A Voltage Control Method and System for a New Energy Transmission System

Abstract

A voltage control method for a new energy transmission system includes: obtaining the optimal series compensation degree at different output levels of a new energy base based on the relationship between the pre-determined system voltage and the output power of the new energy base; according to the optimal series compensation degree, when the voltage of the new energy field station output system in the new energy base exceeds the pre-set normal range, determining the reactive power compensation capacity of the new energy field station; controlling the reactive power compensation device based on the reactive power compensation capacity to make the grid-connected point voltage of the new energy field station reach the pre-set grid-connected point voltage control target; and performing reactive power coordinated control on the new energy field station cluster and the gathering station based on the grid-connected point voltage of the new energy field station to make the bus voltages of the new energy field station cluster and the gathering station reach the pre-set bus voltage control target. The technical solution provided by the present invention adopts the series compensation technology to improve the accessible capacity of the new energy base and the output capacity of the new energy grid-connected system.

Description

Technical Field

[0001] The present invention relates to the field of reactive voltage control, and particularly to a voltage control method and system for a new energy transmission system. Background Art

[0002] "Series compensation" is a device that uses modern power electronics means to perform series compensation on AC transmission lines, which can improve the line power limit and power system stability. The biggest feature is to install corresponding devices on the power grid lines to improve the transmission capacity of the power grid and reduce the erection of long-distance transmission lines at the same time.

[0003] Under normal circumstances, the wind / solar resources and the load center are distributed in the reverse direction, making it inevitable to transmit large-capacity and long-distance new energy. The stability problem of large-scale new energy grid-connected systems under high-impedance weak power grids becomes increasingly important. Adopting series compensation technology is an economically feasible method, which can greatly shorten the electrical distance of new energy connected to the power grid. However, the introduction of series compensation changes the reactive power distribution of the original system, and it is necessary to adjust and control the reactive voltage to ensure the voltage stability of the system after large-scale new energy access.

[0004] The basic control principle of the power system is to achieve hierarchical and zonal control of voltage and reactive power. This method can provide guarantee for the voltage quality of the system on the one hand, and enhance the economic performance of reactive power operation on the other hand. According to the principles of hierarchical and zonal control and local balance, it can effectively ensure the voltage quality and perform reasonable reactive power management on the voltage, making the reactive power distribution of the system more uniform while reducing the active power loss, and controlling and analyzing the appropriateness of the voltage and the level of the global voltage.

[0005] The voltage level of the new energy base is closely related to the impedance value of its transmission system. When the output of the new energy base is relatively high, the reactive power transmitted from the power grid to the new energy base also increases, causing too large a voltage drop in the line between the main grid and the new energy base, resulting in too low a terminal voltage. In engineering terms, it means that the power grid network structure is weak and the reactive power transmission capacity of the network lines is lacking, resulting in too large a voltage drop for transmitting reactive power and unable to guarantee the voltage level at the end of the power grid.

[0006] Therefore, to overcome the above defects, the present invention provides a voltage control method for a large new energy base after series compensation under the condition of hierarchical and zonal reactive power control. Summary of the Invention

[0007] In order to solve the above-mentioned deficiencies in the prior art, the present invention provides a voltage control method and system for a new energy transmission system.

[0008] The technical solution provided by the present invention is:

[0009] A voltage control method for a new energy transmission system, the improvement lies in that the method includes:

[0010] Based on the relationship between the pre-determined system voltage and the new energy base transmission power, obtain the optimal series compensation degree at different transmission levels of the new energy base. According to the optimal series compensation degree, when the voltage of the new energy station transmission system in the new energy base exceeds the pre-set normal range, determine the reactive power compensation capacity of the new energy station;

[0011] Based on the reactive power compensation capacity, control the reactive power compensation device to make the grid-connected point voltage of the new energy station reach the pre-set grid-connected point voltage control target;

[0012] Based on the grid-connected point voltage of the new energy station, perform reactive power coordination control on the new energy station cluster and the collection station to make the bus voltages of the new energy station cluster and the collection station reach the pre-set bus voltage control target.

[0013] Preferably, the pre-determined relationship between voltage and new energy transmission power includes:

[0014] Analyze the reactive power-voltage characteristics of the new energy base transmission system to obtain the relationship between the sending and receiving system voltage and active power.

[0015] The relationship between the sending and receiving system voltage and active power is shown in the following formula:

[0016]

[0017] In the formula, I: the current of the new energy station collection line; E W : the bus voltage of the new energy station; E S : the main system bus voltage; P W : the active and reactive power generated by the new energy station; X: the reactance of the new energy station grid-connected line; B: the susceptance.

[0018] Preferably, the obtaining of the optimal series compensation degree at different transmission levels of the new energy base includes:

[0019] Based on the relationship between the sending and receiving system voltage and active power, through adjusting the compensation series compensation amount, perform sensitivity analysis on the relationship between the active power injected by the new energy station and the grid-connected point voltage under different series compensation amounts;

[0020] Based on the sensitivity analysis results, adjust the series compensation degree according to the output characteristics, and control the voltage at the grid-connected point under all new energy power transmissions within the pre-specified range of the power grid to obtain the optimal series compensation degree at different transmission levels of the new energy base.

[0021] Preferably, when the voltage of the power transmission system of a new energy station in the new energy base exceeds a preset normal range, determining the reactive power compensation capacity of the new energy station includes:

[0022] When the voltage of the new energy station is less than the lower limit of the normal range, set the reactive power compensation capacity as the inductive reactive power compensation capacity, and ensure that the total inductive reactive power can compensate the total charging reactive power of all outgoing lines of the new energy station;

[0023] When the voltage of the new energy station is greater than the upper limit of the normal range, set the reactive power compensation capacity as the capacitive reactive power compensation capacity, and ensure that the total capacitive reactive power can compensate half of the total reactive power loss of the in-station transformer when all new energy stations are fully loaded and the total reactive power loss of all outgoing lines with a voltage of 500 kV or above in the collection station;

[0024] The upper limit of the normal range is the voltage when the output of the power transmission system of each new energy station is greater than 80% of the rated capacity; the lower limit of the normal range is the voltage when the output of the power transmission system of each new energy station is less than 30% of the rated capacity.

[0025] Preferably, based on the reactive power compensation capacity, controlling the reactive power compensation device to make the grid connection point voltage of the new energy station reach a preset grid connection point voltage control target includes:

[0026] When the voltage of the new energy station is greater than the upper limit of the normal range, adopt a capacitive reactive power compensation strategy:

[0027] When the voltage of the new energy station is less than the lower limit of the normal range, adopt an inductive reactive power compensation strategy.

[0028] Preferably, the capacitive reactive power compensation strategy includes:

[0029] When the voltage of the 330 kV / 220 kV busbar of the collection station is lower than the preset first grid connection point voltage control target of the new energy station, emit reactive power until all capacitive reactive power compensation is used up;

[0030] When the voltage of the 330 kV / 220 kV busbar of the collection station is higher than the preset second grid connection point voltage control target of the new energy station, reduce the emitted reactive power until all capacitive reactive power compensation is withdrawn.

[0031] The preset first grid connection point voltage control target of the new energy station is the voltage of the busbar where the new energy station is connected when the power grid is operating in the maximum operating mode and the new energy output is 0;

[0032] The preset second grid connection point voltage control target of the new energy station is the voltage of the busbar where the new energy station is connected when the power grid is operating in the minimum operating mode and the new energy output is 0;

[0033] The reactive power compensation strategy for inductance includes:

[0034] When the bus voltage of the 330 kV / 220 kV substation is higher than the voltage control target of the third new energy power station connection point set in advance, reactive power is absorbed until all the inductive reactive power compensation is used up.

[0035] The preset voltage control target of the third new energy power station connection point is the voltage of the bus connected to the new energy power station when the power grid operates at the highest voltage and the new energy output is zero.

[0036] Preferably, the preset bus voltage control target includes:

[0037] Disconnect the new energy power station from the substation, only keep the connection between the substation and the power grid, take the bus voltage connected by the collector line as the reference, and under the optimal series compensation degree, take the minimum value of the bus voltage in the maximum operation mode of the power grid as the lower limit of the substation voltage control target; take the maximum value of the bus voltage in the minimum operation mode of the power grid as the upper limit of the bus voltage control target.

[0038] Preferably, the reactive power coordinated control of the new energy power station cluster and the substation based on the voltage of each new energy power station connection point includes:

[0039] When the bus voltage of the new energy power station cluster and the substation crosses the lower limit of the preset bus voltage control target, a capacitive reactive power coordinated control strategy is adopted;

[0040] When the bus voltage of the new energy power station cluster and the substation crosses the upper limit of the preset bus voltage control target, an inductive reactive power coordinated control strategy is adopted.

[0041] Preferably, the capacitive reactive power coordinated control strategy includes:

[0042] When the bus voltage of the new energy power station cluster and the substation crosses the lower limit of the preset bus voltage control target, according to the reactive power absorbed and emitted by the reactive power compensation devices of each power station in the new energy cluster, capacitive reactive power compensation is put into use to make the bus voltage higher than the lower limit of the bus voltage control target; if the bus voltage after the reactive power coordinated control of the new energy power station cluster and the substation cannot be higher than the lower limit of the preset bus voltage control target, increase the capacitive compensation capacity, and re-perform the voltage control of each new energy power station connection point and the reactive power coordinated control of the new energy power station cluster and the substation until the bus voltage after the reactive power coordinated control of the new energy power station cluster and the substation reaches the preset bus voltage control target;

[0043] The inductive reactive power coordinated control strategy includes:

[0044] When the bus voltage of the new energy power station cluster and the collecting station exceeds the upper limit of the preset bus voltage control target, according to the reactive power absorbed and emitted by the reactive power compensation devices of each power station in the new energy cluster, the capacitive reactive power compensation is withdrawn and the inductive reactive power compensation is put into operation, so that the bus voltage is lower than the upper limit of the bus voltage control target; if the bus voltage after the reactive power coordinated control of the new energy power station cluster and the collecting station cannot reach the upper limit of the preset bus voltage control target, the inductive compensation capacity is increased, and the voltage control of the connection point of each new energy power station and the reactive power coordinated control of the new energy power station cluster and the collecting station are carried out again until the bus voltage after the reactive power coordinated control of the new energy power station cluster and the collecting station reaches the preset bus voltage control target.

[0045] A voltage control system for a new energy transmission system, comprising: a setting module, a first control module and a second control module;

[0046] The setting module: is used to determine the reactive power compensation capacity when the voltage of the new energy power station transmission system exceeds the preset normal range;

[0047] The first control module: is used to control the reactive power compensation device based on the reactive power compensation capacity, so that the voltage of the connection point of the new energy power station reaches the preset connection point voltage control target;

[0048] The second control module: is used to perform reactive power coordinated control on the new energy power station cluster and the collecting station based on the voltage of the connection point of the new energy power station, so that the bus voltage of the new energy power station cluster and the collecting station reaches the preset bus voltage control target.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] The technical solution provided by the present invention is based on the control characteristics under different grid impedance conditions for new energy access, adopts series compensation technology to improve the transmission capacity under the condition of new energy access to a weak grid, conducts hierarchical and zonal reactive power voltage characteristics and their voltage coordinated control, and improves the accessible capacity of the new energy base and the transmission capacity of the new energy grid-connected system;

[0051] The technical solution provided by the present invention has clear mechanism, simple and feasible operation, and is easy to promote. Description of the Drawings

[0052] Figure 1 It is a schematic diagram of the voltage control method for the new energy transmission system of the present invention;

[0053] Figure 2 It is a schematic diagram of the voltage control system for the new energy transmission system of the present invention;

[0054] Figure 3 It is a flowchart of the reactive power voltage control for the new energy transmission system in Embodiment 3 of the present invention;

[0055] Figure 4 This is the schematic diagram of the equivalent circuit of the wind farm collection system in the third embodiment of the present invention;

[0056] Figure 5 This is the PV curve diagram under different X / R in the third embodiment of the present invention. Detailed implementation manners

[0057] To better understand the present invention, the content of the present invention will be further described below in conjunction with the accompanying drawings of the specification and examples.

[0058] Embodiment 1

[0059] A voltage control method for a new energy transmission system, as Figure 1 shown, the method includes:

[0060] Step 1: Based on the relationship between the system voltage and the new energy base transmission power determined in advance, obtain the optimal series compensation degree at different transmission levels of the new energy base. According to the optimal series compensation degree, when the voltage of the new energy station transmission system in the new energy base exceeds the preset normal range, determine the reactive power compensation capacity of the new energy station;

[0061] Step 2: Based on the reactive power compensation capacity, control the reactive power compensation device to make the voltage at the grid connection point of the new energy station reach the preset grid connection point voltage control target;

[0062] Step 3: Based on the voltage at the grid connection point of the new energy station, perform reactive power coordination control on the new energy station cluster and the collection station to make the bus voltages of the new energy station cluster and the collection station reach the preset bus voltage control target.

[0063] Step 1: Based on the relationship between the system voltage and the new energy base transmission power determined in advance, obtain the optimal series compensation degree at different transmission levels of the new energy base. According to the optimal series compensation degree, when the voltage of the new energy station transmission system in the new energy base exceeds the preset normal range, determine the reactive power compensation capacity of the new energy station.

[0064] Specifically, the relationship between the preset voltage and the new energy transmission power includes:

[0065] Analyze the reactive power-voltage characteristics of the new energy base transmission system to obtain the relationship between the sending and receiving system voltage and the active power.

[0066] The relationship between the sending and receiving system voltage and the active power is shown in the following formula:

[0067]

[0068] Wherein, I: the current of the collection line of the new energy power station; E W : the bus voltage of the new energy power station; E S : the bus voltage of the main system; P W : the active and reactive power generated by the new energy power station; X: the reactance of the grid-connected line of the new energy power station; B: the susceptance.

[0069] Specifically, the obtaining of the optimal series compensation degree under different sending levels of the new energy base includes:

[0070] Based on the relationship between the voltage and active power of the sending and receiving system, by adjusting the compensation series compensation amount, perform a sensitivity analysis on the relationship between the active power injected by the new energy power station and the grid-connected point voltage under different series compensation amounts;

[0071] Based on the sensitivity analysis results, adjust the series compensation degree according to the output characteristics, and control the voltage at the grid-connected point under all new energy power outputs within the range preset by the power grid, so as to obtain the optimal series compensation degree under different sending levels of the new energy base.

[0072] Specifically, when the voltage of the sending system of the new energy power station in the new energy base exceeds the preset normal range, determining the reactive power compensation capacity of the new energy power station includes:

[0073] When the voltage of the new energy power station is less than the lower limit of the normal range, set the reactive power compensation capacity as the inductive reactive power compensation capacity, and ensure that the total inductive reactive power can compensate the total charging reactive power of all outgoing lines of the new energy power station;

[0074] When the voltage of the new energy power station is greater than the upper limit of the normal range, set the reactive power compensation capacity as the capacitive reactive power compensation capacity, and ensure that the total capacitive reactive power can compensate half of the total reactive power loss of the station transformer when all new energy power stations are fully loaded and the total reactive power loss of all outgoing lines with a voltage of 500 kV and above in the collection station;

[0075] The upper limit of the normal range is the voltage when the output of the sending system of each new energy power station is greater than 80% of the rated capacity; the lower limit of the normal range is the voltage when the output of the sending system of each new energy power station is less than 30% of the rated capacity.

[0076] Step 2: Based on the reactive power compensation capacity, control the reactive power compensation device to make the voltage at the grid-connected point of the new energy power station reach the preset grid-connected point voltage control target, including:

[0077] When the voltage of the new energy power station is greater than the upper limit of the normal range, adopt the capacitive reactive power compensation strategy:

[0078] When the voltage of the new energy power station is less than the lower limit of the normal range, adopt the inductive reactive power compensation strategy.

[0079] Specifically, the capacitive reactive power compensation strategy includes:

[0080] When the 330 kV / 220 kV bus voltage of the collection substation is lower than the pre-set voltage control target of the grid connection point of the first new energy power station, reactive power is generated until all the capacitive reactive power compensation is used up;

[0081] When the 330 kV / 220 kV bus voltage of the collection substation is higher than the pre-set voltage control target of the grid connection point of the second new energy power station, the generated reactive power is reduced until all the capacitive reactive power compensation is withdrawn.

[0082] The pre-set voltage control target of the grid connection point of the first new energy power station is the voltage of the bus connected to the new energy power station when the grid operates in the maximum operating mode and the new energy output is 0;

[0083] The pre-set voltage control target of the grid connection point of the second new energy power station is the voltage of the bus connected to the new energy power station when the grid operates in the minimum operating mode and the new energy output is 0;

[0084] The inductive reactive power compensation strategy includes:

[0085] When the 330 kV / 220 kV bus voltage of the collection substation is higher than the pre-set voltage control target of the grid connection point of the third new energy power station, reactive power is absorbed until all the inductive reactive power compensation is used up;

[0086] The pre-set voltage control target of the grid connection point of the third new energy power station is the voltage of the bus connected to the new energy power station when the grid operates at the highest voltage and the new energy output is 0.

[0087] Step 3: Based on the voltage of the grid connection point of the new energy power station, perform reactive power coordinated control on the new energy power station cluster and the collection substation to make the bus voltages of the new energy power station cluster and the collection substation reach the pre-set bus voltage control target, including:

[0088] When the bus voltages of the new energy power station cluster and the collection substation cross the lower limit of the pre-set bus voltage control target, a capacitive reactive power coordinated control strategy is adopted;

[0089] When the bus voltages of the new energy power station cluster and the collection substation cross the upper limit of the pre-set bus voltage control target, an inductive reactive power coordinated control strategy is adopted.

[0090] Specifically, the pre-set bus voltage control target includes:

[0091] Disconnect the new energy power station and the collection station, only keep the collection station connected to the power grid, take the bus voltage connected by the collection line as a reference, and under the optimal series compensation degree, take the minimum value of the bus voltage under the maximum operating mode of the power grid as the lower limit of the voltage control target of the collection station; take the maximum value of the bus voltage under the minimum operating mode of the power grid as the upper limit of the bus voltage control target.

[0092] Specifically, the capacitive reactive power coordination control strategy includes:

[0093] When the bus voltage of the new energy power station cluster and the collection station crosses the preset lower limit of the bus voltage control target, according to the reactive power absorbed and emitted by the reactive power compensation devices of each power station in the new energy cluster, capacitive reactive power compensation is put into operation to make the bus voltage higher than the lower limit of the bus voltage control target; if the bus voltage after the reactive power coordination control of the new energy power station cluster and the collection station cannot be higher than the preset lower limit of the bus voltage control target, increase the capacitive compensation capacity, and re-perform the voltage control at the connection point of each new energy power station and the reactive power coordination control of the new energy power station cluster and the collection station until the bus voltage after the reactive power coordination control of the new energy power station cluster and the collection station reaches the preset bus voltage control target;

[0094] The inductive reactive power coordination control strategy includes:

[0095] When the bus voltage of the new energy power station cluster and the collection station crosses the preset upper limit of the bus voltage control target, according to the reactive power absorbed and emitted by the reactive power compensation devices of each power station in the new energy cluster, the capacitive reactive power compensation is withdrawn and the inductive reactive power compensation is put into operation to make the bus voltage lower than the upper limit of the bus voltage control target; if the bus voltage after the reactive power coordination control of the new energy power station cluster and the collection station cannot reach the preset upper limit of the bus voltage control target, increase the inductive compensation capacity, and re-perform the voltage control at the connection point of each new energy power station and the reactive power coordination control of the new energy power station cluster and the collection station until the bus voltage after the reactive power coordination control of the new energy power station cluster and the collection station reaches the preset bus voltage control target.

[0096] Embodiment 2

[0097] Based on the same inventive concept, the present invention also provides a voltage control system for a new energy transmission system, as Figure 2 described, including: a setting module, a first control module, and a second control module;

[0098] The setting module: is used to obtain the optimal series compensation degree under different output levels of the new energy base based on the relationship between the pre-determined system voltage and the output power of the new energy base, and according to the optimal series compensation degree, when the voltage of the new energy power station output system in the new energy base exceeds the preset normal range, determine the reactive power compensation capacity of the new energy power station;

[0099] The first control module: used to control the reactive power compensation device based on the reactive power compensation capacity, so that the grid connection point voltage of the new energy power station reaches the pre-set grid connection point voltage control target;

[0100] The second control module: used to perform reactive power coordination control on the new energy power station cluster and the collection station based on the grid connection point voltage of the new energy power station, so that the bus voltages of the new energy power station cluster and the collection station reach the pre-set bus voltage control target.

[0101] In the setting module, the relationship between the pre-determined voltage and the new energy output power includes:

[0102] Analyze the reactive power-voltage characteristics of the new energy base transmission system to obtain the relationship between the voltage and active power of the transmission system.

[0103] The relationship between the voltage and active power of the transmission system is shown in the following formula:

[0104]

[0105] In the formula, I: the current of the new energy power station collection line; E W : the bus voltage of the new energy power station; E S : the bus voltage of the main system; P W : the active and reactive power generated by the new energy power station; X: the reactance of the new energy power station grid connection line; B: the susceptance.

[0106] Specifically, the obtaining of the optimal series compensation degree at different transmission levels of the new energy base includes:

[0107] Based on the relationship between the voltage and active power of the transmission system, by adjusting the compensation series compensation amount, perform sensitivity analysis on the relationship between the active power injected into the new energy power station and the grid connection point voltage under different series compensation amounts;

[0108] Based on the sensitivity analysis results, adjust the series compensation degree according to the output characteristics, and control the voltage of the grid connection point under all new energy power outputs within the pre-specified range of the power grid to obtain the optimal series compensation degree at different transmission levels of the new energy base.

[0109] Specifically, when the voltage of the new energy power station transmission system in the new energy base exceeds the pre-set normal range, determining the reactive power compensation capacity of the new energy power station includes:

[0110] When the voltage of the new energy power station is less than the lower limit of the normal range, set the reactive power compensation capacity as the inductive reactive power compensation capacity, and the total inductive reactive power can compensate the total charging reactive power of all outgoing lines of the new energy power station;

[0111] When the voltage of the new energy power station is greater than the upper limit of the normal range, set the reactive power compensation capacity as the capacitive reactive power compensation capacity, and the total capacitive reactive power can compensate for half of the total reactive power loss of the station transformer when all new energy power stations are fully loaded and the total reactive power loss of all outgoing lines with a voltage of 500 kV and above in the collection station;

[0112] The upper limit of the normal range is the voltage when the output of the new energy power station's transmission system is greater than 80% of the rated capacity; the lower limit of the normal range is the voltage when the output of the new energy power station's transmission system is less than 30% of the rated capacity.

[0113] In the first control module, based on the reactive power compensation capacity, control the reactive power compensation device to make the grid connection point voltage of the new energy power station reach the pre-set grid connection point voltage control target, including:

[0114] When the voltage of the new energy power station is greater than the upper limit of the normal range, adopt the capacitive reactive power compensation strategy:

[0115] When the voltage of the new energy power station is less than the lower limit of the normal range, adopt the inductive reactive power compensation strategy.

[0116] Specifically, the capacitive reactive power compensation strategy includes:

[0117] When the voltage of the 330 kV / 220 kV busbar in the collection station is lower than the pre-set first grid connection point voltage control target of the new energy power station, emit reactive power until all capacitive reactive power compensation is used up;

[0118] When the voltage of the 330 kV / 220 kV busbar in the collection station is higher than the pre-set second grid connection point voltage control target of the new energy power station, reduce the emitted reactive power until all capacitive reactive power compensation is withdrawn.

[0119] The pre-set first grid connection point voltage control target of the new energy power station is the voltage of the busbar where the new energy power station is connected when the power grid is operating in the maximum operating mode and the new energy output is 0;

[0120] The pre-set second grid connection point voltage control target of the new energy power station is the voltage of the busbar where the new energy power station is connected when the power grid is operating in the minimum operating mode and the new energy output is 0;

[0121] The inductive reactive power compensation strategy includes:

[0122] When the voltage of the 330 kV / 220 kV busbar in the collection station is higher than the pre-set third grid connection point voltage control target of the new energy power station, start absorbing reactive power until all inductive reactive power compensation is used up;

[0123] The pre-set voltage control target of the third new energy power station connection point is the voltage of the bus connected to the new energy power station when the power grid operates at the highest voltage and the new energy output is zero.

[0124] In the second control module, based on the voltage of the new energy power station connection point, reactive power coordination control is performed on the new energy power station cluster and the collection station to make the bus voltages of the new energy power station cluster and the collection station reach the pre-set bus voltage control target, including:

[0125] When the bus voltages of the new energy power station cluster and the collection station cross the lower limit of the pre-set bus voltage control target, a capacitive reactive power coordination control strategy is adopted;

[0126] When the bus voltages of the new energy power station cluster and the collection station cross the upper limit of the pre-set bus voltage control target, an inductive reactive power coordination control strategy is adopted.

[0127] Specifically, the pre-set bus voltage control target includes:

[0128] Disconnect the new energy power stations and the collection station, only keep the collection station connected to the power grid, take the bus voltage connected by the collection line as a reference, and under the optimal series compensation degree, take the minimum value of the bus voltage in the maximum operating mode of the power grid as the lower limit of the voltage control target of the collection station; take the maximum value of the bus voltage in the minimum operating mode of the power grid as the upper limit of the bus voltage control target.

[0129] Specifically, the capacitive reactive power coordination control strategy includes:

[0130] When the bus voltages of the new energy power station cluster and the collection station cross the lower limit of the pre-set bus voltage control target, according to the reactive power absorbed and emitted by the reactive power compensation devices of each power station in the new energy cluster, capacitive reactive power compensation is invested to make the bus voltage higher than the lower limit of the bus voltage control target; if the bus voltage after the reactive power coordination control of the new energy power station cluster and the collection station cannot be higher than the lower limit of the pre-set bus voltage control target, increase the capacitive compensation capacity, re-perform the voltage control of each new energy power station connection point and the reactive power coordination control of the new energy power station cluster and the collection station until the bus voltage after the reactive power coordination control of the new energy power station cluster and the collection station reaches the pre-set bus voltage control target;

[0131] The inductive reactive power coordination control strategy includes:

[0132] When the bus voltage of the new energy power station cluster and the collecting station exceeds the upper limit of the preset bus voltage control target, according to the reactive power absorbed and emitted by the reactive power compensation devices of each power station in the new energy cluster, the capacitive reactive power compensation is withdrawn and the inductive reactive power compensation is put into operation, so that the bus voltage is lower than the upper limit of the bus voltage control target; if the bus voltage after the reactive power coordination control of the new energy power station cluster and the collecting station cannot reach the upper limit of the preset bus voltage control target, the inductive compensation capacity is increased, and the voltage control at the connection point of each new energy power station and the reactive power coordination control of the new energy power station cluster and the collecting station are carried out again until the bus voltage after the reactive power coordination control of the new energy power station cluster and the collecting station reaches the preset bus voltage control target.

[0133] Embodiment III

[0134] The flowchart of reactive power and voltage control for the new energy transmission system is as Figure 3 shown. The large-scale new energy collection system can be equivalently simplified as a structure where a new energy power station is connected to the main system through a line. Generally, the main system is considered as an infinite system, as Figure 4 shown.

[0135] Step 1: Based on the relationship between the pre-determined system voltage and the power output of the new energy base, obtain the optimal series compensation degree at different power output levels of the new energy base. According to the optimal series compensation degree, when the voltage of the new energy power station transmission system in the new energy base exceeds the preset normal range, determine the reactive power compensation capacity of the new energy power station.

[0136] Based on the reactive power and voltage characteristics of each new energy power station transmission system, analyze and obtain the relationship between the system voltage and the power output of the new energy.

[0137] Assume It can be obtained that

[0138]

[0139]

[0140] In the formula, I: the current of the new energy power station collection line; E W : the bus voltage of the new energy power station main system; E S : the bus voltage of the main system; P W : the active and reactive power generated by the new energy power station; X: the reactance of the new energy power station grid-connected line; B: the susceptance; δ: the angle between the new energy power station and the main bus voltage, ignoring the resistance and ground capacitance of the new energy power station grid-connected line.

[0141] When the new energy power station operates at a unity power factor

[0142]

[0143] Further, the relationship between the voltage and active power of the fetching and delivering system is shown in the following formula:

[0144]

[0145] Based on the relationship between the system voltage and the new energy output power, calculate the optimal series compensation degree at different output levels of the new energy base;

[0146] Adopting the series compensation technology, by changing the impedance characteristics of the new energy output system, the output capacity of the new energy grid-connected system can be improved. Based on Figure 5 the static voltage stability of the new energy station output system analyzed by the PV curve diagram under different X / R values shown. The abscissa P represents the active power injected by the new energy station, that is, P W , and the ordinate V represents the grid connection point voltage. As the series compensation degree increases, the X / R value decreases, and the voltage stability margin of the new energy connected to the grid gradually increases, indicating that the voltage stability of the new energy grid-connected system is improved and the accessible capacity of the new energy station is increased. However, the increase in the series compensation degree may lead to too high a voltage in the output system. Therefore, it is necessary to adjust the appropriate series compensation degree according to different output characteristics. In order to obtain the appropriate series compensation degree, it is necessary to carry out a sensitivity analysis of the relationship between the active power P W injected by the new energy station and the grid connection point voltage V under different X / R based on the relational formula between the fetching and delivering system voltage and active power, and it can be seen from Figure 5 that only after adjusting the series compensation amount so that the X / R value changes from 30 to 10 / 3 can the voltage at the grid connection point be controlled at 0.98 pu under all new energy power outputs.

[0147] Based on the optimal series compensation degree, set the inductive and capacitive reactive power compensation capacities based on hierarchical zoning under large / small output.

[0148] Considering the volatility of the wind speed, many new energy stations gathered at the step-up substation will be in a low-output or even zero-output state for a long time. According to the principle of hierarchical zoning balance, inductive and capacitive reactive power compensation devices should be installed at the new energy gathering step-up substation to balance the charging power and reactive power loss on the output line, so as to ensure that there is little or no reactive power flow between the 500 kV and 220 kV power grid layers. Based on the optimal series compensation degree, determine the reactive power compensation capacity based on hierarchical zoning under large / small output.

[0149] Under the low output of the new energy station, determine the inductive reactive power compensation capacity, and the total configured inductive reactive power should be able to compensate the total charging reactive power of all its outgoing lines; under the large output of the new energy station, determine the capacitive reactive power compensation capacity, and the total configured capacitive reactive power should be able to compensate the total reactive power loss of the station transformer when all new energy stations are fully loaded, and half of the total reactive power loss of all 500 kV outgoing lines of this gathering station.

[0150] Step 2: Based on the reactive power compensation capacity, control the reactive power compensation device to make the grid connection point voltage of the new energy power station reach the pre-set grid connection point voltage control target.

[0151] The control points of the capacitor banks and reactive power compensation devices of the new energy collection and boosting substation are the 330 kV / 220 kV busbars of the collection station. The reactive power control points of the new energy power station are the 330 kV / 220 kV busbars of the grid connection point. When the voltage of the 330 kV / 220 kV busbar of the collection station is lower than 1.03 pu, reactive power is generated until all capacitive reactive power compensation is used up;

[0152] When the voltage at this point is higher than 1.05 pu, the generated reactive power is reduced until all capacitive reactive power compensation is withdrawn;

[0153] When the voltage at this point is higher than 1.07 pu, reactive power is absorbed, and at the same time, it is ensured that the voltage of the 220 kV busbar of the collection station does not exceed 1.1 pu until all inductive reactive power compensation is used up.

[0154] Step 3: Based on the grid connection point voltage of the new energy power station, perform reactive power coordination control on the new energy power station cluster and the collection station to make the busbar voltages of the new energy power station cluster and the collection station reach the pre-set busbar voltage control target.

[0155] Determine the voltage control target of the collection station: Disconnect the new energy cluster and the collection station, and only keep the collection station connected to the power grid. Taking the voltage of the system busbar connected by the collection line as a reference, under the given optimal series compensation degree, take the minimum value of the voltage of the system busbar in the maximum operating mode of the system as the lower limit of the voltage control target of the collection station; take the maximum value of the voltage of the system busbar in the minimum operating mode as the upper limit of the voltage control target of the collection station.

[0156] On this basis: When the voltage control target of the collection station crosses the lower limit, according to the voltage control targets of each power station in the new energy cluster, capacitive compensation is put into operation. When the voltage control target of the collection station is still below the lower limit, the capacitive reactive power compensated by the collection station is put into operation until it is higher than the lower limit; if the voltage is still within the lower limit after all are put into operation, on the basis of ensuring that the voltage of the new energy power station does not exceed the limit, all capacitive compensation is put into operation. If it is still not enough, increase the capacitive compensation capacity, re-determine the inductive and capacitive reactive power compensation capacities based on hierarchical zoning under large / small output, and perform absorption and generation reactive power control on the grid connection point voltage control targets and reactive power compensation devices of each new energy power station until the voltage of the 220 kV busbar after reactive power coordination control of the new energy power station cluster and the collection station does not exceed 1.1 pu.

[0157] Similarly, when the voltage control target of the collection station exceeds the upper limit, according to the voltage control targets of each power station in the new energy cluster, the capacitive compensation is withdrawn and the inductive compensation is put into operation. When the voltage control target of the collection station is still above the upper limit, the inductive reactive power compensated by the collection station is put into operation until it is lower than the upper limit. If the voltage is still within the upper limit after all inductive compensations are put into operation, on the basis of ensuring that the voltage of the new energy power stations does not exceed the limit, all inductive compensations are put into operation. If it is still not enough, the capacitive compensation capacity is increased, and the inductive and capacitive reactive power compensation capacities based on hierarchical zoning under large / small power outputs are re-determined. The absorption and emission of reactive power of the voltage control targets and reactive power compensation devices at the grid connection points of each new energy power station are carried out until the 220 kV bus voltage after the reactive power coordinated control of the new energy power station cluster and the collection station does not exceed 1.1 pu.

[0158] The above facts show that the technical solution provided by the present invention is based on the control characteristics under different grid impedance conditions for new energy access, adopts the series compensation technology to improve the transmission capacity under the condition of new energy access to a weak grid, conducts reactive voltage characteristics and their voltage coordinated control, and improves the accessible capacity of the new energy base and the transmission capacity of the new energy grid-connected system;

[0159] The technical solution provided by the present invention has clear mechanism, simple and feasible operation, and is easy to popularize.

[0160] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0161] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the specified functions in Figure 1 one or more processes or multiple processes and / or blocks Figure 1 one or more blocks or multiple blocks.

[0162] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction device that implements the functions specified in one or more of the processes and / or blocks Figure 1 one or more of the processes and / or blocks Figure 1 specified in the block or blocks.

[0163] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one or more of the processes and / or blocks Figure 1 one or more of the processes and / or blocks Figure 1 specified in the block or blocks.

[0164] The above are only embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included within the scope of the claims of the present invention pending approval of the application.

Claims

1. A voltage control method for a new energy transmission system, characterized in that, The method includes: Based on the pre-determined relationship between the system voltage and the power output of the new energy base, obtaining the optimal series compensation degree at different output levels of the new energy base. According to the optimal series compensation degree, when the voltage of the power transmission system of the new energy power station in the new energy base exceeds the pre-set normal range, determining the reactive power compensation capacity of the new energy power station; Based on the reactive power compensation capacity, controlling the reactive power compensation device to make the grid connection point voltage of the new energy power station reach the pre-set grid connection point voltage control target; Based on the grid connection point voltage of the new energy power station, performing reactive power coordination control on the new energy power station cluster and the collecting station to make the bus voltages of the new energy power station cluster and the collecting station reach the pre-set bus voltage control target; When the voltage of the new energy power station is less than the lower limit of the normal range, setting the reactive power compensation capacity as the inductive reactive power compensation capacity, and the total inductive reactive power can compensate the total charging reactive power of all outgoing lines of the new energy power station; When the voltage of the new energy power station is greater than the upper limit of the normal range, setting the reactive power compensation capacity as the capacitive reactive power compensation capacity, and the total capacitive reactive power can compensate half of the total reactive power loss of the in-station transformer when all new energy power stations are fully loaded and the total reactive power loss of all outgoing lines with a voltage of 500 kV and above at the collecting station; The upper limit of the normal range is the voltage when the output of the power transmission system of each new energy power station is greater than 80% of the rated capacity; the lower limit of the normal range is the voltage when the output of the power transmission system of each new energy power station is less than 30% of the rated capacity; Disconnecting the new energy power station and the collecting station, only keeping the collecting station connected to the power grid. Taking the bus voltage connected by the collecting line as a reference, at the optimal series compensation degree, taking the minimum value of the bus voltage under the maximum operating mode of the power grid as the lower limit of the bus voltage control target; taking the maximum value of the bus voltage under the minimum operating mode of the power grid as the upper limit of the bus voltage control target; When the bus voltage of the new energy power station cluster and the collecting station crosses the pre-set lower limit of the bus voltage control target, adopting a capacitive reactive power coordination control strategy; When the bus voltage of the new energy power station cluster and the collecting station crosses the pre-set upper limit of the bus voltage control target, adopting an inductive reactive power coordination control strategy.

2. The voltage control method of the new energy transmission system according to claim 1, characterized in that, The pre-determined relationship between the system voltage and the power output of the new energy base includes: Analyzing the reactive power-voltage characteristics of the power transmission system of the new energy base to obtain the relationship between the system voltage and the active power; The relationship between the system voltage and the active power is shown in the following formula: Wherein, : The current of the collection line of the new energy power station; : The bus voltage of the new energy power station; : The bus voltage of the main system; : The active power generated by the new energy power station; : The reactance of the grid-connected line of the new energy power station; : Susceptance.

3. The voltage control method for the new energy transmission system according to claim 2, wherein, The obtaining of the optimal series compensation degree at different output levels of the new energy base includes: Based on the relationship between the system voltage and the active power, by adjusting the compensation series compensation amount, performing sensitivity analysis on the relationship between the active power injected by the new energy power station and the grid connection point voltage under different series compensation amounts; Based on the sensitivity analysis results, adjusting the series compensation degree according to the output characteristics, and controlling the voltage of the grid connection point under all new energy power outputs within the pre-specified range of the power grid to obtain the optimal series compensation degree at different output levels of the new energy base.

4. The voltage control method of the new energy transmission system according to claim 1, characterized in that, The controlling the reactive power compensation device based on the reactive power compensation capacity to make the grid connection point voltage of the new energy power station reach the pre-set grid connection point voltage control target includes: When the voltage of the new energy power station is greater than the upper limit of the normal range, a capacitive reactive power compensation strategy is adopted: When the voltage of the new energy power station is less than the lower limit of the normal range, an inductive reactive power compensation strategy is adopted.

5. The voltage control method of the new energy transmission system according to claim 4, wherein The capacitive reactive power compensation strategy includes: When the voltage of the 330kV / 220kV bus of the collection station is lower than the pre-set voltage control target of the grid connection point of the first new energy power station, reactive power is generated until all the capacitive reactive power compensation is used up; When the voltage of the 330kV / 220kV bus of the collection station is higher than the pre-set voltage control target of the grid connection point of the second new energy power station, the generated reactive power is reduced until all the capacitive reactive power compensation is withdrawn; The pre-set voltage control target of the grid connection point of the first new energy power station is the voltage of the bus connected to the new energy power station when the grid operates in the maximum operating mode and the new energy output is 0; The pre-set voltage control target of the grid connection point of the second new energy power station is the voltage of the bus connected to the new energy power station when the grid operates in the minimum operating mode and the new energy output is 0; The inductive reactive power compensation strategy includes: When the voltage of the 330kV / 220kV bus of the collection station is higher than the pre-set voltage control target of the grid connection point of the third new energy power station, reactive power is absorbed until all the inductive reactive power compensation is used up; The pre-set voltage control target of the grid connection point of the third new energy power station is the voltage of the bus connected to the new energy power station when the grid operates at the highest voltage and the new energy output is 0.

6. The voltage control method of the new energy transmission system according to claim 1, characterized in that The capacitive reactive power coordinated control strategy includes: When the bus voltage of the new energy power station cluster and the collection station crosses the lower limit of the pre-set bus voltage control target, capacitive reactive power compensation is input according to the reactive power absorbed and generated by the reactive power compensation devices of each power station in the new energy cluster, so that the bus voltage is higher than the lower limit of the bus voltage control target; if the bus voltage after the reactive power coordinated control of the new energy power station cluster and the collection station cannot be higher than the lower limit of the pre-set bus voltage control target, the capacitive compensation capacity is increased, and the voltage control of the grid connection point of each new energy power station and the reactive power coordinated control of the new energy power station cluster and the collection station are re-performed until the bus voltage after the reactive power coordinated control of the new energy power station cluster and the collection station reaches the pre-set bus voltage control target; The inductive reactive power coordinated control strategy includes: When the bus voltage of the new energy power station cluster and the collection station crosses the upper limit of the pre-set bus voltage control target, the capacitive reactive power compensation is withdrawn and the inductive reactive power compensation is input according to the reactive power absorbed and generated by the reactive power compensation devices of each power station in the new energy cluster, so that the bus voltage is lower than the upper limit of the bus voltage control target; if the bus voltage after the reactive power coordinated control of the new energy power station cluster and the collection station cannot reach the upper limit of the pre-set bus voltage control target, the inductive compensation capacity is increased, and the voltage control of the grid connection point of each new energy power station and the reactive power coordinated control of the new energy power station cluster and the collection station are re-performed until the bus voltage after the reactive power coordinated control of the new energy power station cluster and the collection station reaches the pre-set bus voltage control target.

7. A voltage control system for a new energy transmission system for implementing the method as described in claim 1, characterized in that, The system includes: a setting module, a first control module and a second control module; Setting module: configured to obtain an optimal series compensation degree at different power transmission levels of a new energy base based on the relationship between a pre-determined system voltage and the power transmitted by the new energy base, and determine the reactive power compensation capacity of a new energy power station according to the optimal series compensation degree when the voltage of the power transmission system of the new energy power station in the new energy base exceeds a pre-set normal range; First control module: configured to control a reactive power compensation device based on the reactive power compensation capacity, so that the grid connection point voltage of the new energy power station reaches a pre-set grid connection point voltage control target; Second control module: configured to perform reactive power coordination control on a new energy power station cluster and a collection station based on the grid connection point voltage of the new energy power station, so that the bus voltages of the new energy power station cluster and the collection station reach pre-set bus voltage control targets.

Images