Method and system for calculating new energy bearing capacity of isolated network system

Abstract

The invention discloses a method and system for calculating the new energy bearing capacity of an isolated network system, and relates to the technical field of new energy bearing of the isolated network system.The method comprises the steps that a frequency response model of a single synchronous generator is established, and the relation between torque and rotating speed deviation is described; aggregating a plurality of synchronous generator models to form a system frequency response model, and introducing speed regulator feedback; the frequency regulation effect of the load is considered, and a system frequency response model is perfected; analyzing the influence of wind and light new energy access on system frequency response, and calculating a key dynamic frequency index; and deducing the relationship between the access proportion of the wind-solar new energy and the lowest point of the frequency, and estimating the critical proportion allowed to access. According to the method, the power access critical proportion interval of the wind and light new energy of the island system can be solved by utilizing the lowest frequency variation delta fnair obtained by simulation and the power proportion eta of the wind and light new energy, and the method has practicability and rapidity in engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy bearing capacity of an isolated grid system, and in particular to a method and system for calculating the new energy bearing capacity of an isolated grid system. Background Art

[0002] The frequency stability of power systems with a high proportion of renewable energy is facing severe challenges. On the one hand, wind and solar renewable energy generation has the characteristics of randomness, volatility, and strong intermittency, making the active power balance of the system increasingly difficult. According to statistics, the maximum daily power fluctuation of renewable energy in my country has exceeded 100 million kW, and the power change on a minute-level time scale can reach about 1% of the total installed capacity; on the other hand, power systems with a high proportion of renewable energy have low inertia levels, poor frequency regulation capabilities, and weak anti-interference. This feature is more obvious for isolated grid systems that lack contact with the outside world.

[0003] Assuming that the proportion of wind and solar energy in all units in the isolated grid system is η, according to theoretical analysis, the maximum frequency change Δf of the isolated grid system after a fault impact is nadir The product of the synchronous machine ratio (1-η) is a constant. Based on this theory, a practical engineering method can be designed to quickly determine the proportion of wind and solar renewable energy power allowed to be connected to the system, thereby ensuring that the isolated grid system can operate stably after a fault impact.

[0004] The system frequency response models currently established generally only consider the output of synchronous generators, and rarely involve the frequency response characteristics corresponding to different wind and solar energy feed-in powers in the case of an isolated grid. At the same time, there is also a lack of a calculation method that can quickly solve the wind and solar energy carrying capacity that is practical in engineering. Therefore, the present invention proposes a method for calculating the maximum wind and solar energy receiving ratio based on the frequency stability constraint of the isolated grid system. Using this calculation method, the power ratio of wind and solar energy that the isolated grid system is allowed to access can be quickly and conveniently calculated, and the carrying capacity of the isolated grid system for new energy can be quantitatively evaluated, which is practical and innovative in engineering. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the problem to be solved by the present invention is: how to solve the problem that the existing system frequency response model generally only considers the output of the synchronous generator, and rarely involves the corresponding frequency response characteristics when different wind and solar energy new energy feed-in powers are in the case of an isolated grid.

[0007] To solve the above technical problems, the present invention provides the following technical solutions: a method for calculating the new energy carrying capacity of an isolated grid system, comprising: establishing a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation; aggregating multiple synchronous generator models to form a system frequency response model, and introducing governor feedback; considering the frequency regulation effect of the load to improve the system frequency response model; analyzing the impact of wind and solar new energy access on the system frequency response, and calculating key dynamic frequency indicators; deriving the relationship between the wind and solar new energy access ratio and the lowest frequency point, and estimating the critical ratio allowed for access.

[0008] As a preferred solution of the method for calculating the new energy carrying capacity of an isolated grid system described in the present invention, the relationship between the torque and the speed deviation is expressed as:

[0009]

[0010] Where, ΔT mi and ΔT ei are the mechanical torque and electromagnetic torque increments of the synchronous generator, M i is the inertia time of the synchronous machine, Δω ri is the per-unit speed deviation of the synchronous machine, s is the symbol of the transfer function; according to the conversion relationship between power and torque, the relationship between the unbalanced power and unbalanced torque of the synchronous machine in the per-unit form is derived, which is expressed as:

[0011] ΔP mi -ΔP ei =ΔT mi -ΔT ei

[0012] Then the relationship between the unbalanced power and speed of the synchronous machine is expressed as:

[0013]

[0014] Among them, ΔP mi and ΔP ei are the mechanical power and electromagnetic power of the synchronous generator respectively.

[0015] As a preferred solution of the method for calculating the new energy carrying capacity of an isolated grid system described in the present invention, the system-level frequency response model includes: if the isolated grid system has n synchronous generators, and Δω r1 =Δω r2 =…=Δω rn =Δω r , the aggregate form is expressed as:

[0016]

[0017] The governor feedback includes: if all the isolated grid systems are reheated steam turbine generator sets, ignoring the small time constants of the governor and the steam chamber, and only retaining the turbine reheating time constant, the governor frequency regulation effect is obtained, which is expressed as:

[0018]

[0019] Among them, K mi is the effective gain factor, F Hi is the high pressure cylinder power proportional coefficient, T Ri is the turbine reheat time constant, R i is the speed regulator's adjustment factor.

[0020] As a preferred solution of the method for calculating the new energy carrying capacity of an isolated grid system described in the present invention, the frequency regulation effect of the load includes obtaining an aggregate model of the speed regulator represented as:

[0021]

[0022] Among them, [K m ,T R ,F H ] is obtained by weighting according to the proportional coefficient, and the proportional coefficient is expressed as:

[0023]

[0024] The system frequency response model taking into account the speed regulator is obtained, and the system frequency response model taking into account the frequency regulation effect of the load is obtained.

[0025] As a preferred solution of the method for calculating the new energy carrying capacity of an isolated grid system described in the present invention, the impact of wind and solar new energy access on the system frequency response includes if the proportion of wind and solar new energy access to the isolated grid system is expressed as:

[0026]

[0027] Among them, P W and P G are the active power of wind and solar energy and the active power of synchronous generators, respectively, and the proportion of synchronous generators is 1-η; in a multi-unit large-capacity power system, if the active power of the synchronous generator matches the inertia and frequency regulation capability of the synchronous generator; under different proportions, ΔP d unchanged, if wind and solar energy do not participate in frequency adjustment, ΔP W =0,M T becomes 1-η times of the original value, K L unchanged, ΔP m becomes 1-η times of the original value, but the remaining adjustment parameter T R 、F Hand K m constant.

[0028] As a preferred solution of the method for calculating the new energy carrying capacity of an isolated grid system described in the present invention, wherein: the calculation of the key dynamic frequency index includes when no wind and solar new energy is included, the system frequency response is expressed as:

[0029]

[0030]

[0031] Among them, ω n is the undamped natural oscillation frequency, ζ is the damping ratio; ΔP d The step disturbance is expressed as:

[0032]

[0033] Among them, P Step is the active step amplitude per unit value with the sum of the rated capacities of all synchronous generators when no wind and solar energy is connected as the reference value; the response of the system frequency response model is expressed as:

[0034]

[0035] The time domain analytical solution is expressed as:

[0036]

[0037] Among them, ω r is the damped oscillation frequency; the key dynamic frequency indicators include the initial frequency change rate, the lowest frequency point time, the lowest frequency change and the steady-state frequency. According to the frequency domain and time domain solutions of the system frequency response, the relationship between the key dynamic frequency indicators and the proportion of wind and solar energy is obtained, which is expressed as:

[0038]

[0039] Among them, t nadir is the time when the frequency drops to the lowest point, Δf nadir is the frequency change at the lowest frequency point.

[0040] As a preferred solution of the method for calculating the new energy carrying capacity of an isolated grid system described in the present invention, the relationship between the wind and solar new energy access ratio and the lowest frequency point includes t nadir and Δf nadir is the natural oscillation frequency ω n , Damping ratio and damped oscillation frequency ω r The function of wind and solar energy ratio η and t nadir and Δf nadirThe relationship between η and ω n , and ω r The relationship between Δf and Δf is obtained. If the proportion of wind and solar energy changes, the natural oscillation frequency remains unchanged, the damping ratio remains unchanged, and the damped oscillation frequency remains unchanged, then the time of the lowest frequency point remains unchanged. If the proportion of wind and solar energy access is large, Δf nadir The higher the wind and solar energy access ratio is, the lower the frequency will be. The lower the frequency will be, the lower the frequency will be. The lower the frequency threshold is ...

[0041] Δf security =1Hz

[0042]

[0043] That is the critical ratio estimation formula. If the frequency deviation is allowed to be small, the proportion of wind and solar energy connected is small. If the unbalanced power allowed to the isolated grid system is large, the proportion of wind and solar energy connected is small. If the original frequency regulation capability of the isolated grid system is poor, the proportion of wind and solar energy connected is small.

[0044]

[0045] Due to the adjustment coefficient R, the effective gain coefficient K m It is only related to the synchronous machine in the isolated grid system. When the proportion of wind and solar energy changes, K nadir unchanged, P Step The active step amplitude standard value is based on the sum of the rated capacity of all synchronous generators when no wind and solar energy is connected. It will not change with the change of the proportion of wind and solar energy. The minimum frequency change Δf nadir The product of the remaining synchronous machine ratio 1-η will be equal to the constant K.

[0046] Another object of the present invention is to provide a system for calculating the new energy carrying capacity of an isolated grid system, which can solve the problem of calculating the new energy carrying capacity of an isolated grid system by constructing a calculation system for the new energy carrying capacity of an isolated grid system.

[0047] To solve the above technical problems, the present invention provides the following technical solutions: a calculation system for the new energy carrying capacity of an isolated grid system, comprising a model building module, an aggregation module, a model improvement module, an access module and a result output module; the model building module is used to establish a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation; the aggregation module is used to aggregate multiple synchronous generator models to form a system frequency response model and introduce governor feedback; the model improvement module is used to consider the frequency regulation effect of the load and improve the system frequency response model; the access module is used to analyze the impact of wind and solar new energy access on the system frequency response and calculate key dynamic frequency indicators; the result output module is used to derive the relationship between the wind and solar new energy access ratio and the lowest frequency point and estimate the critical ratio allowed for access.

[0048] A computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for calculating the new energy carrying capacity of an isolated grid system as described above are implemented.

[0049] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for calculating the new energy carrying capacity of an isolated grid system as described above.

[0050] The beneficial effect of the present invention is that the method for calculating the new energy carrying capacity of an isolated grid system provided by the present invention only needs to use the minimum frequency change Δf obtained by simulation nadir By combining the wind-solar renewable energy power ratio η with the critical wind-solar renewable energy power access ratio range of the isolated grid system, it is practical, rapid and innovative in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0052] Figure 1 A flow chart of a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0053] Figure 2 A synchronous machine aggregation model diagram of a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0054] Figure 3A governor feedback link diagram of a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0055] Figure 4 A governor aggregation model diagram of a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0056] Figure 5 A system frequency response model diagram taking into account a speed regulator and a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0057] Figure 6 A system frequency response model diagram of a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0058] Figure 7 A schematic diagram of different proportions of wind and solar energy in a method for calculating the new energy carrying capacity of an isolated grid system provided in the first embodiment of the present invention.

[0059] Figure 8 A frequency response model diagram of a system with different proportions of wind and solar energy, providing a method for calculating the new energy carrying capacity of an isolated grid system in the first embodiment of the present invention.

[0060] Fig. 9 A structural diagram of a system for calculating the new energy carrying capacity of an isolated grid system provided in accordance with a second embodiment of the present invention.

[0061] Fig.10 A curve diagram showing the relationship between the minimum frequency change and the wind power ratio of a method for calculating the new energy carrying capacity of an isolated grid system provided in the third embodiment of the present invention.

[0062] Fig.11 A graph showing the relationship between the minimum frequency change and the photovoltaic ratio of a method for calculating the new energy carrying capacity of an isolated grid system provided in the fourth embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0064] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0065] Example 1, reference Figures 1 to 8, which is the first embodiment of the present invention, provides a method for calculating the renewable energy carrying capacity of an isolated grid system, including: establishing a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation; aggregating multiple synchronous generator models to form a system frequency response model, and introducing governor feedback; considering the frequency regulation effect of the load to improve the system frequency response model; analyzing the impact of wind and solar renewable energy access on the system frequency response, and calculating key dynamic frequency indicators; deriving the relationship between the wind and solar renewable energy access ratio and the lowest frequency point, and estimating the critical ratio allowed for access.

[0066] By establishing an island system frequency response model that takes into account the proportion of wind and solar power, a minimum frequency change Δf obtained by simulation is obtained. nadir And the wind and solar energy power ratio η, the method to solve the critical proportion interval of wind and solar energy power access to the isolated island system can be solved.

[0067] In the actual system, the proportion of η 1 The simulation results show the minimum frequency change Δf nadir1 , calculate the constant K 1 =Δf nadir1 ×(1-η 1 ), draw a curve between the access ratio and the minimum frequency change.

[0068] In the actual system, the proportion of η 2 The simulation results show the minimum frequency change Δf nadir2 , calculate the constant K 2 =Δf nadir2 ×(1-η 2 ), draw a curve between the access ratio and the minimum frequency change.

[0069] The intersection point of the frequency safety threshold and the two curves is the estimated critical ratio interval.

[0070] S1. Establish a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation.

[0071] The derivation process of the system frequency response model is as follows.

[0072] For a single synchronous generator, we have:

[0073]

[0074] Where, ΔT mi and ΔT ei are the mechanical torque and electromagnetic torque increments of the synchronous generator, M i is the inertia time of the synchronous machine, Δω riis the speed deviation per unit value of the synchronous machine, and s is the sign of the transfer function.

[0075] According to the conversion relationship between power and torque, the approximate relationship between the unbalanced power and unbalanced torque of the synchronous machine in per-unit form can be derived:

[0076] ΔP mi -ΔP ei =ΔT mi -ΔT ei (2)

[0077] Among them, ΔP mi and ΔP ei are the mechanical power and electromagnetic power of the synchronous generator respectively. Then we can get the relationship between the unbalanced power and the speed of the synchronous machine:

[0078]

[0079] S2. Aggregate multiple synchronous generator models to form a system frequency response model and introduce governor feedback.

[0080] Assume that there are n synchronous generators in the system and Δω r1 =Δω r2 =… =Δω rn =Δω r , and get the aggregate form:

[0081]

[0082] In the formula Block diagram Figure 2 shown.

[0083] Assuming that all the systems are reheat steam turbine generator sets, ignoring the smaller time constants of the governor and steam chamber, and only retaining the turbine reheat time constant, the feedback block diagram of the governor frequency regulation is obtained as follows: Figure 3 As shown:

[0084]

[0085] Among them, K mi is the effective gain factor, F Hi is the high pressure cylinder power proportional coefficient, T Ri is the turbine reheat time constant, R i is the speed regulator's adjustment factor.

[0086] Furthermore, the aggregate model of the speed regulator is obtained as Figure 4 As shown:

[0087]

[0088] In the formula, [K m ,T R ,F H ]According to the proportionality factor Weighted, in K m For example,

[0089] The system frequency response model taking into account the speed regulator is as follows Figure 5 shown.

[0090] Taking into account the frequency regulation effect of the load, the system frequency response model is obtained as follows: Figure 6 As shown. is the aggregate frequency response factor of the load.

[0091] When the sum of the rated capacities of the entire system is selected as the reference capacity, the values ​​of the above power, time constant and regulation coefficient are equivalent to the typical parameters of a single synchronous machine.

[0092] S3. Consider the frequency regulation effect of the load and improve the system frequency response model.

[0093] Schematic diagram of power system with different proportions of wind and solar energy Figure 7 As shown below. Assume that the proportion of wind and solar energy access system is:

[0094]

[0095] Among them, P W and P G They are the active power of wind and solar energy and the active power of synchronous machines. The proportion of synchronous machines is 1-η.

[0096] In a multi-unit large-capacity power system, it is assumed that the active power of the synchronous generator and the inertia and frequency regulation capability of the synchronous generator match each other.

[0097] Under different proportions, ΔP d unchanged, assuming that wind and solar energy do not participate in frequency adjustment, ΔP W =0,M T becomes 1-η times of the original value, K L unchanged, ΔP m Right now becomes 1-η times of the original value, but the remaining adjustment parameter T R 、F H and K m Therefore, the system frequency response model under different proportions of wind and solar energy is as follows Figure 8 shown.

[0098] S4. Analyze the impact of wind and solar energy access on system frequency response and calculate key dynamic frequency indicators.

[0099] according to Figure 6 , it can be concluded that when there is no wind and solar energy, the system frequency response is:

[0100]

[0101] Where:

[0102]

[0103] are the undamped natural oscillation frequency and the damping ratio.

[0104] Let ΔP d The step disturbance is expressed as:

[0105]

[0106] Among them, P Step is the active step amplitude per unit value with the sum of the rated capacities of all synchronous generators as the reference value when no wind and solar energy is connected. Then the response of the system frequency response model is:

[0107]

[0108] The time domain analytical solution is:

[0109]

[0110] Where:

[0111]

[0112] Among them, ω r is the damped oscillation frequency.

[0113] Based on the frequency domain and time domain solutions of the system frequency response, the relationship between the key dynamic frequency indicators and the proportion of wind and solar energy can be obtained. The key dynamic frequency indicators include: initial frequency change rate (Rate of Change of Frequency, ROCOF), frequency minimum point time (t nadir ), minimum frequency change (Δf nadir ), steady-state frequency (Δf ss ) four items.

[0114] According to the initial value theorem and final value theorem of Laplace transform, we can get:

[0115]

[0116] After joining Fengguang New Energy, you will have:

[0117] M T·new =M T (1-η) (15)

[0118]

[0119] That is, the higher the wind-PV DC ratio, the greater the ROCOF.

[0120]

[0121] After adding wind power photovoltaic DC, there are:

[0122]

[0123] That is, the larger the proportion of wind power and photovoltaic DC, the greater the ss The bigger.

[0124] make:

[0125]

[0126] We can get:

[0127]

[0128] Among them, t nadir is the time when the frequency drops to the lowest point, Δf nadir is the frequency change at the lowest frequency point.

[0129] S5. Derive the relationship between the access ratio of wind and solar energy and the lowest frequency point, and estimate the critical ratio for access.

[0130] From equations (21) and (22), we can see that t nadir and Δf nadir is the natural oscillation frequency ω n , Damping ratio and damped oscillation frequency ω r To obtain the ratio of wind and solar energy to t nadir and Δf nadir First, we need to analyze the relationship between η and ω n , and ω r The relationship between.

[0131] The following analysis shows the effect of the change in the proportion of wind and solar energy on ω n impact.

[0132] According to (7)(15)(18), after the integration of wind and solar energy:

[0133]

[0134] When using typical parameters, K L R≈2×0.05=0.1≈0, so

[0135]

[0136] It can be approximately assumed that when the proportion of wind and solar energy changes, the natural oscillation frequency remains unchanged.

[0137] The following analysis shows the effect of the change in the proportion of wind and solar energy on impact.

[0138] According to the approximate relationship K L R≈2×0.05=0.1≈0, so:

[0139]

[0140] It can be approximately assumed that when the proportion of wind and solar energy changes, the damping ratio remains unchanged.

[0141] It can be seen from formula (12) that when the proportion of wind and solar energy changes, the damped oscillation frequency remains approximately unchanged.

[0142] It can be seen from formula (21) that when the proportion of wind and solar energy changes, the time of the lowest frequency point remains approximately unchanged.

[0143] According to formula (22), we define:

[0144]

[0145] When the proportion of wind and solar energy changes, K nadir Approximately unchanged, and then:

[0146]

[0147] When K L When R≈2×0.05=0.1≈0, we have:

[0148]

[0149] That is, the greater the proportion of wind and solar energy access, the greater the nadir The larger it is, the more the proportion of wind and solar energy access is inversely proportional to the lowest frequency point.

[0150] According to the relationship between the lowest frequency point and the proportion of wind and solar energy access, the greater the proportion of wind and solar energy access, the lower the lowest frequency point. The threshold value of the frequency lower limit is set to not trigger the low-frequency load reduction action, which is:

[0151] Δf security =1Hz (40)

[0152]

[0153] Formula (42) is the critical ratio estimation formula. The smaller the allowable frequency deviation, the smaller the proportion of wind and solar energy that can be connected. The larger the unbalanced power that the system can withstand, the smaller the proportion of wind and solar energy that can be connected. The worse the original frequency regulation capability of the system, the smaller the proportion of wind and solar energy that can be connected.

[0154] According to formula (41), we have:

[0155]

[0156] Due to the adjustment coefficient R, the effective gain coefficient K m It is only related to the synchronous machine in the system. From formula (26), it can be seen that when the proportion of wind and solar energy changes, K nadir Approximately unchanged; P Step The active step amplitude standard value is based on the sum of the rated capacities of all synchronous generators when no wind and solar energy is connected. It will not change with the change of the proportion of wind and solar energy. Therefore, the minimum frequency change Δf nadir The product of the remaining synchronous machine ratio (1-η) will be equal to the constant K.

[0157] Example 2, reference Fig. 9 , which is the second embodiment of the present invention, is different from the previous embodiment in that it provides a calculation system for the new energy carrying capacity of an isolated grid system, including: a model building module 100, an aggregation module 200, a model improvement module 300, an access module 400 and a result output module 500.

[0158] The model building module 100 is used to establish a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation.

[0159] The aggregation module 200 is used to aggregate multiple synchronous generator models to form a system frequency response model and introduce governor feedback.

[0160] The model improvement module 300 is used to consider the frequency regulation effect of the load and improve the system frequency response model.

[0161] The access module 400 is used to analyze the impact of wind and solar energy access on the system frequency response and calculate key dynamic frequency indicators.

[0162] The result output module 500 is used to derive the relationship between the wind and solar energy access ratio and the lowest frequency point, and estimate the critical ratio for allowing access.

[0163] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0164] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0165] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0166] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0167] Example 3, reference Fig.10 , which is the third embodiment of the present invention, and which is different from the first two embodiments in that it is used to verify and illustrate the technical effects adopted in the present invention, so as to verify the real effects of this method.

[0168] In the IEEE-140 node system, when the proportion of wind power is 20%, Δf nadir1 =0.50Hz, calculated K 1 =0.40; when the proportion of wind power is 30%, Δf nadir2 =0.52Hz, calculated K 2 =0.364; draw two curves showing the relationship between the change in the lowest frequency point and the proportion of wind power access, such as Fig.10 As shown in Figure 2, the critical ratio interval estimated from the intersection of the frequency safety threshold 1 Hz and the two curves is [0.60, 0.64], which is very close to the true value of 0.65.

[0169] Example 4, reference Fig.11 , which is the fourth embodiment of the present invention, is used to verify the technical effects adopted in the present invention and to verify the real effects of this method.

[0170] In the IEEE-140 node system, when the photovoltaic ratio is 20%, Δf nadir1 =0.53Hz, calculated K 1 =0.424; when the photovoltaic ratio is 30%, Δf nadir2 =0.57Hz, calculated K 2 = 0.399; draw two curves showing the relationship between the change in the lowest frequency point and the photovoltaic access ratio, such as Fig.11 As shown in Figure 2, the critical ratio interval estimated from the intersection of the frequency safety threshold 1 Hz and the two curves is [0.58, 0.60], which is very close to the true value of 0.62.

[0171] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for calculating the new energy carrying capacity of an isolated grid system, characterized by: include, Establish a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation; Aggregate multiple synchronous generator models to form a system frequency response model and introduce governor feedback; Consider the frequency regulation effect of the load and improve the system frequency response model; Analyze the impact of wind and solar energy access on system frequency response and calculate key dynamic frequency indicators; The relationship between the access ratio of wind and solar energy and the lowest frequency point is derived, and the critical ratio for access is estimated.

2. The method for calculating the new energy carrying capacity of an isolated grid system according to claim 1, characterized in that: The relationship between the torque and the speed deviation is expressed as, Where, ΔT mi and ΔT ei are the mechanical torque and electromagnetic torque increments of the synchronous generator, M i is the inertia time of the synchronous machine, Δω ri is the speed deviation per unit value of the synchronous machine, s is the sign of the transfer function; According to the conversion relationship between power and torque, the relationship between the unbalanced power and unbalanced torque of the synchronous machine in per-unit form is derived and expressed as: ΔP mi -ΔP ei =ΔT mi -ΔT ei Then the relationship between the unbalanced power and speed of the synchronous machine is expressed as: Among them, ΔP mi and ΔP ei are the mechanical power and electromagnetic power of the synchronous generator respectively.

3. The method for calculating the new energy carrying capacity of an isolated grid system according to claim 2, characterized in that: The system-level frequency response model includes the following: if there are n synchronous generators in the isolated grid system, and Δω r1 =Δω r2 =…=Δω rn =Δω r , the aggregate form is expressed as, The governor feedback includes if all the isolated grid systems are reheated steam turbine generator sets, ignoring the small time constants of the governor and the steam chamber, and only retaining the turbine reheating time constant, the governor frequency regulation effect is obtained, which is expressed as: Among them, K mi is the effective gain factor, F Hi is the high pressure cylinder power proportional coefficient, T Ri is the turbine reheat time constant, R i is the speed regulator's adjustment factor.

4. The method for calculating the new energy carrying capacity of an isolated grid system according to claim 3, characterized in that: The frequency regulation effect of the load includes obtaining the aggregate model of the speed regulator as: Among them, [K m ,T R ,F H ] is obtained by weighting according to the proportional coefficient, and the proportional coefficient is expressed as, The system frequency response model taking into account the speed regulator is obtained, and the system frequency response model taking into account the frequency regulation effect of the load is obtained.

5. The method for calculating the new energy carrying capacity of an isolated grid system according to claim 4, characterized in that: The impact of wind and solar energy access on system frequency response includes: if the proportion of wind and solar energy access to the isolated grid system is expressed as: Among them, P W and P G They are the active power of wind and solar energy and the active power of synchronous machines, and the proportion of synchronous machines is 1-η; In a multi-unit large-capacity power system, if the active power of the synchronous generator matches the inertia and frequency regulation capability of the synchronous generator; Under different proportions, ΔP d unchanged, if wind and solar energy do not participate in frequency adjustment, ΔP W =0,M T becomes 1-η times of the original value, K L unchanged, ΔP m becomes 1-η times of the original value, but the remaining adjustment parameter T R 、F H and K m constant.

6. A method for calculating the new energy carrying capacity of an isolated grid system as claimed in claim 5, characterized in that: The calculation of the key dynamic frequency index includes that when there is no wind and solar energy, the system frequency response is expressed as: Among them, ω n is the undamped natural oscillation frequency, ζ is the damping ratio; ΔP d The step disturbance is expressed as, Among them, P Step It is the unit value of the active step amplitude with the sum of the rated capacities of all synchronous generators when no wind and solar energy is connected as the reference value; Then the response of the system frequency response model is expressed as, The time domain analytical solution is expressed as, Among them, ω r is the damped oscillation frequency; The key dynamic frequency indicators include the initial frequency change rate, the lowest frequency point time, the lowest frequency change and the steady-state frequency. According to the frequency domain and time domain solutions of the system frequency response, the relationship between the key dynamic frequency indicators and the proportion of wind and solar energy is obtained, which is expressed as: Among them, t nadir is the time when the frequency drops to the lowest point, Δf nadir is the frequency change at the lowest frequency point.

7. The method for calculating the new energy carrying capacity of an isolated grid system according to claim 6, characterized in that: The relationship between the wind and solar energy access ratio and the lowest frequency point includes t nadir and Δf nadir is the natural oscillation frequency ω n , Damping ratio and damped oscillation frequency ω r The function of wind and solar energy ratio η and t nadir and Δf nadir The relationship between η and ω n , and ω r The relationship between and shows that if the proportion of wind and solar energy changes, the natural oscillation frequency remains unchanged, the damping ratio remains unchanged, and the damped oscillation frequency remains unchanged, then the time of the lowest frequency point remains unchanged; The proportion of wind and solar energy access is large, Δf nadir The access ratio of wind and solar energy is inversely proportional to the lowest frequency point; According to the relationship between the lowest frequency point and the proportion of wind and solar energy access, the higher the proportion of wind and solar energy access, the lower frequency point is smaller. The threshold value of the lower frequency limit is set so as not to trigger the low-frequency load reduction action, which is expressed as, Δf security =1Hz That is the critical ratio estimation formula. If the frequency deviation is allowed to be small, the proportion of wind and solar energy connected is small. If the unbalanced power allowed to the isolated grid system is large, the proportion of wind and solar energy connected is small. If the original frequency regulation capability of the isolated grid system is poor, the proportion of wind and solar energy connected is small. Due to the adjustment coefficient R, the effective gain coefficient K m It is only related to the synchronous machine in the isolated grid system. When the proportion of wind and solar energy changes, K nadir unchanged, P Step The active step amplitude standard value is based on the sum of the rated capacity of all synchronous generators when no wind and solar energy is connected. It will not change with the change of the proportion of wind and solar energy. The minimum frequency change Δf nadir The product of the remaining synchronous machine ratio 1-η will be equal to the constant K.

8. A system using the method for calculating the new energy carrying capacity of an isolated grid system as claimed in any one of claims 1 to 7, characterized in that: It includes a model building module (100), an aggregation module (200), a model improvement module (300), an access module (400) and a result output module (500); The model building module (100) is used to establish a frequency response model of a single synchronous generator to describe the relationship between torque and speed deviation; The aggregation module (200) is used to aggregate multiple synchronous generator models to form a system frequency response model and introduce governor feedback; The model improvement module (300) is used to consider the frequency regulation effect of the load and improve the system frequency response model; The access module (400) is used to analyze the impact of wind and solar energy access on system frequency response and calculate key dynamic frequency indicators; The result output module (500) is used to derive the relationship between the wind and solar energy access ratio and the lowest frequency point, and estimate the critical ratio for allowing access.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the processor implements the steps of a method for calculating the new energy carrying capacity of an isolated grid system according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of a method for calculating the new energy carrying capacity of an isolated grid system according to any one of claims 1 to 7 are implemented.

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