Voltage stability control method for high-permeability photovoltaic power distribution network

Abstract

The invention relates to a voltage stability control method for a high-permeability photovoltaic power distribution network, relates to the field of power systems, and adopts two means of reactive compensation and active reduction through a voltage controller to limit the phenomenon that the voltage deviates from a safety value due to instability of the voltage and further generates serious out-of-limit. The method is composed of three stages of real-time prevention, voltage emergency control and power recovery. The operation stability and reliability of the power distribution network line can be improved.

Description

Technical Field

[0001] The invention relates to the field of power systems, and in particular to a method for controlling voltage stability of a distribution network containing high-penetration photovoltaics. Background Art

[0002] As the penetration rate of distributed photovoltaics in the distribution network increases, the problem of voltage instability becomes serious, mainly because the imbalance between the high power output of photovoltaic power generation and the low load on the user side may cause power flow back and line overvoltage. Existing technologies are difficult to effectively control voltage fluctuations, and network losses increase as the inverter adjusts reactive power. The insufficient level of intelligence in the distribution network limits its adaptability to photovoltaic power generation. At the same time, the space for photovoltaic power consumption is limited, the system and mechanism are not yet perfect, and financing is difficult and costly. There is a gap in technology with the international advanced level, and the DC arcing problem may also lead to safety accidents. These are challenges that need to be solved through technological innovation and policy adjustments. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a method for controlling the voltage stability of a distribution network containing high-penetration photovoltaics. Based on an in-depth analysis of the voltage regulation capability of a distributed photovoltaic system, a distributed voltage control strategy for a distribution network is proposed, which realizes rapid voltage control through coordinated reactive power compensation and active power reduction of the photovoltaic system. The proposed control scheme has the ability to adapt to changes in the distribution network topology. The strategy mainly consists of three stages: real-time prevention, voltage emergency control, and power recovery. The present invention can improve the stability and reliability of the operation of the distribution network lines.

[0004] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a method for controlling voltage stability of a distribution network containing high-penetration photovoltaics, the method comprising the following steps:

[0005] Step 1: When the distribution network lines are operating normally, all voltage controllers adopt real-time preventive control mode to prevent voltage over-limit phenomenon through reactive power compensation to ensure stable voltage operation; when the voltage is close to the upper limit, the photovoltaic prevents overvoltage by absorbing inductive reactive power; when the voltage is close to the lower limit, the photovoltaic prevents over-limit by outputting inductive reactive power;

[0006] Step 2: When the voltage at a node on the line exceeds the limit, if the voltage still does not return to the ideal state after real-time control, the first stage of the voltage emergency control stage is adopted: reactive power emergency coordination; the voltage controller first requests reactive power compensation from the downstream controller. When the voltage controller requests reactive power compensation from the downstream voltage controller, it first calculates the required reactive power compensation amount based on the real-time monitored voltage deviation and reactive power demand, and sends it to the downstream voltage controller in the form of a control signal. After receiving the request, the downstream voltage controller quickly evaluates its own reactive power compensation capability. If the downstream voltage controller has sufficient reactive power compensation capability, it will adjust its control strategy, increase reactive power output to meet the needs of the upstream voltage controller; at the same time, the downstream voltage controller also needs to monitor its own voltage level to ensure that while providing reactive power compensation, it will not affect its own voltage stability; if the reactive power compensation capacity of the downstream voltage controller is not enough to meet the needs of the upstream, it will feedback the actual reactive power compensation that can be provided to the upstream voltage controller, and the upstream controller will increase local reactive power compensation or adjust active power output to help restore the voltage to the ideal state. During the whole process, the downstream voltage controller also needs to continuously monitor the changes in voltage and reactive power so as to further adjust reactive power output when necessary to ensure stable voltage operation;

[0007] Step 3: When the reactive capacity of all upstream and downstream photovoltaics is exhausted, the second stage of the voltage emergency control stage is adopted: active emergency coordination; each voltage controller calculates the change in the voltage of the node that exceeds the limit after the photovoltaic power of each node is reduced by a certain amount based on the local monitoring data and the distributed photovoltaic interaction information of each node. According to the size of the change, the voltage regulation capability index is confirmed, and the voltage regulation capability of each node to the node that exceeds the limit is compared. The voltage controller with the strongest voltage regulation capability is selected to reduce the active power of the local photovoltaic; in addition, the reactive compensation amount in the previous step is related to the active power reduction amount in this step;

[0008] Step 4: After the above steps are completed, the power recovery stage is carried out; each voltage controller sets the photovoltaic active power reduction amount to 0 and restores the reactive power compensation amount to the reference value for local prevention in turn. The control order of the two is active power reduction first and reactive power compensation second, and upstream nodes first and downstream nodes later;

[0009] Step 5: Finally, under the condition of dynamic changes in network topology, each voltage controller determines the impedance value from each voltage controller node to the first power supply node and the upstream and downstream voltage controllers of this node based on the switch status of the interconnection line sent by the power grid automation distribution system to form a distributed communication network.

[0010] The present invention has the following beneficial effects and advantages:

[0011] 1. Combining the advantages and disadvantages of distributed control and centralized control, extracting the advantages of the two methods, the voltage stability control strategy proposed in this invention is formed.

[0012] 2. The adjustment process does not affect the power generation efficiency, and the power recovery speed is fast.

[0013] 3. It can adapt to changes in network topology and adjust output parameters according to the changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a distribution system communication network with 16 nodes;

[0015] Figure 2 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0017] like Figure 1 As shown, the distribution system communication network containing 16 nodes involved in the present invention includes 16 nodes, communication signals, distributed photovoltaics and voltage controllers, which are specifically marked in the picture.

[0018] like Figure 2 As shown, a method for controlling voltage stability of a distribution network containing high-penetration photovoltaics of the present invention comprises the following steps:

[0019] Step 1: When the distribution network lines are operating normally, all voltage controllers use real-time preventive control to prevent voltage over-limit through reactive power compensation, thereby ensuring stable voltage operation. When the voltage approaches the upper limit, distributed photovoltaics prevent overvoltage by absorbing inductive reactive power; when the voltage approaches the lower limit, distributed photovoltaics prevent over-limit by outputting inductive reactive power;

[0020] Step 2: When the voltage of a node on the line exceeds the limit, if the voltage still does not return to the ideal state after real-time control, the first stage of the voltage emergency control stage is adopted: reactive emergency coordination; the voltage controller first requests reactive compensation from the downstream voltage controller. When the voltage controller requests reactive compensation from the downstream voltage controller, it first calculates the required reactive compensation amount based on the voltage deviation and reactive power demand monitored in real time, and sends it to the downstream voltage controller in the form of a control signal. After receiving the request, the downstream voltage controller needs to quickly evaluate its own reactive compensation capability, including the current reactive power reserve, the adjustment range of the photovoltaic inverter, and other factors that may affect the reactive output. If the downstream voltage controller has sufficient reactive compensation capability, it will immediately adjust its control strategy and increase reactive output to meet the needs of the upstream controller. At the same time, the downstream voltage controller also needs to monitor its own voltage level to ensure that while providing reactive compensation, it will not affect its own voltage stability. If the reactive power compensation capacity of the downstream voltage controller is insufficient to meet the upstream demand, it needs to feedback the actual reactive power compensation that can be provided to the upstream voltage controller, and the upstream voltage controller may need to take other measures, such as increasing local reactive power compensation or adjusting active power output, to help restore the voltage to an ideal state. During the entire process, the downstream voltage controller also needs to continuously monitor the changes in voltage and reactive power so as to further adjust reactive power output when necessary to ensure stable voltage operation;

[0021] Step 3: When the reactive capacity of all distributed photovoltaics upstream and downstream is exhausted, the second stage of the voltage emergency control stage is adopted: active power emergency coordination. Each voltage controller calculates the change in voltage of the node that exceeds the limit after the distributed photovoltaics of each node reduce a certain amount of active power based on local monitoring data and the distributed photovoltaic interaction information of each node. According to the size of the change, the voltage regulation capability index is confirmed, and the voltage regulation capability of each node to the node that exceeds the limit is compared. The voltage controller with the strongest voltage regulation capability is selected to reduce the active power of the local distributed photovoltaics. In addition, the reactive compensation amount in the previous step is related to the active power reduction amount in this step;

[0022] Step 4: After the above steps are completed, the power recovery stage is carried out. Each voltage controller sets the photovoltaic active power reduction to 0 and restores the reactive power compensation to the reference value for local prevention in turn. The control order of the two is active power first, then reactive power, and upstream nodes first, then downstream nodes;

[0023] Step 5: Finally, under the condition of dynamic changes in network topology, each voltage controller determines the impedance value from each controller node to the first power supply node and the upstream and downstream controllers of this node based on the switch status of the interconnection line sent by the power grid automation distribution system, thus forming a new distributed communication network.

[0024] Furthermore, in step 2, when requesting reactive power compensation from the downstream and upstream voltage controllers, the reactive power compensation amount is calculated as follows:

[0025] ;

[0026] in, Indicates the reactive power compensation amount when requesting reactive power compensation from the downstream controller. Indicates the reactive power compensation amount when requesting reactive power compensation from the upstream controller. is a constant related to reactive power compensation, Indicates the upstream node The voltage value, Indicates the downstream node The voltage value, Indicates the voltage of the node that exceeds the limit. Indicates the line reactance value between each node.

[0027] Furthermore, in step 3, the calculation formula of the voltage regulation capability index is:

[0028] ;

[0029] in, It indicates the voltage regulation capability of node N after the downstream node of node N reduces the active power of local photovoltaic. It indicates the voltage regulation capability of node N after the upstream node of the over-limit node N reduces the active power of the local photovoltaic. Indicates the active power reduced by the node photovoltaic, Indicates the reactive power compensation amount, The line resistance value between each node.

[0030] Furthermore, in step 3, the relationship between the reactive power compensation amount and the active power reduction amount is:

[0031] ;

[0032] in, Indicates the minimum power factor.

Claims

1. A method for controlling voltage stability of a distribution network containing high penetration photovoltaics, characterized in that: The method comprises the following steps: Step 1: When the distribution network lines are operating normally, all voltage controllers adopt real-time preventive control mode to prevent voltage over-limit phenomenon through reactive power compensation to ensure stable voltage operation; when the voltage is close to the upper limit, the photovoltaic prevents overvoltage by absorbing inductive reactive power; when the voltage is close to the lower limit, the photovoltaic prevents over-limit by outputting inductive reactive power; Step 2: When the voltage at a node on the line exceeds the limit, if the voltage still does not return to the ideal state after real-time control, the first stage of the voltage emergency control stage is adopted: reactive power emergency coordination; the voltage controller first requests reactive power compensation from the downstream controller. When the voltage controller requests reactive power compensation from the downstream voltage controller, it first calculates the required reactive power compensation amount based on the real-time monitored voltage deviation and reactive power demand, and sends it to the downstream voltage controller in the form of a control signal. After receiving the request, the downstream voltage controller quickly evaluates its own reactive power compensation capability. If the downstream voltage controller has sufficient reactive power compensation capability, it will adjust its control strategy, increase reactive power output to meet the needs of the upstream voltage controller; at the same time, the downstream voltage controller also needs to monitor its own voltage level to ensure that while providing reactive power compensation, it will not affect its own voltage stability; if the reactive power compensation capacity of the downstream voltage controller is not enough to meet the needs of the upstream, it will feedback the actual reactive power compensation that can be provided to the upstream voltage controller, and the upstream controller will increase local reactive power compensation or adjust active power output to help restore the voltage to the ideal state. During the whole process, the downstream voltage controller also needs to continuously monitor the changes in voltage and reactive power so as to further adjust reactive power output when necessary to ensure stable voltage operation; Step 3: When the reactive capacity of all upstream and downstream photovoltaics is exhausted, the second stage of the voltage emergency control stage is adopted: active emergency coordination; each voltage controller calculates the change in the voltage of the node that exceeds the limit after the photovoltaic power of each node is reduced by a certain amount based on the local monitoring data and the distributed photovoltaic interaction information of each node. According to the size of the change, the voltage regulation capability index is confirmed, and the voltage regulation capability of each node to the node that exceeds the limit is compared. The voltage controller with the strongest voltage regulation capability is selected to reduce the active power of the local photovoltaic; in addition, the reactive compensation amount in the previous step is related to the active power reduction amount in this step; Step 4: After the above steps are completed, the power recovery stage is carried out; each voltage controller sets the photovoltaic active power reduction amount to 0 and restores the reactive power compensation amount to the reference value for local prevention in turn. The control order of the two is active power reduction first and reactive power compensation second, and upstream nodes first and downstream nodes later; Step 5: Finally, under the condition of dynamic changes in network topology, each voltage controller determines the impedance value from each voltage controller node to the first power supply node and the upstream and downstream voltage controllers of this node based on the switch status of the interconnection line sent by the power grid automation distribution system to form a distributed communication network.

2. A method for controlling voltage stability of a distribution network containing high penetration photovoltaics according to claim 1, characterized in that: In step 2, when requesting reactive power compensation from the downstream and upstream controllers, the reactive power compensation amount is calculated as follows: ； in, Indicates the reactive power compensation amount when requesting reactive power compensation from the downstream controller. Indicates the reactive power compensation amount when requesting reactive power compensation from the upstream controller. is a constant related to reactive power compensation, Indicates the upstream node The voltage value, Represents the downstream node The voltage value, Indicates the voltage of the node that exceeds the limit. Indicates the line reactance value between each node.

3. A method for controlling voltage stability of a distribution network containing high penetration photovoltaics according to claim 1, characterized in that: In step 3, the calculation formula of the voltage regulation capability index is: ； in, It indicates the voltage regulation capability of node N after the downstream node of node N reduces the active power of local photovoltaic. It indicates the voltage regulation capability of node N after the upstream node of the over-limit node N reduces the active power of the local photovoltaic. Indicates the active power reduced by the node photovoltaic, Indicates the reactive power compensation amount, The line resistance value between each node.

4. A method for controlling voltage stability of a distribution network containing high penetration photovoltaics according to claim 1, characterized in that: In step 3, the relationship between the reactive power compensation amount and the active power reduction amount is: ； in, Indicates the minimum power factor.

Images