A method for predicting upper limit of direct current transmission power under state change of direct current engineering reactive power

Abstract

The application discloses a DC engineering reactive state change pre-judgment DC transmission power upper limit method, comprising the following steps: (S1) obtaining a preset reactive state; (S2) setting the running valve group power in the preset reactive state as a valve group limit transmission power value; (S3) performing control calculation according to a reactive control strategy; (S4) outputting a reactive control strategy calculation result; (S5) judging whether there is a reactive device switching, a control command and a reactive control mode switching command in the calculation result; if there is a corresponding command, updating the corresponding preset reactive device state and reactive control function setting value, and performing (S3); if there is no corresponding command, performing (S6); (S6) calculating the DC transmission power upper limit under the current preset reactive state according to the valve group state adjustment command in the calculation result; and (S7) outputting the DC transmission power upper limit under the current preset reactive state. The application has the advantages of no need of manual judgment and simulation resources, short time consumption, accuracy and reliability, convenience and practicality.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and in particular to a method for predicting the upper limit of DC transmission power due to changes in reactive power state in DC projects. Background Technology

[0002] In high-voltage / ultra-high-voltage direct current (HVDC) transmission projects, reactive power control is one of the important functions of the DC control and protection system. Its main control objects are all the reactive power equipment in the station (AC filters, reactors, SVCs (Static Var Compensators), synchronous condensers, etc.). Based on the current DC operating mode and conditions, the reactive power consumption of the entire station is calculated. Through the switching and control of all reactive power equipment, under the premise of ensuring the safety of reactive power equipment and controlling the harmonic impact on the AC system, the reactive power exchange between the converter station and the AC system is kept within the allowable range (reactive power control mode) or the AC bus voltage is kept within the safe operating range (voltage control mode). The effect of reactive power control directly affects the power transmission capacity and power quality of the DC transmission system.

[0003] With the continuous development of DC transmission projects, reactive power control functions are now very mature. Reactive power control can be implemented as follows: First, collect the AC bus status (voltage, frequency, etc.), valve group status (operation / shutdown, valve group operating power, etc.), reactive power equipment status (taking AC filter status as an example, AC filter engaged / disengaged, available / unavailable, etc.), and reactive power control function settings (engaged / disengaged, manual / automatic, voltage control / reactive power control, voltage / reactive power control upper and lower limits, AC filter rated power, AC bus overvoltage setting, etc.). Then, based on the reactive power control strategy table, determine in real time whether the current reactive power of the entire station meets the preset requirements. Finally, output valve group status adjustment commands (DC blocking, power reduction, etc.), reactive power equipment control commands (taking AC filter as an example, AC filter engaged / disengaged, etc.), reactive power control switching commands (reactive power control switching from automatic to manual, etc.), and monitoring system alarm prompts.

[0004] In the operation and maintenance of DC projects, it is often necessary to assess in advance the impact of reactive power status changes on the upper limit of transmission power. These changes include: changes in AC bus status, valve group status, reactive power equipment status, and reactive power control function settings. For example, in converter stations, a common planned maintenance of reactive power equipment (such as large-group or small-group scheduled maintenance or fault repair of AC filters), after receiving the maintenance request, the dispatching department first needs to assess the impact of the reactive power equipment maintenance on the upper limit of DC power, and then adjust the DC operation mode accordingly. Only after the operation mode plan is finalized can the converter station maintenance request be approved. The most crucial task in this process is assessing the impact of reactive power status changes on the upper limit of transmission power. The existing assessment method involves manually comparing the reactive power equipment maintenance plan with the current DC operating conditions using a reactive power control strategy table to determine the upper limit of DC power. To further confirm the accuracy of the results, laboratory simulation is typically used for verification. The current method, which combines manual judgment with simulation verification, is time-consuming and requires experienced technicians, accurate simulation resources and models. In addition, due to the discrepancy between the simulation conditions and the actual engineering operation conditions, the final results may be inaccurate.

[0005] Existing research on reactive power control is based on judging whether reactive power demand is met in real time by the current reactive power equipment status. There is no research on predicting the upper limit of DC transmission power by pre-setting changes in reactive power status. Currently, the prediction scheme for the impact of reactive power status changes on the upper limit of transmission power is still based on a combination of manual judgment and simulation. Therefore, there is an urgent need to develop a fast, convenient, accurate, and engineering-practical method for predicting the upper limit of DC transmission power by reactive power status changes. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a method for predicting the upper limit of DC transmission power by reactive power state changes in DC engineering that is time-efficient, requires no additional simulation resources, and is convenient, practical, accurate, and reliable.

[0007] Technical solution: The method for predicting the upper limit of DC transmission power of the present invention includes the following steps:

[0008] (S1) Obtain the preset reactive power state;

[0009] (S2) Set the power of the valve group in the preset reactive state to the valve group's limit transmission power value;

[0010] (S3) Perform control calculations based on the reactive power control strategy;

[0011] (S4) Output the calculation results of the reactive power control strategy;

[0012] (S5) Determine whether there are reactive power equipment switching, control commands and reactive power control mode switching commands in the calculation results: If there are corresponding commands, update the corresponding preset reactive power equipment status and reactive power control function settings, and execute (S3); if there are no corresponding commands, execute (S6).

[0013] (S6) Determine whether there is a valve group status adjustment command in the calculation result, and calculate the upper limit of DC transmission power under the current preset reactive power state based on whether there is a valve group status adjustment command.

[0014] (S7) Output the maximum DC transmission power under the current preset reactive state.

[0015] Furthermore, in step (S1), the preset reactive power state includes: preset AC bus state, preset valve group state, preset reactive power equipment state, and preset reactive power control function setting value.

[0016] Furthermore, the AC bus status includes voltage and frequency; the valve group status includes valve group operating / stopping status and valve group operating power; the reactive power equipment status includes AC filter on / off / available / unavailable status and SVC / synchronous condenser output reactive power status; the reactive power control function settings include function on / off, manual control / automatic control, voltage control / reactive power control, voltage / reactive power control upper and lower limits, AC filter rated capacity, AC overvoltage setting, and SVC / synchronous condenser setting.

[0017] Furthermore, in step (S1), the preset reactive state is either directly preset by human intervention or formed by superimposing the initial reactive state and the human-preset reactive state change.

[0018] Furthermore, the preset reactive power state changes include: AC bus voltage and frequency changes; valve group operation / shutdown state changes and valve group operating power changes; AC filter activation / deactivation / availability / unavailability state changes and SVC / synchronous condenser output reactive power changes; reactive power control function activation / deactivation / manual control / automatic control / voltage control / reactive power control state changes, voltage control upper and lower limits / reactive power control upper and lower limits changes, AC filter rated capacity changes, AC overvoltage setting changes, and SVC / synchronous condenser setting changes.

[0019] Furthermore, in step (S2), the operating power of the valve group in the expected reactive power state quantity is set to the preset valve group operating power to predict the upper limit of DC transmission power under the preset operating power, or to predict the switching and control status of reactive equipment under the operating power.

[0020] Furthermore, in step (S3), the reactive power control strategy adopts the existing reactive power control strategy of DC control and protection, or rewrites the reactive power control strategy, further simplifying it to retain only the reactive power control strategy that affects the upper limit of DC transmission power.

[0021] Furthermore, in step (S6), the calculation of the upper limit of DC transmission power under the current preset reactive power state is implemented as follows: if there is no valve group state adjustment command, the upper limit of DC transmission power under the current preset reactive power state is the limit transmission power of the currently operating valve group; if there is a valve group state adjustment command and the command is to block DC, the upper limit of DC transmission power under the current preset reactive power state is 0MW; if there is a valve group state adjustment command and the command is to reduce power, the upper limit of DC transmission power under the current preset reactive power state is the target value of power reduction.

[0022] Compared with existing technologies, the present invention has the following significant advantages: 1. By obtaining a preset reactive power state, the present invention can effectively predict the upper limit of DC transmission power when the reactive power state changes, based on existing reactive power control strategies or by rewriting simplified reactive power control strategies that only affect the upper limit of DC transmission power. 2. It is convenient, simple, and practical to use. Only the preset reactive power state or the preset reactive power state change amount needs to be input to obtain the upper limit of DC transmission power under the current expected operation. 3. It can achieve real-time prediction without relying on manual judgment or additional simulation, and the time consumption is short. 4. The present invention can be integrated into the reactive power control strategy of existing DC control systems. The relevant state variables are taken from the existing engineering control system, and the calculation results are accurate and reliable. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention;

[0024] Figure 2 A schematic diagram of the existing reactive power control function in a DC power project;

[0025] Figure 3 This is a schematic diagram illustrating the prediction of the upper limit of DC transmission power in Embodiment 1 of the present invention;

[0026] Figure 4 This is a schematic diagram of the upper limit prediction of DC transmission power in Embodiment 2 of the present invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] The method of this invention is as follows: First, obtain the preset reactive power status (AC bus status, valve group status, reactive power equipment status, and reactive power control function setting). Then, set the operating valve group power in the valve group status to the valve group limit transmission power value. Subsequently, perform control calculations according to the latest reactive power status and reactive power control strategy. Determine whether there are reactive power equipment switching, control commands, or reactive power control mode switching commands in the output results. Update the reactive power status according to the relevant commands and perform control calculations cyclically according to the reactive power control strategy. Finally, calculate the upper limit of DC transmission power under the current preset reactive power status based on the valve group status adjustment command in the calculation results.

[0029] Example 1

[0030] This embodiment proposes a method for predicting the impact of reactive power state changes on the upper limit of transmission power, based on the existing reactive power control functions of DC engineering. A schematic diagram of the existing reactive power control functions of DC engineering is shown below. Figure 2 As shown, it includes:

[0031] Step 1: Acquire the preset acquisition signals (AC bus status, valve group status, reactive power equipment status, reactive power control function setpoints);

[0032] Step 2: Based on the acquired signals, perform control calculations according to the preset reactive power control strategy;

[0033] Step 3: Output the control signals corresponding to the control calculation results (valve group status adjustment command, reactive power equipment switching control command, reactive power control mode switching command, monitoring system event prompt or alarm).

[0034] The existing reactive power control function determines whether the reactive power demand is met in real time based on the current reactive power equipment status, but it does not have the function of predicting the impact of changes in reactive power status on the upper limit of DC power.

[0035] This invention proposes a method for predicting the impact of reactive power state changes on the upper limit of transmission power, as illustrated in the diagram below. Figure 3 As shown, the flowchart is as follows Figure 1 As shown, it includes:

[0036] S1, obtain the preset reactive power state;

[0037] S2, set the operating valve group power in the preset valve group state to the limit transmission power value of the operating valve group;

[0038] S3 performs control calculations based on the existing reactive power control strategy;

[0039] S4 outputs the calculation results of the reactive power control strategy.

[0040] S5, Determine whether there are reactive power equipment switching, control commands, and reactive power control mode switching commands in the calculation results: If there are corresponding commands, update the corresponding preset reactive power equipment status and reactive power control function settings, and execute S3; if there are no corresponding commands, execute S6.

[0041] S6, determine whether there is a valve group status adjustment command in the calculation result: if there is no valve group status adjustment command, the upper limit of DC transmission power under the current preset reactive power state is the limit transmission power of the currently operating valve group; if there is a valve group status adjustment command and the command is DC blocking, the upper limit of DC transmission power under the current preset reactive power state is 0MW; if there is a valve group status adjustment command and the command is power reduction, the upper limit of DC transmission power under the current preset reactive power state is the power reduction target value.

[0042] S7 outputs the maximum DC transmission power under the current preset reactive power state.

[0043] The preset reactive power states include preset AC bus states (voltage and frequency), preset valve group states (valve group operating / stopping state, valve group operating power), preset reactive power equipment states (AC filter on / off / available / unavailable state, SVC / synchronous condenser output reactive power), and preset reactive power control function settings (function on / function off / manual control / automatic control / voltage control / reactive power control, voltage / reactive power control upper and lower limits, AC filter rated capacity, AC overvoltage setting, SVC / synchronous condenser setting).

[0044] The preset reactive power state can be preset directly by human intervention, or it can be formed by superimposing the existing reactive power state and the human-preset reactive power state change.

[0045] The preset reactive power state changes include: AC bus state changes (voltage changes, frequency changes), valve group state changes (valve group operation / shutdown state changes, valve group operating power changes), reactive power equipment state changes (AC filter activation / deactivation / availability / unavailability state changes, SVC / synchronous condenser output reactive power changes), and reactive power control function setpoint changes (function activation / function deactivation / manual control / automatic control / voltage control / reactive power control state changes, voltage control upper and lower limits / reactive power control upper and lower limits changes, AC filter rated capacity changes, AC overvoltage setpoint changes, and SVC / synchronous condenser setpoint changes).

[0046] Furthermore, if the power of the operating valve group in the preset reactive state in step S2 is set to the preset operating power of the valve group, it can be used to predict the upper limit of DC transmission power under the preset operating power, and it can also be used to predict the switching and control status of reactive equipment under the operating power.

[0047] Example 2

[0048] This embodiment can be used independently of the existing reactive power control function of DC engineering to propose the upper limit of DC transmission power for predicting reactive power state changes.

[0049] For ease of explanation, the reactive power equipment in the station will be described using an AC filter as an example. If there are other reactive power equipment, the implementation methods are not substantially different.

[0050] The only condition under which reactive power state changes affect the upper limit of DC transmission power is: the unavailability of the AC filter leading to DC blocking or a decrease in DC power. The unavailability of the AC filter is related to both the filter's own condition and the AC bus voltage. Therefore, this invention proposes a method for predicting the upper limit of DC transmission power based on reactive power state changes, as illustrated in the schematic diagram below. Figure 4 As shown, the flowchart is as follows Figure 1 As shown, it includes:

[0051] S1, obtain the preset reactive power status (AC voltage status, valve group status, AC filter status, reactive power control setpoint);

[0052] S2, set the operating valve group power in the preset valve group state to the limit transmission power value of the operating valve group;

[0053] S3 performs control operations based on the absolute minimum filter control strategy;

[0054] S4 outputs the calculation results of the reactive power control strategy.

[0055] S5, Determine if there are AC filter switching commands and reactive power control mode switching commands in the calculation results: If there are corresponding commands, update the corresponding preset AC filter status and reactive power control function settings, and execute S3; if there are no corresponding commands, execute S6.

[0056] S6, determine whether there is a valve group status adjustment command in the calculation result: if there is no valve group status adjustment command, the upper limit of DC transmission power under the current preset reactive power state is the limit transmission power of the currently operating valve group; if there is a valve group status adjustment command and the command is DC blocking, the upper limit of DC transmission power under the current preset reactive power state is 0MW; if there is a valve group status adjustment command and the command is power reduction, the upper limit of DC transmission power under the current preset reactive power state is the power reduction target value.

[0057] S7 outputs the current preset maximum power output under reactive power conditions.

[0058] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for predicting the upper limit of DC transmission power due to changes in reactive power state in DC engineering, characterized in that, The steps include the following: (S1) Obtain the preset reactive power state; (S2) Set the preset power of the valve group in the reactive state to the valve group's limit transmission power value; (S3) Perform control calculations based on the reactive power control strategy; (S4) Output the calculation results of the reactive power control strategy; (S5) Determine whether there are reactive power equipment switching, control commands and reactive power control mode switching commands in the calculation results: If there are corresponding commands, update the corresponding preset reactive power equipment status and reactive power control function settings, and execute (S3); if there are no corresponding commands, execute (S6). (S6) Determine whether there is a valve group status adjustment command in the calculation result, and calculate the upper limit of DC transmission power under the current preset reactive power state based on whether there is a valve group status adjustment command. (S7) Output the upper limit of DC transmission power under the current preset reactive state.

2. The method for predicting the upper limit of DC transmission power based on reactive power state changes in DC engineering according to claim 1, characterized in that, In step (S1), the preset reactive power states include preset AC bus states, preset valve group states, preset reactive power equipment states, and preset reactive power control function settings.

3. The method for predicting the upper limit of DC transmission power based on reactive power state changes in DC engineering according to claim 2, characterized in that, The AC bus status includes voltage and frequency; the valve group status includes valve group operating / stopping status and valve group operating power; the reactive power equipment status includes AC filter on / off / available / unavailable status and SVC / synchronous condenser output reactive power status; the reactive power control function settings include function on / off, manual control / automatic control, voltage control / reactive power control, voltage control upper and lower limits, reactive power control upper and lower limits, AC filter rated capacity, AC overvoltage setting, and SVC / synchronous condenser setting.

4. The method for predicting the upper limit of DC transmission power based on reactive power state changes in DC engineering according to claim 1, characterized in that, In step (S1), the preset reactive state is either directly preset by human intervention or formed by superimposing the initial reactive state and the change in the preset reactive state.

5. The method for predicting the upper limit of DC transmission power based on reactive power state changes in DC engineering according to claim 4, characterized in that, The preset reactive power state changes include: AC bus voltage / frequency changes; valve group operation / shutdown state changes and valve group operating power changes; AC filter activation / deactivation / availability / unavailability state changes and SVC / synchronous condenser output reactive power changes; reactive power control function activation / deactivation / manual control / automatic control / voltage control / reactive power control state changes, voltage control upper and lower limits / reactive power control upper and lower limits changes, AC filter rated capacity changes, AC overvoltage setpoint changes, and SVC / synchronous condenser setpoint changes.

6. The method for predicting the upper limit of DC transmission power due to reactive power state changes in DC engineering according to claim 1, characterized in that, In step (S2), the power of the operating valve group in the preset reactive state is set to the valve group limit transmission power value, or the power of the operating valve group in the expected reactive state is set to the preset valve group operating power, in order to predict the upper limit of DC transmission power under the preset valve group operating power, or to predict the switching and control status of reactive equipment under the preset valve group operating power.

7. The method for predicting the upper limit of DC transmission power based on reactive power state changes in DC engineering according to claim 1, characterized in that, In step (S3), the reactive power control strategy adopts the existing reactive power control strategy of DC control and protection, or rewrites the reactive power control strategy and further simplifies it to retain only the reactive power control strategy that affects the upper limit of DC transmission power.

8. The method for predicting the upper limit of DC transmission power based on reactive power state changes in DC engineering according to claim 1, characterized in that, In step (S6), the calculation of the upper limit of DC transmission power under the current preset reactive power state is as follows: If there is no valve group status adjustment command, the upper limit of DC transmission power under the current preset reactive power state is the limit transmission power of the currently operating valve group or the preset valve group operating power; if there is a valve group status adjustment command and the command is to block DC, the upper limit of DC transmission power under the current preset reactive power state is 0MW; if there is a valve group status adjustment command and the command is to reduce power, the upper limit of DC transmission power under the current preset reactive power state is the target value of power reduction.

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