Start-up and grid-connection system based on alternating-current excitation and for gravity energy storage system

Abstract

Provided in the present application is a start-up and grid-connection system based on alternating-current excitation and for a gravity energy storage system. The start-up and grid-connection system comprises an energy storage control system and a plurality of groups of start-up and grid-connection modules, wherein each group of start-up and grid-connection modules comprises a tie line, two back-to-back switches, a synchronizing device and two start-up and grid-connection units; each start-up and grid-connection unit comprises a generating set, an outlet circuit breaker and a main transformer, and the generating set comprises a generator-motor, a hoist, and an excitation system; the terminals of the generator-motor are connected to a low-voltage side of the main transformer by means of the outlet circuit breaker, the low-voltage side of the main transformer is further connected to an excitation transformer of the excitation system, and the generator-motor employs an alternating-current excitation mode; the generator-motor is connected to a heavy object by means of the hoist; and the terminals of the two generator-motors in each group of start-up and grid-connection modules are connected by means of the tie line, the two back-to-back switches are arranged on the tie line in series, the energy storage control system is connected to each group of start-up and grid-connection modules, and the synchronizing device is connected to the outlet circuit breaker.

Description

A gravity energy storage system based on AC excitation to start the grid-connected system

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the Patent Office of China on February 2, 2024, with application number 202410151798.3 and invention name “A Gravity Energy Storage System Starting and Grid-Connected System Based on AC Excitation”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of gravity energy storage, and in particular to a gravity energy storage system startup and grid connection system based on AC excitation. Background Art

[0004] The inherent volatility and randomness of large-scale renewable energy grid integration has created a huge demand for energy storage technologies. Compared to pumped hydro, gravity energy storage technology based on solid weights offers significant development potential due to its flexible site selection and low geographical requirements. Many companies both domestically and internationally have conducted exploratory research on gravity energy storage technology. However, the technology still lacks a mature technical approach, which is why it has not been widely adopted.

[0005] According to the "Research Progress and Key Technologies of Vertical Gravity Energy Storage Systems," the gravity energy storage motor is the core component for converting electrical energy into potential energy. It operates in motor mode during forward rotation, converting electrical energy into potential energy; and in generator mode during reverse rotation, converting potential energy into electrical energy. Traditional heavy-duty drive mechanisms primarily utilize squirrel-cage asynchronous motors in conjunction with reduction gears to achieve long-term, stable, high-torque output. However, these mechanisms present numerous problems: copper loss increases with increasing motor load, reducing power factor and motor efficiency; reduction gears are required, resulting in a complex structure prone to wear and high maintenance costs; numerous mechanical structures result in high losses and low overall system efficiency. These issues significantly limit the application of asynchronous motors in low-speed, high-torque systems. To improve the overall performance and efficiency of the system, replacing traditional heavy-duty drive systems with low-speed, high-torque permanent magnet synchronous motors has become a trend. Structurally, permanent magnet motors (PMMs) generate their air gap magnetic field with permanent magnets, resulting in a simpler structure and smaller size. Performance-wise, they can have a large number of pole pairs, resulting in lower stator copper loss, higher power factor and efficiency, and more energy-efficient systems. Furthermore, they can maintain excellent performance over a wide load range. Therefore, low-speed, high-torque PMSMs hold promising application prospects in heavy-load drives. The Institute of Electrical Engineering of the Chinese Academy of Sciences (CAS) has proposed a design for a MW-class permanent magnet semi-direct-drive motor-generator for gravity energy storage and conducted simulation analysis of the motor-generator's efficiency at various speeds and torques.

[0006] While permanent magnet synchronous motors offer many advantages for gravity energy storage, they are relatively expensive and require a full-power converter for grid connection. They also face demagnetization issues when operating under extreme operating conditions. Consequently, many researchers have proposed technical solutions for applying electrically excited synchronous motors, doubly fed asynchronous motors, and squirrel-cage asynchronous motors to gravity energy storage. For example, patent application publication number CN116526565A describes a dedicated starting circuit for the electrically excited synchronous motor starting process, including a phase-shifting transformer, power unit, and reactor. When the synchronous motor voltage phase and frequency meet grid connection requirements, the grid-connected circuit breaker is closed, completing the grid connection and simultaneously disconnecting the starting circuit.

[0007] Summary of the Invention

[0008] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0009] To this end, the purpose of this application is to propose a gravity energy storage system starting grid-connected system based on AC excitation to ensure the system has maximum efficiency under different working conditions without the need for a dedicated starting circuit.

[0010] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a gravity energy storage system starting grid-connected system based on AC excitation, including an energy storage control system and multiple groups of starting grid-connected modules, each group of starting grid-connected modules including a tie line, two back-to-back switches, a synchronization device and two starting grid-connected units;

[0011] Each starting grid-connected unit includes a generator set, an outlet circuit breaker and a main transformer. The generator set includes a generator motor, a hoist and an excitation system. The generator motor is connected to the low-voltage side of the main transformer via the outlet circuit breaker. The low-voltage side of the main transformer is also connected to the excitation transformer of the excitation system. The generator motor adopts AC excitation. The generator motor is connected to a heavy object via the hoist. The generator motor ends of the two generator motors in each group of starting grid-connected modules are connected via the connecting line. The two back-to-back switches are arranged in series on the connecting line. The energy storage control system is connected to each group of starting grid-connected modules, and the synchronization device is connected to the outlet circuit breaker.

[0012] In the AC excitation-based gravity energy storage system starting and grid-connected system provided in the first aspect of the present application, the energy storage control system is connected to the two back-to-back switches in each group of starting and grid-connected modules, and the energy storage control system is also connected to the generator motor and excitation system in each starting and grid-connected unit in each group of starting and grid-connected modules; the energy storage control system is used to control the falling speed of the heavy object, the converter output of the excitation system and the on and off of the back-to-back switches so that the unit meets the grid-connected requirements; the synchronization device is used to control the corresponding output circuit breaker in the corresponding group of starting and grid-connected modules to close to achieve grid connection when it is detected that the unit meets the grid-connected requirements.

[0013] In the AC excitation-based gravity energy storage system startup and grid-connected system provided in the first aspect of the present application, the generator motor is defined as a generator when working in the power generation state, and is defined as a motor when working in the motoring state; the grid-connected requirements include a first grid-connected requirement and a second grid-connected requirement, the first grid-connected requirement is that the phase and amplitude of the stator voltage of the generator motor are the same as the grid voltage, and the frequency of the stator voltage meets the set requirements, and the second grid-connected requirement is that the motor reaches the rated speed.

[0014] In the AC excitation-based gravity energy storage system starting grid-connected system provided in the first aspect of the present application, the energy storage control system is specifically used to: if it is detected that there are two generators in any group of starting grid-connected modules, keep the back-to-back switch in the off state, control the falling speed of each weight in the group of starting grid-connected modules and the output of the converter of each excitation system to meet the first grid-connected requirement.

[0015] In the AC excitation-based gravity energy storage system starting grid-connected system provided in the first aspect of the present application, the control of the falling speed of each heavy object in the group of starting grid-connected modules and the output of the converter of each excitation system to meet the first grid-connected requirement includes: for any unit in the group of starting grid-connected modules, the energy storage control system controls the falling of the heavy object, the heavy object drags the winch to rotate, and the winch coaxially drives the generator to rotate; detects the speed of the generator, applies excitation power through the converter and controls the frequency of the excitation power to be the set frequency; controls and adjusts the output of the converter so that the phase and amplitude of the stator voltage are the same as the grid voltage, thereby meeting the first grid-connected requirement.

[0016] In the AC excitation-based gravity energy storage system startup grid-connected system provided in the first aspect of the present application, if the energy storage control system receives a frequency modulation instruction from the power grid, it adjusts the speed of the generator and simultaneously adjusts the frequency of the excitation power supply in the opposite direction through the excitation system converter to perform frequency modulation response.

[0017] In the AC excitation-based gravity energy storage system starting and grid-connected system provided in the first aspect of the present application, the energy storage control system is specifically used to: if it is detected that any group of starting and grid-connected modules contains a generator and an electric motor, then a back-to-back manner is adopted to use the generator in the group of starting and grid-connected modules to drive the electric motor to meet the second grid-connected requirement.

[0018] In the AC excitation-based gravity energy storage system starting and grid-connected system provided in the first aspect of the present application, the back-to-back method is used to use the generator in the group of starting and grid-connected modules to drive the motor to meet the second grid-connected requirement, including: controlling the two back-to-back switches of the group of starting and grid-connected modules to close, connecting the generator stator winding to the motor stator winding through the back-to-back switches of the connecting line; using the generator to drive the motor until the motor reaches the rated speed, and controlling the two back-to-back switches to disconnect when the second grid-connected requirement is met.

[0019] In the AC excitation-based gravity energy storage system starting and grid-connected system provided in the first aspect of the present application, the energy storage control system is specifically used to: if it is detected that two motors in any group of starting and grid-connected modules have been started and grid-connected in a back-to-back manner, then the other motor in the group of starting and grid-connected modules is controlled to start at no load, and then the output of the converter of the corresponding excitation system is controlled to meet the first grid-connected requirement.

[0020] In the AC excitation-based gravity energy storage system starting and grid-connected system provided in the first aspect of the present application, the control of the no-load starting of another motor in the group of starting and grid-connected modules includes: keeping the other motor no-load, disconnecting the output circuit breaker corresponding to the other motor, short-circuiting the stator winding outlet through the short-circuit switch, and the converter of the excitation system applying a three-phase AC voltage to the rotor winding. When the rotor speed of the other motor exceeds the rated speed, the output of the converter is locked and the short-circuit switch is disconnected at the same time to achieve no-load starting.

[0021] In the present application, the starting grid-connected system includes an energy storage control system and multiple groups of starting grid-connected modules, each group of starting grid-connected modules includes a connecting line, two back-to-back switches, a synchronization device and two starting grid-connected units; each starting grid-connected unit includes a unit, an export circuit breaker and a main transformer, and the unit includes a generator motor, a winch and an excitation system; the generator motor end is connected to the low-voltage side of the main transformer via the export circuit breaker, and the low-voltage side of the main transformer is also connected to the excitation transformer of the excitation system, and the generator motor adopts AC excitation; the generator motor is connected to a heavy object via the winch; the machine ends of the two generator motors in each group of starting grid-connected modules are connected via a connecting line, and the two back-to-back switches are arranged in series on the connecting line, the energy storage control system is connected to each group of starting grid-connected modules, and the synchronization device is connected to the export circuit breaker. In this case, in the starting grid-connected system, each group of starting grid-connected modules includes a connecting line, two back-to-back switches, a synchronization device and two starting grid-connected units; each starting grid-connected unit includes a unit, an output circuit breaker and a main transformer, and the unit includes a generator motor, a winch and an excitation system. The generator used is reversible in working mode and can work in both power generation and motoring states. The generator motor adopts an AC excitation method and can flexibly adjust the power of the generator motor to work at different speeds, thereby ensuring the maximum efficiency of the system under different working conditions, and there is no need to use a dedicated starting circuit. Starting and grid connection can be achieved by arranging a connecting line and two back-to-back switches in each group of starting grid-connected modules.

[0022] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0024] FIG1 is a block diagram of a grid-connected system for starting a gravity energy storage system based on AC excitation provided by an embodiment of the present application;

[0025] FIG2 is a connection diagram of a group of startup and grid-connected modules provided in an embodiment of the present application. DETAILED DESCRIPTION

[0026] Exemplary embodiments are described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numbers in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible implementations consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with certain aspects of the present invention, as detailed in the appended claims.

[0027] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "plurality" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined. It should also be understood that the term "and / or" used in this application refers to and includes any or all possible combinations of one or more associated listed items.

[0029] The following describes in detail embodiments of the present application, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0030] This application proposes a gravity energy storage system starting grid-connected system based on AC excitation to ensure maximum efficiency of the system under different working conditions without the need for a dedicated starting circuit.

[0031] In the first embodiment, Figure 1 is a block diagram of a gravity energy storage system based on AC excitation and grid-connected system provided by an embodiment of the present application. In the present application, the gravity energy storage system based on AC excitation and grid-connected system can be referred to as the grid-connected system.

[0032] As shown in Figure 1, the AC excitation-based gravity energy storage system startup grid-connected system includes an energy storage control system and multiple groups of startup grid-connected modules. The number of groups of startup grid-connected modules is n, and the n groups of startup grid-connected modules are the first group of startup grid-connected modules, the second group of startup grid-connected modules, ..., and the nth group of startup grid-connected modules. The energy storage control system connects each group of startup grid-connected modules.

[0033] In this embodiment, each group of starting grid-connected modules includes a synchronization device, two starting grid-connected units, and a connection unit for connecting the two starting grid-connected units. The connection unit includes a tie line and two back-to-back switches. The two back-to-back switches are arranged in series on the tie line.

[0034] Taking the first group of starting and grid-connected modules as an example, as shown in Figure 1, the first group of starting and grid-connected modules includes a synchronization device, a first starting and grid-connected unit, a second starting and grid-connected unit, and a connection unit. The first starting and grid-connected unit is connected to the second starting and grid-connected unit via the connection unit. The synchronization device connects the starting and grid-connected units.

[0035] In this embodiment, each starting and grid-connected unit includes a generator set, an output circuit breaker, and a main transformer. The generator set includes a generator motor, a hoist, and an excitation system. The generator motor's machine end is connected to the low-voltage side of the main transformer via the output circuit breaker. The low-voltage side of the main transformer is also connected to the excitation transformer of the excitation system. The generator motor is connected to a weight via the hoist. The machine ends of the two generator motors in each starting and grid-connected module are connected via a tie line.

[0036] In this embodiment, each starting and grid-connected unit also includes a reversing switch, which can be arranged between the output circuit breaker and the main transformer. The reversing switch's direction of rotation differs between the power generation mode and the motoring mode. In the power generation mode, the three-phase rotation sequence at the generator end is ABC, while in the motoring mode, the three-phase rotation sequence at the generator end is CBA. Each starting and grid-connected unit also includes a short-circuit switch, which is arranged at the generator end of the motor. When the short-circuit switch is closed, the stator winding output is short-circuited.

[0037] Figure 2 is a connection diagram of a set of starting and grid-connected modules provided in an embodiment of the present application. Figure 2 shows a connection diagram of the first set of starting and grid-connected modules. As shown in Figure 2, the first starting and grid-connected unit includes generator motor No. 1, and the second starting and grid-connected unit includes generator motor No. 2. The generator motor No. 1 is connected to the generator motor No. 2 via a tie line, a first back-to-back switch, and a second back-to-back switch. The first back-to-back switch and the second back-to-back switch are arranged in series on the tie line. The first starting and grid-connected unit also includes a main transformer, a reversing switch, an output circuit breaker, an excitation transformer, a current meter, and a winch. The generator motor No. 1 is connected to the low-voltage side of the main transformer via the output circuit breaker and the reversing switch. The low-voltage side of the main transformer is also connected to the excitation transformer, which is connected to the converter. The high-voltage side of the main transformer is connected to the grid, and the output circuit breaker is connected to a synchronization device (not shown). Generator motor No. 1 is connected to a weight via a winch. The components and connection methods included in the second starting and grid-connected unit can refer to those of the first starting and grid-connected unit.

[0038] In this embodiment, the generator motor used is reversible and can operate in either a power generation state or a motoring state, with different directions of rotation. The generator motor is defined as a generator when operating in the power generation state, and as a motor when operating in the motoring state.

[0039] In this embodiment, the generator motor needs to operate as both a motor and a generator, and the maximum efficiency operating speeds in the two operating conditions are different. At the same time, when operating in motor mode, the motor power needs to be flexibly adjusted, that is, the motor speed needs to be adjusted. To adapt to this variable speed operating condition, in the embodiment of the present application, each generator motor in each group of starting and grid-connected modules adopts an AC excitation method.

[0040] In this embodiment, the synchronization device is connected to the outlet circuit breaker. When the synchronization device detects that the unit meets the grid connection requirements, it controls the corresponding group to start the grid connection module to close the corresponding outlet circuit breaker to achieve grid connection.

[0041] In this embodiment, the energy storage control system is connected to the two back-to-back switches in each group of starting grid-connected modules, and the energy storage control system is also connected to the generator motor and excitation system in each starting grid-connected unit in each group of starting grid-connected modules.

[0042] The energy storage control system is used to detect the rotational speed of each generator motor.

[0043] The energy storage control system is used to control the falling speed of heavy objects, the converter output of the excitation system and the on and off of the back-to-back switches so that the unit meets the grid connection requirements.

[0044] In this embodiment, the grid-connected requirements include a first grid-connected requirement and a second grid-connected requirement. The first grid-connected requirement is that the phase and amplitude of the stator voltage of the generator motor are the same as the grid voltage, and the frequency of the stator voltage meets the set requirements. The second grid-connected requirement is that the motor reaches the rated speed.

[0045] In this embodiment, the energy storage control system is specifically configured to: if it is detected that any group of starting and grid-connected modules contains two generators, keep the back-to-back switches in the off state, and control the falling speed of each weight in the group of starting and grid-connected modules and the output of the converters of each excitation system to meet the first grid-connected requirement.

[0046] In this embodiment, the falling speed of each weight in the group of starting grid-connected modules and the output of the converter of each excitation system are controlled to meet the first grid-connected requirement, including: for any unit in the group of starting grid-connected modules, the energy storage control system controls the falling of the weight, the weight drags the winch to rotate, and the winch coaxially drives the generator to rotate; detects the rotation speed of the generator, applies excitation power through the converter and controls the frequency of the excitation power to be a set frequency; controls and adjusts the output of the converter so that the phase and amplitude of the stator voltage are the same as the grid voltage, thereby meeting the first grid-connected requirement.

[0047] In this embodiment, if the energy storage control system receives a frequency modulation instruction from the power grid, it adjusts the speed of the generator and simultaneously adjusts the frequency of the excitation power supply in the opposite direction through the excitation system converter to perform frequency modulation response.

[0048] In this embodiment, the energy storage control system is specifically configured to: if it is detected that any group of starting and grid-connected modules contains a generator and a motor, then the generator in the starting and grid-connected modules is used to drive the motor in a back-to-back manner to meet the second grid-connected requirement.

[0049] In this embodiment, a back-to-back method is used to utilize the generator in the group of starting and grid-connected modules to drive the motor to meet the second grid-connected requirement, including: controlling the two back-to-back switches in the group of starting and grid-connected modules to close, connecting the stator winding of the generator to the stator winding of the motor through the back-to-back switches of the tie line; utilizing the generator to drive the motor until the motor reaches the rated speed, and controlling the two back-to-back switches to open when the second grid-connected requirement is met.

[0050] In this embodiment, the energy storage control system is specifically configured to: if it is detected that two motors in any group of starting and grid-connected modules have been started and connected to the grid in a back-to-back manner, control the other motor in the group of starting and grid-connected modules to start at no load, and then control the output of the converter of the corresponding excitation system to meet the first grid-connected requirement.

[0051] In this embodiment, controlling the no-load starting of another motor in the group of starting and grid-connected modules includes: maintaining the other motor at no-load, disconnecting the output circuit breaker corresponding to the other motor, short-circuiting the stator winding output via a short-circuit switch, and applying a three-phase AC voltage to the rotor winding of the excitation system by the converter. When the rotor speed of the other motor exceeds the rated speed, the output of the converter is locked and the short-circuit switch is disconnected to achieve the no-load starting.

[0052] Specifically, in conjunction with FIG2 , taking the first group of startup grid-connected modules as an example, the startup grid-connected process of the AC excitation-based gravity energy storage system is as follows:

[0053] Case 1: In the gravity energy storage system, two generator motors are working in the power generation state. The starting and grid-connected processes of the two generator motors are the same. Taking generator motor No. 1 as an example, its starting and grid-connected process is:

[0054] (1) The energy storage control system controls the weight to fall slowly (for example, the falling acceleration is 0.01m / s 2 ) Increase the falling speed;

[0055] (2) The heavy object drags the winch to rotate, and the winch coaxially drives the No. 1 generator motor to rotate, and the speed slowly increases;

[0056] (3) The energy storage control system detects the speed of generator motor No. 1 and applies excitation power through the converter. The frequency of the excitation power is a set frequency, for example, 50-fr+Δf, where 50 Hz is the grid frequency, fr is the frequency corresponding to the current mechanical speed of the rotor, and Δf can be 0.2 to 0.5 Hz.

[0057] (4) Adjust the output of the converter so that the phase and amplitude of the stator voltage are the same as the grid voltage, and the frequency of the stator voltage meets the set requirements (for example, the frequency of the stator voltage is slightly higher than the grid frequency of 50 Hz). That is, when the frequency of the excitation power applied by the converter is 50-fr+△f, it can be ensured that the frequency of the stator voltage is slightly higher than the grid frequency.

[0058] (5) The synchronization device is used to connect to the grid. The synchronization device issues a closing command to close the output circuit breaker at the machine end to connect to the grid;

[0059] (6) After No. 1 generator motor is connected to the grid, it can operate in a continuous power generation condition;

[0060] (7) Generator motor No. 1 can respond to the frequency modulation command of the power grid. According to the frequency modulation command of the power grid, the speed of generator motor No. 1 is adjusted accordingly, that is, the descending speed of the heavy object is adjusted. At the same time, the frequency of the excitation power supply is adjusted in the opposite direction through the converter of the excitation system.

[0061] The second case: There are two generator motors in the gravity energy storage system, where generator motor No. 1 works in the generating (dragging) state and generator motor No. 2 works in the motoring state. The starting and grid-connected process of generator motor No. 2 is:

[0062] (1) Before starting, the No. 1 generator motor is in the dragging state and the No. 2 generator motor is in the starting state. The first back-to-back switch and the second back-to-back switch are controlled to be closed, and the stator winding of the No. 1 generator motor is connected to the stator winding of the No. 2 generator motor through the two back-to-back switches. The energy storage control system sends a back-to-back starting command to the units in the two starting grid-connected units. The excitation systems of the two units adjust the output current to the no-load excitation current of the units. The energy storage control system controls the speed regulator of the No. 1 generator motor to adjust the weight to increase the falling speed from static. The weight drags the unit speed from 0 to the initial speed. The unit in the first starting grid-connected unit (Unit 1) outputs power to drag the unit in the second starting grid-connected unit (Unit 2) to the initial speed. After that, the units begin to enter the continuous speed-up stage. The energy storage control system gradually increases the falling speed of the weight in Unit 1 to increase the speed of the dragging unit.

[0063] (2) Back-to-back starting is to increase the frequency of the output power of Unit 1 to control the accelerating electrical torque. The accelerating electrical torque acts on Unit 2 (i.e., the starting unit) and the speed increases with the speed of the dragging unit (i.e., Unit 1), ensuring that the starting unit is in a synchronous operation state until the starting unit speed reaches the rated speed. During the entire speed-up period, the excitation system output is maintained at the generator no-load excitation current.

[0064] (3) When the speed of Unit 2 reaches the rated speed, the unit starts to synchronize with the grid, and the excitation system switches to voltage closed-loop regulation. The synchronization device controls the stator voltage of the unit to track the grid voltage, and controls the speed of the traction unit to track the grid voltage frequency and phase angle. After the grid connection conditions are met, the synchronization device issues a grid connection command. At the same time, the energy storage control system issues a back-to-back switch disconnection command between the stator windings of the traction unit and the starting unit to disconnect the first back-to-back switch and the second back-to-back switch. Unit 1 exits operation, and after Unit 2 is connected to the grid, it enters the motor lifting heavy object operation mode. The excitation system enters normal excitation regulation operation according to the needs of the unit and the grid.

[0065] The third case: Both generator motors of the gravity energy storage system need to work in the electric state, where generator motor No. 2 is started synchronously back-to-back. The starting and grid-connected process of generator motor No. 1 is as follows:

[0066] (1) Generator motor No. 1 is kept unloaded, and the winch coaxial with generator motor No. 1 is unloaded;

[0067] (2) The outlet circuit breaker of the No. 1 generator motor is disconnected, and the stator winding outlet is short-circuited through the short-circuit switch. The excitation system converter applies a three-phase AC voltage to the rotor winding, and the excitation voltage and frequency gradually increase;

[0068] (3) The rotor of generator motor No. 1 gradually increases in speed due to the electromotive force between the excitation current and the stator current induced by the stator;

[0069] (4) When the rotor speed of generator motor No. 1 exceeds the rated speed, the output of the converter is locked and the short-circuit switch at the stator output of generator motor No. 1 is disconnected to achieve no-load starting. At this time, the speed of generator motor No. 1 slowly decreases due to inertia.

[0070] (5) As the speed of generator motor No. 1 slowly decreases, the excitation system re-supplies power to the rotor winding through the converter, controlling the frequency of the excitation power supply to 50-fr+Δf;

[0071] (6) Adjust the output of the converter so that the phase and amplitude of the stator voltage are the same as those of the grid, and the frequency is slightly higher than the grid frequency by 50 Hz. That is, when the frequency of the excitation power applied by the converter is 50-fr+△f, the frequency of the stator voltage can be ensured to be slightly higher than the grid frequency.

[0072] (7) Grid connection is achieved through the synchronization device, which issues a closing command and closes the machine-side circuit breaker to achieve grid connection;

[0073] (8) After the No. 1 generator motor is connected to the grid, it can operate in a continuous electric mode, dragging the coaxially rotating winch to perform work on the heavy object;

[0074] (9) Generator motor No. 1 can respond to the frequency modulation command of the power grid. According to the frequency modulation command of the power grid, the speed of the generator motor is adjusted accordingly, that is, the rising speed of the heavy object is adjusted. At the same time, the frequency of the excitation power supply is adjusted in the opposite direction through the excitation system converter.

[0075] In the AC excitation-based gravity energy storage system starting grid-connected system of the embodiment of the present application, the starting grid-connected system includes an energy storage control system and multiple groups of starting grid-connected modules, each group of starting grid-connected modules includes a connecting line, two back-to-back switches, a synchronization device and two starting grid-connected units; each starting grid-connected unit includes a unit, an export circuit breaker and a main transformer, and the unit includes a generator motor, a winch and an excitation system; the generator motor end is connected to the low-voltage side of the main transformer via the export circuit breaker, and the low-voltage side of the main transformer is also connected to the excitation transformer of the excitation system, and the generator motor adopts AC excitation; the generator motor is connected to the weight via the winch; the machine ends of the two generator motors in each group of starting grid-connected modules are connected via a connecting line, and the two back-to-back switches are arranged in series on the connecting line, the energy storage control system is connected to each group of starting grid-connected modules, and the synchronization device is connected to the export circuit breaker. In this case, in the starting grid-connected system, each group of starting grid-connected modules includes a connecting line, two back-to-back switches, a synchronization device and two starting grid-connected units; each starting grid-connected unit includes a unit, an output circuit breaker and a main transformer, and the unit includes a generator motor, a winch and an excitation system. The generator used is reversible in working mode and can work in both power generation and motoring states. The generator motor adopts an AC excitation method and can flexibly adjust the power of the generator motor to work at different speeds, thereby ensuring the maximum efficiency of the system under different working conditions, and there is no need to use a dedicated starting circuit. Starting and grid connection can be achieved by arranging a connecting line and two back-to-back switches in each group of starting grid-connected modules.

[0076] The system generator motors of the present application are arranged in pairs, that is, two generator motors form a group, and the two generator motor ends are connected by a connecting line. A back-to-back switch is provided on the connecting line. The beneficial effects of the generator motor using AC excitation include: 1) For the generating condition and the electric working condition of the generator motor, the gravity energy storage system can choose to operate at different speeds to ensure that the system has maximum efficiency; 2) Under the electric working condition / generating condition of the generator motor, the rising speed / falling speed of the heavy object can be adjusted in real time according to the power demand of the power grid, and the frequency modulation demand of the power grid can be responded to in real time; 3) The gravity energy storage system based on AC excitation does not require a dedicated starting circuit.

[0077] The accompanying drawings illustrate schematic diagrams of the structures of the embodiments disclosed herein. These figures are not drawn to scale; for the purpose of clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0078] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this application can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in this application can be achieved. This application is not limited here.

[0079] The above specific embodiments do not constitute a limitation on the scope of protection of this application. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application shall be included within the scope of protection of this application.

Claims

1. A gravity energy storage system based on AC excitation to start the grid-connected system, characterized in that: It includes an energy storage control system and multiple groups of starting and grid-connected modules. Each group of starting and grid-connected modules includes a tie line, two back-to-back switches, a synchronization device and two starting and grid-connected units. Each starting grid-connected unit includes a generator set, an outlet circuit breaker and a main transformer. The generator set includes a generator motor, a hoist and an excitation system. The generator motor is connected to the low-voltage side of the main transformer via the outlet circuit breaker. The low-voltage side of the main transformer is also connected to the excitation transformer of the excitation system. The generator motor adopts AC excitation. The generator motor is connected to a heavy object via the hoist. The generator motor ends of the two generator motors in each group of starting grid-connected modules are connected via the connecting line. The two back-to-back switches are arranged in series on the connecting line. The energy storage control system is connected to each group of starting grid-connected modules, and the synchronization device is connected to the outlet circuit breaker.

2. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 1, characterized in that: The energy storage control system is connected to the two back-to-back switches in each group of starting grid-connected modules, and the energy storage control system is also connected to the generator motor and excitation system in each starting grid-connected unit in each group of starting grid-connected modules; The energy storage control system is used to control the falling speed of the heavy object, the converter output of the excitation system, and the on-off of the back-to-back switch so that the unit meets the grid connection requirements; The synchronization device is used to control the corresponding group to start the corresponding output circuit breaker in the grid connection module to close to achieve grid connection when it detects that the unit meets the grid connection requirements.

3. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 2, characterized in that: The generator motor is defined as a generator when it works in the generating state, and is defined as a motor when it works in the motoring state; the grid-connected requirements include a first grid-connected requirement and a second grid-connected requirement, the first grid-connected requirement is that the phase and amplitude of the stator voltage of the generator motor are the same as the grid voltage, and the frequency of the stator voltage meets the set requirements, and the second grid-connected requirement is that the motor reaches the rated speed.

4. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 3, characterized in that: The energy storage control system is specifically used for: If it is detected that there are two generators in any group of starting grid-connected modules, the back-to-back switch is kept in the off state, and the falling speed of each weight in the starting grid-connected modules and the output of the converter of each excitation system are controlled to achieve the first grid-connected requirement. beg.

5. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 4, characterized in that: The controlling the falling speed of each weight in the group of starting grid-connected modules and the output of the converter of each excitation system to meet the first grid-connected requirement includes: For any unit in the grid-connected module of the group, the energy storage control system controls the weight to fall, and the weight drags the winch to rotate, and the winch coaxially drives the generator to rotate; Detect the speed of the generator, apply excitation power through the converter and control the frequency of the excitation power to the set frequency; The output of the converter is controlled and adjusted so that the phase and amplitude of the stator voltage are the same as the grid voltage, thereby meeting the first grid connection requirement.

6. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 5, characterized in that: If the energy storage control system receives a frequency modulation instruction from the power grid, it adjusts the speed of the generator and simultaneously adjusts the frequency of the excitation power supply in the opposite direction through the excitation system converter to perform frequency modulation response.

7. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 3, characterized in that: The energy storage control system is specifically used for: If it is detected that any group of starting and grid-connected modules contains a generator and a motor, the generator in the starting and grid-connected modules is used to drive the motor in a back-to-back manner to meet the second grid-connected requirement.

8. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 7, characterized in that: The method of using the generator in the group of starting and grid-connected modules in a back-to-back manner to drive the motor to meet the second grid-connected requirement includes: Start the grid connection module for this group, control the two back-to-back switches to close, and connect the stator winding of the generator to the stator winding of the motor through the back-to-back switches of the tie line; The generator is used to drive the motor until the motor reaches the rated speed. When the second grid connection requirement is met, the two back-to-back switches are controlled to disconnect.

9. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 3, characterized in that: The energy storage control system is specifically used for: If it is detected that two motors in any group of starting and grid-connected modules have been started and grid-connected in a back-to-back manner, the control Another motor in the group of starting and grid-connected modules is controlled to start at no load, and then the output of the converter of the corresponding excitation system is controlled to meet the first grid-connected requirement.

10. The AC excitation-based gravity energy storage system startup grid-connected system according to claim 9, characterized in that: The controlling of the no-load starting of another motor in the group of starting and grid-connected modules includes: The other motor is kept unloaded, the output circuit breaker corresponding to the other motor is disconnected, the stator winding outlet is short-circuited through the short-circuit switch, and the converter of the excitation system applies a three-phase AC voltage to the rotor winding. When the rotor speed of the other motor exceeds the rated speed, the output of the converter is locked and the short-circuit switch is disconnected at the same time to achieve no-load starting.

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