Dynamic optimization method and device for low-voltage ride-through threshold value of new energy converter

Abstract

The invention discloses a dynamic optimization method and device for a low-voltage ride-through threshold value of a new energy converter, and the method comprises the steps: carrying out the dynamic adjustment of an active power weight coefficient during a fault period of a new energy station according to the active power outputted by the new energy station before a power grid fault and the total installed capacity of the station; according to the working state, the active power weight coefficient and the power grid voltage drop degree of the new energy station before the fault, the threshold value of the converter entering the low voltage ride-through state is optimized; and according to the low-voltage ride-through threshold optimization result of the new energy station, the station issues the optimized low-voltage ride-through threshold to each converter before the fault occurs, so that each converter responds to the power grid fault according to the set low-voltage ride-through threshold. According to the working condition of the new energy station before the fault and the power grid voltage drop degree, the low-voltage ride-through threshold value of the new energy converter in the station is optimized, and the active power output of the new energy station during the fault period is improved under the condition that certain voltage supporting capacity is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of low voltage ride through control of new energy converters, and particularly to a method and device for dynamically optimizing the low voltage ride through threshold of new energy converters. Background Art

[0002] Currently, during a low voltage fault in the power grid, new energy power stations will, in accordance with national standards, output a certain amount of reactive current according to the degree of voltage drop to support the grid voltage. However, when adopting this strategy, due to the limited capacity of the converter, the active power output of new energy power stations will be reduced. Against the background of high new energy penetration, if a large amount of new energy enters the low voltage ride through state simultaneously, there will be a large shortage of active power in the overall system, which will in turn cause fluctuations in the system frequency and pose a threat to the safety of the power system. Summary of the Invention

[0003] In view of this, embodiments of the present invention provide a method and device for dynamically optimizing the low voltage ride through threshold of new energy converters. According to the working state of the new energy power station before the grid fault and the degree of voltage drop, the dynamic optimization of the low voltage ride through threshold of new energy is realized by establishing and solving an optimization model, thereby improving the output of new energy active power during the fault and improving the frequency safety of the power system.

[0004] According to the first aspect of the embodiments of the present application, a method for dynamically optimizing the low voltage ride through threshold of new energy converters is provided, including:

[0005] Dynamically adjusting the active power weight coefficient during the fault of the power station according to the active power output by the new energy power station before the grid fault and the total installed capacity of the power station;

[0006] Optimizing the threshold for the converter to enter the low voltage ride through state according to the working state of the new energy power station before the fault, the dynamically adjusted active power weight coefficient, and the degree of grid voltage drop;

[0007] According to the optimization result of the low voltage ride through threshold of the new energy power station, sending the reactive current reference command to each converter in the power station, so that each converter responds to the grid fault according to the set low voltage ride through threshold.

[0008] According to the second aspect of the embodiments of the present application, a device for dynamically optimizing the low voltage ride through threshold of new energy converters is provided, including:

[0009] A calculation module, configured to dynamically adjust the active power weight coefficient during the fault of the power station according to the active power output by the new energy power station before the grid fault and the total installed capacity of the power station;

[0010] An optimization module, configured to optimize the threshold for the converter to enter the low-voltage ride-through state according to the pre-fault operating state of the new energy power station, the active power weight coefficient after dynamic adjustment, and the degree of grid voltage dip;

[0011] A communication module, configured to send the optimized low-voltage ride-through threshold to each converter before a fault occurs in the new energy power station according to the optimization result of the low-voltage ride-through threshold of the new energy power station, so that each converter responds to the grid fault according to the set low-voltage ride-through threshold.

[0012] According to a third aspect of the embodiments of the present application, there is provided an electronic device, including:

[0013] One or more processors;

[0014] A memory, configured to store one or more programs;

[0015] When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0016] According to a fourth aspect of the embodiments of the present application, there is provided a computer-readable storage medium, on which computer instructions are stored, and when the instructions are executed by a processor, the steps of the method as described in the first aspect are implemented.

[0017] The beneficial effects of the present invention are as follows:

[0018] The active power weight coefficient is used to quantify the active power output demand level of the new energy power station during a grid fault, overcoming the problem of unclear active power support demand caused by the variable operating conditions of the power station, and improving the coordinated support ability of the power station to the system under different operating conditions; the method of optimizing the low-voltage ride-through threshold of the power station is adopted to overcome the problem of a large shortage of active power output during a power system fault, and improve the frequency security during system faults.

[0019] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings here are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0021] Figure 1 is a flowchart of a method for dynamically optimizing the low-voltage ride-through threshold of a new energy converter according to an exemplary embodiment.

[0022] Figure 2 is an equivalent circuit diagram of a power system during a fault according to an exemplary embodiment.

[0023] Figure 3 It is a block diagram of a device for dynamically optimizing the low-voltage ride-through threshold of a new energy converter according to an exemplary embodiment.

[0024] Figure 4 It is a block diagram of an electronic device according to an exemplary embodiment. Detailed implementation manners

[0025] Here, the exemplary embodiments will be described in detail, and the examples are shown in the accompanying drawings. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0026] The terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "the", and "said" used in the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0027] Figure 1 It is a flowchart of a method for dynamically optimizing the low-voltage ride-through threshold of a new energy converter according to an exemplary embodiment. As Figure 1 shown, the method may include the following steps:

[0028] S1: Dynamically adjust the active power weight coefficient during the fault of the power station according to the active power output by the new energy power station before the grid fault and the total installed capacity of the power station;

[0029] Specifically, the purpose of calculating the active power weight coefficient is to determine the contribution degree of the current new energy power station to the system active power before the fault, and provide a reference for the subsequent optimization of the low-voltage ride-through threshold. For a power station with a relatively high active power output before the fault, a large amount of active power output will be reduced when entering the low-voltage ride-through state, which will cause a relatively greater disturbance to the system frequency. Therefore, a relatively large active power weight coefficient is set to reduce the loss of the system active power after entering the low-voltage ride-through state; on the contrary, for a power station with a relatively low active power output before the fault, the impact on the system frequency when entering the low-voltage ride-through state is small. Therefore, a relatively small active power weight coefficient is set to improve the voltage support level of the power station. The active power weight coefficient λ during the fault of the power station is:

[0030] ;

[0031] Where: P0 is the active power output by the substation before the fault, and S is the total installed capacity of the substation.

[0032] S2: Optimize the threshold for the converter to enter the low-voltage ride-through state according to the pre-fault operating state of the new energy substation, the weighted coefficient of the active power after dynamic adjustment, and the degree of grid voltage dip;

[0033] Specifically, for the low-voltage ride-through threshold U of the new energy substation th The higher it is, the better the voltage support effect, but the less active power output by the substation; U th The lower it is, the more active power output by the substation, but the worse the voltage support effect. Therefore, it is necessary to optimize the value of U th to ensure that the substation has a certain voltage support ability and can maximize the active power output during the fault. According to the requirements of voltage support and active power output, the objective function used is as follows:

[0034] ;

[0035] Where: U PCC is the grid-connected voltage of the substation during the fault, U N is the rated voltage of the grid-connected point of the substation, P is the active power output by the substation during the fault, P0 is the active power output by the substation before the fault occurs, and λ is the weighted coefficient of the active power during the fault of the substation.

[0036] The introduction of the weighted coefficient of active power λ ensures that when the demand for active power output by the substation is high, an optimized result focusing on increasing the active power output is output; when the demand for active power output by the substation is low, an optimized result focusing on improving the voltage support effect is output.

[0037] Next, a series of constraint conditions that the optimization model needs to satisfy are given. The constraint conditions used when optimizing the threshold for the converter to enter the low-voltage ride-through state are as follows:

[0038] ;

[0039] Where: U PCC is the grid-connected voltage of the substation during the fault, I d is the active current output by the substation during the fault, I q is the reactive current output by the substation during the fault, U g is the equivalent grid voltage during the fault, U th is the low-voltage ride-through threshold of the substation, r g is the equivalent resistance value of the grid during the fault, x g is the equivalent reactance value of the grid during the fault, I Nis the rated current of the substation, K is the reactive power droop coefficient of the substation, and I max is the upper limit of the substation current output determined by the converter capacity, and P0 is the active power output by the substation before the fault occurs.

[0040] Specifically, Figure 2 is the equivalent circuit diagram of the power system during the fault. Among them, U g is the equivalent grid voltage under the fault; r g is the equivalent resistance value of the grid under the fault; x g is the equivalent reactance value of the grid under the fault. Using the grid connection point voltage orientation, write the circuit constraint conditions according to Kirchhoff's law:

[0041] ;

[0042] Among them: U PCC is the grid connection point voltage of the substation during the fault, I d is the active current output by the substation under the fault, I q is the reactive current output by the substation under the fault, U g is the equivalent grid voltage under the fault, r g is the equivalent resistance value of the grid under the fault, x g is the equivalent reactance value of the grid under the fault.

[0043] According to the national standard regulations, during the low-voltage fault of the power grid, the reactive current I q output by the new energy substation satisfies the formula:

[0044] ;

[0045] Among them: I q0 is the reactive current output by the substation before the fault; K is the reactive power droop coefficient, U th is the low-voltage ride-through threshold of the substation, U PCC is the grid connection point voltage of the substation during the fault, I N is the rated current of the substation.

[0046] While ensuring the requirement of reactive current output, the converter will try to maintain the output of the active power before the fault as much as possible. Due to the upper limit of the converter capacity, the active current I d output by the substation needs to satisfy the constraint:

[0047] ;

[0048] Among them: P0 is the active power output by the substation before the fault occurs, U PCC is the grid connection point voltage of the substation during the fault, I max is the upper limit of the substation current output determined by the converter capacity, I q is the reactive current output by the substation under the fault.

[0049] Meanwhile, the active power P output by the power station during the fault satisfies the constraint condition:

[0050] ;

[0051] Where: U PCC is the grid connection point voltage of the power station during the fault, and I d is the active current output by the power station during the fault.

[0052] Combining the established objective function and constraint conditions, a complete optimization model for the low voltage ride through threshold can be obtained. Before the fault occurs, the power station will solve the optimization model under different degrees of grid voltage dips, obtain the corresponding thresholds respectively, and adjust them in real time according to the working conditions of the power station.

[0053] S3: According to the optimization result of the low voltage ride through threshold of the new energy power station, before the fault occurs, the power station will send the optimized low voltage ride through threshold to each converter, so that each converter responds to the grid fault according to the set low voltage ride through threshold;

[0054] Specifically, after the new energy power station updates the optimization results under different degrees of grid voltage dips by solving the optimization model each time, it will send the low voltage ride through thresholds under different degrees of grid voltage dips obtained to each converter in the power station. When a grid fault occurs, the converter will judge whether it enters the low voltage ride through state according to the current low voltage ride through threshold. If the current grid connection point voltage is higher than the low voltage ride through threshold, the reactive current output by the converter remains the same as before the fault; if the current grid connection point voltage is lower than the low voltage ride through threshold, the converter needs to output additional reactive current according to the national standard requirements, that is, the output reactive current satisfies the following formula:

[0055] ;

[0056] Where: I q0,i is the reactive current output by the i-th unit before the fault, U th is the low voltage ride through threshold of the power station, U PCC is the grid connection point voltage of the power station during the fault, K i is the reactive droop coefficient of the i-th unit, I N,i is the rated current of the i-th unit, and l is the number of units in the power station.

[0057] Corresponding to the embodiment of the method for dynamically optimizing the low voltage ride through threshold of the new energy converter described above, the present application also provides an embodiment of a device for dynamically optimizing the low voltage ride through threshold of the new energy converter.

[0058] Figure 3It is a block diagram of a device for dynamically optimizing the low-voltage ride-through threshold of a new energy converter shown according to an exemplary embodiment. Referring to Figure 3 , the device includes:

[0059] Calculation module 1, configured to dynamically adjust the active power weight coefficient during the station fault according to the active power output by the new energy power station before the grid fault and the total installed capacity of the station;

[0060] Optimization module 2, configured to optimize the threshold for the converter to enter the low-voltage ride-through state according to the working state of the new energy power station before the fault, the dynamically adjusted active power weight coefficient, and the degree of grid voltage dip;

[0061] Communication module 3, configured to send the optimized low-voltage ride-through threshold to each converter before the fault occurs in the new energy power station according to the optimization result of the low-voltage ride-through threshold of the new energy power station, so that each converter responds to the grid fault according to the set low-voltage ride-through threshold.

[0062] Regarding the device in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment related to the method, and will not be elaborated here.

[0063] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present application. Those of ordinary skill in the art can understand and implement it without creative work.

[0064] Correspondingly, the present application also provides an electronic device, including: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the method for dynamically optimizing the low-voltage ride-through threshold of the new energy converter as described above. As Figure 4 shown, it is a hardware structure diagram of any device with data processing capabilities where the device for dynamically optimizing the low-voltage ride-through threshold of the new energy converter provided by the embodiment of the present invention is located. Except for Figure 4 the processors, memory, DMA controller, disk, and non-volatile memory shown, any device with data processing capabilities where the device in the embodiment is located usually includes other hardware according to the actual functions of the device with data processing capabilities, which will not be elaborated here.

[0065] Correspondingly, the present application further provides a computer-readable storage medium, on which computer instructions are stored. When the instructions are executed by a processor, the new energy converter low voltage ride-through threshold dynamic optimization method as described above is implemented. The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the foregoing embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Further, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capabilities and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store the data that has been output or will be output.

[0066] After considering the specification and the content disclosed herein, those skilled in the art will readily conceive of other embodiments of the present application. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and the embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the claims.

[0067] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A dynamic optimization method for the low voltage ride-through threshold of a new energy converter, characterized in that Including: Dynamically adjust the active power weight coefficient during the fault of the power station according to the active power output by the new energy power station before the grid fault and the total installed capacity of the power station; Optimize the threshold for the converter to enter the low voltage ride-through state according to the working state of the new energy power station before the fault, the dynamically adjusted active power weight coefficient, and the degree of grid voltage dip; According to the optimization result of the low voltage ride-through threshold of the new energy power station, the power station sends the optimized low voltage ride-through threshold to each converter before the fault occurs, so that each converter responds to the grid fault according to the set low voltage ride-through threshold.

2. The method according to claim 1, characterized in that The active power weight coefficient λ during the fault of the power station is: ； Where: P0 is the active power output by the power station before the fault, and S is the total installed capacity of the power station.

3. The method according to claim 2, characterized in that The objective function used when optimizing the threshold for the converter to enter the low voltage ride-through state is as follows: ； Where: U PCC is the voltage at the grid connection point of the substation during the fault, U N is the rated voltage at the grid connection point of the substation, λ is the active power weight coefficient during the fault of the substation, P is the active power output by the substation during the fault, and P0 is the active power output by the substation before the fault occurs.

4. The method according to claim 3, characterized in that, The constraint conditions used when optimizing the threshold for the converter to enter the low voltage ride-through state are as follows: ； Where: U PCC is the grid connection point voltage of the substation during the fault, I d is the active current output by the substation during the fault, I q is the reactive current output by the substation during the fault, U g is the equivalent grid voltage during the fault, U th is the low voltage ride-through threshold of the substation, r g is the equivalent resistance value of the grid during the fault, x g is the equivalent reactance value of the grid during the fault, I N is the rated current of the substation, K is the reactive power droop coefficient of the substation, I max is the upper limit of the substation current output determined by the converter capacity, and P0 is the active power output by the substation before the fault occurs.

5. The method according to claim 1, wherein According to the optimization result of the low voltage ride-through threshold of the new energy power station, the power station sends the optimized low voltage ride-through threshold to each converter before the fault occurs, so that each converter responds to the grid fault according to the set low voltage ride-through threshold, specifically including: According to the optimization results of the low voltage ride-through threshold of the new energy power station, the optimized low voltage ride-through threshold U under different degrees of grid voltage sag th is sent to each converter in the power station. When a system fault occurs, each converter will judge whether to enter the low voltage ride-through state according to the set threshold. If it does not enter the low voltage ride-through state, the converter will not output additional reactive current. If it enters the low voltage ride-through state, the i-th unit will output reactive current I q,i as follows: ； Where: I q0,i is the reactive current output by the i-th unit before the fault, U th is the low voltage ride-through threshold of the substation, U PCC is the grid connection point voltage of the substation during the fault, K i is the reactive power droop coefficient of the i-th unit, I N,i is the rated current of the i-th unit, and l is the number of units in the substation.

6. A device for dynamically optimizing the low voltage ride-through threshold of a new energy converter, characterized in that, Including: A calculation module for dynamically adjusting the active power weight coefficient during the fault of the power station according to the active power output by the new energy power station before the grid fault and the total installed capacity of the power station; An optimization module for optimizing the threshold for the converter to enter the low voltage ride-through state according to the working state of the new energy power station before the fault, the dynamically adjusted active power weight coefficient, and the degree of grid voltage dip; A communication module for, according to the optimization result of the low voltage ride-through threshold of the new energy power station, sending the optimized low voltage ride-through threshold to each converter before the fault occurs, so that each converter responds to the grid fault according to the set low voltage ride-through threshold.

7. An electronic device, characterized in that, Including: One or more processors; A memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1-6.

8. A computer-readable storage medium having computer instructions stored thereon, characterized in that, When the instruction is executed by the processor, the steps of the method according to any one of claims 1-6 are implemented.

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