Cooperative control method and cooperative control device for grid connection of micro-grid

Abstract

The invention discloses a cooperative control method and a cooperative control device for grid connection of a micro-grid. The method comprises the steps of determining whether the micro-grid can balance supply and demand according to a difference value between power supply power of the micro-grid and a load; when the micro-grid can balance supply and demand, the micro-grid islanding operation is controlled; when the micro-grid cannot balance supply and demand, controlling the power distribution network to be connected with the micro-grid through a common connection point, and controlling an energy storage module connected with the common connection point to charge or discharge so as to stabilize the voltage of the common connection point; and when the node voltage of the power distribution node of the power distribution network exceeds the limit, adjusting the node voltage of the power distribution node by adjusting the reactive power of a photovoltaic inverter connected with the power distribution node in the power distribution network or the position of a tap of an on-load tap changing transformer in the power distribution network. According to the invention, the cooperative operation capability of the micro-grid and the power distribution network can be improved, the safety and reliability of a power system are enhanced, and the resource utilization and economic benefits of the power system are optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a cooperative control method and a cooperative control device for a microgrid to be connected to a grid. Background Art

[0002] The coordinated operation of a distribution network and a microgrid can improve the safety, stability, and economy of the entire power system. When the microgrid is connected to the distribution network for operation, the microgrid can not only utilize the power support provided by the distribution network, but also feed its own renewable energy and energy storage resources back to the distribution network, thereby realizing two-way energy flow.

[0003] However, there is a problem in the prior art that it is difficult to ensure the coordinated safety and economy of the overall power system when the microgrid is connected to the distribution network for operation. Summary of the Invention

[0004] The present invention provides a cooperative control method and a cooperative control device for a microgrid to be connected to a grid, so as to ensure the coordinated safety of the entire power network when the microgrid is connected to the distribution network for operation, and improve the reliability and economy of the power system.

[0005] According to one aspect of the present invention, there is provided a cooperative control method for a microgrid to be connected to a grid, including:

[0006] Determining whether the microgrid can balance power supply and demand according to the difference between the power supply power and the load of the microgrid;

[0007] When the microgrid can balance power supply and demand, controlling the microgrid to operate in island mode;

[0008] When the microgrid cannot balance power supply and demand, controlling the distribution network to be connected to the microgrid through a common connection point, and stabilizing the voltage of the common connection point by controlling the charging or discharging of an energy storage module connected to the common connection point;

[0009] When the node voltage of a distribution node of the distribution network is out of limit, adjusting the reactive power of a photovoltaic inverter connected to the distribution node in the distribution network or the position of a tap of a on-load tap-changer in the distribution network to adjust the node voltage of the distribution node.

[0010] According to another aspect of the present invention, there is provided a cooperative control device for a microgrid to be connected to a grid, including: the microgrid is connected to the distribution network at a common connection point; the cooperative control device includes:

[0011] A determination module, configured to determine whether the microgrid can balance power supply and demand according to the difference between the power supply power and the load of the microgrid;

[0012] A first control module, configured to control the microgrid to operate in island mode when the microgrid can balance power supply and demand;

[0013] A second control module, configured to control the connection between the distribution network and the microgrid through a common connection point and charge or discharge an energy storage module connected to the common connection point to stabilize the voltage of the common connection point when the microgrid is unable to balance power supply and demand.

[0014] An adjustment module, configured to adjust the node voltage of a distribution node in the distribution network by adjusting the reactive power of a photovoltaic inverter connected to the distribution node or the position of a tap of a on-load tap-changer in the distribution network when the node voltage of the distribution node in the distribution network exceeds the limit.

[0015] In an embodiment of the present invention, it is determined whether the microgrid needs to operate in coordination with the distribution network according to the difference between the power supply of the microgrid and the load. If the microgrid needs to operate in coordination with the distribution network, the voltage stability at the common connection point between the distribution network and the microgrid is ensured by controlling the energy storage module, and the voltage stability of the distribution node is ensured by controlling the reactive power of the photovoltaic inverter or the tap of the on-load tap-changer. If the microgrid does not need to operate in coordination with the distribution network, the microgrid operates in island mode to achieve the highest economic benefits. The present invention improves the coordinated operation ability of the microgrid and the distribution network through an effective voltage control strategy, not only enhancing the security and reliability of the power system, but also optimizing resource utilization and economic benefits.

[0016] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings without creative efforts based on these drawings.

[0018] Figure 1 It is a flowchart of a coordinated control method for microgrid grid connection provided by an embodiment of the present invention;

[0019] Figure 2 It is a flowchart of another coordinated control method for microgrid grid connection provided by an embodiment of the present invention;

[0020] Figure 3 It is a flowchart of another coordinated control method for microgrid grid connection provided by an embodiment of the present invention;

[0021] Figure 4Schematic diagram of the principle of the photovoltaic inverter control device provided by the embodiment of the present invention;

[0022] Figure 5 Flowchart of a distribution network voltage control provided by the embodiment of the present invention;

[0023] Figure 6 Schematic diagram of the control process of a on-load tap-changer provided by the embodiment of the present invention;

[0024] Figure 7 Flowchart of another coordinated control method for microgrid grid connection provided by the embodiment of the present invention;

[0025] Figure 8 Schematic diagram of the structure of a coordinated control device for microgrid grid connection provided by the embodiment of the present invention;

[0026] Figure 9 Schematic diagram of a coordinated control system for microgrid grid connection provided by the embodiment of the present invention;

[0027] Figure 10 Connection relationship diagram of the transmission network and the distribution network provided by the embodiment of the present invention;

[0028] Figure 11 Topological diagram of the microgrid provided by the embodiment of the present invention;

[0029] Figure 12 Microgrid voltage curve diagram adjusted by using the coordinated control method for microgrid grid connection provided by the embodiment of the present invention;

[0030] Figure 13 Distribution network photovoltaic output and photovoltaic node power curve diagram adjusted by using the coordinated control method for microgrid grid connection provided by the embodiment of the present invention;

[0031] Figure 14 Distribution network voltage curve diagram adjusted by using the coordinated control method for microgrid grid connection provided by the embodiment of the present invention. Detailed implementation manners

[0032] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0034] Figure 1 FIG. is a flowchart of a coordinated control method for a microgrid to be connected to the grid according to an embodiment of the present invention. This embodiment is applicable to the situation where the microgrid is connected to and operates with the distribution grid. This method can be executed by a coordinated control device for microgrid grid connection, and the coordinated control device can be implemented in the form of hardware and / or software. As Figure 1 shown, the method includes:

[0035] S110. Determine whether the microgrid can balance power supply and demand according to the difference between the power supply of the microgrid and the load.

[0036] Among them, the difference between the power supply of the microgrid and the load refers to the difference between the total power provided by all power generation devices (such as photovoltaic, wind energy, energy storage, etc.) in the microgrid (power supply) and the total power required by users (load) at a specific moment. Balancing power supply and demand means that during the operation of the microgrid, the power supply and the load reach a balanced state.

[0037] Specifically, determining whether the microgrid can balance power supply and demand can timely grasp the current operating state of the microgrid, and then judge whether it is necessary to further adjust the microgrid according to the current state of the microgrid, providing a basis for the subsequent adjustment process.

[0038] S120. When the microgrid can balance power supply and demand, control the microgrid to operate in island mode.

[0039] Among them, island operation refers to the state where the microgrid can still operate independently and supply power to its internal load after being disconnected from the main grid. In this mode, the microgrid uses its internal power generation resources (such as renewable energy, energy storage devices, etc.) to meet the power demand by itself and does not rely on the external grid.

[0040] Specifically, when the microgrid can balance power supply and demand, the microgrid operating in island mode can effectively manage its internal power generation and energy storage resources, maximize the utilization rate of renewable energy, reduce the demand for external power supply, and thus reduce energy waste.

[0041] S130. When the microgrid cannot balance power supply and demand, control the connection between the distribution network and the microgrid through the point of common coupling (PCC), and charge or discharge the energy storage module connected to the PCC to stabilize the voltage at the PCC.

[0042] Among them, the point of common coupling refers to the connection interface between the microgrid and the distribution network. Through this interface, the microgrid can exchange electric power with the distribution network. At this connection point, the power flow can be bidirectional, that is, the microgrid can supply power to the distribution network or obtain power from the distribution network. The energy storage module refers to the device connected to the PCC for storing electric energy, which can be charged when the power demand at the PCC is low or the power supply is excessive, and discharged when the power demand is high or the power supply is insufficient, so as to regulate the power supply at the PCC.

[0043] Specifically, when the microgrid cannot balance power supply and demand, by controlling the PCC and the energy storage module, the smooth grid connection between the microgrid and the distribution network can be ensured, the voltage can be effectively stabilized, the flexibility and economy of the power system can be improved, and further the reliability of the coordinated operation between the microgrid and the distribution network can be enhanced.

[0044] S140. When the node voltage of the distribution node in the distribution network exceeds the limit, adjust the reactive power of the photovoltaic inverter connected to the distribution node in the distribution network or the position of the tap of the on-load tap-changer transformer in the distribution network to adjust the node voltage of the distribution node.

[0045] Among them, the distribution node refers to the node in the distribution network for power distribution, usually referring to the interface or distribution point where power flows from the distribution network to users. The node voltage refers to the voltage level measured at the distribution node, which can affect the power transmission efficiency and the normal operation of user equipment. The photovoltaic inverter refers to the device that converts the direct current generated by the photovoltaic power generation system into alternating current. In addition to the conversion function, modern photovoltaic inverters can also adjust the reactive power to support the voltage stability of the power grid. Reactive power refers to the power used to establish the electric field and magnetic field in the power system. By adjusting the reactive power, the node voltage can be maintained within a reasonable range. The on-load tap-changer transformer refers to a transformer that can adjust the output voltage during load operation. It realizes voltage regulation by changing the position of the tap of the transformer to adapt to different load demands and maintain voltage stability. The tap refers to the connection point in the winding of the on-load tap-changer transformer. By changing the position of the tap, the output voltage of the transformer can be adjusted to meet the load change requirements in the distribution network.

[0046] Specifically, by adjusting the reactive power of the photovoltaic inverter and the tap position of the on-load tap-changer transformer, the distribution network can effectively control the voltage level of the distribution nodes, ensure that it remains within a safe and stable range, and prevent damage to the power equipment in the distribution network caused by too high or too low node voltage.

[0047] In the embodiment of the present invention, it is determined whether the microgrid needs to operate in coordination with the distribution network according to the difference between the power supply of the microgrid and the load. If the microgrid needs to operate in coordination with the distribution network, the voltage stability at the common connection point between the distribution network and the microgrid is ensured by controlling the energy storage module, and the voltage stability of the distribution nodes is ensured by controlling the tap of the photovoltaic inverter or the on-load tap-changer transformer. If the microgrid does not need to operate in coordination with the distribution network, the microgrid operates in island mode to achieve the highest economic benefits. Through effective voltage control strategies, the present invention improves the coordinated operation ability of the microgrid and the distribution network, not only enhancing the security and reliability of the power system, but also optimizing resource utilization and economic benefits.

[0048] Figure 2 It is a flowchart of another coordinated control method for microgrid grid connection provided by the embodiment of the present invention. On the basis of the above embodiments, optionally, as Figure 2 shown, the method includes:

[0049] S110. Determine whether the microgrid can balance power supply and demand according to the difference between the power supply of the microgrid and the load.

[0050] S120. When the microgrid can balance power supply and demand, control the microgrid to operate in island mode.

[0051] S131. When the microgrid cannot balance power supply and demand, control the distribution network and the microgrid to be connected through the common connection point.

[0052] Specifically, if the microgrid cannot balance power supply and demand, controlling the connection between the distribution network and the microgrid can effectively adjust the power supply strategy. In the case of insufficient power supply or too high load in the microgrid, additional power can be obtained from the distribution network to meet the demand, ensuring that users can also obtain stable power supply during peak hours. In the case of excessive power supply or too low load in the microgrid, the excess power can be transmitted to the distribution network to reduce energy waste.

[0053] S132. When the voltage on the distribution network side is lower than the voltage on the microgrid side, control the energy storage module to discharge to the common connection point.

[0054] Specifically, in the power system, when the power supply is insufficient, the voltage will drop. By the voltage difference between the distribution network side and the microgrid side, the current supply-demand state and the direction of power flow at the common node can be effectively judged. When the voltage on the distribution network side is lower than that on the microgrid side, the energy storage module is controlled to discharge to the common connection point, which can provide the required power in time and ensure the stability and reliability of the power system.

[0055] S133. When the voltage on the distribution network side is higher than that on the microgrid side, the distribution network is controlled to charge the energy storage module through the common connection point.

[0056] Specifically, in the power system, when the power supply is excessive, the voltage will rise. By the voltage difference between the distribution network side and the microgrid side, the current supply-demand state and the direction of power flow at the common node can be effectively judged. When the voltage on the distribution network side is higher than that on the microgrid side, the energy storage module is controlled to absorb electric energy from the common connection point, timely replenish energy for the energy storage module, and reduce the waste of resources at the same time.

[0057] Optionally, the energy storage module includes an energy storage battery and a capacitor bank.

[0058] Among them, the energy storage battery refers to a device that can convert electric energy into chemical energy for storage and convert it back into electric energy for release when needed. Common types include lithium-ion batteries, lead-acid batteries, nickel-metal hydride batteries, etc. The capacitor bank refers to an energy storage device composed of multiple capacitors, which is used to store electric energy and release it quickly when needed. The capacitor stores energy through an electric field, and typical applications include filtering, smoothing voltage, and providing high-power output for a short time.

[0059] Specifically, the energy storage module includes an energy storage battery and a capacitor bank. The former is suitable for long-term storage and stable energy output, while the latter is suitable for fast response and high-power output within a short time. The combination of the two can improve the flexibility and reliability of the energy storage module and optimize the power management strategy.

[0060] S140. When the node voltage of the distribution node in the distribution network is out of limit, the reactive power of the photovoltaic inverter connected to the distribution node in the distribution network or the position of the tap of the on-load tap-changer in the distribution network is adjusted to adjust the node voltage of the distribution node.

[0061] In the embodiment of the present invention, the charge and discharge state of the energy storage module is determined by the voltage level between the distribution network side and the microgrid side. It charges when the voltage on the distribution network side is high and discharges when the voltage on the distribution network side is low, which helps to balance the supply-demand relationship between the distribution network and the microgrid, can improve the energy utilization efficiency, and ensure the stable supply of power.

[0062] Figure 3 It is a flowchart of another cooperative control method for microgrid grid connection provided by the embodiment of the present invention. On the basis of the above embodiments, optionally, asFigure 3 As shown, the method includes:

[0063] S110. Determine whether the microgrid can balance power supply and demand according to the difference between the power supply power and the load of the microgrid.

[0064] S120. When the microgrid can balance power supply and demand, control the microgrid to operate in island mode.

[0065] S130. When the microgrid cannot balance power supply and demand, control the distribution network and the microgrid to be connected through a common connection point, and charge or discharge the energy storage module connected to the common connection point to stabilize the voltage of the common connection point.

[0066] S141. In the case of node voltage violation, preferentially adjust the node voltage by adjusting the reactive power of the photovoltaic inverter connected to the distribution node.

[0067] In the embodiments of the present invention, the photovoltaic inverter can affect the node voltage by changing its output reactive power (for example, providing or absorbing reactive power). Increasing the reactive power output can increase the node voltage, while absorbing reactive power can reduce the node voltage.

[0068] Specifically, the reactive power regulation of the photovoltaic inverter is usually fast-responding and can affect the node voltage in a short time to adapt to load changes.

[0069] Optionally, based on the above embodiments, S141 can be further refined as follows: in the case of node voltage violation, when the distributed photovoltaic output reaches the set power, adjust the reactive power of the photovoltaic inverter according to the node voltage according to the following formula:

[0070]

[0071] where V represents the node voltage, P pv represents the distributed photovoltaic output, Q pv represents the reactive power of the photovoltaic inverter, represents the set power, Q max represents the maximum reactive power that can be actually compensated when the distributed photovoltaic output reaches the set power, V min represents the minimum voltage limit of the distribution node, V ref1 represents the first reference voltage, V ref2 represents the second reference voltage, the minimum voltage limit is less than the first reference voltage, the first reference voltage is less than the second reference voltage; in the case of voltage violation, the node voltage is less than or equal to the minimum voltage limit.

[0072] Among them, the distributed photovoltaic output refers to the power output generated by a distributed photovoltaic power generation system, which can reflect the energy that the photovoltaic equipment can provide under specific conditions (such as specific illumination and specific temperature). The set power refers to the target output power of the distributed photovoltaic under specific conditions. In the embodiment of the present invention, the set power is the maximum active power that the distributed photovoltaic can generate during actual operation, which is less than the theoretical maximum active power P pv1 , that is The theoretical maximum active power can be the total installed capacity of the distributed photovoltaic system. The minimum voltage limit refers to the lowest voltage level allowed by the distribution node. The first reference voltage refers to the lower limit when the distributed photovoltaic system operates normally. The second reference voltage refers to the upper limit when the distributed photovoltaic system operates normally. Exemplarily, the first reference voltage can be 0.85 times the rated voltage of the distribution node, and the second reference voltage can be 0.95 times the rated voltage of the distribution node.

[0073] Figure 4 is a schematic diagram of the principle of the photovoltaic inverter control device provided by the embodiment of the present invention. Refer to Figure 4 , the method of adjusting the reactive power of the photovoltaic inverter through this formula is described as follows: When the photovoltaic output P pv is located in the red area (between P pv1 and P pv2 ), the active power output by the distributed photovoltaic system is large and the reactive power is small, and voltage regulation cannot be performed at this time. When the photovoltaic output is in the blue area (between P pv2 and P pv3 ), the photovoltaic can output a certain amount of reactive power, that is, it has a certain voltage regulation ability. When the photovoltaic output is in the yellow area (between P pv3 and the horizontal axis Q pv ), at this time, the active power output by the photovoltaic is small and the reactive power is large, that is, the voltage regulation ability is the strongest.

[0074] When the voltage is out of limit, that is, V≤V min , the photovoltaic output reaches the set power (the maximum active power that the photovoltaic can generate during actual operation), and its control scheme is that the node voltage where the photovoltaic is connected to the distribution network is lower than the minimum voltage limit V min of the distribution node. At this time, the photovoltaic performs a compensation action, and the compensation value is Q max . When the reactive power of this node voltage is compensated to be between the minimum voltage limit V min of the distribution node and the first reference voltage V ref1 , continue to control the photovoltaic system to perform reactive power compensation. When the compensated voltage reaches between the first reference voltage V ref1 and the second reference voltage V ref2 , stop the compensation.

[0075] Specifically, by dynamically adjusting the reactive power of the photovoltaic inverter according to the node voltage, the voltage stability of the distribution network can be effectively improved, the utilization of renewable energy can be optimized, and the ability of the system to cope with load changes can be enhanced.

[0076] S142. When the photovoltaic inverter connected to the distribution node cannot regulate the node voltage, the tap position of the on-load tap-changer is adjusted to regulate the node voltage.

[0077] In the embodiment of the present invention, the tap position of the on-load tap-changer determines its output voltage. By changing the tap of the tap-changer, the output voltage of the transformer can be increased or decreased, thereby regulating the voltage of the distribution node.

[0078] Specifically, the on-load tap-changer can effectively cope with large or continuous load changes, can provide voltage support within a large range, and ensure the stability of the distribution network.

[0079] Among them, the priority of using the photovoltaic inverter to regulate reactive power is because it has a rapid response and does not require physical operation, can quickly adapt to the dynamic changes of the power grid, and stabilize the voltage in a timely manner. By preferentially using the photovoltaic inverter, the voltage problem can be quickly alleviated, and time can be gained for the subsequent tap adjustment of the on-load tap-changer if necessary. If the photovoltaic inverter cannot solve the problem, then the tap adjustment of the on-load tap-changer is used as a supplement to ensure the flexibility and redundancy of the power system.

[0080] Specifically, Figure 5 is a flowchart of a distribution network voltage control provided by an embodiment of the present invention. As Figure 5 shown, the process includes: collecting the voltage parameters of the power grid, and then judging whether the voltage value V i collected at the i-th distribution node is out of limit. If it is out of limit, the control target is selected; otherwise, the current control state is maintained. After selecting the control target, it is judged whether the distributed photovoltaic can participate in the regulation. If it can participate in the regulation, the distributed photovoltaic regulation is adopted, and then it is judged whether the adjusted V i meets the requirements; if not, the weighted average value of the distributed photovoltaic and the node voltage is calculated, and then the on-load tap-changer tap operates, and then it is judged whether the adjusted V i meets the requirements. If the adjusted V i meets the adjustment requirements, the current control state is maintained; otherwise, the control target is reselected until V i meets the requirements.

[0081] Optionally, based on the above embodiments, S142 can be further refined as follows: Determine the target tap position of the on-load tap-changer according to the difference between the rated voltage of the distribution network and the weighted average of the node voltages of the distribution nodes connected to the photovoltaic inverter, and the single-step regulated voltage of the on-load tap-changer.

[0082] Among them, the rated voltage of the distribution network refers to the standard voltage value based on which the power system is designed and operated under normal operating conditions, reflecting the working voltage level of the power grid. The single-step regulated voltage refers to the voltage value changed each time when the on-load tap-changer adjusts the output voltage. The single-step regulation is usually a fixed value, used to gradually increase or decrease the output voltage of the transformer to keep the voltage of the distribution network within the set range. The target tap position refers to the specific tap position of the on-load tap-changer determined according to the power system requirements and voltage regulation strategy. Each tap position corresponds to a different output voltage level, and the selection of the target tap position aims to optimize voltage control and system operation.

[0083] Specifically, the weighted average of the node voltages of the distribution nodes can be determined by the following formula:

[0084]

[0085] where, V a is the weighted average of the node voltages of the distribution nodes, σ i is the i-th distribution node, and V i is the voltage value collected at the i-th distribution node.

[0086] Then, the tap position of the on-load tap-changing transformer is determined according to the following formula:

[0087]

[0088] where, ΔN tap is the target tap position of the on-load tap-changer, V step is the single-step regulated voltage of the on-load tap-changer, and V N is the rated voltage of the distribution network.

[0089] Specifically, Figure 6 is a schematic diagram of the control process of an on-load voltage regulator provided by an embodiment of the present invention. As Figure 6 shown, the process includes: obtaining the node voltage of the distribution node, then calculating the weighted average of the node voltages, and adjusting the tap position of the on-load tap-changer according to the weighted average and the rated voltage V N of the distribution network, thereby adjusting the node voltage of the distribution node.

[0090] In the embodiments of the present invention, by preferentially adjusting the reactive power of the photovoltaic inverter to control the node voltage, fast and flexible voltage regulation can be achieved; when the photovoltaic inverter cannot meet the demand, the on-load tap-changing transformer is further used for adjustment to ensure the stability and reliability of the power system. This regulation method of the present invention makes full use of the voltage regulation capabilities of the photovoltaic inverter and the on-load tap-changing transformer, and improves the overall operation efficiency of the power system.

[0091] Optionally, based on the above embodiments, S110 can be further refined and includes:

[0092] When the difference between the power supply of the microgrid and the load is equal to 10% of the load, it is determined that the microgrid can balance power supply and demand; when the difference between the power supply of the microgrid and the load is not equal to 10% of the load, it is determined that the microgrid cannot balance power supply and demand.

[0093] Specifically, the power generation of renewable energy (such as wind energy and solar energy) in the microgrid is greatly affected by weather and environmental changes. A difference of 10% allows the system to have a certain fluctuation space in the short term. By setting a difference of 10%, the need to frequently adjust the operating parameters of the microgrid due to minor fluctuations can be reduced, and the operating efficiency of the power grid is improved.

[0094] Optionally, based on the above embodiments, S120 can be further refined and includes: adjusting the output of the microgrid according to the following formula:

[0095]

[0096] where P mg,i,k is the actual output value of the i-th microgrid at the k-th moment, N mg is the total number of microgrids, is the maximum output of the i-th microgrid at the (k + 1)-th moment.

[0097] Specifically, the maximum output of the i-th microgrid at the (k + 1)-th moment can be calculated based on the output value of the microgrid at the k-th moment and is a fixed value. By distributing the maximum output of the next moment according to the ratio of the output of the current microgrid to the sum of the outputs of all microgrids, it can be ensured that each microgrid reasonably obtains the maximum output according to its actual output situation, thus avoiding waste of electric power resources. Through dynamic adjustment, the microgrid can optimize the power usage efficiency under different operating conditions.

[0098] Figure 7 This is a flowchart of another cooperative control method for microgrid grid connection provided by the embodiments of the present invention. Optionally, based on the above embodiments, the distribution network is electrically connected to the transmission network. As Figure 7 shown, this cooperative control method further includes:

[0099] S210. Establish the first constraint conditions of the transmission grid and the second constraint conditions of the distribution grid respectively.

[0100] Among them, the first constraint conditions refer to the technical and safety limitations that the transmission grid must comply with during operation, including voltage limits, power flow limits, equipment capacities, etc. These conditions ensure that the transmission grid operates in a stable and safe state, preventing overloads and faults. The second constraint conditions refer to the constraint conditions that the distribution grid needs to comply with during operation, usually including requirements such as load balance, regulation range of tap transformers, and power quality. These constraints ensure that the distribution grid can supply power as required and maintain the quality of electrical energy.

[0101] Optionally, the first constraint conditions include:

[0102]

[0103] θ min ≤θ≤θ max

[0104]

[0105] Where P gen,i is the power generation of transmission node i in the transmission grid, P load,i is the load power of transmission node i in the transmission grid, f T,ij is the power flow from transmission node i to its adjacent transmission node j, N T (i) is the set of all neighboring transmission nodes connected to transmission node i in the transmission grid; and are the maximum and minimum values of the power flow from transmission node i to its adjacent transmission node j respectively, θ is the voltage phase angle of the transmission grid, θ min and θ max are the maximum and minimum values of the voltage phase angle respectively, and are the maximum and minimum values of the power generation of transmission node i in the transmission grid respectively.

[0106] Optionally, the second constraint conditions include:

[0107]

[0108] Where f D,ij is the actual power flow from distribution node i to its adjacent distribution node j in the distribution grid, and are the maximum and minimum values of the actual power flow from distribution node i to its adjacent distribution node j respectively, N D (i) is the set of all adjacent distribution nodes connected to distribution node i in the distribution grid, where For the reactive power flow from distribution node i to its adjacent distribution node j in the distribution network, and are the maximum and minimum values of the reactive power flow from distribution node i to its adjacent distribution node j respectively, P pv, i is the active power output of the distributed photovoltaic at distribution node i in the distribution network, and are the maximum and minimum values of the active power output of the distributed photovoltaic at distribution node i in the distribution network respectively, Q pv,i is the reactive power output of the distributed photovoltaic at distribution node i in the distribution network, and are the maximum and minimum values of the reactive power output of the distributed photovoltaic at distribution node i in the distribution network.

[0109] Specifically, defining the respective constraint conditions (the first constraint condition and the second constraint condition) of the transmission network and the distribution network can ensure that the power system complies with relevant technical and safety standards during operation.

[0110] S220. Establish the third constraint condition for the interconnection of the transmission network and the distribution network.

[0111] Among them, the third constraint condition refers to the constraint condition of the interconnected part of the transmission network and the distribution network, which is used to ensure the coordination of power flow and voltage level between the two.

[0112] Optionally, the third constraint condition includes: f p,l = f Tp,l f Dp,l .

[0113] Among them, f p,l is the real power flow on the interconnected line, f Tp,l represents the real power flow output by the transmission network, and f Dp,l represents the real power flow input by the distribution network.

[0114] Specifically, the third constraint condition can ensure the stable operation of the interconnected part between the transmission network and the distribution network, including requirements such as voltage and power balance of the interconnected nodes.

[0115] S230. Establish the first objective function of the transmission network and the second objective function of the distribution network respectively, where the cost of the transmission network is minimized under the first objective function, and the cost of the distribution network is minimized under the second objective function.

[0116] Among them, the first objective function refers to the function for optimizing the performance of the transmission grid, usually aiming to minimize the transmission cost. By considering the equipment operation cost, maintenance cost, and other related costs, this function aims to improve the economic efficiency of the transmission grid. The second objective function refers to the function for optimizing the performance of the distribution grid, usually aiming to minimize the distribution cost. By considering the operation cost, loss, and maintenance cost of the distribution equipment, this objective function realizes the economic optimization of the distribution grid.

[0117] Optionally, the first objective function includes: min(C i +C T,gen ).

[0118] Among them, C i is the investment cost of the transmission lines in the transmission grid, and C T,gen is the power generation cost of the generating units in the transmission grid. The power generation cost constraint of the transmission grid follows the power balance constraint Among them, P gen,i is the power generation power of node i in the transmission grid, is the maximum value of the power generation power of node i in the transmission grid, is the minimum value of the power generation power of node i in the transmission grid.

[0119] Optionally, the second objective function includes: min(C D,pv +C D,rec +C D,ls ).

[0120] Among them, C D,pv is the photovoltaic power generation cost of the distribution grid, C D,rec is the penalty cost for photovoltaic curtailment, and C D,ls is the load shedding cost in the distribution grid. The photovoltaic power generation cost follows the constraints and Among them, is the maximum value of the active power output of the distributed photovoltaic at node i in the distribution grid, is the minimum value of the active power output of the distributed photovoltaic at node i in the distribution grid, is the maximum value of the reactive power output of the distributed photovoltaic at node i in the distribution grid, is the minimum value of the reactive power output of the distributed photovoltaic at node i in the distribution grid, Q pv,i is the reactive power output of the distributed photovoltaic at node i in the distribution grid, and P pv,i is the active power output of the distributed photovoltaic at node i in the distribution grid.

[0121] Specifically, establishing the first and second objective functions can improve the economic efficiency by optimizing the cost, thereby reducing the operating expenses while meeting the power demand.

[0122] S240. Determine the fourth constraint condition for the interaction variables in the coordinated operation of the transmission grid and the distribution grid.

[0123] Among them, the fourth constraint condition refers to the constraints on the interaction variables that need to be jointly observed in the coordinated operation of the transmission grid and the distribution grid, usually including restrictions such as power exchange, load distribution, and mutual influence. These conditions ensure the coordination and consistency of the two during coordinated operation and promote the effective dispatching of electric power.

[0124] Optionally, the fourth constraint condition includes:

[0125]

[0126] Where P l min and P l max are respectively the minimum and maximum values of the interaction power between the transmission grid and the distribution grid, V l min and V l max are respectively the minimum and maximum values of the interaction voltage between the transmission grid and the distribution grid; P Tl and P Dl are respectively the target power variables of the transmission grid and the distribution grid, and V Tl and V Dl are respectively the target voltage variables of the transmission grid and the distribution grid.

[0127] Specifically, setting the fourth constraint condition can clarify the requirements of coordinated operation, improve the coordination between the transmission grid and the distribution grid, and ensure the coherence of power supply.

[0128] S250. Solve the target values of the interaction variables according to the first constraint condition, the second constraint condition, the third constraint condition, the fourth constraint condition, the first objective function, and the second objective function.

[0129] Among them, the target values of the interaction variables refer to the key parameter values of the transmission grid and the distribution grid in coordinated operation obtained by solving the constraint conditions and the objective functions. These variables usually include power flow, load distribution, etc. The target values provide a basis for achieving the optimal operation of the system and ensure the stability and economy of power supply under different operating conditions.

[0130] Specifically, calculating the target values of the interaction variables through a mathematical model can provide a scientific basis for control strategies and ensure the effectiveness of optimization decisions.

[0131] S260. Control the transmission grid and the distribution grid according to the target values of the interaction variables.

[0132] Specifically, according to the obtained target value of the interaction variable, the control strategy is implemented to adjust the operating parameters of the transmission network and the distribution network, so as to achieve optimized power dispatching, which can ensure the efficiency and flexibility of the system during operation.

[0133] In the embodiments of the present invention, by establishing and optimizing the constraint conditions and objective functions of the transmission network and the distribution network, the efficient coordinated operation of the transmission network and the distribution network of the power system is realized. Among them, the clear interaction variables and the optimized control strategy enable the power system to flexibly respond to the continuously changing load and renewable energy fluctuations, ensuring the stability and security of power supply. The present invention not only improves the stability and reliability of the power system, but also improves the economic benefits by reducing costs.

[0134] Figure 8 It is a schematic structural diagram of a coordinated control device for microgrid grid connection provided by an embodiment of the present invention. Optionally, the microgrid is connected to the distribution network at the common connection point. As Figure 8 shown, the coordinated control device includes:

[0135] A determination module 310, configured to determine whether the microgrid can balance power supply and demand according to the difference between the power supply power and the load of the microgrid.

[0136] A first control module 320, configured to control the microgrid to operate in island mode when the microgrid can balance power supply and demand.

[0137] A second control module 330, configured to control the distribution network and the microgrid to be connected through the common connection point and control the energy storage module connected to the common connection point to charge or discharge to stabilize the voltage of the common connection point when the microgrid cannot balance power supply and demand.

[0138] An adjustment module 340, configured to adjust the node voltage of the distribution node in the distribution network by adjusting the reactive power of the photovoltaic inverter connected to the distribution node in the distribution network or the position of the tap of the on-load tap-changer in the distribution network when the node voltage of the distribution node in the distribution network exceeds the limit.

[0139] The coordinated control device for microgrid grid connection provided by the embodiments of the present invention can execute the coordinated control method for microgrid grid connection provided by any embodiment of the present invention, and has corresponding functional modules and beneficial effects for executing the method.

[0140] Figure 9 It is a schematic diagram of a coordinated control system for microgrid grid connection provided by an embodiment of the present invention.

[0141] See Figure 9, the coordinated control system for the microgrid grid connection mainly includes: the transmission grid 410, the distribution grid 420, the point of common coupling 430, and the microgrid 440. Among them, the point of common coupling 430 includes an energy storage battery 432 and a capacitor bank 431 to smooth the energy fluctuations in the power grid; the distribution grid 420 includes a photovoltaic inverter 421 and a on-load tap-changing transformer 422 to regulate the node voltage of the distribution grid.

[0142] Specifically, the capacitor bank 431 can be connected to the rectifier-inverter device through a bidirectional DC-DC device, and then connected to the point of common coupling 430 via a filtering device, etc. The energy storage battery 432 is connected to the point of common coupling 430 through a bidirectional DC-DC device.

[0143] Figure 10 The connection relationship diagram of the transmission grid and the distribution grid provided by the embodiment of the present invention. As Figure 10 shown, the transmission grid 410 includes a first generator G1, a second generator G2, a third generator G3, a fourth generator G4, and a fifth generator G5. The distribution grid 420 includes a first photovoltaic inverter PV1 (connected to the 17th node), a second photovoltaic inverter PV2 (connected to the 32nd node), a first on-load tap-changing transformer MG1 (connected to the 14th node), and a second on-load tap-changing transformer MG2 (connected to the 31st node). Among them, the transmission grid 410 is connected to the 0th node in the distribution grid 420 through the 23rd node to ensure the connection between the transmission and distribution grids.

[0144] Figure 11 The topology diagram of the microgrid provided by the embodiment of the present invention. As Figure 11 shown, the microgrid 440 includes node 1, node 2, node 3, and node 4.

[0145] Figure 12 The microgrid voltage curve diagram after being regulated by the coordinated control method for the microgrid grid connection provided by the embodiment of the present invention. Refer to Figure 11 and Figure 12 , where Figure 12 the vertical axis is the voltage amplitude (p.u.), the horizontal axis is the time (T), the blue curve represents the voltage amplitude curve of node 14 on the distribution grid 420 side, the orange curve represents the voltage amplitude curve of node 1 on the microgrid 440 side, the red curve represents the voltage amplitude curve of node 31 on the distribution grid 420 side, and the green curve represents the voltage amplitude curve of node 2 on the microgrid 440 side. From Figure 12It can be seen that the capacitor bank, in cooperation with the energy storage system, realizes voltage control, stabilizing the voltage amplitudes of Node 14 in the distribution network 420 and Node 31 in the distribution network 420 within the error range of -5% to +5% of the per-unit value corresponding to the rated voltage of the distribution network 420; the voltage amplitudes of Node 1 in the microgrid 440 and Node 31 in the microgrid 440 are finally stabilized within the error range of -5% to +5% of the rated voltage of the microgrid 440.

[0146] Figure 13 It is the curve graph of the photovoltaic output and the photovoltaic node power of the distribution network after being regulated by the cooperative control method for microgrid grid connection provided by the embodiment of the present invention. Refer to Figure 10 and Figure 13 , where Figure 13 the vertical axis represents power (MW), the horizontal axis represents time (T), the dark blue curve represents the processing curve of the first photovoltaic PV1, the green curve represents the output curve of the second photovoltaic PV2, the red curve represents the power curve of Node 17 on the distribution network 420 side, and the light blue curve represents the power curve of Node 32 on the distribution network 420 side. From Figure 13 it can be seen that when the distribution network 420 operates by itself, through the cooperative control of the photovoltaic inverter and the on-load tap-changer transformer, the power of Node 32 on the distribution network 420 side and the power of Node 17 on the distribution network 420 side are finally stabilized within the error range of -5% to +5% of the per-unit value of the rated power of the distribution network 420.

[0147] Figure 14 It is the voltage curve graph of the distribution network after being regulated by the cooperative control method for microgrid grid connection provided by the embodiment of the present invention. Refer to Figure 14 , Figure 10 and Figure 11 , where Figure 14 the horizontal axis represents the voltage amplitude (p.u), the horizontal axis represents time (T), the black curve represents the voltage amplitude curve of Node 14 on the distribution network 420 side, the blue curve represents the voltage amplitude curve of Node 17 on the distribution network 420 side, and the red curve represents the voltage amplitude curve of Node 31 on the distribution network 420 side. From Figure 14 it can be seen that the voltage amplitudes of Node 14 on the distribution network 420 side, Node 17 on the distribution network 420 side, and Node 31 on the distribution network 420 side are finally stabilized within the error range of -5% to +5% of the per-unit value of the rated voltage amplitude of the distribution network 420.

[0148] It should be understood that various forms of the processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved, and no limitations are imposed herein.

[0149] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A coordinated control method for microgrid grid connection, characterized in that: include: Determining whether the microgrid can balance supply and demand according to the difference between the power supply of the microgrid and the load; When the microgrid is capable of balancing supply and demand, controlling the microgrid to operate in an islanded manner; When the microgrid cannot balance supply and demand, controlling the distribution network to be connected to the microgrid through a common connection point, and controlling the energy storage module connected to the common connection point to charge or discharge so as to stabilize the voltage of the common connection point; When the node voltage of a distribution node of the distribution network exceeds a limit, the node voltage of the distribution node is adjusted by adjusting the reactive power of a photovoltaic inverter connected to the distribution node in the distribution network or the position of a tap of an on-load tap-changing transformer in the distribution network.

2. The coordinated control method for microgrid grid connection according to claim 1, characterized in that: When the microgrid cannot balance supply and demand, controlling the distribution network to be connected to the microgrid through a common connection point, and controlling the energy storage module connected to the common connection point to charge or discharge to stabilize the voltage of the common connection point, including: When the microgrid cannot balance supply and demand, controlling the distribution network to be connected to the microgrid through a common connection point; When the voltage on the distribution network side is lower than the voltage on the microgrid side, controlling the energy storage module to discharge toward the common connection point; When the voltage on the distribution network side is higher than the voltage on the microgrid side, controlling the distribution network to charge the energy storage module through the common connection point; Wherein, the energy storage module includes an energy storage battery and a capacitor group.

3. The coordinated control method for microgrid grid connection according to claim 1, characterized in that: When the node voltage of the distribution node in the distribution network exceeds the limit, the node voltage of the distribution node is adjusted by adjusting the reactive power of the photovoltaic inverter connected to the distribution node in the distribution network or the position of the tap of the on-load tap-changing transformer in the distribution network, including: When the node voltage exceeds the limit, the node voltage is adjusted preferentially by adjusting the reactive power of the photovoltaic inverter connected to the power distribution node; When the photovoltaic inverter connected to the power distribution node is unable to regulate the node voltage, the node voltage is regulated by adjusting the position of the tap of the on-load tap-changing transformer.

4. The coordinated control method for microgrid grid connection according to claim 3, characterized in that: When the node voltage exceeds the limit, the node voltage is adjusted by preferentially adjusting the reactive power of the photovoltaic inverter connected to the power distribution node, including: When the node voltage exceeds the limit and the distributed photovoltaic output reaches the set power, the reactive power of the photovoltaic inverter is adjusted according to the node voltage according to the following formula: Wherein, V represents the node voltage, P pv represents the distributed photovoltaic output, Q pv Represents the reactive power of the photovoltaic inverter, represents the set power, Q max Indicates the maximum reactive power that can be compensated when the distributed photovoltaic output reaches the set power, V min Represents the minimum voltage limit of the distribution node, V ref1 Represents the first reference voltage, V ref2 represents a second reference voltage, the minimum voltage limit is less than the first reference voltage, and the first reference voltage is less than the second reference voltage; When the voltage exceeds the limit, the node voltage is less than or equal to the minimum voltage limit.

5. The coordinated control method for microgrid grid connection according to claim 3, characterized in that: When the photovoltaic inverter connected to the power distribution node is unable to regulate the node voltage, adjusting the node voltage by adjusting the position of the tap of the on-load tap-changing transformer comprises: The target gear position of the tap of the on-load tap-changing transformer is determined according to the difference between the rated voltage of the distribution network and the weighted average value of the node voltage of the distribution node connected to the photovoltaic inverter, and the single-step regulation voltage of the on-load tap-changing transformer.

6. The coordinated control method for microgrid grid connection according to claim 1, characterized in that: Determining whether the microgrid can balance supply and demand according to the difference between the power supply power of the microgrid and the load includes: When the difference between the power supply of the microgrid and the load is equal to 10% of the load, determining that the microgrid is capable of balancing supply and demand; When the difference between the power supply of the microgrid and the load is not equal to 10% of the load, it is determined that the microgrid is unable to balance supply and demand.

7. The coordinated control method for microgrid grid connection according to claim 1, characterized in that: When the microgrid is capable of balancing supply and demand, controlling the microgrid to operate in an islanded manner includes: The output of the microgrid is adjusted according to the following formula: Among them, P mg,i,k is the actual output value of the i-th microgrid at time k, N mg is the total number of microgrids, is the maximum output of the i-th microgrid at time k+1.

8. The coordinated control method for microgrid grid connection according to claim 1, characterized in that: The distribution network is electrically connected to the transmission network, and the coordinated control method further includes: Establishing a first constraint condition of the transmission network and a second constraint condition of the distribution network respectively; Establishing a third constraint condition for interconnection between the transmission network and the distribution network; Establishing a first objective function of the transmission network and a second objective function of the distribution network respectively, wherein the cost of the transmission network is minimized under the first objective function, and the cost of the distribution network is minimized under the second objective function; Determining a fourth constraint condition of the interaction variable for the coordinated operation of the transmission network and the distribution network; Solve the target value of the interaction variable according to the first constraint condition, the second constraint condition, the third constraint condition, the fourth constraint condition, the first objective function and the second objective function; The transmission network and the distribution network are controlled according to the target value of the interaction variable.

9. The coordinated control method for microgrid grid connection according to claim 8, characterized in that: The first constraint condition includes: i min ≤θ≤θ max ; Where P gen,i is the power generation power of transmission node i in the transmission network, P load,i is the load power of transmission node i in the transmission network, f T,ij is the power flow from transmission node i to its adjacent transmission node j, N T (i) is the set of all neighboring transmission nodes connected to transmission node i in the transmission network; and are the maximum and minimum values ​​of the power flow from the transmission node i to its adjacent transmission node j, θ is the voltage phase angle of the transmission network, θ min and max are the maximum and minimum values ​​of the voltage phase angle respectively, and are the maximum and minimum power generation power of transmission node i in the transmission network, respectively; The second constraint condition includes: where f D,ij is the actual power flow from distribution node i to its adjacent distribution node j in the distribution network, and are the maximum and minimum values ​​of the actual power flow from distribution node i to its adjacent distribution node j, N D (i) is the set of all adjacent distribution nodes connected to distribution node i in the distribution network, where is the reactive power flow from distribution node i to its adjacent distribution node j in the distribution network, and are the maximum and minimum values ​​of reactive power flow from distribution node i to its adjacent distribution node j, P pv，i is the distributed photovoltaic active power output of distribution node i in the distribution network, and are the maximum and minimum active output of distributed photovoltaic power at distribution node i in the distribution network, Q pv，i is the distributed photovoltaic reactive power output of distribution node i in the distribution network, and is the maximum and minimum value of the distributed photovoltaic reactive power output of distribution node i in the distribution network; The third constraint condition includes: p，l =f Tp，l =f Dp，l ; where f p，l is the active power flow on the interconnection line, f Tp，l represents the real power flow output by the transmission grid, f Dp，l Represents the real power flow input from the distribution network; The fourth constraint condition includes: Where P l min and P l max are the minimum and maximum values ​​of the interaction power between the transmission network and the distribution network, respectively. l min and V l max are the minimum and maximum values ​​of the interaction voltage between the transmission network and the distribution network respectively; P Tl With P Dl are the target power variables of the transmission network and the distribution network, V Tl With V Dl are the target voltage variables of the transmission network and the distribution network respectively; The first objective function includes: min(C i +C T，gen ); Among them C i is the transmission line investment cost of the transmission network, C T，gen is the electricity generation cost of the generators in the transmission grid; The second objective function includes: min(C D，pv +C D，rec +C D，ls ); Among them C D，pv is the cost of photovoltaic power generation in the distribution network, C D，rec is the penalty cost for photovoltaic curtailment, C D，ls Cost of load shedding in distribution networks.

10. A coordinated control device for microgrid grid connection, characterized in that: include: The microgrid and the distribution network are connected to a common connection point; The collaborative control device comprises: A determination module, used to determine whether the microgrid can balance supply and demand according to the difference between the power supply of the microgrid and the load; A first control module, used for controlling the island operation of the microgrid when the microgrid is able to balance supply and demand; A second control module is used to control the distribution network to be connected to the microgrid through a common connection point when the microgrid cannot balance supply and demand, and to control the energy storage module connected to the common connection point to charge or discharge so as to stabilize the voltage of the common connection point; The adjustment module is used to adjust the node voltage of the distribution node in the distribution network by adjusting the reactive power of the photovoltaic inverter connected to the distribution node in the distribution network or the position of the tap of the on-load tap-changing transformer in the distribution network when the node voltage of the distribution node in the distribution network exceeds the limit.

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