Cooperative control method and device for transient voltage instability of new energy cluster grid-connected system

Abstract

The invention discloses a cooperative control method and device for transient voltage instability of a new energy cluster grid-connected system, and relates to the technical field of new energy steady-state control. The method comprises the following steps: firstly, constructing a hybrid system mathematical model considering new energy control sequential switching, analyzing a generation mechanism of a voltage oscillation instability form caused by repeated low-voltage penetration of a new energy system based on a phase diagram manifold theory, and further analyzing a transient response whole process of the new energy system when repeated low-voltage penetration occurs based on a differential-algebraic equation system model; and researching the running track characteristics of the system, and proposing a transient voltage instability discrimination index. And then main influence factors of voltage oscillation degree are analyzed, a new energy unit active power regulation and control proportion quantification method is studied based on a transient voltage instability criterion, and finally an optimization control strategy is obtained.

Description

TECHNICAL FIELD

[0001] The application discloses a coordinated control method and device for transient voltage instability of a new energy cluster grid-connected system, and relates to the technical field of new energy steady-state control. BACKGROUND

[0002] With the continuous growth of new energy penetration, modern power systems are facing increasingly severe voltage stability problems. In particular, in a system with a large-scale new energy cluster, renewable energy is transmitted over long distances to the load center, and a considerable portion of synchronous generators in the system is replaced by new energy, resulting in weakened grid strength and vulnerability to renewable energy uncertainty fluctuations. In a system with a high proportion of new energy cluster access, new types of transient voltage instability phenomena are triggered by the nonlinear switching characteristics of new energy. In particular, in recent years, due to repeated entry and exit of new energy units into LVRT control, voltage and power oscillations occur in the system. This transient voltage instability mode embodies the unique mixed dynamic characteristics of new energy, which couples the continuous differential state quantity response mechanism and the discrete control switching mechanism, so it is difficult to accurately distinguish by traditional voltage stability indicators.

[0003] Some existing research analyzes the voltage oscillation mechanism caused by repeated entry of new energy into LVRT. Based on steady-state flow, the causes of voltage oscillation are explained, and based on control theory, the problem of repeated low penetration of new energy is explained, but the above analysis does not take into account the differential dynamic process when the new energy control mode switches; a new energy dynamic switching model is established by considering the differential algebraic equation, the voltage oscillation mechanism induced by repeated low penetration is explained, and a criterion is constructed based on Lyapunov function; from the perspective of voltage bifurcation theory, in traditional static voltage stability analysis, as a certain parameter in the system monotonically increases, the voltage will undergo saddle-node bifurcation (SNB) or singular-induced bifurcation (SIB), and the system voltage will present a monotonically unstable form. However, considering the nonlinear switching characteristics of new energy, in the process of repeated low penetration, the system operating trajectory repeatedly crosses the switching boundary, and the system voltage presents an oscillatory instability form. This type of voltage oscillation phenomenon is defined for the first time as high-output-induced non-smooth bifurcation (HLINB) under low voltage penetration, and based on the second-order cone algorithm, a calculation method for the maximum output power of a wind farm considering the HLINB constraint is proposed. In summary, existing research mainly studies the voltage oscillation mechanism and its discrimination method of a new energy single-machine grid-connected system based on static voltage stability constraints, but still lacks analysis of the mechanism of the emergence of system voltage instability form and the dynamic response characteristics of new energy in the transient process under the scenario of new energy cluster grid connection, so it is impossible to accurately distinguish the transient voltage instability state in the actual system. SUMMARY

[0004] The application aims at the problems of the prior art, and provides a coordinated control method and device for transient voltage instability of a new energy cluster grid-connected system, and the adopted technical scheme is as follows: In a first aspect, a coordinated control method for transient voltage instability of a new energy cluster grid-connected system comprises the following steps: S1, a hybrid model is built according to the characteristics of the new energy grid-connected system, a control mode switching function is set, a dynamic response is built by combining state evolution and control switching, a differential-algebraic equation system model of the dynamic characteristics of the new energy is established by coupling a state space equation and a network algebraic constraint; S2, when the new energy grid-connected system is in a steady state operation, a unique steady state equilibrium solution is obtained according to the differential-algebraic equation system model; S3, a new energy single-machine system is established according to the differential-algebraic equation system model, a transient operation condition simulation is performed by inputting fault information in a time domain, and a transient variation trajectory is obtained by a solver; S4, a geometric distance between a running point of the transient variation trajectory and a steady state equilibrium point is taken as a transient voltage instability criterion to determine whether the new energy grid-connected system is in a transient voltage instability state; S5, a ratio of a voltage variation of each unit in a new energy station to a PCC voltage variation is taken as a transient voltage participation factor of a node where the unit is located, and a machine tripping ratio in the new energy grid-connected system is determined according to the transient voltage participation factor.

[0005] In some implementations, the S1 comprises the following steps: S11, a hybrid model of the new energy grid-connected system is established, and a switching function of a corresponding new energy control mode is set according to a state variable; S12, a dynamic response is established by the hybrid model of the new energy grid-connected system according to a continuous state evolution mechanism and a discrete control switching behavior; S13, a differential-algebraic equation system model of the dynamic characteristics of the new energy is established by coupling a state space equation and a system network algebraic constraint according to the hybrid model of the new energy grid-connected system.

[0006] In some implementations, in the S4, the geometric distance between the running point of the transient variation trajectory and the steady state equilibrium point is taken as the transient voltage instability criterion, and specifically comprises the following steps: Voltage and power measurement data at the PCC are obtained, and a geometric distance between a running point (Pc, Qc, Uc) at the PCC and a steady state equilibrium point is defined as a bifurcation criterion, as shown in the following formula: (11) Wherein, the steady state equilibrium point is calculated according to the following formula: (12) The effective value of the grid-connected point voltage is obtained as: (13) In some implementations, in S5, the trip-out ratio in the new energy grid-connected system is determined according to the transient voltage participation factor, and the transient voltage of the PCC node and the unit under fault is expressed as the following formula: i (17) (18) The transient voltage participation factor is expressed as the following formula: (19) In a second aspect, an embodiment of the present application provides a coordinated control device for transient voltage instability of a new energy cluster grid-connected system, comprising: A model processing module is configured to build a hybrid model according to the characteristics of the new energy grid-connected system, set a control mode switching function, combine state evolution and control switching to build a dynamic response, and build a differential-algebraic equation system model of the dynamic characteristics of the new energy by coupling the state space equation and the network algebraic constraint. A balanced analysis module is configured to obtain a unique steady-state balance solution according to the differential-algebraic equation system model when the new energy grid-connected system is in steady-state operation. A trajectory analysis module is configured to build a new energy single-machine system according to the differential-algebraic equation system model, input fault information in the time domain for transient operation condition simulation, and obtain a transient change trajectory through a solver. A steady-state analysis module is configured to use the geometric distance between the operating point and the steady-state balance point of the transient change trajectory as a transient voltage instability criterion to determine whether the new energy grid-connected system is in a transient voltage instability state. A trip-out analysis module is configured to set the ratio of the voltage change of each unit in the new energy station to the voltage change of the PCC as the transient voltage participation factor of the node where the unit is located, and determine the trip-out ratio in the new energy grid-connected system according to the transient voltage participation factor.

[0007] In some implementations, the model processing module comprises: A control unit is configured to build a hybrid model of the new energy grid-connected system, and set a switching function of the corresponding new energy control mode according to the state variable. A response unit is configured to build a dynamic response through the hybrid model of the new energy grid-connected system according to the continuous state evolution mechanism and the discrete control switching behavior. A building unit is configured to build a differential-algebraic equation system model of the dynamic characteristics of the new energy by coupling the state space equation and the system network algebraic constraint according to the hybrid model of the new energy grid-connected system. ​

[0008] In some implementations, in the steady-state analysis module, the geometric distance between the operating point of the transient change trajectory and the steady-state equilibrium point is taken as a transient voltage instability criterion, specifically comprising: The voltage and power measurement data at the PCC are obtained, and the geometric distance between the operating point (Pc, Qc, Uc) at the PCC and the steady-state equilibrium point is defined as a bifurcation criterion, as shown in the following formula: (11) The steady-state equilibrium point is calculated according to the following formula: (12) The effective value of the grid-connected point voltage is solved as: (13) In some implementations, in the generator tripping analysis module, the generator tripping proportion in the new energy grid-connected system is determined according to the transient voltage participation factor, and the transient voltage of the PCC node and the generator under fault is expressed as: i (17) (18) The transient voltage participation factor is expressed as: (19) In a third aspect, an embodiment of the present application provides an electronic device, including a memory and a processor, the memory is used to store one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the method of the first aspect. In a fourth aspect, an embodiment of the present application provides a computer storage medium, the computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the method of the first aspect.

[0009] One or more embodiments of the present application can bring at least the following beneficial effects: The present application provides a coordinated control method for transient voltage instability of a new energy cluster grid-connected system. First, a hybrid system mathematical model considering sequential switching of new energy control is constructed. Based on the phase portrait manifold theory, the generation mechanism of voltage oscillation instability caused by repeated low penetration of the new energy system is analyzed. Further based on the differential-algebraic equation system model, the whole process of transient response of the new energy system when repeated low penetration occurs is analyzed, the characteristics of the system operating trajectory are studied, and a discrimination index of transient voltage instability is proposed. Then, the main influencing factors of voltage oscillation degree are analyzed, and based on the transient voltage instability criterion, the quantitative method of active regulation proportion of new energy generators is studied, and finally the optimal control strategy is obtained. BRIEF DESCRIPTION OF DRAWINGS​

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor based on these drawings also belong to the protection scope of the present application.

[0011] Figure 1 It is an equivalent topology structure and control model of a converter single-machine grid-connected system provided by the embodiment of the present application. Figure 2 It is a transient state U w , I p , I q Variation trajectory diagram. Figure 3 It is a system operation trajectory repeatedly crossing the switching surface diagram provided by the embodiment of the present application. Figure 4 It is a PCC voltage operation trajectory diagram in the phase space provided by the embodiment of the present application. Figure 5 It is a new energy station topology structure and transformer, collector line impedance diagram provided by the embodiment of the present application. Figure 6 It is a parameter group diagram before and after optimization provided by the embodiment of the present application. Figure 7 It is a transient state output change diagram before and after parameter adjustment provided by the embodiment of the present application. Figure 8 It is a transient output change diagram before and after adopting the control strategy provided by the embodiment of the present application. DETAILED DESCRIPTION

[0012] The technical solutions in the embodiments of the present application will be described clearly and completely below with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor also belong to the protection scope of the present application.

[0013] Embodiment one: This embodiment provides a collaborative control method for transient voltage instability in a new energy cluster grid-connected system, including: S1. Based on the characteristics of the new energy grid-connected system, a hybrid model is built and a control mode switching function is set. Dynamic response is built by combining state evolution and control switching. By coupling the state space equation and network algebra constraints, a differential-algebraic equation system model of the dynamic characteristics of new energy is established. S2, when the new energy grid-connected system is in steady state, obtain a unique steady-state equilibrium solution based on the differential-algebraic equation system model; S3. Based on the differential-algebraic equation system model, establish a new energy single-machine system, input fault information in the time domain to simulate transient operating conditions, and obtain the transient change trajectory through the solver. S4. Based on the geometric distance between the operating point and the steady-state equilibrium point of the transient change track as the transient voltage instability criterion, determine whether the new energy grid-connected system is in a transient voltage instability state. S5, set the ratio of the voltage change at the terminal of each unit in the new energy power station to the voltage change of the PCC as the transient voltage participation factor of the node where the unit is located; determine the tripping ratio in the new energy grid-connected system based on the transient voltage participation factor.

[0014] The control strategy for new energy sources switches according to changes in operating conditions, and its state-space equations also exhibit nonlinear switching characteristics, thus forming a typical hybrid power system. The equivalent topology and control model of a single-unit grid-connected converter system are as follows: Figure 1 As shown.

[0015] in, I p ,, I q These are the active current and reactive current output by the generator set, respectively. U w Terminal voltage, P w , Q w These represent the output active power and reactive power, respectively. P ref , Q ref These are the reference active power and reactive power, respectively, and the total impedance of the transmission line is... R w + j X w It includes the equivalent reactance of the connecting transformer. X T , U cbus voltage at PCC. In addition, voltage vector control technique is generally adopted in new energy converters, i.e. the synchronous rotating coordinate system d The axis of the rotor is in the same direction as the grid voltage vector, i.e. there is U d = U w , U q = 0, and the expression of the output power of new energy under electromechanical transient state is further obtained as (1) According to the control block diagram shown in Figure 1 K pp , K ip , K pq and K iq represent the PI control parameters of the outer loop of active power and reactive power respectively under normal operating state, at this time, the outer loop control adopts constant active / reactive power regulation mode, wherein Q ref is usually set to zero. During LVRT (low voltage ride through), the new energy system switches to the reactive current priority strategy, and the reactive power support capability is enhanced through the controlled I q , at this time K pp_lv and K pq_lv represent the active and reactive current control parameters respectively, T v , and K re defines the slope of the linear ramp curve of active current during the recovery operation. Since this paper mainly analyzes the problem of repeated entry of the unit into low penetration after fault clearance, the dynamic response of the system in the sequential switching process of normal state-LVRT state-recovery state is focused on. For new energy units, the current dynamics can be described by the following differential state equation: (2) The switching of the above control mode reflects the nonlinear dynamic characteristics of the new energy system, wherein the mode selection of the system depends on the discrete switching function: (3) wherein i represents the control mode, 1 for normal operation, 2 for LVRT, and 3 for recovery operation, U LVRT is the low voltage ride through threshold, which is taken as 0.9 p.u. here, T ​v is the LVRT detection delay time. Let the state equation in equation (2) be 0: (4) The steady-state solution of the corresponding system state equation under different control modes can be obtained. Further, according to the power flow equation, the power-voltage constraint relationship between the new energy terminal and the PCC can be established: (5) Eliminate the phase angle to obtain the following equation: (6) wherein R is the line impedance ratio, i.e. R=R w / X w In the new energy grid-connected system, the order of magnitude of the line reactance and the resistance will usually differ by ten times, and usually the resistance can be ignored for simplicity, i.e. assuming R w = 0, but when the transmission line is long, the resistance cannot be ignored. In each state, the analytical solution of I p and I q is substituted into equation (5) to obtain the steady-state voltage solution of the new energy system.

[0016] In an actual new energy station, multiple generator sets are generally connected to the point of common coupling (PCC) through radial collection lines. Each new energy unit is connected to the main grid through a step-up transformer, the PCC voltage is U c , the grid-side bus voltage is U g , and the equivalent reactance between them is X c The relationship between the PCC voltage and the power output of the new energy station can be represented as: (7) wherein, P c and Q c According to equation (1), n denotes the total number of new energy units: (8) Therefore, x denotes the state variable of the renewable energy system, y represents an algebraic variable, including network parameters such as bus voltage amplitude. By coupling the state space equation with the algebraic constraints of the system network, a differential-algebraic equation system model considering the dynamic characteristics of new energy can be established, and the construction method is as follows: (9) Where F represents the set of differential equations describing the dynamic evolution of state variables, and G represents the algebraic equations reflecting the power flow constraints of the power grid. As shown in equation (3), the variable σ corresponds to the switching function of the new energy control mode. Equation (7) reflects the hybrid dynamic characteristics of the new energy system, which simultaneously includes a continuous state evolution mechanism and discrete control switching behavior in the dynamic response process. Therefore, the DAE system model proposed in this embodiment can accurately characterize the dynamic response characteristics of the system under sequential control switching behavior, laying a theoretical foundation for the subsequent analysis of transient voltage instability mechanisms.

[0017] When the system is in steady state, a unique steady-state equilibrium solution can be obtained by solving the differential-algebraic equation system model. During LVRT, the system will reach a new steady state. Figure 1 Control block diagram under LVRT state, active current at this time for: (10) Steady-state reactive current during LVRT I q This can also be obtained from the control block diagram. After the fault is cleared, U w The power generation instantly recovers to above 0.9 PU, but due to the LVRT detection delay, the new energy source will remain in the LVRT state and continue to generate power. I q When passing through T v The system will switch to recovery mode under LVRT control after a certain period of time, and its active current will follow a certain slope coefficient. K re Restore to rated value, without additional control over reactive current. U w along with I p It decreases as it increases, until... I p Restore to I pref Afterwards, the new energy source switched to normal constant power control. Since the overall system load remained unchanged after the faulty line was disconnected, the power transmission on other lines was increased, which changed the power flow distribution of the system. As a result, the overall system voltage was still slightly lower than the steady-state value before the fault. According to equation (1), the active power output of the new energy source did not reach the rated value at this time. P ref There is a power deficit, and the PI control response in the outer loop is increased. I p As the active power output is gradually increased, the generator terminal voltage will drop until it reaches the low-voltage breakdown threshold, causing the unit to repeatedly enter the low-voltage breakdown state.U w It oscillates continuously and causes voltage instability throughout the system.

[0018] A new energy single-machine system is designed based on a differential-algebraic equation system model. Fault information is input in the time domain to simulate the transient operating conditions of the system. The transient state is obtained using a solver. U w , I p , I q The trajectory of change is as follows Figure 2 As shown.

[0019] according to Figure 2 After the fault was cleared, the new energy source entered a recovery state. I p The slope increases until it recovers to its original value. I pref Switch to normal control. U w The voltage continues to decrease until it re-enters the LVRT. (New energy source terminal voltage) U w The transient response curve repeatedly intersects with the low-break-through threshold, eventually leading to voltage oscillation instability.

[0020] In phase space, the system's trajectory repeatedly traverses the switching surface, such as... Figure 3 As shown.

[0021] exist Figure 6 In (a), U w initial point x1 At the steady-state equilibrium point, at the instant a fault occurs, the voltage drops below 0.9 pu, and the new energy source enters the LVRT until it reaches the fault clearing point. x3 , U w It started to increase, and after switching to recovery and normal states, as... I p The increase, U w Continue to decline until it reaches x5 At this point, new energy sources once again entered a low-price range, and... x6 The point exits the low-level crossing again; thereafter, the trajectory will... x5 arrive x6 The interval changes, and it repeatedly crosses the low-threshold surface.

[0022] According to the above analysis, the essence of transient voltage instability in the system is that the system operating trajectory cannot eventually return to the stable equilibrium surface, that is, the geometric distance between the operating point and the stable equilibrium surface is always deviated from 0, especially, when the system voltage repeatedly low passes, the geometric distance between the operating point and the stable equilibrium surface will oscillate with the repeated switching of the operating state, therefore, the geometric distance between the operating point and the stable equilibrium point can be used as a transient voltage instability criterion to determine whether the system has transient voltage instability.

[0023] According to S4, in actual new energy station, the voltage and power measurement data of PCC can be directly obtained, therefore, the geometric distance between the operating point (Uc, Pcc) at PCC and the stable equilibrium point (Ue, Pcc) is defined as the bifurcation criterion: P c , Q c , U c ) to the stable equilibrium point is the bifurcation criterion: (11) The stable equilibrium point is calculated according to the following formula: (12) The effective value of the grid-connected point voltage is solved as: (13) The actual operating condition of the grid-side AC system voltage U g can be measured, therefore, it is a known quantity. According to formula (11), if d → 0, that is, the system can return to the stable equilibrium solution, and instability does not occur, if d is periodic oscillation, it indicates that the system has transient voltage oscillation instability. In addition, if d is eventually stable at a value greater than 0, it indicates that the system may be in a sustained LVRT, which is one of the new types of voltage instability induced by nonlinear control of new energy, if d has no physical meaning solution, the system has voltage collapse. This paper focuses on the analysis of the transient voltage oscillation instability form, therefore, other types of voltage instability phenomena are not described in detail.

[0024] Based on the above established differential-algebraic equation system model of new energy system, the single machine is expanded to a double machine system, the same parameters are used, and the PCC voltage operating trajectory in the phase space is as shown in Figure 4 .

[0025] According to Figure 4 (a), the overall change trajectory of Uc is similar to Uw in Figure 3 , and the same repeated LVRT occurs, the operating trajectory eventually repeatedly passes through x5 to x6, and Figure 4(b) It can be seen that d oscillates repeatedly and always deviates from 0, which indicates that the system has experienced transient voltage oscillation instability. From this, a practical criterion for transient voltage instability of measurable physical quantities in new energy power plants can be obtained.

[0026] The next step is to develop a coordinated control strategy for transient voltage instability at new energy power plants, in accordance with S5.

[0027] During the recovery phase after fault clearing, as I p Increase, U w Gradually decreasing, during this process, if U w Excessive rate of change can lead to increased oscillation. For new energy hybrid power systems, the most important dynamic characteristics are the reactive current response characteristics in the LVRT state and the active current response characteristics in the recovery state. In the LVRT state, and It shows a positive correlation, in the recovery state. and The correlation is negative, and the steady state during LVRT can be obtained according to equation (4). U w Analytical expression: (14) Combination Figure 1 The impact can be seen Uw The main control parameters for the degree of oscillation are Kpp lv , Kpq lv , Kre and topology parameters, impedance ratio R The objective function for determining the degree of transient voltage oscillation is: (15) The switching function is used as a weight and treated as a step signal, which is applied only when the corresponding control mode is in effect. The value is 1 if it is true, otherwise it is 0. for Switch to The duration. K pp_lv The larger it is, the greater it will maintain in LVRT state. I p , K pq_lv The smaller the value, the fewer additional tokens will be issued in LVRT mode. I q This leads to a more severe voltage drop, thereby exacerbating voltage oscillations. Similarly, K reThe greater the active current recovery rate, the faster the voltage drop speed, and the greater the voltage oscillation degree. In addition, increasing the impedance ratio R , the voltage oscillation degree is also reduced. From the above analysis conclusion, the parameters can be adjusted to reduce the voltage oscillation degree. However, merely changing the parameters is not enough to solve the transient voltage instability problem, which will be analyzed below.

[0028] The essence of transient voltage instability is that the system operating trajectory cannot eventually return to the steady-state equilibrium point. However, adjusting the unit parameters does not change the steady-state equilibrium point of the system, and it is difficult to make the distance between the system operating point and the steady-state equilibrium point become 0. Therefore, considering regulating and controlling a part of the active power reference value of new energy units to reduce the total output of new energy, adjusting the steady-state equilibrium point of the system, and making the system operating trajectory approach the steady-state equilibrium point, so as to avoid system voltage instability.

[0029] Since the actual operation ΔQ c and ΔU c are much smaller than ΔP c , according to formula (11), in order to make the minimum distance d →0, restore system stability, it can be approximately considered that d The minimum value of the oscillation process is the optimal total amount of system regulation: (16) Define the ratio of the change of the terminal voltage of each unit to the change of the PCC voltage as the transient voltage participation factor of the node where the unit is located. The larger the transient voltage participation factor, the closer the electrical connection between the node and the PCC voltage, so these units will be considered when regulating the active power reference value. For each unit in the new energy station, the cutout ratio needs to be determined according to the transient voltage participation factor of the node. The transient voltage of the PCC node and the unit i is expressed as: (17) (18) The transient voltage participation factor of the node can be expressed as: (19) According to formula (19), the active regulation ratio of each unit is proportional to the transient voltage participation factor of the node, that is, the regulation ratio of each unit is proportional to the line impedance between the unit i and the PCC, and has: (20) Therefore, the active control amount regulation scheme for new energy units in the station is proposed in this embodiment.

[0030] Example Two Based on example one, an implementation example of a coordinated control method for transient voltage instability of new energy cluster grid-connected system is provided.

[0031] This example provides a new energy station, which has a total of 22 direct-drive wind turbine generators, with a total rated capacity of 363 MW. There are 6 35kV collection points in the station, of which 4 units are connected under collection points 1-5, and two units are connected under collection point 6. Each unit has a rated voltage of 0.69kV, which is connected to the local collection point 6 through a step-up transformer. The six collection points are connected to the 100kV main collection point through six power collection lines, and finally connected to the 230kV AC main grid through the main transformer. The system reference capacity is set to 100MW, and all parameters in the simulation are expressed in per unit.

[0032] The new energy station topology structure and transformer and power collection line impedance are shown in Figure 5 The transformer used in the station is of the same type, and its equivalent reactance is 0.03p.u. The rated active power of each unit and the current result obtained by voltage calculation in steady-state flow are shown in Table 1.

[0033] Table 1: Rated active power and current parameters of each unit The PI parameters of the units in the station under normal control mode are the same, and three different control parameter combinations are used in LVRT mode and recovery mode. The control parameter values used in LVRT mode and recovery mode are shown in Table 2, and the parameter combinations used by each unit are shown in Table 3.

[0034] Table 2: Parameter values under different combinations Table 3: Parameter combinations used by each unit Since this example mainly focuses on the dynamic response of the new energy cluster, the internal response of the receiving end system is not considered, so the external power grid can be equivalent. Further, the actual operating measurement of the 230kV grid-connected bus voltage can be input to the new energy control system as a known quantity to solve the new energy differential-algebraic equation system model. Based on the above assumptions, this section simulates the fault conditions in the original new energy station and the equivalent station to verify the effectiveness of the proposed optimization control strategy.

[0035] First, the verification of the influence of new energy unit control parameters.

[0036] The original 22 generating units were reduced to 4 units using K-means iso-clustering. A three-phase short-circuit fault was set up within the AC system, with a fault start time of t=5s and a duration of 0.1s. The fault conditions were kept unchanged, and the generating units were adjusted. K pp_lv , K pq_lv , K re The parameters, including the impedance ratio, are then used in a simulation. The combination of control parameters before and after adjustment is as follows: Figure 6 As shown, the original station internal impedance ratio R =0.045, adjusted to R =0.06.

[0037] Depend on Figure 7 As can be seen from (a) and (b), after adjusting the parameters, the active power recovery rate decreases, and the voltage gradually decreases as the active power recovers. Compared with before the parameter adjustment, both the voltage and power response curves become flatter, and the voltage response curves are reduced from the previous curves. Figure 7 (d) It can be seen that after adjusting the parameters, the transient voltage instability index d The values ​​are smaller, with a minimum of 0.261, and the oscillations are less pronounced, indicating that reducing the control parameters of the new energy unit... K pp_lv , K re Increase K pq_lv and station impedance ratio R This can help reduce the degree of transient voltage oscillation, thus verifying the conclusions obtained from the parameter influence analysis in step S5. However, parameter adjustment alone cannot bring the system trajectory back to the steady-state equilibrium point. Therefore, the optimized control strategy proposed in this paper will be used for simulation analysis below.

[0038] The next step is to verify the control scheme for active power consumption of new energy sources.

[0039] Keeping the fault condition settings unchanged, at t=6.14s, the active power control scheme is implemented in both the original renewable energy power station and the equivalent power station. According to... Figure 7 (d) The total amount to be regulated is △P ref =0.348. According to the optimized control strategy described in step S5, the control ratios of each unit in the original new energy power station are shown in Table 4, and the control ratios of each unit in the equivalent power station are shown in Table 5. After the units are switched off, the DAE equations under steady state of the system are solved again, and the coordinates of the new steady-state equilibrium point in phase space are (3.286, 0, 0.979).

[0040] Table 4 Active power regulation ratios for each generating unit Table 5: Regulating proportion of equivalent units Embodiment three: In a second aspect, an embodiment of the present application provides a coordinated control device for transient voltage instability of a new energy cluster grid-connected system, comprising: A model processing module, configured to build a hybrid model according to characteristics of the new energy grid-connected system and set a control mode switching function, build a dynamic response in combination with state evolution and control switching, and build a differential-algebraic equation system model of dynamic characteristics of the new energy by coupling a state space equation and a network algebraic constraint; A balanced analysis module, configured to obtain a unique steady-state balance solution according to the differential-algebraic equation system model when the new energy grid-connected system is in steady-state operation; A trajectory analysis module, configured to build a new energy single-machine system according to the differential-algebraic equation system model, input fault information in a time domain to simulate a transient operation condition, and obtain a transient change trajectory through a solver; A steady-state analysis module, configured to take a geometric distance between a running point of the transient change trajectory and a steady-state balance point as a transient voltage instability criterion, and determine whether the new energy grid-connected system is in a transient voltage instability state; A generator tripping analysis module, configured to set a ratio of a voltage change amount of each unit in a new energy station to a PCC voltage change amount as a transient voltage participation factor of a node where the unit is located, and determine a generator tripping proportion in the new energy grid-connected system according to the transient voltage participation factor.

[0041] Further, the model processing module comprises: A control unit, configured to build a hybrid model of the new energy grid-connected system, and set a switching function of a corresponding new energy control mode according to a state variable; A response unit, configured to build a dynamic response through the hybrid model of the new energy grid-connected system according to a continuous state evolution mechanism and a discrete control switching behavior; A building unit, configured to build a differential-algebraic equation system model of dynamic characteristics of the new energy by coupling a state space equation and a system network algebraic constraint according to the hybrid model of the new energy grid-connected system.

[0042] Further, in the steady-state analysis module, the geometric distance between the running point of the transient change trajectory and the steady-state balance point is taken as the transient voltage instability criterion, which specifically comprises: Voltage and power measurement data at the PCC are obtained, and a geometric distance between a running point (Pc, Qc, Uc) at the PCC and a steady-state balance point is defined as a bifurcation criterion, as shown in the following formula: (11) wherein the steady-state equilibrium point is calculated according to the following formula: (12) The effective value of the grid-connected point voltage is solved as: (13) Further, in the generator tripping analysis module, the generator tripping proportion in the new energy grid-connected system is determined according to the transient voltage participation factor, and the transient voltage of the PCC node and the generator under fault is expressed as follows: i (17) (18) The transient voltage participation factor is expressed as follows: (19) Embodiment Four: The embodiment also provides an electronic device including a memory and a processor, the memory being configured to store one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the method of embodiment one. In actual application, the processor can be an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), a Digital Signal Processing Device (DSPD), a Programmable Logic Device (PLD), a Field Programmable Gate Array (FPGA), a controller, a microcontroller unit (MCU), a microprocessor, or other electronic elements for executing the methods in the above embodiments.

[0043] The method implemented in the embodiment is as described in embodiment one.

[0044] Embodiment Five: The embodiment also provides a computer storage medium, the computer readable storage medium storing a computer program, and the computer program is executed by one or more processors to implement the method of embodiment one. ​The computer readable storage medium can be realized by any type of volatile or nonvolatile storage devices or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk or optical disk.

[0045] The method implemented by the embodiment is as described in the content of Embodiment One.

[0046] In several embodiments provided by the embodiments of the present application, it should be understood that the disclosed system and method can also be implemented by other ways. The system and method embodiments described above are only illustrative.

[0047] It should be noted that in this paper, the terms "first", "second" and the like in the description and claims of the application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. The terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0048] Although the embodiments of the present application are disclosed as above, the content described is only for the purpose of understanding the embodiments adopted by the present application, and is not intended to limit the present application. Any person skilled in the art of the present application can make any modification and change in the form and details without departing from the spirit and scope of the present application, but the patent protection scope of the present application shall be subject to the scope defined by the appended claims.

Claims

1. A collaborative control method for transient voltage instability in a new energy cluster grid-connected system, characterized in that, include: S1. Based on the characteristics of the new energy grid-connected system, a hybrid model is built and a control mode switching function is set. Dynamic response is built by combining state evolution and control switching. By coupling the state space equation and network algebra constraints, a differential-algebraic equation system model of the dynamic characteristics of new energy is established. S2, when the new energy grid-connected system is in steady state, obtain a unique steady-state equilibrium solution based on the differential-algebraic equation system model; S3. Based on the differential-algebraic equation system model, establish a new energy single-machine system, input fault information in the time domain to simulate transient operating conditions, and obtain the transient change trajectory through the solver. S4. Based on the geometric distance between the operating point and the steady-state equilibrium point of the transient change track as the transient voltage instability criterion, determine whether the new energy grid-connected system is in a transient voltage instability state. S5, set the ratio of the voltage change at the terminal of each unit in the new energy power station to the voltage change of the PCC as the transient voltage participation factor of the node where the unit is located; determine the tripping ratio in the new energy grid-connected system based on the transient voltage participation factor.

2. The method according to claim 1, characterized in that, S1 includes: S11, Establish a hybrid model of the new energy grid-connected system, and set the corresponding switching function of the new energy control mode according to the state variables; S12, Based on the continuous state evolution mechanism and discrete control switching behavior, a dynamic response is established through the hybrid model of the new energy grid-connected system; S13. Based on the hybrid model of the new energy grid-connected system, a differential-algebraic equation system model of the dynamic characteristics of new energy is established by coupling the state-space equation with the system network algebraic constraints.

3. The method according to claim 2, characterized in that, In S4, the geometric distance between the operating point and the steady-state equilibrium point of the transient change trajectory is used as the criterion for transient voltage instability, specifically including: Obtain voltage and power measurement data at PCC, and define the geometric distance between the operating point (Pc, Qc, Uc) at PCC and the steady-state equilibrium point as the bifurcation criterion, as shown in the following formula: (11) The steady-state equilibrium point is calculated according to the following formula: (12) The effective value of the grid connection point voltage is obtained as follows: (13)。 4. The method according to claim 3, characterized in that, In S5, the tripping ratio of the new energy grid-connected system is determined based on the transient voltage participation factor, and the PCC node and unit are considered under fault conditions. i The transient voltage is expressed by the following formula: (17) (18) The transient voltage participation factor is expressed by the following formula: (19)。 5. A collaborative control device for transient voltage instability in a new energy cluster grid-connected system, characterized in that, include: The model processing module is used to build a hybrid model based on the characteristics of the new energy grid-connected system and set the control mode switching function. It combines state evolution and control switching to build dynamic response and establishes a differential-algebraic equation system model of the dynamic characteristics of new energy by coupling state space equations and network algebra constraints. The equilibrium analysis module is used to obtain a unique steady-state equilibrium solution based on the differential-algebraic equation system model when the new energy grid-connected system is running in steady state. The trajectory analysis module is used to establish a new energy single-machine system based on the differential-algebraic equation system model, input fault information in the time domain to simulate transient operating conditions, and obtain the transient change trajectory through the solver; The steady-state analysis module is used to determine whether the new energy grid-connected system is in a transient voltage instability state based on the geometric distance between the operating point and the steady-state equilibrium point of the transient change track as a transient voltage instability criterion. The generator tripping analysis module is used to set the ratio of the voltage change at the terminal of each generator unit in the new energy power station to the voltage change of the PCC as the transient voltage participation factor of the node where the generator unit is located; and to determine the generator tripping ratio in the new energy grid-connected system based on the transient voltage participation factor.

6. The apparatus according to claim 5, characterized in that, The model processing module includes: The control unit is used to establish a hybrid model of the new energy grid-connected system and set the corresponding switching function of the new energy control mode according to the state variables; The response unit is used to establish a dynamic response based on the continuous state evolution mechanism and discrete control switching behavior through the hybrid model of the new energy grid-connected system; The building unit is used to establish a differential-algebraic equation system model of the dynamic characteristics of new energy by coupling the state-space equation with the system network algebraic constraints, based on the hybrid model of the new energy grid-connected system.

7. The apparatus according to claim 6, characterized in that, In the steady-state analysis module, the geometric distance between the operating point and the steady-state equilibrium point of the transient change trajectory is used as the criterion for transient voltage instability, specifically including: Obtain voltage and power measurement data at PCC, and define the geometric distance between the operating point (Pc, Qc, Uc) at PCC and the steady-state equilibrium point as the bifurcation criterion, as shown in the following formula: (11) The steady-state equilibrium point is calculated according to the following formula: (12) The effective value of the grid connection point voltage is obtained as follows: (13)。 8. The apparatus according to claim 7, characterized in that, In the generator tripping analysis module, the generator tripping ratio in the new energy grid-connected system is determined based on the transient voltage participation factor, and the PCC node and unit are considered under fault conditions. i The transient voltage is expressed by the following formula: (17) (18) The transient voltage participation factor is expressed by the following formula: (19)。 9. An electronic device, characterized in that, The device includes a memory and a processor, the memory being used to store one or more computer instructions, wherein the one or more computer instructions, when executed by the processor, implement the method as described in any one of claims 1-4.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which, when executed by a processor, is used to implement the method as described in any one of claims 1-4.

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