OPC rotating speed control system for expansion machine of high-capacity pressure storage power station and operation method of OPC rotating speed control system

Abstract

The invention discloses an OPC rotating speed control system for an expansion machine of a high-capacity compressed gas energy storage power station, and relates to the technical field of expansion machines of high-capacity compressed gas energy storage power stations. The system comprises m stages of heat exchangers, m stages of expansion machines, m stages of shut-off valves and m stages of adjusting valves, an outlet of each stage of heat exchanger is connected with an inlet of each stage of expansion machine through the corresponding shut-off valve and the corresponding adjusting valve in sequence, an outlet of each stage of expansion machine is connected with an inlet of the next stage of heat exchanger, and the mth stage of expansion machine is connected with the ambient atmosphere; the system further comprises a plurality of small bypass systems, the nth-stage shut-off valve and the adjusting valve are connected with the small bypass systems in parallel, and n is larger than or equal to 2 and smaller than or equal to m. The small bypass system which is small in drift diameter, electrically adjusted and controllable in adjusting capacity is used for replacing a pressure release valve or bypass valve system which is conventionally arranged and is large in drift diameter and hydraulically / pneumatically adjusted, the investment of a power station can be effectively reduced on the premise that the rotating speed control function is reliably achieved, and the economical efficiency of the power station is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of expanders for large-capacity compressed gas energy storage power stations, and more specifically, to an OPC speed control system for expanders in large-capacity compressed gas energy storage power stations. The present invention also relates to an operating method of such an OPC speed control system for expanders in large-capacity compressed gas energy storage power stations. Background Art

[0002] DL / T 1270-2023 "Guidelines for Load Shedding Tests of Thermal Power Generation Construction Engineering Units" defines OPC as follows: OPC overspeed protection control (over-speed protection control) is an override control system that suppresses turbine overspeed. Once triggered, this function immediately seizes control of the regulating system, momentarily closes the regulating steam valve, and returns control of the regulating system after reset. The conditions for triggering OPC include tripping of the grid-connected switch, speed overspeed to 103%, speed change rate (acceleration) exceeding the limit, load / power imbalance, or a combination of these.

[0003] The working principle of the expander of a compressed gas energy storage power station is similar to that of a steam turbine in a conventional thermal power plant. The difference is that its working medium is air, CO2 and other gases, and there is no extraction heat recovery system. However, its working characteristics and grid connection requirements are similar to those of a steam turbine. Therefore, the expander of a compressed gas energy storage power station is also equipped with an OPC system. The purpose of the OPC system of the expander of a compressed gas energy storage power station is the same as that of a steam turbine. When the grid connection switch of the expander unit and the grid trips or the expander speed exceeds 103% or the speed change rate exceeds the limit or the load / power is unbalanced, the OPC action is triggered, and the regulating valves of each stage of the expander are quickly closed, and the expander stops taking in air. When the expander speed drops to around 100% of the rated speed, the OPC resets, and control is returned to the regulation system. The regulating valves of each stage of the expander are opened, and the expander resumes taking in air, maintaining the expander speed at 100% of the rated speed, thereby realizing the rapid re-grid connection function of the expansion generator set.

[0004] In addition to the differences in working medium and heat recovery system, another difference between the expander system of a large-capacity compressed gas energy storage power station and the steam turbine system is that due to the limited working capacity of the gas medium, the rated flow rate of the expander of the compressed gas energy storage power station is much larger than that of a steam turbine of the same capacity (for example, the rated flow rate of a 300MW-class compressed air energy storage power station is 2900t / h, which is 2.9 times the rated flow rate of 1000t / h of the steam turbine of a conventional 300MW-class thermal power plant). In addition, the working pressure of the expander of the compressed gas energy storage power station is relatively low, so its gas flow rate at each level is much larger than that of the steam turbine. This results in huge diameters of the air intake pipes at each level (taking the expander of a 300MW compressed air energy storage power station with three-stage expansion as an example, the diameter of the first-stage expansion air intake pipe is 2×DN900, the diameter of the second-stage expansion air intake pipe is 2×DN1400, and the diameter of the third-stage expansion air intake pipe is 2×DN2500). Due to the limitation of pipe diameters, butterfly valves are used for the second-stage expansion and third-stage expansion air intake shut-off valves and regulating valves. However, the adjustment characteristics of large-diameter butterfly valves are non-linear and the adjustment accuracy is limited. Especially in the small opening stage, a very small opening can often produce a large flow rate, resulting in very limited adjustment capabilities.

[0005] In order to realize the OPC speed control function of the expander of large-capacity pressure storage power station, such as Figure 3 and 4 As shown, conventional pressure storage power stations (taking three-stage expansion as an example) are usually implemented using the following two solutions.

[0006] like Figure 3 As shown, Option 1: Set large-diameter quick pressure relief valves on the secondary and tertiary intake pipelines. When the unit triggers the OPC action, quickly close the regulating valves at each level, and simultaneously open the secondary and tertiary quick pressure relief valves in a chain manner to quickly release the pressurized gas in the secondary and tertiary intake pipeline systems, so as to avoid a large amount of gas entering the secondary and tertiary expansion after the secondary and tertiary regulating valves are opened after the OPC is reset, causing the speed to soar. After the OPC is reset and the secondary and tertiary pipelines are depressurized, open the regulating valves at each level, and control the expander to stabilize at the rated speed by adjusting the opening of the first-stage expansion regulating valve.

[0007] like Figure 4 As shown in the figure, Option 2: A large-diameter bypass system is set before the shut-off valves of the secondary and tertiary intake pipelines. When the unit triggers the OPC action, the regulating valves at each level are quickly closed, and the secondary and tertiary bypass valves are opened at the same time to quickly release the pressurized gas in the secondary and tertiary intake pipeline systems through the bypass pipeline. After the OPC is reset and the secondary and tertiary pipelines are depressurized, the regulating valves at each level are opened, and the expander is controlled to stabilize at the rated speed by adjusting the opening of the first-stage expansion regulating valve.

[0008] Both of the above solutions can achieve the OPC speed control function, but require the installation of a large-diameter, fast-acting pressure relief valve or bypass valve. This type of valve not only has a large diameter but also requires a hydraulic or pneumatic actuator, which is expensive and the system is complex. The valve is also prone to loose sealing after being opened multiple times, resulting in unnecessary gas leakage and waste, thereby affecting the operating economy of the unit. In addition, when the pressure relief valve system of Solution 1 is adopted, there is also a huge discharge noise problem, which has a certain impact on the environmental protection level of the power station.

[0009] Therefore, it is necessary to develop an OPC speed control system for the expander of a large-capacity pressure storage power station, which can avoid the system configuration of a large-diameter, fast-acting, complex and expensive pressure relief valve or bypass valve under the premise of reliably realizing the OPC speed control function, simplify the system and effectively reduce the cost of the power station, and at the same time has no discharge noise problem, can effectively ensure the safe and stable operation of the unit, and has good economic and environmental benefits. Summary of the Invention

[0010] The first purpose of the present invention is to solve the problem of increased power station cost caused by the configuration of large-diameter, fast-acting pressure relief valves or bypass valves in the OPC speed control system of existing large-capacity pressure storage power stations, solve the system complexity problem caused by the configuration of hydraulic / pneumatic fast pressure relief valves or bypass valves in the OPC speed control system of existing large-capacity pressure storage power stations, and solve the discharge noise problem caused by the configuration of fast pressure relief valves in the OPC speed control system of existing large-capacity pressure storage power stations, and provide a large-capacity pressure storage power station expander OPC speed control system that effectively reduces power station investment and improves power station economy, adopts simple and reliable electric actuators to replace hydraulic or pneumatic actuators, effectively simplifies the system, improves system reliability, reduces power station noise emission levels, and improves the environmental protection of the power station.

[0011] The second object of the present invention is to provide an operating method for the OPC speed control system of the expander of the large-capacity pressure storage power station.

[0012] To achieve the above-mentioned first objective, the technical solution of the present invention is: an OPC speed control system for an expander of a large-capacity pressure storage power station, comprising m-stage heat exchangers, m-stage expanders, m-stage shut-off valves, and m-stage regulating valves, wherein the outlet of the heat exchanger of each stage is connected to the inlet of the expander of each stage via the shut-off valve and the regulating valve in sequence, the outlet of the expander of each stage is connected to the inlet of the heat exchanger of the next stage, and the expander of the mth stage is connected to the ambient atmosphere; It is characterized in that: it also includes a plurality of small bypass systems, wherein the small bypass systems include a small bypass shut-off valve and a small bypass regulating valve, and the small bypass shut-off valve is connected to the small bypass regulating valve; The shut-off valve and regulating valve of the nth stage are connected in parallel with the small bypass system, m≥n≥2.

[0013] In the above technical solution, the small bypass shut-off valve and the small bypass regulating valve are both controlled by electric actuators.

[0014] In the above technical solution, m=3, the small bypass system connected in parallel with the second-stage shut-off valve and regulating valve is the second-stage small bypass system, and the small bypass system connected in parallel with the third-stage shut-off valve and regulating valve is the third-stage small bypass system.

[0015] In order to achieve the above second objective, the technical solution of the present invention is: an operating method of an OPC speed control system for an expander of a large-capacity pressure storage power station, characterized by comprising the following steps: Step 1: After the unit triggers the OPC action, quickly close the first-stage regulating valve, the second-stage regulating valve, and the third-stage regulating valve, quickly close the second-stage shut-off valve and the third-stage shut-off valve, and the expander stops intake; Step 2: When the expander speed drops to near the rated speed, the OPC is reset, and the control system opens the first-stage regulating valve, the second-stage small bypass system, and the third-stage small bypass system, while the second-stage regulating valve, the third-stage regulating valve, the second-stage shut-off valve, and the third-stage shut-off valve remain closed. The expander speed is controlled to the rated speed by adjusting the opening of the first-stage regulating valve, the small bypass regulating valve of the second-stage small bypass system, and the small bypass regulating valve of the third-stage small bypass system. Step 3: After the unit is connected to the grid, slowly open the second-stage regulating valve, the second-stage shut-off valve, the third-stage regulating valve, and the third-stage shut-off valve, and at the same time close the second-stage small bypass system and the third-stage small bypass system, and the unit switches to normal operating control state.

[0016] To achieve the above-mentioned first objective, the technical solution of the present invention is: an OPC speed control system for an expander of a large-capacity pressure storage power station, comprising m-stage heat exchangers, m-stage expanders, m-stage shut-off valves, and m-stage regulating valves, wherein the outlet of the heat exchanger of each stage is connected to the inlet of the expander of each stage via the shut-off valve and the regulating valve in sequence, the outlet of the expander of each stage is connected to the inlet of the heat exchanger of the next stage, and the expander of the mth stage is connected to the ambient atmosphere; It is characterized in that: it also includes a plurality of small bypass systems, and the small bypass systems include small bypass regulating valves; The shut-off valve and regulating valve of the nth stage are connected in parallel with the small bypass system, m≥n≥2.

[0017] In the above technical solution, the small bypass regulating valve is controlled by an electric actuator.

[0018] In the above technical solution, m=3, the small bypass system connected in parallel with the second-stage shut-off valve and regulating valve is the second-stage small bypass system, and the small bypass system connected in parallel with the third-stage shut-off valve and regulating valve is the third-stage small bypass system.

[0019] In order to achieve the above second objective, the technical solution of the present invention is: an operating method of an OPC speed control system for an expander of a large-capacity pressure storage power station, characterized by comprising the following steps: Step 1: After the unit triggers the OPC action, the first-stage regulating valve, the second-stage regulating valve, and the third-stage regulating valve are quickly closed, and the expander stops taking in air; Step 2: When the expander speed drops to near the rated speed, the OPC is reset, and the control system opens the first-stage regulating valve, the second-stage small bypass system, and the third-stage small bypass system. The second-stage regulating valve and the third-stage regulating valve remain closed. The expander speed is controlled to the rated speed by adjusting the opening of the first-stage regulating valve, the small bypass regulating valve of the second-stage small bypass system, and the small bypass regulating valve of the third-stage small bypass system. Step 3: After the unit is connected to the grid, slowly open the second-stage regulating valve and the third-stage regulating valve, and at the same time close the second-stage small bypass system and the third-stage small bypass system, and the unit switches to normal operating control state.

[0020] Compared with the prior art, the present invention has the following advantages: 1) The present invention uses a small bypass system with a small diameter, electric adjustment, and controllable adjustment capacity to replace the conventional large-diameter, hydraulic / pneumatically adjustable pressure relief valve or bypass valve system. Under the premise of reliably achieving the speed control function, it can effectively reduce the investment in the power station and improve the economic efficiency of the power station.

[0021] 2) The present invention uses a small bypass system with small diameter, electric adjustment and controllable adjustment capacity to replace the conventional large diameter, hydraulic / pneumatic adjustment pressure relief valve or bypass valve system. It only uses an electric control system without a complex hydraulic oil or instrument air control system, which simplifies the system configuration and improves the reliability of the power station.

[0022] 3) The present invention uses a small bypass system with small diameter, electric adjustment and controllable adjustment capacity to replace the conventional large diameter, hydraulic / pneumatic adjustment pressure relief valve system. There is no air discharge problem when the OPC is actuated, which can effectively reduce the noise emission problem of the power station and improve the environmental protection of the power station. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural diagram of Example 1 of the present invention.

[0024] Figure 2 This is a structural diagram of Example 2 of the present invention.

[0025] Figure 3 This is a structural diagram of the prior art solution 1.

[0026] Figure 4 This is a structural diagram of the prior art solution 2.

[0027] Figure 5 The following are characteristic curves of the regulating valves in the prior art solutions 1 and 2.

[0028] Among them, 100-heat exchanger, 200-expander, 300-shut-off valve, 400-regulating valve, 500-small bypass system, 510-small bypass shut-off valve, 520-small bypass regulating valve, 610-large diameter quick pressure relief valve, 620-muffler, 700-large diameter bypass system, 710-large diameter bypass valve. DETAILED DESCRIPTION

[0029] The following detailed description of the embodiments of the present invention is given in conjunction with the accompanying drawings, which do not limit the present invention but are merely examples. The advantages of the present invention will become clearer and easier to understand through the description.

[0030] Example 1 like Figure 1 As shown, an OPC speed control system for an expander of a large-capacity pressure storage power station includes m-stage heat exchangers 100, m-stage expanders 200, m-stage shut-off valves 300, and m-stage regulating valves 400. The outlet of each stage of the heat exchanger 100 is connected to the inlet of the expander 200 of each stage through the shut-off valve 300 and the regulating valve 400 in sequence. The outlet of each stage of the expander 200 is connected to the inlet of the heat exchanger 100 of the next stage. The expander 200 of the mth stage is connected to the ambient atmosphere. The system further includes a plurality of small bypass systems 500, each of which includes a small bypass shutoff valve 510 and a small bypass regulating valve 520, wherein the small bypass shutoff valve 510 is connected to the small bypass regulating valve 520; The shut-off valve 300 and the regulating valve 400 of the nth stage are connected in parallel with the small bypass system 500, m≥n≥2.

[0031] The small bypass shut-off valve 510 and the small bypass regulating valve 520 are both controlled by electric actuators.

[0032] m=3, the small bypass system 500 connected in parallel with the second-stage shut-off valve 300 and the regulating valve 400 is the second-stage small bypass system 500, and the small bypass system 500 connected in parallel with the third-stage shut-off valve 300 and the regulating valve 400 is the third-stage small bypass system 500.

[0033] An operating method for an OPC speed control system for an expander of a large-capacity pressure storage power station comprises the following steps: Step 1: After the unit triggers the OPC action, the first-stage regulating valve 400, the second-stage regulating valve 400, and the third-stage regulating valve 400 are quickly closed, and the second-stage shut-off valve 300 and the third-stage shut-off valve 300 are quickly closed, and the expander 200 stops taking in air; Step 2: When the speed of the expander 200 decreases to near the rated speed, the OPC is reset, and the control system opens the first-stage regulating valve 400, the second-stage small bypass system 500, and the third-stage small bypass system 500. The second-stage regulating valve 400, the third-stage regulating valve 400, the second-stage shut-off valve 300, and the third-stage shut-off valve 300 remain closed. The speed of the expander 200 is controlled to the rated speed by adjusting the openings of the first-stage regulating valve 400, the small bypass regulating valve 520 of the second-stage small bypass system 500, and the small bypass regulating valve 520 of the third-stage small bypass system 500. Step 3: After the unit is connected to the grid, slowly open the second-stage regulating valve 400, the second-stage shut-off valve 300, the third-stage regulating valve 400, and the third-stage shut-off valve 300, and at the same time close the second-stage small bypass system 500 and the third-stage small bypass system 500, and the unit switches to normal operating control state.

[0034] In this embodiment, the small bypass shut-off valve 510 and the small bypass regulating valve 520 are both selected according to the unit's flushing flow rate or smaller flow rate to reduce the valve diameter, thereby reducing the cost and improving the control accuracy of the bypass regulating valve; the small bypass shut-off valve 510 and the small bypass regulating valve 520 are both controlled by electric actuators, which simplifies the control system and reduces the cost while meeting the regulation performance; this embodiment is applicable to situations where the secondary / tertiary regulating valve 400 is not sealed tightly or there is air leakage after closing.

[0035] Taking a 300MW pressurized air energy storage power station as an example, when using a small bypass system 500, the second-stage small bypass shut-off valve 510 and the small bypass regulating valve 520 can be DN200 in diameter, with two sets provided; the third-stage small bypass shut-off valve 510 and the small bypass regulating valve 520 can be DN350 in diameter, with two sets provided; the price of a single set of DN200 shut-off valves and regulating valves is 50,000 yuan (of which the price of the electric actuator is 30,000 yuan), and the price of a single set of DN350 shut-off valves and regulating valves is 100,000 yuan (of which the price of the electric actuator is 60,000 yuan), totaling 300,000 yuan.

[0036] Taking a 300MW pressurized air energy storage power station as an example, in the existing technical solution 1, the large-diameter rapid pressure relief valve 610 is selected with a pipe diameter of DN450, the silencer diameter is φ1200mm, and a total of four sets of pressure relief valves + silencers are installed in the second and third stages. The price of a single set of pressure relief valves is 300,000 yuan (including 200,000 yuan for the pneumatic actuator), and the price of the silencer is 50,000 yuan, for a total of 1.4 million yuan. Taking a 300MW pressurized air energy storage power station as an example, in the existing technical solution 2, the second-stage large-diameter bypass valve 710 has a pipe diameter of DN450, and two sets are set; the third-stage large-diameter bypass valve 710 has a pipe diameter of DN600, and two sets are set; the price of the DN450 bypass valve is 300,000 yuan (of which the price of the pneumatic actuator is 200,000 yuan), and the price of the DN600 bypass valve is 450,000 yuan (of which the price of the pneumatic actuator is 300,000 yuan), and the total cost of the four sets is 1.5 million yuan.

[0037] In summary, compared with Scheme 1 and Scheme 2 in the prior art, the adoption of Example 1 of the present invention can effectively reduce the investment in the power station and improve the economy of the power station. Moreover, Example 1 of the present invention only has an electric control system and no complex hydraulic oil or instrument air control system, which simplifies the system configuration and improves the reliability of the power station.

[0038] Example 2 like Figure 2 As shown, an OPC speed control system for an expander of a large-capacity pressure storage power station includes m-stage heat exchangers 100, m-stage expanders 200, m-stage shut-off valves 300, and m-stage regulating valves 400. The outlet of each stage of the heat exchanger 100 is connected to the inlet of the expander 200 of each stage through the shut-off valve 300 and the regulating valve 400 in sequence. The outlet of each stage of the expander 200 is connected to the inlet of the heat exchanger 100 of the next stage. The expander 200 of the mth stage is connected to the ambient atmosphere. It also includes a plurality of small bypass systems 500, each of which includes a small bypass regulating valve 520; The shut-off valve 300 and the regulating valve 400 of the nth stage are connected in parallel with the small bypass system 500, m≥n≥2.

[0039] The small bypass regulating valve 520 is controlled by an electric actuator.

[0040] m=3, the small bypass system 500 connected in parallel with the second-stage shut-off valve 300 and the regulating valve 400 is the second-stage small bypass system 500, and the small bypass system 500 connected in parallel with the third-stage shut-off valve 300 and the regulating valve 400 is the third-stage small bypass system 500.

[0041] An operating method for an OPC speed control system for an expander of a large-capacity pressure storage power station comprises the following steps: Step 1: After the unit triggers the OPC action, the first-stage regulating valve 400, the second-stage regulating valve 400, and the third-stage regulating valve 400 are quickly closed, and the expander 200 stops taking in air; Step 2: When the speed of the expander 200 decreases to near the rated speed, the OPC is reset, and the control system opens the first-stage regulating valve 400, the second-stage small bypass system 500, and the third-stage small bypass system 500, while the second-stage regulating valve 400 and the third-stage regulating valve 400 remain closed. The speed of the expander 200 is controlled to the rated speed by adjusting the openings of the first-stage regulating valve 400, the small bypass regulating valve 520 of the second-stage small bypass system 500, and the small bypass regulating valve 520 of the third-stage small bypass system 500; Step 3: After the unit is connected to the grid, slowly open the second-stage regulating valve 400 and the third-stage regulating valve 400, and at the same time close the second-stage small bypass system 500 and the third-stage small bypass system 500, and the unit switches to the normal operation control state.

[0042] In this embodiment, the small bypass regulating valve 520 is selected according to the unit's flushing flow rate or smaller flow rate to reduce the valve diameter, thereby improving the control accuracy of the small bypass regulating valve 520 while reducing the cost; the small bypass regulating valve 520 is controlled by an electric actuator to simplify the control system and reduce the cost while meeting the regulation performance; this embodiment is applicable to the situation where the secondary / tertiary regulating valve 400 is tightly sealed and has no air leakage after closing.

[0043] Since the small bypass system 500 of this embodiment omits the small bypass shut-off valve 510 compared to embodiment 1, the cost of this embodiment is lower.

[0044] In actual use, the characteristic curves of the control valves of the prior art solutions 1 and 2 are as follows: Figure 5 As shown in the figure, the flow rate cannot be controlled below 10% opening, and the flow rate increases to 20% at an opening of 10%-40%. Taking a 300MW pressurized air energy storage power station as an example, the flow rate is 2900t / h at 100% opening, and the flow rate can reach 145t / h at 10% opening (based on 5% flow rate). That is, a large flow rate enters the expander at a small opening, causing the expander to overspeed.

[0045] For the small-diameter small bypass regulating valve 520 of Example 1 and Example 2, the selected flow rate is the flushing flow rate or smaller, and the fully open flow rate of the valve is considered to be 200t / h. Even according to the same flow characteristic curve, the flow rate at 10% opening is only 10t / h (based on 5% flow rate), which can effectively control the speed.

[0046] In summary, both Example 1 and Example 2 of the present invention can realize the speed control function after OPC action, and even if the small bypass regulating valves 520 at each level have a problem of loose sealing after being opened and closed multiple times, the leaked gas will continue to work inside the system and will not affect the normal operation of the system. Compared with the large-diameter, hydraulic / pneumatically regulated pressure relief valve or bypass valve system set in Scheme 1 and Scheme 2 of the prior art, Example 1 and Example 2 of the present invention can effectively reduce the investment in the power station and improve the economy of the power station while reliably realizing the speed control function. It only has an electric control system and no complex hydraulic oil or instrument air control system, simplifies the system configuration, and improves the reliability of the power station. There is no problem of air discharge during OPC action, which can effectively reduce the noise emission problem of the power station and improve the environmental protection of the power station.

[0047] Other parts not described belong to the prior art.

Claims

1. An OPC speed control system for an expander of a large-capacity pressure storage power station, comprising m-stage heat exchangers (100), m-stage expanders (200), m-stage shutoff valves (300), and m-stage regulating valves (400), wherein the outlet of each stage of the heat exchanger (100) is connected to the inlet of each stage of the expander (200) via the shutoff valve (300) and the regulating valve (400) in sequence, the outlet of each stage of the expander (200) is connected to the inlet of the heat exchanger (100) of the next stage, and the expander (200) of the mth stage is connected to the ambient atmosphere; Its characteristics are: The system further comprises a plurality of small bypass systems (500), wherein the small bypass systems (500) comprise a small bypass shutoff valve (510) and a small bypass regulating valve (520), wherein the small bypass shutoff valve (510) is connected to the small bypass regulating valve (520); The shut-off valve (300) and the regulating valve (400) of the nth stage are connected in parallel with the small bypass system (500), m≥n≥2.

2. The OPC speed control system for the expander of a large-capacity pressure storage power station according to claim 1 is characterized by: The small bypass shut-off valve (510) and the small bypass regulating valve (520) are both controlled by electric actuators.

3. The OPC speed control system for the expander of a large-capacity pressure storage power station according to claim 2 is characterized in that: m=3, the small bypass system (500) connected in parallel with the shut-off valve (300) and the regulating valve (400) of the second stage is the second-stage small bypass system (500), and the small bypass system (500) connected in parallel with the shut-off valve (300) and the regulating valve (400) of the third stage is the third-stage small bypass system (500).

4. The method for operating the OPC speed control system for the expander of a large-capacity pressure storage power station according to claim 3 is characterized in that: The following steps are involved: Step 1: After the unit triggers the OPC action, the first-stage regulating valve (400), the second-stage regulating valve (400), and the third-stage regulating valve (400) are quickly closed, and the second-stage shut-off valve (300) and the third-stage shut-off valve (300) are quickly closed, and the expander (200) stops taking in air; Step 2: When the speed of the expander (200) decreases to near the rated speed, the OPC is reset, and the control system opens the first-stage regulating valve (400), the second-stage small bypass system (500), and the third-stage small bypass system (500), while the second-stage regulating valve (400), the third-stage regulating valve (400), the second-stage shut-off valve (300), and the third-stage shut-off valve (300) remain closed. The speed of the expander (200) is controlled to the rated speed by adjusting the openings of the first-stage regulating valve (400), the small bypass regulating valve (520) of the second-stage small bypass system (500), and the small bypass regulating valve (520) of the third-stage small bypass system (500); Step 3: After the unit is connected to the grid, slowly open the second-stage regulating valve (400), the second-stage shut-off valve (300), the third-stage regulating valve (400), and the third-stage shut-off valve (300), and simultaneously close the second-stage small bypass system (500) and the third-stage small bypass system (500), and the unit switches to the normal operation control state.

5. An OPC speed control system for an expander of a large-capacity pressure storage power station, comprising m-stage heat exchangers (100), m-stage expanders (200), m-stage shutoff valves (300), and m-stage regulating valves (400), wherein the outlet of each stage of the heat exchanger (100) is connected to the inlet of each stage of the expander (200) via the shutoff valve (300) and the regulating valve (400) in sequence, the outlet of each stage of the expander (200) is connected to the inlet of the heat exchanger (100) of the next stage, and the expander (200) of the mth stage is connected to the ambient atmosphere; Its characteristics are: It also includes a plurality of small bypass systems (500), wherein the small bypass systems (500) include small bypass regulating valves (520); The shut-off valve (300) and the regulating valve (400) of the nth stage are connected in parallel with the small bypass system (500), m≥n≥2.

6. The OPC speed control system for the expander of a large-capacity pressure storage power station according to claim 5 is characterized in that: The small bypass regulating valve (520) is controlled by an electric actuator.

7. The OPC speed control system for the expander of a large-capacity pressure storage power station according to claim 6 is characterized in that: m=3, the small bypass system (500) connected in parallel with the shut-off valve (300) and the regulating valve (400) of the second stage is the second-stage small bypass system (500), and the small bypass system (500) connected in parallel with the shut-off valve (300) and the regulating valve (400) of the third stage is the third-stage small bypass system (500).

8. The method for operating the OPC speed control system for the expander of a large-capacity pressure storage power station according to claim 7, characterized in that: The following steps are involved: Step 1: After the unit triggers the OPC action, the first-stage regulating valve (400), the second-stage regulating valve (400), and the third-stage regulating valve (400) are quickly closed, and the expander (200) stops taking in air; Step 2: When the speed of the expander (200) decreases to near the rated speed, the OPC is reset, and the control system opens the first-stage regulating valve (400), the second-stage small bypass system (500), and the third-stage small bypass system (500), while the second-stage regulating valve (400) and the third-stage regulating valve (400) remain closed. The speed of the expander (200) is controlled to the rated speed by adjusting the openings of the first-stage regulating valve (400), the small bypass regulating valve (520) of the second-stage small bypass system (500), and the small bypass regulating valve (520) of the third-stage small bypass system (500); Step 3: After the unit is connected to the grid, slowly open the second-stage regulating valve (400) and the third-stage regulating valve (400), and at the same time close the second-stage small bypass system (500) and the third-stage small bypass system (500), and the unit switches to the normal operation control state.

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