A transient stability analysis method and related device considering current limit

Abstract

The application discloses a kind of transient stability analysis method and related device considering current limit, establish the mathematical model of hydropower system and photovoltaic power generation system;In view of the current-limiting control of photovoltaic inverter and flexible rectifier during fault, the equation of active power sent by hydro-generator before fault removal is derived according to Thevenin theorem;The analytical expression of critical removal angle of sending-out system is derived by using equal-area rule;With critical removal angle as the key index of transient stability limit of sending-out system, the influence of photovoltaic and flexible current transformer saturation current angle parameter value and water-light generation ratio on the transient stability of sending-out system is evaluated.The water-light generation ratio setting method involved in the application can effectively improve the transient stability of the system, and the research results are expected to provide certain theoretical guidance for the stable operation of future new energy power system.

Description

Technical Field

[0001] This invention belongs to the field of novel power system stability control technology, specifically relating to a transient synchronization stability analysis method and related apparatus that takes current limitations into account. Background Technology

[0002] Solar power, a renewable energy source, is highly volatile and intermittent. Furthermore, grid connection via converters weakens the inertia and damping of the power system, jeopardizing its safe and stable operation. To address these issues, multi-energy complementary combined power generation has become an effective way to improve the absorption capacity of solar power.

[0003] The hydro-solar hybrid power generation system forms a transmission system in which a converter interface type power source (CIG) and a synchronous generator (SG) operate in parallel. The power angle characteristics of the hydropower unit and the control scheme of the photovoltaic converter both affect the stability of the transmission system. The CIG connection causes the power angle curve of the SG to become non-sinusoidal, reducing the power transmission capacity of the SG and consequently decreasing the synchronous stability domain of the system. In the event of a transmission system failure, the CIG typically activates its current limiting circuit quickly to protect the converter from overcurrent damage, resulting in significant differences in transient characteristics between the CIG and SG parallel operation system and the SG-dominated system.

[0004] However, existing research mainly focuses on grid-connected systems with single converters that take current limiting into account, and has not revealed the impact of switching the CIG control mode to current limiting state on the transient synchronization stability of the SG operating in parallel in a multi-energy complementary system. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a transient synchronization stability analysis method and related apparatus that takes current limitation into account, which addresses the shortcomings of the prior art and is used to improve the tuning of current limiting control parameters for improving the transient synchronization stability of the system.

[0006] The present invention adopts the following technical solution:

[0007] A transient synchronization stability analysis method considering current limitations includes the following steps:

[0008] Establish the basic control structure for hydropower and photovoltaic power generation systems, and determine the power transmission characteristics of the power transmission system during transient periods.

[0009] Based on the power transmission characteristics during the transient period of the power transmission system, and taking into account the current limiting control of the photovoltaic inverter and flexible DC rectifier during the fault period, the equation for the active power transmitted by the hydropower unit before the fault is cleared is derived.

[0010] Based on the equations of the active power delivered by the hydropower unit before the fault is cleared, the analytical expression of the critical clearing angle of the delivery system is derived using the equal area rule.

[0011] Based on the obtained analytical expression of the critical clearing angle of the sending-out system, the influence of the saturation current angle parameter value of the photovoltaic and flexible rectifier and the water-light generation ratio on the transient stability of the sending-out system is evaluated with the critical clearing angle as the key indicator of the transient synchronous stability limit of the sending-out system.

[0012] Preferably, the basic control structure of the hydroelectric power generation system and the photovoltaic power generation system is as follows:

[0013]

[0014] wherein δ g and ω g are the power angle and the angular frequency of the synchronous generator respectively; P m is the input mechanical power of the synchronous machine; T J is the inertia time constant of the synchronous machine; D hy is the damping of the synchronous machine; ω n is the rated angular frequency; and are the dq components of the output current of the photovoltaic inverter; and are the current dq component reference values output by the current limiting loop; and are the output signals of the power control outer loop; is the maximum amplitude of the output current of the inverter; is the saturation current angle parameter setting value of the current limiting control link.

[0015] Preferably, the equation of the active power sent out by the hydroelectric generator before fault removal is as follows:

[0016]

[0017] wherein P represents the maximum power output by the hydroelectric generator during the fault when the distance from the fault point to the PCC is α, δ g represents the power angle of the synchronous machine, represents the saturation current angle.

[0018] Preferably, the active power of the input DC system of the flexible rectifier is represented as follows:

[0019]

[0020] wherein U pcc represents the voltage at the PCC point, U sec represents the voltage of the flexible rectifier, X L represents the transfer reactance of the flexible rectifier to the PCC point, δ pcc represents the power angle at the PCC point.

[0021] Preferably, the analytical expression of the critical clearing angle of the sending-out system is:

[0022]

[0023] wherein, denotes the saturation current angle, denotes the power angle of the hydroelectric synchronous generator corresponding to the stable equilibrium point of the sending-out system when the current of the photovoltaic inverter and the flexible rectifier is not saturated, and f denotes a monotonic function with respect to the critical clearing angle of the sending-out system.

[0024] Preferably, the ratio of the hydropower and the photovoltaic power of the water-photovoltaic complementary power generation system under the steady state is γ, the power coupling between the photovoltaic power generation system and the hydroelectric unit makes the active power characteristic curve of the synchronous generator under the steady state be downwardly offset, the power angle of the synchronous generator corresponding to the unstable equilibrium point of the system is reduced, and the synchronous stability boundary of the sending-out system is reduced. For the system with constant mechanical power of the hydroelectric unit, the value of continuously decreases with the increase of the photovoltaic power, and the increase of the water-photovoltaic power generation ratio has an adverse effect on the transient synchronous stability of the system.

[0025] Preferably, the optimal parameter value of the saturation current angle of the converter in the sending-out system and the critical clearing angle of the sending-out system under the optimal parameter are:

[0026]

[0027] wherein, denotes the critical clearing angle of the sending-out system under the optimal parameter, P s denotes the rated value of the total power of the water-photovoltaic complementary power generation, denotes the critical clearing angle, P pv denotes the photovoltaic output power, P mppt denotes the active power tracking maximum power output by the photovoltaic power generation adopting the maximum power tracking control, denotes the saturation current angle, and denote the power angles of the hydroelectric synchronous generator corresponding to the stable equilibrium point and the unstable equilibrium point of the sending-out system when the current of the photovoltaic inverter and the flexible rectifier is not saturated, respectively.

[0028] In the second aspect, an embodiment of the present application provides a transient synchronous stability analysis system considering current limitation, comprising:

[0029] a construction module, which establishes the basic control structure of the hydropower system and the photovoltaic power generation system, and determines the transmission power characteristic during the transient state of the sending-out system;

[0030] ​A first derivation module derives an equation of active power output by the hydroelectric generator before fault clearing based on transmission power characteristics during the transient state of the sending-out system and taking into account current limiting control of the photovoltaic inverter and the flexible rectifier during the fault;

[0031] A second derivation module derives an analytical expression of the critical clearing angle of the sending-out system based on the equation of active power output by the hydroelectric generator before fault clearing using the equal-area criterion.

[0032] An analysis module evaluates the influence of the saturation current angle parameter values of the photovoltaic and the flexible rectifier and the proportion of water and light power generation on the transient stability of the sending-out system based on the analytical expression of the critical clearing angle of the sending-out system, taking the critical clearing angle as a key indicator of the transient stability limit of the sending-out system.

[0033] In a third aspect, a chip is provided, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the above-mentioned transient stability analysis method considering current limiting when executing the computer program.

[0034] In a fourth aspect, an electronic device is provided, which includes a computer program, and the computer program implements the steps of the above-mentioned transient stability analysis method considering current limiting when executed by the electronic device.

[0035] Compared with the prior art, the present application has at least the following beneficial effects:

[0036] A transient stability analysis method considering current limiting is provided, which obtains transmission power characteristics during the transient state of the sending-out system by establishing the basic control structure of the hydroelectric power generation system and the photovoltaic power generation system, derives an equation of active power output by the hydroelectric generator before fault clearing based on the Thevenin theorem, and derives an analytical expression of the critical clearing angle of the sending-out system based on the equal-area criterion.

[0037] Further, based on the transmission power characteristics during the transient state of the sending-out system, the current limiting control of the photovoltaic inverter and the flexible rectifier during the fault is established, and the equation of active power output by the hydroelectric generator before fault clearing is derived according to the Thevenin theorem.

[0038] Further, based on the equation of active power output by the hydroelectric generator before fault clearing, the analytical expression of the critical clearing angle of the sending-out system is derived using the equal-area criterion.

[0039] Further, based on the analytical expression of the critical clearance angle of the sending-out system, the critical clearance angle is established as the key index of the transient synchronous stability limit of the sending-out system, and the influence of the saturation current angle parameter value of the photovoltaic and flexible DC converter and the water-light generation ratio on the transient stability of the sending-out system is evaluated.

[0040] It can be understood that the beneficial effects of the second aspect to the fourth aspect can be referred to the related description in the first aspect, which will not be repeated here.

[0041] In summary, the model of the water-light complementary generation through the flexible DC sending-out system considering the current limitation is obtained, and the water-light generation ratio setting method can effectively improve the transient synchronous stability of the system.

[0042] The technical solutions of the present application will be further described in detail below with the help of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a sending end topology structure diagram of the water-light complementary generation through the flexible DC sending-out system.

[0044] Figure 2 It is a control structure diagram of the photovoltaic generation system.

[0045] Figure 3 It is a water turbine output power characteristic curve diagram under steady state.

[0046] Figure 4 It is an equivalent circuit diagram of the sending-out system during the fault.

[0047] Figure 5 It is a Thevenin equivalent circuit diagram of the synchronous machine outlet during the fault.

[0048] Figure 6 It is a water turbine output power characteristic curve diagram.

[0049] Figure 7 It is a power angle curve diagram of different current limiting controller parameter values during the fault.

[0050] Figure 8 It is a curve diagram of the critical clearance angle changing with .

[0051] Figure 9 It is a curve diagram of the critical clearance angle changing with the water-light generation ratio.

[0052] Figure 10 It is a system dynamic diagram when the saturation current angle takes the optimal value and deviates from the optimal value, wherein (a) is the power angle δ g of the hydraulic power generation system under different saturation current angles, and (b) is the angular frequency ω gDynamic diagram under different saturation current angles, (c) is the active output P of the hydroelectric power generation system g Dynamic diagram under different saturation current angles;

[0053] Figure 11 Dynamic diagram of the system for different water-light generation ratios, (a) is the power angle δ of the hydroelectric power generation system g Dynamic diagram under different water-light generation ratios, (b) is the angular frequency ω of the hydroelectric power generation system g Dynamic diagram under different water-light generation ratios, (c) is the active output P of the hydroelectric power generation system g Dynamic diagram under different water-light generation ratios;

[0054] Figure 12 A schematic diagram of a computer device provided by an embodiment of the present application;

[0055] Figure 13 A block diagram of an electronic device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application.

[0057] In the description of the present application, it should be understood that the terms “include” and “contain” indicate the existence of described features, whole, steps, operations, elements and / or components, but do not exclude the existence or addition of one or more other features, whole, steps, operations, elements, components and / or sets thereof.

[0058] It should also be understood that the terms used in the present application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the present application specification and the appended claims, unless otherwise clear from the context, the singular forms “a”, “an” and “the” are intended to include the plural forms.

[0059] It should be further understood that the term “and / or” used in the present application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations, for example, A and / or B can represent three cases of A alone, A and B together, and B alone. In addition, the character “ / ” in the present application generally represents an “or” relationship between the front and rear associated objects.

[0060] It should be understood that, although the terms first, second, third, etc. can be employed in describing the preset ranges, etc. in the embodiments of the present application, the preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from each other. For example, the first preset range can also be referred to as the second preset range, and similarly, the second preset range can also be referred to as the first preset range, without departing from the scope of the embodiments of the present application.

[0061] Depending on the context, the word "if" as used herein can be interpreted to mean "when" or "while" or "in response to determining" or "in response to detecting." Similarly, the phrase "if it is determined" or "if (a stated condition or event) is detected" can be interpreted to mean "when it is determined" or "in response to determining" or "when (the stated condition or event) is detected" or "in response to detecting (the stated condition or event)".

[0062] Various structural diagrams according to the disclosed embodiments of the present application are shown in the accompanying drawings. These diagrams are not drawn to scale, in which certain details are exaggerated for the purpose of clarity, and certain details can be omitted. The shapes of various regions, layers shown in the drawings and their relative sizes and positional relationships are only exemplary, and in actuality, they can deviate due to manufacturing tolerances or technical limitations, and a person skilled in the art can additionally design regions / layers with different shapes, sizes, relative positions according to actual needs.

[0063] The present application provides a transient synchronous stability analysis method considering current limitation, transient synchronous stability of a water-light complementary power generation through flexible DC transmission system considering current limitation, and establishes the basic control structure of the hydropower system and the photovoltaic power generation system. Based on the Thevenin theorem, the transmission power equation of the transmission system when the converter switches to the current limiting mode during the fault is derived, the critical switching angle analytical expression of the transmission system is derived, and the influence of the saturation current angle parameter value and the water-light power generation ratio on the transient synchronous stability of the transmission system is quantitatively evaluated, and a current limiting control parameter setting method for improving the transient synchronous stability of the system is proposed. The present application analyzes the transient synchronous stability mechanism of the water-light complementary power generation through flexible DC transmission system considering current limitation, and the research results are expected to provide certain theoretical guidance for the stable operation of future new energy power systems.

[0064] The present application provides a transient synchronous stability analysis method considering current limitation, transient synchronous stability of a water-light complementary power generation through flexible DC transmission system considering current limitation, and establishes the basic control structure of the hydropower system and the photovoltaic power generation system. Based on the Thevenin theorem, the transmission power equation of the transmission system when the converter switches to the current limiting mode during the fault is derived, the critical switching angle analytical expression of the transmission system is derived, and the influence of the saturation current angle parameter value and the water-light power generation ratio on the transient synchronous stability of the transmission system is quantitatively evaluated, and a current limiting control parameter setting method for improving the transient synchronous stability of the system is proposed. The present application analyzes the transient synchronous stability mechanism of the water-light complementary power generation through flexible DC transmission system considering current limitation, and the research results are expected to provide certain theoretical guidance for the stable operation of future new energy power systems.

[0065] S1, establishing the basic control structure of the hydropower system and the photovoltaic power generation system;

[0066] The topology structure of the water-light complementary power generation through flexible DC transmission system is as follows Figure 1As shown. The flexible direct-transmission rectifier station regulates the voltage and frequency of the transmission system through V / F control; the photovoltaic inverter achieves synchronization with the transmission system based on PLL. The point of common coupling (PCC) for photovoltaic and hydropower generation is connected to the flexible direct-transmission rectifier station via AC transmission lines. In this patent, the hydropower unit is analyzed using the classic model of a synchronous generator, and it is assumed that the photovoltaic power generation base and the hydropower unit are relatively close to the PCC point.

[0067] Figure 1 E' hy and X' d These are the transient electromotive force and transient reactance of the hydroelectric synchronous machine, respectively; X L For AC transmission line reactance; U pv U pcc and U sec These are the voltage amplitudes of the AC bus of the photovoltaic inverter, the PCC bus, and the AC bus of the flexible DC rectifier, respectively; P pv P g and P sec These represent the output power of photovoltaic power, the output power of hydropower, and the active power input to the DC transmission system, respectively. The AC bus of the flexible DC rectifier is used as the reference bus, i.e., the AC voltage vector of the flexible DC rectifier is U. sec ∠0.

[0068] A hydroelectric generating unit consists of a hydraulic turbine and a synchronous generator. The hydraulic turbine converts the mechanical energy of the water head into the kinetic energy of the turbine rotor, which provides mechanical torque to the synchronous generator through the shaft system. Since the mechanical torque output by the hydraulic turbine changes very little in the transient time scale of the power system, the mechanical power input to the synchronous generator is assumed to remain constant during a fault. Therefore, the relationship between the power angle and angular frequency of the synchronous generator and its output electromagnetic power can be expressed by the rotor motion equations as follows:

[0069]

[0070] Where, δ g and ω g These are the power angle and angular frequency of the synchronous generator, respectively; P m Input mechanical power to the synchronizer; T J The inertial time constant of the synchronous machine; D hy For synchronous machine damping; ω n This is the rated angular frequency.

[0071] The overall control structure of a photovoltaic power generation system is as follows: Figure 2As shown, it adopts maximum power point tracking (MPPT) control, the front-stage DC-DC converter maintains the active power output of the system to track the maximum power P by adjusting the DC voltage at the port of the photovoltaic array mppt , the rear-stage inverter maintains the DC bus voltage between the two-stage converters constant and adjusts the reactive power output of the system, and the inverter realizes synchronization with the sending system through PLL. If the power loss of the photovoltaic converter is ignored, the active power output of the photovoltaic power generation system at steady state satisfies P pv =P mppt .

[0072] Since the converter has weak overcurrent resistance, Figure 2 The current saturation algorithm-based current limiting control loop should be embedded between the power control outer loop and the current control inner loop in the photovoltaic inverter, and the current reference signal output by the current limiting loop is expressed as:

[0073]

[0074] wherein, and are the dq components of the output current of the photovoltaic inverter; and are the current dq component reference values output by the current limiting loop; and are the output signals of the power control outer loop; is the maximum amplitude of the output current of the inverter; is the saturation current angle parameter setting value of the current limiting control link. When the current flowing through the photovoltaic inverter reaches saturation, the photovoltaic inverter switches to the current limiting control mode, at which time the photovoltaic power generation system behaves as a current source, with the output current amplitude being and the phase angle being

[0075] The classic VF control is adopted in the HVDC rectifier station, the angular frequency of the HVDC rectifier station at steady state is ω n , and the voltage amplitude U sec is equal to the rated value U n . Similarly with the photovoltaic inverter, when the current flowing through the HVDC rectifier station reaches the limit value , the HVDC rectifier station behaves as a current source, with the output current amplitude being and the phase angle being

[0076] S2, based on the transmission power characteristic of the sending system during the transient state obtained in step S1 and taking into account the current limiting control of the photovoltaic inverter and the HVDC rectifier, the equation of the active power output of the hydroelectric generator set before the fault is cleared is derived according to the Thevenin theorem;

[0077] The current amplitude flowing through each converter is usually less than a defined value in steady state of the sending system, and the converter controls the photovoltaic power generation system to output constant active power. According to the characteristics of the AC transmission line of the sending system, the active power input into the DC system by the HVDC rectifier is expressed as:

[0078]

[0079] The active power output by the photovoltaic power generation system in steady state is equal to the maximum captured power of the photovoltaic array, i.e. P pv = P mppt max.Since the PCC point is close to the photovoltaic power generation base and the hydroelectric unit, and the sub-transient reactance of the hydroelectric unit is small, it is considered that the power angle of the hydroelectric synchronous machine is approximately equal to the power angle of the PCC point, i.e. δ g ≈ δ pcc The active power output by the hydroelectric unit in steady state is expressed as:

[0080]

[0081] Substituting equation (4) into the rotor motion equation (1) of the synchronous generator, the angular frequency of the synchronous machine in steady state is near ω n , and the damping term is ignored. After rearrangement, the second-order dynamic equation of the hydroelectric unit about δ g in steady state is obtained.

[0082]

[0083] According to equation (5), the relationship between the output power P g of the hydroelectric unit and the power angle δ g of the synchronous machine in steady state is represented by the curve shown in FIG. 2. Figure 3

[0084] Figure 3 and are the power angles of the hydroelectric synchronous machine corresponding to the stable equilibrium point and the unstable equilibrium point of the sending system when the currents of the photovoltaic inverter and the HVDC rectifier are not saturated. When a three-phase AC short-circuit fault occurs in the sending system, the currents flowing through the photovoltaic inverter and the HVDC rectifier reach saturation, and the converters are switched to the current-limiting control mode. The output current vector of the photovoltaic inverter is and the output current vector of the HVDC SEC is Therefore, the equivalent circuit of the sending system during the fault is shown in FIG. 3. Figure 4 α represents the proportion of the distance of the fault point from the PCC bus to the transmission distance, and X F is the additional reactance of the positive sequence equivalent circuit during the fault.

[0085] During the fault, the voltages of the PCC bus and the AC bus of the HVDC rectifier usually deviate from the rated value, and the sending system satisfies: ​

[0086]

[0087] wherein, represents the fault point voltage vector.

[0088] The formula (6) is arranged to obtain the balance relationship satisfied by the terminal voltage of the hydroelectric synchronous machine, the output current of the synchronous machine, the output current of the photovoltaic inverter and the output current of the flexible rectifier:

[0089]

[0090] The right side is the equation form of the Thevenin equivalent circuit, and the fault equivalent potential Therefore, the terminal voltage of the hydroelectric synchronous machine during the fault is composed of the equivalent potential and the voltage drop caused by the impedance j(X' d +αX L +X F ) and the current Therefore, the AC system connected by the hydroelectric synchronous machine during the fault of the sending-out system is represented by the equivalent circuit shown in Figure 5 .

[0091] The saturation current amplitude of the photovoltaic inverter and the flexible rectifier in the sending-out system is set as The saturation current angle is Therefore, the fault equivalent potential vector is derived in the form of amplitude and angle as follows:

[0092]

[0093] wherein, the equivalent potential amplitude which is related to the distance between the fault point and the PCC and the fault type; and the equivalent potential phase angle is related to the saturation current angle parameter setting value of the current limiting link of the converter.

[0094] The active power output by the hydroelectric unit during the fault is obtained according to the formula (6) and the formula (7) as shown in the formula (9):

[0095]

[0096] wherein, represents the maximum power output by the hydroelectric unit during the fault when the distance between the fault point and the PCC is α, and the value is:

[0097]

[0098] S3, based on the equation of the active power output by the hydroelectric unit obtained in step S2 before the fault is removed, an analytical expression of the critical removal angle of the sending-out system is derived by using the equal-area rule;

[0099] From equations (4) and (9), the active power output P of the hydropower unit before and after fault clearance is obtained. g Regarding the power angle δ of the synchronous machine g The characteristic curves are as follows Figure 6 As shown, according to EAC, Figure 6 middle and These represent the fault clearing angle and the peak value of the initial swing angle of the hydropower unit at the critical synchronous stability after the fault in the power transmission system has been cleared; S a and S d These represent the acceleration area and deceleration area enclosed by the hydropower output power characteristic curves and mechanical power during and after the fault is cleared.

[0100] According to EAC, the system exists in equilibrium:

[0101]

[0102] in,

[0103]

[0104] The transient synchronization stability condition of the output system is that the peak power angle of the synchronizing machine during the first swing does not exceed the stability boundary of the first swing, i.e. Not greater than the synchronous machine power angle corresponding to the unstable equilibrium point Specifically, this manifests as follows:

[0105]

[0106] If the sum of the acceleration and deceleration areas of the output system is zero. and If the angles are equal, the system is critically synchronously stable, and the fault clearing angle at this point is defined. Critical resection angle According to equations (11) and (12), we get Satisfy the following formula:

[0107]

[0108] Where A and β are constants, taking the following values:

[0109]

[0110] In equation (14), f is the critical cut angle of the delivery system. If it is a monotonic function, then It can be expressed by the following formula:

[0111]

[0112] As can be seen from equation (16), the critical cut-off angle is related to the initial steady-state power angle, the current limiting control parameters, and the fault location, while the initial steady-state power angle is affected by the ratio of hydropower to solar power generation.

[0113] S4. Analytical expression for the critical cut-off angle of the transmission system obtained in step S3: Using the critical cut-off angle as the key indicator of the transient synchronous stability limit of the transmission system, the influence of the values ​​of the saturation current angle parameters of photovoltaic and flexible DC converters and the ratio of hydropower generation on the transient stability of the transmission system was evaluated.

[0114] according to The expression indicates that the values ​​of the saturated current angle control parameters and the ratio of hydropower generation to solar power generation in the converter current limiting control loop are the main factors affecting the transient synchronization stability of the transmission system.

[0115] According to equation (9), adjust It will change the active power transmission characteristic curve during a system failure, such as Figure 7 As shown.

[0116] During the initial swing interval after a short-circuit fault in the transmitting system, the change in the power characteristic curve affects the acceleration area during the fault, thus affecting the transient stability limit of the system. Combined with EAC, equation (16) can be used to solve for the transmitting system under different parameters. Critical cut-off angle under the given value, such as Figure 8 As shown in the figure, for a system with a specific hydro-solar power output ratio, there exists a converter saturation current angle. Parameter values This causes the critical cut-off angle of the system to reach its maximum, therefore Tuning to the optimal value The transient synchronization stability of the system is the strongest.

[0117] Based on equation (16) and the operating conditions of the transmission system, the optimal parameter value of the converter saturation current angle in the transmission system and the critical cut-off angle of the transmission system under the optimal parameters can be solved:

[0118]

[0119] in, The output system is at optimal parameters The critical resection angle below; P s It is the rated value of the total power of the hydro-solar hybrid power generation.

[0120] Solving equation (17) yields the optimal parameters of the power delivery system under different hydro-photovoltaic output ratios. and critical resection angle As shown in the table below.

[0121] Table 1 Optimal Parameter Values ​​of System Saturation Current Angle and Critical Cut-off Angle

[0122]

[0123] The ratio of the hydropower generation and the photovoltaic generation of the water-light complementary power generation system in the steady state is defined as γ. According to formula (5), the power coupling of the photovoltaic power generation system and the hydropower unit makes the active power characteristic curve of the synchronous machine in the steady state downwardly deviate, the power angle of the synchronous machine corresponding to the unstable equilibrium point of the system is reduced , the first swing synchronous stability boundary of the sending-out system is reduced, for the system with constant mechanical power of the hydropower unit, the value of continuously decreases with the increase of the photovoltaic power (γ decreases), and the transient synchronous stability of the sending-out system gradually deteriorates, and the critical clearing angle of the sending-out system under the optimal parameters is as shown by a black curve. Figure 9

[0124] For the system with constant total power of the water-light complementary power generation, according to Table 1, when the photovoltaic power is small and the hydropower is large, the critical clearing angle of the sending-out system adopting the optimal control parameter setting method decreases with the increase of γ, as shown by a red curve. When the photovoltaic power increases, according to the daily short-term scheduling principle of the water-light complementary power generation system, reducing the output of the hydropower unit can enhance the transient synchronous stability of the system. Figure 9

[0125] Those skilled in the art can understand that various aspects of the present application can be implemented as a system, a method or a program product. Therefore, various aspects of the present application can be embodied as a complete hardware embodiment, a complete software embodiment (including firmware, microcode, etc.), or an embodiment combining hardware and software aspects, which can be collectively referred to as "circuitry", "module" or "platform" here.

[0126] In another embodiment of the present application, a transient synchronous stability analysis system considering current limitation is provided, which can be used to implement the above-mentioned transient synchronous stability analysis method considering current limitation. Specifically, the transient synchronous stability analysis system considering current limitation comprises a construction module, a first derivation module, a second derivation module and an analysis module.

[0127] The construction module establishes the basic control structure of the hydropower generation system and the photovoltaic generation system, and determines the transmission power characteristic during the transient state of the sending-out system.

[0128] The first derivation module derives the equation of the sending-out active power of the hydropower unit before fault clearing based on the transmission power characteristic during the transient state of the sending-out system and considering the current-limiting control of the photovoltaic inverter and the flexible rectifier during the fault;

[0129] ​​The second derivation module derives an analytical expression of the critical clearing angle of the sending system based on an equation of active power sent by the hydroelectric generating set before fault clearing, by using the equal-area rule.

[0130] The analysis module evaluates the influence of the saturation current angle parameter value of the photovoltaic and the flexible direct-current converter and the water-light generation ratio on the transient stability of the sending system, based on the analytical expression of the critical clearing angle of the sending system, and taking the critical clearing angle as a key index of the transient synchronous stability limit of the sending system.

[0131] In another embodiment of the present application, a terminal device is provided, which comprises a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions to implement a corresponding method flow or a corresponding function; the processor in the embodiments of the present application can be used for the operation of the transient synchronous stability analysis method considering current limitation, including:

[0132] The basic control structure of the hydroelectric power generation system and the photovoltaic power generation system is established, and the transmission power characteristics during the transient state of the sending system are determined; based on the transmission power characteristics during the transient state of the sending system, and taking into account the current-limiting control of the photovoltaic inverter and the flexible rectifier during the fault, an equation of active power sent by the hydroelectric generating set before fault clearing is derived; based on the equation of active power sent by the hydroelectric generating set before fault clearing, an analytical expression of the critical clearing angle of the sending system is derived by using the equal-area rule; based on the analytical expression of the critical clearing angle of the sending system, the critical clearing angle is taken as a key index of the transient synchronous stability limit of the sending system, and the influence of the saturation current angle parameter value of the photovoltaic and the flexible direct-current converter and the water-light generation ratio on the transient stability of the sending system is evaluated.

[0133] In still another embodiment of the present application, a computer readable storage medium (Memory) is also provided, which is a memory device in the terminal equipment, used for storing programs and data. It can be understood that the computer readable storage medium here can include the built-in storage medium in the terminal equipment, and of course can also include the expansion storage medium supported by the terminal equipment, and can be any tangible medium containing or storing programs, which can be used by or in combination with the instruction execution system, device or apparatus. The computer readable storage medium provides a storage space, which stores the operating system of the terminal. Moreover, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, which can be one or more computer programs (including program codes). It should be noted that more specific examples (non-exhaustive list) of the computer readable storage medium here include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0134] The computer readable storage medium also includes a data signal carried in baseband or propagated as a carrier wave in a propagated data signal, in which the readable program code is carried. Such a propagated data signal can take any of a variety of forms, including but not limited to electro-magnetic, optical, or any suitable combination thereof. The readable storage medium can also be any readable medium that can be used to carry, propagate, or transmit the program for use by or in connection with the instruction execution system, device or apparatus. The program code contained in the readable storage medium can be transmitted in any suitable medium, including but not limited to wireless, wired, optical, RF, etc., or any suitable combination thereof.

[0135] The program code for carrying out operations of the present application can be written in any combination of one or more programming languages, including an object-oriented programming language such as Java, C++, etc., and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code can execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device or entirely on the remote computing device or server. In the latter scenario, the remote computing device can be connected to the user's computing device through any kind of network, including a local area network (LAN) or a wide area network (WAN), or the remote computing device can be connected to the external computing device (for example, using an Internet service provider to connect to the Internet).

[0136] The one or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the method for transient stability analysis considering current limit in the above embodiments; the one or more instructions stored in the computer-readable storage medium are loaded and executed by the processor to implement the following steps:

[0137] The basic control structure of the hydropower system and the photovoltaic power generation system is established, and the transmission power characteristics during the transient period of the sending-out system are determined; based on the transmission power characteristics during the transient period of the sending-out system and in consideration of the current limit control of the photovoltaic inverter and the flexible rectifier during the fault, an equation of the active power sent out by the hydropower generator before the fault is removed is derived; based on the equation of the active power sent out by the hydropower generator before the fault is removed, an analytical expression of the critical removal angle of the sending-out system is derived by using the equal-area rule; based on the analytical expression of the critical removal angle of the sending-out system, the critical removal angle is taken as the key index of the transient synchronous stability limit of the sending-out system, and the influence of the saturation current angle parameter values of the photovoltaic and the flexible rectifier and the water-light power generation ratio on the transient stability of the sending-out system is evaluated.

[0138] Please refer to Figure 12 , the terminal device is a computer device, the computer device 60 of the embodiment includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61, and the computer program 63 implements the method for calculating the fluid composition in the reservoir reconstruction wellbore in the embodiment when executed by the processor 61. To avoid repetition, details are not repeated here. Alternatively, the computer program 63 implements the functions of each model / unit in the reservoir reconstruction wellbore fluid composition calculation system when executed by the processor 61. To avoid repetition, details are not repeated here.

[0139] The computer device 60 can be a desktop computer, a notebook computer, a palm computer, and a cloud server, etc. The computer device 60 can include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art can understand that the computer device 60 can include more or fewer components, or combine certain components, or different components, for example, the computer device can also include an input / output device, a network access device, a bus, etc. Figure 12 The computer device 60 is only an example and does not constitute a limitation on the computer device 60, and can include more or fewer components than the illustration, or combine certain components, or different components, for example, the computer device can also include an input / output device, a network access device, a bus, etc.

[0140] The processor 61 can be a central processing unit (CPU), and can also be other general-purpose processors, central processing units, graphics processing units, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic components, quantum computing-based data processing logic components, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0141] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or a memory of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc.

[0142] Further, the memory 62 can include both an internal storage unit and an external storage device of the computer device 60. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0143] Any reference to storage, databases or other media used to store data in the embodiments provided herein is intended to include at least one of volatile and non-volatile storage. Non-volatile storage can include, for example, optical, floppy disks, hard disks, or solid state drives. Volatile storage can include, for example, random access memory (RAM). A basic input / output system (BIOS), containing the basic routines that help to transfer information between elements within the electronic device, such as during startup, can typically be stored in non-volatile memory. By way of illustration, and not limitation, a basic input / output system based on the BIOS, can include a BIOS, a unified extensible firmware interface (UEFI), or the like, including without limitation basic input / output system software stored in nonvolatile memory that

[0144] The database referred to in the embodiments provided herein can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a blockchain, without being limited thereto. The processor referred to in the embodiments provided herein can be a general processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, without being limited thereto.

[0145] See Figure 13 , the terminal device 600 is an electronic device, which is manifested in the form of a general computing device. The components of the electronic device can include, but are not limited to, at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components including the storage unit 620 and the processing unit 610, a display unit 640, and the like.

[0146] The storage unit stores program codes, which can be executed by the processing unit 610, so that the processing unit 610 performs the steps according to various exemplary embodiments of the present application described in the method part of the present specification. For example, the processing unit 610 can perform the steps as shown in Figure 1 .

[0147] The storage unit 620 can include a readable medium in the form of volatile storage such as random access memory (RAM) 6201 and / or cache memory 6202, and also can include a non-volatile storage such as read only memory (ROM) 6203.

[0148] The storage unit 620 also can include a program / utility 6204 having a set of programs / modules 6205, including an operating system, one or more application programs, other program modules, and program data, each of which can implement aspects of a network environment, as each of these example or some combination thereof.

[0149] The bus 630 can represent one or more of several types of bus structures, including a storage bus or bus controller, a peripheral bus, a graphics bus, a processor or local bus using any of a variety of bus architectures.

[0150] The electronic device 600 also can communicate with one or more external devices 700 such as a keyboard or pointing device, a Bluetooth device, etc.; other devices that enable a user to interact with the electronic device 600; and / or one or more devices that enable the electronic device 600 to communicate with one or more other computing devices. Such communication can occur via an input / output (I / O) interface 650. Still yet, the electronic device 600 can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and / or a public network such as the Internet, via a network adapter 660. The network adapter 660 can be communicatively coupled to the other components of the electronic device 600 via the bus 630. It should be appreciated that the electronic device 600 can be a part of one or more networks, such as virtual networks, which further can include more than one network.

[0151] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application but not all embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present application belong to the scope of protection of the present application.

[0152] To verify the accuracy of the transient stability analysis method of the present application, a simulation model of the water-light complementary power generation and flexible transmission system is built in MATLAB / simulink, a three-phase short-circuit fault is set at the terminal bus of the AC transmission line, and the transient stability of the sending-out system under different control parameters and water-light generation ratios is compared to verify the accuracy of the theoretical analysis conclusion. The main parameters of the simulation model are listed in Table 2. Figure 1

[0153] Table 2 Main parameters of the simulation system

[0154]

[0155] The present application considers that the output of the hydroelectric generator in the simulation system is 5000MW, the output of the photovoltaic power generation is 3000MW, and the fault clearance angle is 1.79 rad. Figure 10 The dynamics of the system with the optimal value of the converter saturation current angle and the simulation system deviating from the optimal control parameters are compared. As can be seen from the figure, the critical synchronous stability of the system after the fault is removed The peak value of the power angle of the hydroelectric synchronous machine during the first swing is slightly less than the power angle corresponding to the unstable equilibrium point The output power of the hydroelectric generator is close to the mechanical power at the end of the first swing, and the angular frequency is near the rated value, while is slightly greater than and slightly less than When the power angle of the hydroelectric synchronous machine reaches the power angle corresponding to the unstable equilibrium point , the output power of the hydroelectric generator is equal to the mechanical power, and the angular frequency is still greater than 0, and the power angle δ g continues to increase, and the sending-out system loses stability. It can be seen that the new energy converter current limiting control parameter optimization setting scheme disclosed in the present application can effectively improve the transient stability of the system.

[0156] The present application studies the influence of the water-light generation ratio on the transient stability of the system, considers that the output of the hydroelectric generator in the simulation system is 5000MW, the output of the photovoltaic power generation is 3000MW, and the short-circuit fault clearance angle is 1.70 rad. The saturation current angle of the converter in the simulation system is set to the optimal parameter value, according to Table 1, when the water-light generation ratio γ is 5 / 3, 6 / 4 and 7 / 1, the critical clearance angle of the system under the optimal parameters is and

[0157] Figure 11 ​The middle solid line represents the dynamic of the simulation system when the fault clearing angle is set to be close to the critical clearing angle, the system is close to critical stability under different water and light power generation ratios, with the increase of the photovoltaic power generation power and the decrease of the hydraulic power generation power, the critical clearing angle of the system increases, and the transient synchronous stability is enhanced. The dashed line in the figure represents the case that the system with γ of 6 / 4 is cleared at the power angle of and the system with γ of 7 / 1 is cleared at the power angle of , at this time, the system is out of synchronization. It can be seen that the optimization and setting scheme of the current limiting control parameter of the new energy converter disclosed in the patent can be applied to the scene of different water and light power generation ratios.

[0158] In summary, the transient synchronous stability analysis method considering current limiting and the related device, based on the Thevenin theorem, derive the transmission power equation of the sending-out system during the fault, and then derive the critical clearing angle of the system, quantitatively analyze the influence of the control parameter and the water and light power generation ratio on the transient synchronous stability of the system, and finally propose a limiting control parameter setting scheme to improve the transient synchronous stability of the system. The water and light power generation ratio setting method proposed in the research results can effectively improve the transient synchronous stability of the system, and is expected to provide certain theoretical guidance for the stable operation of future new energy power systems.

[0159] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above functional units and modules is exemplified, and in actual application, the above functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated in one processing unit, or each unit can be physically present, or two or more units can be integrated in one unit. The above integrated unit can be realized in the form of hardware or software. In addition, the specific names of each functional unit and module are only for easy distinction, and do not limit the protection scope of the application. The specific working process of the units and modules in the above system can refer to the corresponding process in the foregoing method embodiments, which will not be repeated here.

[0160] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described or recorded in a certain embodiment can be referred to the related description of other embodiments.

[0161] Those skilled in the art can understand that the units and algorithm steps of each example described in combination with the embodiments disclosed in the present application can be realized in electronic hardware or in combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0162] In the embodiments provided by the present application, it should be understood that the disclosed apparatus / terminal and method can be implemented in other ways. For example, the apparatus / terminal embodiments described above are merely schematic. The division of the modules or units is merely a logical function division, and there can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed coupling or direct coupling or communication connection between the units can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or in other forms.

[0163] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e. they can be located in one place, or distributed on a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0164] In addition, each functional unit in each embodiment of the present application can be integrated into a processing unit, or each unit can exist physically independently, or two or more units can be integrated into one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0165] The integrated module / unit, if realized in the form of a software function unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on such understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of each method embodiment when executed by a processor. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or some intermediate forms, etc. The computer-readable medium can include any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the computer-readable medium can include or exclude contents according to the requirements of legislation and patent practice in the jurisdiction, for example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0166] The present application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus generate a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 The means for implementing the functions specified in one or more flows and / or blocks in the flowcharts and / or block diagrams. Figure 1 The means for implementing the functions specified in one or more flows and / or blocks in the flowcharts and / or block diagrams.

[0167] These computer program instructions can also be stored in a computer-readable memory capable of guiding a computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a product including instruction means, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The means for implementing the functions specified in one or more flows and / or blocks in the flowcharts and / or block diagrams. Figure 1 The means for implementing the functions specified in one or more flows and / or blocks in the flowcharts and / or block diagrams.

[0168] These computer program instructions can also be loaded into a computer or other programmable data processing devices, so that a series of operational steps are generated to realize the computer-implemented processes in the computer or other programmable devices, and the instructions executed in the computer or other programmable devices provide steps for implementing the functions specified in the flowchart Figure 1 or multiple flows and / or blocks Figure 1 or multiple blocks.

Claims

1. A method for transient stability analysis considering current limit, characterized in that, The method comprises the following steps: establishing a basic control structure of the hydroelectric power generation system and the photovoltaic power generation system, and determining transmission power characteristics during a transient state of the sending-out system; deducing an equation of active power sent out by the hydroelectric generator before fault removal based on the transmission power characteristics during the transient state of the sending-out system and taking into account current limiting control of the photovoltaic inverter and the flexible direct-current rectifier during the fault; deducing an analytical expression of a critical removal angle of the sending-out system based on the obtained equation of active power sent out by the hydroelectric generator before fault removal and using the equal-area rule; Based on the obtained analytical expression of the critical clearing angle of the sending-out system, the critical clearing angle is taken as the key indicator of the transient synchronous stability limit of the sending-out system to evaluate the influence of the saturated current angle parameter of the flexible HVDC converter and the water-light generation ratio on the transient stability of the sending-out system, and the ratio of the hydraulic power generation to the photovoltaic power generation of the water-light complementary power generation system under the steady state is γ The power coupling effect of the photovoltaic power generation system and the hydraulic generator unit makes the active power characteristic curve of the synchronous machine under the steady state deviate downward, the power angle of the system unstable equilibrium point is reduced, and the synchronous stability boundary of the sending-out system is reduced. For the system with constant mechanical power of the hydraulic generator unit, with the increase of the photovoltaic power generation, the value of the sending-out system continuously decreases, and the increase of the water-light generation ratio has an adverse effect on the transient synchronous stability of the system. The optimal parameter value of the saturated current angle of the converter in the sending-out system and the critical clearing angle of the sending-out system under the optimal parameter are: wherein, denotes the critical cut-off angle of the sending-out system under the optimal parameters ; P m is the input mechanical power of the synchronous machine; P s denotes the rated value of the total power of the water-light complementary power generation, denotes the critical cut-off angle, denotes the photovoltaic output power, denotes the active power tracking maximum power output by the photovoltaic power generation adopting the maximum power tracking control, denotes the saturation current angle, and respectively denote the water-power synchronous machine power angle corresponding to the stable equilibrium point and the unstable equilibrium point of the sending-out system when the photovoltaic inverter and the flexible rectifier current are not saturated, and are constants.

2. The method for transient stability analysis considering current limit according to claim 1, wherein, The basic control structure of the hydroelectric power generation system and the photovoltaic power generation system is as follows: where, δ g and ω g are the synchronous generator power angle and angular frequency, respectively; P m is the synchronous machine input mechanical power; T J is the synchronous machine inertia time constant; is the synchronous machine damping; ω n is the rated angular frequency; and are the dq components of the photovoltaic inverter output current, respectively; and are the current dq components reference values output by the current limiting loop; and are the power control outer loop output signals; is the inverter output current maximum amplitude; is the current limiting control loop saturation current angle parameter setting value, is the steady-state hydroelectric generator output power.

3. The method for transient stability analysis considering current limit according to claim 1, wherein, The equation of active power sent out by the hydroelectric generator before fault removal is as follows: wherein, represents the maximum power output of the hydroelectric unit during the fault when the fault point is at a distance of α from the PCC, represents the power angle of the synchronous machine, represents the saturation current angle.

4. The method for transient stability analysis considering current limit according to claim 3, wherein, The active power of the input direct-current system of the flexible direct-current rectifier is represented as follows: wherein, Vpcc represents the voltage at the PCC point, Vcr represents the voltage of the rectifier, Xcr represents the transfer reactance of the rectifier to the PCC point, δpcc represents the power angle at the PCC point.

5. The method for transient stability analysis considering current limit according to claim 1, wherein, The analytical expression of the critical removal angle of the sending-out system is as follows: wherein, denotes the saturation current angle, denotes the power angle of the hydro-synchronous machine corresponding to the stable equilibrium point of the sending system when the photovoltaic inverter and the flexible rectifier current are not saturated, denotes a monotonic function about the critical cut-off angle of the sending system.

6. A system for transient stability analysis with current limit consideration, characterized in that, The method comprises the following steps: a construction module, which establishes a basic control structure of the hydroelectric power generation system and the photovoltaic power generation system, and determines transmission power characteristics during a transient state of the sending-out system; a first deduction module, which deduces an equation of active power sent out by the hydroelectric generator before fault removal based on the transmission power characteristics during the transient state of the sending-out system and taking into account current limiting control of the photovoltaic inverter and the flexible direct-current rectifier during the fault; a second deduction module, which deduces an analytical expression of a critical removal angle of the sending-out system based on the equation of active power sent out by the hydroelectric generator before fault removal and using the equal-area rule; The analysis module is based on the analytical expression of the critical cut-off angle of the sending-out system, takes the critical cut-off angle as the key index of the transient synchronous stability limit of the sending-out system, evaluates the influence of the saturated current angle parameter value of the photovoltaic and flexible DC converter and the water-light generation ratio on the transient stability of the sending-out system, and the ratio of the hydraulic power generation to the photovoltaic power generation of the water-light complementary power generation system under the steady state is γ The power coupling effect of the photovoltaic power generation system and the hydroelectric generating set makes the active power characteristic curve of the synchronous machine under the steady state deviate downward, the power angle of the system unstable equilibrium point is reduced, and the synchronous stability boundary of the sending-out system is reduced. For the system with constant mechanical power of the hydroelectric generating set, with the increase of the photovoltaic power generation, the value of the power angle is continuously reduced, and the increase of the water-light generation ratio has an adverse effect on the transient synchronous stability of the system. The optimal parameter value of the saturated current angle of the converter in the sending-out system and the critical cut-off angle of the sending-out system under the optimal parameter are: wherein, denotes the critical cut-off angle of the sending-out system under the optimal parameters ; P m is the input mechanical power of the synchronous machine; P s denotes the rated value of the total power of the water-light complementary power generation, denotes the critical cut-off angle, denotes the photovoltaic output power, denotes the active power tracking maximum power output by the photovoltaic power generation using the maximum power tracking control, denotes the saturation current angle, and respectively denote the water-power synchronous machine power angle corresponding to the stable equilibrium point and the unstable equilibrium point of the sending-out system when the current of the photovoltaic inverter and the flexible rectifier is not saturated, and are constants.

7. A chip, characterized in that: a memory having a computer program stored thereon; a processor configured to execute the computer program in the memory to implement the steps of the method according to any one of claims 1-5.

8. An electronic device, comprising: The chip according to claim 7 is included.

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