CN110429669B - Master station side frequency control method for coordinating AGC and primary frequency modulation - Google Patents

Abstract

The invention provides a master station side frequency control method for coordinating AGC and primary frequency modulation, and belongs to the technical field of active control of power systems. Firstly, calculating the regional control deviation of a power grid and AGC frequency modulation requirements; traversing all AGC available units, and judging whether the unit is in a primary frequency modulation state and exceeds the set AGC period number; according to the power grid AGC frequency modulation requirement, the AGC available unit primary frequency modulation operation state and the unit rotating speed deviation, the available units are divided into groups; and calculating the units belonging to different groups in different modes and issuing AGC control instructions. The invention considers the relation between the unit running state and the current power grid state when distributing the AGC control instruction, ensures the execution of the unit primary frequency modulation control process and avoids the frequency quality deterioration caused by the conflict between the primary frequency modulation and the AGC control.

Description

A frequency control method on the master station side coordinated by AGC and primary frequency modulation

technical field

The invention belongs to the technical field of active power control of power systems, and in particular relates to a master station side frequency control method coordinated by AGC and primary frequency modulation.

Background technique

Grid frequency is one of the important indicators of power quality. It reflects the balance between active power and load. Ensuring the stability of grid frequency is beneficial to the safety and economic benefits of equipment at multiple levels such as source, grid, and load. One of the most important tasks of a scheduling agency.

In power grid frequency control, primary frequency regulation and AGC (automatic generation control) both play an important role. Primary frequency regulation is to adjust the power of the generator when the frequency deviation is large by using the differential characteristic of the generator set governor to improve the unbalanced condition of power generation and consumption and reduce the frequency deviation; AGC is to issue power to the generator set through the dispatching mechanism order to adjust the active power output of the generator set to achieve the goal of reducing the frequency deviation and the transmission power deviation of the tie line. In comparison, the primary frequency modulation has the characteristics of fast action speed, but its action range is relatively small, and it cannot realize the no-difference adjustment of the frequency; AGC can realize the no-difference adjustment of the frequency, but its action speed is relatively slow. Therefore, the coordinated control of primary frequency regulation and AGC is crucial for grid frequency control.

Because the control objectives, implementation methods, control processes, and time scales of primary frequency regulation and AGC are different, the two may have different requirements on the power regulation direction of the generator set. In an emergency, this may lead to reverse adjustment and over-adjustment of the unit, resulting in slow frequency recovery and repeated oscillations, and even further deterioration of frequency quality, resulting in the expansion of accidents.

In order to solve this problem, the patents "A method of grid frequency adjustment coordinated with primary frequency regulation" (patent application number: CN201410700043.0), "Optimal control system and method for ensuring primary frequency regulation under the AGC mode of thermal power units" (patent application number: CN201410700043.0) Application No.: CN201610119319.5), "Coordinated Control Method of Primary Frequency Modulation and AGC of Thermal Power Units" (Patent Application No.: CN201610461880.1) discloses a variety of coordinated control methods of primary frequency modulation and AGC of thermal power units, aiming to pass the thermal power unit side The improvement of the control strategy, when the primary frequency regulation and the AGC control direction are opposite, the primary frequency regulation process can be smoothly executed to meet the dispatching agency's assessment requirements for the primary frequency regulation, and to ensure the frequency stability and fault recovery of the power grid. The above methods are all strategy optimizations carried out on the power plant side.

However, due to regulations, technologies and other reasons, there are still some power plants that do not have a reasonable primary frequency regulation and AGC coordinated control function, and the aforementioned conflict between primary frequency regulation and AGC may still occur, which will seriously threaten the frequency security of the power grid.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and proposes a master station side frequency control method coordinated by AGC and primary frequency modulation. The present invention considers the relationship between the operating state of the unit and the current grid state when distributing the AGC control command, ensures the execution of the primary frequency regulation control process of the unit, and avoids frequency quality deterioration caused by the conflict between primary frequency regulation and AGC control.

The present invention proposes a master station side frequency control method coordinated by AGC and primary frequency modulation, comprising the following steps:

1) At the beginning of the current AGC cycle, read the frequency deviation data of the power grid area and the transmission power deviation data of the tie line, and calculate the control deviation of the power grid area and the AGC frequency regulation demand; the specific steps are as follows:

1-1) Denote the AGC cycle as T, the start time of the current AGC cycle as t, read the frequency deviation data Δf(t) at time t in the power grid area and the transmission power deviation data ΔP _tie (t) of the tie line at time t, and calculate the power grid at time t Regional control deviation ACE(t)=BΔf(t)+ΔP _tie (t), where B is the regional frequency deviation coefficient of the power grid;

1-2) Calculate the AGC frequency modulation requirement at time t ΔP _R (t)=K _P ACE(t)+K _I IACE(t);

where K _P and K _I are the proportional component and integral component gain coefficients, respectively; IACE(t) is the integral component of the regional control deviation at time t, and the calculation expression is as follows:

IACE(t)=IACE(t-T)+T×ACE(t)

Among them, t-T is the start time of the previous AGC cycle; the initial value of IACE(t) at the start time of the first AGC cycle is 0;

2) Traverse all AGC available units, read the local primary frequency modulation signal and rotational speed data of the unit, and judge whether the unit is in a primary frequency modulation state for more than M AGC cycles; the specific steps are as follows:

2-1) For the AGC available unit with unit serial number i, read the local primary frequency modulation signal F _Local,i (t) at time t of the unit; F _Local,i (t)=1 means the AGC available unit with unit serial number i It is in the primary frequency modulation state at time t, and F _Local,i (t)=0 means that the unit is not in the primary frequency modulation state at time t;

2-2) Use the rotational speed data to supplement the judgment on the primary frequency modulation state of the unit in step 2-1); the specific method is as follows:

2-2-1) For the AGC available unit with unit serial number i, read the rotational speed data ω _i (t) of the unit at time t, and calculate the rotational speed deviation Δω _i (t)=ω _i (t)-ω of the unit at time t _n , where ω _n is the rated speed of the unit;

进行比较：如果

则判断该机组t时刻处于一次调频状态但F_Local,i(t)存在数据缺失或错误，将该机组t时刻远程一次调频标记设置为F_Remote,i(t)＝1；否则判断该机组t时刻不处于一次调频状态，将该机组t时刻远程一次调频标记为F_Remote,i(t)＝0；2-2-2) For the available AGC unit with unit serial number i, compare the speed deviation Δω _i (t) with the corresponding primary frequency modulation action threshold of this unit

To compare: if

Then it is judged that the unit is in the primary frequency modulation state at time t but there is data missing or error in F _Local,i (t), and the remote primary frequency modulation flag of the unit at time t is set to F _Remote,i (t)=1; otherwise, it is judged that the unit t If the time is not in the primary frequency modulation state, the remote primary frequency modulation of the unit at time t is marked as F _{Remote, i} (t) = 0;

则该机组t时刻处于一次调频状态超过M个AGC周期，将该机组t时刻一次调频标记设置为F_i(t)＝1；如果存在

且

则该机组t时刻处于一次调频状态超过M个AGC周期，但F_Local,i(t)存在数据缺失或错误，将该机组t时刻一次调频标记设置为F_i(t)＝1；否则将该机组t时刻一次调频标记设置为F_i(t)＝0；2-3) For the available unit of AGC with unit serial number i, if there is one

Then the unit is in the primary frequency modulation state at time t for more than M AGC cycles, and the primary frequency modulation flag at time t of the unit is set to F _i (t)=1; if there is

and

Then the unit is in the state of primary frequency modulation at time t for more than M AGC cycles, but there is data missing or error in F _Local,i (t), and the primary frequency modulation flag at time t of the unit is set to F _i (t)=1; The first frequency modulation flag at time t of the unit is set to F _i (t) = 0;

3) According to the AGC frequency regulation demand ΔP _R (t) at time t, the primary frequency regulation state of AGC available units at time t, and the unit speed deviation Δω _i (t), divide the control groups to which all AGC available units belong; the specific steps are as follows:

3-1) For the AGC available unit with unit serial number i, if the unit is not in the primary frequency modulation state at time t or in the primary frequency modulation state for less than M AGC cycles, that is, the primary frequency modulation flag F _i (t) = 0, then The unit is classified into control group A, and enters step 4-1);

3-2) For the AGC-available unit with unit serial number i, if the unit is in the primary frequency modulation state at time t for more than M AGC cycles, that is, the primary frequency modulation flag F _i (t)=1, and the primary frequency modulation action direction is the same as the AGC action. If the directions are the same, that is, Δω _i (t)×ΔP _R (t)≥0, then the unit is classified into control group A, and goes to step 4-1);

3-3) For the AGC-available unit with unit serial number i, if the unit is in the primary frequency modulation state at time t for more than M AGC cycles, that is, the primary frequency modulation flag F _i (t)=1, and the primary frequency modulation action direction is the same as the AGC action. If the directions are inconsistent, that is, Δω _i (t)×ΔP _R (t)<0, then the unit is classified into control group B, and the process goes to step 4-2);

4) According to the result of step 3), take corresponding AGC instructions for different groups of units:

4-1) For the units belonging to control group A, the AGC frequency regulation demand is allocated proportionally according to the available frequency regulation capacity, and is set as the current AGC cycle AGC command after superimposing with the current actual output of the unit; the calculation expression is as follows:

P _cmd,j (t)=P _g,j (t)+ΔP _R,j (t),j=1,2,...,J

和P _j分别为属于控制组别A的机组j的出力上限和下限，j为属于控制组别A的机组序号，J为属于控制组别A的机组总数；Among them, P _cmd,j (t) is the AGC command at time t of unit j belonging to control group A in the current AGC cycle, and P _g,j (t) is the current actual output of unit j belonging to control group A at time t , ΔP _R,j (t) is the AGC frequency regulation demand allocated by the unit belonging to the control group A at the time jt, P _avail,j (t) is the available frequency regulation capacity of the unit belonging to the control group A at the time jt,

and P _j are the upper and lower output limits of unit j belonging to control group A, respectively, j is the serial number of units belonging to control group A, and J is the total number of units belonging to control group A;

4-2) For units belonging to control group B, update the current AGC cycle AGC command of the unit to the average value of actual output within 10 seconds before the unit participates in a frequency modulation action; the calculation expression is as follows:

Among them, P _cmd,k (t) is the AGC command at time t of the unit k belonging to the control group B in the current AGC cycle, t ^* is the moment when the unit k belonging to the control group B starts a frequency modulation, Δt is 10 seconds, k is the serial number of units belonging to control group B, and K is the total number of units belonging to control group B;

5) When the next AGC cycle comes, go back to step 1).

The characteristics and beneficial effects of the present invention are:

The invention can ensure that when the primary frequency regulation and the AGC control direction are inconsistent, the execution of the primary frequency regulation control process of the generator set can fully exert the positive effect of the primary frequency regulation on frequency stability, and at the same time, it does not affect the execution of the AGC function in other states. Another advantage of the present invention is that it does not depend on the coordinated control strategy of primary frequency regulation and AGC on the generator set side, and can play a role in generating sets using different coordinated control strategies, ensuring the mutual support of the entire network of generator sets in the frequency emergency state and contribution.

Description of drawings

Figure 1 is an overall flow chart of the method of the present invention.

Detailed ways

A master station side frequency control method for coordination between AGC and primary frequency modulation proposed by the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

A master station side frequency control method for coordination between AGC and primary frequency modulation proposed by the present invention, the overall process is shown in Figure 1, including the following steps:

1) At the beginning of the current AGC cycle, read the grid area frequency deviation data and the tie line transmission power deviation data from the data acquisition and monitoring control system, and calculate the grid area control deviation and AGC frequency regulation requirements. Specific steps are as follows:

1-1) Denote the AGC cycle as T, the current AGC cycle start time as t, and read the frequency deviation data Δf(t) (unit: Hz) in the grid area at time t from the data acquisition and monitoring and control system and the tie line transmission at time t Power deviation data ΔP _tie (t) (unit: MW), calculate the grid area control deviation ACE(t) = BΔf(t) + ΔP _tie (t) at time t, where B is the grid area frequency deviation coefficient (unit: MW/ Hz).

1-2) Calculate the AGC frequency modulation requirement at time t ΔP _R (t)=K _P ACE(t)+KI IACE(t), where K _P and K _I are the proportional component and integral component gain coefficients (the difference between the two coefficients ₎ The value range is usually between -1 and 0), IACE(t) is the integral component of the regional control deviation at time t, and the calculation expression is as follows:

IACE(t)=IACE(t-T)+T×ACE(t)

Among them, t-T is the start time of the previous AGC cycle; the initial value of IACE(t) at the start time of the first AGC cycle is 0.

2) Traverse all available AGC units, read the local primary frequency modulation signal and speed data of the unit from the remote terminal device of the power plant, and judge whether the unit is in the primary frequency modulation state and exceeds M (M is a positive number, and the recommended value is 5~10) AGC cycle. Specific steps are as follows:

2-1) For the available AGC unit whose unit serial number is i, read the local primary frequency modulation signal F _Local,i (t) of the unit at time t from the remote terminal device of the power plant. In particular, F _Local,i (t)=1 indicates that the AGC available unit with unit serial number i is in the primary frequency modulation state at time t, and F _Local,i (t)=0 indicates that the unit is not in the primary frequency modulation state at time t.

2-2) Considering that there may be data missing or errors in the data transmitted through the remote terminal device, the following uses the rotational speed data to supplement the judgment of the primary frequency modulation state of the unit in step 2-1). The specific method is as follows:

The step 2-2) is to prepare data for the result in the verification 2-1) (the verification step is 2-3)). When the result in 2-1) is 1, the calculation result of 2-2) does not play a role in the control strategy, but in order to maintain the validity of the data, the calculation should still be performed.

2-2-1) For the available AGC unit with the unit serial number i, read the rotational speed data ω _i (t) (unit: r/min) of the unit at time t from the remote terminal device of the power plant, and calculate the rotational speed deviation Δω of the unit at time t _i (t)=ω _i (t)-ω _n , where ω _n is the rated speed of the unit, generally 3000r/min. Especially for a unit with multiple rotational speed data, the average or median value of the rotational speed data at time t is selected as the rotational speed data at this time to calculate the rotational speed deviation.

进行比较：如果

则判断该机组t时刻可能处于一次调频状态但F_Local,i(t)存在数据缺失或错误，将该机组t时刻远程一次调频标记设置为F_Remote,i(t)＝1；否则判断该机组t时刻不处于一次调频状态，将该机组t时刻远程一次调频标记为F_Remote,i(t)＝0。特别地，对于水电机组(包括抽水蓄能)，

一般取3r/min，对于其他机组，

一般取2r/min。2-2-2) For the available AGC unit with unit serial number i, compare the speed deviation Δω _i (t) with the corresponding primary frequency modulation action threshold of this unit

To compare: if

Then it is judged that the unit may be in the primary frequency modulation state at time t but there is data missing or error in F _Local,i (t), and the remote primary frequency modulation flag of the unit at time t is set to F _Remote,i (t)=1; otherwise, judge the unit If the unit is not in the primary frequency modulation state at time t, the remote primary frequency modulation of the unit at time t is marked as F _{Remote, i} (t)=0. In particular, for hydroelectric units (including pumped storage),

Generally take 3r/min, for other units,

Generally take 2r/min.

则认为该机组t时刻处于一次调频状态超过M个AGC周期，将该机组t时刻一次调频标记设置为F_i(t)＝1；如果有

但

则认为该机组t时刻处于一次调频状态超过M个AGC周期，但F_Local,i(t)存在数据缺失或错误，仍将该机组t时刻一次调频标记设置为F_i(t)＝1；否则将该机组一次调频标记设置为F_i(t)＝0。2-3) For the available units of AGC with unit serial number i, if any

Then it is considered that the unit is in the first frequency modulation state at time t for more than M AGC cycles, and the first frequency modulation flag of the unit at time t is set to F _i (t) = 1; if there is

but

Then it is considered that the unit is in the primary frequency modulation state at time t for more than M AGC cycles, but there is data missing or error in F _Local,i (t), and the primary frequency modulation flag at time t of the unit is still set to F _i (t) = 1; otherwise Set the primary frequency modulation flag of this unit to F _i (t)=0.

3) According to the AGC frequency regulation demand ΔP _R (t) at time t, the primary frequency regulation state of AGC available units at time t, and the unit speed deviation Δω _i (t), the control groups to which all AGC available units belong are divided. Specific steps are as follows:

3-1) For the AGC available unit with unit serial number i, if the unit is not in the primary frequency modulation state at time t or in the primary frequency modulation state for less than M AGC cycles, that is, the primary frequency modulation flag F _i (t) = 0, then The unit is classified into control group A, and goes to step 4-1).

3-2) For the AGC-available unit with unit serial number i, if the unit is in the primary frequency modulation state at time t for more than M AGC cycles, that is, the primary frequency modulation flag F _i (t)=1, and the primary frequency modulation action direction is the same as the AGC action. If the directions are the same, that is, Δω _i (t)×ΔPR ( _t ) ≥ 0, then the unit is classified into control group A, and the process goes to step 4-1).

3-3) For the AGC-available unit with unit serial number i, if the unit is in the primary frequency modulation state at time t for more than M AGC cycles, that is, the primary frequency modulation flag F _i (t)=1, and the primary frequency modulation action direction is the same as the AGC action. If the directions are inconsistent, that is, Δω _i (t)×ΔPR ( _t )<0, the unit is classified into control group B, and the process goes to step 4-2).

4) According to the result of step 3), take corresponding AGC instructions for different groups of units:

4-1) For the units belonging to control group A, the AGC frequency regulation demand is allocated proportionally according to the available frequency regulation capacity, and is superimposed with the current actual output of the unit and set as the current AGC cycle AGC command; the calculation formula is as follows:

P _cmd,j (t)=P _g,j (t)+ΔP _R,j (t),j=1,2,...,J

和P_j分别为属于控制组别A的机组j的出力上限和下限，j为属于控制组别A的机组序号，J为属于控制组别A的机组总数。Among them, P _cmd,j (t) is the AGC command (unit: MW) at time t of the unit j belonging to the control group A in the current AGC cycle, and P _g,j (t) is the unit j belonging to the control group A. The current actual output at time t (unit: MW), ΔP _R,j (t) is the AGC frequency modulation demand (unit: MW) allocated by the unit belonging to the control group A at time jt, and P _avail,j (t) is the control group A. The available FM capacity (unit: MW) of the unit in group A at time jt,

and P _j are the upper and lower output limits of unit j belonging to control group A, respectively, j is the serial number of units belonging to control group A, and J is the total number of units belonging to control group A.

4-2) For units belonging to control group B, update the current AGC cycle AGC command of the unit to the average actual output within 10 seconds before the unit participates in a frequency modulation action; the calculation formula is as follows:

Among them, P _cmd,k (t) is the AGC command (unit: MW) at time t of the unit k belonging to the control group B in the current AGC cycle, t ^* is the time when the unit k belonging to the control group B starts a frequency modulation, Δt is 10 seconds, k is the serial number of units belonging to control group B, and K is the total number of units belonging to control group B.

5) When the next AGC cycle comes, go back to step 1).

Claims (1)

1. A master station side frequency control method coordinated by AGC and primary frequency modulation, is characterized in that, comprises the following steps: 1) At the beginning of the current AGC cycle, read the frequency deviation data of the power grid area and the transmission power deviation data of the tie line, and calculate the control deviation of the power grid area and the AGC frequency regulation demand; the specific steps are as follows: 1-1) Denote the AGC cycle as T, the start time of the current AGC cycle as t, read the frequency deviation data Δf(t) at time t in the power grid area and the transmission power deviation data ΔP _tie (t) of the tie line at time t, and calculate the power grid at time t Regional control deviation ACE(t)=BΔf(t)+ΔP _tie (t), where B is the regional frequency deviation coefficient of the power grid; 1-2) Calculate the AGC frequency modulation requirement at time t ΔP _R (t)=K _P ACE(t)+K _I IACE(t); where K _P and K _I are the proportional component and integral component gain coefficients, respectively; IACE(t) is the integral component of the regional control deviation at time t, and the calculation expression is as follows: IACE(t)=IACE(t-T)+T×ACE(t) Among them, t-T is the start time of the previous AGC cycle; the initial value of IACE(t) at the start time of the first AGC cycle is 0; 2) Traverse all AGC available units, read the local primary frequency modulation signal and rotational speed data of the unit, and judge whether the unit is in a primary frequency modulation state for more than M AGC cycles; the specific steps are as follows: 2-1) For the AGC available unit with unit serial number i, read the local primary frequency modulation signal F _Local,i (t) at time t of the unit; F _Local,i (t)=1 means the AGC available unit with unit serial number i It is in the primary frequency modulation state at time t, and F _Local,i (t)=0 means that the unit is not in the primary frequency modulation state at time t; 2-2) Use the rotational speed data to supplement the judgment on the primary frequency modulation state of the unit in step 2-1); the specific method is as follows: 2-2-1) For the AGC available unit with unit serial number i, read the rotational speed data ω _i (t) of the unit at time t, and calculate the rotational speed deviation Δω _i (t)=ω _i (t)-ω of the unit at time t _n , where ω _n is the rated speed of the unit; 2-2-2) For the available AGC unit with unit serial number i, compare the speed deviation Δω _i (t) with the corresponding primary frequency modulation action threshold of this unit

To compare: if

Then it is judged that the unit is in the primary frequency modulation state at time t but there is data missing or error in F _Local,i (t), and the remote primary frequency modulation flag of the unit at time t is set to F _Remote,i (t)=1; otherwise, it is judged that the unit t If the time is not in the primary frequency modulation state, the remote primary frequency modulation of the unit at time t is marked as F _{Remote, i} (t) = 0; 2-3) For the available unit of AGC with unit serial number i, if there is one

Then the unit is in the primary frequency modulation state at time t for more than M AGC cycles, and the primary frequency modulation flag at time t of the unit is set to F _i (t)=1; if there is

and

Then the unit is in the state of primary frequency modulation at time t for more than M AGC cycles, but there is data missing or error in F _Local,i (t), and the primary frequency modulation flag at time t of the unit is set to F _i (t)=1; The first frequency modulation flag at time t of the unit is set to F _i (t) = 0; 3) According to the AGC frequency regulation demand ΔP _R (t) at time t, the primary frequency regulation state of AGC available units at time t, and the unit speed deviation Δω _i (t), divide the control groups to which all AGC available units belong; the specific steps are as follows: 3-1) For the AGC available unit with unit serial number i, if the unit is not in the primary frequency modulation state at time t or in the primary frequency modulation state for less than M AGC cycles, that is, the primary frequency modulation flag F _i (t) = 0, then The unit is classified into control group A, and enters step 4-1); 3-2) For the AGC-available unit with unit serial number i, if the unit is in the primary frequency modulation state at time t for more than M AGC cycles, that is, the primary frequency modulation flag F _i (t)=1, and the primary frequency modulation action direction is the same as the AGC action. If the directions are the same, that is, Δω _i (t)×ΔP _R (t)≥0, then the unit is classified into control group A, and goes to step 4-1); 3-3) For the AGC-available unit with unit serial number i, if the unit is in the primary frequency modulation state at time t for more than M AGC cycles, that is, the primary frequency modulation flag F _i (t)=1, and the primary frequency modulation action direction is the same as the AGC action. If the directions are inconsistent, that is, Δω _i (t)×ΔP _R (t)<0, then the unit is classified into control group B, and the process goes to step 4-2); 4) According to the result of step 3), take corresponding AGC instructions for different groups of units: 4-1) For the units belonging to control group A, the AGC frequency regulation demand is allocated proportionally according to the available frequency regulation capacity, and is set as the current AGC cycle AGC command after superimposing with the current actual output of the unit; the calculation expression is as follows: P _cmd,j (t)=P _g,j (t)+ΔP _R,j (t),j=1,2,...,J

Among them, P _cmd,j (t) is the AGC command at time t of unit j belonging to control group A in the current AGC cycle, and P _g,j (t) is the current actual output of unit j belonging to control group A at time t , ΔP _R,j (t) is the AGC frequency modulation demand allocated by unit j belonging to control group A at time t, P _avail,j (t) is the available frequency modulation capacity of unit j belonging to control group A at time t ,

and P _j are the upper and lower output limits of unit j belonging to control group A, respectively, j is the serial number of units belonging to control group A, and J is the total number of units belonging to control group A; 4-2) For units belonging to control group B, update the current AGC cycle AGC command of the unit to the average value of actual output within 10 seconds before the unit participates in a frequency modulation action; the calculation expression is as follows:

Among them, P _cmd,k (t) is the AGC command at time t of the unit k belonging to the control group B in the current AGC cycle, t ^* is the moment when the unit k belonging to the control group B starts a frequency modulation, Δt is 10 seconds, k is the serial number of units belonging to control group B, and K is the total number of units belonging to control group B; 5) When the next AGC cycle comes, go back to step 1).

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