Flow Coordination Operation Control Method for Series Cascade Hydropower Stations

Abstract

This invention discloses a flow coordination operation control method for cascade hydropower stations. The method includes responding to planned load adjustment commands from the power grid, using a load allocation method for each generating unit based on the flow coordination principle of the cascade power stations, obtaining the guide vane opening of the generating unit in a steady state as the target guide vane opening, and then linearly opening / closing the current guide vane opening to the target guide vane opening; or responding to unplanned load disturbances from the user end, adding a proportional control module to the PID governor to adjust the guide vane opening of the generating unit in real time according to the flow deviation between upstream and downstream hydropower stations, thereby achieving adjustment of the generating unit output. This invention is used to maintain flow coordination among cascade power stations after planned load adjustments or unplanned minor load disturbances, ensuring that the power stations can meet the flow coordination requirements during normal operation.

Description

[0001] This invention is a divisional application of application CN202411616965.3, filed on November 13, 2024, entitled "Method for Coordinated Operation Control of Flow Rate in Series Cascade Hydropower Stations". Technical Field

[0002] This invention relates to the field of flow coordination control technology for series cascade hydropower stations, and in particular to a flow coordination operation control method for series cascade hydropower stations. Background Technology

[0003] Hydropower plays a vital role in the development of renewable energy. Its operational flexibility and high responsiveness enable it to undertake important tasks such as peak shaving and frequency regulation in the power grid, which is of great significance for maintaining grid security and stability. However, due to the limitations of conventional hydropower stations and turbines, the development and utilization of ultra-high head hydropower resources are currently not feasible. Therefore, it is possible to consider using cascade hydropower stations in series to develop ultra-high head hydropower resources in stages.

[0004] Cascade hydropower stations are typically connected by regulating reservoirs and water diversion tunnels; their layout is shown in [reference needed]. Figure 1 As shown, each power station includes a surge tank and at least one generating unit. The first power station is connected to the upper reservoir (upstream reservoir) via a water diversion tunnel, and the last power station is connected to the lower reservoir (downstream reservoir). The regulating reservoir acts like a large surge tank, reducing fluctuations in the operating head of the cascade hydropower stations and providing some regulation during emergency conditions. Regulating reservoirs are typically not naturally formed and must be artificially excavated, resulting in relatively small volumes. Therefore, during normal operation, the flow rates of the upstream and downstream power stations must be equal to prevent large fluctuations in the regulating reservoir level due to flow mismatch, which could affect the normal operation of the entire cascade hydropower system.

[0005] Therefore, during normal operation, cascade hydropower stations require hydraulic control measures that meet flow coordination requirements, taking into account waterway parameters and unit characteristics. At the micro level, operational control strategies that ensure flow coordination during the daily operation of cascade hydropower stations are provided. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and defects of the prior art and provide a flow coordination operation control method for cascade hydropower stations. This method is used to maintain the flow coordination among cascade power stations after planned load adjustments or unplanned minor load disturbances occur, and to ensure that the power stations can meet the flow coordination requirements during normal operation.

[0007] A flow-coordinated operation control method for cascade hydropower stations includes responding to planned load adjustment commands from the power grid, using a load allocation method for each unit based on the flow coordination principle of the cascade power stations, obtaining the guide vane opening of the unit in a steady state as the target guide vane opening, and then linearly opening / closing the current unit guide vane opening to the target guide vane opening; or responding to unplanned load disturbances from the user end, adding a proportional control module to the PID governor to adjust the unit guide vane opening in real time according to the flow deviation between upstream and downstream hydropower stations, thereby achieving regulation of unit output.

[0008] The process of obtaining the guide vane opening of the units in steady state based on the load distribution method of each unit in the cascade power station includes the following steps:

[0009] S1. Assume the flow rate of each power station is Q. total ;

[0010] S2. Based on the proportion of the output of different generating units in the same power station to the total output of the power station, calculate the total flow rate Q of the power station. total The allocation is performed to obtain the reference flow Q for each unit. T ;

[0011] S3. Based on the reference traffic Q of each unit T Calculate the head loss of each pipe section, and based on the water levels of the upstream and downstream reservoirs and regulating ponds, estimate the operating head H of each unit in the cascade power station. T ;

[0012] S4. Based on the working head H of each unit T Traffic Q T And the unit speed n of the unit is obtained from the rated speed. 11 and unit flow Q 11 ;

[0013] S5. Based on the unit speed n of the generator set 11 and unit flow Q 11 By analyzing the unit speed-unit flow rate characteristic curve Q of the unit 11 =f(n) 11 Interpolate τ to obtain the unit opening degree τ.

[0014] S6. Based on the guide vane opening τ and the unit rotational speed n 11 By analyzing the unit speed-unit torque characteristic curve m 11 =f(n) 11 Interpolate τ to obtain the unit torque m of the unit. 11 ;

[0015] S7. Based on the unit torque m 11 The unit output P is obtained by performing torque conversion calculation;

[0016] S8. Sum the output P of all units in the cascade hydropower station to obtain the total output, and compare it with the target output; if the difference between the total output and the target output is greater than the allowable error, then use the flow rate Q based on the output deviation correction assumption. total Then return to execute steps S2-S8; otherwise, end the loop calculation and obtain the unit guide vane opening.

[0017] Wherein, the unit speed n of the unit 11 and unit flow Q 11 The calculation formula is:

[0018]

[0019] Where D is the runner diameter and n is the rated speed of the unit.

[0020] The formula for calculating the unit's output is as follows:

[0021]

[0022] In response to unplanned load disturbances from the user end, the PID speed governor first performs unit control regulation to obtain the first relative guide vane opening caused by the PID speed governor control. Then, based on an additional proportional regulation link, the second relative guide vane opening caused by the proportional regulation link is calculated according to the flow deviation between the upstream and downstream hydropower stations. Based on the first relative guide vane opening and the second relative guide vane opening, the actual relative opening value of the unit guide vanes is obtained, thereby realizing the regulation of the unit opening.

[0023] The relative opening value of the actual unit guide vanes is the sum of the first relative guide vane opening caused by the PID speed controller and the second relative guide vane opening caused by the proportional regulation link.

[0024] The PID speed controller control equations include:

[0025]

[0026] Where b t b p T d And T n These are the transient slip coefficient, permanent slip coefficient, buffer time constant, and differential time constant of the speed governor, respectively. μ and μ are the relative values ​​of the unit speed deviation and the guide vane opening deviation, respectively.

[0027] The additional proportional adjustment step is controlled by the following formula:

[0028]

[0029] Where T k This refers to the proportional adjustment coefficient corresponding to the additional proportional adjustment step. The reference flow deviation refers to the real-time flow rate difference between the same numbered units in the upper and lower level hydropower stations. μ1 refers to the relative guide vane opening caused by the PID speed controller, and μ2 refers to the relative guide vane opening caused by the proportional regulation link. μ1+μ2 is the relative opening value of the actual unit's guide vanes.

[0030] Among them, the following formula is used to reverse the relative reference flow of the unit to realize the real-time reference flow of the unit;

[0031]

[0032] Among them, S8, S9 and S 10 These are the characteristic parameters of the unit, where p represents the relative value of the unit's output deviation and q represents the unit's real-time reference flow rate.

[0033] The speed governor is located on the generator set, with one speed governor configured for each generator set.

[0034] This invention relates to an operation control strategy for load adjustments occurring during normal operation of a series-cascade hydropower station. For planned load adjustment commands from the power grid, it provides operating adjustment modes and load allocation strategies for each unit in the cascade power station based on the parameters of the entire cascade power station's waterway system and the unit characteristic curves. For unplanned load disturbances from the user end, it infers the unit flow rate by monitoring the output, speed, and guide vane opening information of each unit in the cascade power station and adjusts the flow rate based on the flow rate deviation between the upstream and downstream power stations. Attached Figure Description

[0035] Figure 1 A simplified layout diagram of a series cascade hydropower station system with regulating pool, as described in an embodiment of the present invention.

[0036] Figure 2 This is a flowchart illustrating the load distribution of each unit in a series-cascade hydropower station as proposed in an embodiment of the present invention.

[0037] Figure 3 This describes the change in total flow rate of power plants at all levels after using the load allocation method for each unit proposed in this invention in an embodiment of the invention.

[0038] Figure 4 This is the stability region when unpredictable minor load disturbances occur when using the speed governor control strategy of the present invention in an embodiment of the invention;

[0039] Figure 5 This describes the process of the total flow deviation between power station A and power station B when the speed governor control strategy of the present invention is adopted in an embodiment of the present invention.

[0040] Figure 6This describes the process of the total flow deviation between power station C and power station B when the speed governor control strategy of the present invention is adopted in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0042] To address the operational flow coordination requirements for developing ultra-high head hydropower resources using a series hydropower station system, this invention proposes an operational control strategy for the entire cascade hydropower station system under load variations. For planned load adjustments from the power grid, a strategy for determining the reference flow rate that satisfies the total output of the cascade hydropower stations is provided based on the parameters of the entire cascade hydropower station waterway system and the unit characteristic curves.

[0043] To address unplanned load disturbances from users, the flow rate of each unit in the cascade power station is inferred by monitoring the output, speed, and guide vane opening information of each unit. Adjustments are then made based on the flow deviation between upstream and downstream power stations to eliminate flow deviations between cascade power stations in a steady state and ensure flow coordination.

[0044] In response to planned load adjustment instructions from the power grid, Figure 2 This paper presents a load distribution method for series-cascade hydropower stations under steady-state conditions that satisfies flow coordination. The main steps include the following:

[0045] (a) Assume that the flow rate of each power station is Q. total ;

[0046] (b) Based on the proportion of the output of different generating units in the same power plant to the total output of the power plant, calculate the total flow rate Q of the power plant. total The data is allocated to obtain the reference flow Q for each unit. T ;

[0047] (c) Once the flow rates of each generating unit are known, the head loss of each pipe section can be calculated. Then, based on the water levels of the upstream and downstream reservoirs and regulating ponds, the operating head H of each generating unit in the cascade power station can be estimated. T ;

[0048] (d) Obtain the unit speed n of each unit based on the operating head, flow rate, and rated speed of each unit. 11 and unit flow Q 11 The specific formula is as follows: Where D is the runner diameter and n is the rated speed of the unit;

[0049] (e) Based on the unit speed n of the generator set 11 and unit flow Q 11By analyzing the unit speed-unit flow rate characteristic curve (Q) of the unit 11 =f(n) 11 Interpolate τ to obtain the unit opening degree τ.

[0050] (f) Based on the guide vane opening τ and the unit rotational speed n 11 By analyzing the unit speed-unit torque characteristic curve (m) of the unit 11 =f(n) 11 Interpolation is performed on τ) to obtain the unit torque m of the unit. 11 ;

[0051] (g) Based on the unit torque m 11 The unit output is obtained by combining the torque conversion formula.

[0052] (h) Sum the output P of all units in the cascade hydropower station to obtain the total output and compare it with the target output.

[0053] (i) If the difference between the total output and the target output is greater than the allowable error, then the flow rate Q is referenced based on the output deviation correction assumption. total Then repeat step (b). If the difference between the total output and the target output is less than the allowable error, then end the loop calculation.

[0054] By following the steps above, all operating parameters of the unit can be obtained, including guide vane opening, flow rate, operating head, and unit output. These steps constitute the load distribution method for each unit in a cascade power station that meets flow coordination requirements. Following these steps, the guide vane opening of the unit under steady-state conditions can be obtained.

[0055] After receiving a load adjustment command from the power grid, the power station can determine the turbine guide vane opening before and after the load adjustment according to the above steps; and then open (or close) the turbine guide vanes linearly to the target guide vane opening. Once the hydraulic transition process reaches a stable state, the flow coordination requirements of the cascade power stations can be met.

[0056] To address unplanned load disturbances from users, this invention adds a proportional control module based on the flow deviation between upstream and downstream hydropower stations to the existing PID governor control model. This proportional control module, based on flow deviation, eliminates flow discrepancies between cascade hydropower stations in steady-state conditions, ensuring flow coordination. The governor control mode proposed in this invention establishes hydraulic connections between upstream and downstream hydropower stations, enabling unified regulation.

[0057] The original PID speed controller control equation is as follows:

[0058]

[0059] Where b t b p T d And T n These are the transient slip coefficient, permanent slip coefficient, buffer time constant, and differential time constant of the speed governor, respectively. μ and μ are the relative values ​​of the unit speed deviation and the guide vane opening deviation, respectively.

[0060] The proportional adjustment module added to the original speed controller in this invention is as follows:

[0061]

[0062] Where T k This refers to the scaling factor corresponding to the additional scaling module.

[0063] In the above formula, The flow deviation refers to the flow rate difference between the same numbered units in upstream and downstream hydropower stations. μ1 refers to the relative guide vane opening caused by the original PID governor control mode, and μ2 refers to the relative guide vane opening caused by the proportional regulation element proposed in this invention. The actual relative guide vane opening value of the unit is: μ1 + μ2.

[0064] Since the unit flow rate cannot be directly monitored, this invention uses real-time monitoring of the unit's relative output, relative speed, and relative guide vane opening, and employs formulas... The wave propagates the relative reference flow of the unit, thereby enabling real-time monitoring of the reference flow of the unit.

[0065] Among them, S8, S9 and S 10 These are the characteristic parameters of the unit, where p represents the relative value of the unit's output deviation and q represents the unit's real-time reference flow rate.

[0066] The present invention relates to an operation control strategy for load adjustments occurring during normal operation of a series-cascade hydropower station. The applicable system layout for the series-cascade hydropower station is described in [reference needed]. Figure 1 As shown.

[0067] Assuming the load adjustment command from the power grid is 10% of the original output, the total output of the cascade hydropower stations under the target state can be obtained based on the power grid load adjustment command. This total output is then incorporated into the present invention. Figure 2 In the load distribution flow shown, let the total output be equal to Figure 2 P in set The target guide vane opening of each unit in the cascade hydropower station is calculated to obtain the target guide vane opening under the target condition. Through linear adjustment, the unit guide vanes are adjusted to the target guide vane opening. After reaching a stable state, the total flow rate between the upstream and downstream hydropower stations can be balanced, such as... Figure 3 As shown.

[0068] Depend on Figure 3 It can be seen that after using the operation control method for planned load adjustment proposed in this invention, the total flow rate of each level of hydropower station is consistent when the system reaches a stable state.

[0069] Figure 4 The system operating stability domain obtained after using the operation control method for unplanned small load disturbances proposed in this invention.

[0070] Depend on Figure 4 It can be seen that the cascade hydropower stations can meet the stability requirements when using the governor control strategy proposed in this invention and in the joint operation mode.

[0071] Assuming a system load disturbance of 5% from the user end, what are the transient slip coefficient and buffer time constant b in the PID controller? t With T d Values Figure 4 Point P1 is obtained. Figure 5 and 6 The difference between the total flow rate of power plants A and B and the total flow rate of power plants B and C.

[0072] Depend on Figure 5 and Figure 6 It can be seen that, for unplanned minor load disturbances, after adopting the PID speed controller control strategy proposed in this invention (T) k =0 indicates that the PID speed governor control strategy proposed in this invention was not adopted. The flow difference between the upper and lower hydropower stations gradually approaches 0, which verifies the effectiveness of the PID speed governor control strategy proposed in this invention.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0074] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0075] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for coordinated flow control of cascade hydropower stations, characterized in that, In response to unplanned load disturbances from the user end, a proportional control link is added to the PID speed controller to adjust the guide vane opening of the unit in real time based on the flow deviation between the upstream and downstream hydropower stations, thereby realizing the adjustment of the unit output and simultaneously meeting the flow coordination principle of cascade power stations and the stability under small load disturbance conditions. In response to unplanned load disturbances from the user end, the PID speed governor first performs unit control regulation to obtain the first relative guide vane opening caused by the PID speed governor control. Then, based on the proportional regulation link, the second relative guide vane opening caused by the proportional regulation link is calculated according to the flow deviation between the upper and lower hydropower stations. Based on the first relative guide vane opening and the second relative guide vane opening, the actual relative opening value of the unit guide vanes is obtained, thereby realizing the regulation of the unit opening. The control equations of the PID speed controller include: ； in , , as well as These are the transient slip coefficient, permanent slip coefficient, buffer time constant, and differential time constant of the speed governor, respectively. and These are the relative values ​​of the unit speed deviation and the relative values ​​of the guide vane opening deviation, respectively. This refers to the relative guide vane opening caused by PID speed controller control; The proportional adjustment mechanism is controlled by the following formula: ； in, This refers to the proportional adjustment coefficient corresponding to the proportional adjustment stage. This refers to the real-time deviation in the reference flow rate of the same numbered generating unit in a hydropower station at different levels. This refers to the relative guide vane opening caused by the proportional adjustment mechanism.

2. The flow coordination operation control method for cascade hydropower stations according to claim 1, characterized in that, The actual relative opening value of the unit's guide vanes is the sum of the first relative guide vane opening caused by the PID speed controller and the second relative guide vane opening caused by the proportional regulation link.

3. The flow coordination operation control method for cascade hydropower stations according to claim 1, characterized in that, The following formula is used to reverse the relative flow rate of the generator unit, thereby enabling real-time monitoring of the generator unit's flow rate; ； in, , as well as These are the characteristic parameters of the unit. p Represents the relative value of the unit's output deviation. q This represents the real-time data usage of the generator unit.

4. The flow coordination operation control method for cascade hydropower stations according to claim 1, characterized in that, The PID speed controllers are installed on the generator sets, with one PID speed controller configured for each generator set.

Images