A three-stage frequency modulation regulation method based on random power correction

Abstract

This invention discloses a tertiary frequency regulation method based on random power correction. The method involves dividing the actual active power generated by the entire plant into equal segments. Random numbers are generated by a real-time monitoring system based on the number of segments, and these random numbers are sequentially assigned to elements in an array. An iterative regulation cycle is defined as several periods. In each cycle, a random power correction is obtained based on the grid frequency deviation, the capacity of the segmented units, the number of specified values ​​in the array, and a preset tertiary frequency regulation power adjustment coefficient. The active power setpoint of the entire plant is then corrected based on this random power correction. After all cycles in one iterative regulation cycle are completed, the next iterative regulation cycle is executed. This invention represents tertiary frequency regulation with an action sequence later than primary and secondary frequency regulation. By dividing the regulation units and introducing random numbers, it prevents resonant regulation at each power station, thereby effectively preventing the negative impact of the tertiary frequency regulation function of this invention on the power system.

Description

Technical Field

[0001] This invention relates to the field of power system automation control technology, and in particular to a three-stage frequency regulation method based on stochastic power correction. Background Technology

[0002] The power grid frequency reflects the balance between power generation and power consumption in a power system. Specifically, when power generation exceeds power consumption, the power grid frequency is higher than the rated frequency (50Hz); when power generation is lower than power consumption, the power grid frequency is lower than the rated frequency. Using the power grid frequency as a reference, the power system adjusts power generation and power consumption to return them to a balanced state. The main adjustment methods are primary and secondary frequency regulation of power generation.

[0003] Primary frequency regulation refers to the adjustment of the active power of each generating unit by its speed governor system according to a preset "frequency-power" adjustment coefficient when the deviation of the grid frequency from the rated frequency exceeds the primary frequency regulation threshold (e.g., 0.05Hz for hydropower and 0.03Hz for thermal power in most grids). This adjustment aims to compensate for the imbalance between the grid's generating power and power consumption to some extent. Because there is no unified control center to coordinate and control the units participating in primary frequency regulation, and because it is related to the calculation mechanism of the adjustment amount, primary frequency regulation cannot completely restore the grid frequency to the rated frequency; therefore, it is also called differential regulation. However, the advantages of primary frequency regulation are: 1) Due to the lack of a unified control center, it avoids the risk of complete failure like secondary frequency regulation (e.g., abnormal exit of the secondary frequency regulation function module), thus achieving extremely high overall reliability; 2) The adjustment command is directly calculated by the generating unit, omitting the scheduling calculation, command transmission, and power plant AGC allocation processes of secondary frequency regulation. Therefore, the response speed to grid frequency anomalies is much faster than that of secondary frequency regulation.

[0004] Secondary frequency regulation refers to the adjustment of the output active power of each grid-connected power station within the control range by the dispatch center when the deviation between the grid frequency and the rated frequency exceeds the secondary frequency regulation threshold. This aims to restore the grid's power generation and power consumption to a balanced state, ensuring that the difference between the grid frequency and the rated frequency remains within the allowable range. Secondary frequency regulation includes the following steps: 1) The dispatching agency calculates the change in power generation required to restore the grid frequency to the rated frequency based on the grid frequency deviation and the grid's "frequency-power" sensitivity coefficient; 2) The dispatching agency corrects the active power setpoints of each grid-connected power station within the control area based on the calculation results and issues power regulation commands; 3) After receiving the new active power setpoints, each power station uses AGC to distribute the total active power setpoints of the power station to each unit controlled by the AGC; 4) The active power control system of each unit performs closed-loop feedback regulation of the unit's active power based on the new individual unit active power setpoints.

[0005] As can be seen from the above, the current frequency regulation mechanism of the power system relies on the speed and stability of primary frequency regulation to reduce the deviation of the grid frequency from the rated frequency when there is an imbalance between power generation and power consumption, causing the grid frequency to deviate from the rated frequency. Then, through the error-free regulation of secondary frequency regulation, the power generation and power consumption of the power system are restored to a balanced state. However, the problem with this frequency regulation mechanism is that its secondary frequency regulation function depends on the calculation and regulation centers located in the power grid dispatch automation control system. If the central node malfunctions, the secondary frequency regulation function will be completely ineffective, and only the spontaneous regulation of the primary frequency regulation of each generating unit can provide limited correction to the grid frequency. Currently, thermal power generating units, which constitute the majority of the power grid, rely on the unit's heat or energy storage for primary frequency regulation. Although this provides better primary frequency regulation performance than hydropower units, it cannot be sustained for long periods. Once the regulation resources are exhausted, the grid frequency will revert to an uncontrolled imbalance. Considering the increasingly severe cybersecurity situation, this frequency regulation mechanism's excessive reliance on the secondary frequency regulation center undoubtedly becomes a significant hidden danger to power system security.

[0006] It should be noted that, in addition to primary and secondary frequency regulation, some literature has proposed the concept of "tertiary frequency regulation", such as "Chang Yekui, Liu Rao, Wang Chong, Zhang Xin, Li Weidong. Research on control strategy for nuclear power participating in tertiary frequency regulation [J]. Power System Protection and Control, 2014, 42(08):71-76.", and "Liu Weilie. Frequency regulation and automatic generation control of power system [M]. Beijing: China Electric Power Press, 2006:28-40. However, the concept of tertiary frequency regulation proposed in the above literature specifically refers to the pre-allocation and pre-arrangement of load by the dispatching system for each power station based on load forecasts. Its function is to ensure that the power generation and power consumption trends of the power system are basically consistent through accurate forecasting and correct planning. Compared with the ex-post regulation mechanisms of primary and secondary frequency regulation, which restore the balance between power generation and power consumption through power regulation after imbalance, the tertiary frequency regulation defined in the literature undoubtedly belongs to a completely different functional category. It is inappropriate to classify it into the field of regulation or frequency regulation and call it "frequency regulation". Considering that its action time is earlier than that of primary and secondary frequency regulation, it is even more unreasonable to put "tertiary" before "frequency regulation". In fact, this concept has never been widely promoted in the field of power system engineering practice.

[0007] Therefore, how to set up a "tertiary frequency modulation" function, whose operation sequence is later than that of "primary frequency modulation" and "secondary frequency modulation," remains an unsolved problem. Furthermore, considering that the adjustment conflicts of primary and secondary frequency modulation functions, which have been in use for many years, have not been fully resolved under certain operating conditions, designing a tertiary frequency modulation adjustment mechanism without interfering with the primary and secondary frequency modulation functions is still a rather difficult problem. Summary of the Invention

[0008] The problem solved by this invention is to provide a three-stage frequency regulation method based on random power correction. This method is an adjustment whose action sequence is later than that of the primary and secondary frequency regulation. When the secondary frequency regulation function of the power system cannot function, it performs randomized power correction on the active power of each power station, so that the power system frequency can be restored to a basically balanced state.

[0009] The present invention is achieved by the following technical solution:

[0010] A tertiary frequency regulation method based on stochastic power correction is proposed. When the secondary frequency regulation of the power system fails and the grid frequency deviates unidirectionally from the rated frequency for a period of time, the active power regulation of the tertiary frequency regulation is performed on a per-power station basis, based on the AGC (Automatic Gain Control) put into operation at the power station.

[0011] The actual active power generated by the entire plant is divided into equal parts. Random numbers are generated by the real-time monitoring system based on the number of division units, and these random numbers are assigned to each element in the array sequentially. An iterative adjustment cycle is defined as several cycles. In each cycle, a random correction power is obtained based on the grid frequency deviation, the capacity of the division units, the number of specified values ​​in the array, and the preset third-order frequency regulation power adjustment coefficient. The active power setpoint of the entire plant is then corrected based on the random correction power. In each iterative adjustment cycle, the value of each element in the array is decremented by one after each cycle correction, and then the correction for the next cycle is performed.

[0012] Based on the corrected plant-wide active power setpoint, the AGC modifies the individual active power setpoint of each unit and performs closed-loop regulation of the individual active power of each unit.

[0013] After the number of cycles in an iterative adjustment cycle has been completed, a new random number is generated to execute the next iterative adjustment cycle.

[0014] The three-stage frequency regulation will stop when the grid frequency deviation falls back or the AGC status changes to the point where the triggering condition is met.

[0015] The three frequency modulations are automatically initiated based on the following conditions:

[0016] 1) Set the parameters used to determine whether the third frequency modulation should start automatically:

[0017] Set the trigger threshold for the third frequency modulation and set the start threshold value △f1 for the third frequency modulation, where △f1≥△f3, and △f3 is the threshold for the first frequency modulation.

[0018] Set the trigger accumulation parameter s for three frequency modulations. Determine whether to clear and reset it every AGC system cycle. If not, accumulate it.

[0019] 2) The cumulative trigger parameters for three frequency modulations are compared with the trigger threshold for three frequency modulations during each AGC system cycle:

[0020] If the cumulative trigger parameter s is less than the trigger threshold of the third frequency modulation, the third frequency modulation will not be started;

[0021] If the cumulative trigger parameter s is greater than the trigger threshold for third-order frequency modulation, then third-order frequency modulation is initiated.

[0022] The triggering of the reset and accumulation of the cumulative parameter s is as follows:

[0023] 1) The reset condition for the trigger cumulative parameter s is determined every AGC system cycle as follows:

[0024] S2210) Compare the absolute value of the grid frequency deviation with the magnitude of the three-stage frequency regulation start threshold value Δf1. If |f-50|<Δf1, then reset the trigger accumulation parameter s to zero, where f is the grid frequency.

[0025] S2220) Determine whether the power station AGC is engaged. If the AGC is not engaged, reset the trigger accumulation parameter s to zero.

[0026] S2230) Determine whether any unit has been put into AGC control. If no unit has been put into AGC control, then the trigger accumulation parameter s is cleared and reset.

[0027] S2240) Determine whether a new AGC adjustment command has been received. If it has been received, clear and reset the trigger accumulation parameter s.

[0028] S2250) Determines whether the third frequency modulation is in the active state or in the exit state. If it is in the exit state, the trigger accumulation parameter s is cleared and reset.

[0029] S2260) If none of the conditions described in S2210 to S2250 are met, then the trigger accumulation parameter s of the third frequency modulation is not cleared and reset.

[0030] 2) The trigger accumulation parameters are accumulated every AGC system cycle as follows:

[0031] S2310) Compare the absolute value of the system frequency deviation collected in the current cycle with the absolute value of the frequency deviation collected in the previous cycle:

[0032] S2311) If the absolute value of the system frequency deviation in the current cycle is less than the absolute value of the system frequency deviation in the previous cycle, that is, if |f-50|<|f'-50|, then skip the following subsequent steps and keep the trigger accumulation parameter s unchanged, where f' is the power grid frequency collected in the previous cycle;

[0033] S2312) If the absolute value of the system frequency deviation in the current cycle is greater than the absolute value of the system frequency deviation in the previous cycle, that is, if |f-50|≥|f'-50|, then execute S2320 to accumulate the trigger accumulation parameter s of the three frequency modulations;

[0034] S2320) Based on the system frequency deviation and integral time, the trigger accumulation parameter s of the three frequency modulations is accumulated:

[0035] S2321) The theoretical calculation formula for accumulating the trigger accumulation parameter s of the third frequency modulation is s=s+∫(|f-50|-Δf2)dt, where Δf2 is a manually set constant that satisfies 0<Δf2<Δf1, and dt is the time integral;

[0036] The actual calculation formula for accumulating the trigger accumulation parameter s of the third frequency modulation (S2322) is s=s+(|f-50|-△f2)×T S If the AGC system has a constant calculation cycle, then T S This is the periodic time; if there is no such period, then T. S This refers to the average or estimated cycle time.

[0037] The adjustment is performed using a three-frequency modulation mode based on random parameters:

[0038] S3100) divides n AGC system cycles into one iterative adjustment cycle, where n is the manually set parameter, and n×T S It should be 2 to 3 times the time required for the power station unit to complete one active power regulation; T S For the AGC system cycle;

[0039] S3200) performs the following operation in the first AGC system cycle of each iteration adjustment cycle:

[0040] S3210) Calculate the number of segmented units m in the power plant participating in the third frequency regulation, m≈actual active power generated by the whole plant ÷ segmented unit capacity β, where the segmented unit capacity β is a parameter set by humans, and m is the natural number closest to the result obtained by dividing the actual active power generated by the whole plant by the segmented unit capacity.

[0041] S3220) Set an array U = [u1, u2, ..., u] containing m elements in the power plant real-time monitoring system. m ];

[0042] S3230) Generate m random integers greater than or equal to 1 and less than or equal to n, with a value range of 1 to n, and assign them to each element of array U in sequence;

[0043] S3240) Count the number γ of elements in array U that have a value of 1;

[0044] Calculate the stochastic correction power Δp3 using S3250:

[0045] S3251) When the grid frequency f > 50 + Δf4, Δp3 = (50 - f + Δf4) × β × γ × k2, where k2 is the manually set third frequency regulation power adjustment coefficient, Δf4 is the manually set parameter, 0 < Δf4 < Δf3, 0 < k2 ≤ first frequency regulation power adjustment coefficient;

[0046] S3252) When the power grid frequency f < 50 - Δf4, Δp3 = (50 - f - Δf4) × β × γ × k2;

[0047] S3253) When the power grid frequency is 50-△f4<f<50+△f4, △p3=0;

[0048] S3260) corrects the plant-wide active power setting value for AGC:

[0049] S3261) If the random correction power Δp3 > 0, then the total active power setpoint = min(total active power setpoint + random correction power Δp3, and the upper limit of the adjustable active power of the total plant).

[0050] S3262) If the random correction power Δp3 < 0, then the total active power setpoint = max(total active power setpoint + random correction power Δp3, lower limit of adjustable total active power).

[0051] After obtaining the corrected active power setpoint for the entire plant, AGC modifies the individual active power setpoint for each unit and performs closed-loop regulation of the individual active power in each unit.

[0052] S3270) Subtract 1 from the value of all elements in array U, i.e., u1 = u1 - 1, u2 = u2 - 1, ... u m =u m -1;

[0053] S3300) performs the following operations from the second system cycle to the nth system cycle in each iterative adjustment period:

[0054] S3310) Count the number γ of elements in array U that have a value of 1;

[0055] S3320) Calculate the stochastic correction power Δp3:

[0056] S3321) When the grid frequency f > 50 + Δf4, Δp3 = (50 - f + Δf4) × β × γ × k2, where k2 is the manually set third frequency regulation power adjustment coefficient, Δf4 is the manually set parameter, 0 < Δf4 < Δf3, 0 < k2 ≤ first frequency regulation power adjustment coefficient;

[0057] S3322) When the grid frequency f < 50 - Δf4, Δp3 = (50 - f - Δf4) × β × γ × k2;

[0058] S3323) When the power grid frequency is 50-△f4<f<50+△f4, △p3=0;

[0059] S3330) corrects the plant-wide active power setting value for AGC:

[0060] S3331) If the random correction power Δp3 > 0, then the total active power setpoint = min(total active power setpoint + random correction power Δp3, and the upper limit of adjustable active power of the total plant).

[0061] S3332) If the random correction power Δp3 < 0, then the total active power setpoint = max(total active power setpoint + random correction power Δp3, lower limit of adjustable total active power).

[0062] After obtaining the corrected active power setpoint for the entire plant, AGC modifies the individual active power setpoint for each unit and performs closed-loop regulation of the individual active power in each unit.

[0063] S3340) Subtract 1 from the value of all elements in array U, i.e., u1 = u1 - 1, u2 = u2 - 1, ... u m =u m -1;

[0064] After the nth system cycle is completed, step S3400 jumps to step S3200 to start the next iteration cycle.

[0065] Compared with the prior art, the present invention has the following beneficial technical effects:

[0066] 1. The three-stage frequency regulation method based on random power correction of the present invention is a "three-stage frequency regulation" that achieves error-free frequency regulation with an action sequence later than the primary and secondary frequency regulation. The three-stage frequency regulation of the present invention is achieved by modifying the active power setpoint of the entire power plant's AGC. In terms of mechanism, it belongs to conventional active power regulation. Almost all functions are deployed on the real-time monitoring system on the power plant side (distributed in each power plant) and do not depend on any central node. The three-stage frequency regulation method based on random power correction of the present invention generally adopts the idea of ​​periodic iterative regulation. Its regulation mechanism is to gradually restore the system frequency to a relatively balanced state through multiple adjustments over a long time scale. Therefore, compared with the existing primary frequency regulation function, the three-stage frequency regulation method of the present invention has the characteristic of error-free regulation.

[0067] 2. The tertiary frequency regulation method based on random power correction of the present invention, compared with the secondary frequency regulation function, completely eliminates the dependence on the central node, thereby significantly improving the reliability of the function. Compared with the primary frequency regulation which regulates by calling the thermal power unit's heat storage or energy storage resources, the tertiary frequency regulation method of the present invention has higher stability and sustainability in terms of regulation effect.

[0068] 3. The three-stage frequency regulation method based on random power correction of the present invention sets strict start conditions. The three-stage frequency regulation function of the power station will only be activated when the grid frequency deviates from the rated frequency in one direction for a long period of time and the secondary frequency regulation function of the dispatching has not been used for a long period of time. This avoids conflict between the three-stage frequency regulation function of the present invention and the existing secondary frequency regulation function, and also avoids the possibility that the three-stage frequency regulation function of the present invention will participate in regulation when the grid frequency oscillates, thus promoting the frequency oscillation.

[0069] 4. The three-stage frequency regulation method based on random correction power of the present invention adopts a variety of prevention mechanisms to avoid grid frequency oscillations that may be caused by distributed regulation. These include setting a longer iterative regulation period, incorporating grid frequency deviations over a longer time scale into the correction power calculation, and preventing resonance regulation of each power station by dividing the regulation unit and introducing random numbers. In this way, the three-stage frequency regulation function of the present invention can effectively prevent the negative impact of the present invention on the power system. Attached Figure Description

[0070] Figure 1 This is a flowchart illustrating the three-stage frequency modulation method based on random power correction according to the present invention.

[0071] Figure 2 This invention provides a comparison of the variation trends of the cumulative parameters for the three-frequency modulation start-up trigger under different Δf2 settings.

[0072] Figure 3This is a simulation model of the three-frequency modulation mode based on random power correction in this invention;

[0073] Figure 4 This invention presents a power simulation adjustment effect based on three-stage frequency modulation with random power correction.

[0074] Figure 5 This invention demonstrates the frequency modulation effect of three-stage frequency modulation based on random power correction in a simulation.

[0075] Figure 6 This is a simulation of the three-stage frequency modulation based on random power correction in this invention under a 5x adjustment coefficient. Detailed Implementation

[0076] The present invention will now be described in further detail with reference to the accompanying drawings.

[0077] Conventional AGC systems have the function of modifying the active power setpoints of the entire plant and distributing them to each unit according to secondary frequency regulation commands or operator commands. This invention adds a tertiary frequency regulation function to the AGC system. The following is a detailed explanation of the start-up, stop, and adjustment of each mode of AGC tertiary frequency regulation.

[0078] A tertiary frequency regulation method based on stochastic power correction is proposed. When the secondary frequency regulation of the power system fails and the grid frequency deviates unidirectionally from the rated frequency for a period of time, the active power regulation of the tertiary frequency regulation is carried out on a per-power station basis, based on the AGC (Automatic Gain Control) system activated at the power station, using the following mode:

[0079] The actual active power generated by the entire plant is divided into equal parts. Random numbers are generated by the real-time monitoring system based on the number of division units, and these random numbers are assigned to each element in the array sequentially. An iterative adjustment cycle is defined as several cycles. In each cycle, a random correction power is obtained based on the grid frequency deviation, the capacity of the division units, the number of specified values ​​in the array, and the preset third-order frequency regulation power adjustment coefficient. The active power setpoint of the entire plant is then corrected based on the random correction power. In each iterative adjustment cycle, the value of each element in the array is decremented by one after each cycle correction, and then the correction for the next cycle is performed.

[0080] Based on the corrected plant-wide active power setpoint, the AGC modifies the individual active power setpoint of each unit and performs closed-loop regulation of the individual active power of each unit.

[0081] After the number of cycles in an iterative adjustment cycle has been completed, a new random number is generated to execute the next iterative adjustment cycle.

[0082] The three-stage frequency regulation will stop when the grid frequency deviation falls back or the AGC status changes to the point where the triggering condition is met.

[0083] like Figure 1As shown, a triple frequency modulation regulation method based on random power correction includes the following steps:

[0084] S1000) Adds a three-stage frequency modulation function block to the AGC system and sets the adjustment mode of the three-stage frequency modulation;

[0085] Adjustments are made based on the system frequency deviation, the preset frequency modulation coefficient, and the random number generated by the real-time monitoring system. This can effectively prevent ultra-low frequency oscillations that may be caused by multiple power plants with similar adjustment performance performing three frequency modulations at the same time.

[0086] Triggering conditions for S2000 triple frequency modulation start:

[0087] S2100) sets various parameters used to determine whether the third frequency modulation starts automatically:

[0088] Set the trigger threshold for the third frequency regulation and the start threshold value △f1 for the third frequency regulation, where △f1≥△f3, and △f3 is the threshold for the first frequency regulation. One option is to directly adjust the start threshold for the third frequency regulation according to the threshold for the first frequency regulation, that is, set the start threshold value △f1 for the third frequency regulation of thermal power plants to 0.03Hz and set the start threshold value △f1 for the third frequency regulation of hydropower plants to 0.05Hz.

[0089] S2130) Set the trigger accumulation parameter s for the third frequency modulation;

[0090] S2140) Set the stop threshold value △f5 for the third frequency regulation, where △f5 < △f1. One option is to set the stop threshold value △f5 for the third frequency regulation of thermal power plants to 0.02Hz and the stop threshold value △f5 for the third frequency regulation of hydropower plants to 0.03Hz.

[0091] S2200 checks the reset condition of the trigger accumulation parameters for three frequency modulations each cycle:

[0092] S2210) Compare the absolute value of the system frequency deviation with the magnitude of the three-stage frequency regulation start threshold value △f1. If |f-50|<△f1, then the trigger accumulation parameter s of the three-stage frequency regulation is cleared and reset, where f is the grid frequency. The absolute value of the system frequency deviation and the system frequency deviation mentioned in this invention are both the absolute value of the grid frequency deviation and the grid frequency deviation.

[0093] The logic design of S2210 is to prevent the third frequency modulation from participating in regulation when the system frequency oscillates. The original design intention of the third frequency modulation is to correct the long-term continuous and unidirectional deviation of the system deviation. In fact, the third frequency modulation, which lacks a control center and aims at zero-error regulation, is more likely to form resonance due to the superposition of its regulation effect with the frequency oscillation when it participates in regulation when the system frequency oscillates than the first and second frequency modulation.

[0094] S2220) Determine whether the power station AGC is engaged. If the AGC is not engaged, reset the trigger accumulation parameter s of the third frequency regulation.

[0095] S2230) Determine whether any unit has been put into AGC control. If no unit has been put into AGC control, then the trigger accumulation parameter s of the three frequency regulation is cleared and reset.

[0096] The third frequency regulation is an active power regulation based on the power station. It is based on the power station's AGC function. Therefore, as described in S2220 and S2230, the normal functioning of the power station's AGC function is a necessary condition for starting the third frequency regulation.

[0097] S2240) Determine whether a new AGC adjustment command has been received. If a new AGC adjustment command has been received, then reset the trigger accumulation parameter s of the three frequency modulations to zero.

[0098] The tertiary frequency regulation of this invention is a spontaneous regulation deployed in the power plant automation control system. Its original design purpose is to automatically correct the frequency of the power grid system when the secondary frequency regulation or manual regulation of the power plant has not been activated for a long time. Since the tertiary frequency regulation and the secondary frequency regulation or manual regulation of the power plant all operate on the active power setpoint of the entire plant, if they are regulated at the same time, it may cause conflicts, cancellations or other unpredictable abnormal operating conditions. Therefore, it is set that only one of the three regulation methods is active at the same time; that is, the AGC regulation source is either set to receive secondary frequency regulation commands only on the dispatch side or set to receive commands from power plant operators only on the power plant side. The mechanism described in S2240 determines that the tertiary frequency regulation will only be activated when the above two regulation methods have not been activated for a long time.

[0099] S2250) Determine whether the three-stage frequency modulation function is in the active or in the inactive state. If the three-stage frequency modulation function is in the inactive state, then clear and reset the trigger accumulation parameter s of the three-stage frequency modulation.

[0100] S2270) If none of the conditions described in S2210 to S2250 are met, then the trigger accumulation parameter s of the third frequency modulation will not be cleared and reset.

[0101] When S2300 is not reset, it accumulates the trigger accumulation parameters for three frequency modulations every cycle:

[0102] S2310) Compare the absolute value of the system frequency deviation collected in the current cycle with the absolute value of the system frequency deviation collected in the previous cycle:

[0103] S2311) If the absolute value of the system frequency deviation in the current cycle is less than the absolute value of the system frequency deviation in the previous cycle, that is, if |f-50|<|f'-50|, then skip the subsequent steps of S2300 and keep the trigger accumulation parameter s of the three frequency modulations unchanged, where f' is the grid frequency collected in the previous cycle.

[0104] S2312) If the absolute value of the system frequency deviation in the current cycle is greater than the absolute value of the system frequency deviation in the previous cycle, that is, if |f-50|≥|f'-50|, then execute S2320 to accumulate the trigger accumulation parameter s of the three frequency modulations.

[0105] The purpose of the logic described in S2310 is to prevent the third frequency regulation from taking effect during the process of the system frequency recovering from the deviation state to the equilibrium state. If the abnormal factors that cause the system frequency deviation are eliminated, or if the dispatching is to carry out the second frequency regulation through other power stations, the action of the third frequency regulation is likely to cause repetition or over-regulation, which may lead to system frequency oscillation. Therefore, the action of the third frequency regulation should be prevented according to the changing trend of the system frequency deviation.

[0106] S2320) Based on the system frequency deviation and integral time, the trigger accumulation parameter s of the three frequency modulations is accumulated and iterated:

[0107] S2321) The theoretical calculation formula for accumulating the trigger accumulation parameter s of the third frequency modulation is s=s+∫(|f-50|-Δf2)dt, where Δf2 is a manually set constant that should satisfy 0<Δf2<Δf1, and dt is the time integral;

[0108] The actual calculation formula for accumulating the trigger accumulation parameter s of the third frequency modulation (S2322) is: s=s+(|f-50|-△f2)×T S If the system has a constant computation period, then T S For this periodic time, if the system does not have a constant computation period, then T S This refers to the average or estimated cycle time.

[0109] The calculation formula described in S2320 introduces a manually set constant Δf2, and requires 0 < Δf2 < Δf1 in order to obtain a better cumulative weight. Although setting Δf2 to 0 or Δf1 can also ensure that a large frequency deviation has a high cumulative weight, the acceleration of the cumulative weight change may be too slow when set to 0, and the acceleration of the cumulative weight change may be too fast when set to Δf1, both of which will cause difficulties in setting the three-frequency modulation trigger threshold.

[0110] Assuming a system cycle time of 2 seconds and Δf1 of 0.05Hz, the changes in the trigger accumulation parameters when Δf2 is assumed to be 0, 0.025Hz, and 0.05Hz are shown in Table 1. The comparison of their trends after coordinate system correction is as follows: Figure 2 As shown.

[0111] Table 1 Changes in Trigger Accumulation Parameters

[0112]

[0113]

[0114] The S2400 compares the cumulative trigger parameters of the three frequency modulations with the three frequency modulation start threshold each cycle:

[0115] S2410) If the cumulative triggering parameter s of the third frequency modulation is less than the third frequency modulation triggering threshold, the third frequency modulation will not be started;

[0116] S2420) If the cumulative triggering parameter s of the third frequency modulation is greater than the third frequency modulation triggering threshold, then the third frequency modulation is started;

[0117] like Figure 1 As shown, the S3000's regulation mechanism and strategy based on stochastic power correction triple frequency modulation specifically includes the following operations:

[0118] S3100) divides n AGC system cycles into one iterative adjustment cycle, where n is the manually set parameter, and n×T S It should be 2 to 3 times the time required for the power station unit to complete one active power regulation; T S For the AGC system cycle;

[0119] S3200) performs the following operations in the first system cycle of each iterative adjustment cycle, including:

[0120] S3210) Calculate the number of segmented units m in the power plant participating in the third frequency regulation. m≈actual active power generated by the whole plant ÷ segmented unit capacity β, where the segmented unit capacity β is a parameter set by humans. m is taken as the natural number closest to the result of dividing the actual active power generated by the whole plant by the segmented unit capacity. Assuming the actual active power generated by the whole plant is 320MW and the segmented unit capacity β is 30MW, then 320 / 30=10.67. m is taken as the natural number 11 closest to 10.67.

[0121] S3220) Set an array U = [u1, u2, ..., um] containing m elements. m In this embodiment, an array [u1, u2, ... u3] containing 11 elements is set up. 11 ];

[0122] S3230) Given a value range of 1 to n, generate m random integers greater than or equal to 1 and less than or equal to n, and assign them to each element of array U in sequence. Assuming n is 5, this embodiment generates 11 random numbers greater than or equal to 1 and less than or equal to 5, assuming they are 5, 1, 5, 4, 3, 3, 2, 3, 5, 3, 3.

[0123] S3240) Count the number γ of elements in array U that have a value of 1. In this implementation, the number of elements in array U that have a value of 1 is 1.

[0124] S3250) calculates the stochastic correction power Δp3, including:

[0125] S3251) When the grid frequency f > 50 + Δf4, Δp3 = (50 - f + Δf4) × β × γ × k2, where k2 is the manually set third frequency regulation power adjustment coefficient, Δf4 is the manually set parameter, 0 < Δf4 < Δf3, 0 < k2 ≤ first frequency regulation power adjustment coefficient;

[0126] Assuming f is 50.05Hz, Δf4 is 0.01Hz, the segmentation unit capacity β is set to 30MW according to S3210, k2 is 20 / Hz, and γ is assumed to be 1 according to S3240, then Δp3=(50-50.05+0.01)×30×1×20=-0.04×30×1×20=-24MW;

[0127] S3252) When the power grid frequency f < 50 - Δf4, Δp3 = (50 - f - Δf4) × β × γ × k2;

[0128] (S3253) When the power grid frequency is 50 - Δf4 < f < 50 + Δf4, Δp3 = 0.

[0129] S3260) corrects the AGC plant-wide active power setpoints, including:

[0130] S3261) If the random correction power Δp3 > 0, then the total active power setpoint = min(total active power setpoint + random correction power Δp3, and the upper limit of the adjustable active power of the total plant).

[0131] S3262) If the corrected power Δp3 < 0, then the plant active power setpoint = max(plant active power setpoint + random corrected power Δp3, plant active power adjustable lower limit).

[0132] S3270) Subtract 1 from the value of all elements in array U, i.e., u1 = u1 - 1, u2 = u2 - 1, ... u m =u m-1, in this embodiment, each element in array U[5, 1, 5, 4, 3, 3, 2, 3, 5, 3, 3] minus 1 equals [4, 0, 4, 3, 2, 2, 1, 2, 4, 2, 2];

[0133] S3300) performs the following operations from the 2nd system cycle to the nth system cycle in each iterative adjustment period, including:

[0134] S3310) Count the number of elements γ with the value 1 in array U. Assuming that the elements in the third system cycle U are [3, -1, 3, 2, 1, 1, 0, 1, 3, 1, 1], then γ equals 4.

[0135] S3320) Calculate the stochastic correction power Δp3, including:

[0136] S3321) When the grid frequency f > 50 + Δf4, Δp3 = (50 - f + Δf4) × β × γ × k2, where k2 is the manually set third frequency regulation power adjustment coefficient, Δf4 is the manually set parameter, 0 < Δf4 < Δf3, 0 < k2 ≤ first frequency regulation power adjustment coefficient;

[0137] Assuming f is 50.05Hz, Δf4 is 0.01Hz, the segmentation unit capacity β is set to 30MW according to S3210, k2 is 20 / Hz, and γ is assumed to be 4 according to S3310, then Δp3=(50-50.05+0.01)×30×4×20=-0.04×30×4×20=-96MW;

[0138] S3322) When the grid frequency f < 50 - Δf4, Δp3 = (50 - f - Δf4) × β × γ × k2;

[0139] (S3323) When the power grid frequency is 50 - Δf4 < f < 50 + Δf4, Δp3 = 0.

[0140] S3330) corrects the plant-wide active power setpoints for AGC, including:

[0141] S3331) If the random correction power Δp3 > 0, then the total active power setpoint = min(total active power setpoint + random correction power Δp3, and the upper limit of adjustable active power of the total plant).

[0142] S3332) If the corrected power Δp3 < 0, then the plant active power setpoint = max(plant active power setpoint + random corrected power Δp3, plant active power adjustable lower limit).

[0143] S3340) Subtract 1 from the value of all elements in array U, i.e., u1 = u1 - 1, u2 = u2 - 1, ... u m =u m-1.

[0144] After the nth system cycle is completed, step S3400 jumps to step S3200 to start the next iteration cycle.

[0145] The simulation modeling of the third frequency modulation mode based on stochastic power correction in this invention is as follows: Figure 3 As shown, T in the model y T is the response time constant of the relay; w T is the inertial time constant of the water flow. a T is the inertial time constant of the unit (load); f To adjust the feedback delay, which reflects the synchronization delay between the output power and the PID control signal, this mainly includes the measurement and transmission time of the output power, as well as the PID calculation time; n The static frequency self-adjustment (characteristic) coefficient of the unit (load); the plant-wide setpoint correction function is responsible for performing the functions described in S3200 to S3300 of this invention.

[0146] This embodiment assumes that three power plants participate in the third frequency regulation of the power grid, with a unit capacity β of 10MW for each. The actual active power generation of the three power plants before the third frequency regulation is approximately 600MW, 400MW, and 300MW respectively. The simulated regulation effect of the third frequency regulation is as follows: Figure 4 , Figure 5 As shown, the adjustment effect is smooth and stable.

[0147] To demonstrate the superiority of the present invention's triple frequency modulation based on random power correction in preventing overshoot and system oscillation caused by overshoot, the adjustment coefficient of the triple frequency modulation of the present invention was amplified by a factor of 5 and then simulated. The adjustment effect is as follows: Figure 6 As shown, it can be seen that under the hypothetical operating condition where the frequency regulation function overshoots due to the mismatch between the three-stage frequency regulation parameter settings and the actual operating conditions of the power system, the three-stage frequency regulation mode based on random power correction of the present invention exhibits very high regulation stability and can effectively avoid the possibility of ultra-low frequency oscillation of the power system due to overshoot.

[0148] The three-stage frequency regulation will stop when the grid frequency deviation falls back or the AGC status changes to the point where the triggering condition is met. The following is a detailed explanation of how the three-stage frequency regulation will stop.

[0149] The trigger conditions for stopping the third frequency modulation of the S4000 include:

[0150] S4100) When the tertiary frequency modulation is in the start state, if any of the following conditions S4200 to S4600 are met, the tertiary frequency modulation function is stopped.

[0151] S4200) Compare the absolute value of the system frequency deviation with the three-stage frequency modulation stop threshold value △f5. If |f-50|<△f5, then stop the three-stage frequency modulation function. Here, △f5 is a manually set parameter and is less than the three-stage frequency modulation start threshold value △f1.

[0152] The logic design of the S4200 is to prevent the tertiary frequency modulation from participating in the regulation when the system frequency oscillates, and to prevent the tertiary frequency modulation function from being unable to stop regulating.

[0153] S4300) determines whether the power station AGC is engaged. If the AGC is not engaged, the tertiary frequency regulation function is stopped.

[0154] S4400) determines whether any unit has been put into AGC control. If no unit has been put into AGC control, the three-stage frequency regulation function is stopped.

[0155] Third-degree frequency regulation is active power regulation based on the power station. It is based on the power station's AGC function. Therefore, as described in S4300 and S4400, the normal functioning of the power station's AGC function is a necessary condition for third-degree frequency regulation.

[0156] S4500) determines whether a new AGC adjustment command has been received. If a new AGC adjustment command has been received, the three-stage frequency modulation function is stopped.

[0157] The tertiary frequency regulation of this invention is a spontaneous regulation deployed in the power plant automation control system. Its original design purpose is to automatically correct the frequency of the power grid system when the secondary frequency regulation or manual regulation of the power plant has not been implemented for a long time. Since the tertiary frequency regulation and the secondary frequency regulation or manual regulation of the power plant all operate on the active power setpoint of the entire plant, if they are regulated at the same time, it may cause conflicts, cancellations or other unpredictable abnormal operating conditions. Therefore, in the engineering design, the three regulation methods are defined as mutually exclusive. That is, the AGC regulation source can only be set on the dispatch side to receive the secondary frequency regulation command or can only be set on the power plant side to receive the command of the power plant operator. The mechanism described in S4500 ensures that the tertiary frequency regulation will not operate together with the above two regulation methods.

[0158] S4600) Determines whether the three-stage frequency modulation function is in the active or in the inactive state. If the three-stage frequency modulation function is in the inactive state, then stops the three-stage frequency modulation function.

[0159] The three-stage frequency regulation method of the present invention is a "three-stage frequency regulation" that achieves error-free frequency regulation with the operation sequence being later than the first and second-stage frequency regulation. The method of the present invention generally adopts the idea of ​​periodic iterative regulation. Its regulation mechanism is to gradually restore the system frequency to a relatively balanced state through multiple adjustments over a long time scale. By dividing the regulation unit and introducing random numbers, resonance regulation of each power station is prevented, thereby effectively preventing the three-stage frequency regulation function of the present invention from having a negative impact on the power system.

[0160] The embodiments given above are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions or substitutions made by those skilled in the art based on the technical features of the present invention are within the protection scope of the present invention.

Claims

1. A three-stage frequency modulation method based on random power correction, characterized in that, When the secondary frequency regulation of the power system fails and the grid frequency deviates unidirectionally from the rated frequency for a period of time, the active power regulation of the tertiary frequency regulation is carried out on a per-power station basis, based on the AGC (Automatic Gain Control) put into operation at the power station: The actual active power generated by the entire plant is divided into equal parts. Random numbers are generated by the real-time monitoring system based on the number of division units, and these random numbers are assigned to each element in the array sequentially. An iterative adjustment cycle is defined as several cycles. In each cycle, a random correction power is obtained based on the grid frequency deviation, the capacity of the division units, the number of specified values ​​in the array, and the preset third-order frequency regulation power adjustment coefficient. The active power setpoint of the entire plant is then corrected based on the random correction power. In each iterative adjustment cycle, the value of each element in the array is decremented by one after each cycle correction, and then the correction for the next cycle is performed. Based on the corrected plant-wide active power setpoint, the AGC modifies the individual active power setpoint of each unit and performs closed-loop regulation of the individual active power of each unit. After the number of cycles in an iterative adjustment cycle has been completed, a new random number is generated to execute the next iterative adjustment cycle. The three-stage frequency regulation will stop when the grid frequency deviation falls back or the AGC status changes to the point where the triggering condition is met.

2. The triple frequency modulation method based on random power correction as described in claim 1, characterized in that, The three frequency modulations are automatically initiated based on the following conditions: 1) Set the parameters used to determine whether the third frequency modulation should start automatically: Set the trigger threshold for the third frequency modulation and set the start threshold value △f1 for the third frequency modulation, where △f1≥△f3, and △f3 is the threshold for the first frequency modulation. Set the trigger accumulation parameter s for three frequency modulations. Determine whether to clear and reset it every AGC system cycle. If not, accumulate it. 2) The cumulative trigger parameters for three frequency modulations are compared with the trigger threshold for three frequency modulations during each AGC system cycle: If the cumulative trigger parameter s is less than the trigger threshold of the third frequency modulation, the third frequency modulation will not be started; If the cumulative trigger parameter s is greater than the trigger threshold for third-order frequency modulation, then third-order frequency modulation is initiated.

3. The triple frequency modulation method based on random power correction as described in claim 2, characterized in that, The triggering of the reset and accumulation of the cumulative parameter s is as follows: 1) The reset condition for the trigger cumulative parameter s is determined every AGC system cycle as follows: S2210) Compare the absolute value of the grid frequency deviation with the magnitude of the three-stage frequency regulation start threshold value Δf1. If |f-50|<Δf1, then reset the trigger accumulation parameter s to zero, where f is the grid frequency. S2220) Determine whether the power station AGC is engaged. If the AGC is not engaged, reset the trigger accumulation parameter s to zero. S2230) Determine whether any unit has been put into AGC control. If no unit has been put into AGC control, then the trigger accumulation parameter s is cleared and reset. S2240) Determine whether a new AGC adjustment command has been received. If it has been received, clear and reset the trigger accumulation parameter s. S2250) Determines whether the third frequency modulation is in the active state or in the exit state. If it is in the exit state, the trigger accumulation parameter s is cleared and reset. S2260) If none of the conditions described in S2210 to S2250 are met, then the trigger accumulation parameter s of the third frequency modulation is not cleared and reset. 2) The trigger accumulation parameters are accumulated every AGC system cycle as follows: S2310) Compare the absolute value of the system frequency deviation collected in the current cycle with the absolute value of the frequency deviation collected in the previous cycle: S2311) If the absolute value of the system frequency deviation in the current cycle is less than the absolute value of the system frequency deviation in the previous cycle, that is, if |f-50|<|f'-50|, then skip the following subsequent steps and keep the trigger accumulation parameter s unchanged, where f' is the power grid frequency collected in the previous cycle; S2312) If the absolute value of the system frequency deviation in the current cycle is greater than the absolute value of the system frequency deviation in the previous cycle, that is, if |f-50|≥|f'-50|, then execute S2320 to accumulate the trigger accumulation parameter s of the three frequency modulations; S2320) Based on the system frequency deviation and integral time, the trigger accumulation parameter s of the three frequency modulations is accumulated: S2321) The theoretical calculation formula for accumulating the trigger accumulation parameter s of the third frequency modulation is s=s+∫(f-50-Δf2)dt, where Δf2 is a manually set constant that satisfies 0<Δf2<Δf1, and dt is the time integral; The actual calculation formula for accumulating the trigger accumulation parameter s of the third frequency modulation (S2322) is s=s+(|f-50|-△f2)×T S If the AGC system has a constant calculation cycle, then T S This is the periodic time; if there is no such period, then T. S This refers to the average or estimated period time.

4. The triple frequency modulation method based on random power correction as described in claim 1, characterized in that, The adjustment is performed using a three-frequency modulation mode based on random parameters: S3100) divides n AGC system cycles into one iterative adjustment cycle, where n is the manually set parameter, and n×T S It should be 2 to 3 times the time required for the power station unit to complete one active power regulation; T S For the AGC system cycle; S3200) performs the following operation in the first AGC system cycle of each iteration adjustment cycle: S3210) Calculate the number of segmented units m in the power plant participating in the third frequency regulation, m≈actual active power generated by the whole plant ÷ segmented unit capacity β, where the segmented unit capacity β is a parameter set by humans, and m is the natural number closest to the result obtained by dividing the actual active power generated by the whole plant by the segmented unit capacity. S3220) Set an array U = [u1, u2, ..., u] containing m elements in the power plant real-time monitoring system. m ]; S3230) Generate m random integers greater than or equal to 1 and less than or equal to n, with a value range of 1 to n, and assign them to each element of array U in turn; S3240) Count the number γ of elements in array U that have a value of 1; Calculate the stochastic correction power Δp3 using S3250: S3251) When the grid frequency f > 50 + Δf4, Δp3 = (50 - f + Δf4) × β × γ × k2, where k2 is the manually set third frequency regulation power adjustment coefficient, Δf4 is the manually set parameter, 0 < Δf4 < Δf3, 0 < k2 ≤ first frequency regulation power adjustment coefficient; S3252) When the power grid frequency f < 50 - Δf4, Δp3 = (50 - f - Δf4) × β × γ × k2; S3253) When the power grid frequency is 50-△f4<f<50+△f4, △p3=0; S3260) corrects the plant-wide active power setting value for AGC: S3261) If the random correction power Δp3 > 0, then the total active power setpoint = min(total active power setpoint + random correction power Δp3, and the upper limit of adjustable active power of the total plant). S3262) If the random correction power Δp3 < 0, then the total active power setpoint = max(total active power setpoint + random correction power Δp3, lower limit of adjustable total active power). After obtaining the corrected active power setpoint for the entire plant, AGC modifies the individual active power setpoint for each unit and performs closed-loop regulation of the individual active power in each unit. S3270) Subtract 1 from the value of all elements in array U, i.e., u1 = u1 - 1, u2 = u2 - 1, ... u m =u m -1; S3300) performs the following operations from the second system cycle to the nth system cycle in each iterative adjustment period: S3310) Count the number γ of elements in array U that have a value of 1; S3320) Calculate the stochastic correction power Δp3: S3321) When the grid frequency f > 50 + Δf4, Δp3 = (50 - f + Δf4) × β × γ × k2, where k2 is the manually set third frequency regulation power adjustment coefficient, Δf4 is the manually set parameter, 0 < Δf4 < Δf3, 0 < k2 ≤ first frequency regulation power adjustment coefficient; S3322) When the grid frequency f < 50 - Δf4, Δp3 = (50 - f - Δf4) × β × γ × k2; S3323) When the power grid frequency is 50-△f4<f<50+△f4, △p3=0; S3330) corrects the plant-wide active power setting value for AGC: S3331) If the random correction power Δp3 > 0, then the total active power setpoint = min(total active power setpoint + random correction power Δp3, and the upper limit of adjustable active power of the total plant). S3332) If the random correction power Δp3 < 0, then the total active power setpoint = max(total active power setpoint + random correction power Δp3, lower limit of adjustable total active power). After obtaining the corrected active power setpoint for the entire plant, AGC modifies the individual active power setpoint for each unit and performs closed-loop regulation of the individual active power in each unit. S3340) Subtract 1 from the value of all elements in array U, i.e., u1 = u1 - 1, u2 = u2 - 1, ... u m =u m -1; After the nth system cycle is completed, step S3400 jumps to step S3200 to start the next iteration cycle.

5. The three-stage frequency modulation method based on random power correction as described in claim 1, characterized in that, The stopping trigger condition for the three-frequency modulation is: S4100) When the third frequency modulation is in the start state, if any of the following conditions S4200 to S4600 are met, the third frequency modulation is stopped. S4200) compares the absolute value of the grid frequency deviation with the value of the three-stage frequency regulation stop threshold △f5. If |f-50| < △f5, the three-stage frequency regulation function is stopped. △f5 is a manually set parameter and is less than the three-stage frequency regulation start threshold △f1. S4300) determines whether the power station's AGC is engaged. If the AGC is not engaged, then the three-stage frequency regulation is stopped. S4400) Determines whether any unit has engaged AGC control. If no unit has engaged AGC control, then stops the third frequency regulation. S4500) determines whether a new AGC adjustment command has been received; if so, it stops three frequency modulations. S4600) Determines whether the third frequency modulation is in the active or in the inactive state. If the third frequency modulation is in the inactive state, then the third frequency modulation is stopped.

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