Small hydroelectric generating set variable-speed operation control method based on optimal guide vane opening

Abstract

The invention relates to a variable-speed operation control method for a small hydroelectric generating set based on optimal guide vane opening, which designs a matched optimal rotating speed of the set, and adjusts the rotating speed of the water turbine set in real time, so that the set can operate at the highest efficiency under different water head conditions, thereby improving the utilization efficiency of water energy and the overall power generation performance. According to the method, it can be ensured that the small hydroelectric generating set always operates at the highest-efficiency working point and the optimal actual rotating speed under the condition of large-range water head changes, and therefore efficient and economical electric power production is achieved.

Description

Technical Field

[0001] The present invention relates to a variable-speed operation control method for small hydropower units based on the optimal guide vane opening, belonging to the technical fields of optimal operation of hydraulic turbines and automatic control. Background Technique

[0002] Under the background of global energy transformation, hydropower, as a clean and renewable energy source, plays a crucial role in achieving the goals of "carbon peak and carbon neutrality". Among them, small hydropower is particularly valued in rural and remote mountainous areas due to its significant advantages such as mature development technology, short construction period, many site resources, and small investment scale. Small hydropower in China refers to small hydropower stations with a total installed capacity not exceeding 50 MW, which play an active role in providing clean electricity, optimizing the power grid structure, and promoting local economic development.

[0003] In the field of hydropower generation, since hydro-generator sets are relatively sensitive to changes in working head, when their operating conditions deviate from the designed conditions, the operating efficiency of the units will decrease significantly. Especially for small hydropower stations, due to their small reservoir regulation capacity, combined with seasonal fluctuations in rivers and large differences in reservoir water levels, the water turbine unit will operate away from the designed operating point for a long time, resulting in a reduction in the utilization rate of water energy and a waste of water energy resources.

[0004] Traditional small hydropower units mostly adopt a constant-speed operation strategy. Although this strategy is simple to control, when the head change range is large, it is difficult for the unit to achieve optimal efficiency operation, resulting in unnecessary waste of energy. In contrast, the variable-speed operation strategy can adjust the unit speed in real time to better adapt to head changes, thereby improving the power generation efficiency of water energy.

[0005] Patent CN110516321A discloses a variable-speed hydraulic turbine runner selection calculation method, and its steps include: taking unit flow as the abscissa and unit speed as the ordinate in a coordinate system, drawing the hydraulic turbine efficiency line and the 95% output limit line; reading the hydraulic turbine efficiency of each operating point in the coordinate system, calculating the unit output, and drawing the equal unit output line; connecting the highest efficiency points to form the variable-speed optimal characteristic curve of the hydraulic turbine; determining the rated operating point of the variable-speed hydraulic turbine with the intersection point of the 95% output limit line and the variable-speed optimal characteristic curve; calculating the hydraulic turbine runner diameter according to the coordinates, efficiency, and the rated power and designed head of the hydraulic turbine determined by water energy calculation. This method simplifies the calculation process of the runner diameter during hydraulic turbine selection, but does not consider the influence of factors such as the optimization of unit operating efficiency and large-scale head changes, and is only applicable to hydraulic turbine selection, without considering the variable-speed operation control problem of the optimal operating efficiency of the actual hydraulic turbine, resulting in a certain degree of waste of water resources.

[0006] Patent CN114865712A discloses that the maximum efficiency tracking of the water turbine is performed based on the grid-side demand power P and the working head H, while planning the reference value of the guide vane opening and the optimal rotational speed value; the output power of the water turbine is adapted to the change of the grid load through the coordinated control of the guide vane opening and the optimal rotational speed. This method is applicable to the situation where the grid-side power needs to be adjusted, which mostly appears in the variable-speed operation field of pumped-storage units. In fact, the optimal rotational speed described in this patent is only the optimal rotational speed for a given power value, and the operating efficiency under different given power values is not the highest value of the unit operating efficiency. In the field of small hydropower, it is not necessary to design the corresponding optimal rotational speed starting from the given value of the grid-side demand power.

[0007] Aiming at the deficiencies of the prior art, the present invention proposes a variable-speed operation control method for small hydropower units based on the optimal guide vane opening. This method starts from analyzing the comprehensive characteristic curve of the water turbine, finds the optimal guide vane opening corresponding to the highest point of the unit operating efficiency, and ensures that the unit always operates at the highest efficiency point by adjusting the unit rotational speed in real time to adapt to the large-range change of the external head, so as to optimize the energy utilization and reduce resource waste. The present invention is proposed to solve the problem that the variable-speed operation control strategy in the prior art fails to fully consider the operating efficiency, so as to realize the efficient and stable operation of small hydropower units under different hydrological conditions. Summary of the Invention

[0008] In the prior art, small hydropower units generally adopt the synchronous rotational speed constant-speed operation strategy. This strategy cannot achieve the optimal efficiency when the head fluctuates greatly, resulting in unnecessary loss of energy. At the same time, the unit may enter an unstable operation condition, which is not conducive to the safe and stable operation of the unit. In order to overcome the deficiencies of the existing small hydropower units, such as low operating efficiency and waste of water resources caused by the constant-speed operation strategy in the face of large-range head changes, the present invention provides a variable-speed operation control method for small hydropower units based on the optimal guide vane opening, designs the matching optimal rotational speed of the unit, and enables the unit to maintain the highest efficiency operation under different head conditions by adjusting the rotational speed of the water turbine unit in real time, thereby improving the utilization efficiency of water energy and the overall power generation performance.

[0009] A variable-speed operation control method for small hydropower units based on the optimal guide vane opening includes the following steps:

[0010] Step 1: Obtain the comprehensive characteristic curve of the selected type of water turbine, with the unit flow rate as the abscissa and the unit rotational speed as the ordinate, and read the abscissa and ordinate corresponding to all efficiency points at all openings.

[0011] Step 2: Compare the values of the highest efficiency points at all openings, determine the maximum efficiency value among the highest efficiency points at all different openings, and the opening corresponding to this value is the optimal guide vane opening.

[0012] Step 3: Obtain the unit speed and unit flow corresponding to the highest point of the unit operation efficiency at the optimal guide vane opening. At this time, the unit speed is the optimal unit speed;

[0013] Step 4: Calculate the optimal actual speed according to the optimal unit speed, working head, and runner diameter;

[0014] Step 5: Combine the optimal speed obtained in Step 4 that adapts to the change of water head and keeps the efficiency at the highest point of operation with the mechanical rotation motion equation, and design the corresponding closed-loop controller, so as to control the unit speed to be consistent with the optimal speed and realize the variable-speed operation of the unit.

[0015] The formula for the optimal actual speed in Step 4 is:

[0016]

[0017] In formula (1), is the optimal unit speed, n op is the optimal actual speed, H is the working head, and D1 is the runner diameter.

[0018] The formula for the actual output in Step 5 is:

[0019] P = 9.81·Q 11 D1 2 H 3 / 2 η(2)

[0020] In formula (2), Q 11 is the unit flow, and H, D1, and η are the working head, runner diameter, and operation efficiency of the water turbine.

[0021] The formula for the mechanical rotation motion equation in Step 6 is:

[0022] J·dω / dt = M t -M g (3)

[0023] In formula (3): J is the moment of inertia of the unit; ω is the angular velocity of the unit rotation; M t is the main torque of the water turbine; M g is the resistance torque of the generator; dω / dt is the rotational acceleration of the unit.

[0024] The regulators of the speed control system and excitation system of the hydropower unit usually adopt the PID control unit as the core control strategy. The transfer function of the parallel PID speed governor can be expressed as:

[0025] G PID (s) = K p +K i / s + K d s / (T d(s + 1)(4)

[0026] In Equation (4): s is a complex variable; K p is the coefficient of the proportional link; K i is the coefficient of the integral link; K d is the coefficient of the differential link; T d is the inertia time constant.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The present invention improves the water energy conversion efficiency. Through variable-speed operation control, the unit can adjust to the optimal operating point according to the real-time head change, achieving the maximization of the water energy conversion efficiency; it optimizes the operating performance of the unit. The variable-speed operation strategy enables the unit to respond quickly when the head fluctuates, reducing the efficiency loss caused by the head change; it has strong adaptability. This method is especially suitable for hydropower units under the condition of a large head change range, especially for small hydropower stations with small reservoir regulation capacity and large seasonal water inflow changes, and has better adaptability and practicability. It reduces energy waste. The present invention avoids the low-efficiency energy consumption under the constant-speed operation strategy by precisely controlling the unit to operate at the optimal speed, thereby making the most efficient use of water resources; it improves economic efficiency. In the long-term operation, improving efficiency and reducing energy waste will directly translate into economic benefits, bringing cost savings to the operation of small hydropower stations.

[0029] By implementing the variable-speed operation control method based on the optimal guide vane opening, the present invention realizes the high-efficiency operation of small hydropower units under different head conditions, significantly improves the water energy conversion efficiency, enhances the adaptability of the unit to large-range head fluctuations, reduces water resource loss, and improves economic efficiency; at the same time, it meets the requirements of environmental protection and sustainable development, demonstrating the important role of technological innovation in improving energy utilization efficiency and promoting the development of green energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 is the flow chart of the variable-speed operation control method of the small hydropower unit based on the optimal guide vane opening of the present invention;

[0032] Figure 2 is the comprehensive characteristic curve diagram of the water turbine provided by the manufacturer for the variable-speed operation control method of the small hydropower unit based on the optimal guide vane opening of the present invention;

[0033] Figure 3 This is the comprehensive characteristic curve graph of the water turbine for the variable-speed operation control method of small hydropower units based on the optimal guide vane opening of the present invention;

[0034] Figure 4 This is the efficiency curve graph at each opening for the variable-speed operation control method of small hydropower units based on the optimal guide vane opening of the present invention;

[0035] Figure 5 This is the optimal actual speed graph at different water heads for the variable-speed operation control method of small hydropower units based on the optimal guide vane opening of the present invention;

[0036] Figure 6 This is the output graph of the optimal guide vane opening and at different water heads for the variable-speed operation control method of small hydropower units based on the optimal guide vane opening of the present invention;

[0037] Figure 7 This is the block diagram of the control system for the variable-speed operation unit. Specific implementation manner

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] The following is a preferred specific embodiment for illustrating the variable-speed operation control method of small hydropower units based on the optimal guide vane opening of the present invention.

[0040] Refer to Figure 1 , a variable-speed operation control method for small hydropower units based on the optimal guide vane opening, comprising the following steps:

[0041] Step 1: Obtain the comprehensive characteristic curve of the selected type of water turbine. Taking the unit flow rate as the abscissa and the unit speed as the ordinate, read the abscissas and ordinates corresponding to all efficiency points at all openings;

[0042] Step 2: Compare the values of the highest efficiency points at all openings, determine the maximum efficiency value among the highest efficiency points at all different openings, and the opening where this value is located is the optimal guide vane opening;

[0043] Step 3: Obtain the unit speed and unit flow rate corresponding to the highest point of the unit operation efficiency at the optimal guide vane opening. At this time, the unit speed is the optimal unit speed;

[0044] Step 4: Calculate the optimal actual speed according to the optimal unit speed, working water head, and runner diameter;

[0045] Step 5: Design a corresponding closed-loop controller by combining the optimal rotational speed and the mechanical rotation motion equation obtained in Step 4 that adapt to the head change and maintain the highest efficiency operation, so as to control the unit speed to be consistent with the optimal speed and achieve the variable-speed operation of the unit.

[0046] The formula of the mechanical rotation motion equation in Step 5 is:

[0047] J·dω / dt=M t -M g (3)

[0048] In formula (3): J is the moment of inertia of the unit; ω is the rotational angular velocity of the unit; M t is the main torque of the water turbine; M g is the resistance torque of the generator; dω / dt is the rotational acceleration of the unit.

[0049] The regulators of the speed control system and the excitation system of the hydropower unit usually adopt the PID control unit as the core control strategy. The transfer function of the parallel PID speed governor can be expressed as:

[0050] G PID (s)=K p +K i / s+K d s / (T d s+1)(4)

[0051] In formula (4): s is the complex variable; K p is the proportional link coefficient; K i is the integral link coefficient; K d is the differential link coefficient; T d is the inertia time constant.

[0052] From Figure 1 The flowchart of the variable-speed operation control method for small hydropower units based on the optimal guide vane opening is shown; First, perform Step 1: The comprehensive characteristic curve of the water turbine is usually provided by the manufacturer, such as Figure 2 shown; or it can be obtained through experimental measurement. In this example, obtain the comprehensive characteristic curve of the water turbine with the model HL260A / 244, such as Figure 3 shown. On this curve, with the unit flow rate as the abscissa and the unit rotational speed as the ordinate, record the abscissa and ordinate corresponding to all efficiency points at different openings. Figure 3 The black circles in

[0053] Next, perform Step 2: On the obtained comprehensive characteristic curve, compare the efficiency points at different opening degrees and find the value of the highest efficiency point among all opening degrees. Through this comparison, determine the opening degree corresponding to the highest operating efficiency of the water turbine, and this opening degree is the optimal guide vane opening degree. From Figure 4 it can be directly seen the curves of efficiency versus unit speed at opening degrees of 14, 16, 18, 20, 22, 24, and 26; after comparing the efficiency values, it is obtained that when the opening degree is 20, the operating efficiency of the unit can reach the highest value, so the opening degree 20 is the optimal guide vane opening degree. In addition, the highest efficiency point and the optimal guide vane opening degree are respectively as shown by the red star and the red dotted line in Figure 4 .

[0054] Then, perform Step 3: After determining the optimal guide vane opening degree, read the unit speed and unit flow corresponding to the highest operating efficiency point of the unit at this opening degree. From Figure 4 the highest efficiency point of the optimal guide vane opening degree in is 0.917, and the unit speed corresponding to this point is 80 r / min, which is the optimal unit speed.

[0055] Next, perform Step 4: According to the optimal unit speed, the actual working head, and the runner diameter, use formula (1) to calculate the optimal actual speed. Formula (1) is as follows:

[0056]

[0057] In formula (1), is the optimal unit speed, taking 80 r / min; D1 is the runner diameter, taking 0.54 m; n op is the optimal actual speed; H is the working head.

[0058] As shown in Figure 5 , the curve of the optimal actual speed considering different head conditions is obtained.

[0059] In addition, according to the unit flow and unit speed data corresponding to all efficiency points at the optimal opening degree, combined with the working head, the actual output of the unit at the optimal opening degree can be calculated using formula (2). Formula (2) is as follows:

[0060] P = 9.81·Q 11 D1 2 H 3 / 2 η(2)

[0061] In formula (2), Q 11 is the unit flow; H is the working head of the water turbine; D1 is the runner diameter, taking 0.54 m; η is the operating efficiency of the unit.

[0062] After calculating the output, it can be obtained Figure 6The curves of the optimal opening degree and the actual output of the unit under different working heads with respect to the actual speed. Among them, the working heads are exemplified by the lowest head of 20 m, the rated head of 23.5 m, and the highest head of 28 m. The abscissa and ordinate of the highest point of each output curve respectively correspond to the optimal actual speed and the maximum output under that head, and the operating efficiency is the highest efficiency of the unit.

[0063] Finally, perform step five: The speed governors of the speed regulation system and the excitation system of the hydropower unit adopt PID control units to achieve closed-loop control of the optimal speed of the speed optimization module.

[0064] The present invention can ensure that small hydropower units always operate at the highest efficiency operating point and the optimal actual speed under the condition of large-range head changes, thereby realizing efficient and economical power production. The implementation of this method not only improves the utilization efficiency of water energy, but also helps to reduce energy waste and enhance the overall performance and economic benefits of small hydropower stations.

[0065] The above has described the embodiments of the present invention in detail in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions, and variations made to these embodiments still fall within the protection scope of the present invention.

Claims

1. A variable speed operation control method for a small hydropower unit based on optimal guide vane opening, characterized in that: The following steps are involved: Step 1: Obtain the comprehensive characteristic curve of the selected model of turbine, with unit flow as the horizontal coordinate and unit speed as the vertical coordinate, and read the horizontal and vertical coordinates corresponding to all efficiency points under all openings; Step 2: Compare the values ​​of the highest efficiency points under all openings, determine the maximum efficiency value among the highest efficiency points under all different openings, and the opening where this value is located is the optimal guide vane opening; Step 3: Obtain the unit speed and unit flow corresponding to the highest point of the unit's operating efficiency under the optimal guide vane opening. The unit speed at this time is the optimal unit speed; Step 4: Calculate the optimal actual speed based on the optimal unit speed, working water head and runner diameter; Step 5: Based on the optimal speed and mechanical rotation motion equation obtained in step 4 to adapt to head changes and maintain the highest efficiency, design a corresponding closed-loop controller to control the unit speed to remain consistent with the optimal speed and achieve variable speed operation of the unit.

2. A variable speed operation control method for a small hydropower unit based on optimal guide vane opening according to claim 1, characterized in that: The formula for the optimal actual speed in step 4 is: In formula (1), is the optimal unit speed, n op is the optimal actual speed, H is the working water head, and D1 is the impeller diameter.

3. The variable speed operation control method of a small hydropower unit based on the optimal guide vane opening according to claim 1 is characterized in that: The formula for the actual output in step 5 is: P=9.81·Q 11 D1 2 H 3 / 2 η (2) In formula (2), Q 11 is the unit flow rate, H, D1, η are the working water head, runner diameter and operating efficiency of the turbine.

4. The variable speed operation control method of a small hydropower unit based on the optimal guide vane opening according to claim 1 is characterized in that: The formula of the mechanical rotation motion equation in step 6 is: J·dω / dt=M t -M g (3) In formula (3), J is the moment of inertia of the unit; ω is the angular velocity of the unit; M t is the main moment of the turbine; M g is the generator resistance torque; dω / dt is the unit rotation acceleration.

5. The variable speed operation control method of a small hydropower unit based on the optimal guide vane opening according to claim 1 is characterized in that: The regulator of the speed control system and the excitation system of the hydropower unit usually adopts a PID control unit as the core control strategy. The transfer function of the parallel PID speed regulator can be expressed as: G PID (s)=K p +K i / s+K d s / (T d s+1) (4) In formula (4), s is a complex variable; K p is the proportional link coefficient; K i is the integral link coefficient; K d is the differential link coefficient; T d is the inertia time constant.

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