A transient stability control method for a heterogeneous hybrid power system

Abstract

The application discloses a kind of transient stability control methods for heterogeneous power supply hybrid power system, when symmetric short-circuit fault occurs to public transmission line, obtain fault point position and fault point voltage effective value, voltage effective value and power angle of grid-connected converter end, voltage effective value and power angle of synchronous generator end and voltage effective value, power angle and active power output value of network-constructing converter end;According to the voltage effective value of grid-connected converter end, the reactive current instruction value of grid-connected converter is calculated;According to the active power output value of network-constructing converter, its active power instruction value is obtained;According to the data obtained, the active current instruction value of grid-connected converter is calculated;The current instruction of obtained grid-connected converter is used as the current control instruction of grid-connected converter during fault, and the active power instruction value of network-constructing converter is used as the power control instruction of network-constructing converter during fault, so that the transient stability of heterogeneous power supply hybrid power system under power grid fault can be improved.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation technology, specifically to a transient stability control method for hybrid power systems with heterogeneous power sources. This method can significantly improve the transient synchronization stability of hybrid power systems with heterogeneous power sources under symmetrical short-circuit faults in the power grid. Background Technology

[0002] With the rapid development of power electronics technology in the field of new energy power generation, new energy sources are largely replacing synchronous generators, and the proportion of traditional power sources continues to decline. The transient stability mechanism of the power system will also change, gradually shifting from a mechanical-electromagnetic system dominated by synchronous generators to a hybrid system jointly dominated by power electronic devices and synchronous machines. The stability characteristics of the system will gradually shift from "electromechanical dominance" to "electromechanical-power electronic device synergistic dominance." This weakens the fundamental elements for maintaining the safety and stability of AC power systems, and the safe and stable operation of the system will face severe challenges under large disturbances such as symmetrical short-circuit faults. Therefore, it is urgent to study the transient stability control methods of heterogeneous power source hybrid power systems under grid short-circuit fault conditions. Currently, scholars at home and abroad have conducted relevant research, as shown in the following published literature:

[0003] [1] Xiuqiang He, Sisi Pan, Hua Geng. Transient Stability of HybridPower Systems Dominated by Different Types of Grid-Forming Devices[J]. IEEE Transactions on Energy Conversion, 2022, 37(2): 868-879.

[0004] [2] Chao Shen, Zhikang Shuai, Yang Shen, et al. Transient Stability and Current Injection Design of Paralleled Current-Controlled VSCs and VirtualSynchronous Generators[J]. IEEE Transactions on Smart Grid, 2021, 12(2): 1118-1134.

[0005] Reference [1] takes a hybrid power system containing a droop-controlled converter and a synchronous machine as the research object. By comparing it with a traditional power system containing only a synchronous machine, it clarifies the novel transient stability characteristics of the hybrid system that are different from those of the traditional system, but does not involve the transient stability collaborative control of complex power systems. For microgrids containing converters with different synchronization methods, Reference [2] proposes a stability boosting control method for a phase-locked loop synchronous converter to track the angular frequency of a virtual synchronous converter. This method quantitatively selects the optimal current injection angle of the phase-locked loop synchronous converter using the Lyapunov energy function method, which can theoretically significantly improve the transient stability of the virtual synchronous converter under grid short-circuit faults. However, this strategy does not consider the stability characteristics of the phase-locked loop synchronous converter itself and cannot guarantee the global stability of the system. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, the present invention aims to propose a transient stability control method for heterogeneous power systems with hybrid power supply. This method, without adding hardware equipment, can significantly improve the transient synchronization stability of heterogeneous power systems with hybrid power supply under symmetrical short-circuit faults in the power grid by simply changing the current command value of the grid-connected converter and the power command value of the grid-connected converter.

[0007] The technical solution of this invention is implemented as follows:

[0008] A transient stability control method for heterogeneous power systems with interconnected power sources includes the following steps:

[0009] Step 1: When a symmetrical short-circuit fault occurs on a common transmission line, obtain the location of the fault point and the effective value of the fault point voltage, the effective value of the voltage and power angle at the grid-type converter terminal, the effective value of the voltage and power angle at the synchronous generator terminal, and the effective value of the voltage, power angle, and active power output value at the grid-type converter terminal.

[0010] Step 2: Calculate the reactive current command value of the grid-connected converter based on the effective value of the terminal voltage of the grid-connected converter; obtain the active power command value of the grid-connected converter based on the active power output value of the grid-connected converter.

[0011] Step 3: Calculate the active current command value of the grid-connected converter based on the reactive current command value of the grid-connected converter, the effective value of the fault point voltage and the fault point location, the power angle of the grid-connected converter, the effective value of the synchronous generator terminal voltage and the power angle, and the effective value of the grid-connected converter terminal voltage and the power angle.

[0012] Step 4: Use the reactive current command of the grid-connected converter calculated in Step 2 and the active current command of the grid-connected converter calculated in Step 3 as the current control command of the grid-connected converter during the fault period, and use the active power command value of the grid-connected converter obtained in Step 2 as the power control command of the grid-connected converter during the fault period. This can improve the transient stability of the heterogeneous power system under grid fault conditions.

[0013] Furthermore, after step 1, the following formula is used to determine whether the grid converter has entered fault ride-through mode:

[0014]

[0015] In the formula, U GFL U represents the effective value of the terminal voltage of the grid-connected converter. th The fault ride-through voltage threshold specified in the power grid guidelines;

[0016] If the network converter enters fault ride-through mode, proceed to step 2; otherwise, repeat step 1.

[0017] In step 2, the reactive current command value of the grid converter is calculated using the following formula:

[0018]

[0019] in, K is the reactive current command value of the grid-type converter; K is the dynamic reactive current proportional coefficient specified in the grid guidelines.

[0020] In step 2, the active power command value of the grid-type converter is calculated using the following formula:

[0021]

[0022] in, and These are the active power command value and active power output value of the grid-type converter, respectively.

[0023] Specifically, step 3 includes the following steps:

[0024] Step 31: Based on the effective value of the fault point voltage and the location of the fault point, obtain the equivalent resistance and reactance of the grid-connected converter branch, the grid-connected converter branch, the synchronous generator branch, and the common transmission line.

[0025] Step 32: Based on the obtained equivalent resistance and reactance, the effective value of the fault point voltage, the power angle of the grid-connected converter and the reactive current command value, the effective value of the synchronous generator terminal voltage and the power angle, and the effective value of the grid-connected converter terminal voltage and the power angle, calculate the active current command value of the grid-connected converter using the following formula:

[0026]

[0027]

[0028]

[0029] Y GFL Y GFM Y SG and Y P These are the equivalent admittances of the grid-connected converter branch, the network-type converter branch, the synchronous generator branch, and the common transmission line, respectively; U g U GFM and E SG These are the effective values ​​of the voltage at the fault point, the effective voltage at the grid-type converter terminal, and the effective voltage at the synchronous generator terminal, respectively; δ GFL0 δ GFM0 and δ SG0 These are the power angles of the grid-type converter, the network-type converter, and the synchronous generator when a fault occurs.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention can calculate the current command value of the grid-connected converter and the power command value of the grid-connected converter based on data such as transmission network impedance information, grid voltage drop, and converter external characteristics. The obtained current command is used as the current control command of the grid-connected converter during a fault, and the obtained power command value is used as the power control command of the grid-connected converter during a fault. This can improve the transient stability of the entire heterogeneous power system while meeting the reactive current requirements of the grid guidelines as much as possible. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the topology of a heterogeneous power system with interconnected power sources.

[0033] Figure 2 This is a schematic diagram of the transient stability control method for heterogeneous power systems proposed in this invention.

[0034] Figure 3 The figure shows a comparison of simulation results before and after applying the control method proposed in this invention to a heterogeneous power system with mixed power sources under a grid short-circuit fault. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0036] This invention is used to improve the transient synchronization stability of heterogeneous power systems under severe short-circuit faults. Figure 1 This is a schematic diagram of the topology of a heterogeneous power system with interconnected power sources. Figure 2 This diagram illustrates the transient stability control method for heterogeneous power systems proposed in this invention. Under severe symmetrical short-circuit fault conditions, calculating the current command value of the grid-connected converter and the power command value of the grid-connected converter according to the method proposed in this invention can significantly improve the transient stability of the heterogeneous power system.

[0037] The specific implementation steps of this invention are as follows:

[0038] Step 1: When a symmetrical short-circuit fault occurs on a common transmission line, obtain the location of the fault point and the effective value of the fault point voltage, the effective value of the voltage and power angle at the grid-type converter terminal, the effective value of the voltage and power angle at the synchronous generator terminal, and the effective value of the voltage, power angle, and active power output value at the grid-type converter terminal.

[0039] Step 2: Calculate the reactive current command value of the grid-connected converter based on the effective value of the terminal voltage of the grid-connected converter; obtain the active power command value of the grid-connected converter based on the active power output value of the grid-connected converter.

[0040] Step 3: Calculate the active current command value of the grid-connected converter based on the reactive current command value of the grid-connected converter, the effective value of the fault point voltage and the fault point location, the power angle of the grid-connected converter, the effective value of the synchronous generator terminal voltage and the power angle, and the effective value of the grid-connected converter terminal voltage and the power angle.

[0041] Step 4: Use the reactive current command of the grid-connected converter calculated in Step 2 and the active current command of the grid-connected converter calculated in Step 3 as the current control command of the grid-connected converter during the fault period, and use the active power command value of the grid-connected converter obtained in Step 2 as the power control command of the grid-connected converter during the fault period. This can improve the transient stability of the heterogeneous power system under grid fault conditions.

[0042] Furthermore, between step 1 and step 2, the following formula is used to determine whether the grid converter has entered fault ride-through mode:

[0043]

[0044] In the formula, U GFL U represents the effective value of the terminal voltage of the grid-connected converter. th The fault ride-through voltage threshold specified in the power grid guidelines;

[0045] If the network converter enters fault ride-through mode, proceed to step 2; otherwise, repeat step 1.

[0046] In step 2, the reactive current command value of the grid converter is calculated using the following formula:

[0047]

[0048] in, K is the reactive current command value of the grid-type converter; K is the dynamic reactive current proportional coefficient specified in the grid guidelines.

[0049] In step 2, the active power command value of the grid-type converter is calculated using the following formula:

[0050]

[0051] in, and These are the active power command value and active power output value of the grid-type converter, respectively.

[0052] Furthermore, step 3 includes the following steps:

[0053] Step 31: Based on the effective value of the fault point voltage and the location of the fault point, obtain the equivalent resistance and reactance of the grid-connected converter branch, the grid-connected converter branch, the synchronous generator branch, and the common transmission line.

[0054] Step 32: Based on the obtained equivalent resistance and reactance, the effective value of the fault point voltage, the power angle of the grid-connected converter and the reactive current command value, the effective value of the synchronous generator terminal voltage and the power angle, and the effective value of the grid-connected converter terminal voltage and the power angle, calculate the active current command value of the grid-connected converter using the following formula:

[0055]

[0056]

[0057]

[0058] Y GFL Y GFM Y SG and Y P These are the equivalent admittances of the grid-connected converter branch, the network-type converter branch, the synchronous generator branch, and the common transmission line, respectively; U g U GFM and E SG These are the effective values ​​of the voltage at the fault point, the effective voltage at the grid-type converter terminal, and the effective voltage at the synchronous generator terminal, respectively; δ GFL0 δ GFM0 and δ SG0 These are the power angles of the grid-type converter, the network-type converter, and the synchronous generator when a fault occurs.

[0059] Description of the effects of this invention:

[0060] Figure 3 Simulation results are presented for a heterogeneous power system before and after applying the control method proposed in this invention when the fault voltage drops to 0.1 pu. In this embodiment, a three-phase short-circuit fault occurs in the power grid at 3.0 s, and the fault is cleared after 0.3 s. When the heterogeneous power system does not use the control method proposed in this invention, from... Figure 3 As shown by the dotted line, the transient stability of the hybrid power system is poor at this time. Both the grid-type converter and the cross-connected converter exhibit large fluctuations in output frequency and power angle during the fault. The output frequency and power angle of the synchronous generator also show some oscillation.

[0061] When a heterogeneous power system with interconnected power sources adopts the control method proposed in this invention, the active and reactive current command values ​​of the grid-connected converter can be set to 0.1982 pu and -1.0 pu, respectively, and the power command value of the grid-connected converter is directly set based on the actual active output value. Figure 3 As can be seen from the solid line, the output frequency fluctuations of both the grid-type converter and the network-type converter are minimal during the fault period, and the power angles are close to their initial values. The output frequency and power angle swings of the synchronous generator are also improved to a certain extent, and the transient stability of the entire hybrid power system is significantly enhanced.

[0062] Therefore, the transient stability control method for heterogeneous power systems proposed in this invention can significantly enhance the overall transient stability level of the hybrid power system and improve its safe and stable operation capability under symmetrical short-circuit faults in the power grid.

[0063] Finally, it should be noted that the above examples of the present invention are merely illustrative and not intended to limit the implementation of the invention. Although the applicant has described the present invention in detail with reference to preferred embodiments, those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A transient stability control method for heterogeneous power systems with interconnected power sources, characterized in that, Includes the following steps: Step 1: When a symmetrical short-circuit fault occurs on a common transmission line, obtain the location of the fault point and the effective value of the fault point voltage, the effective value of the voltage and power angle at the grid-type converter terminal, the effective value of the voltage and power angle at the synchronous generator terminal, and the effective value of the voltage, power angle, and active power output value at the grid-type converter terminal. Step 2: Calculate the reactive current command value of the grid-connected converter based on the effective value of the terminal voltage of the grid-connected converter; obtain the active power command value of the grid-connected converter based on the active power output value of the grid-connected converter. Step 3: Calculate the active current command value of the grid-connected converter based on the reactive current command value of the grid-connected converter, the effective value of the fault point voltage and the fault point location, the power angle of the grid-connected converter, the effective value of the synchronous generator terminal voltage and the power angle, and the effective value of the grid-connected converter terminal voltage and the power angle. Step 4: Use the reactive current command of the grid-connected converter calculated in Step 2 and the active current command of the grid-connected converter calculated in Step 3 as the current control command of the grid-connected converter during the fault period, and use the active power command value of the grid-connected converter obtained in Step 2 as the power control command of the grid-connected converter during the fault period. This can improve the transient stability of the heterogeneous power system under grid fault. Step 3 includes the following steps: Step 31: Based on the effective value of the fault point voltage and the location of the fault point, obtain the equivalent resistance and reactance of the grid-connected converter branch, the grid-connected converter branch, the synchronous generator branch, and the common transmission line. Step 32: Based on the obtained equivalent resistance and reactance, the effective value of the fault point voltage, the power angle of the grid-connected converter and the reactive current command value, the effective value of the synchronous generator terminal voltage and the power angle, and the effective value of the grid-connected converter terminal voltage and the power angle, calculate the active current command value of the grid-connected converter using the following formula: ； In the formula, This is the active current command value for the grid-type converter; This is the reactive current command value of the grid-type converter; Y p θ P Y m θ m Y g θ g Y1, θ1, Y L θ L These are mathematical calculation quantities, without substantial meaning, and are obtained through the following formulas; Y p ∠θ P =Y P / (Y GFL +Y GFM +Y SG ), Y m ∠θ m = Y GFM / (Y GFL +Y GFM +Y SG ), AND g ∠θ g = And SG / (AND GFL +And GFM +And SG ),Y1∠θ1=1 / (Y GFL +And GFM +And SG ),AND L ∠θ L =1 / Y GFL ; Y GFL Y GFM Y SG and Y P These are the equivalent admittances of the grid-connected converter branch, the network-type converter branch, the synchronous generator branch, and the common transmission line, respectively; U g U GFM and E SG These are the effective values ​​of the voltage at the fault point, the effective voltage at the grid-type converter terminal, and the effective voltage at the synchronous generator terminal, respectively; δ GFL0 δ GFM0 and δ SG0 These are the power angles of the grid-type converter, the network-type converter, and the synchronous generator when a fault occurs.

2. The transient stability control method for a heterogeneous power system according to claim 1, characterized in that, After step 1, the following formula is used to determine whether the grid converter has entered fault ride-through mode: In the formula, This refers to the effective value of the terminal voltage of the grid-type converter; The fault ride-through voltage threshold specified in the power grid guidelines; If the network converter enters fault ride-through mode, proceed to step 2; otherwise, repeat step 1.

3. A transient stability control method for a heterogeneous power system according to claim 1 or 2, characterized in that, In step 2, the reactive current command value of the grid converter is calculated using the following formula: ； in, Here, K represents the reactive current command value for the grid-type converter; K is the dynamic reactive current proportional coefficient specified in the grid guidelines. This refers to the effective value of the terminal voltage of the grid-type converter.

4. A transient stability control method for a heterogeneous power system with hybrid power supply according to claim 1 or 2, characterized in that, In step 2, the active power command value of the grid-type converter is calculated using the following formula: ； in, and These are the active power command value and active power output value of the grid-type converter, respectively.

Images