Sending end voltage multi-source coordination control method suitable for wind-light-water alternating-current and direct-current delivery system

Abstract

The invention discloses a sending end voltage multi-source coordination control method suitable for a wind-light-water alternating-current and direct-current delivery system. The method comprises the following steps: firstly, judging whether a direct current commutation failure fault occurs or not through commutation failure detection logic according to an overvoltage fault caused by commutation failure by judging a sending end overvoltage type, and after the commutation failure fault occurs, transmitting a voltage error signal to a direct current sending end converter station through a channel; the error signal enables the hydroelectric generating set to add an excitation control action, and cooperates with a fan and photovoltaic control strategy for real-time response to suppress system voltage fluctuation caused by commutation failure, and finally, simulation verification is performed on the system adopting the coordination control strategy under different operation conditions, so that the system performance is improved. Therefore, the voltage stability of the wind-light-water bundled alternating-current and direct-current delivery system is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, and particularly relates to a voltage multi-source coordinated control method suitable for a wind-solar-water AC / DC sending system sending end. BACKGROUND

[0002] The southwest region is rich in water resources, and is a typical scene of large-scale water power generation as the main body of external transmission. With the continuous improvement of new energy development, the sending end power grid has formed a large-scale wind power, photovoltaic and water power bundled external transmission system. Therefore, the future new energy power grid layout will be more complex and diversified. In large-scale power transmission, line-commutated-converter based high voltage direct current (LCC-HVDC) is widely used due to its mature technology, long transmission distance and other advantages. With the gradual complexity of the grid framework, there are also AC / DC parallel structures in the system. The AC / DC parallel system with a high proportion of new energy is one of the typical grid framework forms. One of the significant features of the AC / DC parallel grid framework structure is that the AC / DC fault disturbance is easily transmitted in the large synchronous grid, the transmission range will be wider, and the impact will be greater. Coupled with the interaction of high proportion of new energy and ultra-high voltage direct current with the characteristics of "double high", the uncertainty will further increase, and the cascading evolution reaction is easy to occur, and the risk of blackout is increased.

[0003] The interaction of high proportion of new energy and ultra-high voltage direct current forms a heterogeneous multi-power electronic system based on different principles such as main grid commutation and voltage source converter. The dynamic autonomous response control interaction characteristics of the multi-power electronic system such as fault ride-through and commutation failure are complex. The local power oscillation and unbalanced power caused by the propagation and evolution of the wide-area AC / DC parallel system and the impact on the safety and stability of the main grid are not fully revealed. At the same time, the influence of the connection and disconnection of important components of the AC system on the stability characteristics and transmission capacity of the power grid is not clear. At present, most of the literature researches are based on single machine models such as hydropower, wind power and photovoltaic power. However, with the more complex grid framework and higher coupling degree of multi-power sources in the sending end system, it is necessary to study the voltage stability under the coupling of multi-power sources in the sending end.

[0004] Therefore, the application provides a voltage multi-source coordinated control method suitable for a wind-solar-hydropower AC / DC external transmission system. SUMMARY

[0005] The application aims to provide a voltage multi-source coordinated control method suitable for a wind-solar-hydropower AC / DC external transmission system, thereby effectively improving the voltage stability of the wind-solar-hydropower AC / DC external transmission system.

[0006] The application is implemented by adopting the following technical scheme:

[0007] The application provides a voltage multi-source coordinated control method suitable for a wind-solar-hydropower AC / DC external transmission system.

[0008] As a preferred scheme of the application, the scheme comprises the following steps:

[0009] Step A1: When the system is normally operated, the voltage of the power system is stable, and each unit is normally operated, so the coordinated control strategy does not need to be put into operation.

[0010] Step A2: The voltage of the DC converter station bus is monitored in real time, and whether the commutation failure fault occurs is determined according to the commutation failure detection logic; when the commutation failure fault is detected, the signal is transmitted to the hydropower and new energy units through a channel.

[0011] Step A3: When the commutation failure fault is detected, the wind-solar-hydropower coordinated control strategy is put into operation, the control strategy of each unit and the output reactive power of each unit are adjusted, and thus the system overvoltage is suppressed.

[0012] The transmission voltage error signal in step A2 is specifically:

[0013] A21: When normally operated, S CF = 0; when the DC is determined to be the commutation failure fault by the commutation failure detection logic, S CF= 1, and transmitted to each unit through the channel:

[0014] The DC sending end converter station AC bus voltage error signal is defined as the difference between the DC sending end converter station AC bus voltage reference value and the actual effective value, and its formula is:

[0015] U s1 = U ref -U T (1)

[0016] In the formula, U s1 is the voltage error signal, U ref is the DC sending end converter station AC bus voltage reference value, and U T is the DC sending end converter station AC bus voltage actual effective value.

[0017] A3: Put in the wind, light and water collaborative control strategy, and the water power strategy is as follows:

[0018] A31: The error signal of the hydroelectric unit is the difference between the hydroelectric unit terminal voltage reference value and the actual effective value, and its formula is:

[0019] U s2 = U ref1 -U T1 (2)

[0020] In the formula, U s2 is the voltage error signal input to the excitation system, U ref1 is the hydroelectric unit terminal voltage reference value, and U T1 is the hydroelectric unit terminal voltage actual effective value.

[0021] The input signal of the additional controller of the hydroelectric unit is a digital S CF = 0, which is equivalent to the additional excitation controller not working, and S CF = 1, the additional controller acts as an additional control for the hydroelectric unit. During the commutation failure overvoltage, in order to fully develop the potential of the water power to absorb reactive power, the water power control terminal voltage is switched to the coordinated control of the water power and the converter station bus voltage, and its formula is:

[0022] U s3 = K·U s1 + U ref1 -U T1 = K(U ref -U T ) + U ref1 -U T1 (3)

[0023] In the formula, K is the gain coefficient of the additional excitation controller.

[0024] A32: New energy unit control strategy, taking wind turbine as an example: the input signal of the additional controller of the wind turbine is digital S CF =0, which is equivalent to the additional controller not working, S CF =1, the additional controller works, the wind turbine receives the difference between the bus voltage signal and the reference value, and the obtained deviation signal is input to the high voltage ride-through control system in the form of an additional voltage signal, and the voltage deviation value U s4 is obtained by operating the actual value and the reference value of the terminal voltage, wherein the expression of U s4 is as follows:

[0025] U s4 =K(U ref -U T1 )+U ref2 -U T2 (4)

[0026] In the formula, U s4 is the voltage deviation value, U ref2 is the wind turbine terminal voltage reference value, U T2 is the actual effective value of the wind turbine terminal voltage, and K is the gain coefficient of the additional controller:

[0027] The reactive power output capability of the GSC during the grid voltage surge mainly depends on the voltage surge amplitude, and is almost not affected by the output active current of the converter. According to the maximum allowable current I gmax of the GSC, the minimum reactive power Q gmin absorbed by the GSC during the commutation failure overvoltage period and the maximum active power P gmax can be obtained:

[0028]

[0029] At the same time, the reactive power output of the wind farm is limited by the capacity of the converter, so the amplitude of the reactive power output is set as:

[0030] BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A flow chart of a wind-solar-hydropower AC / DC transmission system sending end voltage multi-source coordinated control method provided by the application.

[0032] Figure 2 A structure diagram of a certain wind-solar-hydropower AC / DC transmission system, used for verifying the effectiveness of the wind-solar-hydropower AC / DC transmission system sending end voltage multi-source coordinated control method described in the application.

[0033] Figure 3 An additional control schematic diagram of a hydropower unit.

[0034] Figure 4 The additional control schematic diagram for the wind turbine.

[0035] Figure 5 For the wind, light, water, and AC-DC external transmission system, after the DC commutation failure fault, the coordinated control method of suppressing system commutation failure overvoltage is configured for the grid connection point voltage, Figure 5 (a) is the grid connection point voltage schematic diagram after single-phase grounding fault, Figure 5 (b) is the grid connection point voltage schematic diagram after two-phase short circuit, Figure 5 (c) is the grid connection point voltage schematic diagram after two-phase grounding, Figure 5 (d) is the grid connection point voltage schematic diagram after three-phase short circuit.

[0036] Figure 6 For the wind, light, water, and AC-DC external transmission system, after the coordinated control strategy is adopted, time domain simulation analysis is carried out for different additional control gain coefficients K, and when the additional control gain coefficient K is 0.8, 1.0, 1.2, and 1.3, the commutation bus voltage schematic diagram. DETAILED DESCRIPTION

[0037] The application provides a kind of suitable for wind, light, water and AC-DC external transmission system sending end voltage multi-source coordinated control method, to make the purpose, technical scheme and effect of the present application clearer, the specific implementation scheme of the present application is described in detail as follows with reference to drawing and example.The specific examples described in the present application are only used to explain the present application, not to limit the present application.

[0038] 1.Introduction of the specific embodiment of the application

[0039] Figure 1 A kind of suitable for wind, light, water and AC-DC external transmission system sending end voltage multi-source coordinated control method flow chart is provided in the present application.Referring to Figure 1 , the specific steps of the suitable for wind, light, water and AC-DC external transmission system sending end voltage multi-source coordinated control method described in the present application are as follows:

[0040] A1: when the system is normally operated, the system voltage remains stable, and each unit is normally operated without the need to input the coordinated control strategy.

[0041] A2: by real-time monitoring of the DC converter station bus voltage, whether commutation failure fault occurs is judged according to commutation failure detection logic, when commutation failure fault is detected, the signal is transmitted from the channel to the hydropower and new energy units.

[0042] A3: when commutation failure fault is detected, the wind, light and water coordinated control strategy is input, the control strategy of each unit and the output reactive power of each unit are adjusted, so as to suppress system overvoltage.

[0043] Further, the following specific steps are included:

[0044] A2: transmit the voltage error signal, specifically:

[0045] A21: when normal operation, record S CF = 0; when the commutation failure detection logic judges that the DC is a commutation failure fault, record S CF = 1, and transmit to each unit through the channel:

[0046] The DC sending end converter station AC bus voltage error signal is defined as the difference between the DC sending end converter station AC bus voltage reference value and the actual effective value, and its formula is:

[0047] U s1 = U ref -U T (7)

[0048] In the formula, U s1 is the voltage error signal, U ref is the DC sending end converter station AC bus voltage reference value, and U T is the DC sending end converter station AC bus voltage actual effective value.

[0049] A3: put into wind-solar-water collaborative control strategy, and the water power strategy is specifically:

[0050] A31: the error signal of the water power unit is the difference between the water power unit terminal voltage reference value and the actual effective value, and its formula is:

[0051] U s2 = U ref1 -U T1 (8)

[0052] In the formula, U s2 is the voltage error signal input to the excitation system, U ref1 is the water power unit terminal voltage reference value, and U T1 is the water power unit terminal voltage actual effective value.

[0053] The input signal of the additional controller of the water power unit is the digital S CF = 0, which is equivalent to the additional excitation controller not working, S CF = 1, the additional controller acts on the additional control of the water power unit, and during the commutation failure overvoltage, the water power control terminal voltage is switched to the coordinated control of the water power and the converter station bus voltage, and its formula is:

[0054] U s3 = K·U s1 + U ref1 -U T1 = K(U ref -U T ) + U ref1-U T1 (9)

[0055] Wherein, K is the gain coefficient of the additional excitation controller.

[0056] A32: New energy unit control strategy, taking wind turbine as an example: the input signal of the additional controller of the wind turbine is digital S CF =0, which is equivalent to the additional controller not working, S CF =1, the additional controller works, the wind turbine receives the difference between the bus voltage signal and the reference value, and the obtained deviation signal is input to the high voltage ride-through control system in the form of additional voltage signal, and the voltage deviation value U s4 is obtained by operating the actual value and the reference value of the terminal voltage. s4 The expression of U s4 is as follows:

[0057] U ref =K(U T1 -U ref2 )+U T2 (10)

[0058] Wherein, U s4 is the voltage deviation value, U ref2 is the reference value of the terminal voltage of the wind turbine, U T2 is the actual effective value of the terminal voltage of the wind turbine, and K is the gain coefficient of the additional controller.

[0059] The reactive power output capability of GSC during the grid voltage surge mainly depends on the voltage surge amplitude, and is almost not affected by the output active current of the converter. According to the maximum allowable current I gmax of GSC, the minimum reactive power Q gmin absorbed by GSC during commutation failure overvoltage period and the maximum active power P gmax can be obtained:

[0060]

[0061] Wherein, Q gmin is the minimum reactive power absorbed by GSC during commutation failure overvoltage period, P gmax is the maximum active power absorbed by GSC during commutation failure overvoltage period, U gmax is the peak value of grid-connected point phase voltage, and m is the modulation coefficient.

[0062] At the same time, the reactive power output of the wind farm is limited by the capacity of the converter, so the amplitude of the reactive power output is set as:

[0063]

[0064] Wherein, Q wmaxFor reactive output amplitude, S w For converter capacity, P w For active output.

[0065] In summary, the wind and light water through AC and DC transmission system voltage multi-source coordinated control method flow chart as Figure 1 The first monitoring system whether to occur commutation failure fault, in the commutation failure overvoltage stage, timely put in the coordinated control strategy of water and new energy unit, cooperate to absorb the surplus reactive power of system, after commutation failure, readjust the system control mode, finally the system normal operation.

[0066] 2. The technical feasibility of the application

[0067] The simulation example structure diagram as Figure 2 The additional control as Figure 3 , Figure 4 The simulation results as Figure 5 , Figure 6 The effectiveness of the application is verified.

[0068] Figure 3 The additional control schematic diagram of hydroelectric generating set.

[0069] Figure 4 The additional control schematic diagram of wind turbine.

[0070] Figure 5 For wind and light water through AC and DC transmission system, after DC commutation failure, configure the coordinated control method of suppressing system commutation failure overvoltage, the grid connection point voltage, Figure 5 (a) is the grid connection point voltage schematic diagram after single-phase grounding fault, Figure 5 (b) is the grid connection point voltage schematic diagram after two-phase short circuit, Figure 5 (c) is the grid connection point voltage schematic diagram after two-phase grounding, Figure 5 (d) is the grid connection point voltage schematic diagram after three-phase short circuit, from Figure 5 It can be known that when the wind and light water coordinated control strategy is put in, during the commutation failure low voltage, the bus voltage change condition is similar to that of not equipped with coordinated control strategy. And in the overvoltage stage of commutation failure, due to the influence of avoiding reactive current withdrawal delay, and the coordinated cooperation of water and new energy unit, the surplus reactive power at the grid connection point is better absorbed, so that the overvoltage amplitude under different fault types is reduced, which verifies the effectiveness of the wind and light water through AC and DC transmission system voltage multi-source coordinated control method.

[0071] Figure 6For the wind, light and water through AC and DC power transmission system, after adopting the coordinated control strategy, time domain simulation analysis is carried out for different additional control gain coefficients K, when the additional control gain coefficient K is 0.8, 1.0, 1.2 and 1.3, the commutation bus voltage diagram, with the increase of the additional control gain coefficient K, the overvoltage amplitude caused by the commutation failure decreases to a certain extent, and the overvoltage of the wind, light and water sending end system is further suppressed.

[0072] In summary, the wind, light and water through AC and DC power transmission system voltage multi-source coordinated control method can adjust the control mode of each unit after the commutation failure of the wind, light and water through AC and DC power transmission system, the new energy unit is put into the additional controller, and the double control target of the coordinated DC sending end commutation station AC bus voltage is converted, and the overvoltage caused by the commutation failure is suppressed together with the water power, so as to suppress the system overvoltage and improve the voltage stability of the system. The simulation results verify the effectiveness and adaptability of the parameter optimization method.

[0073] Finally, it should be noted that the above examples of the present application are only examples for illustrating the present application, and are not limited to the embodiments of the present application. Although the applicant has described the present application in detail with reference to the preferred embodiments, those skilled in the art can make other different forms of changes and variations on the basis of the above description. It is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A method for multi-source coordinated control of the sending-end voltage of a wind, solar, and hydropower AC / DC transmission system, characterized in that, Includes the following steps: S1: When the system is running normally, the system voltage remains stable and all units are operating normally, without the need to engage in collaborative control strategies; S2: By monitoring the bus voltage of the DC converter station in real time, the system determines whether a commutation failure fault has occurred based on the commutation failure detection logic. When a commutation failure fault is detected, the error signal is transmitted from the channel to the hydropower and new energy units. S3: When a commutation failure is detected, the wind-solar-hydro coordinated control strategy is activated to adjust the control strategies of each unit and the reactive power output of each unit, thereby suppressing system overvoltage.

2. The method for multi-source coordinated control of the sending-end voltage of a wind, solar, and hydropower AC / DC transmission system according to claim 2, characterized in that, Step S2 transmits the voltage error signal, and the specific strategy is as follows: S21: During normal operation, record S CF =0; When the commutation failure detection logic determines that the DC circuit is experiencing a commutation failure fault, record S as 0. CF =1, and transmitted to each unit via the channel; The AC bus voltage error signal of the DC sending-end converter station is defined as the difference between the reference value and the actual effective value of the AC bus voltage of the DC sending-end converter station, and its formula is: IN s1 =U ref -IN T (1) In the formula, U s1 For voltage error signal, U ref U is the reference value for the AC bus voltage of the DC sending-end converter station. T This represents the actual effective value of the AC bus voltage at the DC-to-DC converter station.

3. The method for multi-source coordinated control of the sending-end voltage of a wind, solar, and hydropower AC / DC transmission system according to claim 3, characterized in that, Step S3: Wind-solar-water coordinated control strategy, the specific strategy is as follows: S31: The error signal of a hydropower unit is the difference between the reference value of the turbine terminal voltage and the actual effective value of the turbine terminal voltage. The formula is: [Formula omitted for brevity], where U... s2 To input the voltage error signal of the excitation system, U ref1 U is the reference value for the terminal voltage of the hydropower unit. T1 This represents the actual effective value of the terminal voltage of the hydropower unit. IN s2 =U ref1 -IN T1 (2) The additional controller input signal for the hydroelectric generator is a digital S CF When S = 0, it is equivalent to the additional excitation controller not functioning, S CF When = 1, the additional controller action for the additional control of the hydropower unit, during the overvoltage period of commutation failure, switches the voltage at the hydropower control unit terminal to coordinated control of the hydropower and converter station bus voltages. The formula is: IN s3 =K·U s1 +U ref1 -IN T1 =K(U ref -IN T )+U ref1 -IN T1 (3) In the formula, K is the gain coefficient of the additional excitation controller; S32: Control strategy for new energy units, taking wind turbine units as an example: The input signal of the auxiliary controller for wind turbine units is a digital S CF When S = 0, it is equivalent to the additional controller not functioning. CF When the voltage is equal to 1, the auxiliary controller activates, and the wind turbine subtracts the received converter bus voltage signal from the reference value. The resulting deviation signal is input to the high voltage ride-through control system as an auxiliary voltage signal. This deviation signal is then calculated with the actual terminal voltage value and the reference value to obtain the voltage deviation value U. s4 U s4 The expression is as follows: IN s4 =K(U ref -IN T1 )+U ref2 -IN T2 (4) In the formula, U s4 U is the voltage deviation value. ref2 U is the reference value for the terminal voltage of the wind turbine. T2 is the actual effective value of the wind turbine terminal voltage, and K is the gain coefficient of the additional controller; During a grid voltage surge, the reactive power output capability of the GSC depends primarily on the magnitude of the voltage surge, and is almost unaffected by the converter's output active current. This is based on the GSC's maximum allowable current I. gmax The constraint conditions allow us to obtain the minimum reactive power Q absorbed by the GSC during the commutation failure overvoltage period. gmin and maximum active power P gmax : In the formula, Q gmin P is the minimum reactive power absorbed by the GSC during the commutation failure overvoltage period. gmax The maximum active power absorbed by the GSC during the commutation failure overvoltage period, U gmax The peak value of the phase voltage at the grid connection point is denoted as m, and the modulation coefficient is denoted as m. Meanwhile, the reactive power output of the wind farm is limited by the converter capacity, therefore the reactive power output amplitude is set to: In the formula, Q wmax S represents the reactive power output amplitude. w For converter capacity, P w This is active power output.

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