PMU again, and if the node voltage of the photovoltaic power station changes, determining whether the grid topology has changed, if so, updating the equivalent impedance of the distribution network, otherwise the active and reactive output of the photovoltaic power station needs to be recalculated.

9. A method for adaptively adjusting output of a photovoltaic power station based on PMU measurement data according to claim 8, characterized in that: The specific steps to determine whether the distribution network topology has changed are: S4A, define a threshold value of the power ratio change on both sides caused by the topology change as the switch change coefficient λ, and the selection of this coefficient is determined by the maximum load and the minimum load carried by the node; S4B. Assume that the switch state change of the branch will cause the fluctuation of the power ratio between the secondary side of the distribution station and the photovoltaic power station. Therefore, calculate the power ratio η between the secondary side of the distribution station and the photovoltaic power station measured by the PMU: Where P0 is the power value measured by the PMU at the secondary side of the distribution station, and P1 is the power value measured by the PMU at the node of the photovoltaic power station. When compared with the switch change coefficient λ, if the relationship between the two changes, it is determined that the topology of the distribution network has changed; if the relationship between the two remains unchanged, it is determined that the topology has not changed.

10. The method for adaptively adjusting the output of a photovoltaic power station based on PMU measurement data according to claim 1, characterized in that: The recalculation of the photovoltaic power station node voltage in step S4 is specifically implemented as follows: recalculating the corrected photovoltaic power station node voltage, determining whether the photovoltaic power station node voltage meets the threshold condition, and minimizing the target node voltage deviation and active and reactive power regulation; In the method, the photovoltaic power station reduces network transmission costs and operating computing power by spontaneously performing regulation operations.

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