New energy direct current transmission power self-balancing control method and system

Abstract

The invention belongs to the field of offshore high-voltage direct-current transmission, and particularly relates to a new energy direct-current transmission power self-balancing control method and system. The sea-land power transmission surplus power generated by the sending end is consumed through an energy storage valve connected to the direct current side of the receiving end; the sub-modules in the energy storage valve are controlled through the control instruction obtained according to the difference between the direct-current voltage actual value between the sending end and the receiving end and the set direct-current voltage reference value, so that the energy storage valve is controlled to be charged under the condition that the power of the sending end is larger than the load demand power of the receiving end. And discharging under the condition that the power of the sending end is smaller than the load demand power of the receiving end. According to the method, the condition of processing the surplus power of the new energy on the basis of ensuring the utilization rate of the grid-connected power of the new energy can be met, and the condition of unstable load of the receiving end caused by insufficient power generation output of the new energy can also be processed.

Description

Technical Field

[0001] The present invention belongs to the field of high voltage direct current power transmission, and in particular relates to a new energy direct current power transmission power self-balancing control method and system. Background Art

[0002] With the continuous advancement of the construction of new power systems, flexible direct current transmission technology has ushered in new development opportunities in the fields of large-scale clean energy, cross-regional large-capacity transmission, flexible grid zoning, efficient transmission of deep offshore wind power, massive distributed new energy consumption and DC load access.

[0003] In terms of large-scale economical and efficient transmission of clean energy and flexible interconnection, flexible direct current transmission has been widely used due to its advantages such as rapid control regulation performance and large-capacity long-distance power transmission, especially in the field of offshore high-voltage direct current transmission.

[0004] However, in terms of the connection of new energy to the grid, such as the connection of offshore wind power to the grid with direct current, due to the limitation of the construction cost of the offshore converter platform, the surplus power of new energy caused by the fluctuations or other changes in the power generation of new energy at the offshore sending end and the power consumption of the onshore receiving end load is often consumed by direct current energy consumption on land. Due to the thermal effect of resistors, the traditional direct current energy consumption method consumes the surplus power through energy-consuming resistors, but for the changes in the power generation of new energy at the offshore sending end and the power consumption of the onshore receiving end load, this method can usually only deal with the situation of surplus power, but cannot deal with the situation of unstable receiving end load caused by insufficient output of new energy power generation. Summary of the invention

[0005] The purpose of the present invention is to provide a new energy direct current transmission power self-balancing control method and system, which is used to solve the problem that the method of consuming the surplus power of new energy through energy-consuming resistors in the prior art cannot handle the unstable load on the receiving end caused by insufficient new energy power generation output due to changes in the new energy power generation power at the offshore sending end and the power consumption of the onshore receiving end load.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a new energy direct current transmission power self-balancing control method, which absorbs the transmission surplus power generated by the sending end through an energy storage valve connected to the DC side of the receiving end; the submodule in the energy storage valve is controlled by a control instruction obtained according to the difference between the actual value of the DC voltage between the positive and negative pole line ports of the energy storage valve and the set DC voltage reference value, so as to control the energy storage valve to charge when the power at the sending end is greater than the power required by the receiving end load, and to discharge when the power at the sending end is less than the power required by the receiving end load.

[0007] Furthermore, the energy storage valve is a direct current energy storage valve.

[0008] Furthermore, the submodule in the receiving-end inverter is controlled by a control instruction obtained according to the difference between the actual output power value of the inverter and the current receiving-end load power reference value, so as to control the output power of the inverter.

[0009] Furthermore, the AC voltage required for the new energy grid connection at the sending end is controlled by a control instruction obtained by the sending end converter according to the difference between the actual value of the AC voltage output by the converter and the set AC voltage reference value.

[0010] Furthermore, the method of obtaining the current receiving-end load power reference value based on the prediction includes: obtaining prediction information by constructing a model and training it to predict and evaluate the current receiving-end load power, and transmitting the prediction information to the receiving-end converter after a set time interval as the current receiving-end load power reference value.

[0011] Beneficial effect: The present invention provides a new self-balancing control method for DC power transmission from renewable energy sources. Compared with the traditional DC energy consumption method (i.e., the surplus power can only be processed by consuming the surplus power through energy-consuming resistors), the present invention cannot process the situation where the receiving-end load is unstable due to insufficient output of renewable energy power generation. The present invention obtains control instructions based on the difference between the actual value of the DC voltage between the sending end and the receiving end and the set DC voltage reference value, and controls the energy storage valve to charge when the power at the sending end is greater than the power required by the receiving-end load, and discharge when the power at the sending end is less than the power required by the receiving-end load. The method can not only process the surplus power of renewable energy on the basis of ensuring the utilization rate of the grid-connected power of renewable energy, but also process the unstable load at the receiving end due to insufficient output of renewable energy power generation.

[0012] In order to achieve the above-mentioned purpose, the present invention also provides a new energy direct current transmission power self-balancing control system, which includes: an energy storage valve connected to the direct current side of the receiving end and a corresponding controller thereof; the energy storage valve is used to absorb the transmission surplus power generated by the sending end; the controller corresponding to the energy storage valve is used to control the submodules in the energy storage valve through a control instruction obtained according to the difference between the actual value of the direct current voltage between the sending end and the receiving end and the set direct current voltage reference value, so as to control the energy storage valve to charge when the power at the sending end is greater than the power required by the receiving end load, and to discharge when the power at the sending end is less than the power required by the receiving end load.

[0013] Furthermore, the energy storage valve is a direct current energy storage valve.

[0014] Furthermore, it also includes: a controller corresponding to the inverter at the receiving end; the controller corresponding to the inverter at the receiving end is used to control the sub-modules in the inverter at the receiving end through control instructions obtained according to the difference between the actual output power value of the inverter and the predicted receiving end load power reference value, so as to control the output power of the inverter.

[0015] Furthermore, it also includes: a controller corresponding to the new energy power supply at the sending end; the controller corresponding to the new energy power supply at the sending end is used to control the AC voltage of the new energy power supply at the sending end through a control instruction obtained according to the difference between the actual value of the AC voltage of the power generation system and the set AC voltage reference value.

[0016] Furthermore, it also includes: a prediction module for predicting the current receiving-end load power reference value, and the prediction module predicts the current receiving-end load power reference value in the following manner: obtaining prediction information by constructing a model and training to predict and evaluate the current receiving-end load power, and transmitting the prediction information to the receiving-end converter after a set time interval as the receiving-end load power reference value.

[0017] Beneficial effects: The sea-land power transmission self-balancing control system can achieve the same beneficial effects as the above-mentioned new energy direct current power transmission self-balancing control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of a sea-land power transmission system applicable to the embodiment of the power self-balancing control method of new energy direct current transmission of the present invention;

[0019] Figure 2 It is a schematic diagram of the principle of the AC voltage control method of the offshore station rectifier converter in the embodiment of the new energy direct current power transmission self-balancing control method of the present invention;

[0020] Figure 3 It is a schematic diagram of the principle of the DC voltage control method of the direct-hung energy storage valve on the DC side of the land station in the embodiment of the new energy DC power self-balancing control method of the present invention;

[0021] Figure 4 It is a schematic diagram of the principle of the power control mode of the inverter converter of the land station in the embodiment of the power self-balancing control method of the new energy direct current transmission of the present invention;

[0022] Figure 5 This is a flowchart of the onshore power grid load prediction process in the embodiment of the new energy direct current power transmission self-balancing control method of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Embodiment of a method for controlling power self-balancing of new energy direct current transmission

[0025] This embodiment provides a new energy direct current transmission power self-balancing control method, the method is as follows:

[0026] The surplus power of sea-land power transmission generated by the sending end is absorbed by the energy storage valve connected to the DC side of the receiving end; the submodule in the energy storage valve is controlled by the control instruction obtained according to the difference between the actual value of the DC voltage between the positive and negative poles of the energy storage valve and the set DC voltage reference value, so as to control the energy storage valve (the energy storage valve is a DC direct-hung energy storage valve) to charge when the power at the sending end is greater than the power required by the receiving end load, and to discharge when the power at the sending end is less than the power required by the receiving end load. The receiving end in this embodiment is specifically the onshore receiving end, and the sending end is specifically the offshore sending end; in other embodiments, the receiving end may also be the offshore receiving end, and the sending end may also be the onshore sending end, which does not affect the realization of the self-balancing control method for the new energy DC power transmission.

[0027] On the basis that the receiving end is specifically a land receiving end and the sending end is specifically an offshore sending end, the land-sea power transmission system applicable to this embodiment is as follows: Figure 1 As shown, it includes an offshore wind power generation system, an offshore station rectifier converter, a DC submarine cable, a direct-hung energy storage valve on the DC side of an onshore station, an onshore station inverter converter, and an onshore power grid load.

[0028] Offshore wind power generation systems are used to generate AC voltage at the offshore sending end for renewable energy power generation and grid connection; offshore station rectifier converters use Figure 2 The AC voltage control method shown in the figure provides the above-mentioned synchronous AC voltage for the offshore renewable energy power source to carry out renewable energy power generation and grid connection, so as to convert the AC power generated by the offshore renewable energy power source into DC power for further output; the DC submarine cable establishes a DC transmission channel for power transmission; the DC side direct-hung energy storage valve of the onshore station is used to judge the current state of sea-land power transmission, and adopts the following method: Figure 3 The DC voltage control method shown controls the energy storage valve.

[0029] In this embodiment, Figure 3The DC voltage control method shown specifically includes: if the load of the onshore power grid suddenly decreases or an AC transient fault occurs, and the new energy fails to respond in time to reduce power, the submodule in the above-mentioned energy storage valve controls the energy storage valve through a control instruction obtained according to the difference between the actual value of the DC voltage output by the offshore station rectifier converter and the onshore power grid load and the set DC voltage reference value, so that it adaptively absorbs the surplus power of the new energy to ensure the power balance of the system; if the new energy power source, that is, the offshore wind power generation system, is disconnected due to a fault or the onshore power grid load suddenly increases, resulting in the power output of the offshore station rectifier converter not meeting the onshore power grid load demand, then the submodule in the DC side direct-mounted energy storage valve controls the energy storage valve through a control instruction obtained according to the difference between the actual value of the DC voltage output by the offshore station rectifier converter and the onshore power grid load and the set DC voltage reference value, so that it adaptively emits power to ensure the power balance of the system.

[0030] The submodule in the onshore receiving-end inverter is controlled by a control instruction obtained according to the difference between the actual output power value of the inverter and the current onshore receiving-end load power reference value, so as to control the output power of the above-mentioned inverter. In addition, the current onshore receiving-end load power reference value is obtained by prediction, and the method of obtaining the current receiving-end load power reference value according to the prediction includes: obtaining prediction information by constructing a model and training to predict and evaluate the current receiving-end load power, and transmitting the prediction information to the receiving-end converter after a set interval as the current receiving-end load power reference value.

[0031] In this embodiment, the onshore station DC side direct-mounted energy storage is used as the onshore DC energy storage of the above-mentioned new energy sea-land power transmission power self-balancing system. The onshore station DC side direct-mounted energy storage is responsible for controlling and stabilizing the DC voltage, and the onshore station inverter is responsible for controlling power transmission according to the onshore power grid load forecast. The onshore station inverter adopts a power control method, and the power command value is determined by the onshore power grid load forecast system, such as Figure 5 As shown, it is the prediction process of the power command value. The prediction process is specifically to collect data according to the load in a certain area through the dispatching end, and then obtain the prediction data through training of statistical models, neural network models, machine learning models, etc., and send it to the onshore receiving end converter at intervals of 5-15 minutes after evaluation, as the current receiving end load power reference value, and then change the power command value in real time according to the onshore power grid load change trend to ensure the system power balance. In fact, the prediction method adopted in this embodiment belongs to the prior art, that is, the new energy direct current transmission power self-balancing control method of this embodiment obtains the current onshore receiving end load power reference value through the existing power grid load prediction method, so it will not be repeated here.

[0032] The AC voltage of the renewable energy power generation source at the offshore sending end is controlled by a control instruction obtained according to the difference between the actual value of the AC voltage of the power generation system and the set AC voltage reference value.

[0033] Specifically, in this embodiment, when the offshore wind power generation system is used as the renewable energy power source at the offshore sending end for power generation, since it adopts a grid-following control strategy, it is necessary to adopt a synchronous AC voltage as support, that is, the offshore station rectifier converter adopts an AC voltage control method to provide the required synchronous AC voltage for renewable energy power generation and grid connection. The DC line in this embodiment adopts a DC submarine cable (i.e., an electric cable), and the rectifier converter power device adopts a half-bridge topology structure to reduce construction costs; however, in other embodiments, if the DC line is implemented using overhead lines, the converter power device must adopt a half-bridge and full-bridge hybrid topology structure.

[0034] Embodiment of a self-balancing control system for DC power transmission of new energy

[0035] This embodiment provides a new energy direct current transmission power self-balancing control system, which is suitable for Figure 1 The sea-land power transmission system shown; the new energy direct current power transmission power self-balancing control system specifically includes: an energy storage valve connected to the direct current side of the onshore receiving end and its corresponding controller.

[0036] In this embodiment, the direct-mounted energy storage valve on the DC side of the onshore receiving end is used to absorb the surplus power of sea-to-land power transmission generated by the offshore sending end; the energy storage valve is provided with its corresponding controller, and the corresponding controller is used to control the submodules in the energy storage valve through a control instruction obtained according to the difference between the actual value of the DC voltage between the sending end and the receiving end and the set DC voltage reference value, so as to control the energy storage valve to charge when the power at the sending end is greater than the power required by the receiving end load, and to discharge when the power at the sending end is less than the power required by the receiving end load.

[0037] Specifically, the sea-land power transmission system to which the new energy sea-land power transmission power self-balancing control system of this embodiment is applicable is as follows: Figure 1 As shown, it includes an offshore wind power generation system, an offshore station rectifier converter, a DC submarine cable, a direct-hung energy storage valve on the DC side of an onshore station, an onshore station inverter converter, and an onshore power grid load.

[0038] The direct-hung energy storage valve on the DC side of the onshore station controls the DC voltage through the controller corresponding to the energy storage valve. The DC voltage control method is as follows: Figure 3As shown, the controller controls the submodules in the energy storage valve by comparing the difference between the actual DC voltage output by the offshore sending-end rectifier converter and the onshore receiving-end inverter and the DC voltage command value (the command value is obtained by the onshore power grid load forecasting system to complete the power grid load forecast and changes in real time according to the change trend of the onshore power grid load) to obtain the corresponding control command. If the power output by the offshore station rectifier converter is greater than the power required by the onshore power grid load, the controller controls the onshore receiving-end DC side direct-hung energy storage valve to charge; if the power output by the offshore station rectifier converter is less than the power required by the onshore power grid load, the controller controls the onshore receiving-end DC side direct-hung energy storage valve to discharge.

[0039] The new energy direct current power self-balancing control system of this embodiment also includes a controller corresponding to the inverter at the onshore receiving end; the controller corresponding to the inverter at the onshore receiving end is used to control the sub-modules in the inverter at the onshore receiving end through control instructions obtained according to the difference between the actual output power value of the inverter and the predicted reference value of the onshore receiving end load power, so as to control the output power of the inverter.

[0040] Specifically, the land station inverter is powered by a controller corresponding to the inverter. The control method is as follows: Figure 4 As shown, the controller obtains the corresponding control instruction and controls the output power of the inverter by comparing the actual output power value of the inverter of the land station with the power command value (the command value is obtained by the land power grid load prediction system to complete the prediction of the power grid load and changes in real time according to the change trend of the land power grid load). The new energy sea-land power transmission power self-balancing control system of this embodiment also includes a controller corresponding to the new energy power generation source at the sea sending end; the controller corresponding to the new energy power generation source at the sea sending end is used to control the AC voltage of the new energy power generation source at the sea sending end through the control instruction obtained according to the difference between the actual AC voltage value of the power generation system and the set AC voltage reference value.

[0041] Specifically, the offshore wind power generation system, as the renewable energy power source at the offshore sending end in this embodiment, is also provided with a corresponding controller for control, and the control method is as follows: Figure 2 As shown, the controller obtains a corresponding control instruction by comparing the actual value of the AC voltage output by the offshore wind power generation system with the AC voltage instruction value and controls the AC voltage output by the offshore wind power generation system.

[0042] It also includes a prediction module for predicting the current onshore receiving-end load power reference value. The above prediction module predicts the current onshore receiving-end load power reference value in the following ways: the prediction is collected by the dispatching end according to the load in a certain area, and the prediction data is obtained through training of statistical models, neural network models, machine learning models, etc., and is sent to the onshore receiving-end converter at intervals of 5-15 minutes after evaluation, as the current receiving-end load power reference value, that is, the active power reference value of the onshore receiving-end converter. Specifically, the dispatching end collects data on the load in a certain area, and then obtains prediction data through relevant training through a variety of prediction models. After evaluating this data, it is transmitted to the onshore receiving-end converter, and the evaluated prediction data is used as the onshore receiving-end converter active power reference value, and then the power command value is changed in real time according to the load change trend of the onshore power grid to ensure the power balance of the system. The corresponding power command value is obtained according to the onshore power grid load prediction, and the power command value is changed in real time according to the load change trend of the receiving end, and then the onshore station inverter is changed through the following Figure 4 The power control method shown is used to control and predict the system power balance.

[0043] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, but do not constitute a limitation to the present invention.

Claims

1. A new energy direct current transmission power self-balancing control method, characterized in that: The surplus power of power transmission generated at the sending end is absorbed by the energy storage valve connected to the DC side of the receiving end; the submodule in the energy storage valve is controlled by the control instruction obtained according to the difference between the actual value of the DC voltage between the positive and negative poles of the energy storage valve and the set DC voltage reference value, so as to control the energy storage valve to charge when the power at the sending end is greater than the power required by the receiving end load, and to discharge when the power at the sending end is less than the power required by the receiving end load.

2. The new energy direct current transmission power self-balancing control method according to claim 1 is characterized in that: The energy storage valve is a direct current directly mounted energy storage valve.

3. The new energy direct current transmission power self-balancing control method according to claim 1 is characterized in that: The submodules in the receiving-end inverter are controlled by a control instruction obtained according to the difference between the actual output power value of the inverter and the current receiving-end load power reference value, so as to control the output power of the inverter.

4. The new energy direct current transmission power self-balancing control method according to any one of claims 1 to 3, characterized in that: The AC voltage required for the new energy grid connection at the sending end is controlled by a control instruction obtained by the sending end converter according to the difference between the actual value of the AC voltage output by the converter and the set AC voltage reference value.

5. The new energy direct current transmission power self-balancing control method according to claim 3 is characterized in that: The method of obtaining the current receiving-end load power reference value based on the prediction includes: obtaining prediction information by constructing a model and training it to predict and evaluate the current receiving-end load power, and transmitting the prediction information to the receiving-end converter after a set time interval as the current receiving-end load power reference value.

6. A new energy direct current transmission power self-balancing control system, characterized in that: include: An energy storage valve and its corresponding controller connected to the DC side of the receiving end; the energy storage valve is used to absorb the surplus power of power transmission generated by the sending end; the controller corresponding to the energy storage valve is used to control the submodules in the energy storage valve through a control instruction obtained according to the difference between the actual value of the DC voltage between the sending end and the receiving end and the set DC voltage reference value, so as to control the energy storage valve to charge when the power at the sending end is greater than the power required by the receiving end load, and to discharge when the power at the sending end is less than the power required by the receiving end load.

7. The new energy direct current transmission power self-balancing control system according to claim 6 is characterized in that: The energy storage valve is a direct current directly mounted energy storage valve.

8. The new energy direct current transmission power self-balancing control system according to claim 6 is characterized in that: Also includes: A controller corresponding to the inverter at the receiving end; the controller corresponding to the inverter at the receiving end is used to control the sub-modules in the inverter at the receiving end by means of control instructions obtained according to the difference between the actual output power value of the inverter and the predicted receiving end load power reference value, so as to control the output power of the inverter.

9. The new energy direct current transmission power self-balancing control system according to claim 6 is characterized in that: Also includes: A controller corresponding to the renewable energy power source at the sending end; the controller corresponding to the renewable energy power source at the sending end is used to control the AC voltage of the renewable energy power source at the sending end by means of a control instruction obtained according to the difference between the actual value of the AC voltage of the power generation system and the set AC voltage reference value.

10. The new energy direct current transmission power self-balancing control system according to claim 8, characterized in that: Also includes: A prediction module for predicting the current receiving-end load power reference value, wherein the prediction module predicts the current receiving-end load power reference value in the following manner: obtaining prediction information by constructing a model and training it to perform a prediction evaluation on the current receiving-end load power, and transmitting the prediction information to the receiving-end converter after a set time interval as the current receiving-end load power reference value.

Images