High-proportion renewable energy power grid low-frequency load shedding method and control device

Abstract

The invention discloses a low-frequency load shedding method for a high-proportion renewable energy power grid. The method comprises the steps of obtaining first and last round frequency action values, a total round of a low-frequency load shedding scheme and action delay of each round; setting a low-frequency load shedding capacity and a frequency setting value of each round; acquiring a frequency change rate during initial disturbance of the power grid; when each round of low-frequency load shedding is carried out, if the frequency drop amount is greater than the current-round frequency setting value, the current-round load shedding amount is determined according to the minimum load shedding risk, and otherwise, the low-frequency load shedding is ended; and after each round of low-frequency load shedding is carried out, if the frequency change rate is greater than the frequency drop rate setting value of the current round, the current round of low-frequency load shedding is ended, otherwise, the next round of low-frequency load shedding is carried out. The method can effectively solve the influence on the reduction of the equivalent inertia of the system after the high-proportion renewable energy is accessed to the power grid, thereby preventing the excessive load shedding phenomenon during the low-frequency load shedding, reducing the load shedding risk, and guaranteeing the safe and stable operation of the power grid.

Description

Technical Field

[0001] The invention relates to a low-frequency load shedding method and a control device for a high-proportion renewable energy power grid, belonging to the technical field of low-frequency load shedding for power grids. Background Art

[0002] Energy shortages and environmental crises in the world's development process have led many countries to increase their efforts to develop renewable energy, but the high proportion of renewable energy in the power grid has brought new challenges to the safety and stability of the power grid. The equivalent inertia time constant of the power grid reflects the time required for the power system to reach a steady state with external interference when external interference occurs. When a power disturbance occurs in the power system, a system with a larger equivalent inertia time constant can better resist the impact of the disturbance and maintain the frequency stability of the system, while a high proportion of renewable energy reduces the equivalent inertia time constant of the power grid.

[0003] When the power system frequency drops due to a shortage between power generation and power load demand, the power grid needs to automatically remove a portion of the pre-arranged secondary loads in the system according to the magnitude of the frequency drop, so that the system active power tends to balance again and the frequency recovers. The low-frequency load reduction device is an automatic device that implements low-frequency load reduction measures. As the last line of defense for the safe and stable operation of the power system, low-frequency load reduction plays an important role in preventing the power grid from having a large power shortage that causes the system frequency to collapse and ensuring the reliability of power supply to important users.

[0004] However, the traditional low-frequency load reduction scheme does not take into account the proportion of each power structure in the system when setting the load removal capacity. When the proportion of renewable energy in the power grid is high, low-frequency load reduction is prone to cause over-load when a large power shortage occurs. This is because as new energy power electronic devices are connected to the power grid and replace conventional power sources, the equivalent moment of inertia of the system gradually decreases, resulting in the system's frequency response speed to power shortages. The frequency drops too fast, leaving less time for the system to react, and the frequency stability ability decreases, thus threatening the safety of the power grid. Therefore, the low-frequency load reduction method for power grids with a high proportion of renewable energy needs to reasonably arrange the frequency setting, time setting, and load removal during load reduction, so as to improve the adaptability of power grid systems with a high proportion of renewable energy to power shortages. Summary of the invention

[0005] The purpose of the present invention is to provide a low-frequency load reduction method and control device for a high-proportion renewable energy power grid, so as to solve the technical problem that the low-frequency load reduction method for a high-proportion renewable energy power grid in the prior art easily causes load overcutting when a large power shortage occurs.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for reducing load on a power grid with a high proportion of renewable energy at low frequency, wherein the power grid contains a high proportion of renewable energy, and the method comprises the following steps:

[0008] S1. Obtain the first and last frequency action values ​​set by the power grid, the total number of rounds N of the low-frequency load reduction scheme, and the action delay Δt of each round i ;

[0009] S2. Set the low frequency load reduction capacity P D , the i-th frequency setting value Δf i ;

[0010] S3. Detect and obtain the maximum frequency drop rate (df / dt) at the moment of initial disturbance of the power grid max ;

[0011] S4, judge i≤N and Is it true? If it is true, execute step S5. If it is not true, the low-frequency load reduction ends. ΔP i is the load removal amount of the i-th round;

[0012] S5, obtaining the difference between the rated frequency of the power grid and the power grid frequency at the i-th round as the frequency drop Δf;

[0013] S6. Determine Δf>Δf i Is it true? If true, the load shedding amount ΔP in the i-th round is determined based on the minimum risk cost of low-frequency load shedding. i And delay Δt i Execute load shedding ΔP i , if not established, the low-frequency load shedding ends;

[0014] S7, judgment (df / dt) max >df i Is it true? If it is true, the low-frequency load reduction ends. If it is not true, execute S8, where df i is the setting value of the frequency decrease rate of the i-th round;

[0015] S8. Update the value of i, that is, i=i+1, and continue to execute step S4.

[0016] The purpose of the present invention can also be further achieved by the following technical measures:

[0017] In the above-mentioned method for reducing load at low frequency in a high-proportion renewable energy grid, in step S2, the low-frequency load reduction capacity P D Equal to the maximum power shortage in the power grid.

[0018] In the above-mentioned method for low-frequency load shedding of a high-proportion renewable energy power grid, in step S2, the frequency setting value Δf of the i-th round of low-frequency load shedding is iSet to: {50-first round frequency action value + (i-1)(first round frequency action value-last round frequency action value) / (N-1)} Hz.

[0019] In the above-mentioned method for reducing load of a power grid with a high proportion of renewable energy, in step S6, the load amount ΔP is removed in each round. i The method to optimize and adjust to minimize the risk cost of low-frequency load shedding is:

[0020] S6a, load removal ΔP for round i i Take an initial value;

[0021] S6b, calculate the change value of the risk cost of low-frequency load shedding in the i-th round and the frequency setting value Δf in the i-th round i The ratio R i :

[0022]

[0023] Among them, C(ΔP i ,γ i ) is the risk cost of low-frequency load shedding in the i-th round, and is the load shedding amount ΔP in the i-th round i and the load removal cost factor γ i Function, C(ΔP i ,γ i )=γ i / ΔP i ; C′(ΔP i ,γ i ) is C(ΔP i ,γ i ) for ΔP i Derivatives to be found;

[0024] S6c, judge R i ≤0 is true, if true, then output the load removal amount ΔP i If it does not hold, let the iterative amount of load removal be ΔP i_last =ΔP i and execute S6d;

[0025] S6d, based on R i , update the load removal amount ΔP i :

[0026] ΔP i =ΔP i_last +m1·tanh(m2·R i )

[0027] Wherein m1 and m2 are preset adjustment coefficients, tanh() represents the hyperbolic tangent function, and then the process returns to step S6b to continue execution.

[0028] In the above-mentioned low-frequency load reduction method for a high-proportion renewable energy grid, the preset adjustment coefficients m1 and m2 need to meet the following requirements:

[0029] m1≤P D / tanh(m2·P D / Δf N );

[0030] Where Δf N It is the frequency setting value of the Nth round.

[0031] In the above-mentioned low-frequency load reduction method for a high-proportion renewable energy grid, the frequency reduction rate setting value df in the i-th round is i for:

[0032]

[0033] T s Represents the equivalent inertia time constant of the power grid.

[0034] A low-frequency load shedding control device for a high-proportion renewable energy grid comprises: a processor and a memory, wherein the processor communicates with the memory, and the memory is used to store executable instructions of the processor, and the processor is configured to execute any of the above-mentioned low-frequency load shedding methods for a high-proportion renewable energy grid by executing the executable instructions.

[0035] A low-frequency load shedding control device for a high-proportion renewable energy grid is provided, which executes any of the above-mentioned low-frequency load shedding methods for a high-proportion renewable energy grid, and the device comprises:

[0036] The parameter acquisition setting module is used to obtain the first and last frequency action values ​​set by the power grid, the total number of rounds N of the low-frequency load reduction scheme, and the action delay Δt of each round i ; Set the low frequency load reduction capacity P D , the i-th frequency setting value Δf i ; Detect and obtain the maximum frequency drop rate (df / dt) at the moment of initial disturbance of the power grid max ;

[0037] The low-frequency load shedding process control module is used to determine i≤N and Is it true? If so, the difference between the rated frequency of the power grid and the frequency of the power grid at the i-th round is obtained as the frequency drop amount Δf. If not, the low-frequency load shedding ends.

[0038] Determine Δf>Δf i Is it true? If true, the load shedding amount ΔP in the i-th round is determined based on the minimum risk cost of low-frequency load shedding. i And delay Δt i Execute load shedding ΔP i , if not established, the low-frequency load shedding ends;

[0039] Judgment (df / dt) max >df i Is it true? If so, the low-frequency load reduction ends. If not, the value of i is updated.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention determines whether the current round of low-frequency load reduction method is completed by the maximum frequency decrease rate at the initial stage of power disturbance, thereby reducing the removal time and preventing a sharp drop in frequency, overcoming the load over-cut phenomenon caused by the traditional low-frequency load reduction scheme not taking into account the proportion of each power supply structure in the system when setting the load removal capacity; by iteratively optimizing and calculating the value of the load removal amount in each round, Ri≤0 is made, thereby reducing the risk cost of load removal and ensuring the safe and stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of the low-frequency load reduction method for a high-proportion renewable energy power grid of the present invention;

[0042] Figure 2 This is a round-by-round optimization flow chart for the load removal amount in each round of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0044] like Figure 1 The figure shows a flow chart of a method for low-frequency load shedding in a power grid with a high proportion of renewable energy according to an embodiment of the present invention. The method for low-frequency load shedding in a power grid with a high proportion of renewable energy includes the following steps S1 to S8.

[0045] S1. Obtain the first and last round frequency action values, the total number of rounds N of the low-frequency load reduction scheme, and the action delay Δt of each round i ;

[0046] S2. Set the low frequency load reduction capacity P D , the i-th frequency setting value Δf i ;

[0047] S3, obtain the maximum frequency drop rate (df / dt) at the moment of initial disturbance of the power grid through detection max ;

[0048] S4, judge i≤N and Is it true? If it is true, execute step S5. If it is not true, the low-frequency load reduction ends. ΔP i is the load removal amount of the i-th round;

[0049] S5, obtaining the difference between the rated frequency of the power grid and the power grid frequency at the i-th round as the frequency drop Δf;

[0050] S6. Determine Δf>Δf i Is it true? If true, the load shedding amount ΔP in the i-th round is determined based on the minimum risk cost of low-frequency load shedding. i And delay Δt i Execute load shedding ΔP i , if not established, the low-frequency load shedding ends;

[0051] S7, judgment (df / dt) max >df i Is it true? If it is true, the low-frequency load reduction ends. If it is not true, execute S8, where df i is the setting value of the frequency decrease rate of the i-th round;

[0052] S8. Update the value of i, that is, i=i+1, and continue to execute S4.

[0053] Therefore, considering the impact of a high proportion of renewable energy in the power grid on the reduction of the equivalent inertia time constant of the power grid, after each round of low-frequency load shedding, it is judged whether the maximum decrease rate is less than the setting value of the frequency decrease rate of each round to prevent excessive load shedding during low-frequency load shedding.

[0054] In one embodiment of the present invention, the power grid has a maximum frequency drop rate at the initial moment when a large power shortage occurs, which is expressed as:

[0055]

[0056] From the above formula, we can know that when a large power disturbance occurs in the power grid, the power shortage of the system ΔP D The larger the frequency is, the greater the frequency drop slope is. The frequency drop rate when a large power shortage occurs can be obtained by the grid equivalent inertia time constant T s Then we can estimate ΔP D , where the grid equivalent inertia time constant T s It can be obtained by the following formula:

[0057]

[0058] Where k represents the proportion of renewable energy in the power grid, S g Represents the total installed capacity of the power grid, W f Represents the kinetic energy of the thermal power generator in the power grid.

[0059] Based on the above principle analysis, (df / dt)max can be used to determine whether the corresponding round has excessively removed the load, thereby terminating the corresponding round of low-frequency load reduction, that is, the i-th round of the power grid is terminated when the following inequality is satisfied.

[0060]

[0061] Among them, ΔP i represents the load shedding amount of the i-th round of low-frequency load shedding, S g represents the total installed capacity of the power grid, then the frequency drop rate setting value df in the i-th round is i It can be expressed as:

[0062]

[0063] Wherein, step S6 also includes optimizing and adjusting the load removal amount in each round, such as Figure 2 As shown, the risk cost of low-frequency load shedding is minimized, specifically:

[0064] S6a, load removal ΔP for the i-th round i Take an initial value;

[0065] S6b, calculate the change value of the i-th round load shedding risk cost and the i-th round frequency setting value Δf i The ratio R i :

[0066]

[0067] Among them, C(ΔP i ,γ i ) is the risk cost of low-frequency load shedding in the i-th round, and is the load shedding amount ΔP in the i-th round i and the load removal cost factor γ i Function, C(ΔP i ,γ i )=γ i / ΔP i ; C′(ΔP i ,γ i ) is C(ΔP i ,γ i ) for ΔP i Derivatives to be found;

[0068] S6c, judge R i ≤0 is true, if true, then output the load removal amount ΔP i If it does not hold, let the iterative amount of load removal be ΔP i_old =ΔP i and execute S6d;

[0069] S6d, based on R i , update the load removal amount ΔP i :

[0070] ΔP i =ΔP i_old +m1·tanh(m2·R i )

[0071] Where m1 and m2 are preset adjustment coefficients, tanh() represents the hyperbolic tangent function, and the process returns to step S6b to continue. The preset adjustment coefficients m1 and m2 need to satisfy:

[0072] m1≤P D / tanh(m2·P D / Δf N )

[0073] Where Δf N is the frequency setting value of the Nth round. Therefore, the values ​​of m1 and m2 can be set according to the above inequality.

[0074] The present invention includes a technical solution for a low-frequency load reduction control device for a high-proportion renewable energy grid. The control device includes: a processor and a memory. The processor communicates with the memory. The memory is used to store executable instructions of the processor. The processor is configured to execute any of the above-mentioned low-frequency load reduction methods for a high-proportion renewable energy grid by executing the executable instructions.

[0075] Another technical solution of the control device is: the low-frequency load shedding control device for a high-proportion renewable energy grid implements the above-mentioned low-frequency load shedding method for a high-proportion renewable energy grid, and the device comprises:

[0076] The parameter acquisition setting module is used to obtain the first and last frequency action values ​​set by the power grid, the total number of rounds N of the low-frequency load reduction scheme, and the action delay Δt of each round i ; Set the low frequency load reduction capacity P D , the i-th frequency setting value Δf i ; Detect and obtain the maximum frequency drop rate (df / dt) at the moment of initial disturbance of the power grid max ;

[0077] The low-frequency load shedding process control module is used to determine i≤N and Is it true? If so, the difference between the rated frequency of the power grid and the frequency of the power grid at the i-th round is obtained as the frequency drop amount Δf. If not, the low-frequency load shedding ends.

[0078] Determine Δf>Δf i Is it true? If true, the load shedding amount ΔP in the i-th round is determined based on the minimum risk cost of low-frequency load shedding. i And delay Δt i Execute load shedding ΔP i , if not established, the low-frequency load shedding ends;

[0079] Judgment (df / dt) max >df i Is it true? If so, the low-frequency load reduction ends. If not, the value of i is updated.

[0080] The embodiment of the present invention considers that after a high proportion of renewable energy is connected to the power grid, the system equivalent inertia is reduced, the system frequency reacts sensitively to power disturbances, and the frequency drops rapidly, so that low-frequency load shedding is very likely to overcut. The present invention determines whether the low-frequency load shedding method is completed by the maximum frequency drop rate at the initial stage of power disturbance, reduces the shedding time, prevents a sharp drop in frequency, and prevents overcutting of the power grid.

[0081] Any process or method description described in a flowchart or otherwise may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing specific logical functions or steps of a process, and the scope of the embodiments of the present invention includes other implementations that may not be in the order shown, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved.

[0082] 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, 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.

[0083] A person of ordinary skill in the art can understand that all or part of the steps carried by the method of the above-mentioned embodiment can be completed by instructing the relevant hardware through a program, and the program can be stored in a computer-readable storage medium, and the program, when executed, includes one or a combination of the steps of the method embodiment. In addition, each functional unit in each embodiment of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into one module. The above-mentioned integrated module can be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0084] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A method for low-frequency load reduction in a high-proportion renewable energy grid, characterized in that: The power grid contains a high proportion of renewable energy, and the method for low-frequency load reduction of the power grid with a high proportion of renewable energy comprises the following steps: S1. Obtain the first and last frequency action values ​​set by the power grid, the total number of rounds N of the low-frequency load reduction scheme, and the action delay Δt of each round i ; S2. Set the low frequency load reduction capacity P D , the i-th frequency setting value Δf i ; S3. Detect and obtain the maximum frequency drop rate (df / dt) at the moment of initial disturbance of the power grid max ; S4, judge i≤N and Is it true? If it is true, execute step S5. If it is not true, the low-frequency load reduction ends. ΔP i is the load removal amount of the i-th round; S5, obtaining the difference between the rated frequency of the power grid and the power grid frequency at the i-th round as the frequency drop Δf; S6. Determine Δf>Δf i Is it true? If true, the load shedding amount ΔP in the i-th round is determined based on the minimum risk cost of low-frequency load shedding. i And delay Δt i Execute load shedding ΔP i , if not established, the low-frequency load shedding ends; S7, judgment (df / dt) max >df i Is it true? If it is true, the low-frequency load reduction ends. If it is not true, execute S8, where df i is the setting value of the frequency decrease rate of the i-th round; S8. Update the value of i, that is, i=i+1, and continue to execute step S4.

2. A method for low-frequency load reduction in a high-proportion renewable energy grid according to claim 1, characterized in that: In step S2, the low frequency load reduction capacity P D Equal to the maximum power shortage in the power grid.

3. The method for low-frequency load reduction in a high-proportion renewable energy grid according to claim 1, characterized in that: In step S2, the frequency setting value Δf of the i-th round of low-frequency load shedding is i Set to: {50-first round frequency action value + (i-1)(first round frequency action value-last round frequency action value) / (N-1)} Hz.

4. The method for low-frequency load reduction in a high-proportion renewable energy grid according to claim 1, characterized in that: In step S6, the load removal amount ΔP is i The method to optimize and adjust to minimize the risk cost of low-frequency load shedding is: S6a, load removal ΔP for the i-th round i Take an initial value; S6b, calculate the change value of the risk cost of low-frequency load shedding in the i-th round and the frequency setting value Δf in the i-th round i The ratio R i : Among them, C(ΔP i ,γ i ) is the risk cost of low-frequency load shedding in the i-th round, and is the load shedding amount ΔP in the i-th round i and the load removal cost factor γ i Function, C(ΔP i ,γ i )=γ i ΔP i ; C′(ΔP i ,γ i ) is C(ΔP i ,γ i ) for ΔP i The derivative to be found; S6c, judge R i ≤0 is true, if true, then output the load removal amount ΔP i If it does not hold, let the iterative amount of load removal be ΔP i_last =ΔP i and execute S6d; S6d, based on R i , update the load removal amount ΔP i : ΔP i =ΔP i_last +m1·tanh(m2·R i ) Wherein m1 and m2 are preset adjustment coefficients, tanh() represents the hyperbolic tangent function, and then the process returns to step S6b to continue execution.

5. A method for low-frequency load reduction in a high-proportion renewable energy grid according to claim 4, characterized in that: The preset adjustment coefficients m1 and m2 need to meet the following requirements: m1≤P D / tanh(m2·P D / Δf N ) Where Δf N It is the frequency setting value of the Nth round.

6. The method for low-frequency load reduction in a high-proportion renewable energy grid according to claim 1, characterized in that: Frequency reduction rate setting value df for round i i for: T s Represents the equivalent inertia time constant of the power grid.

7. A low-frequency load reduction control device for a high-proportion renewable energy power grid using the low-frequency load reduction method according to any one of claims 1 to 6, characterized in that: The device includes: The parameter acquisition setting module is used to obtain the first and last frequency action values ​​set by the power grid, the total number of rounds N of the low-frequency load reduction scheme, and the action delay Δt of each round i ; Set the low frequency load reduction capacity P D , the i-th frequency setting value Δf i ; Detect and obtain the maximum frequency drop rate (df / dt) at the moment of initial disturbance of the power grid max ; The low-frequency load shedding process control module is used to determine i≤N and Is it true? If so, the difference between the rated frequency of the power grid and the frequency of the power grid at the i-th round is obtained as the frequency drop amount Δf. If not, the low-frequency load shedding ends. Determine Δf>Δf i Is it true? If true, the load shedding amount ΔP in the i-th round is determined based on the minimum risk cost of low-frequency load shedding. i And delay Δt i Execute load shedding ΔP i , if not established, the low-frequency load shedding ends; Judgment (df / dt) max >df i Is it true? If so, the low-frequency load reduction ends. If not, the value of i is updated.

8. A low-frequency load reduction control device for a high-proportion renewable energy power grid, characterized in that: include: A processor and a memory, wherein the processor is connected to the memory, and the memory is used to store executable instructions of the processor, and the processor is configured to execute the low-frequency load reduction method for a high-proportion renewable energy power grid as described in any one of claims 1-6 by executing the executable instructions.

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