Electromagnetic transient initialization method and system suitable for flexible direct current island mode

Abstract

The application discloses a kind of electromagnetic transient initialization method and system suitable for flexible direct current island mode, comprising: according to the result of power flow calculation, the control instruction value of new energy and flexible direct current converter station is determined;Based on clamping voltage source and the control instruction value, the initialization of new energy field station and flexible direct current converter station is carried out;When new energy and flexible direct current converter station initialization is completed, cut off clamping voltage source, switch the control strategy of sending end converter station, from network type control switch to island type control, complete electromagnetic transient initialization.The present application makes full use of electromechanical power flow result, and uses the initialization idea of flexible direct current controller smooth switching, avoids the cumbersome switch process;It can be directly configured in the control strategy of flexible direct current converter station and packaged, the degree of automation is high, the disturbance in initialization process is small, greatly improves the efficiency and success rate of initialization.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and more specifically, to an electromagnetic transient initialization method and system suitable for flexible DC islanding mode. Background Technology

[0002] Initialization refers to the process of solving for the steady-state operating state of a system based on an electromagnetic transient model. It is one of the main steps in electromagnetic transient simulation, which can initially verify the rationality of the electromagnetic transient model and is also a prerequisite for subsequent simulation of fault characteristics. Over the years, a great deal of research has been conducted both domestically and internationally on electromagnetic transient initialization methods, including initialization methods for electromagnetic transient models of different devices, such as synchronous generators, doubly-fed wind turbines, conventional DC, new energy, and flexible DC. However, the above research only focuses on individual devices and does not consider the joint initialization process of different devices and different control strategies. In this process, there is power interaction between different devices, which requires a lot of time to adjust the initialization strategy when facing different scenarios, affecting the efficiency of electromagnetic transient simulation. Some scholars have also studied the initialization of new energy systems connected to flexible DC grids, proposing a joint initialization method of open-circuit initialization of islanded control flexible DC converter stations followed by integration with new energy. However, this method has large power fluctuations and long transition times during the transition process of flexible DC, and the configuration process is relatively cumbersome with low automation. The initialization problem in the islanded mode of flexible DC has not been completely solved.

[0003] Therefore, a fast electromagnetic transient initialization method suitable for flexible DC islanding mode is needed. Summary of the Invention

[0004] This invention proposes an electromagnetic transient initialization method and system suitable for flexible DC islanding mode, in order to solve the problem of how to smoothly switch and quickly complete the initialization of electromagnetic transient simulation.

[0005] To address the aforementioned problems, according to one aspect of the present invention, an electromagnetic transient initialization method suitable for flexible DC islanding mode is provided, the method comprising: The control command values ​​for new energy sources and flexible DC converter stations are determined based on the power flow calculation results. Initialization of the new energy power station and flexible DC converter station is performed based on the clamping voltage source and the control command value; When the initialization of the new energy source and the flexible DC converter station is completed, the clamping voltage source is cut off, the control strategy of the sending-end converter station is switched from grid-based control to islanded control, and the electromagnetic transient initialization is completed.

[0006] Preferably, determining the control command values ​​for the new energy source and the flexible DC converter station based on the power flow calculation results includes: , in, This refers to the active power command value on the renewable energy side. The results are the active power flow calculation results for the new energy side; This refers to the reactive power command value on the new energy side; The results are the reactive power flow calculation results for the new energy side; This refers to the active power command value on the flexible DC converter station side; The results are the active power flow calculations for the flexible DC converter station side. This refers to the DC voltage command value on the flexible DC converter station side; The results of DC voltage power flow calculations on the flexible DC converter station side; This refers to the reactive power command value on the flexible DC converter station side; The results are the reactive power flow calculations for the flexible DC converter station side. This refers to the AC voltage command value on the flexible DC converter station side; The results are the AC voltage power flow calculations for the flexible DC converter station side.

[0007] Preferably, the initialization of the new energy power station and flexible DC converter station based on the clamping voltage source and the control command value includes: A clamping voltage source with a switch is connected to the primary side of the boost transformer of the new energy converter; the voltage amplitude and phase angle of the clamping voltage source are determined by power flow results. , in, and The voltage amplitude and phase angle of the clamping voltage source; and The voltage magnitude and phase angle obtained from power flow calculations; Both the renewable energy power plant and the flexible DC converter station are controlled by grid-connected control. The active and reactive power of the renewable energy power plant are set based on the control command values, as are the DC voltage, active power, and reactive power of the flexible DC converter station. The sending-end converter station adopts constant power control, and the receiving-end converter station adopts constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of the sending-end converter station and the receiving-end converter station, respectively.

[0008] Preferably, the control strategy for switching the sending-end converter station is changed from grid-based control to islanded control, including: The phase angle of the Parker converter at the converter station is switched from the phase angle of grid-type control to the phase angle of island-type control; Switch the dq axis current reference value from the grid mode to the island mode.

[0009] Preferably, switching the phase angle of the converter station Parker transformation from the phase angle of grid-type control to the phase angle of island-type control includes: Before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the phase angle is updated to the sum of the phase-locked angle of the islanded control and the phase-locked angle of the meshed control at the switching moment, so that the phase angle after switching changes from the switching point according to the slope of the islanded control mode between 0 and 2π. Among them, the Parker transformation matrix T abc-dq for: , In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop as follows: , In islanded control, phase angle Generated based on a fixed angular frequency, as follows: , in, Phase angle; and These are the proportional and integral coefficients in a phase-locked loop PI control, respectively. This refers to the q-axis voltage output by the controller. The initial angular frequency; The complex frequency of the Laplace transform; It is a fixed angular frequency for islanded control.

[0010] Preferably, switching the dq-axis current reference value from the mesh mode to the island mode includes: The reference value of the dq-axis current after the grid control stabilizes is used as the initial value of the PI controller that generates the dq-axis current in islanded mode after the control mode switch, so that the dq-axis current in islanded mode is calculated from the initial value after the control mode switch. The reference values ​​for the dq-axis current after the grid control has stabilized are determined using the following methods: , , , in, and These are the reference values ​​for the d-axis and q-axis currents after the grid control has stabilized; and These are the active power command value and reactive power command value on the flexible DC converter station side, respectively. This is the baseline value for system capacity. System voltage reference value; This is the system current reference value.

[0011] According to another aspect of the present invention, an electromagnetic transient initialization system suitable for flexible DC islanding mode is provided, the system comprising: The control command value determination unit is used to determine the control command values ​​for new energy sources and flexible DC converter stations based on power flow calculation results. An initialization unit is used to initialize the new energy power station and the flexible DC converter station based on the clamping voltage source and the control command value; The control switching unit is used to cut off the clamping voltage source and switch the control strategy of the sending-end converter station when the initialization of the new energy and flexible DC converter station is completed, switching from grid-based control to islanded control, and completing electromagnetic transient initialization.

[0012] Preferably, the control command value determination unit is used to determine the control command values ​​for the new energy source and the flexible DC converter station based on the power flow calculation results, including: , in, This refers to the active power command value on the renewable energy side. The results are the active power flow calculation results for the new energy side; This refers to the reactive power command value on the new energy side; The results are the reactive power flow calculation results for the new energy side; This refers to the active power command value on the flexible DC converter station side; The results are the active power flow calculations for the flexible DC converter station side. This refers to the DC voltage command value on the flexible DC converter station side; The results of DC voltage power flow calculations on the flexible DC converter station side; This refers to the reactive power command value on the flexible DC converter station side; The results are the reactive power flow calculations for the flexible DC converter station side. This refers to the AC voltage command value on the flexible DC converter station side; The calculation results are for the AC voltage flow at the flexible DC converter station. Preferably, the initialization unit initializes the new energy power station and the flexible DC converter station based on the clamping voltage source and the control command value, including: A clamping voltage source with a switch is connected to the primary side of the boost transformer of the new energy converter; the voltage amplitude and phase angle of the clamping voltage source are determined by power flow results. , in, and The voltage amplitude and phase angle of the clamping voltage source; and The voltage magnitude and phase angle obtained from power flow calculations; Both the renewable energy power plant and the flexible DC converter station are controlled by grid-connected control. The active and reactive power of the renewable energy power plant are set based on the control command values, as are the DC voltage, active power, and reactive power of the flexible DC converter station. The sending-end converter station adopts constant power control, and the receiving-end converter station adopts constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of the sending-end converter station and the receiving-end converter station, respectively.

[0013] Preferably, the control switching unit switches the control strategy of the sending-end converter station from grid-based control to islanded control, including: The phase angle of the Parker converter at the converter station is switched from the phase angle of grid-type control to the phase angle of island-type control; Switch the dq axis current reference value from the grid mode to the island mode.

[0014] Preferably, the control switching unit switches the phase angle of the converter station Parker transformation from the phase angle of grid-type control to the phase angle of island-type control, including: Before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the phase angle is updated to the sum of the phase-locked angle of the islanded control and the phase-locked angle of the meshed control at the switching moment, so that the phase angle after switching changes from the switching point according to the slope of the islanded control mode between 0 and 2π. Among them, the Parker transformation matrix T abc-dq for: , In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop as follows: , In islanded control, phase angle Generated based on a fixed angular frequency, as follows: , in, Phase angle; and These are the proportional and integral coefficients in a phase-locked loop PI control, respectively. This refers to the q-axis voltage output by the controller. The initial angular frequency; The complex frequency of the Laplace transform; It is a fixed angular frequency for islanded control.

[0015] Preferably, the control switching unit switches the dq-axis current reference value from the mesh mode to the island mode, including: The reference value of the dq-axis current after the grid control stabilizes is used as the initial value of the PI controller that generates the dq-axis current in islanded mode after the control mode switch, so that the dq-axis current in islanded mode is calculated from the initial value after the control mode switch. The reference values ​​for the dq-axis current after the grid control has stabilized are determined using the following methods: , , , in, and These are the reference values ​​for the d-axis and q-axis currents after the grid control has stabilized; and These are the active power command value and reactive power command value on the flexible DC converter station side, respectively. This is the baseline value for system capacity. System voltage reference value; This is the system current reference value.

[0016] Based on another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the electromagnetic transient initialization methods applicable to flexible DC islanding mode.

[0017] According to another aspect of the present invention, the present invention provides an electronic device, comprising: The aforementioned computer-readable storage medium; and One or more processors for executing a program in the computer-readable storage medium.

[0018] This invention provides an electromagnetic transient initialization method and system suitable for flexible DC islanding mode, comprising: determining control command values ​​for renewable energy and flexible DC converter stations based on power flow calculation results; initializing renewable energy plants and flexible DC converter stations based on clamping voltage sources and the control command values; and, upon completion of the initialization of renewable energy and flexible DC converter stations, disconnecting the clamping voltage source, switching the control strategy of the sending-end converter station from grid-following control to islanding control, thus completing the electromagnetic transient initialization. This invention fully utilizes electromechanical power flow results and adopts an initialization approach that allows for smooth switching of flexible DC controllers, avoiding cumbersome switching processes. It can be directly configured and encapsulated within the control strategy of the flexible DC converter station, resulting in high automation, minimal disturbance during initialization, and significantly improved initialization efficiency and success rate. Attached Figure Description

[0019] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures: Figure 1 This is a flowchart of an electromagnetic transient initialization method 100 applicable to flexible DC islanding mode according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the electromagnetic transient rapid initialization process applicable to the flexible straight island mode according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the initialization of a new energy and flexible DC converter station via a clamping voltage source according to an embodiment of the present invention; Figure 4 This is a reference diagram of the Parker transformation coordinate system according to an embodiment of the present invention; Figure 5 This is a schematic diagram of smooth phase-locked angle switching according to an embodiment of the present invention; Figure 6 This is a phase-locked angle switching control diagram according to an embodiment of the present invention; Figure 7 This is a control diagram for switching the dq-axis reference current according to an embodiment of the present invention; Figure 8 This is a topology diagram of a flexible DC converter station connected to a new energy island according to an embodiment of the present invention; Figure 9 The graph shows the change in input phase angle of the Parker transform before and after applying the method of this invention. Figure 10 The waveforms of the outer loop dq-axis current of the flexible DC converter station controller before and after applying the method of the present invention are shown. Figure 11 A comparison chart showing the effects of initializing AC voltage, converter station active power, converter station reactive power, and wind turbine power using the strategy of the present invention versus the strategy of the prior art. Figure 12 A comparison chart showing the effects of initializing AC voltage, converter station active power, converter station reactive power, and wind turbine power using the strategy of the present invention versus the strategy of the prior art. Figure 13 A comparison chart showing the effects of initializing AC voltage, converter station active power, converter station reactive power, and wind turbine power using the strategy of the present invention versus the strategy of the prior art. Figure 14 A comparison chart showing the effects of initializing AC voltage, converter station active power, converter station reactive power, and wind turbine power using the strategy of the present invention versus the strategy of the prior art. Figure 15 This is a schematic diagram of the structure of an electromagnetic transient initialization system 1500 suitable for flexible DC islanding mode according to an embodiment of the present invention. Detailed Implementation

[0020] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0021] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0022] Figure 1 This is a flowchart of an electromagnetic transient initialization method 100 applicable to flexible DC islanding mode according to an embodiment of the present invention. Figure 1 As shown, the electromagnetic transient initialization method for flexible DC islanding mode provided by this invention fully utilizes electromechanical power flow results and adopts an initialization approach that allows for smooth switching of the flexible DC controller, avoiding cumbersome switching processes. It can be directly configured and encapsulated in the control strategy of the flexible DC converter station, exhibiting a high degree of automation and minimal disturbance during the initialization process, greatly improving the efficiency and success rate of initialization. The electromagnetic transient initialization method 100 for flexible DC islanding mode provided by this invention begins at step 101, where the control command values ​​for the new energy source and the flexible DC converter station are determined based on the power flow calculation results.

[0023] Preferably, determining the control command values ​​for the new energy source and the flexible DC converter station based on the power flow calculation results includes: , in, This refers to the active power command value on the renewable energy side. The results are the active power flow calculation results for the new energy side; This refers to the reactive power command value on the new energy side; The results are the reactive power flow calculation results for the new energy side; This refers to the active power command value on the flexible DC converter station side; The results are the active power flow calculations for the flexible DC converter station side. This refers to the DC voltage command value on the flexible DC converter station side; The results of DC voltage power flow calculations on the flexible DC converter station side; This refers to the reactive power command value on the flexible DC converter station side; The results are the reactive power flow calculations for the flexible DC converter station side. This refers to the AC voltage command value on the flexible DC converter station side; The results are the AC voltage power flow calculations for the flexible DC converter station side.

[0024] Combination Figure 2 As shown, in this invention, an electromagnetic transient initialization strategy based on power flow solution is first adopted, and the power flow result is used as the control command value of the new energy grid-connected converter.

[0025] Specifically, at time zero, the command values ​​for new energy sources and the command values ​​for each converter station of the flexible DC power supply are set to the results of the power flow calculation: (1) In the formula, the subscript ref indicates that the parameter is a command value, and the subscript 0 indicates that the parameter is a power flow calculation result.

[0026] In step 102, the new energy power station and the flexible DC converter station are initialized based on the clamping voltage source and the control command value.

[0027] Preferably, the initialization of the new energy power station and flexible DC converter station based on the clamping voltage source and the control command value includes: A clamping voltage source with a switch is connected to the primary side of the boost transformer of the new energy converter; the voltage amplitude and phase angle of the clamping voltage source are determined by power flow results. , in, and The voltage amplitude and phase angle of the clamping voltage source; and The voltage magnitude and phase angle obtained from power flow calculations; Both the renewable energy power plant and the flexible DC converter station are controlled by grid-connected control. The active and reactive power of the renewable energy power plant are set based on the control command values, as are the DC voltage, active power, and reactive power of the flexible DC converter station. The sending-end converter station adopts constant power control, and the receiving-end converter station adopts constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of the sending-end converter station and the receiving-end converter station, respectively.

[0028] Combination Figure 2 As shown, in this invention, a clamping voltage source with a switch is connected to the primary side of the step-up transformer at the renewable energy converter station to initialize the renewable energy station. Simultaneously, during the initialization of the renewable energy station, the sending and receiving end flexible DC converter stations adopt grid-following control and are initialized using the same clamping voltage source with a switch as the renewable energy station.

[0029] Specifically, based on the clamping voltage source and the control command value, the initialization of new energy and flexible DC transmission is quickly initiated, including: Step 1: Connect a clamping voltage source with a switch to the primary side of the boost transformer of the new energy converter. The voltage amplitude and phase angle of the clamping voltage source are determined by the power flow results. (2) Step 2: Both the renewable energy power station and the flexible DC converter station adopt grid-connected control. Based on the control command values, the active and reactive power of the renewable energy power station are set, as are the DC voltage, active and reactive power of the flexible DC converter station. The sending-end converter station uses constant power control, and the receiving-end converter station uses constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of both the sending-end and receiving-end converter stations.

[0030] In step 103, when the initialization of the new energy and flexible DC converter station is completed, the clamping voltage source is cut off, the control strategy of the sending-end converter station is switched from grid-based control to islanded control, and electromagnetic transient initialization is completed.

[0031] Preferably, the control strategy for switching the sending-end converter station is changed from grid-based control to islanded control, including: The phase angle of the Parker converter at the converter station is switched from the phase angle of grid-type control to the phase angle of island-type control; Switch the dq axis current reference value from the grid mode to the island mode.

[0032] Preferably, switching the phase angle of the converter station Parker transformation from the phase angle of grid-type control to the phase angle of island-type control includes: Before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the phase angle is updated to the sum of the phase-locked angle of the islanded control and the phase-locked angle of the meshed control at the switching moment, so that the phase angle after switching changes from the switching point according to the slope of the islanded control mode between 0 and 2π. Among them, the Parker transformation matrix T abc-dq for: , In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop as follows: , In islanded control, phase angle Generated based on a fixed angular frequency, as follows: , in, Phase angle; and These are the proportional and integral coefficients in a phase-locked loop PI control, respectively. This refers to the q-axis voltage output by the controller. The initial angular frequency; The complex frequency of the Laplace transform; It is a fixed angular frequency for islanded control.

[0033] Preferably, switching the dq-axis current reference value from the mesh mode to the island mode includes: The reference value of the dq-axis current after the grid control stabilizes is used as the initial value of the PI controller that generates the dq-axis current in islanded mode after the control mode switch, so that the dq-axis current in islanded mode is calculated from the initial value after the control mode switch. The reference values ​​for the dq-axis current after the grid control has stabilized are determined using the following methods: , , , in, and These are the reference values ​​for the d-axis and q-axis currents after the grid control has stabilized; and These are the active power command value and reactive power command value on the flexible DC converter station side, respectively. This is the baseline value for system capacity. System voltage reference value; This is the system current reference value.

[0034] Combination Figure 2 As shown, in this invention, when the initialization of the new energy source and the flexible DC converter station is completed, the clamping voltage source is cut off, and the sending-end flexible DC converter station is switched to islanded control. During the switching process: firstly, the phase-locked angle is switched from the phase-locked angle generated by the phase-locked loop in grid-based control to a fixed phase-locked angle spontaneously generated by islanded control; simultaneously, the d-axis reference current is... i sdref and q-axis reference current i sqref The reference current is switched from grid-based control to islanded control; finally, the flexible DC converter station is smoothly switched between the two control strategies through inner and outer loop control, realizing the rapid initialization of the flexible DC converter station and the new energy islanded system.

[0035] Specifically, after the new energy source and flexible DC transmission are fully operational, the process of switching the control strategy of the sending-end converter station from grid-connected control to islanded control includes: Step 1: Switch the phase angle of the converter station's Parker converter from the phase angle of grid-type control to the phase angle of island-type control.

[0036] The control of the flexible DC converter station adopts a dual-loop control based on Parker transformation. In this invention, the q-axis leads the d-axis by 90°, and the transformation angle... Let d be the angle by which the d-axis leads phase A. In this coordinate system, the Parker transformation matrix... T abc-dq As shown in formula (3): (3) In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop, and its formula is shown in (4): (4) In the formula, , These are the proportional and integral coefficients in a phase-locked loop (PLL) PI control, respectively. This is the q-axis voltage output by the controller.

[0037] In islanded control, phase angle Based on the fixed angular frequency, its formula is shown in (5): (5) The switching strategy is as follows: before switching, the phase angle is determined by the PLL (phase-locked loop). During switching, the slope of the phase angle change is switched, rather than directly switching the value of the phase angle. This ensures that the phase angle after switching varies between 0 and 2π from the switching point, following the slope of the islanded control mode. Specifically, the islanded control phase-locked angle is given an initial value, initially 0. This initial value is then changed to the corresponding value of the mesh-type control phase-locked angle at the instant of switching and remains at this value.

[0038] After the Parker transformation, active and reactive power are represented by electrical quantities along the dq axis, as shown in formula (6): (6) Under steady state, the q-axis component of the voltage is 0, hence formula (7) holds: (7) Here , , For the corresponding amplitude, and the voltage d-axis component Equal to phase voltage amplitude .

[0039] Step 2: Switch the dq-axis current reference value from grid-based mode to islanded mode. Specifically, before switching, an initial value needs to be frozen for the PI control loop that generates the dq-axis current in islanded mode. This ensures that after the control mode switch, the dq-axis current in islanded mode can be calculated directly from this initial value, instead of starting from 0. This initial value corresponds to the dq-axis current reference value after grid-based control has stabilized. After the system stabilizes, complete the initialization.

[0040] The dq-axis current reference value is obtained from power flow calculations, and the specific process is as follows: Step 21: Using the effective values ​​of phase voltage and phase current as voltage and current reference values, calculate the system capacity reference according to formula (8). : (8) Step 22: Express the voltage and current components in formula (7) using per-unit values, as shown in formula (9). Note the relationship between amplitude and effective value here: (9) Step 23: Using formula (2), substitute the results of the power flow calculation as the command values ​​of active power and reactive power into formulas (8) and (9) to obtain the reference value of the dq axis current, as shown in formula (10): (10) In the formula, and These are the active and reactive power command values ​​for the converter station. This is the baseline value for system capacity.

[0041] To address the cumbersome and slow initialization process of new energy transmission systems via flexible DC transmission, this invention proposes a rapid electromagnetic transient initialization method suitable for flexible DC islanding modes. This method achieves rapid completion of electromagnetic transient simulation initialization through smooth switching of the flexible DC converter station control strategy during the initialization process. Furthermore, this method can be directly encapsulated within the control strategy of the flexible DC converter station, allowing different systems to directly use the encapsulated control strategy, significantly improving the configuration efficiency of electromagnetic transient simulation.

[0042] The following specific examples illustrate the embodiments of the present invention. In an embodiment of the present invention, the electromagnetic transient rapid initialization method applicable to flexible DC islanding mode is as follows: (1) Determine the control command values ​​for new energy sources and each flexible DC converter station based on the power flow calculation data; (1) (2) For example Figure 3As shown, the flexible DC converter station uses grid-connected control. The sending-end converter station employs constant power control, while the receiving-end converter station uses constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of both the sending-end and receiving-end converter stations. Simultaneously, a clamping voltage source with a switch is connected to the primary side of the new energy converter's step-up transformer. The voltage amplitude and phase angle of the clamping voltage source are determined using power flow results. (2) (3) When the initialization of the new energy power station is completed, the clamping voltage source is cut off, and the control mode of the sending-end flexible DC converter station is switched to island control at the same time. This switch is divided into the switching of Parker transformation phase angle and the switching of dq axis reference current.

[0043] 1) The control of the flexible DC converter station adopts a dual-loop control based on Parker transformation. In this invention, the q-axis leads the d-axis by 90°, and the transformation angle... The angle by which the d-axis leads phase A, such as Figure 4 As shown. Parker transformation matrix. T abc-dq As shown in formula (3): (3) 2) In the grid-type control mode, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop, and its formula is shown in (4): (4) In the formula, , These are the proportional and integral coefficients in a phase-locked loop (PLL) PI control, respectively. This is the q-axis voltage output by the controller.

[0044] 3) In islanded control mode, phase angle Based on the fixed angular frequency, its formula is shown in (5): (5) 4) such as Figure 5-6 As shown, the phase angle switching strategy is as follows: before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the slope of the phase angle change is switched, rather than directly switching the value of the phase angle. This allows the phase angle after switching to cycle between 0 and 2π from the switching point, following the slope of the islanded control mode. The specific implementation method in this invention is to add an initial value to the islanded control phase-locked angle. This initial value is initially 0, and at the instant of switching, it becomes the value of the corresponding mesh control phase-locked angle at that moment, and remains at this value. Figure 6 In .

[0045] 5) such as Figure 7As shown, the dq-axis current reference value is switched from grid-based control to islanded control. With grid-based control, the dq-axis current reference value is obtained through direct calculation; with islanded control, the dq-axis current reference value is obtained through PI control.

[0046] The switching process is as follows: Before switching, an initial value needs to be frozen for the PI control loop of the islanded control. This ensures that after the control mode switch, the dq-axis current of the islanded control can be calculated directly from this initial value, instead of starting from 0. This initial value corresponds to the reference value of the dq-axis current after the grid control has stabilized.

[0047] The specific calculation methods for the reference current of the dq axis in mesh control and the initial value of the PI element in islanded control are as follows: After Parker transformation, active and reactive power are expressed in terms of dq-axis electrical quantities, as shown in formula (6): (6) Under steady state, the q-axis component of the voltage is 0, hence formula (7) holds: (7) Here , , For the corresponding amplitude, and the voltage d-axis component Equal to phase voltage amplitude .

[0048] Transforming formula (6), we obtain the reference value for the dq axis current when using mesh control: (8) Using the effective values ​​of phase voltage and phase current as voltage and current reference values, the system capacity reference is obtained according to formula (9). : (9) The voltage and current components in formula (7) are expressed in per-unit values, as shown in formula (10). Note the relationship between amplitude and effective value here: (10) From formula (2), the results obtained from the power flow calculation are substituted into the command values ​​of active power and reactive power and combined into formulas (9) and (10) to obtain the initial values ​​of the islanded control PI link, as shown in formula (11): (11) In the formula, and These are the active and reactive power command values ​​for the converter station. This is the baseline value for system capacity.

[0049] In the PSModel (Power System Model) electromagnetic transient simulation software developed by the System Research Institute of China Electric Power Research Institute, such as Figure 8 As shown in Table 1, an electromagnetic transient simulation model of a flexible DC converter station connected to a renewable energy island is constructed. The electrical system parameters are shown in Table 1, and the unlocking sequence of the converter station and the renewable energy is shown in Table 2.

[0050] Table 1 Electrical System Parameters

[0051] Table 2 Unlocking Timing

[0052] The electromagnetic transient rapid initialization method proposed in this invention, applicable to flexible DC islanding mode, is compared with the scheme of directly switching control mode without using the strategy of this invention and the method used in the background art.

[0053] Figure 9 This is a graph showing the change in input phase angle before and after applying the Parker transform according to the present invention. For example... Figure 9 As shown, before adopting this invention, a sudden change in phase angle occurs after the 2.6s control mode switch. Under extremely severe conditions, this sudden change may directly cause the renewable energy source to disconnect from the grid. To prevent this sudden change in phase angle, the phase angle values ​​of the islanded controller and the grid controller need to be aligned at the moment of switching. This is difficult to achieve in practice, and the corresponding values ​​differ between different systems, which is detrimental to improving initialization efficiency. After adopting this invention, there is no sudden change in phase angle after the 2.6s control mode switch, achieving a smooth transition of phase angle during the switching process.

[0054] Figure 10 The diagram shows the dq-axis current waveforms of the outer loop of the flexible DC converter station controller before and after the application of this invention. Figure 10 As shown, before adopting this invention, the dq-axis current fluctuated drastically after the 2.6s control mode switch, accompanied by a long transition time. After adopting this invention, the dq-axis current fluctuates almost no after the 2.6s control mode switch, and the transition time is almost zero.

[0055] like Figure 11 As shown, using the strategy of the prior art, after the clamping voltage source is cut off at 2.6s and the sending-end converter station is connected, the AC voltage fluctuates significantly, exceeding 1.2pu at one point, and the transition time is relatively long, with the AC voltage only stabilizing after about 5s. Using the strategy of this invention, after the clamping voltage source is cut off at 2.6s, the AC voltage transition is smooth and without fluctuations, stabilizing within 3s; as... Figure 12As shown, using the prior art strategy, before the clamping voltage source is cut off at 2.6 seconds and the sending-end converter station is connected, the active power is 0 because the converter station is open. Using the strategy of this invention, before the clamping voltage source is cut off at 2.6 seconds, since the converter station and the new energy power station are always connected, power transmission begins immediately after the converter station is unlocked. Figure 13 As shown, using the background technology strategy, before the 2.6s operation, the reactive power is 0 because the converter station is open, and after the 2.6s operation, the reactive power fluctuates significantly with a long transition time, only stabilizing completely after about 6s. Using the strategy of this invention, before the 2.6s operation, because the converter station and the new energy power station are continuously connected, power transmission begins immediately after the converter station is unlocked. Furthermore, after the 2.6s operation, the reactive power transition is smooth with no significant fluctuations, reaching stability within 3s. Figure 14 As shown in the background technology strategy, after 2.6 seconds of operation, the active and reactive power of the wind turbines in the new energy power plant fluctuates significantly. Using the strategy of this invention, after 2.6 seconds of operation, the active and reactive power of the wind turbines in the new energy power plant fluctuates almost completely, quickly reaching a stable state.

[0056] Figure 15 This is a schematic diagram of the structure of an electromagnetic transient initialization system 1500 suitable for flexible DC islanding mode according to an embodiment of the present invention. Figure 15 As shown, the electromagnetic transient initialization system 1500 for flexible DC islanding mode provided by the embodiment of the present invention includes: a control command value determination unit 1501, an initialization unit 1502, and a control switching unit 1503.

[0057] Preferably, the control command value determination unit 1501 is used to determine the control command values ​​for new energy sources and flexible DC converter stations based on power flow calculation results.

[0058] Preferably, the control command value determination unit 1501 is used to determine the control command values ​​for the new energy source and the flexible DC converter station based on the power flow calculation results, including: , in, This refers to the active power command value on the renewable energy side. The results are the active power flow calculation results for the new energy side; This refers to the reactive power command value on the new energy side; The results are the reactive power flow calculation results for the new energy side; This refers to the active power command value on the flexible DC converter station side; The results are the active power flow calculations for the flexible DC converter station side. This refers to the DC voltage command value on the flexible DC converter station side; The results of DC voltage power flow calculations on the flexible DC converter station side; This refers to the reactive power command value on the flexible DC converter station side; The results are the reactive power flow calculations for the flexible DC converter station side. This refers to the AC voltage command value on the flexible DC converter station side; The results are the AC voltage power flow calculations for the flexible DC converter station side.

[0059] Preferably, the initialization unit 1502 is used to initialize the new energy power station and the flexible DC converter station based on the clamping voltage source and the control command value.

[0060] Preferably, the initialization unit 1502 initializes the new energy power station and the flexible DC converter station based on the clamping voltage source and the control command value, including: A clamping voltage source with a switch is connected to the primary side of the boost transformer of the new energy converter; the voltage amplitude and phase angle of the clamping voltage source are determined by power flow results. , in, and The voltage amplitude and phase angle of the clamping voltage source; and The voltage magnitude and phase angle obtained from power flow calculations; Both the renewable energy power plant and the flexible DC converter station are controlled by grid-connected control. The active and reactive power of the renewable energy power plant are set based on the control command values, as are the DC voltage, active power, and reactive power of the flexible DC converter station. The sending-end converter station adopts constant power control, and the receiving-end converter station adopts constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of the sending-end converter station and the receiving-end converter station, respectively.

[0061] Preferably, the control switching unit 1503 is used to cut off the clamping voltage source and switch the control strategy of the sending-end converter station from grid-based control to islanded control when the initialization of the new energy and flexible DC converter station is completed, thereby completing the electromagnetic transient initialization.

[0062] Preferably, the control switching unit 1503 switches the control strategy of the sending-end converter station from grid-based control to islanded control, including: The phase angle of the Parker converter at the converter station is switched from the phase angle of grid-type control to the phase angle of island-type control; Switch the dq axis current reference value from the grid mode to the island mode.

[0063] Preferably, the control switching unit 1503 switches the phase angle of the converter station Parker transformation from the phase angle of grid-type control to the phase angle of island-type control, including: Before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the phase angle is updated to the sum of the phase-locked angle of the islanded control and the phase-locked angle of the meshed control at the switching moment, so that the phase angle after switching changes from the switching point according to the slope of the islanded control mode between 0 and 2π. Among them, the Parker transformation matrix T abc-dq for: , In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop as follows: , In islanded control, phase angle Generated based on a fixed angular frequency, as follows: , in, Phase angle; and These are the proportional and integral coefficients in a phase-locked loop PI control, respectively. This refers to the q-axis voltage output by the controller. The initial angular frequency; The complex frequency of the Laplace transform; It is a fixed angular frequency for islanded control.

[0064] Preferably, the control switching unit 1503 switches the dq axis current reference value from the mesh mode to the island mode, including: The reference value of the dq-axis current after the grid control stabilizes is used as the initial value of the PI controller that generates the dq-axis current in islanded mode after the control mode switch, so that the dq-axis current in islanded mode is calculated from the initial value after the control mode switch. The reference values ​​for the dq-axis current after the grid control has stabilized are determined using the following methods: , , , in, and These are the reference values ​​for the d-axis and q-axis currents after the grid control has stabilized; and These are the active power command value and reactive power command value on the flexible DC converter station side, respectively. This is the baseline value for system capacity. System voltage reference value; This is the system current reference value.

[0065] The electromagnetic transient initialization system 1500 for flexible DC islanding mode in an embodiment of the present invention corresponds to the electromagnetic transient initialization method 100 for flexible DC islanding mode in another embodiment of the present invention, and will not be described again here.

[0066] Based on another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the electromagnetic transient initialization methods applicable to flexible DC islanding mode.

[0067] According to another aspect of the present invention, the present invention provides an electronic device, comprising: The aforementioned computer-readable storage medium; and One or more processors for executing a program in the computer-readable storage medium.

[0068] The present invention has been described with reference to a few embodiments. However, it will be apparent to those skilled in the art that other embodiments besides those disclosed above fall equivalently within the scope of the present invention.

[0069] Generally, all terms used in this invention are interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

[0070] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0071] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0072] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0073] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. An electromagnetic transient initialization method suitable for flexible DC islanding mode, characterized in that, The method includes: The control command values ​​for new energy sources and flexible DC converter stations are determined based on the power flow calculation results. Initialization of the new energy power station and flexible DC converter station is performed based on the clamping voltage source and the control command value; When the initialization of the new energy source and the flexible DC converter station is completed, the clamping voltage source is cut off, the control strategy of the sending-end converter station is switched from grid-based control to islanded control, and the electromagnetic transient initialization is completed.

2. The method according to claim 1, characterized in that, The control command values ​​for the new energy source and flexible DC converter station are determined based on the power flow calculation results, including: ， in, This refers to the active power command value on the renewable energy side. The results are the active power flow calculation results for the new energy side; This refers to the reactive power command value on the new energy side; The results are the reactive power flow calculation results for the new energy side; This refers to the active power command value on the flexible DC converter station side; The results are the active power flow calculations for the flexible DC converter station side. This refers to the DC voltage command value on the flexible DC converter station side; The results of DC voltage power flow calculations on the flexible DC converter station side; This refers to the reactive power command value on the flexible DC converter station side; The results are the reactive power flow calculations for the flexible DC converter station side. This refers to the AC voltage command value on the flexible DC converter station side; The results are the AC voltage power flow calculations for the flexible DC converter station side.

3. The method according to claim 1, characterized in that, Initialization of the new energy power station and flexible DC converter station based on the clamping voltage source and the control command value includes: A clamping voltage source with a switch is connected to the primary side of the boost transformer of the new energy converter; the voltage amplitude and phase angle of the clamping voltage source are determined by power flow results. ， in, and The voltage amplitude and phase angle of the clamping voltage source; and The voltage magnitude and phase angle obtained from power flow calculations; Both the renewable energy power plant and the flexible DC converter station are controlled by grid-connected control. The active and reactive power of the renewable energy power plant are set based on the control command values, as are the DC voltage, active power, and reactive power of the flexible DC converter station. The sending-end converter station adopts constant power control, and the receiving-end converter station adopts constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of the sending-end converter station and the receiving-end converter station, respectively.

4. The method according to claim 1, characterized in that, Switching the control strategy of the sending-end converter station from grid-based control to islanded control includes: The phase angle of the Parker converter at the converter station is switched from the phase angle of grid-type control to the phase angle of island-type control; Switch the dq axis current reference value from the grid mode to the island mode.

5. The method according to claim 4, characterized in that, Switching the phase angle of the converter station's Parker converter from the phase angle of grid-type control to the phase angle of island-type control includes: Before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the phase angle is updated to the sum of the phase-locked angle of the islanded control and the phase-locked angle of the meshed control at the switching moment, so that the phase angle after switching changes from the switching point according to the slope of the islanded control mode between 0 and 2π. Among them, the Parker transformation matrix T abc-dq for: ， In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop as follows: , In islanded control, phase angle Generated based on a fixed angular frequency, as follows: ， in, Phase angle; and These are the proportional and integral coefficients in a phase-locked loop PI control, respectively. This refers to the q-axis voltage output by the controller. The initial angular frequency; The complex frequency of the Laplace transform; It is a fixed angular frequency for islanded control.

6. The method according to claim 4, characterized in that, Switching the dq axis current reference value from mesh mode to island mode includes: The reference value of the dq-axis current after the grid control stabilizes is used as the initial value of the PI controller that generates the dq-axis current in islanded mode after the control mode switch, so that the dq-axis current in islanded mode is calculated from the initial value after the control mode switch. The reference values ​​for the dq-axis current after the grid control has stabilized are determined using the following methods: ， ， ， in, and These are the reference values ​​for the d-axis and q-axis currents after the grid control has stabilized; and These are the active power command value and reactive power command value on the flexible DC converter station side, respectively. This is the baseline value for system capacity. System voltage reference value; This is the system current reference value.

7. An electromagnetic transient initialization system suitable for flexible DC islanding mode, characterized in that, The system includes: The control command value determination unit is used to determine the control command values ​​for new energy sources and flexible DC converter stations based on power flow calculation results. An initialization unit is used to initialize the new energy power station and the flexible DC converter station based on the clamping voltage source and the control command value; The control switching unit is used to cut off the clamping voltage source and switch the control strategy of the sending-end converter station when the initialization of the new energy and flexible DC converter station is completed, switching from grid-based control to islanded control, and completing electromagnetic transient initialization.

8. The system according to claim 7, characterized in that, The control command value determination unit is used to determine the control command values ​​for new energy sources and flexible DC converter stations based on power flow calculation results, including: ， in, This refers to the active power command value on the renewable energy side. The results are the active power flow calculation results for the new energy side; This refers to the reactive power command value on the new energy side; The results are the reactive power flow calculation results for the new energy side; This refers to the active power command value on the flexible DC converter station side; The results are the active power flow calculations for the flexible DC converter station side. This refers to the DC voltage command value on the flexible DC converter station side; The results of DC voltage power flow calculations on the flexible DC converter station side; This refers to the reactive power command value on the flexible DC converter station side; The results are the reactive power flow calculations for the flexible DC converter station side. This refers to the AC voltage command value on the flexible DC converter station side; The results are the AC voltage power flow calculations for the flexible DC converter station side.

9. The system according to claim 7, characterized in that, The initialization unit initializes the new energy power station and the flexible DC converter station based on the clamping voltage source and the control command value, including: A clamping voltage source with a switch is connected to the primary side of the boost transformer of the new energy converter; the voltage amplitude and phase angle of the clamping voltage source are determined by power flow results. ， in, and The voltage amplitude and phase angle of the clamping voltage source; and The voltage magnitude and phase angle obtained from power flow calculations; Both the renewable energy power plant and the flexible DC converter station are controlled by grid-connected control. The active and reactive power of the renewable energy power plant are set based on the control command values, as are the DC voltage, active power, and reactive power of the flexible DC converter station. The sending-end converter station adopts constant power control, and the receiving-end converter station adopts constant DC voltage control. Clamping voltage sources with switches are connected to the grid connection points of the sending-end converter station and the receiving-end converter station, respectively.

10. The system according to claim 7, characterized in that, The control switching unit switches the control strategy of the sending-end converter station from grid-based control to islanded control, including: The phase angle of the Parker converter at the converter station is switched from the phase angle of grid-type control to the phase angle of island-type control; Switch the dq axis current reference value from the grid mode to the island mode.

11. The system according to claim 10, characterized in that, The control switching unit switches the phase angle of the converter station's Parker transformation from the phase angle of grid-type control to the phase angle of island-type control, including: Before switching, the phase angle is determined by the PLL phase-locked loop. During switching, the phase angle is updated to the sum of the phase-locked angle of the islanded control and the phase-locked angle of the meshed control at the switching moment, so that the phase angle after switching changes from the switching point according to the slope of the islanded control mode between 0 and 2π. Among them, the Parker transformation matrix T abc-dq for: ， In mesh control, the phase angle of the Parker transform The phase of the AC voltage of phase A in the power grid is determined by the PLL phase-locked loop as follows: , In islanded control, phase angle Generated based on a fixed angular frequency, as follows: ， in, Phase angle; and These are the proportional and integral coefficients in a phase-locked loop PI control, respectively. This refers to the q-axis voltage output by the controller. The initial angular frequency; The complex frequency of the Laplace transform; It is a fixed angular frequency for islanded control.

12. The system according to claim 10, characterized in that, The control switching unit switches the dq-axis current reference value from the mesh mode to the island mode, including: The reference value of the dq-axis current after the grid control stabilizes is used as the initial value of the PI controller that generates the dq-axis current in islanded mode after the control mode switch, so that the dq-axis current in islanded mode is calculated from the initial value after the control mode switch. The reference values ​​for the dq-axis current after the grid control has stabilized are determined using the following methods: ， ， ， in, and These are the reference values ​​for the d-axis and q-axis currents after the grid control has stabilized; and These are the active power command value and reactive power command value on the flexible DC converter station side, respectively. This is the baseline value for system capacity. System voltage reference value; This is the system current reference value.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method as described in any one of claims 1-6.

14. An electronic device, characterized in that, include: The computer-readable storage medium as described in claim 13; as well as One or more processors for executing a program in the computer-readable storage medium.

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