A reactive power and voltage control method for suppressing reactive circulating current in a new energy collection area

Abstract

The present invention relates to a reactive power and voltage control method for suppressing reactive circulating current in a new energy gathering area. By setting the reactive power at the end of the new energy transmission line to zero, the reactive power control between each new energy station is completely decoupled; by setting the bus voltage limit of the new energy station, when the voltage exceeds the line, the reactive value is locked and stays at the maximum or minimum value of the voltage. The present invention can realize the coordinated reactive power and voltage control between each new energy power station and different types of voltages in the new energy gathering area. In most cases, the reactive power between each new energy station can be completely decoupled, and the reactive power inside each new energy station can be balanced. In a few extreme cases, when the bus voltage of the new energy station exceeds the limit, the reactive output of the station is maintained at a fixed value to meet the bus voltage assessment index.

Description

Technical Field

[0001] The present invention belongs to the technical field of reactive power and voltage control of a new type of power system new energy development system, and in particular relates to a reactive power and voltage control method for suppressing reactive circulating current in a new energy collection area. Background Art

[0002] The reactive power and voltage control field of new power system new energy development system covers new energy equipment, such as photovoltaic equipment, wind turbine equipment, and inverter-based adjustable loads, such as hydrogen production equipment, charging piles, battery swap stations, as well as inverter-based energy storage equipment, station reactive equipment SVG, capacitors, etc.

[0003] New energy sources are intermittent. In order to ensure system stability, wind power and photovoltaic power are often bundled with thermal power generation and then transmitted over long distances.

[0004] At present, voltage control in areas where new energy is connected generally adopts a secondary voltage control framework and a voltage command control mode. The voltage at the new energy grid connection point and the voltage at the new energy power station are assessed separately to achieve reactive voltage control of the collecting bus and the new energy power station, thereby ensuring voltage stability in the entire area.

[0005] However, since each new energy station has its own voltage command, the independent regulation cannot take into account the differences between new energy stations. In actual operation, it often happens that some new energy stations take on more reactive tasks but still cannot adjust the voltage of the station to the target value, or some stations do not have to take on reactive tasks at all, and even some stations have voltage crossing the line, causing wind turbines to be disconnected from the grid. The fundamental reason for this phenomenon is the reactive imbalance or reactive circulation between thermal power, wind power, and photovoltaic power. Therefore, studying the control method to suppress reactive circulation plays an important role in the voltage stability and safe power delivery of the power generation system.

[0006] The reactive power control strategy in the existing wind power collection area is: the dispatching AVC master station calculates the voltage command, and the wind farm AVC substation executes the voltage command. The AVC master station determines the 500kV bus and collects the bus voltage reference value. Each wind farm AVC adopts the voltage command tracking mode to convert the voltage command into reactive power command, adjust the reactive source power in the field, and make the voltage of each bus close to the voltage command issued by the dispatcher.

[0007] In areas where new energy sources converge, existing reactive power control strategies may have the following problems:

[0008] 1. Different control states (determined by new energy stations). New energy stations that participate in and do not participate in AVC control lead to unreasonable reactive power flow between stations.

[0009] 2. Different adjustment capabilities (determined by new energy stations). When the reactive power output of a new energy station reaches the limit, other new energy stations help the station to adjust the reactive power, resulting in reactive power flowing between stations.

[0010] 3. Different adjustment speeds (determined by new energy stations). The reactive power adjustment rates of wind turbines, inverters and SVGs in different new energy stations are different, and the adjustment strategies implemented by AVC substations are different, resulting in some new energy stations with fast reactive power adjustment and some with slow adjustment, causing reactive power flow between new energy stations.

[0011] 4. Different adjustment set values ​​(determined by the control center). Different renewable energy stations may be determined by different control center AVCs. The control algorithms used by each control center and the constraints considered are different. This may lead to large differences in the adjustment set values ​​between renewable energy stations, resulting in reactive power flowing between renewable energy stations.

[0012] For example, for Figure 1 In the wind, solar and thermal bundled transmission system, wind farm No. 1 and photovoltaic station No. 2 are connected in series, and then radially connected to the 500kV bus of the thermal power plant with wind farms No. 3, 4 and 5. After the energy is bundled, it is connected to the large power grid through the line.

[0013] In the operation of this type of system, when the distance between wind farms is close and there is voltage regulation coupling between wind farms, the actual reactive power adjustment during voltage regulation may deviate greatly from the ideal distribution, resulting in reactive power imbalance or reactive power circulation, such as Figure 1 The reactive imbalance between the thermal power plant and the new energy interconnection transformer, the reactive circulating current between the cascaded stations 1 and 2, and the reactive circulating current between stations 4 and 5 are shown in the figure. These reactive circulating current problems may cause transformer overheating, increase line losses, make protection setting difficult, make it difficult to adjust the voltage, and even cause the new energy unit to be disconnected from the grid.

[0014] In summary, existing technologies cannot avoid reactive power imbalance and reactive circulating current between wind farms and between renewable energy and thermal power. These reactive circulating current problems may cause transformer overheating, increase line losses, make protection setting difficult, make voltage adjustment difficult, and even cause renewable energy units to be disconnected from the grid. Summary of the invention

[0015] The purpose of the present invention is to provide a reactive power and voltage control method for suppressing reactive circulating current in a new energy gathering area. In a wind-solar-thermal bundled power generation system, by suppressing reactive circulating current between new energy stations and between new energy and thermal power, problems such as transformer overheating, increased line loss, difficulty in protection setting, difficulty in adjusting voltage, and disconnection of new energy units from the grid due to unreasonable reactive flow can be avoided.

[0016] The present invention provides

[0017] A reactive power and voltage control method for suppressing reactive circulating current in a new energy collection area, which realizes complete decoupling of reactive power control between various new energy stations by setting the reactive power at the end of the new energy transmission line to zero; by setting the bus voltage limit of the new energy station, when the voltage exceeds the line, the reactive value is locked and stays at the maximum or minimum value of the voltage;

[0018] For the wind, solar and fire bundling delivery system, the specific steps include:

[0019] Step 1, receiving the voltage instruction of the AVC master station; the instruction includes the collection of 500kV bus voltage operation reference value The operating range of 220kV bus voltage for each new energy station

[0020] Step 2: Select the number of FCs to be put into operation on the 66kV side and execute;

[0021] Step 3: Taking the reactive power at the end of the transmission line of the new energy station as 0 as the control target, the reactive power decoupling control between the new energy stations is realized by estimating the reactive power command:

[0022] The calculation formula of reactive power command is as follows:

[0023]

[0024] In the formula, ignoring the voltage drop on the impedance, Q i.ref is the reactive power control target value, P i.t , Q i.t , U i.t is the active power, reactive power and voltage at the reactive power control point of the bus at time t at the i-th station; L i , C i is the equivalent inductance and capacitance of the transmission line of the ith station, ω is the electrical angular frequency; the first half of the formula Represents the inductive reactive power on the line, where the second half Indicates line capacitive reactive power;

[0025] Step 4, voltage over-limit prevention control, includes:

[0026] (1) Setting bus voltage operating limit

[0027] Let U i,min , U i,max is the maximum and minimum values ​​allowed for the bus voltage of wind farm i. i,min , U i,max It is sent down by the scheduling AVC master station, or obtained by the AVC substation through iterative calculation based on the grid structure.

[0028] (2) Solving the reactive power transmission limit

[0029] Let U i,t is the bus voltage value of wind farm i at time t; U i,min , U i,max Q is the minimum and maximum values ​​allowed for the operation of the bus voltage of wind farm i. It is calculated by the voltage controller and, after the reactive power limit change rate and amplitude limit value links, the reactive power minimum and maximum values ​​corresponding to limiting the bus voltage to the maximum and minimum values ​​are obtained: i,min and Q i,max In this way, the reactive power transmission limit of wind farm i at time t is Q i,min , Q i,max .

[0030] (3) Prevent over-limit of reactive power instruction in step 3

[0031] The reactive power command calculated in step 3 is Q set =Q i,ref The real-time monitored reactive power value is Q measure , after the reactive power controller and Q i,min , Q i,max After exceeding the limit, the final reactive power command can be obtained as Q setpoint .

[0032] Step 5: According to the obtained reactive power command Q setpoint , distribute reactive power instructions to new energy units, SVG, and FC.

[0033] Furthermore, the step 2 comprises:

[0034] According to the active output level of all renewable energy stations, 1, 2, 3 and 4 groups of FC are put into operation at 30%, 60%, 80% and 100% respectively, and an action dead zone is set near the action point. The resulting fluctuations are smoothed by the thermal power AVC system.

[0035] Through the above scheme, the reactive power and voltage control method of suppressing reactive circulation in the new energy gathering area can be used to achieve reactive decoupling control between new energy stations and between new energy and thermal power. At the same time, the voltage limiting module is used to ensure that the dispatching voltage instruction requirements are met, which greatly reduces line network losses and avoids the waste of reactive power regulation capacity.

[0036] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the reactive circulation problem in the transmission system of the new energy collection area in the prior art;

[0038] Figure 2 This is a schematic diagram of a 66kVFC switching strategy in an embodiment of the present invention;

[0039] Figure 3 is a schematic diagram of a collection station and reactive power control points in one embodiment of the present invention;

[0040] Figure 4 It is a block diagram of voltage over-limit prevention control in one embodiment of the present invention. DETAILED DESCRIPTION

[0041] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0042] This embodiment provides a reactive power and voltage control method for suppressing reactive circulating current in a new energy gathering area, and realizes complete decoupling of reactive power control between various new energy stations by setting the reactive power at the end of the new energy transmission line to zero. By setting the bus voltage limit of the new energy station, when the voltage exceeds the line, the reactive value is locked and stays at the maximum or minimum value of the voltage. This control method can realize coordinated reactive power and voltage control between various new energy power stations and different types of voltages in the new energy gathering area. In most cases, it can realize complete reactive power decoupling between various new energy stations, and achieve reactive power balance within each new energy station. In a few extreme cases, when the bus voltage of the new energy station exceeds the limit, the reactive output of the station is maintained at a fixed value to meet the bus voltage assessment index.

[0043] Below Figure 1 The wind-solar-thermal bundled transmission system shown in the figure is taken as an example to illustrate its reactive power decoupling control strategy. Figure 3 , voltage over-limit prevention control strategy see Figure 4 The specific steps include:

[0044] 1. Receive the voltage command of the AVC master station. The command includes the collection of 500kV bus voltage operating reference value The operating range of 220kV bus voltage for each new energy station

[0045] 2. Select the number of FCs (fixed capacitors) to be put into operation on the 66kV side and execute.

[0046] The function of the 66kV fixed capacitor FC of the interconnection transformer is to compensate for the inductive reactive power of the interconnection transformer. Its reactive power demand increases with the increase of the transmitted active power. Figure 2According to the active output level of all new energy stations, 1, 2, 3, and 4 groups of FC are put into use at 30%, 60%, 80%, and 100% respectively. To avoid frequent switching of FC in a short time, an action dead zone is set near the action point. The size of the action dead zone can be selected in a certain area, such as Figure 2 As shown, 5% can be selected. Since switching FC is not a smooth reactive power regulation, the fluctuation generated in this link is smoothed by the thermal power AVC system.

[0047] 3. Reactive power decoupling control between new energy stations

[0048] like Figure 3 As shown, the upper (4) dot positions are for information monitoring and reactive power control, and the lower (4) dot positions are for reactive power zero positions.

[0049] During operation, the control target is: the reactive power at the end of the new energy station transmission line is 0, thereby achieving reactive power decoupling control.

[0050] The following formula is one of the calculation methods for estimating reactive power demand.

[0051]

[0052] In the formula, ignoring the voltage drop on the impedance, Q i.ref is the reactive power control target value, P i.t , Q i.t , U i.t is the active power, reactive power and voltage at the reactive power control point of the bus at time t at the i-th station. i , C i is the equivalent inductance and capacitance of the transmission line of the ith station, and ω is the electrical angular frequency. The first half of the formula Represents the inductive reactive power on the line, where the second half Indicates line capacitive reactive power.

[0053] The voltage drop across the impedance can also be considered to estimate the reactive power loss on the transmission line.

[0054] 4. Voltage over-limit control

[0055] (1) Setting bus voltage operating limit

[0056] Let U i,min , U i,max is the maximum and minimum values ​​allowed for the bus voltage of wind farm i. i,min , U i,max It is sent down by the scheduling AVC master station, or obtained by the AVC substation through iterative calculation based on the grid structure.

[0057] (2) Solving the reactive power transmission limit

[0058] Let U i,t is the bus voltage value of wind farm i at time t; U i,min , U i,max Q is the minimum and maximum values ​​allowed for the operation of the bus voltage of wind farm i. It is calculated by the voltage controller and, after the reactive power limit change rate and amplitude limit value links, the reactive power minimum and maximum values ​​corresponding to limiting the bus voltage to the maximum and minimum values ​​are obtained: i,min and Q i,max In this way, the reactive power transmission limit of wind farm i at time t is Q i,min , Q i,max .

[0059] (3) Prevent over-limit of reactive power instruction in step 3

[0060] The reactive power command calculated in step 3 is Q set =Q i,ref The real-time monitored reactive power value is Q measure , after the reactive power controller and Q i,min , Q i,max After exceeding the limit, the final reactive power command can be obtained as Q setpoint .

[0061] 5. Send reactive power command and adjust

[0062] According to the reactive power command Q setpoint , reactive power instructions can be allocated to new energy units, SVG, and FC according to the situation.

[0063] By adopting the reactive power and voltage control method for suppressing reactive circulation in the new energy gathering area, reactive power decoupling control between new energy stations and between new energy and thermal power can be achieved. At the same time, the voltage limiting module is used to ensure that the dispatching voltage instruction requirements are met, which greatly reduces the line network loss and avoids the waste of reactive power regulation capacity.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A reactive power and voltage control method for suppressing reactive circulating current in a new energy collection area. It is characterized in that By setting the reactive power at the end of the renewable energy transmission line to zero, the reactive power control between the renewable energy stations is completely decoupled; by setting the bus voltage limit of the renewable energy station, when the voltage exceeds the limit, the reactive power value is locked and stays at the maximum or minimum voltage value; For the wind, solar and fire bundling delivery system, the specific steps include: Step 1, receiving the voltage instruction of the AVC master station; the instruction includes the collection of 500kV bus voltage operation reference value The operating range of 220kV bus voltage for each new energy station Step 2: Select the number of FCs to be put into operation on the 66kV side and execute; Step 3: Taking the reactive power at the end of the transmission line of the new energy station as 0 as the control target, the reactive power decoupling control between the new energy stations is realized by estimating the reactive power command: The calculation formula of reactive power command is as follows: In the formula, ignoring the voltage drop on the impedance, Q i.ref is the reactive power control target value, P i.t , Q i.t , U i.t is the active power, reactive power and voltage at the reactive power control point of the bus at time t at the i-th station; L i , C i is the equivalent inductance and capacitance of the transmission line of the ith station, ω is the electrical angular frequency; the first half of the formula Represents the inductive reactive power on the line, where the second half Indicates line capacitive reactive power; Step 4, voltage over-limit prevention control, includes: (1) Setting bus voltage operating limit Let U i,min , U i,max is the maximum and minimum values ​​allowed for the bus voltage of wind farm i. i,min , U i,max Issued by the dispatching AVC master station, or obtained by iterative calculation by the AVC substation based on the grid structure; (2) Solving the reactive power transmission limit Let U i,t is the bus voltage value of wind farm i at time t; U i,min , U i,max The minimum and maximum values ​​of the bus voltage allowed to operate in the wind farm i are calculated by the voltage controller, and after the reactive power limit change rate and amplitude limit value link, the reactive power minimum and maximum values ​​Q corresponding to the bus voltage limit of the maximum and minimum values ​​are obtained. i,min and Q i,max , that is, the reactive power transmission limit of wind farm i at time t is Q i,min , Q i,max ; (3) Prevent over-limit of reactive power instruction in step 3 The reactive power command calculated in step 3 is Q set =Q i,ref The real-time monitored reactive power value is Q measure , after the reactive power controller and Q i,min , Q i,max After exceeding the limit, the final reactive power command is Q setpoint ; Step 5: According to the obtained reactive power command Q setpoint , and distribute reactive power instructions to new energy units, SVG, and FC.

2. The reactive power and voltage control method for suppressing reactive circulating current in a new energy collection area according to claim 1, It is characterized in that The step 2 comprises: According to the active output level of all renewable energy stations, 1, 2, 3 and 4 groups of FC are put into operation at 30%, 60%, 80% and 100% respectively, and an action dead zone is set near the action point. The resulting fluctuations are smoothed by the thermal power AVC system.

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