A method, device and medium for quantitatively calculating a first swing stability margin of a power droop type network configuration converter

Abstract

The application discloses a power droop type network construction converter first swing stability margin quantitative calculation method and equipment and medium, wherein the method comprises the following steps: judging whether the system has a stable equilibrium point based on the active ring model of the power droop type network construction converter; if yes, further calculating the power angle of the stable equilibrium point and the unstable equilibrium point, so as to obtain the system stability domain; taking the fault clearing angle as the representation of the current state of the system, and quantifying the first swing stability margin of the power droop type network construction converter through the distance between the current state of the system and the boundary of the corresponding system stability domain. The application realizes the quantitative evaluation of the synchronous stability of the network construction converter system adopting the droop control, overcomes the limitation that the traditional qualitative analysis cannot accurately measure the stability degree, is efficient in calculation, has clear physical meaning, does not need complex numerical integration, and is convenient for engineering application.

Description

Technical Field

[0001] This invention belongs to the field of power system stability analysis and control technology, and particularly relates to a quantitative calculation method, equipment and medium for the first swing stability margin of a power droop type grid converter. Background Technology

[0002] With the increasing global demand for clean energy, the proportion of renewable energy in the power system is rapidly rising. Simultaneously, power electronic equipment (such as converters and flexible DC transmission equipment) is widely used in the power system, leading to the gradual development of modern power systems towards a "high-proportion, high-renewable-energy" model. While this new type of power system brings many advantages, it also presents unprecedented challenges to the stability of the power system. Renewable energy grid connection is achieved through converters, so in addition to traditional synchronous generators, the impact of grid-connected converters in a "high-proportion, high-energy" power system cannot be ignored.

[0003] Droop control is one of the widely adopted control strategies in grid-connected converters for new energy sources. In a single-machine infinite bus system, the power angle motion under droop control can be characterized by a first-order nonlinear ordinary differential equation, which can guarantee that the system maintains synchronous operation. However, after a fault, the system may not stabilize to the initial operating point and may stabilize to a stable equilibrium point in another cycle. When the system stabilizes to another equilibrium point, various electrical quantities will experience large fluctuations during the transient process, which may cause safety problems such as overvoltage and overcurrent in electrical equipment. Therefore, quantifiable indicators are needed to determine the stability of the initial droop control. Summary of the Invention

[0004] Objective of this invention: The objective of this invention is to provide a quantitative calculation method for the first-swing stability margin of a droop-type grid converter. The resulting quantitative calculation results can provide guidance for improving the synchronous stability of future droop-type grid converter systems. Another objective of this invention is to provide an electronic device and a computer-readable storage medium for implementing the above method.

[0005] Technical solution: The quantitative calculation method for the first swing stability margin of the power droop grid converter includes:

[0006] Based on the active power loop model of the power droop grid converter, determine whether the system has a stable equilibrium point; if it does, calculate the power angles of the stable and unstable equilibrium points; otherwise, determine that the system has no stable equilibrium point and end the calculation.

[0007] The system stability region is obtained from the work angles of adjacent unstable equilibrium points;

[0008] The fault clearing angle characterizes the current state of the system, and the first swing stability margin of the power droop grid converter is quantified by the distance between the current state of the system and the boundary of the corresponding system stability domain.

[0009] Optionally, the active power loop model of the power droop grid converter is shown in the following formula:

[0010]

[0011] In the formula, This is the active power droop coefficient; This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. The line reactance from the converter port to the grid connection point is ignored when resistance is disregarded; This is the command value for the active power output of the converter; The virtual power angle of the converter is the virtual angular frequency generated by the active power loop of the grid-type converter. and the rated angular frequency of the power grid difference; For time.

[0012] Optionally, the determination of whether the system has a stable equilibrium point is based on the command value of the converter's output active power. :

[0013] like At this point, the work angle is stable, and a stable equilibrium point exists;

[0014] like At this point, the system is critically stable, and the stable equilibrium point coincides with the unstable equilibrium point.

[0015] like At this point, the work angle becomes unstable, and there is no stable equilibrium point.

[0016] Therefore, if P ref ≤P max If the equilibrium point is such that a stable equilibrium exists, then a stable equilibrium point exists; otherwise, it does not exist. .

[0017] Optionally, the work angles of the stable equilibrium point and the unstable equilibrium point are defined as follows:

[0018]

[0019]

[0020] In the formula, For the first The work angle at the stable equilibrium point of the cycle; For the first The work angle at the unstable equilibrium point of the period; This is the command value for the active power output of the converter; This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. The line reactance from the converter port to the grid connection point is negligible when resistance is ignored.

[0021] Optionally, the power droop grid converter employs first-order nonlinear droop control, and the system stability region is when the power angle is at... The interval is defined as follows: at this point, the system converges to the corresponding stable equilibrium point; where, For the first The work angle at the unstable equilibrium point of the period.

[0022] Optionally, the quantification formula for the first swing stability margin of the droop-type grid converter is as follows:

[0023]

[0024] In the formula, The primary indicator is the stability margin. For the system stability region, For the first The work angle at the unstable equilibrium point of the period; For the first The work angle at the stable equilibrium point of the cycle; This is the current fault clearing angle for the system.

[0025] Optionally, the method further includes: based on the initial swing stability margin Determine the system stability of the power droop grid converter; when At that time, the system stabilized at ;when The closer it is to 1, the higher the current fault clearing angle. The closer The better the stability; when This indicates stability at other stable points; wherein, the... For the first The work angle at the stable equilibrium point of the cycle.

[0026] The electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements some or all of the steps in the above-described quantitative calculation method for the first swing stability margin of the power droop grid converter.

[0027] The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, implements some or all of the steps in the above-described quantitative calculation method for the first swing stability margin of a power droop grid converter.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0029] 1. This invention achieves a quantitative assessment of the synchronous stability of a droop-controlled grid converter system. Addressing the lack of effective quantitative indicators in existing technologies to determine whether a droop-controlled converter can stabilize back to its initial operating point after a fault, this invention utilizes differential equations to obtain analytical solutions to the droop control equations (i.e., analytical solutions for the power angles at stable and unstable equilibrium points), and further constructs an initial swing stability margin index (…). This indicator translates system stability into specific numerical values, overcoming the limitation of traditional qualitative analysis in accurately measuring the degree of stability.

[0030] 2. This invention directly determines the stable and unstable equilibrium points of the system through the analytical solution of the differential equation, and constructs a normalized stability margin index based on this. It involves low computational cost, high computation speed, and clear physical meaning, directly using the change in work angle to characterize energy change, avoiding complex energy integration processes. It is very suitable for real-time or near-real-time stability criterion applications and is convenient for engineering applications.

[0031] 3. This invention can extend the identification of synchronous stability risks in multi-equilibrium-point systems. In high-voltage and high-efficiency power systems, droop-controlled converters may stabilize to a periodic stable point other than the initial point after a fault. In addition to the initial swing, the index proposed in this invention can accurately define the stability domain boundary (composed of adjacent unstable equilibrium points) of any periodic stable equilibrium point and calculate and quantify the stability margin relative to any periodic stable equilibrium point. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the workflow of the present invention;

[0033] Figure 2 When the first swing is stable Trajectory diagram;

[0034] Figure 3 To stabilize to other periodic stability points Trajectory diagram;

[0035] Figure 4 For theoretical ideals Line graph;

[0036] Figure 5 A schematic diagram of a single-unit infinite bus system for a grid converter using droop control.

[0037] Figure 6 for time Trajectory diagram;

[0038] Figure 7 for time Trajectory diagram;

[0039] Figure 8 for time Trajectory diagram;

[0040] Figure 9 For simulation results Line graph;

[0041] Figure 10 for time Trajectory diagram;

[0042] Figure 11 for time Trajectory diagram;

[0043] Figure 12 for time Trajectory diagram. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0045] like Figure 1 As shown, the derivation process of the quantitative formula for the first swing stability margin of the power droop type grid converter described in this invention is as follows:

[0046] Step 1: Establish the active power loop model of the power droop grid converter.

[0047] For grid-type converters that employ droop control, the active power-frequency linear droop relationship of traditional synchronous generators can be simulated using an active power loop model.

[0048] First, the control equation shown in equation (1) is constructed, which reflects the power angle motion characteristics of the synchronous machine, enabling the converter to actively respond to external disturbances.

[0049]

[0050] In the formula, This is the active power droop coefficient; and These are the actual and commanded values ​​of the converter's output angular frequency, respectively. To synchronize speed; and These are the actual and commanded values ​​of the active power output by the converter, respectively. The virtual power angle of the converter is the virtual angular frequency generated by the active power loop of the grid-type converter. and the rated angular frequency of the power grid difference; For time.

[0051] For equation (1), let the instruction value equal to synchronous speed When that happens, the transformation can be further combined as shown in equation (2).

[0052]

[0053] Converter output active power can be derived from formula express.

[0054]

[0055] In the formula, This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. This is the line reactance from the converter port to the grid connection point (ignoring resistance).

[0056] Combining equations (2) and (3), we can obtain the active power loop model of the power droop grid converter:

[0057]

[0058] By separating the variables of the active power loop model represented by equation (4), we can obtain:

[0059]

[0060] make Then we have the identity and .

[0061] Substituting the above identity into equation (5) yields:

[0062]

[0063] Summarized as follows:

[0064]

[0065] Completing the square by subtracting the fraction from the denominator yields:

[0066]

[0067] Integrating, we can obtain the expression for the work angle with respect to time:

[0068]

[0069] According to equation (9), the exponent term can be seen. It plays a dominant role in the change of the system's power angle:

[0070] (1) If Exponential decay occurs when the power angle is stable, resulting in a stable equilibrium point (SEP) and an unstable equilibrium point (UEP).

[0071] (2) If The exponential rate does not decay, indicating critical stability, where SEP and UEP coincide.

[0072] (3) If When the exponent becomes an imaginary number, the power angle becomes unstable, and SEP and UEP no longer exist.

[0073] Therefore, P ref ≤P max SEP and UEP only exist at that time.

[0074] Setting equation (4) to 0 to solve for the work angles of the stable and unstable equilibrium points, we can obtain the following equation: As shown.

[0075]

[0076] Simplifying equation (10) yields the following equation: .

[0077]

[0078] The analytical solutions for the power angles of SEP and UEP can be obtained using the inverse trigonometric function calculation formula, as shown in equations (12) and (13) below, respectively.

[0079]

[0080]

[0081] In the formula, For the first The power angle of the periodic SEP; For the first The power angle of the periodic UEP.

[0082] Based on the control equations and their SEP and UEP of the droop control active loop, a first-swing stability margin index is constructed to achieve a quantitative assessment of the system's transient synchronization stability. ).

[0083] First, the active power loop model of the power droop grid converter is integrated: integrating both sides of the equation with respect to time, we can obtain the expression for the energy accumulated by the power imbalance during the transient process.

[0084]

[0085] , For the start and end times; , The work angles are the starting and ending times.

[0086] Further integral transformation of the work angle variable yields the functional relationship between the unbalanced energy and the work angle variation:

[0087]

[0088] As the above derivation shows, the unbalanced energy of the system during the disturbance process has a monotonic correspondence with the change in the power angle, meaning that the power angle shift can directly characterize the energy change of the system. Therefore, the acceleration and deceleration energy characteristics of the system during the fault process can be characterized by the change in the power angle.

[0089] Furthermore, analogous to the extended equal-area method in the transient stability analysis of traditional synchronous generators, this invention transforms the energy change of the system during disturbance into the concept of "area" in the power angle space, thereby achieving a quantitative description of stability. However, unlike traditional methods that rely on the area of ​​the power-power angle curve for calculation, this invention directly utilizes the power angle variable to construct a stability margin index based on droop control characteristics, thus avoiding complex energy integration processes and improving computational efficiency.

[0090] For a first-order nonlinear droop control system, the... SEP cycle The stability region is determined by its neighboring UEPs. and The defined condition is that the system is only valid if the work angle is within the interval. Within a certain timeframe, the signal will converge to the corresponding SEP.

[0091] Based on the aforementioned stability region characteristics, the margin index is quantified using the distance from the current system state to the stability region boundary. Therefore, the current system state (with the fault clearing angle as the reference point) is used as the metric. The normalized distance between the first pendulum and the corresponding stability region boundary is defined as the stability margin index η. droop The expression is:

[0092]

[0093] The current fault clearing angle of the system is obtained through measurement or simulation. Substituting it into equation (16) yields the corresponding result. Then it can be passed through The value is used to determine the stability of the system. For example... Figure 4 As shown, this is the theoretical ideal. A line graph. When At that time, the system can stabilize at ;when The closer it is to 1, the higher the current fault clearing angle. The closer The better the stability; when This indicates that stability exists at other stable points.

[0094] like Figure 2 As shown, this is the state when the initial swing is stable. Trajectory diagram, corresponding The situation is as follows. In the diagram, the solid line represents the normal state. The trajectory, with the dashed line representing the fault. Trajectory, represented by a horizontal straight line Point a is SEP, and point f is UEP. The initial running point a is... At point b, after a voltage drop fault occurs, the voltage drops to point b because at this time... Therefore, it will follow the fault. The trajectory moves to the right, and the fault is cleared at point c, restoring to point d. At this point, it has not yet crossed the unstable equilibrium point f, and there will be... Therefore, it will follow the normal The trajectory returns to point a to the left.

[0095] Figure 3 To stabilize to other periodic stability points Trajectory diagram, corresponding The situation is as follows. In the diagram, the solid line represents the normal state. The trajectory, with the dashed line representing the fault. Trajectory, represented by a horizontal straight line Points a and e are SEPs, and points f and g are UEPs. The initial running point a is... At point b, after a voltage drop fault occurs, the voltage drops to point b because at this time... Therefore, it will follow the fault. The trajectory moves to the right, and the fault is cleared at point c, restoring to point d. At this point, it has already passed the unstable equilibrium point f, and there will be... Therefore, it will follow the normal The trajectory continues to move to the right to the stable equilibrium point e of the next cycle, that is: .

[0096] Example 1

[0097] To address the shortcomings of existing research, based on the above derivation process of this invention, this invention provides a quantitative calculation method for the first-swing stability margin of a power droop grid converter, comprising the following steps:

[0098] (1) Based on the active loop model of the power droop type grid converter, determine whether the system has a SEP; if it does, calculate the power angle of the SEP and UEP; otherwise, determine that the system has no stable equilibrium point, and therefore there is no subsequent quantitative calculation of the first swing stability margin.

[0099] (2) Obtain the system stability region based on the power angles of adjacent UEPs;

[0100] (3) The fault clearing angle characterizes the current state of the system, and the first swing stability margin of the power droop grid converter is quantified by the distance between the current state of the system and the boundary of the corresponding system stability domain.

[0101] In step (1), the active power loop model of the power droop grid converter is shown in the above formula (4).

[0102] The determination of whether a SEP exists in the system is based on the command value of the converter's output active power. conduct:

[0103] like At this point, the work angle is stable, and a stable equilibrium point exists;

[0104] like At this point, the system is critically stable, and the stable equilibrium point coincides with the unstable equilibrium point.

[0105] like At this point, the work angle becomes unstable, and there is no stable equilibrium point.

[0106] in, ; This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. The line reactance from the converter port to the grid connection point is negligible when resistance is ignored.

[0107] In step (2), the work angles of the stable equilibrium point and the unstable equilibrium point are defined as follows:

[0108]

[0109]

[0110] In the formula, For the first The work angle at the stable equilibrium point of the cycle; For the first The work angle at the unstable equilibrium point of the period; This is the command value for the active power output of the converter; This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. The line reactance from the converter port to the grid connection point is negligible when resistance is ignored.

[0111] Furthermore, the system stability region is when the power angle is at... The system converges to the corresponding stable equilibrium point within the interval.

[0112] In step (3), the quantitative formula for the first swing stability margin of the droop-type grid converter is as follows:

[0113]

[0114] In the formula, The primary indicator is the stability margin. For the system stability region, For the first The work angle at the unstable equilibrium point of the period; For the first The work angle at the stable equilibrium point of the cycle; This is the current fault clearing angle for the system.

[0115] This embodiment builds a single-unit infinite bus system of a droop-controlled grid converter in the PSCAD / EMTDC simulation platform, such as... Figure 5 As shown, the method is verified through simulation. Key system parameters include: grid-side converter port voltage. The grid side is simulated using an infinite power grid, and its voltage... Line reactance between the converter and the infinite power grid The grid-side converter employs droop control, and its active power droop coefficient... .

[0116] First of all, This is to verify the theoretical view that a stable equilibrium point can only be reached at a certain time:

[0117] It can be calculated from the known parameters. , corresponding to , , Three operating conditions are set separately. =2 pu, 2.625 pu, 3.25 pu. During a fault, the grid-side voltage drops to 0.1 pu for 0.05 seconds and then recovers. Simulation results show... The trajectory is attached. Figure 6 , Figure 7 , Figure 8 As shown. Figure 6 middle Only when SEP and UEP do not overlap can a situation occur where the system returns to the initial running point. Figure 7 middle If SEP and UEP overlap, a fault will cause the system to skip UEP and stabilize at the next cycle's stable point. Figure 8 middle Without SEP, it would definitely not be stable, consistent with the theoretical result. SEP is only available for components with a power consumption of 2.625 pu or less.

[0118] Assuming the converter output power is 0.8 pu, and the grid-side voltage drops to 0.1 pu during a fault, the typical equilibrium point parameters are calculated theoretically in this embodiment as follows: =-3.4812 rad; =0.3096 rad; =2.8303rad, then the system stability domain is determined by the adjacent UEP. and constitute.

[0119] Obtain the corresponding fault clearing angle ,draw Curves Figure 9 As shown. Compared to the theoretical... Curves Figure 4 The patterns shown are basically the same: an initial rise followed by a fall. reach The maximum value is 1. and place as =0, which is the boundary for the stability of the first pendulum.

[0120] Select one =0.936、 =0.012 and = -0.13 as three typical scenarios, each scenario The trajectories are as follows Figure 10 , Figure 11 and Figure 12 As shown. Figure 10 for =0.936, which is closer to the case. It can return to the initial running point; Figure 11 for =0.012, distance It's quite far, but we haven't crossed it. It can still return to the initial running point; Figure 12 for = -0.13, has already exceeded the threshold. It will stabilize until the next SEP cycle. Therefore, it can be seen that the corresponding value obtained through simulation... Trajectory and The results of the analysis correspond to, when At that time, the system can stabilize at ;when The closer it is to 1, the higher the current fault clearing angle. The closer The better the stability; when This indicates that stability exists at other stable points. This means that the quantitative calculation method for the first-swing stability margin of a power droop-type grid converter proposed in this invention can effectively and accurately quantify the first-swing stability margin of a grid converter system using droop control.

[0121] To implement the above method, the present invention also provides a device and a computer storage medium.

[0122] The electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements some or all of the steps in the above-described quantitative calculation method for the first swing stability margin of the power droop grid converter.

[0123] The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, implements some or all of the steps in the above-described quantitative calculation method for the first swing stability margin of a power droop grid converter.

Claims

1. A quantitative calculation method for the first-swing stability margin of a power droop-type grid converter, characterized in that, The method includes: Based on the active power loop model of the power droop grid converter, determine whether the system has a stable equilibrium point; if it does, calculate the power angles of the stable and unstable equilibrium points; otherwise, determine that the system has no stable equilibrium point and end the calculation. The system stability region is obtained from the work angles of adjacent unstable equilibrium points; The fault clearing angle characterizes the current state of the system, and the first swing stability margin of the power droop grid converter is quantified by the distance between the current state of the system and the boundary of the corresponding system stability domain.

2. The quantitative calculation method for the first swing stability margin of a power droop grid converter according to claim 1, characterized in that, The active power loop model of the power droop grid converter is shown in the following formula: In the formula, This is the active power droop coefficient; This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. The line reactance from the converter port to the grid connection point is ignored when resistance is disregarded; This is the command value for the active power output of the converter; The virtual power angle of the converter is the virtual angular frequency generated by the active power loop of the grid-type converter. and the rated angular frequency of the power grid difference; For time.

3. The quantitative calculation method for the first swing stability margin of a power droop-type grid converter according to claim 1, characterized in that, judge Is it less than or equal to? If so, then a stable equilibrium point exists; otherwise, a stable equilibrium point does not exist. .

4. The quantitative calculation method for the first swing stability margin of a power droop grid converter according to claim 1, characterized in that, The work angles of the stable equilibrium point and the unstable equilibrium point are defined as follows: In the formula, For the first The work angle at the stable equilibrium point of the cycle; For the first The work angle at the unstable equilibrium point of the period; This is the command value for the active power output of the converter; This refers to the voltage at the converter output port. This refers to the voltage at the grid connection point. The line reactance from the converter port to the grid connection point is negligible when resistance is ignored.

5. The quantitative calculation method for the first swing stability margin of a power droop-type grid converter according to claim 1, characterized in that, The power droop-type grid converter adopts first-order nonlinear droop control, and the system stability region is when the power angle is at... The interval is defined as follows: at this point, the system converges to the corresponding stable equilibrium point; where, For the first The work angle at the unstable equilibrium point of the period.

6. The quantitative calculation method for the first swing stability margin of a power droop grid converter according to claim 1, characterized in that, The quantitative formula for the first swing stability margin of the droop-type grid converter is as follows: In the formula, The primary indicator is the stability margin. For the system stability region, For the first The work angle at the unstable equilibrium point of the period; For the first The work angle at the stable equilibrium point of the cycle; This is the current fault clearing angle for the system.

7. The quantitative calculation method for the first swing stability margin of a power droop grid converter according to claim 1, characterized in that, The method further includes: based on the initial swing stability margin Determine the system stability of the power droop grid converter; when At that time, the system stabilized at ;when The closer it is to 1, the higher the current fault clearing angle. The closer The better the stability; when This indicates stability at other stable points; wherein, the... For the first The work angle at the stable equilibrium point of the cycle.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the quantitative calculation method for the first swing stability margin of the power droop grid converter as described in any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the quantitative calculation method for the first swing stability margin of the power droop grid converter as described in any one of claims 1 to 7.

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