Operating condition switching structure and control strategy of vertical gravity energy storage system

Abstract

The invention relates to a vertical gravity energy storage system operation condition switching structure and a control strategy. The vertical gravity energy storage system operation condition switching structure comprises a main motor, a clutch, a winding drum, a steel cable, a lift car and an auxiliary motor. The main motor and the auxiliary motor are connected with the winding drum through couplings respectively, clutches are arranged between the main motor and the corresponding couplings, the car is connected with the winding drum through steel cables, one end of each steel cable is fixedly connected with the winding drum and wound on the winding drum, and the winding drum rotates to drive the car to move up and down through the steel cables. The main motor and the winding drum are disconnected through the clutch, the auxiliary motor drives the winding drum to rotate to pay off the cable, the lift car moves downwards till the winding drum pays off the cable completely, at the moment, the lift car moves to the bottommost end of the stroke, the winding drum continues to rotate in the same direction, the steel cable is wound in the reverse direction, and the lift car is driven to move upwards; the rotation direction of the main motor is not changed, the movement direction of the car is driven to be switched, charging and discharging working conditions can be rapidly switched in combination with a working condition switching strategy, and the response speed of the system is increased.

Description

Technical Field

[0001] The invention relates to an operating condition switching structure and a control strategy of a vertical gravity energy storage system, and belongs to the technical field of gravity energy storage. Background Art

[0002] With the continuous growth of installed capacity of new energy power generation such as wind power and photovoltaic power, the stability and regulation capacity of the power system are also facing unprecedented challenges. In order to meet these challenges, gravity energy storage technology has attracted widespread attention for its high efficiency and environmental protection. This technology realizes the storage and release of energy through the mutual conversion of gravitational potential energy and electrical energy, thus providing strong support for the stable operation of the power system.

[0003] In the gravity energy storage system, the motor plays a vital role. It is connected in parallel between the renewable energy power generation system and the power grid. When the renewable energy system generates electricity, the motor rotates forward to lift the mass block to a certain height and store electrical energy in the form of gravitational potential energy. When the power grid needs to peak load or cope with load fluctuations, the mass block is released, dragging the motor to reverse, converting the stored gravitational potential energy into electrical energy and feeding it back to the power grid.

[0004] Despite this, current gravity energy storage systems still have significant problems when switching between charging and discharging conditions. In most existing systems, the charging and discharging conditions are separate and independent. That is, after completing one charging or discharging condition, the system needs to be shut down for a short time before switching to another condition. This design is particularly insufficient when there are load fluctuations on the grid side, because the system cannot respond quickly and switch conditions, and thus cannot provide the required electrical energy in time. This delay not only affects the stability of the grid, but also reduces the quality of power supply. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of slow response of motor forward and reverse rotation and switching working conditions in the prior art, and to provide a structure and control strategy for fast switching of operating conditions of a vertical gravity energy storage system.

[0006] In order to achieve the above-mentioned purpose, the technical solution proposed by the present invention is: a vertical gravity energy storage system operating condition switching structure, including a main motor, a clutch, a drum, a steel cable, a car and an auxiliary motor;

[0007] The main motor is connected to the power grid, the main motor and the auxiliary motor are connected to the drum through couplings, a clutch is provided between the main motor and the corresponding coupling, the car is connected to the drum through a steel cable, one end of the steel cable is fixedly connected to the drum and wound on the drum, the drum rotates, and the car is driven to move up and down through the steel cable;

[0008] The main motor and the drum are disconnected by the clutch, and the auxiliary motor drives the drum to rotate and release the cable. The car moves downward until the drum has completely released the cable. At this time, the car reaches the bottom of the stroke, and the drum continues to rotate in the same direction, winding the steel cable in the opposite direction, driving the car to move upward. The main motor and the drum are then connected by the clutch to keep the main motor's rotation direction unchanged, thereby switching the direction of movement of the car.

[0009] The above technical solution is further designed as follows: a first sensor, a second sensor and a third sensor are arranged from top to bottom corresponding to the travel range of the car, the first sensor and the second sensor are respectively located at the upper stacking area and the lower stacking area, and the third sensor is located at the bottom of the car travel; a mass block is placed in the car, and the mass block can be removed from the car and placed in the upper stacking area or the lower stacking area.

[0010] The main motor is connected with a reducer, and the auxiliary motor is driven by a frequency converter; the reel is provided with a brake.

[0011] One end of the reel is provided with an annular electromagnet and a baffle.

[0012] A control strategy for switching an operating condition switching structure of a vertical gravity energy storage system from a charging condition to a discharging condition, including strategy one and strategy two;

[0013] The strategy 1 includes:

[0014] S1.1, use the main motor to drag the car and mass from the current position to the position of the first sensor of the upper stack, the time taken is t1, disconnect the clutch connected to the main motor, make the main motor run without load, start the brake to stop the drum from rotating;

[0015] S1.2, unload the mass block from the car and place it in the upper stacking area, the time taken is t2;

[0016] S1.3, start the inverter to drive the auxiliary motor, and drive the empty car to run to the lower stacking area where the second sensor is located at a speed of n1, and the time taken is t3;

[0017] S1.4, when the empty car runs to the position of the second sensor, the inverter is controlled to make the auxiliary motor drive the empty car to decelerate and run to the position of the third sensor at a speed of n2, and then wait until the steel cable is reversely wound to make the empty car rise to the position of the second sensor. The time taken is t4;

[0018] S1.5, control the frequency converter to accelerate the auxiliary motor to the speed n1, so that the empty car rises to the position of the stacking area on the first sensor. The time taken is t3, and the total time for the working mode switching is T1=t1+t2+2t3+t4;

[0019] The second strategy includes:

[0020] S2.1, disconnect the clutch connected to the main motor, release the car and mass directly from the current position, the car and mass drag the auxiliary motor to generate electricity, and wait until they fall to the position of the second sensor in the lower stacking area, activate the brake device to stop the drum from rotating, and the time taken is t5;

[0021] S2.2, unload the mass block from the car and place it in the lower stacking area, the time taken is t2;

[0022] S2.3, control the inverter to decelerate the auxiliary motor and drive the empty car to the position of the third sensor at a speed of n2, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4;

[0023] S2.4, start the inverter to drive the auxiliary motor, and lift the empty car to the position of the stacking area on the first sensor at a speed of n1. The time taken is t3; the total time for the working condition switching is T2=t2+t3+t4+t5.

[0024] A further design of the above technical solution is: compare T1 and T2, and select the strategy with less total time as the preferred strategy.

[0025] The time t1 is:

[0026]

[0027] In the formula, x1 is the distance from the current position of the mass block to the upper stacking area, n is the speed of the main motor after passing through the reducer, and D is the radius of the reel;

[0028] The time t3 is:

[0029]

[0030] Where, h is the distance from the upper stack area to the lower stack area;

[0031] The time t4 is:

[0032]

[0033] Where x3 is the distance from the second sensor to the third sensor in the lower stack area;

[0034] The time t5 is:

[0035]

[0036] Where x2 is the distance from the current position of the mass block to the second sensor in the lower stack area.

[0037] When the car runs to the position of the third sensor, the electromagnet is started to make the steel cable tightly wound from the end of the drum when it is reversely wound; when the steel cable reversely winds and drives the empty car to rise to the position of the second sensor, the electromagnet is turned off.

[0038] A control strategy for switching a vertical gravity energy storage system operating condition switching structure from a discharge condition to a charge condition, comprising:

[0039] S3.1. Use the main motor to lower the car and mass from the current position to the position of the second sensor in the lower stacking area. The time taken is t6. Disconnect the clutch connected to the main motor to make the main motor run without load. Start the brake to stop the drum from rotating.

[0040] S3.2, unload the mass block from the car and place it in the lower stacking area, the time taken is t2;

[0041] S3.3, control the frequency converter to make the auxiliary motor drive the empty car to decelerate and run at a speed of n2 to the position of the third sensor, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4; the total time for the working condition switching is T3=t2+t4+t6.

[0042] The time t4 is:

[0043]

[0044] Where x3 is the distance from the second sensor to the third sensor in the lower stacking area, and D is the radius of the roll;

[0045] The time t6 is:

[0046]

[0047] Where x2 is the distance from the current position of the mass block to the lower stacking area, and n is the speed of the main motor after passing through the reducer.

[0048] The beneficial effects of the present invention are:

[0049] The present invention ensures that the direction of the main motor remains unchanged when the system switches working conditions through the design of the main structure of the mechanical transmission device. At the same time, combined with the real-time state of the mass block when the working condition switching scheduling command is issued, the working condition switching control strategy is selected based on the total working condition switching response time. Different working condition switching methods are used to ensure that the working condition switching time can be minimized, so that the gravity energy storage system can quickly respond to the needs of grid load changes.

[0050] The method of the present invention realizes the rapid and smooth switching of charging and discharging conditions without shutting down the system, avoids the shutdown delay during switching of the traditional system, greatly improves the response speed of the system, and can quickly respond to grid load fluctuations. In addition, the method enhances the stability and power supply quality of the power grid, enables the system to quickly compensate for the power imbalance caused by fluctuations in renewable energy power generation, and provides strong support for the power system with extensive access to renewable energy. The seamless switching design also reduces the wear of equipment during frequent start-stop processes, helps to extend the service life of the system, and further improves the reliability and economy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a schematic diagram of the transmission structure of the present invention;

[0052] Figure 2 It is a schematic diagram of the auxiliary motor driving hardware of the present invention;

[0053] Figure 3 It is a schematic side view of the structure of the reel of the present invention;

[0054] Figure 4 It is a side view principle schematic diagram of the gravity energy storage module elevator device of the present invention;

[0055] Figure 5 It is a schematic diagram of the process of switching the charging working condition to the discharging working condition of the present invention.

[0056] In the figure: 1-main motor, 2-auxiliary motor, 3-reel, 4-coupling, 5-clutch, 6-reducer, 7-brake, 8-cable, 9-electromagnet, 10-baffle, 11-car, 12-mass block, 13-upper stacking area, 14-lower stacking area, 15-pit, 16-first sensor, 17-second sensor, 18-third sensor. DETAILED DESCRIPTION

[0057] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] Embodiment 1

[0059] like Figure 1 As shown, the operating condition switching structure of the vertical gravity energy storage system of this embodiment includes a main motor 1 (main generator motor), a drum 3 and an auxiliary motor 2; the main motor 1 is directly connected to the power grid, the main motor 1 and the auxiliary motor 2 are respectively connected to the rotating shaft of the drum 3 through a coupling 4, a clutch 5 is provided between the main motor 1 and the corresponding coupling 4, and the main motor 1 is also provided with a reducer 6; Figure 2As shown, the auxiliary motor 2 is connected to the auxiliary motor power supply through the frequency converter, and the frequency converter is controlled by the PLC control system; the main motor 1 and the auxiliary motor 2 can both drive the drum 3 to rotate. The drum 3 is connected to the car 11 through the steel cable 8, one end of the steel cable 8 is fixedly connected to one end of the drum 3 and can be wound on the drum 3 as the drum 3 rotates, and drives the car 11 to move up and down.

[0060] The drum 3 is provided with a brake 7, which is used to provide a certain braking force when the car 11 falls, so as to maintain the safe operation of the system. Figure 3 As shown, one end of the drum 3 connected to the steel cable 8 is also provided with an annular electromagnet 9 and a baffle 10. When the electromagnet 9 is energized, the steel cable 8 can be tightly wound starting from this end of the drum 3 when the system working condition switches and the steel cable 8 is wound in the reverse direction. The baffle 10 can ensure that the steel cable does not fall off.

[0061] The working condition switching structure of this embodiment disconnects the main motor 1 and the drum 3 through the clutch 5, and drives the drum 3 to rotate and release the cable through the auxiliary motor 2, and the car 11 moves downward until the drum releases the cable completely and the steel cable 8 is completely straightened. At this time, the car 11 reaches the bottom of the stroke and continues to drive the drum 3 to rotate in the same direction, and the steel cable 8 is reversely wound on the drum 3, driving the car 11 to move upward, and then connecting the main motor and the drum through the clutch 5; through the above operation, the main motor 1 can drive the car 11 to switch its movement direction without changing the rotation direction of the main motor 1, such as initially the main motor 1 rotates forward to drive the car 11 to descend, and after the above operation, the drum 3 reversely winds the steel cable 8, and then the main motor 1 and the drum 3 are connected, and the main motor 1 rotates forward to drive the car 11 to rise.

[0062] Combination Figure 4 As shown, a first sensor 16, a second sensor 17 and a third sensor 18 are arranged from top to bottom corresponding to the travel range of the car 11, and are used to monitor the running position of the car 11. The upper stacking area 13 and the lower stacking area 14 are arranged at the first sensor 16 and the second sensor 17 respectively. The third sensor 18 is at the bottom of the travel of the car 11, corresponding to the pit 15. A mass block 12 is placed in the car 11, and the mass block 12 can be removed from the car 11 and placed in the upper stacking area 13 or the lower stacking area 14 when the operating condition is switched.

[0063] Embodiment 2

[0064] This embodiment provides a control strategy for switching the operating mode switching structure of the first embodiment from the charging operating mode to the discharging operating mode, including strategy one and strategy two;

[0065] Combination Figure 4 and Figure 5 As shown, strategy one includes:

[0066] S1.1, use the main motor to drag the car and mass from the current position to the position of the first sensor of the upper stack, the time taken is t1, disconnect the clutch connected to the main motor, make the main motor run without load, start the brake to stop the drum from rotating;

[0067] Time t1 is:

[0068]

[0069] In the formula, x1 is the distance from the current position of the mass block to the upper stacking area, n is the speed of the main motor after passing through the reducer, and D is the radius of the reel;

[0070] S1.2, unload the mass block from the car and place it in the upper stacking area, the time taken is t2;

[0071] S1.3, start the inverter to drive the auxiliary motor, and drive the empty car to run to the lower stacking area where the second sensor is located at the frequency f1 and the speed n1, and the time taken is t3;

[0072] Time t3 is:

[0073]

[0074] Where, h is the distance from the upper stack area to the lower stack area;

[0075] S1.4, when the empty car runs to the position of the second sensor, the inverter is controlled to make the auxiliary motor drive the empty car to decelerate and run to the position of the third sensor at a frequency of f2 and a speed of n2, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4; because the car 1 in this section needs to run to the bottom, the steel cable 8 is completely straightened and then reversely wound, so it is necessary to slow down and reduce inertia to make the system run smoothly at this stage.

[0076] Time t4 is:

[0077]

[0078] Where x3 is the distance from the second sensor to the third sensor in the lower stack area;

[0079] S1.5, control the frequency converter to accelerate the auxiliary motor to the speed n1, so that the empty car rises to the position of the stacking area on the first sensor. The time taken is t3, and the total time for the working mode switching is T1=t1+t2+2t3+t4;

[0080] Strategy 2 includes:

[0081] S2.1, disconnect the clutch connected to the main motor, release the car and mass directly from the current position, the car and mass drag the auxiliary motor to generate electricity, and wait until they fall to the position of the second sensor in the lower stacking area, activate the brake device to stop the drum from rotating, and the time taken is t5;

[0082] Time t5 is:

[0083]

[0084] Where x2 is the distance from the current position of the mass block to the second sensor in the lower stack area.

[0085] S2.2, unload the mass block from the car and place it in the lower stacking area, the time taken is t2;

[0086] S2.3, control the inverter to decelerate the auxiliary motor and drive the empty car to the position of the third sensor at a speed of n2, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4;

[0087] S2.4, start the inverter to drive the auxiliary motor, and lift the empty car to the position of the stacking area on the first sensor at a speed of n1. The time taken is t3; the total time for the working condition switching is T2 = t2 + t3 + t4 + t5. In this strategy, t2, t3 and t4 are the same as those in strategy 1.

[0088] In actual operation, the total switching times T1 and T2 of the two strategies mentioned above can be compared, and the strategy with the shorter total time can be selected as the preferred strategy.

[0089] During this operating mode switching process, when the car 11 runs to the position of the third sensor 18, the electromagnet 9 is started, so that the steel cable 8 is tightly wound from that end of the drum when it is reversely wound; when the steel cable 8 is reversely wound and drives the empty car to rise to the position of the second sensor 17, the electromagnet is turned off.

[0090] Embodiment 3

[0091] The gravity energy storage system of this embodiment needs to switch from the charging condition to the discharging condition. The current gravity energy storage system height is set to h=100m, the speed of the main motor after the reducer is 40r / min, and when the auxiliary motor runs at a frequency of f1, the speed of dragging the empty car is 80r / min. When it runs at a frequency of f2, the speed of dragging the empty car is 30r / min. The mass block is at a distance of x1=10m from the upper stacking area. The time required for the trolley to unload the mass block is t2=3s. The distance from sensor 2 to sensor 3 is x3=5m, and the drum diameter D is 0.5m.

[0092] The time for switching using Strategy 1 of Example 2 is calculated as follows:

[0093] S1.1: Lift the mass block from its current position to the upper stack area and calculate the lifting speed v of the mass block 质 ,

[0094]

[0095] The mass block rises a distance of 10m, so the time t1 required is:

[0096]

[0097] S1.2: The time t2 = 2s required to unload the mass block from the car and place it in the upper stacking area using a trolley.

[0098] S1.3: The auxiliary motor lowers the empty car at a frequency of f1 and a speed of n1. Calculate the falling speed v of the mass block. 质

[0099]

[0100] Then the time t3 required to descend from the upper stack area (100m) to the bottom is:

[0101]

[0102] S1.4, the time t4 taken by the auxiliary motor to drag the empty car from the second sensor to the third sensor and then back to the second sensor is

[0103]

[0104] S1.5, control the inverter to accelerate the auxiliary motor to the speed n1, so that the empty car rises to the position of the stacking area on the first sensor. The required time t3 is:

[0105]

[0106] The total time for switching working conditions is T1=t1+t2+2t3+t4=4.76+2+47.73+6.37=60.88s.

[0107] The time calculation for switching using strategy 2 is as follows:

[0108] S2.1: Disconnect the main motor clutch and lower the mass block to the position of the first sensor in the lower stack area.

[0109] Assuming that the mass block drives the auxiliary motor to fall at a speed of v2 = 4m / s, the time t5 required from the current position to the lower stacking area (90m descent) is:

[0110]

[0111] S2.2: Use a trolley to unload the mass block to the upper stacking area, and the required time t2 = 2 seconds.

[0112] S2.3, the time t4 taken by the auxiliary motor to drag the empty car from sensor 2 to sensor 3 and then back to sensor 2 is

[0113]

[0114] S2.4: The auxiliary motor lifts the empty car to the upper stacking area at a frequency of f1 and a speed of n1. Calculate the falling speed v of the mass block. 质

[0115]

[0116] The time t3 required to rise from the lower stack area (50m) to the upper stack area is:

[0117]

[0118] Strategy 2 working condition switching total time T2:

[0119] T2=t2+t3+t4+t5=2+23.87+6.37+22.5=54.74s

[0120] The total time of strategy 2 is shorter, so strategy 2 is selected for working condition switching.

[0121] Embodiment 4

[0122] This embodiment provides a control strategy for switching the operating mode switching structure of the first embodiment from the discharge operating mode to the charging operating mode, combined with Figure 4 and Figure 5 As shown, including:

[0123] S3.1. Use the main motor to lower the car and mass from the current position to the position of the second sensor in the lower stacking area. The time taken is t6. Disconnect the clutch connected to the main motor to make the main motor run without load. Start the brake to stop the drum from rotating.

[0124] S3.2, unload the mass block from the car and place it in the lower stacking area, the time taken is t2;

[0125] S3.3, control the frequency converter to make the auxiliary motor drive the empty car to decelerate and run at a speed of n2 to the position of the third sensor, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4; the total time for the working condition switching is T3=t2+t4+t6.

[0126] The time t6 is:

[0127]

[0128] In the formula, x2 is the distance from the current position of the mass block to the lower stacking area, n is the speed of the main motor after passing through the reducer; t2 and t4 are the same as those in the second embodiment.

[0129] The technical solutions of the present invention are not limited to the above-mentioned embodiments, and any technical solutions obtained by equivalent replacement methods fall within the scope of protection required by the present invention.

Claims

1. A vertical gravity energy storage system operating condition switching structure, comprising a main motor connected to a power grid, characterized in that: It also includes clutches, drums, cables, cars and auxiliary motors; The main motor and the auxiliary motor are connected to the drum through couplings respectively, a clutch is provided between the main motor and the corresponding coupling, the car is connected to the drum through a steel cable, one end of the steel cable is fixedly connected to the drum and wound on the drum, the drum rotates, and the car is driven to move up and down through the steel cable; The main motor and the drum are disconnected by the clutch, and the auxiliary motor drives the drum to rotate and release the cable. The car moves downward until the drum has completely released the cable. At this time, the car reaches the bottom of the stroke, and the drum continues to rotate in the same direction, winding the steel cable in the opposite direction, driving the car to move upward. The main motor and the drum are then connected by the clutch to keep the main motor's rotation direction unchanged, thereby switching the direction of movement of the car.

2. According to claim 1, the operating condition switching structure of the vertical gravity energy storage system is characterized in that: A first sensor, a second sensor and a third sensor are arranged from top to bottom corresponding to the travel range of the car, the first sensor and the second sensor are respectively located at the upper stacking area and the lower stacking area, and the third sensor is located at the bottom of the car travel; a mass block is placed in the car, and the mass block can be unloaded from the car and placed in the upper stacking area or the lower stacking area.

3. According to claim 2, the operating condition switching structure of the vertical gravity energy storage system is characterized in that: The main motor is connected with a reducer, and the auxiliary motor is driven by a frequency converter; the reel is provided with a brake.

4. According to claim 3, the operating condition switching structure of the vertical gravity energy storage system is characterized in that: One end of the reel is provided with an annular electromagnet and a baffle.

5. A control strategy for switching the operating condition switching structure of the vertical gravity energy storage system according to claim 4 from a charging condition to a discharging condition, characterized in that: Includes strategy one and strategy two; The strategy 1 includes: S1.1, use the main motor to drag the car and mass from the current position to the position of the first sensor of the upper stack, the time taken is t1, disconnect the clutch connected to the main motor, make the main motor run without load, start the brake to stop the drum from rotating; S1.2, unload the mass block from the car and place it in the upper stacking area, the time taken is t2; S1.3, start the inverter to drive the auxiliary motor, and drive the empty car to run to the lower stacking area where the second sensor is located at a speed of n1, and the time taken is t3; S1.4, when the empty car runs to the position of the second sensor, the inverter is controlled to make the auxiliary motor drive the empty car to decelerate and run to the position of the third sensor at a speed of n2, and then wait until the steel cable is reversely wound to make the empty car rise to the position of the second sensor. The time taken is t4; S1.5, control the frequency converter to accelerate the auxiliary motor to the speed n1, so that the empty car rises to the position of the stacking area on the first sensor. The time taken is t3, and the total time for the working mode switching is T1=t1+t2+2t3+t4; The second strategy includes: S2.1, disconnect the clutch connected to the main motor, release the car and mass directly from the current position, the car and mass drag the auxiliary motor to generate electricity, and wait until they fall to the position of the second sensor in the lower stacking area, activate the brake device to stop the drum from rotating, and the time taken is t5; S2.2, unload the mass block from the car and place it in the lower stacking area, the time taken is t2; S2.3, control the inverter to decelerate the auxiliary motor and drive the empty car to the position of the third sensor at a speed of n2, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4; S2.4, start the inverter to drive the auxiliary motor, and lift the empty car to the position of the stacking area on the first sensor at a speed of n1. The time taken is t3; the total time for the working condition switching is T2=t2+t3+t4+t5.

6. The control strategy for switching the vertical gravity energy storage system from the charging condition to the discharging condition according to claim 5 is characterized by: Compare T1 and T2, and select the strategy with less total time as the preferred strategy.

7. The control strategy for switching the vertical gravity energy storage system from the charging condition to the discharging condition according to claim 6 is characterized by: The time t1 is: In the formula, x1 is the distance from the current position of the mass block to the upper stacking area, n is the speed of the main motor after passing through the reducer, and D is the radius of the reel; The time t3 is: Where, h is the distance from the upper stack area to the lower stack area; The time t4 is: Where x3 is the distance from the second sensor to the third sensor in the lower stack area; The time t5 is: Where x2 is the distance from the current position of the mass block to the second sensor in the lower stack area.

8. The control strategy for switching the vertical gravity energy storage system from the charging condition to the discharging condition according to claim 7 is characterized by: When the car runs to the position of the third sensor, the electromagnet is activated to make the steel cable tightly wound from the end of the drum when winding in the reverse direction; When the steel cable is reversely wound and drives the empty car to rise to the position of the second sensor, the electromagnet is turned off.

9. A control strategy for switching the operating mode switching structure of the vertical gravity energy storage system according to claim 4 from a discharge mode to a charge mode, characterized in that: include: S3.

1. Use the main motor to lower the car and mass from the current position to the position of the second sensor in the lower stacking area. The time taken is t6. Disconnect the clutch connected to the main motor to make the main motor run without load. Start the brake to stop the drum from rotating. S3.2, unload the mass block from the car and place it in the lower stacking area, the time taken is t2; S3.3, control the frequency converter to make the auxiliary motor drive the empty car to decelerate and run at a speed of n2 to the position of the third sensor, and then wait until the steel cable is reversely wound to raise the empty car to the position of the second sensor. The time taken is t4; the total time for the working condition switching is T3=t2+t4+t6.

10. The control strategy for switching the vertical gravity energy storage system from the charging condition to the discharging condition according to claim 9 is characterized in that: The time t4 is: Where x3 is the distance from the second sensor to the third sensor in the lower stacking area, and D is the radius of the roll; The time t6 is: Where x2 is the distance from the current position of the mass block to the lower stacking area, and n is the speed of the main motor after passing through the reducer.

Images