Method for limiting rotating speed of variable-rotating-speed pumped storage unit in power closed-loop mode

Abstract

The invention discloses a method for limiting the rotating speed of a variable-rotating-speed pumped storage unit in a power closed-loop mode. The method includes the steps that firstly, the unit is controlled to work according to set operation electric power; 2, respectively comparing the detected actual rotating speeds; if the actual rotating speed is greater than the set highest safety rotating speed / lowest safety rotating speed, outputting a power positive value / power negative value, and turning to the step 3 / 4; 3, superposing the power positive value and the set operation electric power, controlling the unit to operate according to the obtained superposed electric power A, and limiting the actual rotating speed at the highest safe rotating speed; and 4, the negative power value and the set operation electric power are superposed to obtain superposed electric power B, the unit is controlled to operate according to the obtained superposed electric power B, and the actual rotating speed is limited to the lowest safe rotating speed. According to the method, when the actual rotating speed of the unit exceeds the set safe rotating speed, the actual rotating speed can be rapidly and accurately controlled to run at the highest / low safe rotating speed, and the technical problem that rotating speed control errors exist in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of speed control of a pumped storage unit, and in particular to a method for limiting the speed of a variable speed pumped storage unit in a power closed-loop mode. Background Art

[0002] Pumped-storage power stations are flexible and reliable in operation, have rapid operating condition changes and low environmental pressure. They are recognized to date as the most mature, economical and largest-capacity energy storage method, and can play an important role in peak shaving and valley filling and smoothing the output power of large-scale renewable energy.

[0003] At present, pumped storage units mainly include fixed speed units and variable speed units, but fixed speed units can no longer fully meet the urgent needs of large-scale rapid power fluctuations in the power grid in recent years. Variable speed units can not only quickly adjust active power and reactive power to improve the stability and rapid response capability of the system, realize flexible connection of electromechanical systems, and improve power generation efficiency, but also effectively control the load frequency of the power grid, balance the frequency fluctuations caused by renewable energy, and improve the quality of power, so they are increasingly widely used.

[0004] During the actual operation of the variable speed unit, it is necessary to limit the unit speed so that the unit speed always runs within a safe speed range to prevent the unit equipment from being damaged due to speed exceeding the range. To this end, the following related speed control technologies are proposed in the prior art: For example, the patent document with the announcement number CN116614026A proposes a speed over-limit suppression and protection method for a doubly-fed variable-speed pumped storage unit. This method organically combines the speed over-limit suppression method with the speed over-limit protection method. It uses the method of limiting the rate of change of the power reference value to make it less than the rate of change of the guide vane opening, and reduces the difference between the output of the pump turbine and the active power of the generator to suppress the rate of change of the unit speed and achieve speed over-limit suppression; using the speed limiting link including the artificial dead zone, when the unit speed exceeds the limit, the proportional control is used to limit the unit speed within the upper and lower limits of the speed to achieve speed over-limit protection. The upper and lower limits of the speed are obtained according to the relationship between the active power on the rotor side and the converter capacity, and can change in real time with the operating point. While ensuring the safe operation of the rotor-side converter, this method overcomes the large fluctuation of the unit active power during the adjustment process, reduces its adverse effect on the stability of the power grid, and enhances the stability of the power system. However, analysis has revealed that this method uses proportional control to limit the speed, but there is an error between the proportionally limited speed and the minimum / maximum speed, resulting in the inability to accurately control the unit speed. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art, and to provide a method for speed limitation in the power closed-loop mode of a variable-speed pumped-storage unit. The method detects the actual speed of the unit in real time. When it is found that the actual speed of the unit exceeds the set maximum safe speed and minimum safe speed, the method can quickly and accurately control the actual speed to operate at the maximum safe speed or the minimum safe speed based on the principle that electric power controls the unit quickly and accurately, thereby ensuring that the unit always operates within the safe speed range, and solving the technical problem of speed control error in the existing speed control method.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for speed limiting in a power closed-loop mode of a variable speed pumped storage unit, the method is implemented based on an AC excitation system, and specifically comprises the following steps: Step 1: The AC excitation system sets the operating power of the unit and controls the unit to operate according to the set operating power; Step 2: Detect the actual speed of the unit in real time, and input the detected actual speed into the maximum speed PID controller and the minimum speed PID controller for comparison; If the actual speed in the maximum speed PID controller is greater than the set maximum safe speed, the maximum speed PID controller outputs a positive power value and goes to step 3; If the actual speed in the minimum speed PID controller is less than the set minimum safe speed, the minimum speed PID controller outputs a negative power value and goes to step 4; Step 3: The AC excitation system superimposes the positive power value with the set operating electric power to obtain the superimposed electric power A of the actual power increase, and controls the unit to operate according to the superimposed electric power A. When the superimposed electric power A is equal to the mechanical power of the unit, the actual speed of the unit is limited to the maximum safe speed; Step 4: The AC excitation system superimposes the negative power value with the set operating electric power to obtain the superimposed electric power B with the actual power reduced. The unit is controlled to operate according to the superimposed electric power B. When the superimposed electric power B is equal to the mechanical power of the unit, the actual speed of the unit is limited to the minimum safe speed.

[0007] In step 2, if the actual speed in the maximum speed PID controller is less than the set maximum safe speed, the maximum speed PID controller will not output.

[0008] In step 2, if the actual speed in the minimum speed PID controller is greater than the set minimum safe speed, the minimum speed PID controller will not output.

[0009] In step 2, the positive value of the power output by the highest speed PID controller is 0~1; the negative value of the power output by the lowest speed PID controller is -1~0.

[0010] In step 2, the actual speed is acquired by a speed sensor, and the detection frequency of the acquisition sensor is 180-240us.

[0011] In step three, when the superimposed electric power A is greater than the mechanical power of the unit, the actual speed of the unit decreases; when the superimposed electric power is smaller than the mechanical power of the unit, the actual speed of the unit increases.

[0012] By adopting the above technical solution, the beneficial technical effects of the present invention are: 1. The present invention detects the actual speed of the unit in real time. When it is found that the actual speed of the unit exceeds the set maximum safe speed and minimum safe speed, the actual speed can be quickly and accurately controlled to run at the maximum safe speed or the minimum safe speed based on the principle that the electric power controls the unit quickly and accurately, thereby ensuring that the unit always runs within the safe speed range, solving the technical problem of speed control errors in the existing speed control method.

[0013] 2. The present invention adopts two high-speed PID controllers and a minimum speed PID controller, and both controllers are PID controlled. Due to the effect of integration, the actual speed of the unit will be limited. In any overspeed situation, the actual speed of the unit will be limited to the maximum safe speed / minimum safe speed.

[0014] 3. When controlling power, the present invention does not require manual attention to the rotation speed. When the rotation speed exceeds the minimum / maximum actual rotation speed, the method will automatically maintain the actual rotation speed of the unit within a safe range.

[0015] 4. The present invention corresponds to different units and can change the control performance by changing the parameters of the high speed PID controller and the minimum speed PID controller.

[0016] 5. In the process of limiting the speed beyond the range, the power change of the unit is relatively stable and the impact on the unit is relatively small. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flowchart of the present invention; Figure 2 This is a comparison diagram of the minimum speed limit under different parameters of the present invention; Figure 3 It is a power and speed curve diagram of the present invention under the lowest speed control. DETAILED DESCRIPTION

[0018] like Figure 1As shown, the present invention provides a method for limiting the speed of a variable speed pumped storage unit in a power closed-loop mode. The method is implemented based on an AC excitation system and can limit the actual speed of the unit in the power closed-loop mode so that the actual speed of the unit is always within a safe speed range. The method specifically includes the following steps: Step 1: The AC excitation system sets the unit's operating power, which is also the unit's actual operating power, and then controls the unit to operate at the set operating power.

[0019] Step 2: Detect the actual speed of the unit in real time, and input the detected actual speed into the highest speed PID controller and the lowest speed PID controller for comparison.

[0020] If the actual speed in the maximum speed PID controller is greater than the set maximum safe speed, the maximum speed PID controller outputs a positive power value and goes to step 3. If the actual speed in the maximum speed PID controller is less than the set maximum safe speed, the maximum speed PID controller does not output.

[0021] If the actual speed in the minimum speed PID controller is less than the set minimum safety speed, the minimum speed PID controller outputs a negative power value and goes to step 4. If the actual speed in the minimum speed PID controller is greater than the set minimum safety speed, the minimum speed PID controller does not output.

[0022] Those skilled in the art can understand that the actual speed of the unit can be detected by the speed sensor provided by the equipment, and the speed sensor can be an encoder provided by the unit equipment, and the actual speed can be calculated according to the encoder signal. In addition, in order to effectively prevent the actual speed of the unit from exceeding the set safety speed, the detection frequency of the acquisition sensor can be 180-240us, but the detection frequency of the acquisition sensor is preferably 200us. Step 3: The AC excitation system superimposes the positive power value with the set operating electric power to obtain the superimposed electric power A with actual power increase. The AC excitation system controls the unit to operate according to the superimposed electric power A. When the superimposed electric power A is equal to the mechanical power of the unit, the actual speed of the unit is limited to the maximum safe speed.

[0023] In step three, when the superimposed electric power A is greater than the mechanical power of the unit, the actual speed of the unit decreases; when the superimposed electric power is smaller than the mechanical power of the unit, the actual speed of the unit increases.

[0024] Step 4: The AC excitation system superimposes the negative power value with the set operating electric power to obtain the superimposed electric power B with the actual power reduced. The unit is controlled to operate according to the superimposed electric power B. When the superimposed electric power B is equal to the mechanical power of the unit, the actual speed of the unit is limited to the minimum safe speed.

[0025] It should be noted that the AC excitation system power closed-loop mode controls the electric power of the unit. In the power generation mode, the unit generates electric power, and its operating electric power is a positive value. The mechanical power of the unit is the driving force. If the input mechanical power is greater than the output electric power, the unit will accelerate and increase the speed, otherwise it will reduce the speed. In the pumping mode, the unit absorbs electric power, and its operating electric power is a negative value. The power is the driving force. If the input electric power is greater than the output mechanical power, the unit will accelerate and increase the speed, otherwise it will reduce the speed.

[0026] The positive power value output by the maximum speed PID controller in the present invention can be 0~1; the negative power value output by the minimum speed PID controller can be -1~0. Preferably, the positive power value output by the maximum speed PID controller is 0.3, and the negative power value output by the minimum speed PID controller can be -0.3. Of course, the positive power value and negative power value of the aforementioned output can also be adjusted accordingly according to actual conditions. The purpose of controlling the maximum speed is achieved by superimposing the output of the maximum speed PID controller with the set operating electric power, and the purpose of controlling the minimum speed is achieved by superimposing the output of the minimum speed PID controller with the set operating electric power. The maximum speed PID controller can only output positive power values, and it will not work when the actual speed is less than the set maximum safe speed. The minimum speed PID controller can only output negative power values, and it will not work when the actual speed is greater than the set maximum safe speed.

[0027] The present invention is further described in detail below by actually applying the present invention to a 100kW test unit.

[0028] In this test, the maximum safe speed is set to 1080 rpm, the minimum safe speed is set to 910 rpm, the positive power output of the maximum speed PID controller is 0.3, and the negative power output of the minimum speed PID controller is -0.3.

[0029] The minimum speed test condition is: the actual speed of the unit is 930 rpm, the AC excitation output power is 50kW, and then the AC excitation power is changed to 80kW. The actual speed of the unit is reduced to 910 rpm within 3 seconds. After triggering the set minimum safety speed limit, the actual speed of the unit is limited to 910 rpm.

[0030] The highest test condition is: the actual speed of the unit is 930 rpm, and the AC excitation output power is 60kW. When the power is changed to 30kW, the actual speed of the unit rises to 1080 rpm within 5 seconds. After triggering the set maximum safety speed limit, the actual speed of the unit is limited to 1080 rpm.

[0031] like Figure 2As shown in the figure, the proportional coefficient Kp of the minimum speed limit PID controller is changed in the test to observe the speed change. When Kp is 0 (no speed limit), the speed is reduced to 890 rpm. When Kp is changed within the range of 0-20, the larger the Kp, the lower the speed reduction of the unit, and the shorter the time the unit is limited to the minimum speed.

[0032] like Figure 3 As shown, during the test, the unit speed was 0.98 (980 rpm), the AC excitation set electric power was 0.45 (45kW), and the electric power was quickly and gradually increased to 65kW. The unit guide vane opening slowly increased to 0.75. Since the electric power was greater than the mechanical power, the actual speed gradually decreased. After triggering the minimum safety speed limit, the power output of the AC excitation was superimposed on the output of the low speed limit, the actual output electric power of the AC excitation was controlled, and the actual speed of the unit was limited to a safe range. Since the target power of the AC excitation is 65kW, the input mechanical power is also rising slowly. Under the joint action of the minimum speed limit, the actual output electric power of the AC excitation is consistent with the mechanical power increase rate, and the actual speed of the unit is never lower than the minimum speed. The actual output electric power of the AC excitation changes relatively smoothly, without large fluctuations.

[0033] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for speed limiting of a variable speed pumped storage unit in a power closed loop mode, the method being implemented based on an AC excitation system and characterized in that: The following steps are involved: Step 1: The AC excitation system sets the operating power of the unit and controls the unit to operate according to the set operating power; Step 2: Detect the actual speed of the unit in real time, and input the detected actual speed into the maximum speed PID controller and the minimum speed PID controller for comparison; If the actual speed in the maximum speed PID controller is greater than the set maximum safe speed, the maximum speed PID controller outputs a positive power value and goes to step 3; If the actual speed in the minimum speed PID controller is less than the set minimum safe speed, the minimum speed PID controller outputs a negative power value and goes to step 4; Step 3: The AC excitation system superimposes the positive power value with the set operating electric power to obtain the superimposed electric power A of the actual power increase, and controls the unit to operate according to the superimposed electric power A. When the superimposed electric power A is equal to the mechanical power of the unit, the actual speed of the unit is limited to the maximum safe speed; Step 4: The AC excitation system superimposes the negative power value with the set operating electric power to obtain the superimposed electric power B with the actual power reduced. The unit is controlled to operate according to the superimposed electric power B. When the superimposed electric power B is equal to the mechanical power of the unit, the actual speed of the unit is limited to the minimum safe speed.

2. The method for speed limiting of a variable speed pumped storage unit in a power closed loop mode according to claim 1, characterized in that: In step 2, if the actual speed in the maximum speed PID controller is less than the set maximum safe speed, the maximum speed PID controller will not output.

3. The method for speed limiting of a variable speed pumped storage unit in a power closed loop mode according to claim 1, characterized in that: In step 2, if the actual speed in the minimum speed PID controller is greater than the set minimum safe speed, the minimum speed PID controller will not output.

4. The method for speed limiting of a variable speed pumped storage unit in a power closed loop mode according to claim 1, characterized in that: In step 2, the positive value of the power output by the highest speed PID controller is 0~1; the negative value of the power output by the lowest speed PID controller is -1~0.

5. The method for speed limiting of a variable speed pumped storage unit in a power closed loop mode according to claim 1, characterized in that: In step 2, the actual speed is acquired by a speed sensor, and the detection frequency of the acquisition sensor is 180-240us.

6. The method for speed limiting of a variable speed pumped storage unit in a power closed loop mode according to claim 1, characterized in that: In step three, when the superimposed electric power A is greater than the mechanical power of the unit, the actual speed of the unit decreases; when the superimposed electric power is smaller than the mechanical power of the unit, the actual speed of the unit increases.

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